Patent Application
20140030697
Biological surfaces, e.g., surfaces of cells or viruses, can be modified in order to modulate surface function or to confer new functions to such surfaces. Surface functionalization may, for example, include an addition of a detectable label or binding moiety to a surface protein, allowing for detection or isolation of the functionalized cell or virus, or for the generation of new cell-cell or virus-host interactions that do not naturally occur. Functionalization of surface proteins can be achieved by genetic engineering or by chemical modifications. Both approaches are, however, limited in their capabilities, for example, in that many surface proteins do not tolerate insertions above a certain size without suffering impairments in their function or expression, and in that many chemical modifications require non-physiological reaction conditions and are not specific to a single viral surface protein.
The present invention stems in part from the recognition that bacterial sortases can be exploited to attach a variety of moieties to proteins on the surface of a virus. Such sortase-mediated modification reactions can be performed under physiological conditions. Methods, reagents, and kits are provided herein that can be used to functionalize proteins on the surface of viral particles via a sortase-mediated transpeptidation reaction. For example, some aspects of the invention provide methods and reagents for the functionalization of a protein on the surface of a virus by the addition of an entity, e.g., a small molecule (e.g., a fluorophore, biotin), a detectable label, a binding agent, a peptide, or a protein (e.g., GFP, an antibody or a fragment thereof, streptavidin). Some of the methods provided herein allow for functionalization of proteins on the surface of a virus in a site-specific manner, and with yields that surpass those of any currently known technologies, including, but not limited to, chemical modification and recombinant technologies (e.g., phage display technology). For example, the methods provided herein are useful for functionalization of phage surface proteins, such as M13 bacteriophage surface proteins.
In one aspect, the present invention provides methods, reagents, and kits for sortase-mediated functionalization of M13 bacteriophage capsid proteins pIII, pVIII, and pIX with various moieties. A comparison to commonly used techniques using chemical modification or genetic engineering demonstrates that the inventive sortase-based technology provided herein yields functionalized viral particles with greater efficiency and greater labeling density than these known methods. Further, some aspects of this disclosure provide a technology that takes advantage of orthogonal sortases that specifically target different recognition sequences, allowing for the functionalization of a plurality of different proteins on the surface of the same viral particle, e.g., with a different modification introduced into each of the different proteins, while maintaining excellent specificity. The methods provided herein are simple and effective for adding a variety of structures on the surface of viruses, and are useful for creating new viral surface modifications that can be exploited for the creation of novel surface interactions.
In some aspects, this invention provides methods of modifying a target protein comprising a sortase recognition motif on the surface of a virus. In some embodiments, the method comprises contacting the target protein with a sortase substrate conjugated to an agent, e.g., a detectable label, a binding agent, a click-chemistry handle, a reactive moiety, or a small molecule, in the presence of a sortase under conditions suitable for the sortase to conjugate the target protein and the sortase substrate. In some embodiments, the target protein comprises an N-terminal sortase recognition motif. In some embodiments, the N-terminal sortase recognition motif comprises an oligoglycine or an oligoalanine sequence. In some embodiments, the oligoglycine and/or the oligoalanine comprises 1-10 N-terminal glycine residues or 1-10 N-terminal alanine residues, respectively. In some embodiments, the sortase substrate comprises a C-terminal sortase recognition motif. In some embodiments, the C-terminal recognition motif is LPXTX, wherein each instance of X independently represents any amino acid residue. In some embodiments, the C-terminal recognition motif is LPETG (SEQ ID NO: 10) or LPETA (SEQ ID NO: 11). In some embodiments, the sortase is sortase A from Staphylococcus aureus (SrtAaureus) or sortase A from Streptococcus pyogenes (SrtApyogenes). In some embodiments, the virus is an RNA virus. In some embodiments, the virus is a DNA virus. In some embodiments, the virus is a single-stranded DNA virus. In some embodiments, the virus is a bacteriophage. In some embodiments, the virus is an M13 bacteriophage. In some embodiments, the target protein is a viral capsid protein. In some embodiments, the target protein is an M13 pIII, pVIII, or pIX capsid protein. In some embodiments, the agent is a protein, a carbohydrate, a lipid, a detectable label, a binding agent, a click-chemistry handle, or a small molecule. In some embodiments, the agent is a fluorescent protein, streptavidin, biotin, a fluorophore, an antibody or an antibody fragment, a nucleic acid molecule, an alkyne, an azide, a diene, a dienophile, a thiol, an alkene, an aryne, a tetrazine, a tetrazole, a dithioester, an anthracene, a maleimide, an enone, or an amine. In some embodiments, the method comprises multiple rounds of modifying a target protein on the surface of the same virus, wherein a different target protein is modified in each round. In some embodiments, different target proteins are modified using different sortases which recognize different sortase recognition motifs. For example, in some embodiments, at least one of the target proteins is modified using SrtAaureus, and at least one other target protein is modified using SrtApyogenes. In some embodiments, a different agent is conjugated to each different type of target protein, for example, one type of protein, e.g., M13 pIII, may be conjugated to a binding agent, and a different type of protein, e.g., M13 pVIII, may be conjugated to a detectable label. In some embodiments, a virus is provided that comprises a target protein that has been modified by a method described herein.
Some aspects of this invention provide methods of associating viral particles. In some embodiments, the method comprises conjugating a first target protein on the surface of the viral particle with a first binding agent via a sortase-mediated transpeptidation reaction; conjugating a second target protein on the surface of the viral particle with a second binding agent, wherein the second binding agent binds the first binding agent; and incubating a plurality of such viral particles under conditions suitable for the first and the second binding agent of different viral particles to bind each other. In some embodiments, the first binding agent binds the second binding agent directly. In some embodiments, the first binding agent binds the second binding agent indirectly (e.g., via binding to a third binding agent bound by the first binding agent). For example, in some embodiments, the first binding agent may be a first oligonucleotide, the second binding agent may be a second oligonucleotide, and the third binding agent may be a third oligonucleotide that can hybridize simultaneously with the first and the second oligonucleotide. In some embodiments, a method is provided that comprises conjugating a target protein on the surface of a viral particle with a binding agent via a sortase-mediated transpeptidation reaction, wherein the binding agent binds a binding partner on the surface of another viral particle; and incubating a plurality of such viral particles under conditions suitable for the binding agent to bind its binding partner. For example, in some such embodiments, the binding agent is an antibody binding a viral surface antigen. In some embodiments, a method is provided that comprises functionalizing a first population of viral particles with a first binding agent; functionalizing a second population of viral particles with a second binding agent, wherein the first binding agent binds the second binding agent; and incubating a plurality of viral particles from each population together under conditions suitable for the first and the second binding agent of different viral particles to bind each other. In some such embodiments, the viral particles of the first population are different from the viral particles of the second population, e.g., the first population comprises viral particles of elongate shape (e.g., M13) and the second population comprises particles of more spherical shape (e.g., T4 or Qβ). In some embodiments, the viral particles are DNA virus particles. In some embodiments, the viral particles are bacteriophage particles. In some embodiments, the viral particles are M13 bacteriophage particles. In some embodiments, at least one target protein comprises an N-terminal sortase recognition motif. In some embodiments, the N-terminal sortase recognition motif comprises an oligoglycine or an oligoalanine sequence. In some embodiments, the oligoglycine and/or the oligoalanine comprises 1-10 N-terminal glycine residues or 1-10 N-terminal alanine residues, respectively. In some embodiments, at least one of the target proteins comprises a C-terminal sortase recognition motif. In some embodiments, the C-terminal recognition motif is LPXTX, wherein each instance of X independently represents any amino acid residue. In some embodiments, the C-terminal recognition motif is LPETG (SEQ ID NO: 10) or LPETA (SEQ ID NO: 11). In some embodiments, the sortase used for the sortase-mediated transpeptidation of the first target protein is different from the sortase used for the sortase-mediated transpeptidation of the second target protein. In some embodiments, the sortase used for the sortase-mediated transpeptidation of the first target protein is sortase A from Staphylococcus aureus (SrtAaureus). In some embodiments, the sortase used for the sortase-mediated transpeptidation of the second target protein is sortase A from Streptococcus pyogenes (SrtApyogenes). In some embodiments, the first and/or the second target protein is a viral capsid protein. In some embodiments, the first and the second target protein is selected from the group consisting of M13 pIII, pVIII, or pIX. In some embodiments, the binding agent is a ligand, a receptor, an extracellular receptor domain, streptavidin, biotin, an antibody, or an antibody fragment. Other suitable binding agents include click chemistry handles, SNAP-, Clip-, ACP-, and MCP-tags, nucleic acid molecules (e.g., complementary DNA strands or non-complementary DNA strands that can hybridize to a third DNA strand), leucine zippers, GFP, as well as toxins, e.g., bacterial and plant toxins.
In some embodiments, viral particles that are functionalized with a binding agent are used in chip-based assays in which the viral particles are conjugated to a solid support. In some embodiments, viral particles that are functionalized with binding agents can be used as a handle in single molecule force spectroscopy, e.g., by linking a bead to a specific target on a surface.
Some aspects of this invention provide viruses comprising a target protein that is conjugated to an agent via a sortase recognition motif. In some embodiments, the target protein is conjugated to the agent via a linker. In some embodiments, the target protein has been conjugated to the agent by a sortase-mediated transpeptidation reaction. In some embodiments, the sortase recognition motif is LPXTX, wherein each instance of X independently represents any amino acid residue. In some embodiments, the sortase recognition motif is LPETG (SEQ ID NO: 10) or LPETA (SEQ ID NO: 11). In some embodiments, the sortase recognition motif is a sequence created by a SrtAaureus mediated transpeptidation reaction or by a SrtApyogenes transpeptidation reaction. In some embodiments, the virus is a DNA virus. In some embodiments, the virus is a bacteriophage. In some embodiments, the virus is an M13 bacteriophage. In some embodiments, the target protein is a viral capsid protein. In some embodiments, the target protein is an M13 pIII, pVIII, or pIX capsid protein. In some embodiments, the agent is a protein, a peptide, a detectable label, a binding agent, a click-chemistry handle, or a small molecule. In some embodiments, the agent is a molecule that cannot be genetically encoded, e.g., a carbohydrate, a lipid, or a small molecule. In some embodiments, the agent is a fluorescent protein, streptavidin, biotin, a fluorophore, an antibody, or an antigen-binding antibody fragment. In some embodiments, the virus comprises a plurality of different target proteins conjugated to an agent via a sortase recognition motif. In some embodiments, at least one target protein is modified using SrtAaureus, and at least one target protein is modified using SrtApyogenes. In some embodiments, a different agent is conjugated to each different target protein. In some embodiments, the virus is an M13 bacteriophage comprising a pIII capsid protein conjugated to streptavidin via a sortase recognition sequence, and a pVIII capsid protein conjugated to biotin via a sortase recognition sequence.
The present invention, in some aspects, provides viruses comprising a recombinant target protein, wherein the recombinant target protein comprised a sortase recognition motif. In some embodiments, the virus is a DNA virus. In some embodiments, the virus is a bacteriophage. In some embodiments, the virus is an M13 bacteriophage. In some embodiments, the target protein is a capsid protein. In some embodiments, the target protein is an M13 pIII, pVIII, or pIX capsid protein. In some embodiments, the sortase recognition motif is an N-terminal oligoglycine and/or the oligoalanine, comprising 1-10 N-terminal glycine residues or 1-10 N-terminal alanine residues, respectively. In some embodiments, the sortase recognition sequence comprises a C-terminal sortase recognition motif. In some embodiments, the C-terminal recognition motif is LPXTX, wherein each instance of X represents independently any amino acid residue. In some embodiments, the C-terminal recognition motif is LPETG (SEQ ID NO: 10) or LPETA (SEQ ID NO: 11). In some embodiments, the recombinant target protein comprises a loop structure harboring the sortase recognition motif and a protease cleavage site, e.g., a loop structure as disclosed in U.S. patent application Ser. No. 13/642,458, publication number US2013/0122043, by Guimaraes and Ploegh, the entire contents of which are incorporated herein by reference. In some embodiments, the loop structure comprises two cysteine residues that flank the sortase recognition motif and the protease cleavage site. In some embodiments, the loop structure is formed by a disulfide bond between the two cysteine residues. In some embodiments, the loop structure comprises an amino acid sequence derived from a bacterial toxin comprising a loop structure, e.g., an amino acid sequence of at least 40, at least 50, at least 60, at least 70, at least 80, at least 90 amino acid residues that is homologous to, or that is at least 70%, at least 80%, at least 90%, at least 95% or at least 98% identical to the sequence of a bacterial toxin. In some embodiments, the bacterial toxin is a bacterial toxin that comprises a protease-sensitive loop. In some embodiments, the bacterial toxin is a bacterial exotoxin. In some embodiments, the toxin is an AB5 toxin. In some embodiments, the toxin is a cholera toxin, Shiga toxin (ST), the Shiga-like toxins (e.g., SLT1, SLT2, SLT2c, and SLT2e), E. coli heat labile enterotoxins LT-I (e.g., the two variants LT-Ih from human isolates and LT-Ip from porcine isolates), LT-IIa, and LT-IIB, or pertussis toxin (PT). The sequences of these and other suitable toxins are well known to those of skill in the art. See, e.g., U.S. patent application Ser. No. 13/642,458, publication number US2013/0122043, by Guimaraes and Ploegh, the entire contents of which are incorporated herein by reference. Some aspects of this invention provide engineered viral capsid proteins comprising such artificial loop structures harboring a sortase recognition motif and a protease cleavage site. It will be apparent to those of skill in the art that the methods, reagents, and strategies for engineering target proteins to comprise cleavable loop structures with sortase recognition motifs can be applied to viral capsid proteins, as described in more detail herein, but is not limited to such proteins. As will be apparent to those of skill in the art from the instant disclosure, the inventive methods, reagents, and strategies disclosed herein can be applied to install cleavable loop structures comprising a sortase recognition motif on any protein, including, but not limited to cytoskeletal proteins, extracellular matrix proteins, cell surface proteins, plasma proteins, coagulation factors, cell adhesion proteins, hormones and growth factors, receptors, DNA-binding proteins, transcription factors, antibodies and antibody fragments, chaperone proteins, histones, and enzymes. In some embodiments, the present disclosure provides such engineered proteins, e.g., an antibody or antibody fragment, an enzyme, a transcription factor, etc., comprising a cleavable loop structure with a sortase recognition motif. Methods of using such proteins, e.g., in the context of sortase-mediated functionalization of such proteins, described in more detail herein, are also provided.
Some aspects of this invention provide a kit comprising a recombinant nucleic acid encoding a viral capsid protein comprising a sortase recognition motif. In some embodiments, the recombinant nucleic acid is comprised in an expression vector. In some embodiments, the sortase recognition motif is an N-terminal oligoglycine and/or the oligoalanine, comprising 1-10 N-terminal glycine residues or 1-10 N-terminal alanine residues, respectively. In some embodiments, the sortase recognition motif is a C-terminal LPXTX sequence, wherein each instance of X represents independently any amino acid residue. In some embodiments, the C-terminal recognition motif is LPETG (SEQ ID NO: 10) or LPETA (SEQ ID NO: 11). In some embodiments, the kit further comprises a sortase. In some embodiments, the kit comprises SrtAaureus and/or SrtApyogenes. In some embodiments, the kit further comprises a substrate comprising a sortase recognition motif conjugated to an agent. In some embodiments, the sortase catalyzes a transpeptidation reaction involving the sortase recognition motif comprised in the viral capsid protein. In some embodiments, the kit further comprises a buffer or reagent useful for carrying out a sortase-mediated transpeptidation reaction.
The above summary is intended to provide an overview over some aspects of this invention and is not to be construed to limit the invention in any way. Additional aspects, advantages, and embodiments of this invention are described herein, and further embodiments will be apparent to those of skill in the art based on the instant disclosure. The entire contents of all references cited above and herein are hereby incorporated by reference.
MVSKGEELFT GVVPILVELD GDVNGHKFSV SGEGEGDATY GKLTLKFICT
TGKLPVPWPT LVTTLTYGVQ CFSRYPDHMK QHDFFKSAMP EGYVQERTIF
FKDDGNYKTR AEVKFEGDTL VNRIELKGID FKEDGNILGH KLEYNYNSHN
VYIMADKQKN GIKVNFKIRH NIEDGSVQLA DHYQQNTPIG DGPVLLPDNH
YLSTQSALSK DPNEKRDHMV LLEFVTAAGI TLGMDELYK
S HTENSFTNVW KDDKTLDRYA NYEGCLWNAT GVVVCTGDET
QCYGTWVPIG LAIPENEGGG SEGGGSEGGG SEGGGTKPPE YGDTPIPGYT
YINPLDGTYP PGTEQNPANP NPSLEESQPL NTFMFQNNRF RNRQGALTVY
TGTVTQGTDP VKTYYQYTPV SSKAMYDAYW NGKFRDCAFH SGFNEDLFVC
EYQGQSSDLP QPPVNAGGGS GGGSGGGSEG GGSEGGGSEG GGSEGGGSGG
GSGSGDFDYE KMANANKGAM TENADENALQ SDAKGKLDSV ATDYGAAIDG
FIGDVSGLAN GNGATGDFAG SNSQMAQVGD GDNSPLMNNF RQYLPSLPQS
VECRPFVFGA GKPYEFSIDC DKINLFRGVF AFLLYVATFM YVFSTFANIL
RNKES.
The sequences of pIII and GFP are shown in underline and double underline, respectively. The peptides identified are in bold. The tryptic peptide comprising the GFP C-terminus, followed by the SrtAaureus cleavage site, fused to the N-terminal glycines of pIII is italicized.
MVSKGEELFT GVVPILVELD GDVNGHKFSV SGEGEGDATY GKLTLKFICT
TGKLPVPWPT LVTTLTYGVQ CFSRYPDHMK QHDFFKSAMP EGYVQERTIF
FKDDGNYKTR AEVKFEGDTL VNRIELKGID FKEDGNILGH KLEYNYNSHN
VYIMADKQKN GIKVNFKIRH NIEDGSVQLA DHYQQNTPIG DGPVLLPDNH
YLSTQSALSK DPNEKRDHMV LLEFVTAAGI TLGM
DVPDYAQGG QGVDMSVLVY SFASFVLGWC LRSGITYFTR LMETSS.
The sequences of GFP and pIX are underlined and double underlined, respectively. The peptides identified are in bold. The AspN digestion-resultant peptide comprising the GFP C-terminus, followed by the SrtAaureus cleavage site, fused to the N-terminal glycines of pIX is italicized.
MVSKGEELFT GVVPILVELD GDVNGHKESV SGEGEGDATY GKLTLKFICT
TGKLPVPWPT LVTTLTYGVQ CFSRYPDHMK QHDFFKSATP EGYVQQDPTI
FCKDDGNYKT RAEVKFEGDT LVNRIELKGI DFKEDGNILG HKLEYNYNSH
NVYIMADKQK NGTKVNFKTR HNTEDGSVQL ADHYQQNTPI GDGPVLLPDN
HYLSTQSALS KDPNEKRDHM VLLEFVTAAG ITLGMDELYK
AAFNSL QASATEYIGY AWAMVVVTVG ATTGTKLFKK FTSAS.
The sequences of GFP and pVIII are shown in underline and double underline, respectively. The peptides identified are in bold. The tryptic peptide comprising the GFP C-terminus, followed by the SrtApyogenes cleavage site, fused to the N-terminal alanines of pVIII is italicized.
MAEAGITGTW YNQLGSTFIV TAGADGALTG TYESAVGNAE SRYVLTGRYD
SAPATDGSGT ALGWTVAWKN NYRNAHSATT WSGQYVGGAE ARINTQWLLT
SGTTEANAWK STLVGHDTFT K
SHTENSFTNV WKDDKTLDRY ANYEGCLWNA TGVVVCTGDE TQCYGTWVPI
GLAIPENEGG GSEGGGSEGG GSEGGGTKPP EYGDTPIPGY TYINPLDGTY
PPGTEQNPAN PNPSLEESQP LNTFMFQNNR FRNRQGALTV YTGTVTQGTD
PVKTYYQYTP VSSKAMYDAY WNGKFRDCAF HSGFNEDLFV CEYQGQSSDL
PQPPVNAGGG SGGGSGGGSE GGGSEGGGSE GGGSEGGGSG GGSGSGDFDY
EKMANANKGA MTENADENAL QSDAKGKLDS VATDYGAAID GFIGDVSGLA
NGNGATGDFA GSNSQMAQVG DGDNSPLMNN FRQYLPSLPQ SVECRPFVFG
AGKPYEFSID CDKINLFRGV FAFLLYVATF MYVFSTFANI LRNKES.
The sequences of streptavidin monomer and pIII and are shown in underline and double underline, respectively. The peptides identified are in bold. The tryptic peptide comprising the streptavidin C-terminus, followed by the SrtAaureus cleavage site, fused to the N-terminal glycines of pIII is italicized.
HNTQIHT LNDKIFSYTE
SLAGKREMAI ITFKNGATFQ VEVPGSQHID SQKKAIERMK DTLRIAYLTE
AKVEKLCVWN NKTPHAIAAI SMAN
YANYEGCLWN ATGVVVCTGD ETQCYGTWVP IGLAIPENEG GGSEGGGSEG
GGSEGGGTKP PEYGDTPIPG YTYINPLDGT YPPGTEQNPA NPNPSLEESQ
PLNTFMFQNN RFRNRQGALT VYTGTVTQGT DPVKTYYQYT PVSSKAMYDA
YWNGKFRDCA FHSGFNEDLF VCEYQGQSSD LPQPPVNAGG GSGGGSGGGS
EGGGSEGGGS EGGGSEGGGS GGGSGSGDFD YEKMANANKG AMTENADENA
LQSDAKGKLD SVATDYGAAI DGFIGDVSGL ANGNGATGDF AGSNSQMAQV
GDGDNSPLMN NFRQYLPSLP QSVECRPFVF GAGKPYEFSI DCDKINLFRG
VFAFLLYVAT FMYVFSTFAN ILRNKES.
The amino acid sequence of pIII is underlined and the sequence of CtxB is shown in bold in the sequence above. The chymotryptic peptide comprising the C-terminus of the loop, followed by the SrtAaureus cleavage site, fused to the N-terminal glycines of CtxB is double underlined. The cysteine residues forming the S—S bond are framed.
FIG. 18—Conjugation of DNA to peptides. Thiolated DNA was conjugated to either (maleimide)-LPETGG (SEQ ID NO: 13) or GGGK(maleimide) peptide SEQ ID NO: 127. The conjugated peptides were analyzed by MALDI-TOF mass-spectrometry (a) and by TBE-Urea PAGE followed by fluorescent imaging (b).
Definitions of specific functional groups and chemical terms are described in more detail below. For purposes of this invention, the chemical elements are identified in accordance with the Periodic Table of the Elements, CAS version, Handbook of Chemistry and Physics, 75th Ed., inside cover, and specific functional groups are generally defined as described therein. Additionally, general principles of organic chemistry, as well as specific functional moieties and reactivity, are described in Organic Chemistry, Thomas Sorrell, University Science Books, Sausalito, 1999; Smith and March March's Advanced Organic Chemistry, 5th Edition, John Wiley & Sons, Inc., New York, 2001; Larock, Comprehensive Organic Transformations, VCH Publishers, Inc., New York, 1989; Carruthers, Some Modern Methods of Organic Synthesis, 3rd Edition, Cambridge University Press, Cambridge, 1987.
The term “aliphatic,” as used herein, includes both saturated and unsaturated, nonaromatic, straight chain (i.e., unbranched), branched, acyclic, and cyclic (i.e., carbocyclic) hydrocarbons, which are optionally substituted with one or more functional groups. As will be appreciated by one of ordinary skill in the art, “aliphatic” is intended herein to include, but is not limited to, alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, and cycloalkynyl moieties. Thus, as used herein, the term “alkyl” includes straight, branched and cyclic alkyl groups. An analogous convention applies to other generic terms such as “alkenyl,” “alkynyl,” and the like. Furthermore, as used herein, the terms “alkyl,” “alkenyl,” “alkynyl,” and the like encompass both substituted and unsubstituted groups. In certain embodiments, as used herein, “aliphatic” is used to indicate those aliphatic groups (cyclic, acyclic, substituted, unsubstituted, branched or unbranched) having 1-20 carbon atoms (C1-20 aliphatic). In certain embodiments, the aliphatic group has 1-10 carbon atoms (C1-10 aliphatic). In certain embodiments, the aliphatic group has 1-6 carbon atoms (C1-6 aliphatic). In certain embodiments, the aliphatic group has 1-5 carbon atoms (C1-5 aliphatic). In certain embodiments, the aliphatic group has 1-4 carbon atoms (C1-4 aliphatic). In certain embodiments, the aliphatic group has 1-3 carbon atoms (C1-3 aliphatic). In certain embodiments, the aliphatic group has 1-2 carbon atoms (C1-2 aliphatic). Aliphatic group substituents include, but are not limited to, any of the substituents described herein, that result in the formation of a stable moiety.
The term “alkyl,” as used herein, refers to saturated, straight- or branched-chain hydrocarbon radicals derived from a hydrocarbon moiety containing between one and twenty carbon atoms by removal of a single hydrogen atom. In some embodiments, the alkyl group employed in the invention contains 1-20 carbon atoms (C1-20alkyl). In another embodiment, the alkyl group employed contains 1-15 carbon atoms (C1-15alkyl). In another embodiment, the alkyl group employed contains 1-10 carbon atoms (C1-10alkyl). In another embodiment, the alkyl group employed contains 1-8 carbon atoms (C1-8alkyl). In another embodiment, the alkyl group employed contains 1-6 carbon atoms (C1-6alkyl). In another embodiment, the alkyl group employed contains 1-5 carbon atoms (C1-5alkyl). In another embodiment, the alkyl group employed contains 1-4 carbon atoms (C1-4alkyl). In another embodiment, the alkyl group employed contains 1-3 carbon atoms (C1-3alkyl). In another embodiment, the alkyl group employed contains 1-2 carbon atoms (C1-2alkyl). Examples of alkyl radicals include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, iso-butyl, sec-butyl, sec-pentyl, iso-pentyl, tert-butyl, n-pentyl, neopentyl, n-hexyl, sec-hexyl, n-heptyl, n-octyl, n-decyl, n-undecyl, dodecyl, and the like, which may bear one or more substituents. Alkyl group substituents include, but are not limited to, any of the substituents described herein, that result in the formation of a stable moiety. The term “alkylene,” as used herein, refers to a biradical derived from an alkyl group, as defined herein, by removal of two hydrogen atoms. Alkylene groups may be cyclic or acyclic, branched or unbranched, substituted or unsubstituted. Alkylene group substituents include, but are not limited to, any of the substituents described herein, that result in the formation of a stable moiety.
The term “alkenyl,” as used herein, denotes a monovalent group derived from a straight- or branched-chain hydrocarbon moiety having at least one carbon-carbon double bond by the removal of a single hydrogen atom. In certain embodiments, the alkenyl group employed in the invention contains 2-20 carbon atoms (C2-20alkenyl). In some embodiments, the alkenyl group employed in the invention contains 2-15 carbon atoms (C2-15alkenyl). In another embodiment, the alkenyl group employed contains 2-10 carbon atoms (C2-10alkenyl). In still other embodiments, the alkenyl group contains 2-8 carbon atoms (C2-8alkenyl). In yet other embodiments, the alkenyl group contains 2-6 carbons (C2-6alkenyl). In yet other embodiments, the alkenyl group contains 2-5 carbons (C2-5alkenyl). In yet other embodiments, the alkenyl group contains 2-4 carbons (C2-4alkenyl). In yet other embodiments, the alkenyl group contains 2-3 carbons (C2-3alkenyl). In yet other embodiments, the alkenyl group contains 2 carbons (C2alkenyl). Alkenyl groups include, for example, ethenyl, propenyl, butenyl, 1-methyl-2-buten-1-yl, and the like, which may bear one or more substituents. Alkenyl group substituents include, but are not limited to, any of the substituents described herein, that result in the formation of a stable moiety. The term “alkenylene,” as used herein, refers to a biradical derived from an alkenyl group, as defined herein, by removal of two hydrogen atoms. Alkenylene groups may be cyclic or acyclic, branched or unbranched, substituted or unsubstituted. Alkenylene group substituents include, but are not limited to, any of the substituents described herein, that result in the formation of a stable moiety.
The term “alkynyl,” as used herein, refers to a monovalent group derived from a straight- or branched-chain hydrocarbon having at least one carbon-carbon triple bond by the removal of a single hydrogen atom. In certain embodiments, the alkynyl group employed in the invention contains 2-20 carbon atoms (C2-20alkynyl). In some embodiments, the alkynyl group employed in the invention contains 2-15 carbon atoms (C2-15alkynyl). In another embodiment, the alkynyl group employed contains 2-10 carbon atoms (C2-10alkynyl). In still other embodiments, the alkynyl group contains 2-8 carbon atoms (C2-8alkynyl). In still other embodiments, the alkynyl group contains 2-6 carbon atoms (C2-6alkynyl). In still other embodiments, the alkynyl group contains 2-5 carbon atoms (C2-5alkynyl). In still other embodiments, the alkynyl group contains 2-4 carbon atoms (C2-4alkynyl). In still other embodiments, the alkynyl group contains 2-3 carbon atoms (C2-3alkynyl). In still other embodiments, the alkynyl group contains 2 carbon atoms (C2alkynyl). Representative alkynyl groups include, but are not limited to, ethynyl, 2-propynyl (propargyl), 1-propynyl, and the like, which may bear one or more substituents. Alkynyl group substituents include, but are not limited to, any of the substituents described herein, that result in the formation of a stable moiety. The term “alkynylene,” as used herein, refers to a biradical derived from an alkynylene group, as defined herein, by removal of two hydrogen atoms. Alkynylene groups may be cyclic or acyclic, branched or unbranched, substituted or unsubstituted. Alkynylene group substituents include, but are not limited to, any of the substituents described herein, that result in the formation of a stable moiety.
The term “aptamer” as used herein refers to a nucleic acid ligand or receptor that binds to a target molecule. In some embodiments, an aptamer binds a target molecule with high affinity, e.g., with an KD of less than 10−6 M, less than 10−7 M, less than 10−8 M, less than 10−9 M, or less than 10−10 M. In some embodiments, an aptamer binds a target molecule with high specificity, e.g., in that it does not bind a ligand other than the target ligand with an affinity of less than 10−6 M. Typically, an aptamer forms a secondary structure resulting in a three-dimensional complementarity to the target molecule or a substructure thereof.
The term “carbocyclic” or “carbocyclyl” as used herein, refers to an as used herein, refers to a cyclic aliphatic group containing 3-10 carbon ring atoms (C3-10-carbocyclic). Carbocyclic group substituents include, but are not limited to, any of the substituents described herein, that result in the formation of a stable moiety.
The term “heteroaliphatic,” as used herein, refers to an aliphatic moiety, as defined herein, which includes both saturated and unsaturated, nonaromatic, straight chain (i.e., unbranched), branched, acyclic, cyclic (i.e., heterocyclic), or polycyclic hydrocarbons, which are optionally substituted with one or more functional groups, and that further contains one or more heteroatoms (e.g., oxygen, sulfur, nitrogen, phosphorus, or silicon atoms) between carbon atoms. In certain embodiments, heteroaliphatic moieties are substituted by independent replacement of one or more of the hydrogen atoms thereon with one or more substituents. As will be appreciated by one of ordinary skill in the art, “heteroaliphatic” is intended herein to include, but is not limited to, heteroalkyl, heteroalkenyl, heteroalkynyl, heterocycloalkyl, heterocycloalkenyl, and heterocycloalkynyl moieties. Thus, the term “heteroaliphatic” includes the terms “heteroalkyl,” “heteroalkenyl,” “heteroalkynyl,” and the like. Furthermore, as used herein, the terms “heteroalkyl,” “heteroalkenyl,” “heteroalkynyl,” and the like encompass both substituted and unsubstituted groups. In certain embodiments, as used herein, “heteroaliphatic” is used to indicate those heteroaliphatic groups (cyclic, acyclic, substituted, unsubstituted, branched or unbranched) having 1-20 carbon atoms and 1-6 heteroatoms (C1-20heteroaliphatic). In certain embodiments, the heteroaliphatic group contains 1-10 carbon atoms and 1-4 heteroatoms (C1-10heteroaliphatic). In certain embodiments, the heteroaliphatic group contains 1-6 carbon atoms and 1-3 heteroatoms (C1-6heteroaliphatic). In certain embodiments, the heteroaliphatic group contains 1-5 carbon atoms and 1-3 heteroatoms (C1-5heteroaliphatic). In certain embodiments, the heteroaliphatic group contains 1-4 carbon atoms and 1-2 heteroatoms (C1-4heteroaliphatic). In certain embodiments, the heteroaliphatic group contains 1-3 carbon atoms and 1 heteroatom (C1-3heteroaliphatic). In certain embodiments, the heteroaliphatic group contains 1-2 carbon atoms and 1 heteroatom (C1-2heteroaliphatic). Heteroaliphatic group substituents include, but are not limited to, any of the substituents described herein, that result in the formation of a stable moiety.
The term “heteroalkyl,” as used herein, refers to an alkyl moiety, as defined herein, which contain one or more heteroatoms (e.g., oxygen, sulfur, nitrogen, phosphorus, or silicon atoms) in between carbon atoms. In certain embodiments, the heteroalkyl group contains 1-20 carbon atoms and 1-6 heteroatoms (C1-20 heteroalkyl). In certain embodiments, the heteroalkyl group contains 1-10 carbon atoms and 1-4 heteroatoms (C1-10 heteroalkyl). In certain embodiments, the heteroalkyl group contains 1-6 carbon atoms and 1-3 heteroatoms (C1-6 heteroalkyl). In certain embodiments, the heteroalkyl group contains 1-5 carbon atoms and 1-3 heteroatoms (C1-5 heteroalkyl). In certain embodiments, the heteroalkyl group contains 1-4 carbon atoms and 1-2 heteroatoms (C1-4 heteroalkyl). In certain embodiments, the heteroalkyl group contains 1-3 carbon atoms and 1 heteroatom (C1-3 heteroalkyl). In certain embodiments, the heteroalkyl group contains 1-2 carbon atoms and 1 heteroatom (C1-2 heteroalkyl). The term “heteroalkylene,” as used herein, refers to a biradical derived from an heteroalkyl group, as defined herein, by removal of two hydrogen atoms. Heteroalkylene groups may be cyclic or acyclic, branched or unbranched, substituted or unsubstituted. Heteroalkylene group substituents include, but are not limited to, any of the substituents described herein, that result in the formation of a stable moiety.
The term “heteroalkenyl,” as used herein, refers to an alkenyl moiety, as defined herein, which further contains one or more heteroatoms (e.g., oxygen, sulfur, nitrogen, phosphorus, or silicon atoms) in between carbon atoms. In certain embodiments, the heteroalkenyl group contains 2-20 carbon atoms and 1-6 heteroatoms (C2-20 heteroalkenyl). In certain embodiments, the heteroalkenyl group contains 2-10 carbon atoms and 1-4 heteroatoms (C2-10 heteroalkenyl). In certain embodiments, the heteroalkenyl group contains 2-6 carbon atoms and 1-3 heteroatoms (C2-6 heteroalkenyl). In certain embodiments, the heteroalkenyl group contains 2-5 carbon atoms and 1-3 heteroatoms (C2-5 heteroalkenyl). In certain embodiments, the heteroalkenyl group contains 2-4 carbon atoms and 1-2 heteroatoms (C2-4 heteroalkenyl). In certain embodiments, the heteroalkenyl group contains 2-3 carbon atoms and 1 heteroatom (C2-3 heteroalkenyl). The term “heteroalkenylene,” as used herein, refers to a biradical derived from an heteroalkenyl group, as defined herein, by removal of two hydrogen atoms. Heteroalkenylene groups may be cyclic or acyclic, branched or unbranched, substituted or unsubstituted.
The term “heteroalkynyl,” as used herein, refers to an alkynyl moiety, as defined herein, which further contains one or more heteroatoms (e.g., oxygen, sulfur, nitrogen, phosphorus, or silicon atoms) in between carbon atoms. In certain embodiments, the heteroalkynyl group contains 2-20 carbon atoms and 1-6 heteroatoms (C2-20 heteroalkynyl). In certain embodiments, the heteroalkynyl group contains 2-10 carbon atoms and 1-4 heteroatoms (C2-10 heteroalkynyl). In certain embodiments, the heteroalkynyl group contains 2-6 carbon atoms and 1-3 heteroatoms (C2-6 heteroalkynyl). In certain embodiments, the heteroalkynyl group contains 2-5 carbon atoms and 1-3 heteroatoms (C2-5 heteroalkynyl). In certain embodiments, the heteroalkynyl group contains 2-4 carbon atoms and 1-2 heteroatoms (C2-4 heteroalkynyl). In certain embodiments, the heteroalkynyl group contains 2-3 carbon atoms and 1 heteroatom (C2-3 heteroalkynyl). The term “heteroalkynylene,” as used herein, refers to a biradical derived from an heteroalkynyl group, as defined herein, by removal of two hydrogen atoms. Heteroalkynylene groups may be cyclic or acyclic, branched or unbranched, substituted or unsubstituted.
The term “heterocyclic,” “heterocycles,” or “heterocyclyl,” as used herein, refers to a cyclic heteroaliphatic group. A heterocyclic group refers to a non-aromatic, partially unsaturated or fully saturated, 3- to 10-membered ring system, which includes single rings of 3 to 8 atoms in size, and bi- and tri-cyclic ring systems which may include aromatic five- or six-membered aryl or heteroaryl groups fused to a non-aromatic ring. These heterocyclic rings include those having from one to three heteroatoms independently selected from oxygen, sulfur, and nitrogen, in which the nitrogen and sulfur heteroatoms may optionally be oxidized and the nitrogen heteroatom may optionally be quaternized. In certain embodiments, the term heterocyclic refers to a non-aromatic 5-, 6-, or 7-membered ring or polycyclic group wherein at least one ring atom is a heteroatom selected from O, S, and N (wherein the nitrogen and sulfur heteroatoms may be optionally oxidized), and the remaining ring atoms are carbon, the radical being joined to the rest of the molecule via any of the ring atoms. Heterocycyl groups include, but are not limited to, a bi- or tri-cyclic group, comprising fused five, six, or seven-membered rings having between one and three heteroatoms independently selected from the oxygen, sulfur, and nitrogen, wherein (i) each 5-membered ring has 0 to 2 double bonds, each 6-membered ring has 0 to 2 double bonds, and each 7-membered ring has 0 to 3 double bonds, (ii) the nitrogen and sulfur heteroatoms may be optionally oxidized, (iii) the nitrogen heteroatom may optionally be quaternized, and (iv) any of the above heterocyclic rings may be fused to an aryl or heteroaryl ring. Exemplary heterocycles include azacyclopropanyl, azacyclobutanyl, 1,3-diazatidinyl, piperidinyl, piperazinyl, azocanyl, thiaranyl, thietanyl, tetrahydrothiophenyl, dithiolanyl, thiacyclohexanyl, oxiranyl, oxetanyl, tetrahydrofuranyl, tetrahydropuranyl, dioxanyl, oxathiolanyl, morpholinyl, thioxanyl, tetrahydronaphthyl, and the like, which may bear one or more substituents. Substituents include, but are not limited to, any of the substituents described herein, that result in the formation of a stable moiety.
The term “aryl,” as used herein, refers to an aromatic mono- or polycyclic ring system having 3-20 ring atoms, of which all the ring atoms are carbon, and which may be substituted or unsubstituted. In certain embodiments of the present invention, “aryl” refers to a mono, bi, or tricyclic C4-C20 aromatic ring system having one, two, or three aromatic rings which include, but are not limited to, phenyl, biphenyl, naphthyl, and the like, which may bear one or more substituents. Aryl substituents include, but are not limited to, any of the substituents described herein, that result in the formation of a stable moiety. The term “arylene,” as used herein refers to an aryl biradical derived from an aryl group, as defined herein, by removal of two hydrogen atoms. Arylene groups may be substituted or unsubstituted. Arylene group substituents include, but are not limited to, any of the substituents described herein, that result in the formation of a stable moiety. Additionally, arylene groups may be incorporated as a linker group into an alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene, or heteroalkynylene group, as defined herein.
The term “heteroaryl,” as used herein, refers to an aromatic mono- or polycyclic ring system having 3-20 ring atoms, of which one ring atom is selected from S, O, and N; zero, one, or two ring atoms are additional heteroatoms independently selected from S, O, and N; and the remaining ring atoms are carbon, the radical being joined to the rest of the molecule via any of the ring atoms. Exemplary heteroaryls include, but are not limited to pyrrolyl, pyrazolyl, imidazolyl, pyridinyl, pyrimidinyl, pyrazinyl, pyridazinyl, triazinyl, tetrazinyl, pyyrolizinyl, indolyl, quinolinyl, isoquinolinyl, benzoimidazolyl, indazolyl, quinolinyl, isoquinolinyl, quinolizinyl, cinnolinyl, quinazolynyl, phthalazinyl, naphthridinyl, quinoxalinyl, thiophenyl, thianaphthenyl, furanyl, benzofuranyl, benzothiazolyl, thiazolynyl, isothiazolyl, thiadiazolynyl, oxazolyl, isoxazolyl, oxadiaziolyl, oxadiaziolyl, and the like, which may bear one or more substituents. Heteroaryl substituents include, but are not limited to, any of the substituents described herein, that result in the formation of a stable moiety. The term “heteroarylene,” as used herein, refers to a biradical derived from an heteroaryl group, as defined herein, by removal of two hydrogen atoms. Heteroarylene groups may be substituted or unsubstituted. Additionally, heteroarylene groups may be incorporated as a linker group into an alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene, or heteroalkynylene group, as defined herein. Heteroarylene group substituents include, but are not limited to, any of the substituents described herein, that result in the formation of a stable moiety.
The term “acyl,” as used herein, is a subset of a substituted alkyl group, and refers to a group having the general formula —C(═O)RA, —C(═O)ORA, —C(═O)—O—C(═O)RA, —C(═O)SRA, —C(═O)N(RA)2, —C(═S)RA, —C(═S)N(RA)2, and —C(═S)S(RA), —C(═NRA)RA, —C(═NRA)ORA, —C(═NRA)SRA, and —C(═NRA)N(RA)2, wherein RA is hydrogen; halogen; substituted or unsubstituted hydroxyl; substituted or unsubstituted thiol; substituted or unsubstituted amino; acyl; optionally substituted aliphatic; optionally substituted heteroaliphatic; optionally substituted alkyl; optionally substituted alkenyl; optionally substituted alkynyl; optionally substituted aryl, optionally substituted heteroaryl, aliphaticoxy, heteroaliphaticoxy, alkyloxy, heteroalkyloxy, aryloxy, heteroaryloxy, aliphaticthioxy, heteroaliphaticthioxy, alkylthioxy, heteroalkylthioxy, arylthioxy, heteroarylthioxy, mono- or di-aliphaticamino, mono- or di-heteroaliphaticamino, mono- or di-alkylamino, mono- or di-heteroalkylamino, mono- or di-arylamino, or mono- or di-heteroarylamino; or two RA groups taken together form a 5- to 6-membered heterocyclic ring. Exemplary acyl groups include aldehydes (—CHO), carboxylic acids (—CO2H), ketones, acyl halides, esters, amides, imines, carbonates, carbamates, and ureas. Acyl substituents include, but are not limited to, any of the substituents described herein, that result in the formation of a stable moiety.
The term “acylene,” as used herein, is a subset of a substituted alkylene, substituted alkenylene, substituted alkynylene, substituted heteroalkylene, substituted heteroalkenylene, or substituted heteroalkynylene group, and refers to an acyl group having the general formulae: —R0—(C═X1)—R0—, —R0—X2(C═X1)—R0—, or —R0—X2(C═X1)X3—R0—, where X1, X2, and X3 is, independently, oxygen, sulfur, or NRr, wherein Rr is hydrogen or optionally substituted aliphatic, and R0 is an optionally substituted alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene, or heteroalkynylene group, as defined herein. Exemplary acylene groups wherein R0 is alkylene includes —(CH2)T—O(C═O)—(CH2)T—; —(CH2)T—NRr(C═O)—(CH2)T—; —(CH2)T—O(C═NRr)—(CH2)T—; —(CH2)T—NRr(C═NRr)—(CH2)T—; —(CH2)T—(C═O)—(CH2)T—; —(CH2)T—(C═NRr)—(CH2)T—; —(CH2)T—S(C═S)—(CH2)T—; —(CH2)T—NRr(C═S)—(CH2)T—; —(CH2)T—S(C═NRr)—(CH2)T—; —(CH2)T—O(C═S)—(CH2)T—; —(CH2)—(C═S)—(CH2)—; or —(CH2)T—S(C═O)—(CH2)T—, and the like, which may bear one or more substituents; and wherein each instance of T is, independently, an integer between 0 to 20. Acylene substituents include, but are not limited to, any of the substituents described herein, that result in the formation of a stable moiety.
The term “amino,” as used herein, refers to a group of the formula (—NH2). A “substituted amino” refers either to a mono-substituted amine (—NHRh) of a disubstituted amine (—NRh2), wherein the Rh substituent is any substituent as described herein that results in the formation of a stable moiety (e.g., an amino protecting group; aliphatic, alkyl, alkenyl, alkynyl, heteroaliphatic, heterocyclic, aryl, heteroaryl, acyl, amino, nitro, hydroxyl, thiol, halo, aliphaticamino, heteroaliphaticamino, alkylamino, heteroalkylamino, arylamino, heteroarylamino, alkylaryl, arylalkyl, aliphaticoxy, heteroaliphaticoxy, alkyloxy, heteroalkyloxy, aryloxy, heteroaryloxy, aliphaticthioxy, heteroaliphaticthioxy, alkylthioxy, heteroalkylthioxy, arylthioxy, heteroarylthioxy, acyloxy, and the like, each of which may or may not be further substituted). In certain embodiments, the Rh substituents of the di-substituted amino group (—NRh2) form a 5- to 6-membered heterocyclic ring.
The term “hydroxy” or “hydroxyl,” as used herein, refers to a group of the formula (—OH). A “substituted hydroxyl” refers to a group of the formula (—ORi), wherein Ri can be any substituent which results in a stable moiety (e.g., a hydroxyl protecting group; aliphatic, alkyl, alkenyl, alkynyl, heteroaliphatic, heterocyclic, aryl, heteroaryl, acyl, nitro, alkylaryl, arylalkyl, and the like, each of which may or may not be further substituted).
The term “thio” or “thiol,” as used herein, refers to a group of the formula (—SH). A “substituted thiol” refers to a group of the formula (—SRr), wherein Rr can be any substituent that results in the formation of a stable moiety (e.g., a thiol protecting group; aliphatic, alkyl, alkenyl, alkynyl, heteroaliphatic, heterocyclic, aryl, heteroaryl, acyl, sulfinyl, sulfonyl, cyano, nitro, alkylaryl, arylalkyl, and the like, each of which may or may not be further substituted).
The term “imino,” as used herein, refers to a group of the formula (═NRr), wherein Rr corresponds to hydrogen or any substituent as described herein, that results in the formation of a stable moiety (for example, an amino protecting group; aliphatic, alkyl, alkenyl, alkynyl, heteroaliphatic, heterocyclic, aryl, heteroaryl, acyl, amino, hydroxyl, alkylaryl, arylalkyl, and the like, each of which may or may not be further substituted).
The term “azide” or “azido,” as used herein, refers to a group of the formula (—N3).
The terms “halo” and “halogen,” as used herein, refer to an atom selected from fluorine (fluoro, —F), chlorine (chloro, —Cl), bromine (bromo, —Br), and iodine (iodo, —I).
The term “agent,” as used herein, refers to any molecule, entity, or moiety that can be conjugated to a sortase recognition motif. For example, an agent may be a protein, an amino acid, a peptide, a polynucleotide, a carbohydrate, a detectable label, a binding agent, a tag, a metal atom, a contrast agent, a catalyst, a non-polypeptide polymer, a synthetic polymer, a recognition element, a lipid, a linker, or chemical compound, such as a small molecule. In some embodiments, the agent is a binding agent, for example, a ligand or a ligand-binding molecule, streptavidin, biotin, an antibody or an antibody fragment. In some embodiments, the agent cannot be genetically encoded. In some such embodiments, the agent is a lipid, a carbohydrate, or a small molecule. Additional agents suitable for use in embodiments of the present invention will be apparent to the skilled artisan. The invention is not limited in this respect.
The term “amino acid,” as used herein, includes any naturally occurring and non-naturally occurring amino acid. There are many known non-natural amino acids any of which may be included in the polypeptides or proteins described herein. See, for example, S. Hunt, The Non-Protein Amino Acids: In Chemistry and Biochemistry of the Amino Acids, edited by G. C. Barrett, Chapman and Hall, 1985. Some non-limiting examples of non-natural amino acids are 4-hydroxyproline, desmosine, gamma-aminobutyric acid, beta-cyanoalanine, norvaline, 4-(E)-butenyl-4(R)-methyl-N-methyl-L-threonine, N-methyl-L-leucine, 1-amino-cyclopropanecarboxylic acid, 1-amino-2-phenyl-cyclopropanecarboxylic acid, 1-amino-cyclobutanecarboxylic acid, 4-amino-cyclopentenecarboxylic acid, 3-amino-cyclohexanecarboxylic acid, 4-piperidylacetic acid, 4-amino-1-methylpyrrole-2-carboxylic acid, 2,4-diaminobutyric acid, 2,3-diaminopropionic acid, 2,4-diaminobutyric acid, 2-aminoheptanedioic acid, 4-(aminomethyl)benzoic acid, 4-aminobenzoic acid, ortho-, meta- and para-substituted phenylalanines (e.g., substituted with —C(═O)C6H5; —CF3; —CN; -halo; —NO2; —CH3), disubstituted phenylalanines, substituted tyrosines (e.g., further substituted with —C(═O)C6H5; —CF3; —CN; -halo; —NO2; —CH3), and statine. In the context of amino acid sequences, “X” or “Xaa” represents any amino acid residue, e.g., any naturally occurring and/or any non-naturally occurring amino acid residue.
The term “antibody”, as used herein, refers to a protein belonging to the immunoglobulin superfamily. The terms antibody and immunoglobulin are used interchangeably. With some exceptions, mammalian antibodies are typically made of basic structural units each with two large heavy chains and two small light chains. There are several different types of antibody heavy chains, and several different kinds of antibodies, which are grouped into different isotypes based on which heavy chain they possess. Five different antibody isotypes are known in mammals, IgG, IgA, IgE, IgD, and IgM, which perform different roles, and help direct the appropriate immune response for each different type of foreign object they encounter. In some embodiments, an antibody is an IgG antibody, e.g., an antibody of the IgG1, 2, 3, or 4 human subclass. Antibodies from mammalian species (e.g., human, mouse, rat, goat, pig, horse, cattle, camel) are within the scope of the term, as are antibodies from non-mammalian species (e.g., from birds, reptiles, amphibia) are also within the scope of the term, e.g., IgY antibodies.
Only part of an antibody is involved in the binding of the antigen, and antigen-binding antibody fragments, their preparation and use, are well known to those of skill in the art. As is well-known in the art, only a small portion of an antibody molecule, the paratope, is involved in the binding of the antibody to its epitope (see, in general, Clark, W. R. (1986) The Experimental Foundations of Modern Immunology Wiley & Sons, Inc., New York; Roitt, I. (1991) Essential Immunology, 7th Ed., Blackwell Scientific Publications, Oxford). Suitable antibodies and antibody fragments for use in the context of some embodiments of the present invention include, for example, human antibodies, humanized antibodies, domain antibodies, F(ab′), F(ab′)2, Fab, Fv, Fc, and Fd fragments, antibodies in which the Fc and/or FR and/or CDR1 and/or CDR2 and/or light chain CDR3 regions have been replaced by homologous human or non-human sequences; antibodies in which the FR and/or CDR1 and/or CDR2 and/or light chain CDR3 regions have been replaced by homologous human or non-human sequences; antibodies in which the FR and/or CDR1 and/or CDR2 and/or light chain CDR3 regions have been replaced by homologous human or non-human sequences; and antibodies in which the FR and/or CDR1 and/or CDR2 regions have been replaced by homologous human or non-human sequences. In some embodiments, so-called single chain antibodies (e.g., ScFv), (single) domain antibodies, and other intracellular antibodies may be used in the context of the present invention. Domain antibodies, camelid and camelized antibodies and fragments thereof, for example, VHH domains, or nanobodies, such as those described in patents and published patent applications of Ablynx NV and Domantis are also encompassed in the term antibody. Further, chimeric antibodies, e.g., antibodies comprising two antigen-binding domains that bind to different antigens, are also suitable for use in the context of some embodiments of the present invention.
The term “antigen-binding antibody fragment,” as used herein, refers to a fragment of an antibody that comprises the paratope, or a fragment of the antibody that binds to the antigen the antibody binds to, with similar specificity and affinity as the intact antibody. Antibodies, e.g., fully human monoclonal antibodies, may be identified using phage display (or other display methods such as yeast display, ribosome display, bacterial display). Display libraries, e.g., phage display libraries, are available (and/or can be generated by one of ordinary skill in the art) that can be screened to identify an antibody that binds to an antigen of interest, e.g., using panning. See, e.g., Sidhu, S. (ed.) Phage Display in Biotechnology and Drug Discovery (Drug Discovery Series; CRC Press; 1st ed., 2005; Aitken, R. (ed.) Antibody Phage Display: Methods and Protocols (Methods in Molecular Biology) Humana Press; 2nd ed., 2009.
The term “binding agent,” as used herein refers to any molecule that binds another molecule with high affinity. In some embodiments, a binding agent binds its binding partner with high specificity. Examples for binding agents include, without limitation, antibodies, antibody fragments, nucleic acid molecules, receptors, ligands, aptamers, and adnectins.
The term “click chemistry” refers to a chemical philosophy introduced by K. Barry Sharpless of The Scripps Research Institute, describing chemistry tailored to generate covalent bonds quickly and reliably by joining small units comprising reactive groups together (see H. C. Kolb, M. G. Finn and K. B. Sharpless (2001). Click Chemistry: Diverse Chemical Function from a Few Good Reactions. Angewandte Chemie International Edition 40 (11): 2004-2021. Click chemistry does not refer to a specific reaction, but to a concept including, but not limited to, reactions that mimic reactions found in nature. In some embodiments, click chemistry reactions are modular, wide in scope, give high chemical yields, generate inoffensive byproducts, are stereospecific, exhibit a large thermodynamic driving force>84 kJ/mol to favor a reaction with a single reaction product, and/or can be carried out under physiological conditions. In some embodiments, a click chemistry reaction exhibits high atom economy, can be carried out under simple reaction conditions, use readily available starting materials and reagents, uses no toxic solvents or use a solvent that is benign or easily removed (preferably water), and/or provides simple product isolation by non-chromatographic methods (crystallisation or distillation).
The term “click chemistry handle,” as used herein, refers to a reactant, or a reactive group, that can partake in a click chemistry reaction. For example, a strained alkyne, e.g., a cyclooctyne, is a click chemistry handle, since it can partake in a strain-promoted cycloaddition (see, e.g., Table 1). In general, click chemistry reactions require at least two molecules comprising click chemistry handles that can react with each other. Such click chemistry handle pairs that are reactive with each other are sometimes referred to herein as partner click chemistry handles. For example, an azide is a partner click chemistry handle to a cyclooctyne or any other alkyne. Exemplary click chemistry handles suitable for use according to some aspects of this invention are described herein, for example, in Tables 1 and 2. Other suitable click chemistry handles are known to those of skill in the art. For two molecules to be conjugated via click chemistry, the click chemistry handles of the molecules have to be reactive with each other, for example, in that the reactive moiety of one of the click chemistry handles can react with the reactive moiety of the second click chemistry handle to form a covalent bond. Such reactive pairs of click chemistry handles are well known to those of skill in the art and include, but are not limited to, those described in Table 1:
In some embodiments, click chemistry handles are used that can react to form covalent bonds in the absence of a metal catalyst. Such click chemistry handles are well known to those of skill in the art and include the click chemistry handles described in Becer, Hoogenboom, and Schubert, Click Chemistry beyond Metal-Catalyzed Cycloaddition, Angewandte Chemie International Edition (2009) 48: 4900-4908:
[a]RT = room temperature, DMF = N,N-dimethylformamide, NMP = N-methylpyrolidone, THF = tetrahydrofuran, CH3CN = acetonitrile.
The term “conjugated” or “conjugation” refers to an association of two molecules, for example, two proteins or a protein and an agent, e.g., a small molecule, with one another in a way that they are linked by a direct or indirect covalent or non-covalent interaction. In certain embodiments, the association is covalent, and the entities are said to be “conjugated” to one another. In some embodiments, a protein is post-translationally conjugated to another molecule, for example, a second protein, a small molecule, a detectable label, a click chemistry handle, or a binding agent, by forming a covalent bond between the protein and the other molecule after the protein has been formed, and, in some embodiments, after the protein has been isolated. In some embodiments, two molecules are conjugated via a linker connecting both molecules. For example, in some embodiments where two proteins are conjugated to each other to form a protein fusion, the two proteins may be conjugated via a polypeptide linker, e.g., an amino acid sequence connecting the C-terminus of one protein to the N-terminus of the other protein. In some embodiments, two proteins are conjugated at their respective C-termini, generating a C—C conjugated chimeric protein. In some embodiments, two proteins are conjugated at their respective N-termini, generating an N—N conjugated chimeric protein. In some embodiments, conjugation of a protein to a peptide is achieved by transpeptidation using a sortase. See, e.g., Ploegh et al., International PCT Patent Application, PCT/US2010/000274, filed Feb. 1, 2010, published as WO/2010/087994 on Aug. 5, 2010, and Ploegh et al., International Patent Application PCT/US2011/033303, filed Apr. 20, 2011, published as WO/2011/133704 on Oct. 27, 2011, the entire contents of each of which are incorporated herein by reference, for exemplary sortases, proteins, recognition motifs, reagents, and methods for sortase-mediated transpeptidation.
The term “detectable label” refers to a moiety that has at least one element, isotope, or functional group incorporated into the moiety which enables detection of the molecule, e.g., a protein or peptide, or other entity, to which the label is attached. Labels can be directly attached (i.e., via a bond) or can be attached by a linker (such as, for example, an optionally substituted alkylene; an optionally substituted alkenylene; an optionally substituted alkynylene; an optionally substituted heteroalkylene; an optionally substituted heteroalkenylene; an optionally substituted heteroalkynylene; an optionally substituted arylene; an optionally substituted heteroarylene; or an optionally substituted acylene, or any combination thereof, which can make up a linker). It will be appreciated that the label may be attached to or incorporated into a molecule, for example, a protein, polypeptide, or other entity, at any position. In general, a detectable label can fall into any one (or more) of five classes: a) a label which contains isotopic moieties, which may be radioactive or heavy isotopes, including, but not limited to, 2H, 3H, 13C, 14C, 15N, 18F, 31P, 32P, 35S, 67Ga, 99mTc (Tc-99m), 111In, 123I, 125I, 131I, 153Gd, 169Yb, and 186Re; b) a label which contains an immune moiety, which may be antibodies or antigens, which may be bound to enzymes (e.g., such as horseradish peroxidase); c) a label which is a colored, luminescent, phosphorescent, or fluorescent moieties (e.g., such as the fluorescent label fluorescein-isothiocyanate (FITC); d) a label which has one or more photo affinity moieties; and e) a label which is a ligand for one or more known binding partners (e.g., biotin-streptavidin, FK506-FKBP). In certain embodiments, a label comprises a radioactive isotope, preferably an isotope which emits detectable particles, such as β particles. In certain embodiments, the label comprises a fluorescent moiety. In certain embodiments, the label is the fluorescent label fluorescein-isothiocyanate (FITC). In certain embodiments, the label comprises a ligand moiety with one or more known binding partners. In certain embodiments, the label comprises biotin. In some embodiments, a label is a fluorescent polypeptide (e.g., GFP or a derivative thereof such as enhanced GFP (EGFP)) or a luciferase (e.g., a firefly, Renilla, or Gaussia luciferase). It will be appreciated that, in certain embodiments, a label may react with a suitable substrate (e.g., a luciferin) to generate a detectable signal. Non-limiting examples of fluorescent proteins include GFP and derivatives thereof, proteins comprising fluorophores that emit light of different colors such as red, yellow, and cyan fluorescent proteins. Exemplary fluorescent proteins include, e.g., Sirius, Azurite, EBFP2, TagBFP, mTurquoise, ECFP, Cerulean, TagCFP, mTFP1, mUkG1, mAG1, AcGFP1, TagGFP2, EGFP, mWasabi, EmGFP, TagYPF, EYFP, Topaz, SYFP2, Venus, Citrine, mKO, mKO2, mOrange, mOrange2, TagRFP, TagRFP-T, mStrawberry, mRuby, mCherry, mRaspberry, mKate2, mPlum, mNeptune, T-Sapphire, mAmetrine, mKeima. See, e.g., Chalfie, M. and Kain, S R (eds.) Green fluorescent protein: properties, applications, and protocols Methods of biochemical analysis, v. 47 Wiley-Interscience, Hoboken, N.J., 2006; and Chudakov, D M, et al., Physiol Rev. 90(3):1103-63, 2010, for discussion of GFP and numerous other fluorescent or luminescent proteins. In some embodiments, a label comprises a dark quencher, e.g., a substance that absorbs excitation energy from a fluorophore and dissipates the energy as heat.
The term “linker,” as used herein, refers to a chemical group or molecule covalently linked to a molecule, for example, a protein, and a chemical group or moiety, for example, a click chemistry handle. In some embodiments, the linker is positioned between, or flanked by, two groups, molecules, or moieties and connected to each one via a covalent bond, thus connecting the two. In some embodiments, the linker is an amino acid or a plurality of amino acids. In some embodiments, the linker comprises 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or more than 20 amino acids. In some embodiments, the linker comprises a poly-glycine sequence. In some embodiments, the linker comprises a GGGGS sequence (SEQ ID NO: 19), or a plurality of such sequences, e.g., a GGGGSGGGGS sequence (SEQ ID NO: 20). In some embodiments, the linker comprises a non-protein structure. In some embodiments, the linker is an organic molecule, group, polymer, or chemical moiety.
The terms “nucleic acid” and “nucleic acid molecule,” as used herein, refer to a compound comprising a nucleobase and an acidic moiety, e.g., a nucleoside, a nucleotide, or a polymer of nucleotides. Typically, polymeric nucleic acids, e.g., nucleic acid molecules comprising three or more nucleotides are linear molecules, in which adjacent nucleotides are linked to each other via a phosphodiester linkage. In some embodiments, “nucleic acid” refers to individual nucleic acid residues (e.g. nucleotides and/or nucleosides). In some embodiments, “nucleic acid” refers to an oligonucleotide chain comprising three or more individual nucleotide residues. As used herein, the terms “oligonucleotide” and “polynucleotide” can be used interchangeably to refer to a polymer of nucleotides (e.g., a string of at least three nucleotides). In some embodiments, “nucleic acid” encompasses RNA as well as single and/or double-stranded DNA. Nucleic acids may be naturally occurring, for example, in the context of a genome, a transcript, an mRNA, tRNA, rRNA, siRNA, snRNA, a plasmid, cosmid, chromosome, chromatid, or other naturally occurring nucleic acid molecule. On the other hand, a nucleic acid molecule may be a non-naturally occurring molecule, e.g., a recombinant DNA or RNA, an artificial chromosome, an engineered genome, or fragment thereof, or a synthetic DNA, RNA, DNA/RNA hybrid, or including non-naturally occurring nucleotides or nucleosides. Furthermore, the terms “nucleic acid,” “DNA,” “RNA,” and/or similar terms include nucleic acid analogs, i.e. analogs having other than a phosphodiester backbone. Nucleic acids can be purified from natural sources, produced using recombinant expression systems, chemically synthesized, and, optionally, purified. Where appropriate, e.g., in the case of chemically synthesized molecules, nucleic acids can comprise nucleoside analogs such as analogs having chemically modified bases or sugars, and backbone modifications. In some embodiments, a nucleic acid is or comprises natural nucleosides (e.g. adenosine, thymidine, guanosine, cytidine, uridine, deoxyadenosine, deoxythymidine, deoxyguanosine, and deoxycytidine); nucleoside analogs (e.g., 2-aminoadenosine, 2-thiothymidine, inosine, pyrrolo-pyrimidine, 3-methyl adenosine, 5-methylcytidine, 2-aminoadenosine, C5-bromouridine, C5-fluorouridine, C5-iodouridine, C5-propynyl-uridine, C5-propynyl-cytidine, C5-methylcytidine, 2-aminoadeno sine, 7-deazaadenosine, 7-deazaguanosine, 8-oxoadenosine, 8-oxoguanosine, O(6)-methylguanine, and 2-thiocytidine); chemically modified bases; biologically modified bases (e.g., methylated bases); intercalated bases; modified sugars (e.g., 2′-fluororibose, ribose, 2′-deoxyribose, arabinose, and hexose); and/or modified phosphate groups (e.g., phosphorothioates and 5′-N-phosphoramidite linkages).
The terms “protein,” “peptide” and “polypeptide” are used interchangeably herein, and refer to a polymer of amino acid residues linked together by peptide (amide) bonds. The terms refer to a protein, peptide, or polypeptide of any size, structure, or function. Typically, a protein, peptide, or polypeptide will be at least three amino acids long. A protein, peptide, or polypeptide may refer to an individual protein or a collection of proteins. One or more of the amino acids in a protein, peptide, or polypeptide may be modified, for example, by the addition of a chemical entity such as a carbohydrate group, a hydroxyl group, a phosphate group, a farnesyl group, an isofarnesyl group, a fatty acid group, a linker for conjugation, functionalization, or other modification, etc. A protein, peptide, or polypeptide may also be a single molecule or may be a multi-molecular complex. A protein, peptide, or polypeptide may be just a fragment of a naturally occurring protein or peptide. A protein, peptide, or polypeptide may be naturally occurring, recombinant, or synthetic, or any combination thereof.
The term “small molecule” is used herein to refer to molecules, whether naturally-occurring or artificially created (e.g., via chemical synthesis) that have a relatively low molecular weight. Typically, a small molecule is an organic compound (i.e., it contains carbon). A small molecule may contain multiple carbon-carbon bonds, stereocenters, and other functional groups (e.g., amines, hydroxyl, carbonyls, heterocyclic rings, etc.). In some embodiments, small molecules are monomeric and have a molecular weight of less than about 1500 g/mol. In certain embodiments, the molecular weight of the small molecule is less than about 1000 g/mol or less than about 500 g/mol. In certain embodiments, the small molecule is a drug, for example, a drug that has already been deemed safe and effective for use in humans or animals by the appropriate governmental agency or regulatory body.
The term “sortase,” as used herein, refers to an enzyme able to carry out a transpeptidation reaction conjugating the C-terminus of a protein to the N-terminus of a protein via transamidation. Sortases are also referred to as transamidases, and typically exhibit both a protease and a transpeptidation activity. Various sortases from prokaryotic organisms have been identified. For example, some sortases from Gram-positive bacteria cleave and translocate proteins to proteoglycan moieties in intact cell walls. Among the sortases that have been isolated from Staphylococcus aureus, are sortase A (Srt A) and sortase B (Srt B). Thus, in certain embodiments, a transamidase used in accordance with the present invention is sortase A, e.g., from S. aureus, also referred to herein as SrtAaureus. In certain embodiments, a transamidase is a sortase B, e.g., from S. aureus, also referred to herein as SrtBaureus.
Sortases have been classified into 4 classes, designated A, B, C, and D, designated sortase A, sortase B, sortase C, and sortase D, respectively, based on sequence alignment and phylogenetic analysis of 61 sortases from Gram-positive bacterial genomes (Dramsi S, Trieu-Cuot P, Bierne H, Sorting sortases: a nomenclature proposal for the various sortases of Gram-positive bacteria. Res Microbiol. 156(3):289-97, 2005; the entire contents of which are incorporated herein by reference). These classes correspond to the following subfamilies, into which sortases have also been classified by Comfort and Clubb (Comfort D, Clubb R T. A comparative genome analysis identifies distinct sorting pathways in gram-positive bacteria. Infect Immun., 72(5):2710-22, 2004; the entire contents of which are incorporated herein by reference): Class A (Subfamily 1), Class B (Subfamily 2), Class C (Subfamily 3), Class D (Subfamilies 4 and 5). The aforementioned references disclose numerous sortases and recognition motifs. See also Pallen, M. J.; Lam, A. C.; Antonio, M.; Dunbar, K. TRENDS in Microbiology, 2001, 9(3), 97-101; the entire contents of which are incorporated herein by reference. Those skilled in the art will readily be able to assign a sortase to the correct class based on its sequence and/or other characteristics such as those described in Drami, et al., supra. The term “sortase A” is used herein to refer to a class A sortase, usually named SrtA in any particular bacterial species, e.g., SrtA from S. aureus. Likewise “sortase B” is used herein to refer to a class B sortase, usually named SrtB in any particular bacterial species, e.g., SrtB from S. aureus. The invention encompasses embodiments relating to a sortase A from any bacterial species or strain. The invention encompasses embodiments relating to a sortase B from any bacterial species or strain. The invention encompasses embodiments relating to a class C sortase from any bacterial species or strain. The invention encompasses embodiments relating to a class D sortase from any bacterial species or strain.
Amino acid sequences of Srt A and Srt B and the nucleotide sequences that encode them are known to those of skill in the art and are disclosed in a number of references cited herein, the entire contents of all of which are incorporated herein by reference. The amino acid sequences of S. aureus SrtA and SrtB are homologous, sharing, for example, 22% sequence identity and 37% sequence similarity. The amino acid sequence of a sortase-transamidase from Staphylococcus aureus also has substantial homology with sequences of enzymes from other Gram-positive bacteria, and such transamidases can be utilized in the ligation processes described herein. For example, for SrtA there is about a 31% sequence identity (and about 44% sequence similarity) with best alignment over the entire sequenced region of the S. pyogenes open reading frame. There is about a 28% sequence identity with best alignment over the entire sequenced region of the A. naeslundii open reading frame. It will be appreciated that different bacterial strains may exhibit differences in sequence of a particular polypeptide, and the sequences herein are exemplary.
In certain embodiments a transamidase bearing 18% or more sequence identity, 20% or more sequence identity, or 30% or more sequence identity with an S. pyogenes, A. naeslundii, S. mutans, E. faecalis or B. subtilis open reading frame encoding a sortase can be screened, and enzymes having transamidase activity comparable to Srt A or Srt B from S. aureas can be utilized (e.g., comparable activity sometimes is 10% of Srt A or Srt B activity or more).
Thus in some embodiments of the invention the sortase is a sortase A (SrtA). SrtA recognizes the motif LPXTX (wherein each occurrence of X represents independently any amino acid residue), with common recognition motifs being, e.g., LPKTG (SEQ ID NO: 21), LPATG (SEQ ID NO: 22), LPNTG (SEQ ID NO: 23). In some embodiments LPETG (SEQ ID NO: 10) is used as the sortase recognition motif. However, motifs falling outside this consensus may also be recognized. For example, in some embodiments the motif comprises an ‘A’ rather than a ‘T’ at position 4, e.g., LPXAG (SEQ ID NO: 24), e.g., LPNAG (SEQ ID NO: 25). In some embodiments the motif comprises an ‘A’ rather than a ‘G’ at position 5, e.g., LPXTA (SEQ ID NO: 26), e.g., LPNTA (SEQ ID NO: 27). In some embodiments the motif comprises a ‘G’ rather than ‘P’ at position 2, e.g., LGXTG (SEQ ID NO: 28), e.g., LGATG (SEQ ID NO: 29). In some embodiments the motif comprises an ‘I’ rather than ‘L’ at position 1, e.g., IPXTG (SEQ ID NO: 30), e.g., IPNTG (SEQ ID NO: 31) or IPETG (SEQ ID NO: 32). Additional suitable sortase recognition motifs will be apparent to those of skill in the art, and the invention is not limited in this respect. It will be appreciated that the terms “recognition motif” and “recognition sequence”, with respect to sequences recognized by a transamidase or sortase, are used interchangeably.
In some embodiments of the invention the sortase is a sortase B (SrtB), e.g., a sortase B of S. aureus, B. anthracis, or L. monocytogenes. Motifs recognized by sortases of the B class (SrtB) often fall within the consensus sequences NPXTX, e.g., NP[Q/K]-[T/sHN/G/s], such as NPQTN (SEQ ID NO: 33) or NPKTG (SEQ ID NO: 34). For example, sortase B of S. aureus or B. anthracis cleaves the NPQTN (SEQ ID NO: 35) or NPKTG (SEQ ID NO: 36) motif of IsdC in the respective bacteria (see, e.g., Marraffini, L. and Schneewind, O., Journal of Bacteriology, 189(17), p. 6425-6436, 2007). Other recognition motifs found in putative substrates of class B sortases are NSKTA (SEQ ID NO: 37), NPQTG (SEQ ID NO: 38), NAKTN (SEQ ID NO: 39), and NPQSS (SEQ ID NO: 40). For example, SrtB from L. monocytogenes recognizes certain motifs lacking P at position 2 and/or lacking Q or K at position 3, such as NAKTN (SEQ ID NO: 41) and NPQSS (SEQ ID NO: 42) (Mariscotti J F, García-Del Portillo F, Pucciarelli M G. The listeria monocytogenes sortase-B recognizes varied amino acids at position two of the sorting motif. J Biol Chem. 2009 Jan. 7.)
In some embodiments, the sortase is a sortase C (Srt C). Sortase C may utilize LPXTX as a recognition motif, with each occurrence of X independently representing any amino acid residue.
In some embodiments, the sortase is a sortase D (Srt D). Sortases in this class are predicted to recognize motifs with a consensus sequence NA-[E/A/S/H]-TG (Comfort D, supra). Sortase D has been found, e.g., in Streptomyces spp., Corynebacterium spp., Tropheryma whipplei, Thermobifida fusca, and Bifidobacterium longhum. LPXTA (SEQ ID NO: 43) or LAXTG (SEQ ID NO: 44) may serve as a recognition sequence for sortase D, e.g., of subfamilies 4 and 5, respectively subfamily-4 and subfamily-5 enzymes process the motifs LPXTA (SEQ ID NO: 45) and LAXTG (SEQ ID NO: 46), respectively). For example, B. anthracis Sortase C has been shown to specifically cleave the LPNTA (SEQ ID NO: 47) motif in B. anthracis BasI and BasH (see Marrafini, supra).
See Barnett and Scott for description of a sortase that recognizes QVPTGV (SEQ ID NO: 48) motif (Barnett, T C and Scott, J R, Differential Recognition of Surface Proteins in Streptococcus pyogenes by Two Sortase Gene Homologs. Journal of Bacteriology, Vol. 184, No. 8, p. 2181-2191, 2002; the entire contents of which are incorporated herein by reference). Additional sortases, including, but not limited to, sortases recognizing additional sortase recognition motifs are also suitable for use in some embodiments of this invention. For example, sortases described in Chen I, Dorr B M, and Liu D R., A general strategy for the evolution of bond-forming enzymes using yeast display. Proc Natl Acad Sci USA. 2011 Jul. 12; 108(28):11399, the entire contents of which are incorporated herein.
The use of sortases found in any gram-positive organism, such as those mentioned herein and/or in the references (including databases) cited herein is contemplated in the context of some embodiments of this invention. Also contemplated is the use of sortases found in gram negative bacteria, e.g., Colwellia psychrerythraea, Microbulbifer degradans, Bradyrhizobium japonicum, Shewanella oneidensis, and Shewanella putrefaciens. Such sortases recognize sequence motifs outside the LPXTX consensus, for example, LP[Q/K]T[A/S]T (SEQ ID NO: 289). In keeping with the variation tolerated at position 3 in sortases from gram-positive organisms, a sequence motif LPXT[A/S], e.g., LPXTA (SEQ ID NO: 49) or LPSTS (SEQ ID NO: 50) may be used.
Those of skill in the art will appreciate that any sortase recognition motif known in the art can be used in some embodiments of this invention, and that the invention is not limited in this respect. For example, in some embodiments the sortase recognition motif is selected from: LPKTG (SEQ ID NO: 51), LPITG (SEQ ID NO: 52), LPDTA (SEQ ID NO: 53), SPKTG (SEQ ID NO: 54), LAETG (SEQ ID NO: 55), LAATG (SEQ ID NO: 56), LAHTG (SEQ ID NO: 57), LASTG (SEQ ID NO: 58), LAETG (SEQ ID NO: 59), LPLTG (SEQ ID NO: 60), LSRTG (SEQ ID NO: 61), LPETG (SEQ ID NO: 10), VPDTG (SEQ ID NO: 62), IPQTG (SEQ ID NO: 63), YPRRG (SEQ ID NO: 64), LPMTG (SEQ ID NO: 65), LPLTG (SEQ ID NO: 66), LAFTG (SEQ ID NO: 67), LPQTS (SEQ ID NO: 68), it being understood that in various embodiments of the invention the 5th residue may be replaced with any other amino acid residue. For example, the sequence used may be LPXT, LAXT, LPXA, LGXT, IPXT, NPXT, NPQS (SEQ ID NO: 69), LPST (SEQ ID NO: 70), NSKT (SEQ ID NO: 71), NPQT (SEQ ID NO: 72), NAKT (SEQ ID NO: 73), LPIT (SEQ ID NO: 74), LAET (SEQ ID NO: 75), or NPQS (SEQ ID NO: 76). The invention encompasses embodiments in which ‘X’ in any sortase recognition motif disclosed herein or known in the art is amino acid, for example, any naturally-occurring or any non-naturally occurring amino acid. In some embodiments, X is selected from the 20 standard amino acids found most commonly in proteins found in living organisms. In some embodiments, e.g., where the recognition motif is LPXTG (SEQ ID NO: 78) or LPXT, X is D, E, A, N, Q, K, or R. In some embodiments, X in a particular recognition motif is selected from those amino acids that occur naturally at position 3 in a naturally occurring sortase substrate. For example, in some embodiments X is selected from K, E, N, Q, A in an LPXTG (SEQ ID NO: 78) or LPXT motif where the sortase is a sortase A. In some embodiments X is selected from K, S, E, L, A, N in an LPXTG (SEQ ID NO: 78) or LPXT motif and a class C sortase is used.
In some embodiments, a sortase recognition sequence further comprises one or more additional amino acids, e.g., at the N or C terminus. For example, one or more amino acids (e.g., up to 5 amino acids) having the identity of amino acids found immediately N-terminal to, or C-terminal to, a 5 amino acid recognition sequence in a naturally occurring sortase substrate may be incorporated. Such additional amino acids may provide context that improves the recognition of the recognition motif.
In some embodiments, a sortase recognition motif is masked. In contrast to an unmasked sortase recognition motif, which can be can be recognized by a sortase, a masked sortase recognition motif is a motif that is not recognized by a sortase but that can be readily modified (“unmasked”) such that the resulting motif is recognized by the sortase. For example, in some embodiments at least one amino acid of a masked sortase recognition motif comprises a side chain comprising a moiety that inhibits, e.g., prevents, recognition of the sequence by a sortase of interest, e.g., SrtAaureus. Removal of the inhibiting moiety, in turn, allows recognition of the motif by the sortase. Masking may, for example, reduce recognition by at least 80%, 90%, 95%, or more (e.g., to undetectable levels) in certain embodiments. By way of example, in certain embodiments a threonine residue in a sortase recognition motif such as LPXTG (SEQ ID NO: 78) may be phosphorylated, thereby rendering it refractory to recognition and cleavage by SrtA. The masked recognition sequence can be unmasked by treatment with a phosphatase, thus allowing it to be used in a SrtA-catalyzed transamidation reaction.
The term “sortase substrate,” as used herein refers to any molecule that is recognized by a sortase, for example, any molecule that can partake in a sortase-mediated transpeptidation reaction. A typical sortase-mediated transpeptidation reaction involves a substrate comprising a C-terminal sortase recognition motif, e.g., an LPXTX motif, and a second substrate comprising an N-terminal sortase recognition motif, e.g., an N-terminal polyglycine or polyalanine. A sortase substrate may be a peptide or a protein, for example, a target protein on the surface of a virus, or a peptide comprising a sortase recognition motif such as an LPXTX motif or a polyglycine or polyalanine, wherein the peptide is conjugated to an agent, e.g., a small molecule, a binding agent, or a fluorophore. Accordingly, both proteins and non-protein molecules can be sortase substrates as long as they comprise a sortase recognition motif. Some examples of sortase substrates are described in more detail elsewhere herein and additional suitable sortase substrates will be apparent to the skilled artisan. The invention is not limited in this respect.
The term “sortagging,” as used herein, refers to the process of adding a tag, e.g., a moiety or molecule, for example, a protein, polypeptide, detectable label, binding agent, or click chemistry handle, onto a target molecule, for example, a target protein on the surface of a viral particle via a sortase-mediated transpeptidation reaction. Examples of additional suitable tags include, but are not limited to, amino acids, nucleic acids, polynucleotides, sugars, carbohydrates, polymers, lipids, fatty acids, and small molecules. Other suitable tags will be apparent to those of skill in the art and the invention is not limited in this aspect. In some embodiments, a tag comprises a sequence useful for purifying, expressing, solubilizing, and/or detecting a polypeptide. In some embodiments, a tag can serve multiple functions. In some embodiments, the tag is relatively small, e.g., ranging from a few amino acids up to about 100 amino acids long. In some embodiments, a tag is more than 100 amino acids long, e.g., up to about 500 amino acids long, or more. In some embodiments, a tag comprises an HA, TAP, Myc, 6×His, Flag, streptavidin, biotin, or GST tag, to name a few examples. In some embodiments, a tag comprises a solubility-enhancing tag (e.g., a SUMO tag, NUS A tag, SNUT tag, or a monomeric mutant of the Ocr protein of bacteriophage T7). See, e.g., Esposito D and Chatterjee D K. Curr Opin Biotechnol.; 17(4):353-8 (2006). In some embodiments, a tag is cleavable, so that it can be removed, e.g., by a protease. In some embodiments, this is achieved by including a protease cleavage site in the tag, e.g., adjacent or linked to a functional portion of the tag. Exemplary proteases include, e.g., thrombin, TEV protease, Factor Xa, PreScission protease, etc. In some embodiments, a “self-cleaving” tag is used. See, e.g., Wood et al., International PCT Application PCT/US2005/05763, filed on Feb. 24, 2005, and published as WO/2005/086654 on Sep. 22, 2005.
The term “target protein,” as used herein in the context of sortase-mediated modification of viral particles, refers to a protein on the surface of a virus that is the target of a sortase-mediated conjugation. For example, in an embodiment where M13 pIII is modified by sortagging, e.g., by adding a detectable label or a binding agent to M13 pIII on the surface of an M13 bacteriophage particle, pIII is the target protein. The term “target protein” may refer to a wild type or naturally occurring form of the respective protein, or to an engineered form, for example, to a recombinant protein variant comprising a sortase recognition motif not contained in a wild-type form of the protein. The term “modifying a target protein,” as used herein in the context of sortase-mediated protein modification, refers to a process of altering a target protein comprising a sortase recognition motif via a sortase-mediated transpeptidation reaction. Typically, the modifying results in the target protein being conjugated to an agent, for example, a peptide, protein, binding agent, detectable label, or small molecule.
The term “virus,” as used interchangeably herein with the term “viral particle,” refers to an infectious agent that can infect a living cell. A virus particle typically comprises the viral genome, e.g., as DNA, RNA, or a DNA/RNA hybrid, proteins associated with the viral genome that form a viral coat, and, in some cases an envelope of lipids that surrounds the viral protein coat. In some embodiments, a viral particle comprises a viral genome that can replicate inside a host cell once the virus has infected the cell. In some embodiments, the viral functions encoded in the viral genome result in the production of new viral particles by the host cell. In some embodiments, the newly generated viral particles can themselves infect additional host cells. Suitable viruses for use in the context of this invention typically comprise at least one surface protein comprising a sortase recognition motif. In some embodiments, the sortase recognition motif is comprised in a wild-type viral protein (e.g., a capsid protein or a viral surface protein). In some embodiments, the sortase recognition motif is encoded by a recombinant viral genome, e.g., a viral genome in which an open reading frame has been altered to insert a sortase recognition motif. A virus suitable for use according to aspects of this invention may be recombinant, and comprise genetic alterations other than the addition of a sortase recognition motif to a surface protein. For example, in some embodiment, a virus may be used that is replication-incompetent, or that carries in its genome a selectable marker, e.g., an antibiotic resistance marker, that can be used to identify cells infected by the virus. Viruses can be classified according to their genome structure and type of nucleic acid comprised in the respective viral particles. A suitable virus according to aspects of this invention may be a dsDNA virus comprising a double-stranded DNA genome (e.g. adenoviruses, herpesviruses, poxviruses), an ssDNA virus comprising a single-stranded DNA genome (e.g. parvoviruses), a dsRNA virus comprising a double-stranded RNA genome (e.g. reoviruses), a (+)ssRNA virus comprising a single stranded (+)sense strand RNA genome (e.g. picornaviruses, togaviruses), a (−)ssRNA virus comprising a single stranded (−)sense RNA (e.g. orthomyxoviruses, rhabdoviruses), an ssRNA-RT virus comprising a single-stranded (+)sense RNA with a DNA intermediate genome in its life-cycle that is generated by reverse transcription of the RNA genome (e.g. retroviruses), or a dsDNA-RT virus (e.g. hepadnaviruses). Exemplary viruses include, e.g., Retroviridae (e.g., lentiviruses such as human immunodeficiency viruses, such as HIV-I); Caliciviridae (e.g. strains that cause gastroenteritis); Togaviridae (e.g. equine encephalitis viruses, rubella viruses); Flaviridae (e.g. dengue viruses, encephalitis viruses, yellow fever viruses, hepatitis C virus); Coronaviridae (e.g. coronaviruses); Rhabdoviridae (e.g. vesicular stomatitis viruses, rabies viruses); Filoviridae (e.g. Ebola viruses); Paramyxoviridae (e.g. parainfluenza viruses, mumps virus, measles virus, respiratory syncytial virus); Orthomyxoviridae (e.g. influenza viruses); Bunyaviridae (e.g. Hantaan viruses, bunga viruses, phleboviruses and Nairo viruses); Arenaviridae (hemorrhagic fever viruses); Reoviridae (erg., reoviruses, orbiviurses and rotaviruses); Birnaviridae; Hepadnaviridae (Hepatitis B virus); Parvoviridae (parvoviruses); Papovaviridae (papilloma viruses, polyoma viruses); Adenoviridae; Herpesviridae (herpes simplex virus (HSV) 1 and 2, varicella zoster virus, cytomegalovirus (CMV), EBV, KSV); Poxyiridae (variola viruses, vaccinia viruses, pox viruses); and Picornaviridae (e.g. polio viruses, hepatitis A virus; enteroviruses, human coxsackie viruses, rhinoviruses, echoviruses). In some embodiments, the virus is a bacteriophage, for example, a bacteriophage belonging to the family of Myoviridae (e.g., T4 phage), Siphoviridae (e.g., k phage, Bacteriophage T5), Podoviridae (e.g., T7 phage), Ligamenvirales, Lipothrixviridae, Rudiviridae, Ampullaviridae, Bacilloviridae, Bicaudaviridae, Clavaviridae, Corticoviridae, Cystoviridae, Fuselloviridae, Globuloviridae, Guttavirus, Inoviridae, Leviviridae (e.g., MS2, Qβ), Microviridae (e.g., ΦX174), Plasmaviridae, or Tectiviridae. Exemplary suitable bacteriophages include, without limitation, Lambda phage (λ phage, lysogen), T2 phage, T4 phage, T7 phage, T12 phage, R17 phage, M13 phage, MS2 phage, G4 phage, P1 phage, Enterobacteria phage P2, P4 phage, ΦX174 phage, N4 phage, Φ6 phage, and Φ29 phage. Additional bacteriophages suitable for surface functionalization using methods, reagents, and kits provided herein will be apparent to those of skill in the art. Suitable bacteriophages include, for example, bacteriophages described in Stephen T. Abedon, The Bacteriophages, Oxford University Press, USA; 2nd edition, Dec. 15, 2005, ISBN: 0195148509; particularly in parts III-V, pages 129-653; Elizabeth Kutter and Alexander Sulakvelidze: Bacteriophages: Biology and Applications. CRC Press; 1st edition (December 2004), ISBN: 0849313368; Martha R. J. Clokie and Andrew M. Kropinski: Bacteriophages: Methods and Protocols, Volume 1: Isolation, Characterization, and Interactions (Methods in Molecular Biology) Humana Press; 1st edition (December, 2008), ISBN: 1588296822; Martha R. J. Clokie and Andrew M. Kropinski: Bacteriophages: Methods and Protocols, Volume 2: Molecular and Applied Aspects (Methods in Molecular Biology) Humana Press; 1st edition (December 2008), ISBN: 1603275649; all of which are incorporated herein in their entirety by reference for disclosure of suitable phages and host cells as well as methods and protocols for isolation, culture, and manipulation of such phages.
In some embodiments, the phage is a filamentous phage. In some embodiments, the phage is an M13 phage. Wild-type M13 phage particles comprise a circular, single-stranded genome of approximately 6.4 kb. The wild-type genome includes ten genes, gI-gX, which, in turn, encode the ten M13 proteins, pI-pX, respectively. gVIII encodes pVIII, also often referred to as the major structural protein of the phage particles, while gIII encodes pIII, also referred to as the minor coat protein, which is required for infectivity of M13 phage particles. The M13 phage genome has extensively been studied and can be manipulated with recombinant techniques well known to those of skill in the art. For example, one or more of the wild-type genes can be deleted in whole or in part, and/or a heterologous nucleic acid construct can be inserted into the M13 genome. Such recombinant M13 phage genomes can be packaged into M13 phage particles in the presence of packaging proteins (e.g., pIII, pVI, pVII, pVIII, and pIX). The size of the M13 particles depends mainly on the size of the packaged genome. M13 does not have stringent genome size restrictions, and insertions of up to 42 kb have been reported. The M13 phage genome has been sequences, and M13 genomic sequences can be retrieved from public databases, such as the National Center for Biotechnology Information (NCBI) database (www.ncbi.nlm,nih.gov) and the ENSEMBL database (www.ensembl.org). An exemplary M13 genomic sequence is provided in entry V00604 of the National Center for Biotechnology Information (NCBI) database (www.ncbi.nlm,nih.gov):
The term “viral capsid,” as used herein, refers to a protein coat, also sometimes referred to as a protein shell, of a virus. The viral capsid encloses the viral genetic material. The capsid of most viruses comprises a plurality of oligomeric structural subunits made of proteins called protomers. The observable 3-dimensional morphological subunits, which may or may not correspond to individual proteins, are called capsomeres. Viral capsids can be classified according to their structure, e.g., into helical and icosahedral capsids. Some viruses, e.g., bacteriophages, have developed more complicated structures. Some viral capsids are enveloped with a lipid membrane known as the viral envelope, which is typically acquired by the capsid from a membrane of the host cell.
This invention is based, at least in part, on the recognition that sortases can be exploited to conjugate a variety of moieties to the proteins on the surface of viruses, for example, to the capsid proteins of M13 bacteriophage. Such sortase-mediated conjugation approaches can be used to confer new functions to viral particles. For example, the conjugation of a detectable label allows for the isolation and/or quantification of viral particles and can also be used to label cells bound or infected by the viral particles. For another example, sortase-mediated conjugation of binding moieties, for example, of antibodies or antibody fragments, nucleic acids, or of biotin and streptavidin, can be used to confer new binding properties to viral particles, e.g., in order to generate complex structures of associated, e.g., concatenated, viral particles.
Some aspects of this disclosure provide methods, reagents, and kits that can be used to functionalize proteins on the surface of viruses, for example, by conjugating such proteins to a molecule or a plurality of molecules conferring a desired function. Examples of such molecules include, without limitation, detectable labels, small molecules, and binding agents. The sortase-mediated techniques described herein allow for functionalization of viral surface proteins with high specificity and with efficiencies that surpass those of any known recombinant techniques, such as methods used in the context of phage display technology. Another advantage of the methods, reagents, and kits provided herein is that agents (e.g., proteins, binding agents, or small molecules) can be conjugated to viral surface proteins that cannot be genetically encoded, e.g., because of size limitations for insertions into the viral gene or genome encoding a target viral protein to be modified, or because the agent is not a gene product that can be encoded by the viral genome.
For example, capsid proteins (e.g., pIII, pIX, and pVIII) of bacteriophage M13 can be functionalized, according to some aspects of this disclosure, with entities ranging from small molecules (e.g., fluorophores, biotin) to folded proteins (e.g., GFP, antibodies, streptavidin) in a site-specific manner and with yields that surpass those of any reported using phage display technology. A non-limiting example of phage protein modification according to some aspects of this disclosure is the sortase-mediated modification of pVIII, which is difficult to modify with conventional approaches of genetic engineering or chemical labeling. While a phage vector limits the size of an insert into pVIII to a few amino acids, a phagemid system limits the number of copies actually displayed on the surface of M13 phage. Using sortase-based reactions, a 100-fold increase in the efficiency of display of GFP onto pVIII is achieved, as described in more detail elsewhere herein.
Taking advantage of orthogonal sortases, a plurality of viral capsid proteins can be modified in the same viral particle while maintaining excellent specificity of labeling. The methods provided herein are simple and effective for creating a variety of structures on the surface of viral particles, e.g., of M13 phage capsid proteins.
The methods, reagents, and kits provided herein can be used to generate complex, virus-templated structures, e.g., branched concatemers, such as lampbrush structures, that can be engineered to carry out novel functions, e.g., structural functions or the harvesting of light. The methods, reagents, and kits provided herein allow for the use of biological structures, e.g., viral particles, as building blocks for the engineering of new materials and structures and for the functionalization of the surface of such structures. The methods, reagents, and kits provided herein can also be used to engineer new functionalities into viral particles, for example, the binding of a new spectrum of cells, the interaction with a specific target protein, e.g., a specific receptor on the surface of a cell of interest, or the delivery of a payload to a specific type of cell expressing a surface molecule of interest. Viral particles can be functionalized using the strategies disclosed herein to attach a cell targeting motif, e.g., a binding agent such as an antibody, nucleic acid, or a bacterial toxin, to the viral surface, in order to increase the uptake/internalization of the functionalized virus by a specific cell or cell type. In some embodiments, the methods and strategies disclosed herein can be used to generate a viral particle that can bind and deliver its genome to a previously uninfectable host cell, resulting in expression of a viral gene product in the host cell. The strategies and methods disclosed herein can also be used to attach a payload, e.g., a functional protein or a small molecule to the surface of a virus that can be delivered upon entry into a target cell.
The strategies, methods, reagents, and kits disclosed herein can also be used to improve the identification of binding targets in phage display libraries, for example, by using fluorescently labeled phage for the detection of binding events; to generate functionalized viral particles for use as a handle in single molecule force spectroscopy experiments, allowing, for example, to post-translationally attach properly folded complex proteins to the surface of a viral particle; to create complex structures comprising viral particles functionalized with binding agents as building blocks, e.g., using connections between specific viral capsid proteins; to target viral particles to specific cells; and to deliver payloads to target cells upon binding or infection, e.g., toxic agents such as plant or bacterial toxins, antibiotics, and drugs.
The present invention provides methods, reagents, and kits for the functionalization of viral capsid proteins. Typically, a method of functionalizing a viral capsid protein as provided herein comprises conjugating the target capsid protein with an agent via a sortase-mediated transpeptidation reaction. In order for a sortase-mediated transpeptidation to be possible, both the target protein and the agent must be recognized by the sortase and must be capable of acting as a substrate of the sortase in the transpeptidation reaction. Accordingly, the methods for functionalization of viral capsid proteins provided herein involve viral proteins and agents that comprise or are conjugated to a sortase recognition motif. Some viral proteins and some agents (e.g., proteins) may comprise a suitable sortase recognition motif. However, in some embodiments, the target protein and/or the agent is engineered to comprise a suitable sortase recognition motif, for example, via protein engineering (e.g., using recombinant technologies) or via chemical synthesis (e.g., linking a non-protein agent to a sortase recognition motif).
Typically, a method for viral capsid protein functionalization as provided herein comprises contacting a target protein, e.g., a viral capsid protein comprising a sortase recognition motif that is accessible on the surface of a viral particle, with an agent comprising a sortase recognition motif, in the presence of a sortase under conditions suitable for the sortase to conjugate the target protein to the agent via a sortase-mediated transpeptidation reaction.
For example, some embodiments provide methods for modifying a target protein, for example, a target viral capsid protein, comprising a sortase recognition motif on the surface of a virus, that includes contacting the target protein with a sortase substrate conjugated to an agent in the presence of a sortase under conditions suitable for the sortase to ligate the sortase substrate to the target protein. In some embodiments, the target protein comprises an N-terminal sortase recognition motif, and the sortase substrate conjugated to the agent comprises a C-terminal sortase recognition motif. In other embodiments, the target protein comprises a C-terminal sortase recognition motif, and the sortase substrate conjugated to the agent comprises an N-terminal sortase recognition motif. The C- and N-terminal recognition motif are recognized as substrates by the sortase being employed and ligated in a transpeptidation reaction.
In a given embodiment, whether a viral target protein comprises (e.g., is engineered to comprise) a C-terminal or an N-terminal sortase recognition motif will depend on the accessibility of the C-terminus and/or the N-terminus of the target protein on the surface of the virus. For example, if the C-terminus of the target protein is accessible on the surface of the virus, e.g., on the surface of the viral capsid, and the N-terminus is not, then a C-terminal sortase recognition motif is suitable and vice versa. For example, in some embodiments, an M13 phage is provided that comprises a pIII protein containing an N-terminal sortase recognition motif, e.g., an N-terminal polyglycine sequence, and is functionalized at the N-terminus by contacting it with a sortase substrate comprising a C-terminal sortase recognition motif, e.g., an LPETG (SEQ ID NO: 10) sequence, conjugated to an agent, e.g., GFP, in the presence of a sortase, e.g., a SrtAaureus, under suitable conditions for the sortase to conjugate pIII and GFP via a sortase-mediated transpeptidation reaction.
Whether the C-terminus and/or the N-terminus of a given viral target protein is accessible or not on the surface of the respective virus will be apparent to those of skill in the art. Many viruses have been sequenced and the structures of the respective viral capsids have been investigated and can be accessed in publicly available databases, such as ENSEMBL (www.ensembl.org) and NCBI (www.ncbi.nlm.nih.gov). Where structural data is lacking, those of skill in the art will be able to determine the accessibility of the C-terminus and/or the N-terminus of a given viral protein on the surface of the respective viral capsid with no more than routine experimentation.
In some embodiments, methods are provided that allow for the functionalization, or sortagging, of a plurality of different viral proteins of a virus. For example, in some embodiments, a method is provided that allows for the functionalization of 2, 3, 4, 5, 6, 7, 8, 9, or different viral proteins. In some embodiments, specific functionalization of a plurality of viral capsid proteins involves the use of different sortases, each specifically recognizing a different sortase recognition motif. For example, in some embodiments, a first target protein is functionalized with SrtAaureus, recognizing the C-terminal sortase recognition motif LPETGG (SEQ ID NO: 13) and the N-terminal sortase recognition motif (G)n, and a second target protein is functionalized with SrtApyogenes, recognizing the C-terminal sortase recognition motif LPETAA (SEQ ID NO: 12) and the N-terminal sortase recognition motif (A)n. The sortases in this example recognize their respective recognition motif but do not recognize the other sortase recognition motif to a significant extent, and, thus, “specifically” recognize their respective recognition motif. In some embodiments, a sortase binds a sortase recognition motif specifically if it binds the motif with an affinity that is at least 5-fold, 10-fold, 20-fold, 50-fold, 100-fold, 200-fold, 500-fold, 1000-fold, or more than 1000-fold higher than the affinity that the sortase binds a different motif. Such a pairing of orthogonal sortases and their respective recognition motifs, e.g., of the orthogonal sortase A enzymes SrtAaureus and SrtApyogenes, can be used to site-specifically conjugate two different moieties onto two different capsid proteins (e.g., a first binding agent to pIII and a second binding agent to pVIII of M13 bacteriophage particles). In some embodiments, sortagging of a plurality of different proteins is achieved by sequentially contacting a virus comprising the different proteins with a first sortase recognizing a sortase recognition motif of a first target protein and a suitable first sortase substrate, and then with a second sortase recognizing a sortase recognition motif of a second target protein and a second suitable sortase substrate, and so forth. Alternatively, the virus may be contacted with a plurality of sortases in parallel, for example, with a first sortase recognizing a sortase recognition motif of a first target protein and a suitable first sortase substrate, and with a second sortase recognizing a sortase recognition motif of a second target protein and a second suitable sortase substrate, and so forth. It will be understood by those of skill in the art, that suitable orthogonal sortases preferentially recognize their own motifs over the motifs of other sortases, but that a basal level of recognition of other sortase recognition motifs is not detrimental. For example, SrtApyogenes is able to recognize an LPXTG (SEQ ID NO: 78) motif, but strongly prefers an LPXTA (SEQ ID NO: 91) motif, while SrtAaureus shows no cleavage activity for the LPXTA (SEQ ID NO: 91) motif. These two sortases are suitable orthogonal sortases according to some aspects of this invention, as are sortases that exclusively recognize their own sortase recognition sequence.
For example, in some embodiments, a first viral target protein, e.g., M13 pIII comprising an N-terminal poly-G sequence, is functionalized using sortase A from Staphylococcus aureus (SrtAaureus), and a second target protein, e.g., M13 pVIII comprising an N-terminal poly-A sequence, is functionalized using sortase A from Streptococcus pyogenes (SrtApyogenes). In some such embodiments, the virus, e.g., the M13 phage, may be contacted first with SrtAaureus (and a suitable substrate) and subsequently with SrtApyogenes (and a suitable substrate), or, since the two sortases are orthogonal sortases, the respective virus may be contacted with both sortases and both substrates at the same time.
Any sortases that recognize sufficiently different sortase recognition motifs with sufficient specificity are suitable for sortagging of a plurality of viral proteins of the same virus. The respective sortase recognition motifs can be inserted into the target proteins using recombinant technologies known to those of skill in the art. In some embodiments, suitable sortase recognition motifs may be present in a wild type target protein, for example, an N-terminal polyglycine or polyalanine sequence, in which case no further engineering of the target protein may be required. The skilled artisan will understand that the choice of a suitable sortase for the functionalization of a given target protein may depend on the sequence of the target protein, e.g., on whether or not the target protein comprises a sequence at its C-terminus or its N-terminus that can be recognized as a substrate by any known sortase. In some embodiments, use of a sortase that recognizes a naturally-occurring C-terminal or N-terminal recognition motif is preferred since further engineering of the target protein can be avoided.
In some embodiments, a plurality of different target proteins is functionalized on the surface of the same viral particle. In some embodiments, the different target proteins are functionalized with different agents. For example, in some embodiments, a first target protein may be functionalized with a first binding agent, and a second target protein may be functionalized with a second binding agent. One example of such an embodiment is the functionalization of M13 pIII with biotin and the functionalization of M13 pVIII with streptavidin on the surface of the same M13 phage particle. Another example of such an embodiment is the functionalization of M13 pIII with a nucleic acid molecule, e.g., an oligonucleotide, and the functionalization of M13 VIII with a different nucleic acid molecule, e.g., a different oligonucleotide. For another example, in some embodiments, a first target protein is functionalized with a binding agent, and a second target protein is functionalized with a detectable label. In some embodiments, a first target protein is functionalized with a binding agent, a second target protein is functionalized with a detectable label, and a third target protein is functionalized with a click chemistry handle. Additional embodiments in which a plurality of different target proteins is sortagged with a plurality of different agents are provided herein, and further embodiments will be apparent to those of skill in the art based on the present disclosure. It will be understood that the invention is not limited in the number of different target proteins to be functionalized nor the number of different agents to be conjugated to the target proteins.
In some embodiments, an engineered viral capsid protein provided herein comprises a sortase recognition motif, e.g., a C-terminal or an N-terminal sortase recognition motif, within a loop structure. In some embodiments, the loop structure is formed by disulfide bonds between two cysteine residues flanking the sortase recognition motif. In some embodiments, the loop structure is situated at the N-terminus or the C-terminus of the engineered viral capsid protein, or inserted into the sequence of the viral capsid protein near the N- or the C-terminus (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, less than 15, less than 20, or less than 25 amino acid residues away from the N- or C-terminus of the viral capsid protein). In some embodiments, the loop structure comprises a cleavable site or a cleavable bond, the cleavage of which opens the loop. In some embodiments, the cleavable bond is a photocleavable bond. In some embodiments, the cleavable bond is a peptide bond, e.g., a peptide bond situated in a protease cleavage site comprised in the loop structure. In some embodiments, the loop structure comprises a protease cleavage site situated between the cysteine residues forming the loop and is, thus, sensitive to cleavage by the protease. In some embodiments, cleavage of the engineered viral capsid protein by the protease opens the loop structure. In some embodiments, the loop structure comprises an N-terminal cysteine, a sortase recognition motif situated C-terminally of the N-terminal cysteine, a protease cleavage site situated C-terminally of the sortase recognition motif, and a C-terminal cysteine. In some embodiments, the loop structure comprises an N-terminal cysteine, a protease cleavage site situated C-terminally of the N-terminal cysteine, a sortase recognition motif situated C-terminally of the protease cleavage site, and a C-terminal cysteine. In some embodiments, an amino acid residue, sequence, or structure comprised in the loop structure (e.g., the N-terminal cysteine, sortase recognition motif, protease cleavage site, and C-terminal cysteine) may be conjugated to another residue, sequence or structure of the loop via a linker, e.g., an amino acid or peptide linker. In some embodiments, the linker is a cleavable linker. In some embodiments, the linker is 3, 4, 5, 6, 7, 8, 9, or 10 amino acid residues long. In some embodiments, the linker comprises more than 10 amino acids. Suitable protease cleavage sites (and corresponding proteases cleaving such sites) are described herein. Exemplary suitable cleavage sites and corresponding proteases include, e.g., thrombin, TEV protease, Factor Xa, PreScission protease, and papain cleavage sites. Additional suitable proteases and cleavage sites will be apparent to the skilled artisan, and such suitable proteases and cleavage sites include, without limitation, those reported in the passage from paragraph [0093] to paragraph [0097], and in Table 2 and the Table following paragraph [0097] of U.S. patent application Ser. No. 13/642,458, publication number US2013/0122043, by Guimaraes and Ploegh, the entire contents of which passage and tables are incorporated herein by reference. In some embodiments, the loop structure comprises a bacterial toxin sequence, e.g., a sequence of a bacterial protein that comprises a loop structure. Exemplary suitable bacterial toxin sequences are described herein, and additional suitable sequences will be apparent to those of skill in the art based on the instant disclosure. Such suitable sequences include, without limitation, those reported in the passage from paragraph [0044] to paragraph [0080] and in paragraph [0175] of U.S. patent application Ser. No. 13/642,458, publication number US2013/0122043, by Guimaraes and Ploegh, the entire contents of which passage and paragraph are incorporated herein by reference. Exemplary suitable loop structures that are useful for engineering viral capsid proteins are disclosed herein, and additional suitable loop structures will be apparent to those of skill in the art. Such additional loop structures include, for example, those reported in U.S. patent application, U.S. Ser. No. 13/642,458, publication number US2013/0122043, by Guimaraes and Ploegh, the entire contents of which are incorporated herein by reference.
Sortases, sortase-mediated transacylation reactions, and their use in transpeptidation (sometimes also referred to as transacylation) for protein engineering are well known to those of skill in the art (see, e.g., Ploegh et al., International PCT Patent Application, PCT/US2010/000274, filed Feb. 1, 2010, published as WO 2010/087994 on Aug. 5, 2010, and Ploegh et al., International PCT Patent Application PCT/US2011/033303, filed Apr. 20, 2011, published as WO 2011/133704 on Oct. 27, 2011, the entire contents of which are incorporated herein by reference). In general, the transpeptidation reaction catalyzed by sortase results in the conjugation of a protein containing a C-terminal sortase recognition motif e.g., LPXTX (wherein each occurrence of X independently represents any amino acid residue), with a peptide comprising an N-terminal sortase recognition motif, e.g., one or more N-terminal glycine residues. In some embodiments, the sortase recognition motif is a sortase recognition motif described herein. In certain embodiments, the sortase recognition motif is LPXT motif or LPXTG (SEQ ID NO: 78).
The sortase transacylation reaction provides means for efficiently linking an acyl donor with a nucleophilic acyl acceptor. This principle is widely applicable to many acyl donors and a multitude of different acyl acceptors. Previously, the sortase reaction was employed for ligating proteins and/or peptides to one another, ligating synthetic peptides to recombinant proteins, linking a reporting molecule to a protein or peptide, joining a nucleic acid to a protein or peptide, conjugating a protein or peptide to a solid support or polymer, and linking a protein or peptide to a label. Such products and processes save cost and time associated with ligation product synthesis and are useful for conveniently linking an acyl donor to an acyl acceptor. However, the modification and functionalization of proteins on the surface of viral particles via sortagging, as provided herein, has not been described previously.
Sortase-mediated transpeptidation reactions (also sometimes referred to as transacylation reactions) are catalyzed by the transamidase activity of sortase, which forms a peptide linkage (an amide linkage), between an acyl donor compound and a nucleophilic acyl acceptor containing an NH2—CH2-moiety. In some embodiments, the sortase employed to carry out a sortase-mediated transpeptidation reaction is sortase A (SrtA). However, it should be noted that any sortase, or transamidase, catalyzing a transacylation reaction can be used in some embodiments of this invention, as the invention is not limited to the use of sortase A.
In certain embodiments, a sortase-mediated transpeptidation reaction for C-terminal functionalization of a viral surface protein, for example, of an M13 capsid protein, is provided that comprises a step of contacting a virus comprising a surface protein comprising a C-terminal sortase recognition sequence of the structure:
wherein
with a nucleophilic moiety conjugated to an agent, according to the formula:
wherein
in the presence of a sortase, under conditions suitable to form a functionalized viral surface protein of formula:
In certain embodiments, a sortase-mediated transpeptidation reaction for N-terminal functionalization of a viral surface protein, for example, of an M13 capsid protein, is provided that comprises a step of contacting a virus comprising a surface protein comprising an N-terminal sortase recognition sequence of the structure:
wherein
wherein
in the presence of a sortase, under conditions suitable to form a functionalized viral surface protein of formula:
In some embodiments, the C-terminal sortase recognition motif is LPXT, wherein X is a standard or non-standard amino acid. In some embodiments, X is selected from D, E, A, N, Q, K, or R. In some embodiments, the recognition sequence is selected from LPXT, LPXT, SPXT, LAXT, LSXT, NPXT, VPXT, IPXT, and YPXR. In some embodiments, X is selected to match a naturally occurring transamidase recognition sequence. In some embodiments, the transamidase recognition sequence is selected from LPKT (SEQ ID NO: 93), LPIT (SEQ ID NO: 94), LPDT (SEQ ID NO: 95), SPKT (SEQ ID NO: 96), LAET (SEQ ID NO: 97), LAAT (SEQ ID NO: 98), LAET (SEQ ID NO: 99), LAST (SEQ ID NO: 100), LAET (SEQ ID NO: 101), LPLT (SEQ ID NO: 102), LSRT (SEQ ID NO: 103), LPET (SEQ ID NO: 104), VPDT (SEQ ID NO: 105), IPQT (SEQ ID NO: 106), YPRR (SEQ ID NO: 107), LPMT (SEQ ID NO: 108), LPLT (SEQ ID NO: 109), LAFT (SEQ ID NO: 110), LPQT (SEQ ID NO: 111), NSKT (SEQ ID NO: 112), NPQT (SEQ ID NO: 113), NAKT (SEQ ID NO: 114), and NPQS (SEQ ID NO: 115). In some embodiments, e.g., in certain embodiments in which sortase A is used, the transamidase recognition motif comprises the amino acid sequence X1PX2X3, where X1 is leucine, isoleucine, valine, or methionine; X2 is any amino acid; X3 is threonine, serine, or alanine; P is proline and G is glycine. In specific embodiments, as noted above, X1 is leucine and X3 is threonine. In certain embodiments, X2 is aspartate, glutamate, alanine, glutamine, lysine, or methionine. In certain embodiments, e.g., where sortase B is utilized, the recognition sequence often comprises the amino acid sequence NPX1TX2, where X1 is glutamine or lysine; X2 is asparagine or glycine; N is asparagine; P is proline, and T is threonine. The invention encompasses the recognition that selection of X may be based at least in part in order to confer desired properties on the compound containing the recognition motif. In some embodiments, X is selected to modify a property of the compound that contains the recognition motif, such as to increase or decrease solubility in a particular solvent. In some embodiments, X is selected to be compatible with reaction conditions to be used in synthesizing a compound comprising the recognition motif, e.g., to be unreactive towards reactants used in the synthesis. One of ordinary skill will appreciate that, in certain embodiments, the C-terminal amino acid of the C-terminal sortase recognition motif may be omitted. For example, an acyl group, e.g., of formula
may replace the C-terminal amino acid of the sortase recognition motif. In some embodiments, the acyl group is
In certain embodiments, R1 is substituted aliphatic. In certain embodiments, R1 is unsubstituted aliphatic. In some embodiments, R1 is substituted C1-12 aliphatic. In some embodiments, R1 is unsubstituted C1-12 aliphatic. In some embodiments, R1 is substituted C1-6 aliphatic. In some embodiments, R1 is unsubstituted C1-6 aliphatic. In some embodiments, R1 is C1-3 aliphatic. In some embodiments, R1 is butyl. In some embodiments, R1 is n-butyl. In some embodiments, R1 is isobutyl. In some embodiments, R1 is propyl. In some embodiments, R1 is n-propyl. In some embodiments, R1 is isopropyl. In some embodiments, R1 is ethyl. In some embodiments, R1 is methyl. In certain embodiments, R1 is substituted aryl. In certain embodiments, R1 is unsubstituted aryl. In certain embodiments, R1 is substituted phenyl. In certain embodiments, R1 is unsubstituted phenyl. In some embodiments, the acyl group is
In some embodiments, the agent to be conjugated to the target protein comprises a protein. In some embodiments, the agent comprises a peptide. In some embodiments, the agent comprises a binding agent. In some embodiments, the agent comprises biotin. In some embodiments, the agent comprises streptavidin. In some embodiments, the agent comprises an antibody, an antibody chain, an antibody fragment, an antibody epitope, an antigen-binding antibody domain, a VHH domain, a single-domain antibody, a camelid antibody, a nanobody, or an adnectin. In some embodiments, the agent comprises a recombinant protein, a protein comprising one or more D-amino acids, a branched peptide, a therapeutic protein, an enzyme, a polypeptide subunit of a multisubunit protein, a transmembrane protein, a cell surface protein, a methylated peptide or protein, an acylated peptide or protein, a lipidated peptide or protein, a phosphorylated peptide or protein, or a glycosylated peptide or protein. In some embodiments, the agent is an amino acid sequence comprising at least 3 amino acids. In some embodiments, the agent comprises a fluorophore, a chromophore, or a fluorescent or phosphorescent moiety, or a radiolabel. In some embodiments, the agent comprises green fluorescent protein. In some embodiments, the agent comprises ubiquitin. In some embodiments, the agent comprises a small molecule. In some embodiments, the agent comprises a drug.
In certain embodiments, n (designating the number of amino acids in the N-terminal sortase recognition motif) is an integer from 0 to 50, inclusive. In certain embodiments, n is an integer from 0 to 20, inclusive. In certain embodiments, n is 0. In certain embodiments, n is 1. In certain embodiments, n is 2. In certain embodiments, n is 3. In certain embodiments, n is 4. In certain embodiments, n is 5. In certain embodiments, n is 6.
Any sortase that can carry out a transpeptidation reaction under conditions suitable for maintaining structural and functional integrity of the viral particle and the viral capsid protein to be modified can be used this invention. Examples of suitable sortases include, but are not limited to sortase A and sortase B, for example, from Staphylococcus aureus, or Streptococcus pyogenes. Additional sortases suitable for use in this invention will be apparent to those of skill in the art, including, but not limited to any of the 61 sortases described in Dramsi S, Trieu-Cuot P, Bierne H, Sorting sortases: a nomenclature proposal for the various sortases of Gram-positive bacteria. Res Microbiol. 156(3):289-97, 2005, the entire contents of which are incorporated herein by reference. Sortases belonging to any class of sortases, e.g., class A, class B, class C, and class D sortases, and sortases belonging to any sub-family of sortases (subfamily 1, subfamily 2, subfamily 3, subfamily 4 and sub-family 5) can be used in this invention.
Any amino acid sequence recognized by a sortase can be used the present invention. It will be understood by those of skill in the art, however, that in order for a certain sortase to carry out a transpeptidation reaction, the sortase recognition motif of the target protein to be modified and the sortase recognition motif the agent is conjugated to need to be recognized by that sortase. Numerous suitable sortase recognition motifs are provided herein, and additional suitable sortase recognition motifs will be apparent to the skilled artisan. Aside from naturally occurring sortase recognition motifs, some embodiments of this invention contemplate the use of non-naturally occurring sortase recognition motifs and sortases recognizing such motifs, for example, sortase motifs and sortases described in Piotukh et al., Directed evolution of sortase A mutants with altered substrate selectivity profiles. J Am Chem Soc. 2011 Nov. 9; 133(44):17536-9; and Chen I, Dorr B M, and Liu D R. A general strategy for the evolution of bond-forming enzymes using yeast display. Proc Natl Acad Sci USA. 2011 Jul. 12; 108(28):11399-404; the entire contents of each of which are incorporated herein by reference. In some embodiments, a recognition sequence, e.g., a sortase recognition sequence as provided herein further comprises one or more additional amino acids, e.g., at the N and/or C terminus. For example, one or more amino acids (e.g., up to 5 amino acids) having the identity of amino acids found immediately N-terminal to, or C-terminal to, a five amino acid recognition sequence in a naturally occurring sortase substrate may be incorporated. Such additional amino acids may provide context that improves the recognition of the recognition motif.
The methods for functionalization of viral proteins via sortase-mediated transpeptidation provided herein can be used to modify surface proteins on any virus. As described in the Examples section herein, the method has been demonstrated to be capable to efficiently modify surface proteins of the bacteriophage M13. However, it will be apparent to those of skill in the art that the methods, reagents, and kits provided herein can be used to modify and functionalize surface proteins on other viruses as well.
Wild type M13 bacteriophage has a cylindrical shape with a length of about 880 nm and a diameter of about 6 nm. It encapsulates a single-strand genome that encodes five different capsid proteins (
The capsid proteins of M13 bacteriophage have been used to express combinatorial peptide libraries or protein variants (ranging from single domains to antibodies) to screen for target ligands in a process known as phage display2. This technique has enabled not only identification of peptides with affinity for biological targets such as proteins, cells, and tissues3-6, but also allowed the identification of biomolecules that bind inorganics7-8. These molecules, when expressed on the M13 capsid proteins, can serve as scaffolds for nanowires, structures, and devices9-13. Functionalization of a virion capsid such as M13 is currently accomplished using chemical and/or genetic approaches14-15. However both strategies have limitations. Chemical conjugations are convenient and versatile, but they label motifs found on multiple M13 capsid proteins and oftentimes require non-physiological pH and reducing conditions that compromise the activity of the molecule that is being attached or of the moieties already displayed on other capsid proteins14.
Genetic engineering of phage allows the encoded protein/peptide to be displayed precisely13, 16, but it has intrinsic restrictions. Two classes of vectors are available for genetic phage display: phagemid and phage. A phagemid allows expression of large fusions with any of the five M13 phage capsid proteins, but these fusions are incorporated at low efficiency17-21. In a phage vector, the M13 bacteriophage genome is modified directly. As a result, every copy of the recombinant capsid protein incorporated into the virus displays the modified protein. However, this strategy does not support display of large moieties22-24. pVIII allows the display of a larger number of recombinant molecules per phage particle, but it also has the strictest size limitation in phage vector display. pVIII peptide libraries are mostly limited to sizes of up to 10 amino acids, as phage with longer insertions rarely assemble25-26. Insertions of 6-20 amino acids onto pVIII are possible using phagemid, but their display is inefficient with less than 25% of the copies of pVIII containing the desired fusion product20. Incorporation of proteins is even less efficient on pVIII: a 23 kDa protein is displayed, on average, on less than a single copy of the pVIII fusion per phage particle using a phagemid vector18. Phage display methods on the pVIII have been able to increase the binding affinity of phage displaying a moiety23, but the displayed copy number of the moiety has not been determined. Large moieties of at least 23 kDa have been genetically fused to all four minor capsid proteins using a phagemid vector22, 27-28, but only pIII has been extensively used in the phage vector system29. However, viability of the resultant phage fusions does not guarantee that the recombinant peptide/protein of interest displays its native structure and/or maintains its wild type function. Both the environment where phage assembles and the phage coat protein to which the protein of interest is fused may interfere with proper folding30. This is particularly critical for enzymes and antibodies as they might not be functional when incorporated into the phage structure.
The technology provided by this disclosure expands the versatility of M13 as a display platform, by employing a strategy based on sortase-mediated chemo-enzymatic reactions to covalently attach a variety of moieties to the N-terminus of pIII, pVIII, and pIX. The technology provided herein allows for the conjugation of functional moieties and molecules at a high efficiency, as illustrated by a comparison to published labeling data described in more detail in the Examples section. For example, as described in more detail in the Examples section, the instantly described sortase-based functionalization technology represents a significant improvement over current methodologies in the copy number of displayed peptides and proteins, particularly on pVIII.
Sortase A enzymes allow modification of proteins by enzymatic ligation with a wide range of molecules, moieties, and functional groups (including biotin, fluorophores, and other proteins) at the C-terminus, N-terminus, or at both termini of the protein of interest31-35 (see, e.g., Ploegh et al., International PCT Patent Application, PCT/US2010/000274, filed Feb. 1, 2010, published as WO/2010/087994 on Aug. 5, 2010, and Ploegh et al., International Patent Application PCT/US2011/033303, filed Apr. 20, 2011, published as WO/2011/133704 on Oct. 27, 2011, the entire contents of which are incorporated herein by reference). Different sortase enzymes are known to those of skill in the art, and any sortase carrying out a transpeptidation reaction can be used in the context of the instant disclosure. For example, the widely used sortase A from Staphylococcus aureus (SrtAaureus) recognizes substrates that contain an LPXTG (SEQ ID NO: 78) sequence36-38, whereas sortase A from Streptococcus pyogenes (SrtApyogenes) recognizes substrates with an LPXTA (SEQ ID NO: 91) motif33,39. The sortase enzymes cleave between the threonine and glycine or alanine residue, respectively, to yield a covalent acyl-enzyme intermediate that is resolved by nucleophilic attack of a suitably exposed amine, namely oligoglycine or oligoalanine-containing peptides39 in the case of SrtAaureus or SrtApyogenes, respectively (
The sortase labeling methods provided herein have several advantages over genetic and chemical methods. First, the sortase transpeptidation reaction is site-specific. This is advantageous, as it allows one to specifically target sortase activity towards a genetically engineered target protein. For example, in the case of sortagging of an M13 capsid protein, as none of the M13 coat proteins naturally display a sortase recognition motif required to participate in sortase-mediated reactions, a capsid protein engineered to comprise such a motif will be specifically targeted by a sortase, while the non-engineered proteins will not participate in the sortase reaction. Second, sortase recognition motifs are small and, therefore, can be easily inserted into the host genome, e.g., the M13 phage genome, thus maximizing the number of potential attachment sites. Third, a protein to be conjugated to a cell surface or particle surface protein by means of sortase, e.g., a protein to be displayed on a phage particle, can be properly folded separate from the conjugation reaction, and, as the case may be, separate from the assembly of phage particles. The site-specific nature of the reaction fixes the orientation of the displayed protein. Fourth, the reactions are performed under physiological conditions. Fifth, sortase reactions afford attachment of a wide range of molecules, including those that cannot be genetically encoded such as fluorophores and biotin.
Some aspects of this description provide reagents and methods to build phage structures that have new material and biological applications. Some non-limiting examples are described in detail: the creation of a new lampbrush structure by fusing different phage particles through pIII/pVIII, a fluorescently labeled phage containing a cell-targeting moiety to stain and to sort cells by FACS, and the formation of multiphage particles of a specific, predetermined structure via hybridization-mediated linkage of DNA oligonucleotides conjugated to pIII/pVIII of phage particles. It will be apparent to the skilled artisan that the described examples are illustrative and non-limiting, as various additional applications of the technology described herein will be apparent to the skilled artisan.
In some embodiments, the ability to fluorescently stain cells can be used in the panning of phage display libraries against specific cells. Phage particles functionalized with fluorescent moieties or proteins allow for more sensitive detection of binding events and/or for decreasing the number of panning rounds needed for identifying a biomolecule of interest in phage display screens.
The ability to generate structures using functionalized phage as building blocks can be used to produce complex hybrid material structures. For example, in some embodiments, functionalized phage particles can be created that can bind to and nucleate different materials, including other phage particles, organic materials, and inorganic materials. In some embodiments, hybrid structures of inorganic matter and phage particles can be generated.
Some aspects of this invention provide methods for associating viral particles, for example, M13 phage particles, with viral particles of the same type (e.g., with other M13 phage particles), with viral particles of a different type (e.g., with phage particles of a different strain), or with cells or other entities (e.g., with target cells, e.g., bacterial cells not typically bound or infected by wild-type M13 phage, or with non-target cells, e.g. yeast, insect, or mammalian cells, or with organic particles, e.g., nanoparticles).
Typically, a method for associating viral particles of the same type comprises conjugating a first target protein on the surface of the viral particle with a first binding agent via sortase-mediated transpeptidation; conjugating a second target protein on the surface of the viral particle with a second binding agent, wherein the second binding agent binds the first binding agent; and incubating a plurality of viral particles comprising the first and the second binding agent under conditions suitable for the first and the second binding agent of different viral particles to bind each other. In some embodiments, the first binding agent is a ligand-binding agent, for example, a receptor, or a receptor fragment, and the second binding agent comprises the ligand bound by the ligand-binding agent. For example, in some embodiments, the first binding agent is biotin, and the second binding agent is streptavidin. In some embodiments, the first binding agent comprises an antibody or an antigen-binding antibody fragment, and the second binding agent comprises the antigen bound by the antibody or antibody fragment. In some embodiments, an M13 capsid protein is sortagged with a first binding agent, e.g., pIII with biotin or a first oligonucleotide, and a second M13 capsid protein is sortagged with a second binding agent binding the first binding agent, e.g., pVIII with streptavidin or a second oligonucleotide. As described in more detail elsewhere herein, the M13 particles functionalized in this manner associate when incubated under suitable conditions, e.g., under suitable conditions for biotin and streptavidin to bind or under suitable conditions for the first and second oligonucleotide to become associated with each other (e.g., via hybridization to a third oligonucleotide), and can form complex, branched structures not observed in non-functionalized phage particles.
A method for associating viral particles of one type to viral particles of a different type typically comprises conjugating a target protein on the surface of a first viral particle with a first binding agent via sortase-mediated transpeptidation reaction; conjugating a target protein on the surface of a second viral particle with a second binding agent, wherein the second binding agent binds the first binding agent directly or can otherwise become associated with the first binding agent (e.g., by binding a molecule bound by the first binding agent); and contacting and incubating a plurality of viral particles comprising the first binding agent with a plurality of viral particles comprising the second binding agent under conditions suitable for the first and the second binding agent of different viral particles to bind each other. In some embodiments, the first binding agent is a ligand-binding agent, for example, a receptor, or a receptor fragment, or an adhesion molecule, and the second binding agent comprises the ligand bound by the ligand-binding agent. For example, in some embodiments, the first binding agent is biotin and the second binding agent is streptavidin. In some embodiments, the first binding agent comprises an antibody or an antigen-binding antibody fragment, and the second binding agent comprises the antigen bound by the antibody or antibody fragment. In some embodiments, an M13 capsid protein of a first M13 particle is sortagged with a first binding agent, e.g., pIII with biotin, and a second M13 capsid protein of a second M13 particle is sortagged with a second binding agent binding the first binding agent, e.g., pVIII with streptavidin. In other embodiments, the same capsid protein is sortagged with a first binding agent on a first M13 particle and with a second binding agent on a second M13 particle, e.g., pVIII is sortagged with biotin on a first M13 particle and with streptavidin on a second M13 particle. The M13 particles functionalized in this manner are then incubated under conditions suitable for them to associate, resulting in a branched structure of associated, differently sortagged M13 particles.
Viral particles can be functionalized with any suitable binding agent, for example, with a binding agent binding an antigen or ligand on the surface of a cell, e.g., a bacterial cell, a yeast cell, an insect cell, a vertebrate cell, or a mammalian cell. Incubation of the functionalized viral particle with the cell results in binding of the functionalized viral particle to the cell. In some embodiments, the binding agent is biotin/streptavidin. Other suitable binding agents include, without limitation, complementary DNA strands, ligands of receptors expressed on the surface of the target cells, and leucine zippers. In some embodiments, direct attachment of phage to a cell or other biological structure is effected by placing a sortase substrate on the surface of the phage, and a compatible sortase substrate on the surface of the cell or biological structure and then effecting a sortase-mediated transpeptidation reaction between the two. Association of viral particles and cells can be achieved if a plurality of particles is contacted with a plurality of cells under suitable conditions. The association of viral particles with other viral particles of a different type, or with cells, e.g., with cells that are not naturally bound or infected by the viral particles allows for the generation of novel hybrid structures and materials the characteristics of which will be determined by the structure of the associated entities, and by the agents and target proteins used for functionalization of the viral particles.
Some aspects of this invention provide functionalized viral particles, in which at least one viral capsid protein has been sortagged according to methods, or using reagents or strategies provided herein. In some embodiments, the functionalized virus comprises a target protein, for example, a viral capsid protein, that is conjugated to an agent via a sortase recognition motif as described herein. In some embodiments, the agent is conjugated to the target protein via a linker. In some embodiments, the linker is a peptide linker, e.g., a linker comprising a sequence of amino acids. In some embodiments, the linker is a cleavable linker, for example, a linker comprising a protease cleavage site, or a photocleavable linker. Cleavable linkers including, but not limited to linkers comprising protease cleavage sites and photocleavable linkers, are well known to those of skill in the art, and the invention is not limited in this respect. In some embodiments, the agent has been conjugated to the target protein by a sortase-mediated transpeptidation reaction, e.g., by a method provided herein. Typically, a sortase-mediated transpeptidation reaction leaves a “scar” in the generated protein, which comprises the C-terminal sortase recognition motif (e.g., LPXT, or any other C-terminal sortase recognition motif described herein) and, in some embodiments, a plurality of N-terminal amino acids comprised in the respective N-terminal sortase recognition motif, e.g., (G)n or (A)n, wherein n is an integer equal to or greater than 2. The sortase recognition motif in the product of the transpeptidation reaction is typically a sequence created by the sortase reaction, e.g., by a SrtAaureus mediated transpeptidation reaction or by a SrtApyogenes transpeptidation reaction.
In some embodiments, the agent conjugated to the capsid protein is a protein, a detectable label, a binding agent, a click-chemistry handle, a small molecule, or any other agent described herein. In some embodiments, the virus comprises a plurality of different target proteins conjugated to an agent (e.g., different types of target proteins to different agents) via a sortase recognition motif. In some embodiments, different target proteins of the virus are conjugated to different agents, for example, a binding agent and a detectable label; two different detectable labels; a first binding agent, a second binding agent, and a detectable label, and so on. In some embodiments, the different target proteins are conjugated to the respective agents via sortase recognition motifs of orthogonal sortases. For example, in some embodiments, a virus is provided comprising a first target protein conjugated to a first agent via a SrtAaureus recognition motif, and a second target protein conjugated to a second agent via a SrtApyogenes recognition motif.
In some embodiments, a functionalized M13 bacteriophage is provided that comprises a pIII conjugated to an agent via a sortase recognition motif. In some embodiments, a functionalized M13 bacteriophage is provided that comprises a pVIII conjugated to an agent via a sortase recognition motif. In some embodiments, a functionalized M13 bacteriophage is provided that comprises a pIX conjugated to an agent via a sortase recognition motif. In some embodiments, the agent is an agent as described herein, for example, a binding agent or a detectable label. In some embodiments, a functionalized M13 bacteriophage is provided that comprises a pIII conjugated to a first agent, and a pVIII conjugated to a second, different agent. In some embodiments, a functionalized M13 bacteriophage is provided that comprises a pIII conjugated to a first agent, and a pIX conjugated to a second, different agent. In some embodiments, a functionalized M13 bacteriophage is provided that comprises a pVIII conjugated to a first agent, and a pIX conjugated to a second, different agent. In some embodiments, the first agent is a binding agent (e.g., biotin). In some embodiments, the second agent is a binding agent that binds the first binding agent (e.g., streptavidin). Additional suitable agents include, but are not limited to, click chemistry handles, SNAP-, Clip-, ACP-, and MCP-tags, complementary DNA strands, leucine zippers, GFP, and toxins, e.g., bacterial and plant toxins In some embodiments, three different target proteins are conjugated to three different agents, four different agents to four different target proteins, and so on. The invention is not limited in this respect.
The virus may be any virus suitable for sortase-mediated functionalization as described herein, including, but not limited to, a dsDNA virus comprising a double-stranded DNA genome, an ssDNA virus comprising a single-stranded DNA genome, a dsRNA virus comprising a double-stranded RNA genome, a (+)ssRNA virus comprising a single stranded (+)sense strand RNA genome, a (−)ssRNA virus comprising a single stranded (−)sense RNA, an ssRNA-RT virus comprising a single-stranded (+)sense RNA with a DNA intermediate genome in its life-cycle that is generated by reverse transcription of the RNA genome, or a dsDNA-RT virus. Exemplary functionalized viruses include, e.g., Retroviridae (e.g., lentiviruses such as human immunodeficiency viruses, such as HIV-I); Caliciviridae (e.g. strains that cause gastroenteritis); Togaviridae (e.g. equine encephalitis viruses, rubella viruses); Flaviridae (e.g. dengue viruses, encephalitis viruses, yellow fever viruses, hepatitis C virus); Coronaviridae (e.g. coronaviruses); Rhabdoviridae (e.g. vesicular stomatitis viruses, rabies viruses); Filoviridae (e.g. Ebola viruses); Paramyxoviridae (e.g. parainfluenza viruses, mumps virus, measles virus, respiratory syncytial virus); Orthomyxoviridae (e.g. influenza viruses); Bunyaviridae (e.g. Hantaan viruses, bunga viruses, phleboviruses and Nairo viruses); Arenaviridae (hemorrhagic fever viruses); Reoviridae (erg., reoviruses, orbiviurses and rotaviruses); Birnaviridae; Hepadnaviridae (Hepatitis B virus); Parvoviridae (parvoviruses); Papovaviridae (papilloma viruses, polyoma viruses); Adenoviridae; Herpesviridae (herpes simplex virus (HSV) 1 and 2, varicella zoster virus, cytomegalovirus (CMV), EBV, KSV); Poxyiridae (variola viruses, vaccinia viruses, pox viruses); and Picornaviridae (e.g. polio viruses, hepatitis A virus; enteroviruses, human coxsackie viruses, rhinoviruses, echoviruses). In some embodiments, the functionalized virus provided is a DNA virus. In some embodiments, the functionalized virus is a phage, or bacteriophage. In some embodiments, the functionalized virus is a filamentous phage. In some embodiments, the functionalized virus is an M13 bacteriophage. In some embodiments, the functionalized virus provided is a bacteriophage, for example, a bacteriophage belonging to the family of Myoviridae (e.g., T4 phage), Siphoviridae (e.g., λ phage, Bacteriophage T5), Podoviridae (e.g., T7 phage), Ligamenvirales, Lipothrixviridae, Rudiviridae, Ampullaviridae, Bacilloviridae, Bicaudaviridae, Clavaviridae, Corticoviridae, Cystoviridae, Fuselloviridae, Globuloviridae, Guttavirus, Inoviridae, Leviviridae (e.g., MS2, Qβ), Microviridae (e.g., ΦX174), Plasmaviridae, or Tectiviridae. Exemplary functionalized bacteriophages provided herein include, without limitation, Lambda phage (λ phage, lysogen), T2 phage, T4 phage, T7 phage, T12 phage, R17 phage, M13 phage, MS2 phage, G4 phage, P1 phage, Enterobacteria phage P2, P4 phage, ΦX174 phage, N4 phage, Φ6 phage, and Φ29 phage. Further, any virus that may be functionalized using the methods, reagents, and/or kits provided herein is within the scope of the present invention, including, but not limited to, those viruses described on pages 129-653 of Stephen T. Abedon, The Bacteriophages, Oxford University Press, USA; 2nd edition, Dec. 15, 2005, ISBN: 0195148509; the entire contents of which are incorporated herein by reference.
Some aspects of this invention provide viruses that comprise an engineered capsid protein comprising a sortase recognition motif, for example, a C-terminal or N-terminal sortase recognition motif described herein. Such engineered viruses can readily be functionalized according to methods described herein without the need for further engineering of the virus, for example, using recombinant methods. For example, in some embodiments, a phage is provided that comprises a capsid protein that does not naturally comprise a sortase recognition motif at a terminus that is accessible on the surface of the phage. In some embodiments, the phage is an M13 phage, comprising an engineered capsid protein, for example, a pIII, pVIII, or pIX protein comprising a recombinant poly-glycine or poly-alanine sequence (e.g., (G)n or (A)n, wherein n is equal to or greater than 2 at its N-terminus.
Some aspects of this invention provide nucleic acids encoding an engineered capsid protein comprising a sortase recognition motif. Such nucleic acids can be used to generate virus particles comprising the engineered capsid proteins, which can then be functionalized according to the methods described herein. In some embodiments, an isolated nucleic acid is provided that encodes a viral capsid protein comprising an N-terminal or a C-terminal sortase recognition motif. In some embodiments, the nucleic acid is a recombinant nucleic acid. In some embodiments, the sortase recognition motif is inserted into a wild-type nucleic acid sequence encoding the capsid protein. In some embodiments, the nucleic acid is comprised in an expression vector. Such vectors are also provided by aspects of this invention. Such expression vectors typically comprise the encoding nucleic acid and additional nucleic acid elements mediating the expression and/or replication of the nucleic acid in a host cell, for example, a bacterial host cell in the case of bacteriophages. In some embodiments, the expression construct also comprises nucleic acid sequences encoding one or more additional capsid proteins of the virus. In some embodiments, the expression construct encodes at least two engineered capsid proteins, each comprising a sortase recognition motif. In some embodiments, the sortase recognition motifs comprised in the at least two engineered capsid proteins are recognized by orthogonal sortases. In some embodiments, proteins encoded by the nucleic acids and expression constructs described herein are provided.
Some aspects of this invention provide kits useful for the expression of viral capsid proteins comprising a sortase recognition motif, and for the generation of viral particles that can be functionalized via a sortagging technique described herein. In some embodiments, such a kit comprises a recombinant nucleic acid encoding a viral capsid protein comprising a sortase recognition motif. In some embodiments, the kit further comprises a nucleic acid encoding additional viral genes. In some embodiments, the additional viral genes may comprise at least one additional capsid protein comprising a sortase recognition motif. In some embodiments, the kit comprises nucleic acid sequences encoding two or more capsid proteins comprising different sortase recognition motifs. In some embodiments, the different sortase recognition motifs are recognized by orthogonal sortases, for example, one by SrtAaureus and another by SrtApyogenes. In some embodiments, the kit comprises one or more nucleic acid molecules that together provide all viral genes necessary to generate a viral particle. For example, in some embodiments, the kit provides a nucleic acid sequence encoding M13 pIII comprising a sortase recognition sequence (e.g., poly-glycine) at its N-terminus, and also one or more nucleic acid sequences encoding the M13 genome except wild-type pIII. In some embodiments, the kit provides a nucleic acid sequence encoding M13 pIII comprising a sortase recognition sequence (e.g., poly-glycine) at its N-terminus, a nucleic acid sequence encoding M13 pVIII comprising a sortase recognition sequence (e.g., poly-alanine) at its N-terminus, and one or more nucleic acid sequences encoding the M13 genome except wild-type pIII and pVIII. In some embodiments, the kit provides a nucleic acid sequence encoding M13 pVIII comprising a sortase recognition sequence (e.g., poly-glycine) at its N-terminus, a nucleic acid sequence encoding M13 pIX comprising a sortase recognition sequence (e.g., poly-alanine) at its N-terminus, and one or more nucleic acid sequences encoding the M13 genome except wild-type pVIII and pIX.
Some kits provided herein comprise the nucleic acids described herein as part of one or more expression constructs. Expression constructs may be in the form of a vector, e.g., a plasmid or phagemid, which can readily be introduced into a host cell, e.g., a bacterial cell that can be infected by a bacteriophage, to generate recombinant viral particles, e.g., M13 particles comprising an M13 pIII protein that contains a sortase recognition motif. Recombinant phage generated from such kits can then be functionalized by a sortagging method described herein.
In some embodiments, the kit further comprises a sortase. Typically, the sortase comprised in the kit recognizes a sortase recognition motif encoded by a nucleic acid comprised in the kit. In some embodiments, the sortase is provided in a storage solution and under conditions preserving the structural integrity and/or the activity of the sortase. In some embodiments, where two or more orthogonal sortase recognition motifs are encoded by the nucleic acid(s) comprised in the kit, a plurality of sortases is provided, each recognizing a different sortase recognition motif encoded by the nucleic acid(s). In some embodiments, the kit comprises SrtAaureus and/or SrtApyogenes.
In some embodiments, the kit further comprises a sortase substrate. In some embodiments, the sortase substrate comprises a sortase recognition motif conjugated to an agent. For example, the kit may comprise a sortase substrate comprising a sortase recognition motif that is compatible with a sortase recognition motif encoded by a nucleic acid in the kit in that both motifs can partake in a sortase-mediated transpeptidation reaction catalyzed by the same sortase. For example, if the kit comprises a nucleic acid encoding a capsid protein comprising a SrtAaureus N-terminal recognition sequence, the kit may also comprise SrtAaureus and a SrtAaureus substrate conjugated to an agent, wherein the sortase substrate will comprise the C-terminal sortase recognition motif. In some embodiments, the kit further comprises a buffer or reagent useful for carrying out a sortase-mediated transpeptidation reaction, for example, a buffer or reagent described in the Examples section.
The following working examples are intended to describe exemplary reductions to practice of the methods, reagents, and compositions provided herein and do not limited the scope of the invention.
Generation of the M13 Phage Constructs.
The oligonucleotides used to design the different phage constructs are compiled in Table 3. The G5-pIII phage (SEQ ID NO: 77) was engineered by inserting the G5pIIIC and G5pIIINC (SEQ ID NO: 77) annealed oligonucleotides into the M13KE vector (New England Biolabs), previously digested with EagI and Acc65I restriction enzymes. To construct the A2G4-pVIII phage, the M13SK vector40 was digested with PstI and BamHI restriction enzymes and the A2G4pVIIIC (SEQ ID NO: 9) and A2G4pVIIINC (SEQ ID NO: 9) annealed oligonucleotides were inserted. To engineer the G5HA-pIX construct (SEQ ID NO: 77), the 983 vector was used. This vector was created by refactoring the M13SK vector so the pIX and pVII genes are not overlapping. Upon digestion of this vector with SfiI, the annealed G5HApIXC and G5HApIXNC (SEQ ID NO: 77) oligonucleotides were inserted. The G5-pIII-A2-pVIII (SEQ ID NO: 77) phage construct was created using a modified M13SK vector40, which has a DSPHTELP (SEQ ID NO: 116) sequence on pVIII and a biotin acceptor peptide (GLQDIFEAQKIEWHE (SEQ ID NO: 117)) on pIII. Five N-terminal glycines were added to pIII following the above strategy described for G5-pIII phage (SEQ ID NO: 77). The resultant vector was then modified at the N-terminus of pVIII using the QuikChange II site-directed mutagenesis kit (Stratagene) and the pVIIIAADSPH oligonucleotide pair. All the generated phage vectors were transformed into the XL-1 Blue bacterial strain, plated in agar top on LB agar plates containing 1 mM IPTG, 40 μg/mL X-Gal, and 30 μg/mL tetracycline. Plaques were selected and DNA was isolated and sequenced to check for the insertion.
For phage amplification, the E. coli strain ER2738 (New England Biolabs) in LB media supplemented with 30 μg/mL tetracycline, was infected with phage for at least 12 hrs at 37° C. The cultures were centrifuged at 12000 g for 20 min and the phage was precipitated from the supernatant at 4° C. with the addition of ⅕ of the supernatant volume of 20% PEG8000/2.5M NaCl solution. Upon centrifugation at 13500 g for 20 min, the pellet was resuspended in 25 mM Tris, 150 mM NaCl, pH 7.0-7.4 (TBS). For further purification, this resuspension was subjected to two rounds of centrifugation/precipitation. The final phage concentration averaged between 1013-1014 plaque forming units (pfu) per mL as determined by UV-vis spectrometry41.
Sortase-Mediated Reactions.
SrtApyogenes and SrtAaureus were expressed and purified as described33, 42. Sortase reactions were performed as indicated in the figures. A typical sortase reaction with SrtAaureus included 200 nM phage, 50 μM SrtAaureus, and 50 μM substrate for small peptides or 20 μM for proteins. The reactions were incubated for 3 hrs at 37° C. (for small peptides) or at room temperature (for proteins) in TBS with 10 mM CaCl2. SrtApyogenes-mediated reactions included 8 nM phage, 50 μM SrtApyogenes, and 20 μM substrate, incubated for 3 hr at 37° C. in TBS. Where indicated, phage was purified by PEG 8000/NaCl precipitation after diluting the reactions with TBS such that the substrate concentration was below 600 nM.
For the flow cytometry experiments, the G5-pIII-A2-pVIII (SEQ ID NO: 77) phage construct was labeled with K(TAMRA)-LPETAA (SEQ ID NO: 12) on pVIII. The resultant labeled phage was purified by PEG8000/NaCl precipitation, resuspended in TBS, and split into three parts. One part remained unlabeled, and the other two were labeled with either VHH7.LPETG (SEQ ID NO: 10) or anti-GFP.LPETG (SEQ ID NO: 10) on pIII. As assessed by the anti-pIII antibody, a yield of 2.5 antibody molecules per virion was achieved in both cases.
The yield of the sortase-mediated biotinylation reactions was determined using biotinylated GFP as a standard. This was prepared labeling GFP—comprising a LPETG (SEQ ID NO: 10) at its C-terminus—with a biotin group using SrtAaureus (GFP.LPETGGGK(biotin))42 (SEQ ID NO: 281). Known amounts of the purified GFP.LPETGGGK(biotin) standard (SEQ ID NO: 281) and varying volumes of the phage labeling reactions were loaded onto the same SDS-PAGE gel and analyzed by immunoblot using streptavidin-HRP (GE Healthcare). The signal obtained in the phage labeling reactions was compared with the signal derived from the GFP.LPETGGGK(biotin) (SEQ ID NO: 281) calibration curve allowing us to infer the amount of phage protein labeled in the reaction. To calculate the labeling efficiency, the amount of labeled protein was divided by the amount of total phage protein loaded into the gel. The phage concentration was determined by UV-vis spectrometry and it was assumed that there were 2700 copies of pVIII, 5 copies of pIII, and 5 copies of pIX per phage particle.
To determine the yield of GFP-pVIII phage labeling, unincorporated GFP and sortase was removed from phage by PEG8000/NaCl precipitation. Varying volumes of GFP-pVIII phage and known amounts of GFP were loaded onto the same SDS-PAGE gel and analyzed by immunoblot using an anti-GFP-HRP antibody (Santa Cruz Biotechnology). The signal of the GFP-pVIII fusion protein was compared to the signal of the GFP calibration curve as described for the biotinylation reactions. For GFP-pIII and GFP-pIX labeling, the signal of the fusion protein was compared to the input amount of pIII or pIX as detected by anti-pIII (New England Biolabs) or anti-HA (Roche) antibodies, respectively. For GFP-pIII, the input signal consisted of only intact pIII molecules and lower molecular weight anti-pIII reactive proteins were not included. These proteins can be attributed to proteolyzed pIII43. Because the anti-pIII antibody recognizes the C-terminus of the protein, these fragments cannot be labeled using SrtAaureus. In all cases the blots were scanned and densitometric analysis was performed using the ImageJ program (National Institutes of Health). The labeling yield was averaged over three independent reactions with three aliquots from each reaction analyzed. The standard deviation of the reactions was calculated from the averages of the three independent reactions.
Dynamic Light Scattering (DLS).
DLS measurements were obtained with a Beckman Delsa-Nano C Particle Analyzer (Beckman Coulter Inc). Phage mixtures were diluted to ˜1011 pfu/mL in 1 mL of water and loaded into a cuvette. Samples from each experiment were measured in triplicate and the results were averaged by cumulant analysis. Autocorrelation functions were used as a direct comparison of aggregation because aggregates have a slower Brownian motion causing the signal correlation to be delayed to longer relaxation times.
Atomic Force Microscopy (AFM).
Phage preparations were diluted to a concentration of ˜1011 pfu/mL, and 100 μL of this mixture were deposited on a freshly cleaved mica disc. AFM images were taken on a Nanoscope IV (Digital Instruments) in air using tapping mode. The tips had spring constants of 20-100N/m driven near their resonant frequency of 200-400 kHz (MikroMasch). Scan rates were approximately 1 Hz. Images were leveled using a first-order plane fit to remove sample tilt.
Flow Cytometry Analysis.
C57BL/6 mice were purchased from Jackson Labs. Animals were housed at the Whitehead Institute for Biomedical Research and were maintained according to guidelines approved by the Massachusetts Institute of Technology (MIT) Committee on Animal Care. Lymph nodes were isolated from 6-8 week old C57BL/6 mice and crushed through a 40 μM cell strainer. Cells were washed once with PBS, resuspended at 2×107 cells per mL, aliquoted at ˜1×106 cells per sample, and incubated with staining agents in 5% milk in PBS for 1 hr at room temperature. 1011 VHH7 molecules and 1011 anti-GFP molecules either directly conjugated to TAMRA using SrtAaureus, or covalently attached to phage (5×1010 phage particles of VHH7-G5-pIII-TAMRA-A2-pVIII (SEQ ID NO: 77) or anti-GFP-G5-pIII-TAMRA-A2-pVIII (SEQ ID NO: 77), see Sortase-mediated reactions section) were incubated with the cells. The same amount of non-targeted fluorescent phage particles (i.e., G5-pIII-TAMRA-A2-pVIII) (SEQ ID NO: 77) was used as a negative control. B cells were stained with Pacific Blue anti-mouse B220 (BD Pharmingen, clone RA3-6B2). Upon staining, the cells were centrifuged at 170 g for 5 min, washed with PBS three times, and resuspended in 500 μL of PBS. Flow cytometry was performed using a FACSAria (BD). 100,000 events were collected for each sample.
Estimating Nearest Neighbor Packing of GFP on Phage Surface.
Using the crystal structure of the pVIII capsid protein (1IFJ, see Marvin, D. A., Hale, R. D., Nave, C., and Helmer-Citterich, M. (1994) Molecular models and structural comparisons of native and mutant class I filamentous bacteriophages Ff (fd, fl, M13), Ifl and IKe. J. Mol. Biol. 235, 260-86.), a model viral capsid was constructed with fivefold symmetry serving as a model of the phage surface. A crystal structure of GFP (1GFL, see, Yang, F., Moss, L. G., and Phillips, G. N., Jr. (1996) The molecular structure of green fluorescent protein. Nat. Biotechnol. 14, 1246-51) was oriented such that its C-terminus was adjacent to the N-terminus of pVIII. By analyzing this image, it was determined that one GFP molecule blocked the N-termini of the six pVIII proteins surrounding the GFP-pVIII fusion meaning at most one out of seven pVIII proteins can be labeled with a GFP. From this, it was calculated that a single virion with 2700 pVIII proteins would have at most 385 GFP molecules. The visualizations were performed using WinCoot (see Emsley, P., Lohkamp, B., Scott, W. G., and Cowtan, K. (2010) Features and development of Coot. Acta Crystallogr. D Biol. Crystallogr. 66, 486-501). All references referred to in the above paragraph are incorporated herein by reference in their entirety.
Miscellaneous.
Expression and purification of GFP.LPETG.His6 (SEQ ID NO: 287) and GFP.LPETA.His6 (SEQ ID NO: 283), were performed as described33. Identification, characterization, expression, and purification of VHH7.LPETG.His6 (SEQ ID NO: 287) will be published elsewhere. Streptavidin was cloned as a streptavidin.LPETG.HAtag.His6 (SEQ ID NO: 10 and 288) fusion protein using the template Addgene 2086044, and expressed as a soluble tetrameric streptavidin45. Purification was performed following the same protocol used for GFP33. Sortase reactions were analyzed on 4-12% Bis-Tris SDS-PAGE gels with MES running buffer except for
The K(biotin)-LPETGG (SEQ ID NO: 13), K(biotin)-LPETAA (SEQ ID NO: 12), K(TAMRA)-LPETAA (SEQ ID NO: 12), and GGGK(biotin) (SEQ ID NO: 127) peptides were obtained from the Swanson Biotechnology Center. For mass spectrometry, the protein bands of interest were excised, subjected to protease digestion, and analyzed by electrospray ionization tandem mass spectrometry (MS/MS). Fluorescent gel images were obtained using a variable mode imager (Typhoon 9200; GE Healthcare).
N-Terminal Labeling of pIII Using SrtAaureus.
P111 has been the most extensively explored of the M13 capsid proteins in phage display because of the flexibility and accessibility of its N-terminus46. Thus, we introduced five glycines at the N-terminus of pIII (G5-pIII phage) (SEQ ID NO: 77) and used SrtAaureus to covalently attach a K(biotin)-LPETGG peptide (SEQ ID NO: 13) (
To determine whether sortase could be exploited to attach pre-folded proteins onto pIII, we used GFP containing an LPETG (SEQ ID NO: 10) motif at its C-terminus as a substrate. The reaction was analyzed by immunoblot using an anti-pIII antibody (
N-Terminal Labeling of pIX Using SrtAaureus.
Because the C-terminus of pIX is buried in the phage structure and therefore unavailable for labeling47, we attempted to label its N-terminus. However, this region of the protein is not as accessible as in pIII and our first attempts at labeling a phage construct displaying five glycines at the N-terminus of pIX using sortase failed (data not shown). To increase accessibility of the five glycines, the N-terminus of pIX was extended with an HA tag, a useful handle for detection, as no pIX-specific antibodies are available. This G5HA-pIX (SEQ ID NO: 282) phage construct was labeled with the K(biotin)-LPETGG peptide (SEQ ID NO: 13) and the reactions were analyzed by immunoblot using streptavidin-HRP and an anti-HA antibody. A 5 kDa polypeptide, reactive with both streptavidin and anti-HA, was seen only in the complete reaction (
N-Terminal Labeling of pVIII Using SrtApyogenes.
In the course of phage biogenesis the N-terminus of pVIII is proteolytically cleaved, resulting in the display of an N-terminal alanine41. We took advantage of this feature and exploited SrtApyogenes to label pVIII. Also, the ability of using two orthogonal sortase enzymes (SrtApyogenes for pVIII and SrtAaureus for pIII and pIX labeling) would further enable dual labeling of the same phage particle.
To be used as a nucleophile in SrtApyogenes-mediated reactions, pVIII requires display of two N-terminal alanines. Thus, the N-terminus of the mature form of pVIII was modified to AAGGGG (A2G4-pVIII phage) (SEQ ID NO: 9). The glycines were introduced to extend the N-terminus of pVIII away from the body of the phage, thus improving the accessibility of the Ala-Ala motif for participation in the sortase reaction. Using SrtApyogenes and a K(biotin)-LPETAA (SEQ ID NO: 12) substrate peptide, we showed robust labeling of pVIII based on an immunoblot using streptavidin-HRP (
Phage assembly limits either the size of the modifications displayed on pVIII to a few residues when using a phage vector, or it limits the number of labels attached to pVIII when using a phagemid vector20. In this context, the sortase-labeling strategy is an obvious alternative to overcome such limitations. Using 20 μM GFP containing a LPETA (SEQ ID NO: 11) motif at its C-terminus, 50 μM SrtApyogenes, and 8 nM A2G4-pVIII phage (SEQ ID NO: 9), we were able to attach 91±20 GFP molecules on average per phage particle upon incubation at 37° C. for 3 hrs (
Building End-to-Body Phage Structures.
The ability to site-specifically label the M13 capsid proteins provides the opportunity to create novel multi-phage structures, which may provide scaffolds for new materials and devices. One such structure (
Streptavidin, modified to contain a C-terminal LPETG (SEQ ID NO: 10) motif in each of its monomers, was attached to the G5-pIII (SEQ ID NO: 77) phage using SrtAaureus. The samples were boiled, loaded onto an SDS-PAGE gel, and analyzed by immunoblot using an anti-pIII antibody. A 90 kDa polypeptide, consistent with the size of pIII fused to a streptavidin monomer, was seen only when all the reaction components were mixed together (
The streptavidin-pIII phage and the biotin-pVIII phage were mixed at a 5:1 molar ratio and incubated at room temperature for 15 min. Analysis of these samples by DLS showed an increase of the hydrodynamic diameter for the lampbrush phage mixture (700 nm) when compared to streptavidin-pIII (516 nm) and biotin-pVIII (204 nm) phage preparations. When the two types of phage were mixed, the ACF (
Site-Specific Labeling of Two Capsid Proteins in the Same Phage Particle.
The two orthogonal sortases used to label different capsid proteins offer the possibility to attach different moieties to the body (using SrtApyogenes) and to the end of phage (using SrtAaureus) within the same virion. In such a strategy, either pIII or pIX could be labeled with SrtAaureus orthogonally to the pVIII, so as a proof-of-concept, a phage variant that contains a double alanine at the N-terminus of pVIII and the pentaglycine motif at the N-terminus of pIII was generated (this construct is referred to as G5-pIII-A2-pVIII (SEQ ID NO: 77)). Conditions were optimized to label each of these proteins in a site-specific manner. Because such dual-labeled phage could be a useful tool to sort cells by FACS (see below and discussion section), we here provide the proof-of-concept by labeling the body of phage with a fluorophore and the tip of phage with a cell-targeting moiety.
pVIII was labeled with a K(TAMRA)-LPETAA (SEQ ID NO: 12) peptide and purified using PEG/NaCl precipitation to remove free peptide and sortase (
Flow Cytometry Experiments Using Fluorescent Phage.
Fluorescent phage has been used for targeted staining in vivo50-51 as well as flow cytometry experiments52. However, these have been performed with short peptide phage display libraries. The ability to label phage with a large number of fluorophores that are site-specifically attached to pVIII is a tool useful for selecting phage of interest from phage display libraries of large moieties (such as antibodies) by fluorescence. With libraries of this type, less specific labeling methods can alter the displayed moiety. To provide proof-of-concept that fluorescent phage can be used for this purpose, we tested the ability of the dual labeled phage—containing TAMRA fluorophore sortagged onto pVIII and VHH7 onto pIII—to stain B cells. As a negative control, we used a fluorescent phage containing an anti-GFP VHH attached to pIII53. An average yield of 2.5 antibodies per phage virion was achieved for both VHH7 and anti-GFP VHH as determined by densitometric analysis.
Mouse lymphocytes obtained from lymph nodes were stained for B cells using a fluorescent Pacific Blue anti-mouse B220 antibody and incubated with phage-VHH7, phage-anti-GFP, or non-targeted phage. All phage preparations were similarly labeled with TAMRA on pVIII. After removal of unbound materials by washing, cells were subjected to flow cytometry (
We show that sortase-mediated reactions overcome many of the limitations of current methods to functionalize M13 capsid proteins. The main body and both ends of the viral capsid can be functionalized with substituents that cannot be encoded genetically (such as biotin and fluorophores), and we can also install properly folded and assembled proteins (such as GFP and streptavidin) in a manner that could easily be extended to oligomeric proteins as well.
One of the major challenges has been the modification of the major capsid protein pVIII. Using sortase, labeling efficiencies were greater than those obtained genetically (Table 4). In the past, biotinylated phage has been produced by display of the biotin acceptor peptide (BAP)54, a 15-amino acid sequence. Peptides similar in size have been displayed at no more than 400-700 copies per phage, with the efficiency being sequence-dependent20. Here we attach 1350 biotin molecules on average per phage particle, a great improvement in the display of a small molecule. Moreover, because the peptide substrate for sortase can be modified with peptides, proteins, fluorophores, etc.31-35, phage can be decorated with a wide range of substituents. As far as display of proteins is concerned, proteins similar in size to GFP have been incorporated at fewer than one copy per phage on pVIII using a phagemid system18. Using sortase, we display 91 GFP molecules on average per phage particle.
For the pIII and pIX proteins, we show that every phage can be labeled with multiple copies of the desired peptide/protein (Table 4). An advantage of using sortase to covalently attach proteins to phage over genetically engineering pIII directly is that it ensures display of the correct quaternary structure of the protein. This can be inferred from our experiments using streptavidin. The mixing of two phage particles, one containing streptavidin on pIII and the other containing biotin on pVIII results in a novel and complex phage structure. This shows that the streptavidin structure displayed on phage remains fully active and binds biotin.
Sortase enzymes in combination with the streptavidin-biotin pair45 or in conjunction with click-chemistry can generate novel structures. The ability of patterning and aligning materials on phage or of increasing its surface area is important for the development of new materials. For example, the lampbrush phage structure generated here (
In addition to N-terminal labeling of single capsid proteins, two capsid proteins were labeled site-specifically on a single phage particle using two orthogonal sortases. This could be explored for panning of antibody libraries displayed on pIII. Due to the exquisite site-specificity of sortase, fluorescent peptides can be added to pVIII without modification of the moiety displayed at pIII. Fluorescent labeling by other chemistries does not easily afford such specificity, especially when displaying a large moiety, such as an antibody fragment. The sensitivity of detection should increase when a phage particle contains many fluorophore groups on pVIII. This is indeed what we observe in our flow cytometry experiments, showing that this strategy greatly enhances the sensitivity of detection. Increased sensitivity would be instrumental in the context of a future panning strategy for detection of rare binding events, whether due to low concentration of the target or low phage concentration.
Modification of pIII and pIX by sortase will be useful for material applications, where the physical properties of phage and not its utility as a library vector are of prime concern. Fluorescent modification of pVIII is compatible with the construction and screening of libraries created using pIII genetic fusions. In this case, the site-specificity and yield of the sortase reaction allow the generation of libraries that can be screened directly by fluorescence. Thus, the versatility of the sortase-based labeling strategy described here will enable development of a wide array of tools, expanding the use of phage either for the creation of new materials or for new biological applications.
All publications, patents, patent applications, and database entries mentioned anywhere herein, including, but not limited to, those items listed above, are hereby incorporated by reference in their entirety as if each individual publication, patent, patent application, and database entry was specifically and individually indicated to be incorporated by reference. In case of conflict, the present application, including any definitions herein, will control.
A major goal of synthetic biology is to control and program biological molecules to perform a desired function, such as the organization of materials to create devices.1 In this context, the self-assembling capsid proteins of M13 bacteriophage have been explored to form nanowire structures,2-3 which have been used to build battery and solar devices.4-5 M13 bacteriophage is an attractive building block for more complex multi-material devices such as transistors and diodes, because its major capsid protein (pVIII) can been engineered to bind and nucleate different materials.2,4,6
The building of more complex materials requires construction of multi-phage scaffolds, but this has been hampered by the inability to freely manipulate the major capsid protein located in the body of phage and the four minor capsid proteins located at the ends of the phage (pIII, pVI, pVII, pIX) to form specific connections between different M13 particles. Streptavidin-based conjugates6-8 and leucine zippers9 have been explored to connect virions through the pIII, pVIII, or pIX proteins, but the resultant structures neither displayed a 1:1 stoichiometry—as streptavidin can bind up to four biotin molecules—nor did they allow precise control over structure length.9
DNA hybridization is a commonly used strategy to establish nanoscale connections. It has been used to order spherical viruses10-11 and order gold nanoparticles into crystal lattices.12-13 Although these and polymer-based particles can be conjugated with DNA14-15, the use of M13 offers two main advantages: high aspect ratio scaffolds and five proteins that may be engineered for different functions. Crosslinking individual M13 phage particles by means of DNA hybridization would have several advantages: first, a 1:1 stoichiometry with easier control over the number of phage coming together at a single connection; second, specificity and versatility, as the sequence of a DNA oligonucleotide can be modified to form new orthogonal complementary pairs; and third, reversible ligations, as DNA-DNA interactions can be disrupted by heat and reformed by cooling.
We accomplished specific labeling of the N-termini of pIII and pIX, with a variety of substituents using the sortase enzyme from Staphylococcus aureus (SrtAaureus).7 Sortase-catalyzed transpeptidation reactions comprise two steps: initial recognition of an LPXTG (SEQ ID NO: 78) motif placed near the C-terminus of a polypeptide which SrtAaureus cleaves after the threonine residue to form a thioester-linked acyl-enzyme intermediate. This is followed by a nucleophilic attack by the α-amine of an oligoglycine (poly)peptide, which resolves the intermediate. Because the LPXTG (SEQ ID NO: 78) motif-containing (poly)peptide can be conjugated beforehand with any substituent of choice (e.g., fluorophore), the final product is the protein of interest—in this case pIII or pIX—labeled at the N-terminus with that substituent. The SrtAaureus catalyzed reactions are orthogonal to Streptococcus pyogenes sortase A (SrtApyogenes)-mediated labeling of pVIII, as the enzyme recognizes an LPXTA (SEQ ID NO: 92) motif and the intermediate is resolved by an N-terminal double alanine nucleophile7,16 instead of the (Gly)n preferred by SrtAaureus.
Here we describe the installation of a loop structure comprising the LPXTG (SEQ ID NO: 78) sortase recognition motif on pIII to enable C-terminal display. Using an M13 construct containing three sortase labeling motifs within the same virion, we demonstrate orthogonal labeling of pIII, pVIII, and pIX proteins. Using this construct, we built end-to-end multi-phage structures in a specific order by labeling the pIII and pIX proteins with DNA and different fluorophores on the pVIII.
C-Terminal Phage Vector Display of the Sortase Substrate Motif.
We first examined whether we could display the LPXTG (SEQ ID NO: 78) sortase-recognition motif at the C-terminus of the pIII, pVI, or pIX proteins. Although genetic engineering of the M13 phage genome yielded the desired modifications as confirmed by PCR (
We then engineered the N-terminus of pIII to display a 50 amino acid sequence comprised of an LPETG (SEQ ID NO: 10) recognition motif for SrtAaureus flanked by two cysteines. When these cysteines engage in disulfide bond formation, they form a loop similar to that displayed by the subunit A of cholera toxin.17 Because proteolytic cleavage of the loop improves labeling efficiency,17 we inserted a linker followed by a Factor Xa protease cleavage site immediately downstream of the LPETG (SEQ ID NO: 10) motif (
C-Terminal Sortase-Mediated Labeling of pIII.
We labeled the loopXa-pIII phage construct at pIII with a GGGK(TAMRA) peptide (SEQ ID NO: 127) using SrtAaureus (
Sortase-mediated transpeptidation reactions afford attachment of a wide range of molecules to this loop structure, including a pre-assembled protein complex of ˜58 kDa (
To determine whether the loop engineered onto pIII renders itself suitable for labeling with larger molecules, we attempted to attach an oligomeric protein complex: the B subunit pentamer of cholera toxin (CtxB). CtxB represents a 58 kDa soluble complex (Zhang, R. G.; Westbrook, M. L.; Westbrook, E. M.; Scott, D. L.; Otwinowski, Z.; Maulik, P. R.; Reed, R. A.; Shipley, G. G., The 2.4 A crystal structure of cholera toxin B subunit pentamer: choleragenoid. J Mol Biol 1995, 251 (4), 550-62), which is disrupted by SDS at high temperatures. We endowed each single subunit of CtxB with three consecutive Gly residues at the N-terminus, expressed it in E. coli and purified the established pentamer (G3-CtxB) (Antos, J. M.; Chew, G. L.; Guimaraes, C. P.; Yoder, N. C.; Grotenbreg, G. M.; Popp, M. W.; Ploegh, H. L., Site-specific N- and C-terminal labeling of a single polypeptide using sortases of different specificity. J Am Chem Soc 2009, 131 (31), 10800-1). Upon incubation of the LoopXa-pIII phage with Factor Xa, SrtAaureus, and G3-CtxB for 5 hrs at room temperature, the samples were boiled and analyzed by SDS-PAGE under non-reducing conditions, followed by immunoblot with anti-pIII and anti-CtxB antibodies (
Orthogonal Labeling of Three Phage Capsid Proteins.
In a first attempt to establish end-to-end phage dimers, we tried to directly link the loopXa-pIII phage and a phage containing a pentaglycine motif at the N-terminus of its pIII (G5-pIII phage) (SEQ ID NO: 77) via SrtAaureus. No dimers were observed after 24 hrs of incubation and only ˜3% of structures were dimeric after 60 hrs of incubation (
We attempted to directly fuse two phage particles through their ends using SrtAaureus. One of the phage constructs contained a pentaglycine nucleophile motif (G5-pIII phage) (SEQ ID NO: 77) and the other the loop structure (loopXa-pIII phage), both on pIII. 120 nM loopXa-pIII phage, 180 nM G5-pIII phage (SEQ ID NO: 77), 230 nM Factor Xa, 30 μM SrtAaureus, and 10 mM CaCl2 in TBS were incubated at room temperature. Aliquots were taken at 24 hrs (no phage dimers were observed) and 60 hrs. The reaction was diluted with TBS, such that the loopXa-pIII concentration was below 10 nM, and purified by PEG8000/NaCl precipitation. Phage was resuspended in water and diluted to a concentration of 2·1011 pfu/mL and imaged by atomic force microscopy (AFM) (
Given the slow kinetics of direct phage-phage fusion using SrtAaureus, we hypothesized that the loopXa and pentaglycine motifs on phage could be individually labeled with oligoglycine or LPXTG-based (SEQ ID NO: 78) peptides before phage-phage fusions occur. With the ability to label pVIII orthogonally with SrtApyogenes, we created a phage construct (hereafter referred to as triSrt) containing three sortaggable motifs: loopXa on pIII, (A)2 on pVIII, and G5HA (SEQ ID NO: 77) on pIX (all at the N-terminus of the respective proteins). This combination enables selective labeling of three proteins on the same phage particle. The HA tag was added to pIX to extend its N-terminus and allow identification of the protein by immunoblots, as no antibodies are commercially available for pIX. We labeled each of these proteins in the triSrt construct with different fluorescent molecules (
Labeling of pIII and pIX with DNA.
Because we can now functionalize the ends of the same phage particle orthogonally with different molecules, we sought to form phage trimers by DNA hybridization (
Using SrtAaureus and the triSrt phage, we attached DNA-peptides to pIII and to pIX forming three different phage constructs: DNA A-pIX phage, DNA B-pIII-DNA D-pIX phage, and DNA E-pIII phage (
Formation of Ordered Phage Trimers.
We mixed equimolar amounts of the above DNA-labeled virions, followed by addition of the hybridizing oligonucleotides DNA C and DNA F in 10-fold excess over phage (Table 5 and
To confirm that the observed multi-phage structures were indeed formed by DNA hybridization, we incubated them with restriction enzymes: AatII cleaves the annealed DNA structure between DNA A-C, AgeI cleaves the connections between DNA D-F (
To ensure that the multi-phage structures were connected in the desired order, we fluorescently labeled the pVIII of the triSrt phage using SrtApyogenes with different fluorophores7, followed by DNA labeling. This yielded the following phage particles: TAMRA-pVIII-DNA A-pIX, DNA B-pIII-FAM-pVIII-DNA D-pIX, and DNA E-pIII-Alexa647-pVIII. We mixed these phage in equimolar amounts with a 10-fold excess DNA C and F, and imaged them by fluorescence microscopy (
Here we expand sortase-mediated labeling of M13 bacteriophage by engineering a loop onto pIII to enable C-terminal labeling. The insertion of a cleavable loop allows C-terminal exposure of the sortase motif LPXTG (SEQ ID NO: 78), and thus enables attachment of a substituted peptide or protein at that site via exposed Gly residues. Using this new structure, we attach a fluorophore and an oligomeric complex protein, neither of which could ever be displayed on the phage capsid genetically. Engineering of this loop onto pIII enables labeling orthogonal to the previously established N-terminal labeling method.7,18 Thus, we created a new phage construct with the loop structure on pIII, a pentaglycine motif on pIX, and a double alanine motif on pVIII. Although this configuration should theoretically allow direct phage to phage conjugation, we found this to be an inefficient reaction, possibly for steric reasons, and therefore resorted to the use of complementary DNA crossbridges to achieve our goal. We demonstrated as a proof of concept that the minor capsid proteins of phage can be labeled with DNA and used to form specific connections between different phage particles. This reaction was more efficient, with over 50% of observed phage structures displaying the length of trimers. The precision of this strategy surpasses earlier accomplishments in which phage were linked using leucine zippers: heterodisperse multi-phage structures were obtained with mean lengths of 3-4.5 μm (6-8 phage) and variability of length from monomers to longer than 20 phage.9
The DNA modified phage as a scaffold building block not only allows better control over the structures that can be produced, but this strategy should be readily extendable to create much longer multimers by the proper choice of different DNA sequences. Our work sets the stage for building more complex multi-phage structures, such as multi-way junctions,19 or combinations with DNA origami structures10 with the potential to control positions in three dimensions.20 Attached DNA may also be used as a functional material sensitive to the environment such as pH,21 or bind substrates through the use of DNA aptamers,22-23 which extend the properties of the proteins or peptides displayed on the phage capsid, which has potential in biosensing applications.24
The specific connection of phage particles, which we demonstrate, provides control of interactions between multiple materials at the nanoscale. Although the phage particles connected in this work were identical genetically, we attached different fluorophores to their pVIII body protein to establish that the requisite linkages were being formed in a pre-determined order. In principle, the ability to pattern phage with different pVIII proteins enables self-assembly of junctions between materials and formation of multi-material axial nanowires or even circuits. This ability potentially allows for phage-based devices where configuration and the proximity of materials are critical including transistor- and diode-based electronic devices.25-26
Phage Engineering.
The oligonucleotides used in engineering phage are shown in Table S2. LoopXa-pIII phage was constructed from an M13KE vector (New England Biolabs). The vector was digested with Acc65I and EagI. The annealed oligonucleotides pIIILoop-C and pIIILoop-NC were annealed and ligated into the digested vector. The Factor Xa recognition site was introduced by mutagenesis using the Quik II Site-Directed Mutagenesis kit (Stratagene) with oligonucleotides pIIILoopXaTop and pIIILoopXaBottom. The p9G5HA vector phage construct7 served as template for the creating the triSrt phage. The loop containing the Factor Xa recognition site was installed on pIII as described above. Two alanine codons were introduced at the 5′ end of pVIII using PstI and BamHI restriction enzymes and the annealed pVIII-AA-C and pVIII-AA-NC oligonucleotides. The phage constructs were transformed, plated, and amplified as described.7
Sortase-Mediated Reactions.
Sortase reactions were performed as indicated in the figures. A typical sortase reaction for labeling LoopXa-pIII phage consisted of 160 nM phage, 30 μM SrtAaureus, 230 nM Factor Xa, 100 μM GGGK(TAMRA) (SEQ ID NO: 127) or G3 fused to the N-terminus of the B subunit of cholera toxin (G3-CtxB), and 10 mM CaCl2 in TBS (25 mM Tris, pH 7.0-7.4, and 150 mM NaCl) incubated for 5 hrs at room temperature. The concentration reported for G3-CtxB is the monomer concentration. The sortase labeling reactions with GGGK(TAMRA) (SEQ ID NO: 127) were monitored by SDS-PAGE under reducing and non-reducing conditions followed by fluorescent imaging and immunoblot with an anti-pIII antibody (New England Biolabs). The CtxB labeling reactions were analyzed by SDS-PAGE in non-reducing conditions followed by immunoblot using an anti-pIII and anti-CtxB antibody (GenWay Biotech).
Typical conditions for labeling the pVIII of the triSrt phage were 160 nM phage, 40 μM SrtApyogenes, and 200 μM fluorophore conjugated LPETAA peptide (SEQ ID NO: 12) incubated for 3 hrs at room temperature followed by PEG8000/NaCl precipitation.7 The end labeling reactions of pIII and pIX consisted of 160 nM phage, 30 μM SrtAaureus, 230 nM Factor Xa, and 100 μM of fluorescent peptide or 50 μM of DNA peptide in 10 mM CaCl2 incubated for 5 hrs at room temperature followed by PEG8000/NaCl precipitation. For the DNA-phage reactions, additional purification was performed by dialysis against water with a 1 MDa molecular weight cut-off (Spectrum Labs), followed by another round of PEG8000/NaCl precipitation to purify and concentrate the samples.
DNA Peptide Conjugation.
The DNA oligonucleotides attached to the ends of phage are shown in Table 5. The thiol group on the DNA oligonucleotides was activated overnight with 0.1M DTT in PBS at 37° C. The DNA was then purified from excess DTT on a NAPS column (GE Healthcare) and eluted in water. The solution was dried and resuspended in PBS. (maleimide)-LPETGG (SEQ ID NO: 13) or GGGK(maleimide) (SEQ ID NO: 127) peptide in PBS was added in 2:1 molar excess of the activated DNA and reacted for 5 hrs at 37° C. In order to deactivate the excess maleimide, DTT was added to the mixture to give a concentration of 0.1M DTT and incubated at 37° C. for 15 min. The excess DTT and peptide was removed by purifying the reaction on a NAPS column. The DNA-peptide was dried under vacuum and resuspended in TBS. The concentration of the DNA-peptide was determined by UV-vis spectrometry using the absorbance at 260 nm. DNA-peptides were analyzed by a Micromass microMX MALDI with a pulsed 337 nm nitrogen laser. Spectra were acquired in positive ion, linear mode with a mass range of 2-30 kDa.
Atomic Force Microscopy and Dynamic Light Scattering.
The three DNA labeled phage were mixed together at 7.1013 pfu/mL in water. Hybridizing oligonucleotides DNA C and F were added in 10-fold molar excess. The reactions were heated to 95° C. for 5 minutes and cooled down to 20° C. at 0.5° C. per minute. For restriction enzyme digestion the phage were resuspended in NEB Buffer 4 (50 mM potassium acetate, 20 mM Tris-acetate, 10 mM magnesium acetate, 1 mM DTT, pH 7.9), and incubated at 37° C. for 3 hrs. We verified that the DTT in the NEB buffer did not disrupt the LoopXa-pIII structure by exposing LoopXa-pIII phage with Factor Xa to the buffer. We analyzed the reactions by SDS-PAGE followed by immunoblot with an anti-pIII antibody and estimated by densitometry that 10% of the LoopXa-pIII structures were disrupted, which represents only 1 pIII molecule for every two phage suggesting this did not significantly affect the connections.
To visualize the samples by AFM, phage preparations were diluted in water to a concentration of 2.1011 pfu/mL. 90 μL of the phage solution was deposited on a freshly cleaved mica disc. AFM images were captured on a Nanoscope IV (Digital Instruments) in air using tapping mode. The tips had spring constants of 20-100N/m driven near their resonant frequency of 200-400 kHz (MikroMasch). The AFM images were analyzed and processed using Gwyddion. The histograms were collected by measuring the length of all phage events observed in seven 20 μm×20 μm areas.
DLS measurements were obtained with a DynaPro NanoStar (Wyatt Technology). Phage mixtures in NEB buffer 4 were diluted to 1·1013 pfu/mL in water. Samples from each experiment were measured 20 times and the results were averaged by cumulant analysis.
Fluorescence Microscopy.
The phage samples were diluted to 6·1011 pfu/mL in water and 300 μL were deposited and dried on a glass cover slip. The samples were imaged using an inverted DeltaVision microscope equipped with an epifluorescent illumination module—488 nm laser (FAM—488 nm) and solid state illumination (TAMRA—543 nm and Alexa647), an oil immersion 100× objective (N.A.=1.40, 100×, Olympus) and Photometrics CoolSNAP HQ camera. All images were processed using ImageJ program (National Institutes of Health).
Miscellaneous.
Expression and purification of SrtApyogenes, SrtAaureus and G3-CtxB were performed as described.18 The LoopXa-pIII reactions were analyzed on 10% Laemmli SDS-PAGE gels. The pIX-DNA reactions were analyzed on a 16% Tricine-SDS PAGE gel, and the DNA-peptide conjugation reactions were analyzed on a 10% TBE-Urea PAGE gel (Life Technologies). All fluorescent gel images were collected on a Typhoon Trio (GE Healthcare). The GGGK(TAMRA) (SEQ ID NO: 127), K(FAM)-LPETGG (SEQ ID NO: 13), GGGK(maleimide) (SEQ ID NO: 127), (maleimide)-LPETGG (SEQ ID NO: 13), K(TAMRA)-LPETAA (SEQ ID NO: 279), and K(FAM)-LPETAA (SEQ ID NO: 12) peptides were obtained from the Swanson Biotechnology Center. For mass-spectrometry, the protein bands of interest were excised, subjected to protease digestion, and analyzed by electrospray ionization tandem mass-spectrometry (MS/MS).
2009, 4 (5), 325-330.
All publications, patents, patent applications, and database entries mentioned anywhere herein, including, but not limited to, those items listed above, are hereby incorporated by reference in their entirety as if each individual publication, patent, patent application, and database entry was specifically and individually indicated to be incorporated by reference. In case of conflict, the present application, including any definitions herein, will control.
The foregoing written specification is considered to be sufficient to enable one skilled in the art to practice the invention. The present invention is not to be limited in scope by examples provided, since the examples are intended as a single illustration of one aspect of the invention and other functionally equivalent embodiments are within the scope of the invention. Various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and fall within the scope of the appended claims. The advantages and objects of the invention are not necessarily encompassed by each embodiment of the invention.
The present application claims priority under 35 U.S.C. §119(e) to U.S. provisional application, U.S. Ser. No. 61/659,661, filed Jun. 14, 2012, the entire contents of which is incorporated herein by reference.
This invention was made with U.S. government support under grant 5R01AI033456 awarded by the National Institutes of Health and under grant number W911NF-09-0001 awarded by the U.S. Army Research Office. The Government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 61659661 | Jun 2012 | US |
