Patent Application
20150044254
The present invention relates to bioconjugates, specifically bioconjugate vaccines, made from recombinant glycoproteins, namely N-glycosylated proteins. The invention comprises one or more introduced N-glycosylated proteins with optimized amino acid consensus sequence(s), nucleic acids encoding these proteins as well as corresponding vectors and host cells. In addition, the present invention is directed to the use of said proteins, nucleic acids, vectors and host cells for preparing bioconjugate vaccines. Furthermore, the present invention provides methods for producing bioconjugate vaccines.
Glycoproteins are proteins that have one or more covalently attached sugar polymers. N-linked protein glycosylation is an essential and conserved process occurring in the endoplasmic reticulum of eukarotic organisms. It is important for protein folding, oligomerization, stability, quality control, sorting and transport of secretory and membrane proteins (Helenius, A., and Aebi, M. (2004). Roles of N-linked glycans in the endoplasmic reticulum. Annu. Rev. Biochem. 73, 1019-1049).
Protein glycosylation has a profound influence on the antigenicity, the stability and the half-life of a protein. In addition, glycosylation can assist the purification of proteins by chromatography, e.g. affinity chromatography with lectin ligands bound to a solid phase interacting with glycosylated moieties of the protein. It is therefore established practice to produce many glycosylated proteins recombinantly in eukaryotic cells to provide biologically and pharmaceutically useful glycosylation patterns.
It has been demonstrated that a bacterium, the food-borne pathogen Campylobacter jejuni, can also N-glycosylate its proteins (Szymanski, et al. (1999). Evidence for a system of general protein glycosylation in Campylobacter jejuni. Mol. Microbiol. 32, 1022-1030). The machinery required for glycosylation is encoded by 12 genes that are clustered in the so-called pgl locus. Disruption of N-gylcosylation affects invasion and pathogenesis of C. jejuni but is not lethal as in most eukaryotic organisms (Burda P. and M. Aebi, (1999). The dolichol pathway of N-linked glycosylation. Biochim Biophys Acta 1426(2):239-57). It is possible to reconstitute the N-glycosylation of C. jejuni proteins by recombinantly expressing the pgl locus and acceptor glycoprotein in E. coli at the same time (Wacker et al. (2002). N-linked glycosylation in Campylobacter jejuni and its functional transfer into E. coli. Science 298, 1790-1793).
Diarrheal illness is a major health problem associated with international travel in terms of frequency and economic impact. Traveller's diarrhea refers to an enteric illness acquired when a person travels from a developed to a developing country. Today, over 50 million people travel each year from developed countries to developing countries and up to 50% of these travelers report having diarrhea during the first 2 weeks of their week of their stay. There has been no significant decline in the incidence of traveller's diarrhea since the 1970s, despite efforts made by the tourism industry to improve local infrastructure.
Traveller's diarrhea is acquired through the ingestion of faecally contaminated food and less commonly water. Bacteria are the main cause of traveller diarrhea's, being responsible for up to 80% of the infections. Enterotoxigenic E. coli(ETEC) is the most frequently isolated bacterium in all parts of the world associated with traveler's diarrhea, followed by Shigella spp and C. jejuni.
Shigellosis remains a serious and common disease. In addition to causing watery diarrhea, Shigellae are a major cause of dysentery (fever, cramps, and blood and/or mucus in the stool). Man is the only natural host for this bacterium. The estimated number of Shigella infections is over 200 million annually. About 5 million of these cases need hospitalization and a million people die. Three serogroups are mostly responsible for the disease described as bacillary dysentery: S. dysenteriae, S. flexneri and S. sonnei.
S. dysenteriae and S. flexneri are responsible for most infections in the tropics, with case fatalities up to 20%. Shigellosis occurs both endemically and as epidemics. In many tropical countries, endemic infection is largely due to S. flexneri whereas major epidemics of S. dysenteriae have occurred in Central America, Central Africa and Southeast Asia. These epidemics are major public-health risks. Infections, primarily due to S. sonnei and less frequently flexneri continue to occur in industrialized countries.
Conjugate vaccines have shown promising results against Shigella infections. O-specific polysaccharides of S. dysenteriae type 1 have been used to synthesize a conjugate vaccine that has elicited an immune response in mice. Such vaccines have been synthesized chemically and conjugated to human serum albumin or has been developed where the O-polysaccharide has been purified from Shigella. The O-specific polysaccharides of S. sonnei and S. flexneri also have been conjugated chemically to P. aeruginosa exotoxin and have elicited a significant immune response in mice. Additionally, they have been shown to be immunogenic and safe in humans. However, chemical conjugation is an expensive and time-consuming process that does not always yield reliable and reproducible vaccines. This leads to good manufacturing practices (GMP) problems when seeking to develop such bioconjugate vaccines on a commercial scale.
In one aspect, the present invention is directed to a bioconjugate vaccine comprising: a protein carrier comprising an inserted consensus sequence, D/E-X-N-Z-S/T, wherein X and Z may be any natural amino acid except proline; at least one antigenic polysaccharide from at least one bacterium, linked to the protein carrier, wherein the at least one antigenic polysaccharide is at least one bacterial O-antigen from one or more strains of Shigella, E. coli or Pseudomonas aeruginosa; and, optionally, an adjuvant.
In another aspect, the present invention is directed to a Shigella bioconjugate vaccine comprising: a protein carrier comprising Exotoxin of Pseudomonas aeruginosa (EPA) that has been modified to contain at least one consensus sequence D/E-X-N-Z-S/T, wherein X and Z may be any natural amino acid except proline; at least one polysaccharide chain linked to the protein carrier and having the following structure:
and, optionally, an adjuvant.
In yet another aspect, the present invention is directed to a Shigella dysenteriae O1 bioconjugate vaccine comprising: a protein carrier having the sequence provided in SEQ. ID NO.: 7; at least one polysaccharide chain linked to the protein carrier and having the following structure:
and an adjuvant.
In yet additional aspects, the present invention is directed to: a plasmid comprising SEQ. ID NO. 5; a genetic sequence comprising SEQ. ID NO. 5; an amino acid sequence comprising SEQ. ID NO. 6; an amino acid sequence comprising SEQ. ID NO. 7; or vector pGVXN64.
In another aspect, the present invention is directed to an expression system for producing a bioconjugate vaccine against at least one bacterium comprising: a nucleotide sequence encoding an oligosaccharyl transferase (OST/OTase); a nucleotide sequence encoding a protein carrier; and at least one antigenic polysaccharide synthesis gene cluster from the at least one bacterium, wherein the antigenic polysaccharide is a bacterial O-antigen.
In still another aspect, the present invention is directed to an expression system for producing a bioconjugate vaccine against Shigella dysenteriae O1 comprising: a nucleotide sequence encoding PgIB having SEQ. ID NO. 2; a nucleotide sequence encoding a modified EPA having SEQ. ID NO. 6; and a polysaccharide synthesis gene cluster comprising SEQ. ID NO. 5.
In yet another aspect, the present invention contemplates a method of producing an O1-bioconjugate in a bioreactor comprising the steps: expressing in bacteria: modified EPA containing at least one consensus sequence, D/E-X-N-Z-S/T, wherein X and Z may be any natural amino acid except proline, or AcrA; PgIB; and one or more O1-polysaccharides; growing the bacteria for a period of time to produce an amount of the O1-bioconjugate comprising the AcrA or the modified EPA linked to the one more O1-polysaccharides; extracting periplasmic proteins; and separating the O1-bioconjugate from the extracted periplasmic proteins.
In an additional aspect, the present invention contemplates a method of producing an S. dysenteriae bioconjugate vaccine, said method comprising: assembling a polysaccharide of S. dysenteriae in a recombinant organism through the use of glycosyltransferases; linking said polysaccharide to an asparagine residue of one or more target proteins in said recombinant organism, wherein said one or more target proteins contain one or more T-cell epitopes.
In a further aspect, the present invention contemplates a method of producing an S. dysenteriae bioconjugate vaccine, said method comprising: introducing genetic information encoding for a metabolic apparatus that carries out N-glycosylation of a target protein into a prokaryotic organism to produce a modified prokaryotic organism, wherein the genetic information required for the expression of one or more recombinant target proteins is introduced into said prokaryotic organism, and wherein the metabolic apparatus comprises specific glycosyltransferases for the assembly of a polysaccharide of S. dysenteriae on a lipid carrier and an oligosaccharyltransferase, the oligosaccharyltransferase covalently linking the polysaccharide to an asparagine residue of the target protein, and the target protein containing at least one T-cell epitope; producing a culture of the modified prokaryotic organism; and obtaining glycosylated proteins from the culture medium.
The present invention provides a versatile in vivo glycosylation platform.
European Patent Application No. 03 702 276.1 (European Patent 1 481 057) teaches a procaryotic organism into which is introduced a nucleic acid encoding for (i) specific glycosyltransferases for the assembly of an oligosaccharide on a lipid carrier, (ii) a recombinant target protein comprising a consensus sequence “N-X-S/T”, wherein X can be any amino acid except proline, and (iii) an oligosaccharyl transferase of C. jejuni (OTase) that covalently links said oligosaccharide to the consensus sequence of the target protein. Said procaryotic organism produces N-glycans with a specific structure which is defined by the type of the specific glycosyltransferases.
The known N-glycosylation consensus sequence in a protein allows for the N-glycosylation of recombinant target proteins in procaryotic organisms comprising the oligosaccharyl transferase (OTase) of C. jejuni.
The object of the present invention is to provide proteins as well as means and methods for producing such proteins having an optimized efficiency for N-glycosylation that can be produced in procaryotic organisms in vivo. Another object of the present invention aims at the more efficient introduction of N-glycans into recombinant proteins for modifying antigenicity, stability, biological, prophylactic and/or therapeutic activity of said proteins. A further object is the provision of a host cell that efficiently displays recombinant N-glycosylated proteins of the present invention on its surface.
In a first aspect, the present invention provides a recombinant N-glycosylated protein, comprising one or more of the following N-glycosylated optimized amino acid sequence(s):
D/E-X-N-Z-S/T, (optimized consensus sequence)
wherein X and Z may be any natural amino acid except Pro, and wherein at least one of said N-glycosylated partial amino acid sequence(s) is introduced.
It was surprisingly found that the introduction of specific partial amino acid sequence(s) (optimized consensus sequence(s)) into proteins leads to proteins that are efficiently N-glycosylated by the oligosaccharyl transferase (OST, OTase) from Campylobacter spp., preferably C. jejuni, in these introduced positions.
The term “partial amino acid sequence(s)” as it is used in the context of the present invention will also be referred to as “optimized consensus sequence(s)” or “consensus sequence(s)”. The optimized consensus sequence is N-glycosylated by the oligosaccharyl transferase (OST, OTase) from Campylobacter spp., preferably C. jejuni, much more efficiently than the regular consensus sequence “N-X-SIT” known in the prior art.
In general, the term “recombinant N-glycosylated protein” refers to any heterologous poly- or oligopeptide produced in a host cell that does not naturally comprise the nucleic acid encoding said protein. In the context of the present invention, this term refers to a protein produced recombinantly in any host cell, e.g. an eukaryotic or prokaryotic host cell, preferably a procaryotic host cell, e.g. Escherichia ssp., Campylobacter ssp., Salmonella ssp., Shigella ssp., Helicobacter ssp., Pseudomonas ssp., Bacillus ssp., more preferably Escherichia coli, Campylobacter jejuni, Salmonella typhimurium etc., wherein the nucleic acid encoding said protein has been introduced into said host cell and wherein the encoded protein is N-glycosylated by the OTase from Campylobacter spp., preferably C. jejuni, said transferase enzyme naturally occurring in or being introduced recombinantly into said host cell.
In accordance with the internationally accepted one letter code for amino acids the abbreviations D, E, N, S and T denote aspartic acid, glutamic acid, asparagine, serine, and threonine, respectively. Proteins according to the invention differ from natural or prior art proteins in that one or more of the optimized consensus sequence(s) D/E-X-N-Z-S/T is/are introduced and N-glycosylated. Hence, the proteins of the present invention differ from the naturally occurring C. jejuni proteins which also contain the optimized consensus sequence but do not comprise any additional (introduced) optimized consensus sequences.
The introduction of the optimized consensus sequence can be accomplished by the addition, deletion and/or substitution of one or more amino acids. The addition, deletion and/or substitution of one or more amino acids for the purpose of introducing the optimized consensus sequence can be accomplished by chemical synthetic strategies well known to those skilled in the art such as solid phase-assisted chemical peptide synthesis. Alternatively, and preferred for larger polypeptides, the proteins of the present invention can be prepared by standard recombinant techniques.
The proteins of the present invention have the advantage that they may be produced with high efficiency and in any procaryotic host comprising a functional pgl operon from Campylobacter spp., preferably C. jejuni. Preferred alternative OTases from Campylobacter spp. for practicing the aspects and embodiments of the present invention are Campylobacter coli and Campylobacter lari (see Szymanski, C. M. and Wren, B. W. (2005). Protein glycosylation in bacterial mucosal pathogens. Nat. Rev. Microbiol. 3:225-237). The functional pgl operon may be present naturally when said procaryotic host is Campylobacter spp., preferably C. jejuni. However, as demonstrated before in the art and mentioned above, the pgl operon can be transferred into cells and remain functional in said new cellular environment.
The term “functional pgl operon from Campylobacter spp., preferably C. jejuni” is meant to refer to the cluster of nucleic acids encoding the functional oligosaccharyl transferase (OTase) of Campylobacter spp., preferably C. jejuni, and one or more specific glycosyltransferases capable of assembling an oligosaccharide on a lipid carrier, and wherein said oligosaccharide can be transferred from the lipid carrier to the target protein having one or more optimized amino acid sequence(s): D/E-X N-Z-S/T by the OTase. It to be understood that the term “functional pgl operon from Campylobacter spp., preferably C. jejuni’ in the context of this invention does not necessarily refer to an operon as a singular transcriptional unit. The term merely requires the presence of the functional components for N-glycosylation of the recombinant protein in one host cell. These components may be transcribed as one or more separate mRNAs and may be regulated together or separately. For example, the term also encompasses functional components positioned in genomic DNA and plasmid(s) in one host cell. For the purpose of efficiency, it is preferred that all components of the functional pgl operon are regulated and expressed simultaneously.
It is important to realize that only the functional oligosaccharyl transferase (OTase) should originate from Campylobacter spp., preferably C. jejuni, and that the one or more specific glycosyltransferases capable of assembling an oligosaccharide on a lipid carrier may originate from the host cell or be introduced recombinantly into said host cell, the only functional limitation being that the oligosaccharide assembled by said glycosyltransferases can be transferred from the lipid carrier to the target protein having one or more optimized consensus sequences by the OTase. Hence, the selection of the host cell comprising specific glycosyltransferases naturally and/or incapacitating specific glycosyltransferases naturally present in said host as well as the introduction of heterologous specific glycosyltransferases will enable those skilled in the art to vary the N-glycans bound to the optimized N-glycosylation consensus site in the proteins of the present invention.
As a result of the above, the present invention provides for the individual design of N-glycan-patterns on the proteins of the present invention. The proteins can therefore be individualized in their N-glycan pattern to suit biological, pharmaceutical and purification needs.
In a preferred embodiment, the proteins of the present invention may comprise one but also more than one, preferably at least two, preferably at least 3, more preferably at least 5 of said N-glycosylated optimized amino acid sequences.
The presence of one or more N-glycosylated optimized amino acid sequence(s) in the proteins of the present invention can be of advantage for increasing their antigenicity, increasing their stability, affecting their biological activity, prolonging their biological half-life and/or simplifying their purification.
The optimized consensus sequence may include any amino acid except proline in position(s) X and Z. The term “any amino acids” is meant to encompass common and rare natural amino acids as well as synthetic amino acid derivatives and analogs that will still allow the optimized consensus sequence to be N-glycosylated by the OTase. Naturally occurring common and rare amino acids are preferred for X and Z. X and Z may be the same or different.
It is noted that X and Z may differ for each optimized consensus sequence in a protein according to the present invention.
The N-glycan bound to the optimized consensus sequence will be determined by the specific glycosyltransferases and their interaction when assembling the oligosaccharide on a lipid carrier for transfer by the OTase. Those skilled in the art can design the N-glycan by varying the type(s) and amount of the specific glycosyltransferases present in the desired host cell.
N-glycans are defined herein as monO-, oligO- or polysaccharides of variable compositions that are linked to an c-amide nitrogen of an asparagine residue in a protein via an N-glycosidic linkage. Preferably, the N-glycans transferred by the OTase are assembled on an undecaprenol-pyrophosphate lipid-anchor that is present in the cytoplasmic membrane of gram-negative or positive bacteria. They are involved in the synthesis of O antigen, O polysaccharide and peptidoglycan (Bugg, T. D., and Brandish, P. E. (1994). From peptidoglycan to glycoproteins: common features of lipid-linked oligosaccharide biosynthesis. FEMS Microbiol Lett 119, 255-262; Valvano, M. A. (2003). Export of O-specific lipopolysaccharide. Front Biosci 8, s452-471).
In a preferred embodiment, the recombinant protein of the present invention comprises one or more N-glycans selected from the group of N-glycans from Campylobacter spp., preferably C. jejuni, the N-glycans derived from oligO- and polysaccharides transferred to O antigen forming O polysaccharide in Gram-negative bacteria or capsular polysaccharides from Gram-positive bacteria, preferably: P. aeruginosa 09, 011; E. coli 07, 09, 016, 0157 and Shigella dysenteriae O1 and engineered variants thereof obtained by inserting or deleting glycosyltransferases and epimerases affecting the polysaccharide structure.
In a further preferred embodiment, the recombinant protein of the present invention comprises two or more different N-glycans.
For example, different N-glycans on the same protein can prepared by controlling the timing of the expression of specific glycosyltransferases using early or late promoters or introducing factors for starting, silencing, enhancing and/or reducing the promoter activity of individual specific glycosyltransferases. Suitable promoters and factors governing their activity are routinely available to those in the art.
There is no limitation on the origin of the recombinant protein of the invention. Preferably said protein is derived from mammalian, bacterial, viral, fungal or plant proteins. More preferably, the protein is derived from mammalian, most preferably human proteins. For preparing antigenic recombinant proteins according to the invention, preferably for use as active components in vaccines, it is preferred that the recombinant protein is derived from a bacterial, viral or fungal protein.
In a further preferred embodiment, the present invention provides for recombinant proteins wherein either the protein and/or the N-glycan(s) is (are) therapeutically and/or prophylactically active. The introduction of at least one optimized and N-glycosylated consensus sequence can modify or even introduce therapeutic and/or prophylactic activity in a protein. In a more preferred embodiment, it is the protein and/or the N-glycan(s) that is (are) immunogenically active. In this case, the introduced N-glycosylation(s) may have a modifying effect on the proteins biological activity and/or introduce new antigenic sites and/or may mask the protein to evade degrading steps and/or increase the half-life.
The recombinant proteins of the present invention can be efficiently targeted to the outer membrane and/or surface of host cells, preferably bacteria, more preferably gram-negative bacteria. For assisting the surface display and/or outer membrane localization, it is preferred that the recombinant protein of the invention further comprise at least one polypeptide sequence capable of targeting said recombinant protein to the outer membrane and/or cell surface of a bacterium, preferably a gram-negative bacterium.
In a preferred embodiment, the recombinant protein of the invention is one, wherein said targeting polypeptide sequence is selected from the group consisting of type II signal peptides (Paetzel, M., Karla, A., Strynadka, N. C., and Dalbey, R. E. 2002. Signal peptidases. Chem Rev 102: 4549-4580.) or outer membrane proteins (reviewed in Wemerus, H., and Stahl, S. 2004. Biotechnological applications for surface-engineered bacteria. Biotechnol Appl Biochem 40: 209-228.), preferably selected from the group consisting of the full length protein or the signal peptides of OmpH1 from C. jejuni, JIpA from C. jejuni, outer membrane proteins from E. coli, preferably OmpS, OmpC, OmpA, OprF, PhoE, LamB, Lpp′OmpA (a fusion protein for surface display technology, see Francisco, JA1 Earhart, C. F., and Georgiou, G. 1992. Transport and anchoring of beta-lactamase to the external surface of Escherichia coli. Proc Natl Acad Sci USA 89: 2713-2717.), and the lnp protein from Pseudomonas aeruginosa.
In a different aspect, the present invention relates to a nucleic acid encoding a recombinant protein according to the invention. Preferably, said nucleic acid is a mRNA, a DNA or a PNA, more preferably a mRNA or a DNA, most preferably a DNA. The nucleic acid may comprise the sequence coding for said protein and, in addition, other sequences such as regulatory sequences, e.g. promoters, enhancers, stop codons, start codons and genes required to regulate the expression of the recombinant protein via the mentioned regulatory sequences, etc. The term “nucleic acid encoding a recombinant protein according to the invention” is directed to a nucleic acid comprising said coding sequence and optionally any further nucleic acid sequences regardless of the sequence information as long as the nucleic acid is capable of producing the recombinant protein of the invention in a host cell containing a functional pgl operon from Campylobacter spp., preferably C. jejuni. More preferably, the present invention provides isolated and purified nucleic acids operably linked to a promoter, preferably linked to a promoter selected from the group consisting of known inducible and constitutive prokaryotic promoters, more preferably the tetracycline promoter, the arabinose promoter, the salicylate promoter, lac-, trc-, and lac promotors (Baneyx, F. (1999). Recombinant protein expression in Escherichia coli. Curr Opin Biotechnol 10, 411-421; Billman-Jacobe, H. (1996). Expression in bacteria other than Escherichia coli. Curr Opin Biotechnol 7, 500-504.). Said operably linked nucleic acids can be used for, e.g. vaccination.
Furthermore, another aspect of the present invention relates to a host cell comprising a nucleic acid and/or a vector according to the present invention. The type of host cell is not limiting as long as it accommodates a functional pgl operon from C. jejuni and one or more nucleic acids coding for recombinant target protein(s) of the present invention. Preferred host cells are prokaryotic host cells, more preferably bacteria, most preferably those selected from the group consisting of Escherichia ssp., Campylobacter ssp., Salmonella ssp., Shigella ssp., Helicobacter ssp., Pseudomonas ssp., Bacillus ssp., preferably Escherichia coli, more preferably E. coli strains Top10, W3110, CLM24, BL21, SCM6 and SCM7 (Feldman et al., (2005). Engineering N-linked protein glycosylation with diverse O antigen lipopolysaccharide structures in Escherichia coli. Proc. Natl. Acad. Sci. USA 102, 3016-3021; Alaimo, C, Catrein, I., Morf, L., Marolda, C. L., Callewaert, N., Valvano, M. A., Feldman, M. F., Aebi, M. (2006). Two distinct but interchangeable mechanisms for flipping of lipid-linked oligosaccharides. EMBO Journal 25, 967-976) and S. enterica strains SL3261 (Salmonella enterica sv. Typhimurium LT2 (delta) aroA, see Hoiseth, S. K., and Stocker, B. A. 1981, Aromatic-dependent Salmonella typhimurium are non-virulent and effective as live vaccines. Nature 291:238-239), SL3749 (Salmonella enterica sv. Typhimurium LT2 waaL, see Kaniuk et al., J. Biol. Chem. 279: 36470-36480) and SL3261 ΔwaaL.
In a more preferred embodiment, the host cell according to the invention is one that is useful for the targeting to the outer membrane and/or surface display of recombinant proteins according to the invention, preferably one, wherein said host cell is a recombinant gram-negative bacterium having:
i) a genotype comprising nucleotide sequences encoding for
ii) a phenotype comprising a recombinant N-glycosylated protein according to the invention that is located in and/or on the outer membrane of the gram-negative bacterium.
The host cell for the above embodiment is preferably selected from the group consisting of Escherichia ssp., Campylobacter ssp., Shigella ssp, Helicobacter ssp. and Pseudomonas ssp., Salmonella ssp., preferably E. coli, more preferably E. coli strains Top10, W3110, CLM24, BL21, SCM6 and SCM7, and S. enterica strains SL3261, SL3749 and SL326iδwaaL (see Hoiseth, S. K., and Stocker, B. A. 1981. Aromatic-dependent Salmonella typhimurium are non-virulent and effective as live vaccines. Nature 291: 238-239), SL3749 (Kaniuk, N. A., Vinogradov, E., and Whitfield, C. 2004. Investigation of the structural requirements in the lipopolysaccharide core acceptor for ligation of O antigens in the genus Salmonella: WaaL “ligase” is not the sole determinant of acceptor specificity. J Biol Chem 279: 36470-36480).
Because preferred proteins of the present invention may have a therapeutic or prophylactic activity by themselves and/or due to the introduced N-glycosylation sites, they can be used for the preparation of a medicament. The type of protein for practicing the invention is not limited and, therefore, proteins of the invention such as EPO, IFN-alpha, TNFalpha, IgG, IgM, IgA, interleukins, cytokines, viral and bacterial proteins for vaccination like C. jejuni proteins such as HisJ (CjO734c), AcrA (CjO367c), OmpH1 (CjO982c), Diphteria toxin (CRM 197), Cholera toxin, P. aeruginosa exoprotein, to name just a few, and having introduced therein the optimized N-glycosylated consensus sequence are useful for preparing a medicament (Wyszynska, A., Raczko, A., Lis, M., and Jagusztyn-Krynicka, E. K. (2004). Oral immunization of chickens with avirulent Salmonella vaccine strain carrying C. jejuni 72Dz/92 cjaA gene elicits specific humoral immune response associated with protection against challenge with wild-type Campylobacter. Vaccine 22, 1379-1389).
In addition, the nucleic acids and/or vectors according to the invention are also useful for the preparation of a medicament, preferably for use in gene therapy.
Moreover, a host cell according to the invention, preferably one that has a phenotype comprising an N-glycosylated recombinant protein of the invention that is located in and/or on the outer membrane of a bacterium, preferably a gram-negative bacterium, more preferably one of the above-listed gram-negative bacteria, is particularly useful for the preparation of a medicament.
More preferably, a protein of the invention is used for the preparation of a medicament for the therapeutic and/or prophylactic vaccination of a subject in need thereof.
In a more preferred embodiment, the present invention relates to the use of a nucleic acid and/or a vector according to the invention for the preparation of a medicament for the therapeutic and/or prophylactic vaccination of a subject in need thereof, preferably by gene therapy.
The host cells of the invention displaying said N-glycosylated recombinant proteins are particularly useful for preparing vaccines, because the displayed N-glycosylated proteins are abundantly present on the host cell's surface and well accessible by immune cells, in particular their hydrophilic N-glycans, and because the host cells have the added effect of an adjuvant, that, if alive, may even replicate to some extent and amplify its vaccination effects.
Preferably, the host cell for practicing the medical aspects of this invention is an attenuated or killed host cell.
Another advantage of the use of the inventive host cells for preparing medicaments, preferably vaccines, is that they induce IgA antibodies due to the cellular component.
Preferably, said host cells are used according to the invention for inducing IgA antibodies in an animal, preferably a mammal, a rodent, ovine, equine, canine, bovine or a human. It is preferred that said subject in need of vaccination is avian, mammalian or fish, preferably mammalian, more preferably a mammal selected from the group consisting of cattle, sheep, equines, dogs, cats, and humans, most preferably humans. Fowls are also preferred.
A further aspect of the present invention relates to a pharmaceutical composition, comprising at least one protein, at least one nucleic acid, a least one vector and/or at least one host cell according to the invention. The preparation of medicaments comprising proteins or host cells, preferably attenuated or killed host cells, and the preparation of medicaments comprising nucleic acids and/or vectors for gene therapy are well known in the art. The preparation scheme for the final pharmaceutical composition and the mode and details of its administration will depend on the protein, the host cell, the nucleic acid and/or the vector employed.
In a preferred embodiment, the pharmaceutical composition of the invention comprises a pharmaceutically acceptable excipient, diluent and/or adjuvant.
The present invention provides for a pharmaceutical composition comprising at least one of the following, (i) a recombinant protein, a host cell, a nucleic acid and/or a recombinant vector being/encoding/expressing a recombinant protein according to the present invention, and (ii) a pharmaceutically acceptable excipient, diluent and/or adjuvant.
Suitable excipients, diluents and/or adjuvants are well-known in the art. An excipient or diluent may be a solid, semi-solid or liquid material which may serve as a vehicle or medium for the active ingredient. One of ordinary skill in the art in the field of preparing compositions can readily select the proper form and mode of administration depending upon the particular characteristics of the product selected, the disease or condition to be treated, the stage of the disease or condition, and other relevant circumstances (Remington's Pharmaceutical Sciences, Mack Publishing Co. (1990)). The proportion and nature of the pharmaceutically acceptable diluent or excipient are determined by the solubility and chemical properties of the pharmaceutically active compound selected, the chosen route of administration, and standard pharmaceutical practice. The pharmaceutical preparation may be adapted for oral, parenteral or topical use and may be administered to the patient in the form of tablets, capsules, suppositories, solution, suspensions, or the like. The pharmaceutically active compounds of the present invention, while effective themselves, can be formulated and administered in the form of their pharmaceutically acceptable salts, such as acid addition salts or base addition salts, for purposes of stability, convenience of crystallization, increased solubility, and the like.
A further aspect of the present invention is directed to a method for producing N-linked glycosylated proteins, comprising the steps of:
a) providing a recombinant organism, preferably a prokaryotic organism, comprising nucleic acids coding for
b) culturing the recombinant organism in a manner suitable for the production and N-glycosylation of the target protein(s).
Preferably, the target protein is one of the above described recombinant proteins according to the invention.
In a preferred method of the invention, the functional pgl operon from Campylobacter spp., preferably C. jejuni, comprises nucleic acids coding for
Moreover, in a preferred embodiment the present invention relates to a method for preparing a host cell according to the invention comprising the steps of:
i) providing a gram-negative bacterium,
ii) introducing into said bacterium at least one nucleotide sequence encoding for
iii) culturing said bacterium until at least one recombinant N-glycosylated protein coded by the nucleotide sequence of c) is located in and/or on the outer membrane of the gram-negative bacterium.
For practicing the preferred methods above, the recombinant procaryotic organism or host cell is preferably selected from the group of bacteria consisting of Escherichia ssp., Campylobacter ssp., Salmonella ssp., Shigella ssp., Helicobacter ssp., Pseudomonas ssp., Bacillus ssp., preferably Escherichia coli, preferably E. coli strains Top 10, W3110, W3110ΔwaaL, BL21, SCM6 and SCM7, and S. enterica strains SL3261, SL3749 and SL3261 ΔwaaL.
Another preferred method for producing, isolating and/or purifying a recombinant protein according to the invention comprises the steps of:
a) culturing a host cell,
b) removing the outer membrane of said recombinant gram-negative bacterium; and
c) recovering said recombinant protein.
Exemplary methods for removing the outer membrane of a cell, preferably a prokaryotic cell, more preferably a gram-negative bacterial cell, are suitable enzymatic treatment methods, osmotic shock detergent solubilisation and the French press method.
Most preferred, the present invention relates to a method, wherein recombinant or natural specific glycosyltransferases from species other than Campylobacter spp., preferably C. jejuni, are selected from the group of glycosyltransferases and epimerases originating from bacteria, archea, and/or eukaryota that can be functionally expressed in said host cell.
An embodiment of the invention involves novel bioconjugate vaccines. A further embodiment of the invention involves a novel approach for producing such bioconjugate vaccines that uses recombinant bacterial cells that directly produce immunogenic or antigenic bioconjugates. In one embodiment, bioconjugate vaccines can be used to treat or prevent bacterial diseases, such as diarrhea, nosocomial infections and meningitis. In further embodiments, biooconjugate vaccines may have therapeutic and/or prophylactic potential for cancer or other diseases.
Conjugate vaccines can be administered to children to protect against bacterial infections and can provide a long lasting immune response to adults. Constructs of the invention have been found to generate an IgG response in animals. It has been found that an IgG response to a Shigella O-specific polysaccharide-protein conjugate vaccine in humans correllates with immune protection in humans. (Passwell, J. H. et al., “Safety and Immunogenicity of Improved Shigella O-Specific Polysaccharide-Protein Conjugate Vaccines in Adults in Israel” Infection and Immunity, 69(3):1351-1357 (Mar. 2001).) It is believed that the polysaccharide (i.e. sugar residue) triggers a short-term immune response that is sugar-specific. Indeed, the human immune system generates a strong response to specific polysaccharide surface structures of bacteria, such as O-antigens and capular polysaccharides. However, since the immune response to polysaccharides is IgM dependent, the immune system develops no memory. The protein carrier that carries the polysaccharide triggers an IgG response that is T-cell dependent and that provides long lasting protection since the immune system develops memory.
A typical vaccination dosage for humans is about 1 to 25 μg, preferably about 1 μg to about 10 μg, most preferably about 10 μg. Optionally, a vaccine, such as a bioconjugate vaccine of the present invention, includes an adjuvant.
Synthesized complexes of polysaccharides (i.e., sugar residues) and proteins (i.e., protein carriers) can be used as conjugate vaccines to protect against a number of bacterial infections. In one aspect, the instant invention is directed to a novel bioengineering approach for producing immunogenic conjugate vaccines that provide advantages over classical chemical conjugation methods. In one embodiment, the approach involves in vivo production of glycoproteins in bacterial cells, for example, Gram-negative cells such as E. coli.
The biosynthesis of different polysaccharides is conserved in bacterial cells. The polysaccharides are assembled on carrier lipids from common precursors (activated sugar nucleotides) at the cytoplasmic membrane by different glycosyltransferases with defined specificity. Lipopolysaccharides (LPS) are provided in gram-negative bacteria only, e.g. Shigella spp., Pseudomonas spp. and E. coli (ExPEC, EHEC).
The synthesis of lipopolysaccharides (LPS) starts with the addition of a monosaccharide to the carrier lipid undecaprenyl phosphate at the cytoplasmic side of the membrane. The antigen is built up by sequential addition of monosaccharides from activated sugar nucleotides by different glycosyltransferases and the lipid-linked polysaccharide is flipped through the membrane by a flippase. The antigen-repeating unit is polymerized by an enzymatic reaction. The polysaccharide is then transferred to the Lipid A by the Ligase WaaL forming the LPS that is exported to the surface, whereas the capsular polysaccharide is released from the carrier lipid after polymerization and exported to the surface. The biosynthetic pathway of these polysaccharides enables the production of LPS bioconjugates in vivo, capturing the polysaccharides in the periplasm to a protein carrier. Bioconjugates, such as LPS bioconjugates, are preferred in the present invention.
As shown in
Conjugate vaccines have been successfully used to protect against bacterial infections. The conjugation of an antigenic polysaccharide to a protein carrier is required for protective memory response, as polysaccharides are T-cell independent antigens. Polysaccharides have been conjugated to protein carriers by different chemical methods, using activation reactive groups in the polysaccharide as well as the protein carrier.
As shown in the bottom panel of
The present invention is directed to a novel conjugation process involving engineering bacterial cells to produce the final bioconjugate vaccines. One embodiment of the invention allows the production of bioconjugate vaccines in vivo, circumventing the chemical conjugation and therefore simplifying the production process. The technology includes a novel genetic/enzymatic mechanism for the in vivo synthesis of novel bioconjugates consisting of protein-linked saccharides.
The basis of one aspect of the invention includes the discovery that Campylobacter jejuni contains a general N-linked protein glycosylation system, an unusual feature for prokaryotic organisms. Various proteins of C. jejuni have been shown to be modified by a heptasaccharide. This heptasaccharide is assembled on undecaprenyl pyrophosphate, the carrier lipid, at the cytoplasmic side of the inner membrane by the stepwise addition of nucleotide activated monosaccharides catalyzed by specific glycosyltransferases. The lipid-linked oligosaccharide then flip-flops (diffuses transversely) into the periplasmic space by a flipppase, e.g., PgIK. In the final step of N-linked protein glycosylation, the oligosaccharyltransferase (e.g., PgIB) catalyzes the transfer of the oligosaccharide from the carrier lipid to Asn residues within the consensus sequence Asp/Glu-Xaa-Asn-Zaa-Ser/Thr (i.e., D/E-X-N-Z-S/T), where the Xaa and Zaa can be any amino acid except Pro (
We have been able to demonstrate that PgIB does not have a strict specificity for the lipid-linked sugar substrate. The antigenic polysaccharides assembled on undecaprenyl pyrophosphate are captured by PglB in the periplasm and transferred to a protein carrier (Feldman, 2005; Wacker, M., et al., Substrate specificity of bacterial oligosaccharyltransferase suggests a common transfer mechanism for the bacterial and eukaryotic systems. Proc Natl Acad Sci USA, 2006. 103(18): p. 7088-93.) The enzyme will also transfer a diverse array of undecaprenyl pyrophosphate (UPP) linked oligosaccharides if they contain an N-acetylated hexosamine at the reducing terminus. The nucleotide sequence for pgIB is provided at SEQ. ID NO. 1, whereas the amino acid sequence for PgIB is provided at SEQ. ID. NO. 2.
In an embodiment of the expression system for a bacterial bioconjugate that is compatible with Good Manufacturing Practices (GMP), DNA encoding the inducible oligosaccharyltransferase and carrier protein can be stably integrated into a bacterial (e.g., E. coli) genome such that genes for antibiotic selection can be omitted. For example, as shown in
In another embodiment,
In an embodiment, an expression plasmid for a bacterial O antigen, such as the Shigella dysenteriae O1 antigen, can be constructed as in pGVXN64 shown in
The host organism for an expression system of the invention can be, e.g., an Escherichia coli strain such as Escherichia coli W31110ΔwaaL. The deletion of WaaL prevents the transfer of any polysaccharide to the lipid A core. The chromosomal copy of WaaL can also be replaced by PglB. The strain also contains mutation in wbbL, therefore it does not produce any E. coli O16 polysaccharide. To further increase the production of carrier lipid linked polysaccharide, wecG has been deleted to prevent the formation of ECA (Entero Common Antigen).
In one aspect, the instant invention is further directed to the development of bioconjugate vaccines, preferably LPS bioconjugate vaccines, against one or more Shigella species, which are invasive, gram-negative bacteria. Shigella species cause Shigellosis, a severe inflammation of the colon. There are 165 million cases in the world every year, with 70% of such cases being in children under 5 years of age. In developing countries, Shigellosis causes 1.1 million of deaths per year. This is a serious disease that is spread via the fecal-oral route and is highly transmissible. Potential groups that would benefit from immunization against Shigella species include, for example, children, travelers and people in refugee camps.
There are four different serogroups of Shigella, namely, S. dysenteriae, S. flexneri, S. sonnei and S. boydii. In embodiments of the present invention, immunogenic bioconjugates can be made against each of these different serogroups of Shigella. For example,
In further embodiments of the present invention, immunogenic LPS bioconjugates could be made against other bacteria using the teachings in this specification, including bacteria: (1) that cause nosocomial infections, such as Pseudomonas aeruginosa; and (2) that cause urinary tract infection, such as Extraintestinal E. coli (ExPEC).
In an embodiment, the inventors have developed a Shigella dysenteriae O1 LPS bioconjugate vaccine (also referred to as a S. dysenteriae bioconjugate), using genetically engineered E. coli with simple fermentation and purification methods.
PgIB transfers the activated polysaccharide to Asn residues of protein carriers, forming the Shigella bioconjugates. The protein carrier can be, for example, AcrA or a protein carrier that has been modified to contain the consensus sequence for protein glycosylation, i.e., D/E-X-N-Z-S/T, wherein X and Z can be any amino acid except proline (e.g., a modified Exotoxin Pseudomonas aeruginosa (EPA)). EPA has been used successfully in conjugate vaccines.
In an embodiment illustrated in
The production of a bacterial bioconjugate, such as a Shigella bioconjugate, is described in an embodiment in further detail with reference to
Step 2 in the production of a bacterial bioconjugate involves engineering a suitable protein carrier. Protein carriers that are useful preferably should have certain immunological and pharmacological features. From an immunological perspective, preferably, a protein carrier should: (1) have T-cell epitopes; (2) be capable of delivering an antigen to antigen presenting cells (APCs) in the immune system; (3) be potent and durable; and (4) be capable of generating an antigen-specific systemic IgG response. From a pharmacological perspective, preferably, a protein carrier should: (1) be non-toxic; and (2) be capable of delivering antigens efficiently across intact epithelial barriers. More preferably, in addition to these immunological and pharmacological features, a protein carrier suitable for the production of a bacterial bioconjugate should: (1) be easily secreted into the periplasmic space; and (2) be capable having antigen epitopes readily introduced as loops or linear sequences into it.
The inventors have found genetically detoxified Pseudomonas aeruginosa Exotoxin (EPA) and the Campylobacter protein AcrA to be suitable protein carriers, most preferably EPA. AcrA contains natural glycosylation sites whereas EPA needs to be modified to encode glycosylation sites. Preferably, EPA is modified to introduce two glycosylation sites directed to the Shigella O1 antigen. More preferably, two consensus sequences are introduced as discussed in Example 10.
The amino acid sequence of EPA, as modified in an embodiment of this invention to contain two glycosylation sites, is provided as SEQ. ID NO.: 6 (with signal sequence) and SEQ. ID NO.: 7 (without signal sequence) in the Sequence Listing provided below. The glycosylation sites in each of SEQ. ID NO.: 6 and SEQ. ID NO.: 7 are denoted with an underline.
Consequently, the bacterial bioconjugates of the present invention show in vivo immnogenicity. In an embodiment, bacterial bioconjugates are capable of exhibiting: (1) a carbohydrate specific response; and (2) a carrier specific response or a similar response irrespective of the carrier protein. Moreover, an IgG specific response shows T-cell dependency of the immune response, such that memory of the response is expected.
In summary, in one aspect, the technology of the present invention has been used to develop a vaccine against S. dysenteriae O1 infection. For example, the polysaccharide of S. dysenteriae O1 can be conjugated to EPA in E. coli. This is very beneficial since EPA previously has been successfully used in clinical trials with different conjugate vaccines. In the instant invention, the S. dysenteriae O1 bioconjugate was produced in a bioreactor at 31 scale. The cells were grown to high OD and the bioconjugate was extracted by osmotic shock. The bioconjugates were purified to 98% purity by anionic exchange and size exclusion chromatography. The bioconjugates were injected into different mice strains. After two as well as three injections, a sugar specific IgG response against the polysaccharide was detected using LPS from Shigella dysenteriae O1 for analysis (
These results strongly suggest that our inventive E. coli strain is suitable for the potential production of an antigenic bacterial vaccine, such as an antigenic Shigella vaccine. In an embodiment, the EPA-Shigella bioconjugate was characterized intensively by different methods, like NMR, HPLC and MS.
Using this technology, bacterial bioconjugates can be produced that are immunogenic. Genetic modifications can be made allowing in vivo conjugation of bacterial polysaccharides in desired proteins and at desired positions. For example, in an embodiment and as discussed above, the antigenic polysaccharide of S. dysenteriae O1 can be expressed in E. coli and conjugated to two different protein carriers in vivo (i.e., EPA and AcrA). Both bioconjugates elicit a specific IgG response against the polysaccharide in mice. As another example, Table 1 below depicts different polysaccharide substrates for bacterial OSTs/OTases such as PgIB that can be used in the in vivo method of the present invention for conjugating a protein carrier with the polysaccharide.
C. jejuni N-glycan
Shigella dysenteriae O1
Pseudomonas aeruginosa O11
E. coli O16
Table 2 below depicts yet additional different LPS polysaccharide substrates that could be utilized in the present invention with respect to various strains of Shigella and E. coli., as well as of Pseudomonas aeruginosa O11 and Francisella tularensis.
Shigella dysenteriae O1
S. flexneri 2a
S. flexneri 3a
S. flexneri 3b
S. flexneri 6
S. sonnei
E. coli O4: K52 (ExPEC)
E. coli O4: K6 (ExPEC)
E. coli O6: K2 (ExPEC)
E. coli O6: K54 (ExPEC)
E. coli O22 (ExPEC)
E. coli O75 (ExPEC)
E. coli O83 (ExPEC)
E. coli O7
E. coli O9
E. coli O16
E. coli O121
E. coli 0157
Pseudomonas aeruginosa O11
Francisella tularensis
For example, in a further embodiment of the invention, bioconjugate vaccines against E. coil can also be developed. E. coli is a well-known bacterial species. From a genetic and clinical perspective, E. coli strains of biological significance to humans can be broadly categorized as commensal strains, intestinal pathogenic strains and extraintestinal pathogenic E. coli (ExPEC). ExPEC strains can be part of the normal intestinal flora and are isolated in 11% of healthy individuals. They do not cause gastroenteritis in humans but their main feature is their capacity to colonize extraintestinal sites and to induce infections in diverse organs or anatomical sites. They are the main cause of urinary tract infections (UTI), are involved in septicemia, diverse abdominal infections and meningitis. Bacteremia can arise with a risk of severe sepsis. Severe sepsis due to ExPEC was associated with 41,000 estimated deaths in 2001. ExPEC strains have been susceptible to antibiotics; however more and more antibiotic resistant strains have evolved, both in hospital and in the community. This antimicrobial resistance is making the management of ExPEC infections more difficult; therefore, new vaccines would be an alternative strategy to prevent these infections.
In animal models, passive or active immunization against capsule, O-specific antigen and different outer membrane proteins have afforded protection against systemic infections and immunization with these different antigens are protective against urinary tract infections from ExPEC strains expressing these virulence factors. The serotypes O4, O6, O14, O22, O75 and O83 cause 75% of UTI. In one embodiment, the novel technology of the present invention can be used to develop a monovalent LPS bioconjugate including one antigen (e.g., serotype O6, one of the major serotypes) and even a multivalent LPS bioconjugate including these 6 antigens. For example, the gene cluster encoding for the enzymes that synthesize the O-antigen for ExPEC could be amplified and then expressed in the Shigella production strain.
The instant invention involves a highly efficient production process with high potential yields that can be used for industrial scale preparations in a cost-efficient process. This novel, cost efficient bioengineering approach to producing bioconjugate can be applied to other conjugates and for other applications. An additional feature of the invention involves a considerable simplification of the production of bacterial vaccines with high reproducibility and a potentially reduced risk of lot failures.
It is now possible to engineer bacterial expression systems so that specific bioconjugates are produced that are biologically active. For example, the O-specific polysaccharide of S. dysenteriae has been conjugated to different protein carriers and the resulting bioconjugate has elicited a specific IgG response against the polysaccharide in mice. In an embodiment, the technology of the invention makes use of an oligosaccharyl transferase, for example, PgIB of Campylobacter jejuni to couple bacterial polysaccharides (O antigens) in vivo to simultaneously express recombinant carrier proteins, yielding highly immunogenic bioconjugate vaccines.
A production process has been established that can be used on an industrial scale. This opens up the possibility that a multitude of various conjugate vaccines can be developed and manufactured using simple bacterial fermentation. The process has several advantages compared to the in vitro conjugation method depicted in the top panel of
In an embodiment, the instant invention relates to the scaled-up production of recombinant glycosylated proteins in bacteria and factors determining glycosylation efficiency. For example, recombinant glycosylated proteins of the present invention can be made using the shakeflask process. Bioconjugates have previously been mainly produced in LB shake flask cultures. More preferably, in one aspect of the invention, a first fed-batch process can be used for the production of recombinant glycosylated proteins in bacteria. In a preferred manufacturing process, the aim is to achieve markedly increased final biomass concentrations while maintaining glycosylation efficiency and recombinant protein yield per cell and while maintaining simplicity and reproducibility in the process.
In one embodiment, bacterial bioconjugates of the present invention can be manufactured on a commercial scale by developing an optimized manufacturing method using typical E. coli production processes. First, one can use various types of feed strategies, such as batch, chemostat and fed-batch. Second, one can use a process that requires oxygen supply and one that does not require an oxygen supply. Third, one can vary the manner in which the induction occurs in the system to allow for maximum yield of product.
It has found been that, in contrast to expression of the carrier protein, the degree of N-linked glycosylation strongly reacts to changes in nutrient availability, type of carbon- and energy source, oxygen supply and time-point of induction. For example, in a fed-batch process, the addition of inducers to the batch and fed-batch cultures immediately leads to a 3-fold decrease in specific growth rate, indicating a high metabolic burden and/or stress due to synthesis of the carrier protein and membrane-bound oligosaccharyltransferase. Based on the inventors' finding of a recurring retardation of the appearance of glycosylated carrier protein compared to the non-glycosylated form after induction, it is concluded that glycosylation appears to be the rate-limiting step in bioconjugate biosynthesis.
Based on these results, in an example of an embodiment of the invention, the following process design for cultivation has been developed: fed-batch cultivation mode for achieving high cell densities; extended incubation after induction to facilitate maximal glycosylation; surplus nutrient supply (e.g., LB components yeast extract and tryptone) during biomass build-up until induction to provide a sufficient supply of building blocks for the production process; and glycerol as the main carbon and energy source to prevent catabolite repression and acetate formation. This bioprocess allows a 50-fold increase in yield compared to LB batch culture, paving the way towards a cost-effective production of conjugate vaccines in recombinant Escherichia coli. In this example, one can have oxic conditions throughout the production process, for example, achieved through oxygen-enriched aeration; however, low oxygen content is also feasible. Example 9 sets forth this example of a fed-batch process in greater detail. It should be recognized, however, that other processes may be used to produce the bacterial LPS bioconjugates of the present invention.
Consequently, in one embodiment of the invention, E. coli can be used for in vivo production of glycosylated proteins and is suitable for industrial production of glycosylated proteins.
The following examples serve to illustrate further the present invention and are not intended to limits its scope in any way.
To optimize the acceptor protein requirements for N-glycosylation detailed studies were performed on the C. jejuni glycoprotein AcrA (CjO367c). AcrA is a periplasmic lipoprotein of 350 amino acid residues. It has been shown that secretion to the periplasm but not lipid-anchoring is a prerequisite for glycosylation (Nita-Lazar et al., 2005, supra). The signal for export can either be the native AcrA signal sequence or the heterologous PeIB signal when expressed in E. coli. Of the five potential Winked glycosylation sequons (N117, N123, N147, N273, N274) the same two ones are used in C. jejuni and E. coli (N123 and N273 (Nita-Lazar et al., 2005, supra)). AcrA was chosen as model because it is the only periplasmic N-glycoprotein of C. jejuni for which detailed structural information is available. Recently, the crystal structure of an AcrA homologue, the MexA protein from the Gram-negative bacterium P. aeruginosa, was published (Higgins et al., (2004). Structure of the periplasmic component of a bacterial drug efflux pump. Proc. Natl. Acad. Sci. USA 7Of1 9994-9999). Both proteins are members of the so-called periplasmic efflux pump proteins (PEP,(Johnson, J. M. and Church, G. M. (1999). Alignment and structure prediction of divergent protein families: periplasmic and outer membrane proteins of bacterial efflux pumps. J. Mol. Biol. 287, 695-715)). The elongated molecule contains three linearly arranged subdomains: an a-helical, anti-parallel coiled-coil which is held together at the base by a lipoyl domain, which is followed by a six-stranded β-barrel domain. The 23-28 residues at the N-terminus and 95-101 residues in the C-terminus are unstructured in the crystals. MexA and AcrA protein sequences are 29.3% identical and 50% similar. Thus, the two proteins likely exhibit a similar overall fold.
It is known that lipoyl domains similar to MexA of P. aeruginosa and accordingly also in AcrA of C. jejuni form a compact protein that can be individually expressed in E. coli (reviewed by Berg, A., and de Kok, A. (1997). 2-Oxo acid dehydrogenase multienzyme complexes. The central role of the lipoyl domain. Biol. Chem. 378, 617-634). To check which acceptor peptide sequence was required for N-glycosylation by the pgl machinery in E. coli the lipoyl domain of AcrA was taken. It was used as a molecular scaffold to transport peptides of different lengths to the periplasm and present them to the pgl machinery in vivo.
Therefore, a plasmid coding for the lipoyl domain (Lip) was constructed and N-terminally fused to the signal sequence of OmpA (Choi, J. H., and Lee, S. Y. (2004). Secretory and extracellular production of recombinant proteins using Escherichia coli. Appl Microbiol Biotechnol 64, 625-635) and C-terminally to a hexa histag. Cloning was performed to place the gene expression under the control of the arabinose promoter. For the Lip domain borders amino acid positions were chosen that appeared at the same positions as the domain borders of the Lipoyl domain part in MexA. To test different peptides for their ability to accept an N-glycan stretches of the sequence were inserted between the two hammerhead-like parts of the Lip domain. The stretches consisted of sequences comprising the N-glycosylation site N123 of C. jejuni AcrA. The resulting open reading frames consisted of the sequences coding for the OmpA signal sequence, the N-terminal hammerhead-like part of AcrA (D60-D95, the numbering of the amino acids refers to the mature AcrA polypeptide sequence numbering), the different stretches containing the native N123 glycosylation site of AcrA (see below), the C-terminal hammerhead-like part of AcrA-Lip (L167-D210) and the C-terminal his-tag.
Construction of the plasmids was achieved by standard molecular biology techniques. Three stretches containing the native N123 glycosylation site of AcrA of different lengths were inserted between the two halves of Lip resulting in three different ORFs:
Construct A contains A118-S130 resulting in a protein sequence of:
MKKTAIAIAVALAGFATVAQADVIIKPQVSGVIVNKLFKAGDKVKKGQT
Construct B contains F122-E138 resulting in a protein sequence of:
MKKTAIAIAVALAGFATVAQADVIIKPQVSGVIVNKLFKAGDKVKKGQ
Construct C contains D121-A127 resulting in a protein sequence of:
MKKTAIAIAVALAGFATVAQADVIIKPQVSGVIVNKLFKAGDKVKKG
The underlined stretches of sequence indicate the OmpA signal peptide, singly underlined residues were introduced for cloning reasons or to render the protein resistant to degradation. Bold: glycosylation site corresponding to N123 of AcrA. Italics: hexa-histag. The corresponding genes were expressed under the control of the arabinose promoter in the backbone of the plasmid pEC415 (Schulz, H., Hennecke, H., and Thony-Meyer, L. (1998). Prototype of a heme chaperone essential for cytochrome c maturation. Science 281, 1197-1200).
To check which of the three stretches triggered glycosylation of the Lip proteins protein expression experiments were performed. E. coli Top 10 cells (Invitrogen, Carlsbad, Calif., USA) carrying pACYCpgl or pACYCpglmut (Wacker et al., 2002, supra) and a plasmid coding constructs A1 B or C were grown in LB medium containing ampicillin and chloramphenicol up to an OD of 0.5 at 37° C. For induction 1/1000 volume 20% arabinose (w/v) solution was added and the cells were grown for another 2 hrs. The cells were then harvested by centrifugation and resuspended in 20 mM Tris/HCl, pH 8.5, 20% sucrose (w/v), 1 mM EDTA, 1 mM PMSF, and 1 g/l (w/v) lysozyme and incubated at 4° C. for 1 hr. Periplasmic extracts were obtained after pelletting of the spheroblasts and diluted with 1/9 volume (v/v) of 10× buffer A (3 M NaCl, 0.5 M Tris/HCl, pH 8.0 and 0.1 M imidazole) and MgSO4 added to 2.5 mM. Ni-affinity purification was performed on 1 ml Ni-Sepharose columns from Amersham Pharmacia Biotech (Uppsala, Sweden) in buffer A. Proteins were eluted in buffer A containing 0.25 M imidazole.
To confirm the findings from the peptide display approach an aspartate to alanine mutation was inserted at position 121 (D121A, i.e. 2 residues before the glycosylated N123) in the full length soluble version of the AcrA protein and it was tested whether the site N123 could still be glycosylated in E. coli. In order to test this AcrA-D121A was expressed and its glycosylation status was analyzed. For the analysis an engineered AcrA was used. It differed from the original C. jejuni gene in that it contains the PeIB signal sequence (Choi and Lee, 2004, supra) for secretion into the periplasm and a C-terminal hexa histag for purification. It has been shown that this AcrA variant gets secreted, signal peptide-cleaved and glycosylated as the lipid anchored, native protein (Nita-Lazar et al., 2005, supra). The following is the amino acid sequence of the soluble AcrA protein:
MKYLLPTAAAGLLLLAAQPAMAMHMSKEEAPKIQMPPQPVTTMSAKSE
The underlined residues are the PelB signal peptide, italics the hexa-histag, and bold the two natural glycosylation sites at N123 and N273. A plasmid containing the ORF for the above protein in the pEC415 plasmid (Schulz et al., 1998) was constructed to produce pAcrAper.
The assay to test the glycosylation status of AcrA and mutants thereof (see below) was as follows: expression of AcrA was induced with 0.02% arabinose in exponentially growing E. coli CLM24 (Feldman et al., 2005, supra) cells containing the plasmid-borne pgl operon in its active or inactive form (pACYCpg/or pACYCpg/mut, see (Wacker et al., 2002, supra)) and a plasmid coding for AcrA (pAcrAper). After four hours of induction, periplasmic extracts were prepared as described above and analyzed by SDS-PAGE, electrotransfer and immunodetection with either anti-AcrA antiserum or R12 antiserum. The latter is specific for C. jejuni N-glycan containing proteins (Wacker et al., 2002, supra).
The first two lanes of
To test if the introduction of an aspartate residue could generate a glycosylation site, AcrA mutants were generated in which the residue in the −2 position of the not used glycosylation sites in positions N117 and N147 of soluble AcrA were exchanged for aspartate (F115D, T145D). It was then tested whether the modified glycosylation sites could be glycosylated by the same assay as described in example 2. Both mutations were individually inserted either into the wildtype sequence of the soluble version of AcrA or in the double mutant in which both used glycosylation sites were deleted (N123Q and N273Q). Periplasms extracts of cultures induced for 4 hrs were prepared, separated by SDS page and analyzed by Western blotting (
To further confirm that it is possible to introduce a glycosylation site by inserting an aspartate residue in the −2 position, the natively not used sites N117-S119 and N274-T276 were changed to optimize N-glycosylation. For this purpose further mutants were generated (
The above experiments confirm the finding that the bacterial N-glycosylation site recognized by the OTase of C. jejuni consists partly of the same consensus as the eukaryotic one (N-X-S/T, with X≠P) but, in addition, an aspartate in the −2 position is required for increasing efficiency. Furthermore, they demonstrate that it is possible to glycosylate a protein at a desired site by recombinantly introducing such an optimized consensus sequence.
A further experiment was performed to test whether the −1 position in the bacterial glycosylation site exhibits the same restrictions as the +1 position in eukaryotes (Imperiali, B., and Shannon, K. L. (1991). Differences between Asn-Xaa-Thr-containing peptides: a comparison of solution conformation and substrate behaviour with oligosaccharyl-transferase. Biochemistry 30, 4374-4380; Rudd, P. M., and Dwek, R. A. (1997). Glycosylation: heterogeneity and the 3D structure of proteins. Crit. Rev. Biochem. Mol. Biol. 32, 1-100). A proline residue at +1 is thought to restrict the peptide in such a way that glycosylation is inhibited. To test if a similar effect could also be observed in the −1 position a proline residue was introduced at that position of the first natively used site in a point mutant that had the second native site knocked out (AcrA-N273Q-F122P). The control expression of AcrA-N273Q showed a monoglycosylated protein in the presence of a functional pgl operon (
Sequence alignments of all the sites known to be glycosylated by the C. jejuni pgl machinery indicate that they all comprise a D or E in the −2 position (Nita-Lazar et al., 2005, supra; Wacker et al., 2002, supra; Young et al., (2002). Structure of the N-linked glycan present on multiple glycoproteins in the Gram-negative bacterium, Campylobacter jejuni. J. Biol. Chem. 277, 42530-42539). Thus, it was established that the glycosylation consensus sequence for bacteria can be optimized by a negatively charged amino acid in the −2 position, resulting in D/E-X-N-Z-S/T, wherein X & Z≠P.
To demonstrate that the primary sequence requirement (optimized consensus sequence) is sufficient for N-glycosylation in bacteria, it was tested whether a non-C. jejuni protein could be glycosylated by applying the above strategy. Cholera toxin B subunit (CtxB) was employed as a glycosylation target. The corresponding gene was amplified from Vibrio cholerae in such a way that it contained the coding sequence of the OmpA signal sequence on the N-terminus and a hexahistag at the C-terminus, just the same as constructs A through C in example 1. The resulting DNA was cloned to replace construct A in the plasmids employed in example 1. A point mutation of W88 to D or a D insertion after W88 generated an optimized glycosylation site (DNNKT). The wildtype and W88D CtxB proteins containing the signal sequence and his-tag were expressed in E. coli Top 10 and other cell types in the presence and absence of the functional pg/locus from C. jejuni. When periplasmic extracts from Top 10 cells were analyzed by SDS-PAGE, electrotransfer and consecutive immunoblotting with a CtxB antiserum, only CtxB W88D produced a higher and thus glycosylated band in the pgl locus background (
The amino acid sequence of the CtxB protein used here is indicated below (recombinant OmpA signal sequence underlined, hexa-histag italics, W88 bold):
MKKTAIAIAVALAGFATVAQATPQNITDLCAEYHNTQIHTLNDKIFS
A potential application of the N-glycosylation in bacteria is the display of the glycan on the surface of a bacterial host cell in order to link the phenO- to the genotype and thereby select for specific genetic mutations. To demonstrate that N-glycans can be presented on outer membrane proteins the OmpH1 protein was engineered in a way that it contained multiple optimized consensus sites according to the invention. The sites were engineered into loop regions of the protein as deduced from the known crystal structure (Muller, A., Thomas, G. H., Horler, R., Brannigan, J. A., Blagova, E., Levdikov, V. M., Fogg, M. J., Wilson, K. S., and Wilkinson, A. J. 2005. An ATP-binding cassette-type cysteine transporter in Campylobacter jejuni inferred from the structure of an extracytoplasmic solute receptor protein. Mol. Microbiol. 57: 143-155). Previous experiments showed that the best glycosylation sequons were generated by the mutations V83T, K59N-G601-N61T, R190N-G191I-D192T and H263D-F264S-G265N-D2661-D267T. For surface display it was desired to evaluate different combinations of those introduced sites in order to establish the most N-glycan-specific sample. The combinations were generated in a wild type OmpH1 encoding plasmid construct and tested in a similar manner as described for AcrA.
The following is the amino acid sequence of the OmpH1 protein of Campylobacter jejuni (strain 81-176) with attached myc tag in italics:
MKKILLSVLTTFVAVVLAACGGNSDSKTLNSLDKIKQNGWRIGVFGDK
The native glycosylation site in the protein is bold, the signal sequence underlined.
In order to answer the question whether multiple glycosylated OmpH1 variants can be displayed on the surface of bacterial cells, immunofluorescence was performed on bacterial CLM24 or SCM6 (which is SCM7 ΔwaaL) cells expressing various OmpH1 variants. A wild type OmpH1 and a mutant lacking the critical asparagine for glycosylation were included in the experiment. In addition, a C20S mutant was constructed in order to retain the protein in the periplasm, thus serving as a control in the experiment. Immunostaining was carried out on the cells treated with paraformaldehyde. Paraformaldehyde fixes cells without destroying the cell structure or compartimentalization. The c-Myc- and N-glycan-specific immuneserum in combination with corresponding secondary antibodies conjugated to FITC and Cy3 were used to detect the protein (red fluorescence) and N-glycan (green) on the bacterial cell surface, respectively. Additionally, 4,6-diaminO-2-phenylindole (DAPI, blue) was employed to stain for bacterial DNA to unambiguously differentiate between bacterial cells and cellular debris. When the cells expressing wild type OmpH1 were stained, immunofluorescence specific to the protein as well as the N-glycan was detected (
This is an example of a production process; however, different conditions also lead to similar product formation.
A. Production Process
E. coli strain W3110ΔwaaL containing three plasmids expressing PglB, EPA and the enzymes for the biosynthesis of the Shigella O1 polysaccharide was used for the production of the LPS bioconjugate. A single colony was inoculated in 50 ml LB medium and grown at 37° C. O/N. The culture was used to inoculate a 11 culture in a 21 bioreactor. The bioreactor was stirred with 500 rpm, pH was kept at 7.0 by autO-controlled addition of either 2 M KOH or 20% H3PO4 and the cultivation temperature was set at 37° C. The level of dissolved oxygen (pO2) was kept between 0 and 10% oxygen. The cells were grown in a semi defined glycerol medium containing Kanamycin to an OD600=15. The medium contained the following ingredients: 330 mM Glycerol, 10 g Yeast extract, 20 g Tryptone, 34 mM K2HPO4, 22 mM KH2PO4, 38 mM (NH4)2SO4.2 mM MgSO4.7H2O and 5 mM Citric acid. After an initial batch phase around 5 h, a first nutrient pulse was added to sustain fast biomass build-up (glycerol, tryptone and yeast extract). After an additional 1.5 h the culture reached an OD600=30. At this timepoint a second nutrient pulse of glycerol and tryptone was added together with the required inducers 1% L-arabinose and 1 mM IPTG. In order to keep induction at maximum levels and supply further amino acids for recombinant protein synthesis, a linear nutrient/inducer feed (28.8 ml/h) was started with the addition this pulse. The feed was sustained until the end of the process. The bioreactor culture was harvested after a total of 24 h cultivation, when it should have reached an OD600 of ±80.
The production process was analyzed by Western blot as described previously (Wacker, M., et at, N-linked glycosylation in Campylobacter jejuni and its functional transfer into E. coli. Science, 2002. 298(5599): p. 1790-3.). After being blotted on nitrocellulose membrane, the sample was immunostained with the specific anti-EPA (Wacker, M., et al., N-linked glycosylation in Campylobacter jejuni and its functional transfer into E. coli. Science, 2002. 298(5599): p. 1790-3.). Anti-rabbit IgG-HRP (Biorad) was used as secondary antibody. Detection was carried out with ECL™ Western Blotting Detection Reagents (Amersham Biosciences, Little Chalfont Buchinghamshire).
B. Periplasmic Protein Extraction
The cells were harvested by centrifugation for 20 min at 10,000 g and resuspended in 1 volume 0.9% NaCl. The cells were pelleted by centrifugation during 25-30 min at 7,000 g. The cells were resuspended in Suspension Buffer (25% Sucrose, 100 mM EDTA
200 mM Tris HCl pH 8.5, 250 OD/ml) and the suspension was incubated under stirring at 4-8° C. during 30 min. The suspension was centrifuged at 4-8° C. during 30 min at 7,000-10,000 g. The supernatant was discarded, the cells were resuspended in the same volume ice cold 20 mM Tris HCl pH 8.5 and incubated under stirring at 4-8° C. during 30 min. The spheroblasts were centrifuged at 4-8° C. during 25-30 min at 10,000 g, the supernatant was collected and passed through a 0.2μ membrane.
As shown in
C. Bioconjugate Purification
The supernatant containing periplasmic proteins obtained from 100,000 OD of cells was loaded on a Source Q anionic exchange column (XK 26/40≈180 ml bed material) equilibrated with buffer A (20 mM Tris HCl pH 8.0). After washing with 5 column volumes (CV) buffer A, the proteins were eluted with a linear gradient of 15CV to 50% buffer B (20 mM Tris HCl+1M NaCl pH 8.0) and then 2CV to 100% buffer B. Protein were analyzed by SDS-PAGE and stained by Coomassie. Fractions containing O1-EPA were pooled. Normally the bioconjugate eluted at conductivity between 6-17 mS. The sample was concentrated 10 times and the buffer was exchanged to 20 mM Tris HCl pH 8.0.
As shown in
The O1-Bioconjugate was loaded a second time on a Source Q column (XK 16/20≈28 ml bed material) that has been equilibrated with buffer A: 20 mM Tris HCl pH 8.0. The identical gradient that was used above was used to elute the bioconjugate. Protein were analyzed by SDS-PAGE and stained by Coomassie. Fractions containing O1-EPA were pooled. Normally the bioconjugate eluted at conductivity between 6-17 mS. The sample was concentrated 10 times and the buffer was exchanged to 20 mM Tris HCl pH 8.0.
As shown in
The O1-Biconjugate was loaded on Superdex 200 (Hi Load 26/60, prep grade) that was equilibrated with 20 mM Tris HCl pH 8.0.
As shown in
As shown in
Exotoxin A of Pseudomonas aeruginosa (EPA) is a 67 kDa extracellulary secreted protein encoding mature 613 amino acids in its mature form and containing four disulfide bridges (C11-C15, C197-C214, C265-C287, C372-C379). To enable its glycosylation in E. coli, the protein must locate to the periplasmic space for glycosylation to occur. Therefore, a the signal peptide of the protein DsbA from E. coli was genetically fused to the N-terminus of the mature EPA sequence. A plasmid derived from pEC415 [Schulz, H., Hennecke, H., and Thony-Meyer, L., Prototype of a heme chaperone essential for cytochrome c maturation, Science, 281, 1197-1200, 1998] containing the DsbA signal peptide code followed by a RNase sequence was digested (NdeI to EcoRI) to keep the DsbA signal and remove the RNase insert. EPA was amplified using PCR (forward oligo was 5′-AAGCTAGCGCCGCCGAGGAAGCCTTCGACC (SEQ. ID NO. 14) and reverse oligo was 5′-AAGAATTCTCAGTGGTGGTGGTGGTGGTGCTTCAGGTCCTCGCGCGGCGG (SEQ. ID NO. 15)) and digested NheI/EcoRI and ligated to replace the RNase sequence removed previously. The resulting construct (pGVXN69) encoded a protein product with an DsbA signal peptide, the mature EPA sequence and a hexa-histag. Detoxification was achieved by mutating/deleting the catalytically essential residues L552VΔE553 according to [Lukac, M., Pier, G. B., and Collier, R. J., Toxoid of Pseudomonas aeruginosa exotoxin A generated by deletion of an active-site residue, Infect Immun, 56, 3095-3098, 1988] and [Ho, M. M., et al., Preclinical laboratory evaluation of a bivalent Staphylococcus aureus saccharide-exotoxin A protein conjugate vaccine, Hum Vaccin, 2, 89-98, 2006] using quick change mutagenesis (Stratagene) and phosphorylated oligonucleotides 5′-GAAGGCGGGCGCGTGACCATTCTCGGC (SEQ. ID NO. 16) and 5′-GCCGAGAATGGTCACGCGCCCGCCTTC (SEQ. ID NO. 17) resulting in construct pGVXN70.
It is known that insertion of a pentapeptide sequence of the type D/E-Z—N-X-S/T into a suitable position results in glycosylation. To glycosylate EPA in E. coli cells, two different glycosylation sites were inserted into the previously described constructs according to the following description.
To insert a site at position 375, two steps were performed. First, quick change mutagenesis using oligos 5′-CCTGACCTGCCCCGGGGAATGCGCGG (SEQ. ID NO. 18) and 5′-CCGCGCATTCCCCGGGGCAGGTCAGG (SEQ. ID NO. 19) with pGVXN70 as a template resulted in a construct containing a single SmaI site at amino acid position 375 of EPA protein sequence by deleting three residues but otherwise keeping the starting protein sequence intact. In a second step, an insert composed of two complementary, phosphorylated oligonucleotides coding for (i) the previously deleted residues (when inserting the SmaI site), (ii) the pentapeptide glycosylation sequon and (iii) additional lysine residues flanking the consensus for optimization of glycosylation efficiency (as was found by further experiments) was ligated into this SmaI site (5′-GTCGCCAAAGATCAAAATAGAACTAAA (SEQ. ID NO. 20) and 5′-TTTAGTTCTATTTTGATCTTTGGCGAC (SEQ. ID NO. 21). The resulting construct was pGVXN137.
To insert an additional glycosylation site in the construct at amino acid 240, a one step procedure using quick change mutagenesis with oligonucleotides 5′-CATGACCTGGACATCAAGGATAATAATAATTCTACTCCCACGGTCATCAGTCATC (SEQ. ID NO. 22) and 5′-GATGACTGATGACCGTGGGAGTAGAATTATTATTATCCTTGATGTCCAGGTCATG (SEQ. ID NO. 23) was applied on construct pGVXN137. The resulting construct thus contained various changes compared to the wild type EPA protein: two glycosylation sites, a DsbA signal peptide, detoxification mutation.
While this invention has been particularly shown and described with references to embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention encompassed by the claims. Moreover, in instances in the specification where specific nucleotide or amino acid sequences are noted, it will be understood that the present invention encompasses homologous sequences that still embody the same functionality as the noted sequences. Preferably, such sequences are at least 85% homologous. More preferably, such sequences are at least 90% homologous. Most preferably, such sequences are at least 95% homologous.
| Number | Date | Country | |
|---|---|---|---|
| 61064163 | Feb 2008 | US | |
| 61071545 | May 2008 | US | |
| 61129480 | Jun 2008 | US | |
| 61129852 | Jul 2008 | US | |
| 61136687 | Sep 2008 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12735773 | Dec 2010 | US |
| Child | 14522254 | US |
