Patent Application
20230151354
The instant application contains a Sequence Listing which has been submitted electronically in XML file format and is hereby incorporated by reference in its entirety. Said XML copy, created on Dec. 22, 2022, is named 57123-702_301_SL.xml and is 192,400 bytes in size.
Disclosed herein are systems, methods, reagents, apparatuses, vectors, and host cells for the discovery and evolution of metabolic pathways that produce small molecules that modulate enzyme function.
Natural products and their derivatives represent a longstanding source of pharmaceuticals and medicinal preparations1-3. These molecules—perhaps, as a result of their biological origin—tend to exhibit favorable pharmacological properties (e.g., bioavailability and “metabolite-likeness”)1,4 and can exert a striking variety of therapeutic effects (e.g., analgesic, antiviral, antineoplastic, anti-inflammatory, cytotoxic, immunosuppressive, and immunostimulatory)5-10. Recent advances in synthetic biology and metabolic engineering have suppled new approaches for the efficient biosynthesis and functionalization of known, pharmaceutically relevant natural products11-13; complementary methods for the discovery and optimization of new products with specific, therapeutically relevant activities, however, remain underdeveloped14.
Existing strategies for natural product discovery are largely undirected and/or limited in scope. For example, screens of large natural product libraries—augmented, on occasion, with combinatorial (bio)chemistry15-17—have uncovered molecules with important medicinal properties18, but these screens are resource-intensive and largely subject to serendipityl9. Bioinformatic tools, by contrast, permit the identification of biosynthetic gene clusters20,21, where co-localized resistance genes, if present, can reveal the biochemical function of their products22. The therapeutic activities of many pharmaceutically relevant metabolites, however, differ from their native functions23, and most biosynthetic pathways can, when appropriately reconfigured, yield entirely new—and, perhaps, more effective—therapeutic molecules12,24.
Microbial systems have emerged as powerful platforms for the biosynthesis of natural products from unculturable or low-yielding organisms.25,26 Recent work showed that such systems can also permit the discovery and evolution of metabolic pathways with specific, therapeutically relevant activities (PCT/US2019/40896).
Disclosed herein are systems, methods, reagents, apparatuses, vectors, and host cells for the discovery and evolution of metabolic pathways that produce small molecules that modulate enzyme function. For example, a microorganism is provided in which a first genetically encoded system links cell growth to the activity of a target enzyme and in which a second genetically encoded system—to be discovered or evolved—produces a metabolite that modulates the activity of the target enzyme. This disclosure applies this approach to a subset of target enzymes that post-translationally modify proteins, to metabolic pathways that produce phenylpropanoids or nonribosomal peptides, and to the discovery of cryptic metabolic pathways. Some aspects of this disclosure provide specific reconfigured or evolved pathways that produce specific modulators of enzyme activity, that yield improved titers of such modulators (relative to a starting pathway), and/or that exhibit reduced host toxicity (relative to a starting pathway). Metabolic products with specific inhibitory effects are also disclosed.
According to one aspect, methods for the discovery and evolution of metabolic pathways that produce molecules that modulate protein function are provided. The methods include contacting a population of host cells that comprise a protein of interest, such as an enzyme of interest, with a population of expression vectors comprising different metabolic pathways, wherein the host cells are amenable to transfer of the population of expression vectors; expressing the metabolic pathways in the population of host cells, wherein a cell or subset of the population of host cells produce a detectable output when the metabolic pathway within said cell or population of host cells produces a product that modulates the protein of interest, such as the enzyme of interest; screening the population of host cells under conditions that enable measurement of the detectable output in the cell or the subset of the population of host cells; isolating the cell or the subset of the population of host cells that produce a detectable output; isolating the expression vectors that yield detectable outputs higher than (p<0.05) the output of a reference vector that harbors a reference pathway, for example, a vector that encodes a pathway that does not produce molecules with concentrations and/or potencies sufficient to modulate the activity of a protein of interest, such as an enzyme of interest, in the cell or the subset of the population of host cells; and characterizing the products of the metabolic pathways encoded by the expression vectors that yield detectable outputs that are higher than the output of said reference vector in the cell or the subset of the population of host cells.
In some embodiments, the host cells comprise a genetically encoded system in which the activity of a protein of interest, such as an enzyme of interest, controls the assembly of a protein complex with an activity that is not possessed by either of two or more components of the complex and, thus, yields a detectable output in proportion to the amount of complex formed.
In some embodiments, the protein of interest is an enzyme that adds a post-translational modification that causes two proteins, which are initially dissociated, to be covalently linked or to form a noncovalent complex.
In some embodiments, the complex is formed by two proteins with a dissociation constant (Kd) less than or equal to the Kd of the complexes formed between SH2 domains and their phosphorylated substrates.
In some embodiments, the enzyme of interest is an enzyme that adds a post-translational modification other than the addition or removal of a phosphate, and that modification causes two proteins, which are initially dissociated inside of the cell, to be covalently linked or to form a complex with a dissociation constant (Kd) less than or equal to the Kd of the complex formed between a SH2 domain and a phosphorylated SH2-substrate domain (e.g., as shown in
In some embodiments, the metabolic pathways produce phenylpropanoids or nonribosomal peptides.
In some embodiments, the expression vectors comprising different metabolic pathways comprise a library of pathways generated by mutating one or more genes within a starting metabolic pathway.
In some embodiments, one or more of the metabolic pathways comprises a set of genes of unknown biosynthetic capability.
In some embodiments, one or more of the metabolic pathways that produces a detectable output higher than the output of the reference pathway produces a product that differs from the products of other metabolic pathways.
In some embodiments, one or more of the metabolic pathways that produces a detectable output higher than the output of the reference pathway produces a larger quantity of a product than the quantity of product generated by other metabolic pathways.
In some embodiments, one or more of the metabolic pathways that produces a detectable output higher than the output of the reference pathway exhibits a lower cellular toxicity than other metabolic pathways.
In some embodiments, the products of the metabolic pathways are characterized by standard analytical methods, preferably by gas chromatography-mass spectrometry (GC/MS), liquid chromatography-mass spectrometry (LC/MS), and/or nuclear magnetic resonance (NMR) spectroscopy.
In some embodiments, the methods further include isolating the products.
In some embodiments, the methods further include concentrating the products, preferably using a rotary evaporator.
In some embodiments, the methods further include testing the effects of the products on the protein of interest, such as the enzyme of interest.
In some embodiments, the protein of interest, such as the enzyme of interest, is a ubiquitin ligase, a SUMO transferase, a methyltransferase, a demethylase, an acetyltransferase, a glycosyltransferase, a palmitoyltransferase, or a related hydrolase.
In some embodiments, the products or molecules identified (e.g., amorphadiene and derivatives, taxadiene and derivatives, β-bisabolene and derivatives, α-bisabolene and derivatives, and α-longipinene and derivatives) are provided as drugs or drug leads for the treatment of diseases to which PTPs contribute, for example, type 2 diabetes, HER2-positive breast cancer, or Rett syndrome, as are methods of treatment of such diseases by administering an effective amount of the molecule(s) to a subject in need of such treatment.
According to another aspect, compositions or systems are provided that include a population of host cells that comprise a protein of interest and a population of expression vectors comprising different metabolic pathways, wherein a cell or subset of the population of host cells produce a detectable output when the metabolic pathway produces a product that modulates the protein of interest, and optionally wherein the expression vectors yield detectable outputs higher than the output of a reference vector that harbors a reference pathway, for example, a vector that encodes a pathway that does not produce molecules with concentrations and/or potencies sufficient to modulate the activity of a protein of interest, in the cell or the subset of the population of host cells.
In some embodiments, the host cells comprise a genetically encoded system in which the activity of a protein of interest controls the assembly of a protein complex with an activity that is not possessed by either of two or more components of the complex and, thus, yields a detectable output in proportion to the amount of complex formed.
In some embodiments, the protein of interest is an enzyme that adds a post-translational modification that causes two proteins, which are initially dissociated, to be covalently linked or to form a noncovalent complex.
In some embodiments, the complex is formed by two proteins with a dissociation constant (Kd) less than or equal to the Kd of the complexes formed between SH2 domains and their phosphorylated substrates.
In some embodiments, the metabolic pathways produce phenylpropanoids or nonribosomal peptides.
In some embodiments, the expression vectors comprising different metabolic pathways comprise a library of pathways generated by mutating one or more genes within a starting metabolic pathway.
In some embodiments, one or more of the metabolic pathways comprises a set of genes of unknown biosynthetic capability.
In some embodiments, one or more of the metabolic pathways that produces a detectable output higher than the output of the reference pathway produces a product that differs from the products of other metabolic pathways.
In some embodiments, one or more of the metabolic pathways that produces a detectable output higher than the output of the reference pathway produces a larger quantity of a product than the quantity of product generated by other metabolic pathways.
In some embodiments, one or more of the metabolic pathways that produces a detectable output higher than the output of the reference pathway exhibits a lower cellular toxicity than other metabolic pathways.
In some embodiments, the protein of interest is a ubiquitin ligase, a SUMO transferase, a methyltransferase, a demethylase, an acetyltransferase, a glycosyltransferase, a palmitoyltransferase, or a related hydrolase.
According to another aspect, kits are provided that include a population of expression vectors as described herein. In some embodiments, the kits also include the population of host cells that comprise a protein of interest as described herein.
Each of the limitations of the invention can encompass various embodiments of the invention. It is therefore anticipated that each of the limitations of the invention involving any one element or combinations of elements can be included in each aspect of the invention. This invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.
d. Analysis of alternative terpene synthases.
-humulene production.
-humulene by a strain of E. coli engineered to produce it (i.e., pMBIS+pGHS).
E. coli is a valuable platform for the production of terpenoids27-29. The inventors hypothesized that a strain of E. coli programmed to detect the inactivation of a human drug target might enable the rapid discovery and biosynthesis of terpenoids that inhibit that target. To program such a strain, a bacterial two-hybrid (B2H) system was assembled in which a protein tyrosine kinase (PTK) and protein tyrosine phosphatase (PTP) from H. sapiens control gene expression. PTKs are targets of over 30 FDA-approved drugs30; PTPs lack clinically approved inhibitors but contribute to an enormous number of diseases31,32. The first proof-of-concept system was specifically designed to detect inhibitors of protein tyrosine phosphatase 1B (PTP1B), an elusive therapeutic target for the treatment of type 2 diabetes, obesity, and breast cancer (
B2H development was carried out in several steps. To begin, a luminescent “base” system was assembled in which Src modulates the binding of a substrate domain to a substrate homology 2 (SH2) domain; this system was based on a previous design in which protein-protein association controls GOI expression37. The initial system did not yield a phosphorylation-dependent transcriptional response, however, so it was complemented with inducible plasmids—each harboring a different system component—to identify proteins that might exhibit suboptimal activities. Notably, secondary induction of Src increased luminescence, an indication that insufficient substrate phosphorylation depressed GOI expression in the base system (
The B2H system was used to identify new inhibitors of PTP1B by coupling it with metabolic pathways that might generate such molecules in E. coli. Previous screens of plant extracts have identified structurally complex terpenoids that inhibit PTP1B39; pathways were, thus, constructed for several simpler terpenoid scaffolds that lack established inhibitory effects: amorphadiene, γ-humulene, abietadiene, and taxadiene. Abietadiene is a metabolic precursor to a weak inhibitor of PTP1B40; the other three terpenoids represent a structurally diverse set of molecules. Each pathway consisted of two plasmid-borne modules (
Each pathway was screened for its ability to produce inhibitors of PTP1B by transforming E. coli with plasmids harboring both the pathway of interest and the B2H system. GC-MS traces confirmed that all pathways generated terpenoids in the presence of the B2H system (
Microbially-assisted directed evolution (MADE) refers to the approach described herein for using microbial systems to discover and evolve metabolic pathways that produce inhibitors or activators of a therapeutically relevant enzyme target, wherein both the metabolic pathway and the target enzyme exist within a host cell, for example, an E. coli cell (
Previous work demonstrated (i) the assembly of a detection system that links the activities of a protein kinase and a protein phosphatase to antibiotic resistance (
Described herein are strategies, systems, methods, and reagents to expand the scope of capabilities of MADE and to address the needs of previously described evolution experiments. The MADE methods herein utilize one or more of the following: 1) target enzymes that post-translationally modify proteins (PTM enzymes) in a manner other than adding or removing a phosphate group; 2) a metabolic pathway that generates phenylpropanoids or nonribosomal peptides; 3) a cryptic gene cluster that encodes putative natural products; and 4) natural products with specific inhibitory effects.
In some embodiments, provided are methods for using MADE to discover and evolve metabolic pathways that produce inhibitors or activators of PTM enzymes (
In some embodiments, the target PTM enzyme naturally inhibits the growth of a host cell, for example, an S. cerevisiae cell in which a heterologously expressed kinase slows cell growth.
In some embodiments, the PTM enzymes are ubiquitin ligases, SUMO transferases, methyltransferases, demethylases, acetyltransferases, glycosyltransferases, palmitoyltransferases, and/or related hydrolases. In some embodiments, a bacterial two-hybrid (B2H) system links the activity of one or more PTM enzymes to the transcription of a gene of interest (GOI;
In some embodiments, provided are methods for the discovery and evolution of phenylpropanoids or nonribosomal peptides that inhibit or activate a target enzyme, wherein a metabolic pathway that produces phenylpropanoids or nonribosomal peptides is encoded by at least one plasmid or one genome (
In some embodiments, provided are methods for the discovery and evolution of cryptic metabolic pathways that generate inhibitors or activators of a target enzyme, wherein said cryptic metabolic pathways comprise a set of genes with unknown or poorly characterized products, or wherein said cryptic metabolic pathways comprise a set of genes in which one gene hinders the biosynthesis of an important product, wherein subsequent mutagenesis and/or reconfiguration of said pathway causes it to generate more of that product, and wherein MADE enables the discovery of a pathway thus mutated and/or reconfigured. For example, the removal of a biosynthetic gene may enable the accumulation of a metabolic intermediate that modulates the activity of a target enzyme (
In some embodiments, provided are methods for the discovery and evolution of metabolic pathways with higher titers and/or lower toxicities, wherein starting pathways are mutated and/or reconfigured to create a library of pathways, and said library of pathways is screened using MADE to identify pathways that (i) produce higher quantities of inhibitor or activator than the starting pathway and/or (ii) exhibit a lower toxicity than the starting pathway (
Some aspects of this disclosure provide molecules that inhibit protein tyrosine phosphatases (PTPs), for example, protein tyrosine phosphatase 1B (PTP1B;
Also provided are compositions or systems that include a population of host cells that comprise a protein of interest and a population of expression vectors comprising different metabolic pathways, wherein a cell or subset of the population of host cells produce a detectable output when the metabolic pathway produces a product that modulates the protein of interest, and optionally wherein the expression vectors yield detectable outputs higher than the output of a reference vector that harbors a reference pathway, for example, a vector that encodes a pathway that does not produce molecules with concentrations and/or potencies sufficient to modulate the activity of a protein of interest, in the cell or the subset of the population of host cells.
In some embodiments, the host cells comprise a genetically encoded system in which the activity of a protein of interest controls the assembly of a protein complex with an activity that is not possessed by either of two or more components of the complex and, thus, yields a detectable output in proportion to the amount of complex formed. In some embodiments, the protein of interest is an enzyme that adds a post-translational modification that causes two proteins, which are initially dissociated, to be covalently linked or to form a noncovalent complex. In some embodiments, the complex is formed by two proteins with a dissociation constant (Kd) less than or equal to the Kd of the complexes formed between SH2 domains and their phosphorylated substrates.
In some embodiments, the metabolic pathways encoded by the expression vectors produce phenylpropanoids or nonribosomal peptides. In some embodiments, the expression vectors comprising different metabolic pathways comprise a library of pathways generated by mutating one or more genes within a starting metabolic pathway. In some embodiments, one or more of the metabolic pathways comprises a set of genes of unknown biosynthetic capability.
In some embodiments, one or more of the metabolic pathways that produces a detectable output higher than the output of the reference pathway produces a product that differs from the products of other metabolic pathways. In some embodiments, one or more of the metabolic pathways that produces a detectable output higher than the output of the reference pathway produces a larger quantity of a product than the quantity of product generated by other metabolic pathways. In some embodiments, one or more of the metabolic pathways that produces a detectable output higher than the output of the reference pathway exhibits a lower cellular toxicity than other metabolic pathways.
In some embodiments, the protein of interest is a ubiquitin ligase, a SUMO transferase, a methyltransferase, a demethylase, an acetyltransferase, a glycosyltransferase, a palmitoyltransferase, or a related hydrolase.
Also provided herein are kits that include a population of expression vectors as described herein. In some embodiments, the kits also include the population of host cells that comprise a protein of interest as described herein.
The summary above is meant to illustrate, in a non-limiting manner, some of the embodiments, advantages, features, and uses of the technology described herein. Other embodiments, advantages, features, and uses of the technology disclosed herein will be apparent from the Detailed Description, Drawings, Examples, and Claims.
The term “metabolic pathway,” as used herein, refers to a collection of genes that enable the synthesis of metabolite.
The term “metabolite,” as used herein, refers to an organic molecule assembled within a living system.
The term “small molecule,” as used herein, refers to a molecule with a molecular weight less than 900 daltons.
The term “phenylpropanoids,” as used herein, refers to an organic compound synthesized from the amino acids phenylalanine and/or tyrosine.
The term “nonribosomal peptide,” as used herein, refers to peptides synthesized without messenger RNA. For example, peptides synthesized from nonribosomal peptide synthases.
The term “modulator,” as used herein, refers to a molecule, peptide, protein, polynucleotide, or entity that changes the activity of another molecule, peptide, protein, polynucleotide, or entity.
The term “inhibitor,” as used herein, refers to a small molecule that reduces the activity of an enzyme.
The term “activator,” as used herein, refers to a small molecule that increases the activity of an enzyme.
The term “natural product,” as used herein, refers to a chemical compound or substance produced by a living organism.
The term “detection system,” as used herein, refers to a system that links the activity of a target enzyme to a detectable output.
The term “bacterial two-hybrid (B2H) system,” as used herein, refers to a genetically encoded system that links a protein-protein interaction to a detectable output.
The term “detectable output,” as used herein, refers to an output that can be detected with standard analytical instrumentation. Examples include fluorescence, luminescence, antibiotic resistance, or microbial growth.
The term “split protein,” as used herein, refers to a protein that exists as two separate halves, which, upon reassembly, restore the function of the protein.
The term “substrate domain,” as used herein, refers to a protein that includes a peptide fragment or protein component acted upon by a protein of interest. For example, a substrate domain may include the peptide fragment of a receptor protein targeted by a kinase or phosphatase of interest.
The term “vector,” as used herein, refers to a deoxyribonucleic acid (DNA) molecule used as a vehicle to artificially carry foreign genetic material into a cell.
The term “host cell,” as used herein, refers to a cell that can host the genetically encoded systems, on vectors or genomes, necessary for MADE. For example, as host cell may contain plasmids that encode both (i) a genetically encoded detection system that links the activity of a target enzyme to a detectable output and (ii) a metabolic pathway capable of synthesizing molecules that might or might not inhibit said target enzyme.
In previous work, a strain of E. coli was generated with two genetically encoded modules—a B2H system that links the inhibition of PTP1B to the expression of a gene for antibiotic resistance, and a metabolic pathway for the production of amorphadiene—exhibited greater antibiotic resistance that similar strains with different metabolic pathways (
The microbial system provides an interesting opportunity to explore how metabolic pathways evolve to generate functional molecules. To look for evolutionarily accessible changes in the activities ADS and GHS that improve their ability to generate inhibitors of PTP1B, mutants of both enzymes were prepared. For ADS, error-prone PCR and site-saturation mutagenesis of poorly conserved residues was used; for GHS, site-saturation mutagenesis of the wild-type enzyme was paired with a screen of several previously developed mutants with distinct product profiles47 (
The G34S/K51N mutant of ADS, which improved antibiotic resistance more than other mutants, is particularly intriguing because its mutated residues are located outside of the active site and alter neither product profile nor titer (
Intriguingly, the mutants of GHS that conferred enhanced antibiotic resistance (relative to the wild-type enzyme) altered product profile and/or titer (
To expand the study, the survival conferred by terpene synthases that primarily generate β-bisabolene and α-bisabolene was also examined. Both of these enzymes enhanced antibiotic resistance; strikingly, kinetic studies of α-bisabolene purified from culture supernatant indicate that this molecule is particularly potent (i.e., IC50˜20 μM in 10% DMSO;
The results of the analyses of terpene synthases suggest that amorphadiene and derivatives, taxadiene and derivatives, α-longipinene and derivatives, β-bisabolene and derivatives, and α-bisabolene and derivatives, and may provide an important source of pharmaceutically relevant PTP inhibitors.
Bacterial strains. E. coli DH10B, chemically competent NEB Turbo, or electrocompetent One Shot Top10 (Invitrogen) were used to carry out molecular cloning and to perform preliminary analyses of terpenoid production; E. coli BL2-DE31 were used to express proteins for in vitro studies; and E. coli s103048 were used for luminescence studies and for all experiments involving terpenoid-mediated growth (i.e., evolution studies).
For all strains, chemically competent cells were generated by carrying out the following steps: (i) each strain was plated on LB agar plates with the required antibiotics. (ii) One colony of each strain was used to inoculate 1 mL of LB media (25 g/L LB with appropriate antibiotics listed in TABLE 2) in a glass culture tube, and this culture was grew overnight (37° C., 225 RPM). (iii) The 1-mL culture was used to inoculate 100-300 mL of LB media (as above) in a glass shake flask, and this culture was grown for several hours (37° C., 225 RPM). (iv) When the culture reached an OD of 0.3-0.6, the cells were centrifuged (4,000×g for 10 minutes at 4° C.), the supernatant was removed, and the cells were resuspended in 30 mL of ice cold TFB1 buffer (30 mM potassium acetate, 10 mM CaCl2, 50 mM MnCl2, 100 mM RbCl, 15% v/v glycerol, water to 200 mL, pH=5.8, sterile filtered), and the suspension was incubated at 4° C. for 90 min. (v) Step iv was repeated, but resuspended in 4 mL of ice cold TFB2 buffer (10 mM MOPS, 75 mM CaCl2, 10 mM RbCl2, 15% glycerol, water to 50 mL, pH=6.5, sterile filtered). (iv) The final suspension as split into 100 aliquots and frozen at −80° C. until further use.
Electrocompetent cells were generated by following an approach similar to the one above. In step iv, however, the cells were resuspended in 50 mL of ice cold MilliQ water and repeated this step twice—first with 50 mL of 20% sterile glycerol (ice cold) and, then, with 1 mL of 20% sterile glycerol (ice cold). The pellets were frozen as before.
Materials. Methyl abietate was purchased from Santa Cruz Biotechnology; trans-caryophyllene, farnesol, tris(2-carboxyethyl)phosphine (TCEP), bovine serum albumin (BSA), M9 minimal salts, phenylmethylsulfonyl fluoride (PMSF), and DMSO (dimethyl sulfoxide) were purchased from Millipore Sigma; glycerol, bacterial protein extraction reagent II (B-PERII), and lysozyme from were purchased VWR; cloning reagents were purchased from New England Biolabs; amorphadiene was purchased from Ambeed, Inc.; and all other reagents (e.g., antibiotics and media components) were purchased from Thermo Fisher. Taxadiene was a kind gift from Phil Baran of the The Scripps Research Institute. Mevalonate was prepared by mixing 1 volume of 2 M DL-mevalanolactone with 1.05 volumes of 2 M KOH and incubating this mixture at 37° C. for 30 minutes.
Cloning and molecular biology. All plasmids were constructed by using standard methods (i.e., restriction digest and ligation, Golden Gate and Gibson assembly, Quikchange mutagenesis, and circular polymerase extension cloning). TABLE 1 describes the source of each gene; TABLES 2 and 3 describe the composition of all final plasmids.
Construction of the B2H system was begun by integrating the gene for HA4-rpoZ from pAB094a into pAB078d and by replacing the ampicillin resistance marker of pAB078d with a kanamycin resistance marker (Gibson Assembly). The resulting “combined” plasmid was modified, in turn, by replacing the HA4 and SH2 domains with kinase substrate and substrate recognition (i.e., SH2) domains, respectively (Gibson assembly), and by integrating genes for Src kinase, CDC37, and PTP1B in various combinations (Gibson assembly). The functional B2H system was finalized by modifying the SH2 domain with several mutations known to enhance its affinity for phosphopeptides (K15L, T8V, and C10A, numbered as in Kaneko et. al.40), by exchanging the GOI for luminescence (LuxAB) with one for spectinomycin resistance (SpecR), and by toggling promoters and ribosome binding sites to enhance the transcriptional response (Gibson assembly and Quickchange Mutagenesis, Agilent Inc.). Note: For the last step, Prol to ProD was also converted by using the Quikchange protocol. When necessary, plasmids with arabinose-inducible components were constructed by cloning a single component from the B2H system into pBAD (Golden Gate assembly). TABLES 4 and 5 list the primers and DNA fragments used to construct each plasmid.
Pathways for terpenoid biosynthesis were assembled by purchasing plasmids encoding the first module (pMBIS) and sesquiterpene synthases (ADS or GHS in pTRC99a) from Addgene, and by building the remaining plasmids. Genes for ABS, TXS, and GGPPS were integrated into pTRC99t (i.e., pTRC99a without BsaI sites), and a version of pADS was modified by adding a gene for P450BM3 with three mutations that enable the epoxidation of amorphadiene (F87A, R47L, and Y51F; P450G3; Gibson Assembly and Quickchange Mutagenesis)49. TABLE 6 lists the primers and DNA fragments used to construct each plasmid.
Luminescence assays. Preliminary B2H systems (which contained LuxAB as the GOI) were characterized with luminescence assays. In brief, necessary plasmids were transformed into E. coli s1030 (TABLE 2), the transformed cells were plated onto LB agar plates (20 g/L agar, 10 g/L tryptone, 10 g/L sodium chloride, and 5 g/L yeast extract with antibiotics described in TABLE 2), and all plates were incubated overnight at 37° C. Individual colonies were used to inoculate 1 ml of terrific both (TB at 2%, or 12 g/L tryptone, 24 g/L yeast extract, 12 mL/L 100% glycerol, 2.28 g/L KH2PO4, 12.53 g/L K2HPO4, pH=7.0, and antibiotics described in TABLE 2), and we incubated these cultures overnight (37° C. and 225 RPM). The following morning, each culture was diluted by 100-fold into 1 ml of TB media (above), and these cultures were incubated in individual wells of a deep 96-well plate for 5.5 hours (37° C., 225 RPM). (Note: When pBAD was present, the TB media was supplemented with 0-0.02 w/v % arabinose). An amount of 100 μL of each culture was transferred into a single well of a standard 96-well plate and measured both OD600 and luminescence (gain: 135, integration time: 1 second, read height: 1 mm) on a Biotek Synergy plate reader. Analogous measurements of cell-free media were performed to measure background signals, which were subtracted from each measurement prior to calculating OD-normalized luminescence (i.e., Lum/OD600).
Analysis of antibiotic resistance. The spectinomycin resistance conferred by various B2H systems in the absence of terpenoid pathways was evaluated by carrying out the following steps: (i) E. coli were transformed with the necessary plasmids (TABLE 2) and the transformed cells were plated onto LB agar plates (20 g/L agar, 10 g/L tryptone, 10 g/L sodium chloride, 5 g/L yeast extract, 50 μg/ml kanamycin, 10 μg/ml tetracycline). (ii) Individual colonies were used to inoculate 1-2 ml of TB media (12 g/L tryptone, 24 g/L yeast extract, 12 mL/L 100% glycerol, 2.28 g/L KH2PO4, 12.53 g/L K2HPO4, 50 μg/ml kanamycin, 10 μg/ml tetracycline, pH=7.0), and these cultures were incubated overnight (37° C., 225 RPM). In the morning, each culture was diluted by 100-fold into 4 ml of TB media (as above) with 0-500 μg/ml spectinomycin (spectinomycin was used only for the results depicted in
To examine terpenoid-mediated resistance, steps i and ii were performed as described above with the addition of 34 μg/ml chloramphenicol and 50 μg/ml carbenicillin in all liquid/solid media. The experiment then proceeded with the following steps: (iii) Samples were diluted from 1-ml cultures to an OD600 of 0.05 in 4.5 ml of TB media (supplemented with 12 g/L tryptone, 24 g/L yeast extract, 12 mL/L 100% glycerol, 2.28 g/L KH2PO4, 12.53 g/L K2HPO4, 50 μg/ml kanamycin, 10 μg/ml tetracycline, 34 μg/ml chloramphenicol, and 50 μg/ml carbenicillin), which were incubated in deep 24-well plates (37° C., 225 RPM). (iv) At an OD600 of 0.3-0.6, 4 ml of each culture was transferred to a new well of a deep 24-well plate, 500 μM isopropyl β-D-1-thiogalactopyranoside (IPTG) and 20 mM of mevalonate was added, and incubated for 20 hours (22° C., 225 RPM). (v) Each 4-ml culture was diluted to an OD600 of 0.1 with TB media and plated 10 μL of the diluent onto either LB or TB plates supplemented with 500 μM IPTG, 20 mM mevalonate, 50 μg/ml kanamycin, 10 μg/ml tetracycline, 34 μg/ml chloramphenicol, 50 μg/ml carbenicillin, and 0-1200 μg/ml spectinomycin (for both plates, 20 g/L agar was used with media and buffer components described above). Note: to control the range of antibiotic resistance, LB plates were used for ADS and its mutants, and TB plates, which improve terpenoid titers, were used for GHS and its mutants. (iv) All plates were incubated at 30° C. and photographed after 2 days.
Terpenoid biosynthesis. E. coli were prepared for terpenoid production by transforming cells with plasmids harboring requisite pathway components (TABLE 2) and plating them onto LB agar plates (20 g/L agar, 10 g/L tryptone, 10 g/L sodium chloride, and 5 g/L yeast extract with antibiotics described in TABLE 2). One colony from each strain was used to inoculate 2 ml TB (12 g/L tryptone, 24 g/L yeast extract, 12 mL/L 100% glycerol, 2.28 g/L KH2PO4, 12.53 g/L K2HPO4, pH=7.0, and antibiotics described in TABLE 2) in a glass culture tube for ˜16 hours (37° C. and 225 RPM). These cultures were diluted by 75-fold into 10 ml of TB media and the new cultures were incubated in 125 mL glass shake flasks (37° C. and 225 RPM). At an OD600 of 0.3-0.6, 500 μM IPTG and 20 mM mevalonate were added. After 72-88 hours of growth (22° C. and 225 RPM), terpenoids were extracted from each culture.
To measure terpenoid production over time, the approach described above was used with the following modifications: (i) Overnight cultures were diluted with 1:75 mL in 4.5 mL TB supplemented with antibiotics in a glass culture tube. (ii) When cultures reached an OD600 of 0.3-0.6, 4 mL of each culture were moved to a new culture tube and 500 μM IPTG, 20 mM mevalonate, 0-800 μg/mL spectinomycin, and 1 mL dodecane were added (to extract terpenoids). Every 4 hours, 100 μL of the dodecane sample was removed for GC/MS analysis.
Protein expression and purification. PTPs were expressed and purified as described previously42. Briefly, E. coli BL21(DE3) cells were transformed with pET21b vectors, and induced with 500 μM IPTG at 22° C. for 20 hours. PTPs were purified from cell lysate by using desalting, nickel affinity, and anion exchange chromatography (HiPrep 26/10, HisTrap HP, and HiPrep Q HP, respectively; GE Healthcare). The final protein (30-50 μM) was stored in HEPES buffer (50 mM, pH 7.5, 0.5 mM TCEP) in 20% glycerol at −80° C.
Extraction and purification of terpenoids. Hexane was used to extract terpenoids generated in liquid culture. For 10-mL cultures, 14 mL of hexane was added to 10 ml of culture broth in 125-mL glass shake flasks, the mixture (100 RPM) shaken for 30 minutes, centrifuged (4000×g), and 10 mL of the hexane layer was withdrawn for further analysis. For 4-mL cultures, 600 μL hexane were added to 1 mL of culture broth in a microcentrifuge tube, the tubes were vortexed for 3 minutes, the tubes were centrifuged for 1 minute (17000×g), and 300-400 μL of the hexane layer was saved for further analysis.
To purify amorphadiene, 500-1000 mL culture broth was supplemented with hexane (16.7% v/v), the mixture was shaken for 30 minutes (100 RPM), the hexane layer was isolated with a separatory funnel, the isolated organic phase was centrifuged (4000×g), and the hexane layer withdrawn. To concentrate the terpenoid products, excess hexane was evaporated in a rotary evaporator to bring the final volume to 500 μL, and the resulting mixture was passed over a silica gel one or two times (Sigma-Aldrich; high purity grade, 60 Å pore size, 230-400 mesh particle size)). Elution fractions (100% hexane) were analyzed on the GC/MS and pooled fractions with the compound of interest (amorphadiene). Once purified, pooled fractions were dried under a gentle stream of air, the terpenoid solids were resuspended in DMSO, and the final samples were quantified as outlined below.
GC-MS analysis of terpenoids. Terpenoids generated in liquid culture were measured with a gas chromatograph/mass spectrometer (GC-MS; a Trace 1310 GC fitted with a TG5-SilMS column and an ISQ 7000 MS; Thermo Fisher Scientific). All samples were prepared in hexane (directly or through a 1:100 dilution of DMSO) with 20 μg/ml of caryophyllene or methyl abietate as an internal standard. When the peak area of an internal standard exceeded ±30% of the average area in hexane samples containing only standard, the corresponding samples were re-analyzed. For all runs, the following GC method was used: hold at 80° C. (3 min), increase to 250° C. (15° C./min), hold at 250° C. (6 min), increase to 280° C. (30° C./min), and hold at 280° C. (3 min). To identify various analytes, m/z ratios were scanned from 50 to 550.
Sesquiterpenes generated by variants of ADS were examined by using select ion mode (SIM) to scan for the molecular ion (m/z=204). For quantification, we used Eq. 1:
where Ai is the area of the peak produced by analyte i, Astd is the area of the peak produced by Cstd of caryophyllene in the sample, and R is the ratio of response factors for caryophyllene and amorphadiene in a reference sample.
Sesquiterpenes generated by variants of GHS were quantified by using the aforementioned procedure with several modifications: Methyl abietate was used as an internal standard (several mutants of GHS generate caryophyllene as a product); both m/z=204 and m/z=121, a common ion between sesquiterpenes and methyl abietate were scanned for; a ratio of response factors for amorphadiene and methyl abietate at m/z=121 for R was used; and peak areas were calculated at m/z=121. For all analyses, the analysis was focused on peaks with areas that exceeded 1% of the total area of all peaks at m/z=204.
Diterpenoids were quantified by, once again, accompanying the general procedure with several modifications: A different molecular ion (m/z=272) and an ion common to both diterpenoids and caryophyllene (m/z=93) was scanned for; a ratio of response factors for pure taxadiene (a kind gift from Phil Baran) and caryophyllene at m/z=93 was used; and peak areas m/z=93 were calculated. For all analyses, only peaks with areas that exceeded 1% of the total area of all peaks at m/z=272 were examined.
Molecules were identified by using the NIST MS library and, when necessary, this identification was confirmed with analytical standards or mass spectra reported in the literature. Note: The assumption of a constant response factor for different terpenoids (e.g., all sesquiterpenes and diterpenes ionize like amorphadiene and taxadiene, respectively) can certainly yield error in estimates of their concentrations; the analyses described herein, which are consistent with those of other studies of terpenoid production in microbial systems50,51, thus supply rough estimates of concentrations for all compounds except amorphadiene and taxadiene (which had analytical standards).
Homology modeling of ADS and GHS. Homology models of ADS and GHS were constructed by using SWISS-MODEL with structures for α-bisabolol synthase (pdb entry 4gax) and α-bisabolene synthase (pdb entry 3sae) as templates, respectively52. This software package uses ProMod3 to build models from a target-template alignment, which preserves the structures of conserved regions and remodels insertions and deletions with a fragment library53,54.
Preparation of mutant libraries. Libraries of enzyme mutants were prepared by using site-saturation mutagenesis (SSM) and error-prone PCR (ePCR). For SSM, the following steps were performed: (i) Genes were amplified with NNK primers that targeted select sites. (ii) The amplified genes were digested with DpnI, purified with gel electrophoresis, and either Gibson Assembly or circular polymerase extension cloning (CPEC)55 was used to integrate them into plasmids (pTSxx). (iii) Heat shock was used to transform the fully assembled plasmids into chemically competent NEB Turbo cells. (iv) Library size was determined by plating dilutions of the transformation reactions on several LB agar plates (20 g/L agar, 10 g/L tryptone, 10 g/L sodium chloride, 5 g/L yeast extract, 50 μg/ml carbenicillin), and all remaining cells were plated over 9-10 plates for subsequent analysis. (v) Colonies were sequenced to verify that at least 5 of 6 transformants contained mutated genes. (vi) Plates were scraped into LB media (25 g/L LB broth mix, no antibiotics) and the final transformants were miniprepped to recover the DNA Library. (vii) All final libraries were frozen in MilliQ water at −20° C.
For ePCR, the Genemorph II kit (Agilent) was used with ˜0.5-2.5 mutations/kb. The final plasmids were dialyzed and electroporated into One Shot electrocompetent Top 10 cells, and the final plasmids were sequenced, extracted, and stored as described above.
Analysis of mutant libraries. Each mutant library was screened by carrying out the following steps: (i) 100 ng of each site-specific SSM library for a given terpene synthase was pooled. (ii) Each complete library (i.e., ePCR or pooled SSM) was dialyzed for 2 hours. (iii) Up to 10 μL (<1 μg) of each library was electroporated into a strain of E. coli harboring both the pMBIS pathway and the B2H system. (iv) 1 mL of SOC was added to the transformed cells and incubated for 1 hour (37° C. and 225 RPM). (v) 100 μL of the SOC outgrowth was serial diluted and plated onto LB agar plates (20 g/L agar, 10 g/L tryptone, 10 g/L sodium chloride, 5 g/L yeast extract, 50 μg/ml carbenicillin, 10 μg/ml tetracycline, 50 μg/ml kanamycin, and 34 μg/ml chloramphenicol) and the plates were incubated overnight (37° C.). This step allowed for quantification of the number of transformants screened (i.e., a number determined by counting colonies). (vi) The remaining 900 μL of transformed cells was added to 100 mL of TB (12 g/L tryptone, 24 g/L yeast extract, 12 mL/L 100% glycerol, 2.28 g/L KH2PO4, 12.53 g/L K2HPO4, 50 μg/ml carbenicillin, 10 μg/ml tetracycline, 34 μg/ml chloramphenicol, 50 μg/ml kanamaycin, pH=7.0) in 500-mL Erlenmeyer flasks, and these flasks were incubated overnight (37° C. and 225 RPM). (vii) In the morning, an aliquot of each culture was diluted to an OD600 of 0.05 in 4 mL of TB and incubated in glass culture tubes (37° C. and 225 RPM). (viii) At an OD600 of 0.3-0.6, terpenoid production was induced by adding 5-20 mM mevalonate and 500 μM IPTG, and the resulting cultures were incubated for 20 hours (22° C. and 225 RPM). (ix) Each culture was diluted to an OD600 of 0.001 and 100 μL of diluent was plated onto agar plates containing 500 μM IPTG, 5-20 mM mevalonate, 50 μg/ml kanamycin, 10 μg/ml tetracycline, 34 μg/ml chloramphenicol, 50 μg/ml carbenicillin, and 0-1000 μg/ml spectinomycin. (x) Colonies that survived high concentrations of spectinomycin were used to inoculate 4 mL of LB media (25 g/L LB broth mix, 50 μg/ml carbenicillin, 10 μg/ml tetracycline, 34 μg/ml chloramphenicol, 50 μg/ml kanamaycin, which was incubated overnight (37° C., 225 RPM). (xi) Plasmid DNA was extracted from the overnight culture for Sanger sequencing.
The influence of interesting mutations—and a check for false positive—were confirmed by rescreening them in freshly prepared mutants. Site directed mutagenesis was used to introduce mutations found in the hits and then their antibiotic resistance was analyzed using the drop-based plating method described above.
Enzyme kinetics. To examine terpenoid-mediated inhibition, PTP1B-catalyzed hydrolysis of p-nitrophenyl phosphate (pNPP) was measured in the presence of various concentrations of terpenoids. Each reaction included PTP1B (0.05 μM), pNPP (0.33, 0.67, 2, 5, 10, and 15 mM), inhibitors (110 μM, 50 μM, and 15 μM for amorphadiene; 100 μM, 50 μM, and 16.7 μM for taxadiene), and buffer (50 mM HEPES pH=7.5, 0.5 mM TCEP, 50 μg/ml BSA, 10% DMSO). The formation of p-nitrophenol was monitored by measuring absorbance at 405 nm every 10 seconds for 5 minutes on a Spectramax M2 plate reader.
Kinetic models were evaluated in three steps: (i) Initial-rate measurements collected in the absence and presence of inhibitors were fitted to Michaelis-Menten and inhibition models, respectively (here, the nlinfit and fminsearch functions from MATLAB were used). (ii) An F-test was used to compare the mixed model to the single-parameter model with the least sum squared error (here, the fcdf function from MATLAB was used to assign p-values), and the mixed model was accepted when p<0.05. (iii) The Akaike's Information Criterion (AIC) was used to compare the best-fit single parameter model to each alternative single parameter model, and the “best-fit” model was accepted when the difference in AIC (Δi) exceed 10 for all comparisons.56 Note: For amorphadiene, this criterion was not met; both noncompetitive and uncompetitive models, however, yielded indistinguishable IC50's.
The half maximal inhibitory concentration (IC50) of inhibitors were estimated by using the best-fit kinetic models to determine the concentration of inhibitor required to reduce initial rates of PTP-catalyzed hydrolysis of 15 mM of pNPP by 50%. The MATLAB function “nlparci” was used to determine the confidence intervals of kinetic parameters, and those intervals were propagated to estimate corresponding confidence on IC50's.
The design of small molecules that inhibit disease-relevant proteins represents a longstanding challenge of medicinal chemistry. Here, we describe an approach for encoding this challenge—the inhibition of a human drug target—into a microbial host and using it to guide the discovery and biosynthesis of targeted, biologically active natural products. This approach identified two previously unknown terpenoid inhibitors of protein tyrosine phosphatase 1B (PTP1B), an elusive therapeutic target for the treatment of diabetes and cancer. At least one inhibitor targets an allosteric site, which confers unusual selectivity; both can inhibit PTP1B in living cells. A screen of 24 uncharacterized terpene synthases from a pool of 4,464 genes uncovered additional hits, demonstrating a scalable discovery approach, and the incorporation of different PTPs into the microbial host yielded PTP-specific detection systems. Findings illustrate the potential for using microbes to discover and build natural products that exhibit precisely defined biochemical activities yet possess unanticipated structures and/or binding sites.
Despite advances in structural biology and computational chemistry, the design of small molecules that bind tightly and selectively to disease-relevant proteins remains exceptionally difficult1. The free energetic contributions of rearrangements in the molecules of water that solvate binding partners and structural changes in the binding partners themselves are particularly challenging to predict and, thus, to incorporate into molecular design2,3. Drug development, as a result, often begins with screens of large compound libraries4.
Nature has endowed living systems with the catalytic machinery to build an enormous variety of biologically active molecules—a diverse natural library5. These molecules evolved to carry out important metabolic and ecological functions (e.g., the phytochemical recruitment of predators of herbivorous insects6) but often also exhibit useful medicinal properties. Over the years, screens of environmental extracts and natural product libraries—augmented, on occasion, with combinatorial (bio)chemistry7-9—have uncovered a diverse set of therapeutics, from aspirin to paclitaxel10. Unfortunately, these screens tend to be resource intensive11, limited by low natural titers12, and largely subject to serendipity13. Bioinformatic tools, in turn, have permitted the identification of biosynthetic gene clusters14,15, where co-localized resistance genes can reveal the biochemical function of their products16,17. The therapeutic applications of many natural products, however, differ from their native functions18, and many biosynthetic pathways can, when appropriately reconfigured, produce entirely new and, perhaps, more effective therapeutic molecules19,20. Methods for efficiently identifying and building natural products that inhibit specific disease-relevant proteins remain largely undeveloped.
Protein tyrosine phosphatases (PTPs) are an important class of drug targets that could benefit from new approaches to inhibitor discovery. These enzymes catalyze the hydrolytic dephosphorylation of tyrosine residues and, together with protein tyrosine kinases (PTKs), contribute to an enormous number of diseases (e.g., cancer, autoimmune disorders, and heart disease, to name a few)21,22. The last several decades have witnessed the construction of many potent inhibitors of PTKs, which are targets for over 30 approved drugs23. Therapeutic inhibitors of PTPs, by contrast, have proven difficult to develop. These enzymes possess well conserved, positively charged active sites that make them difficult to inhibit with selective, membrane-permeable molecules24; they lack targeted therapeutics of any kind.
In this study, we describe an approach for using microbial systems to find natural products that inhibit difficult-to-drug proteins. We focused on protein tyrosine phosphatase 1B (PTP1B), a therapeutic target for the treatment of type 2 diabetes, obesity, and HER2-positive breast cancer25. PTP1B possesses structural characteristics that are generally representative of the PTP family26 and regulates a diverse set of physiological processes (e.g., energy expenditure27, inflammation28, and neural specification in embryonic stem cells29). In brief, we assembled a strain of Escherichia coli with two genetic modules—(i) one that links cell survival to the inhibition of PTP1B and (ii) one that enables the biosynthesis of structurally varied terpenoids. In a study of five well-characterized terpene synthases, this strain identified two previously unknown terpenoid inhibitors of PTP1B. Both inhibitors were selective for PTP1B, exhibited distinct binding mechanisms, and increased insulin receptor phosphorylation in mammalian cells. A screen of 24 uncharacterized terpene synthases from eight phylogenetically diverse clades uncovered additional hits, demonstrating a scalable approach for finding inhibitor-synthesizing genes. A simple exchange of PTP genes, in turn, permitted the facile extension of our genetically encoded detection system to new targets. Our findings illustrate a versatile approach for using microbial systems to find targeted, readily synthesizable inhibitors of disease-relevant enzymes.
E. coli is a versatile platform for building natural products from unculturable or low-yielding organisms30,31. We hypothesized that a strain of E. coli programmed to detect the inactivation of PTP1B (i.e., a genetically encoded objective) might enable the discovery of natural products that inhibit it (i.e., molecular solutions to the objective). To program such a strain, we assembled a bacterial two-hybrid (B2H) system in which PTP1B and Src kinase control gene expression (
We carried out B2H development in several steps. To begin, we assembled a luminescent “base” system in which Src modulates the binding of a substrate domain to an Src homology 2 (SH2) domain (
To search for inhibitors of PTP1B that bind outside of its active site, we coupled the B2H system with metabolic pathways for terpenoids, a structurally diverse class of secondary metabolites with largely nonpolar structures (-humulene, α-bisabolene (AB), abietadiene, and taxadiene. Each terpenoid pathway consisted of two plasmid-borne modules: (i) the mevalonate-dependent isoprenoid pathway from S. cerevisiae (optimized for expression in E. coli40) and (ii) a terpene synthase previously demonstrated to express and produce one of the five selected terpenoids in E. coli40-41. The terpene synthase was supplemented, when necessary for diterpenoid production, with a geranylgeranyl diphosphate synthase. These modules generated terpenoids at titers of 0.3-18 mg/L in E. coli (
We screened each pathway for its ability to produce inhibitors of PTP1B by transforming E. coli with plasmids harboring both the pathway of interest and the B2H system (
We confirmed the inhibitory effects of purified terpenoids by examining their influence on PTP1B-catalyzed hydrolysis of p-nitrophenyl phosphate (pNPP;
Allosteric inhibitors of PTPs are valuable starting points for drug development. These molecules bind outside of the well conserved, positively charged active sites of PTPs and tend to have improved selectivities and membrane permeabilities over substrate analogs21. Motivated by these considerations, an early screen identified a benzbromarone derivative that inhibited PTP1B weakly (IC50=350 μM) without competing with substrates; subsequent optimization of this compound led to two improved inhibitors (IC50's=8 and 22 μM) that bind to an allosteric site45 (
Our microbial system could grant access to new compounds that bind in unexpected ways. AD and AB provide examples. They are highly nonpolar and, thus, incapable of engaging in the hydrogen bonds and electrostatic interactions on which most other PTP inhibitors rely21,45. To examine their binding mechanisms in detail, we sought to collect X-ray crystal structures of PTP1B bound to AD and α-bisabolol, a soluble analogue of AB (a ligand for which poor solubility precluded soaking experiments). Unfortunately, only the structure of PTP1B bound to AD was sufficient for unambiguous determination of a binding site (
We probed the binding of AD and AB further with several additional analyses. First, we examined the inhibition of PTP1B by dihydroartemisinic acid. This structural analogue of AD has a carboxyl group that, according to our crystal structure, should interfere with binding to the hydrophobic cleft created by the α7 helix (
AD and AB are lipophilic molecules that could be valuable for their ability to pass through the membranes of mammalian cells. To examine the biological activity of these molecules, we incubated them with HEK293T/17 cells and used an enzyme-linked immunosorbent assay to measure shifts in insulin receptor (IR) phosphorylation. IR is a receptor tyrosine kinase that undergoes PTP1B-mediated dephosphorylation from the cytosolic side of the plasma membrane (PTP1B, in turn, localizes to the endoplasmic reticulum of the cell). Both molecules increased IR phosphorylation over a negative control (
Other PTPs can promote IR dephosphorylation; SHP1 and SHP2 provide two examples51-53. To examine the potential contribution of these enzymes to the increase in IR phosphorylation observed in our ELISA, we measured their inhibition by AD and AB. Briefly, AD inhibited SHP2 three-fold less potently than PTP1B, and its inhibition of SHP1 was too weak to measure (
Our microbial strain provides a powerful tool for screening genes for their ability to generate novel PTP1B inhibitors. Most terpenoids, as a case study, are not commercially available, and even when their metabolic pathways are known, their biosynthesis, purification, and in vitro analysis is a resource-intensive process that is difficult to parallelize with existing methods54. Our B2H system offers a potential solution: It can identify inhibitor-synthesizing genes with a simple growth-coupled assay. We explored its application to discovery efforts by using it to screen a diverse set of uncharacterized biosynthetic genes. In brief, we carried out a bioinformatic analysis of the largest terpene synthase family (PF03936) by building and annotating a cladogram of its 4,464 constituent members (
Guided by our initial screen, we searched for sesquiterpene inhibitors by pairing each of the uncharacterized genes with the FPP pathway. To our surprise, six genes conferred a significant survival advantage (
We explored the versatility of our B2H system by assessing its ability to detect the inactivation of several other diseases-relevant PTPs. In short, we swapped out the gene for PTP1B with genes for PTPN2, PTPN6, or PTPN12; these enzymes are targets for immunotherapeutic enhancement55, the treatment of ovarian cancer56, and acute myocardial infarction57, respectively. Their catalytic domains share 31-65% sequence identity with the catalytic domain of PTP1B. Interestingly, the new B2H systems were immediately functional; PTP inactivation permitted growth at high concentrations of spectinomycin (
PTP-specific B2H systems could facilitate the identification of natural products that selectively inhibit one PTP over another. We explored this application by comparing the antibiotic resistance conferred by PTP1B- and TC-PTP-specific systems in response to metabolic pathways for AD and α-bisabolene (
This study addresses an important challenge of medicinal chemistry—the design of molecular structures that inhibit disease-relevant enzymes—by using a desired biochemical activity (i.e., an objective) as a genetically encoded constraint to guide molecular biosynthesis. This approach enabled the identification of two selective, biologically active inhibitors of PTP1B, an elusive drug target58. These molecules are not drugs, but they are promising scaffolds for lead development. Their mechanisms of modulation—which elicit allosteric conformational changes yet appear to rely on loose, conformationally flexible binding—are unusual (and computationally elusive59), and demonstrate the ability of microbial systems to find new solutions to difficult challenges in molecular design. Our identification of unusual inhibitors in relatively small libraries, in turn, suggests that microbial systems can access a rich molecular landscape that is not efficiently explored by existing approaches to molecular discovery.
The B2H system at the core of our approach is a valuable tool for identifying biologically active natural products, which are structurally complex, difficult to synthesize, and often hidden in cryptic gene clusters60. It has several key advantages over contemporary approaches to inhibitor discovery: (i) It incorporates synthesizability as a search criterion—an important attribute of drug leads61. (ii) It is scalable. We used a growth-coupled assay to screen 24 uncharacterized terpene synthases; this type of assay is also compatible with very large mutagenesis libraries (e.g., 1010)62. (iii) It can use cellular machinery to stabilize proteins (e.g., CDC37 for Src); this capability could facilitate the integration of unstable and/or disordered targets. Future efforts to exploit these advantages by incorporating large libraries of mutated and/or reconfigured pathways, alternative biosynthetic enzymes (e.g., cytochromes P450, halogenases, and methyltransferases), or new classes of disease-relevant enzymes would be informative.
The B2H system also has important limits. When used alongside metabolic pathways, it links survival not only to the potency of metabolites, but also to their titers, off-target effects, and pathway toxicities. These limitations can be beneficial; they bias the discovery process toward potent, readily synthesizable inhibitors and could, thus, facilitate post-discovery efforts to improve the titers of interesting molecules63. Nonetheless, they will exclude some types of structurally complex molecules that are difficult to synthesize in E. coli. The use of similar activity-based screens in other organisms (e.g., Streptomyces) could be interesting.
The compatibility of our discovery approach with different PTPs is valuable in light of their increasingly well validated potential as a rich—and essentially untapped—source of new therapeutic targets64. We anticipate that some PTPs will require the use of chaperones and/or transcriptional adjustments to be incorporated into B2H systems. Our systematic optimization of the PTP1B-based system provides an experimental framework for exploring these modifications. Side-by-side comparisons of B2H systems, in turn, offer a promising strategy for evaluating inhibitor selectivity in secondary screens. In future work, new varieties of objectives (e.g., B2H systems or genetic circuits that detect the selective inhibition—or, perhaps, activation—of one PTP over another) could facilitate the discovery of molecules with sophisticated mechanisms of modulation in primary screens. The versatility of genetically encoded objectives highlights the power of using microbial systems to find targeted, biologically active molecules.
Note 1: The orthogonality of proteomes. E. coli and S. cerevisiae are both well-developed platforms for the production of pharmaceutically relevant natural products20,65,66. We chose to use E. coli for this study because its machinery for phosphorylating proteins is dissimilar from that of eukaryotic cells and thus less likely to interfere with the function of genetically encoded systems that link the inhibition of PTP1B to cellular growth67. By contrast, the overexpression of Src kinase in S. cerevisiae is lethal and is mitigated by PTP1B68; these effects are inconsistent with our biochemical objective. More broadly, S. cerevisiae and humans, despite having evolved from a common ancestor approximately 1 billion years ago69, share many functionally equivalent proteins; orthologous genes, in fact, account for more than one-third of the yeast genome70. Most strikingly, a recent study found that nearly half (47%) of 414 essential genes from S. cerevisiae could be replaced with human orthologs without growth defects71. This finding suggests that yeast is a particularly restrictive host for genetically encoded systems that link arbitrary changes in the activities of human regulatory enzymes to fitness advantage.
Bacterial strains. We used E. coli DH10B, chemically competent NEB Turbo, or electrocompetent One Shot Top10 (Invitrogen) to carry out molecular cloning and to perform preliminary analyses of terpenoid production; we used E. coli BL2-DE31 to express proteins for in vitro studies; and we used E. coli s103072 for our luminescence studies and for all experiments involving terpenoid-mediated growth (i.e., evolution studies).
For all strains, we generated chemically competent cells by carrying out the following steps: (i) We plated each strain on LB agar plates with the required antibiotics. (ii) We used one colony of each strain to inoculate 1 mL of LB media (25 g/L LB with appropriate antibiotics listed in TABLE 8) in a glass culture tube, and we grew this culture overnight (37° C., 225 RPM). (iii) We used the 1-mL culture to inoculate 100-300 mL of LB media (as above) in a glass shake flask, and we grew this culture for several hours (37° C., 225 RPM). (iv) When the culture reached an OD of 0.3-0.6, we centrifuged the cells (4,000×g for 10 minutes at 4° C.), removed the supernatant, resuspended them in 30 mL of ice cold TFB1 buffer (30 mM potassium acetate, 10 mM CaCl2, 50 mM MnCl2, 100 mM RbCl, 15% v/v glycerol, water to 200 mL, pH=5.8, sterile filtered), and incubated the suspension at 4° C. for 90 min. (v) We repeated step iv, but resuspended in 4 mL of ice cold TFB2 buffer (10 mM MOPS, 75 mM CaCl2, 10 mM RbCl2, 15% glycerol, water to 50 mL, pH=6.5, sterile filtered). (iv) We split the final suspension into 100 μL aliquots and froze them at −80° C. until further use.
We generated electrocompetent cells by following an approach similar to the one above. In step iv, however, we resuspended the cells in 50 mL of ice cold MilliQ water and repeated this step twice—first with 50 mL of 20% sterile glycerol (ice cold) and, then, with 1 mL of 20% sterile glycerol (ice cold). We froze the pellets as before.
Materials. We purchased methyl abietate from Santa Cruz Biotechnology; trans-caryophyllene, tris(2-carboxyethyl)phosphine (TCEP), bovine serum albumin (BSA), M9 minimal salts, phenylmethylsulfonyl fluoride (PMSF), and DMSO (dimethyl sulfoxide) from Millipore Sigma; glycerol, bacterial protein extraction reagent II (B-PERII), and lysozyme from VWR; cloning reagents from New England Biolabs; AD from Ambeed, Inc.; and all other reagents (e.g., antibiotics and media components) from Thermo Fisher. Taxadiene was a kind gift from Phil Baran of the The Scripps Research Institute. We prepared mevalonate by mixing 1 volume of 2 M DL-mevalanolactone with 1.05 volumes of 2 M KOH and incubating this mixture at 37° C. for 30 minutes.
Cloning and molecular biology. We constructed all plasmids by using standard methods (i.e., restriction digest and ligation, Golden Gate and Gibson assembly, Quikchange mutagenesis, and circular polymerase extension cloning). TABLE 7 describes the source of each gene; TABLE 8 and TABLE 3 describe the composition of all final plasmids.
We began construction of the B2H system by integrating the gene for HA4-RpoZ from pAB094a into pAB078d and by replacing the ampicillin resistance marker of pAB078d with a kanamycin resistance marker (Gibson Assembly). We modified the resulting “combined” plasmid, in turn, by replacing the HA4 and SH2 domains with kinase substrate and substrate recognition (i.e., SH2) domains, respectively (Gibson assembly), and by integrating genes for Src kinase, CDC37, and PTP1B in various combinations (Gibson assembly). We finalized the functional B2H system by modifying the SH2 domain with several mutations known to enhance its affinity for phosphopeptides (K15L, T8V, and C10A, numbered as in Kaneko et. al.35), by exchanging the GOI for luminescence (LuxAB) with one for spectinomycin resistance (SpecR), and by toggling promoters and ribosome binding sites to enhance the transcriptional response (Gibson assembly and Quickchange Mutagenesis, Agilent Inc.). We note: For the last step, we also converted Prol to ProD by using the Quikchange protocol. When necessary, we constructed plasmids with arabinose-inducible components by cloning a single component from the B2H system into pBAD (Golden Gate assembly). TABLE 4, TABLE 9, and TABLE 10 list the primers and DNA fragments used to construct each plasmid.
We assembled pathways for terpenoid biosynthesis by purchasing plasmids encoding the first module (pMBIS) and various sesquiterpene synthases (ADS or GHS in pTRC99a) from Addgene, and by building the remaining plasmids. We replaced the tetracycline resistance in pMBIS with a gene for chloramphenicol resistance to create pMBISCmR. We integrated genes for ABS, TXS, ABA, and GGPPS into pTRC99t (i.e., pTRC99a without BsaI sites). TABLE 4, TABLE 9, and TABLE 10 list the primers and DNA fragments used to construct each plasmid.
Luminescence assays. We characterized preliminary B2H systems (which contained LuxAB as the GOI) with luminescence assays. In brief, we transformed necessary plasmids into E. coli s1030 (TABLE 8), plated the transformed cells onto LB agar plates (20 g/L agar, 10 g/L tryptone, 10 g/L sodium chloride, and 5 g/L yeast extract with antibiotics described in TABLE 8), and incubated all plates overnight at 37° C. We used individual colonies to inoculate 1 ml of terrific both (TB at 2%, or 12 g/L tryptone, 24 g/L yeast extract, 12 mL/L 100% glycerol, 2.28 g/L KH2PO4, 12.53 g/L K2HPO4, pH=7.3, and antibiotics described in TABLE 8), and we incubated these cultures overnight (37° C. and 225 RPM). The following morning, we diluted each culture by 100-fold into 1 ml of TB media (above), and we incubated these cultures in individual wells of a deep 96-well plate for 5.5 hours (37° C., 225 RPM). (We note: When pBAD was present, we supplemented the TB media with 0-0.02 w/v % arabinose). We transferred 100 μL of each culture into a single well of a standard 96-well clear plate and measured both OD600 and luminescence on a Biotek Synergy plate reader (gain: 135, integration time: 1 second, read height: 1 mm). Analogous measurements of cell-free media allowed us to measure background signals, which we subtracted from each measurement prior to calculating OD-normalized luminescence (i.e., Lum/OD600).
Analysis of antibiotic resistance. We evaluated the spectinomycin resistance conferred by various B2H systems in the absence of terpenoid pathways by carrying out the following steps: (i) We transformed E. coli with the necessary plasmids (TABLE 8) and plated the transformed cells onto LB agar plates (20 g/L agar, 10 g/L tryptone, 10 g/L sodium chloride, 5 g/L yeast extract, 50 μg/ml kanamycin, 10 μg/ml tetracycline). (ii) We used individual colonies to inoculate 1-2 ml of TB media (12 g/L tryptone, 24 g/L yeast extract, 12 mL/L 100% glycerol, 2.28 g/L KH2PO4, 12.53 g/L K2HPO4, 50 μg/ml kanamycin, 10 μg/ml tetracycline, pH=7.3), and we incubated these cultures overnight (37° C., 225 RPM). In the morning, we diluted each culture by 100-fold into 4 ml of TB media (as above) with 0-500 μg/ml spectinomycin (we used spectinomycin in the liquid culture only for
To examine terpenoid-mediated resistance, we began with steps i and ii as described above with the addition of 34 μg/ml chloramphenicol and 50 μg/ml carbenicillin in all liquid/solid media. We then proceeded with the following steps: (iii) We diluted samples from 1-ml cultures to an OD600 of 0.05 in 4.5 ml of TB media (supplemented with 12 g/L tryptone, 24 g/L yeast extract, 12 mL/L 100% glycerol, 2.28 g/L KH2PO4, 12.53 g/L K2HPO4, 50 μg/ml kanamycin, 10 μg/ml tetracycline, 34 μg/ml chloramphenicol, and 50 μg/ml carbenicillin), which we incubated in deep 24-well plates (37° C., 225 RPM). (iv) At an OD600 of 0.3-0.6, we transferred 4 ml of each culture to a new well of a deep 24-well plate, added 500 μM isopropyl β-D-1-thiogalactopyranoside (IPTG) and 20 mM of mevalonate, and incubated for 20 hours (22° C., 225 RPM). (v) We diluted each 4-ml culture to an OD600 of 0.1 with TB media and plated 10 μL of the diluent onto either LB or TB plates supplemented with 500 μM IPTG, 20 mM mevalonate, 50 μg/ml kanamycin, 10 μg/ml tetracycline, 34 μg/ml chloramphenicol, 50 μg/ml carbenicillin, and 0-1200 μg/ml spectinomycin (for both plates, we used 20 g/L agar with media and buffer components described above).
Terpenoid biosynthesis. We prepared E. coli for terpenoid production by transforming cells with plasmids harboring requisite pathway components (TABLE 8) and plating them onto LB agar plates (20 g/L agar, 10 g/L tryptone, 10 g/L sodium chloride, and 5 g/L yeast extract with antibiotics described in TABLE 8). We used one colony from each strain to inoculate 2 ml TB (12 g/L tryptone, 24 g/L yeast extract, 12 mL/L 100% glycerol, 2.28 g/L KH2PO4, 12.53 g/L K2HPO4, pH=7.0, and antibiotics described in TABLE 8) in a glass culture tube for ˜16 hours (37° C. and 225 RPM). We diluted these cultures by 75-fold into 10 ml of TB media and incubated the new cultures in 125 mL glass shake flasks (37° C. and 225 RPM). At an OD600 of 0.3-0.6, we added 500 μM IPTG and 20 mM mevalonate. After 72-88 hours of growth (22° C. and 225 RPM), we extracted terpenoids from each culture as outlined below.
Protein expression and purification. We expressed and purified PTPs as described previously73. Briefly, we transformed E. coli BL21(DE3) cells with pET16b or pET21b vectors (see TABLE 8 for details), and we induced with 500 μM IPTG at 22° C. for 20 hours. We purified PTPs from cell lysate by using desalting, nickel affinity, and anion exchange chromatography (HiPrep 26/10, HisTrap HP, and HiPrep Q HP, respectively; GE Healthcare). We stored the final protein (30-50 μM) in HEPES buffer (50 mM, pH 7.5, 0.5 mM TCEP) in 20% glycerol at ˜80° C.
Extraction and purification of terpenoids. We used hexane to extract terpenoids generated in liquid culture. For 10-mL cultures, we added 14 mL of hexane to 10 ml of culture broth in 125-mL glass shake flasks, shook the mixture (100 RPM) for 30 minutes, centrifuged it (4000×g), and withdrew 10 mL of the hexane layer for further analysis. For 4-mL cultures, we added 600 μL hexane to 1 mL of culture broth in a microcentrifuge tube, vortexed the tubes for 3 minutes, centrifuged the tubes for 1 minute (17000×g), and saved 300-400 μL of the hexane layer for further analysis.
To purify AD, AB, and (+)-1(10),4-cadinadiene, we supplemented 500-1000 mL culture broth with hexane (16.7% v/v), shook the mixture for 30 minutes (100 RPM), isolated the hexane layer with a separatory funnel, centrifuged the isolated organic phase (4000×g), and withdrew the hexane layer. To concentrate the terpenoid products, we evaporated excess hexane in a rotary evaporator to bring the final volume to 500 μL, and we passed the resulting mixture over a silica gel 1-3 times (Sigma-Aldrich; high purity grade, 60 Å pore size, 230-400 mesh particle size). We analyzed elution fractions (100% hexane) on the GC/MS and pooled fractions with the compound of interest (AD). Once purified, we dried pooled fractions under a gentle stream of air, resuspended the concentrated terpenoids in DMSO, and quantified the final samples as outlined below. We repeated the purification process until samples (in DMSO) were >95% pure by GC/MS unless otherwise noted.
GC-MS analysis of terpenoids. We measured terpenoids generated in liquid culture with a gas chromatograph/mass spectrometer (GC-MS; a Trace 1310 GC fitted with a TG5-SilMS column and an ISQ 7000 MS; Thermo Fisher Scientific). We prepared all samples in hexane (directly or through a 1:100 dilution of DMSO) with 20 μg/ml of caryophyllene as an internal standard. Highly concentrated samples were diluted 10-20× prior to preparation to bring concentrations within the MS detection limit. When the peak area of an internal standard exceeded ±40% of the average area of all samples containing that standard, we re-analyzed the corresponding samples. For all runs, we used the following GC method: hold at 80° C. (3 min), increase to 250° C. (15° C./min), hold at 250° C. (6 min), increase to 280° C. (30° C./min), and hold at 280° C. (3 min). To identify various analytes, we scanned m/z ratios from 50 to 550.
We examined sesquiterpenes generated by variants of ADS by using select ion mode (SIM) to scan for the molecular ion (m/z=204). For quantification, we used Eq. 1: where Ai
is the area of the peak produced by analyte i, Astd is the area of the peak produced by Cstd of caryophyllene in the sample, and R is the ratio of response factors for caryophyllene and AD in a reference sample. TABLE 11 provides the concentrations of all standards and reference compounds used in this analysis.
We quantified diterpenoids by, once again, accompanying our general procedure with several modifications: We scanned for a different molecular ion (m/z=272) and an ion common to both diterpenoids and caryophyllene (m/z=93); we used a ratio of response factors for pure taxadiene (a kind gift from Phil Baran) and caryophyllene at m/z=93; and we calculated peak areas m/z=93. For all analyses, we examined only peaks with areas that exceeded 1% of the total area of all peaks at m/z=272.
We identified molecules by using the NIST MS library and, when necessary, confirmed this identification with analytical standards or mass spectra reported in the literature. We note: The assumption of a constant response factor for different terpenoids (that is, the assumption that all sesquiterpenes and diterpenes ionize like AD and taxadiene, respectively) can certainly yield error in estimates of their concentrations; our analyses, which are consistent with those of other studies of terpenoid production in microbial systems74,75, supply rough estimates of concentrations for all compounds except AD and taxadiene (which had analytical standards).
Bioinformatics. We used a bioinformatic analysis to identify a phylogenetically diverse set of terpene synthases. Briefly, we downloaded (i) all constituent genes of PF03936 (the largest terpene synthase family grouped by a C-terminal domain) from the PFAM Database and (ii) all enzymes with Enzyme Commission (EC) number of 4.2.3.# from the Uniprot Database; this string, which defines carbon oxygen lyases that act on phosphates, includes terpene synthases. We cleaned both datasets in Excel (i.e., we ensured that every identifier had only one row), and we used a custom R script to designate each PF03936 member as characterized (i.e., in possession of a Uniprot-based EC number) or uncharacterized. Finally, we used FastTree76 with default settings to create a phylogenetic tree of the PF03936 family and the R-package ggtree77 to visualize the resulting tree and function data as a cladogram and heatmap.
After annotating the cladogram by hand, we selected three genes from each of six clades: six with no characterized genes and two with some characterized genes. We avoided clades proximal to known monoterpene synthases or diterpene synthases known to act on GGPP isomers absent in our system (e.g., ent-copalyl diphosphate); these enzymes are unlikely to act on FPP, the primary product of pMBISCmR. When selecting enzymes within clades, we biased our choice towards bacterial/fungal species and selected genes with a minimal number of common ancestors within the Glade. The selected genes were synthesized and cloned into the pTrc99a vector by Twist Biosciences and assayed for antibiotic resistance as described above.
Enzyme kinetics. To examine terpenoid-mediated inhibition, we measured PTP-catalyzed hydrolysis of p-nitrophenyl phosphate (pNPP) or 4-methylumbelliferyl phosphate (4-MUP, used when KM for pNPP was large) in the presence of various concentrations of terpenoids. Each reaction included PTP (0.05 μM PTP1B/TCPTP or 0.1 μM SHP1/SHP2 in 50 mM HEPES, 0.5 mM TCEP, 50 μg/ml BSA), pNPP (0.33, 0.67, 2, 5, 10, and 15 mM) or 4-MUP (0.13, 0.27, 0.8, 2.27, 2.93, 4.53, 7.07, and 8 mM), inhibitor (with concentrations listed in the figures), buffer (50 mM HEPES pH=7.3, 50 μg/ml BSA), and DMSO at 10% v/v. We monitored the formation of p-nitrophenol by measuring absorbance at 405 nm every 10 seconds for 5 minutes on a SpectraMax M2 plate reader and the formation of 4-methylumbelliferyl by measuring fluorescence at 450 nm (370 nm ex, 435 nm cutoff, medium gain).
We used a custom MATLAB script to process all raw kinetic data. This script removed all concentration values that fell outside of either (i) the range of our standard curve (absorbance/fluorescence vs. μM;
We evaluated kinetic models in three steps: (i) We fit initial-rate measurements collected in the absence and presence of inhibitors to Michaelis-Menten and inhibition models, respectively (here, we used the nlinfit and fminsearch functions from MATLAB; TABLE 12). (ii) We used an F-test to compare the mixed model to the single-parameter model with the least sum squared error (here, we used the fcdf function from MATLAB to assign p-values), and we accepted the mixed model when p<0.05. (iii) We used the Akaike's Information Criterion (AIC) to compare the best-fit single parameter model to each alternative single parameter model, and we accepted the “best-fit” model when the difference in AIC (Δi) exceed 5 for all comparisons.78 We note: For AD, AB, and (+)1-(10),4-cadinadiene this criterion was not met; both noncompetitive and uncompetitive models, however, yielded indistinguishable IC50's.
We estimated the half maximal inhibitory concentration (IC50) of inhibitors by using the best-fit kinetic models to determine the concentration of inhibitor required to reduce initial rates of PTP-catalyzed hydrolysis of 15 mM of pNPP by 50%. We used the MATLAB function “nlparci” to determine the confidence intervals of kinetic parameters, and we propagated those intervals to estimate corresponding confidence intervals for each IC50.
X-ray crystallography. We prepared crystals of PTP1B by using hanging drop vapor diffusion. In brief, we added 2 μL of PTP1B (˜600 μM PTP1B, 50 mM HEPES, pH 7.3) to 6 μL of crystallization solution (100 mM HEPES, 200 mM magnesium acetate, and 14% polyethylene glycol 8000, pH 7.5) and incubated the resulting droplets over crystallization solution for one week at 4° C. (EasyXtal CrystalSupport, Qiagen). We soaked crystals with ligand by transferring them to droplets formed with 6 μL of crystallization solution and 1 μL of ligand solution (10 mM in DMSO), which we incubated for 2-5 days at 4° C. We prepared all ligands for freezing by soaking them in cryoprotectant formed from a 70/30 (v/v) mixture of buffer (100 mM HEPES, 200 mM magnesium acetate, and 25% polyethylene glycol 8000, pH 7.5) and glycerol.
We collected X-ray diffraction data through the Collaborative Crystallography Program at Lawrence Berkeley National Lab (ALS ENABLE, beamline 8.2.1, 100 K, 1.00003 Å). We performed integration, scaling, and merging of X-ray diffraction data using the xia2 software package79, and we carried out molecular replacement and structure refinement with the PHENIX graphical interface,80 supplemented with manual model adjustment in COOT81 and one round of PDB-REDO82 (the latter, only for the PTP1B-AD complex).
Molecular dynamics (MD) simulations. Full-length PTP1B contains a disordered region that extends beyond the α7 helix (i.e., 299-435). In this study, we used a well-studied truncation variant (i.e., PTP1B1-321) that includes residues from the disordered region. To model PTP1B, we used CAMPARI v.283 to generate structures of the disordered region of each complex (i.e., residues 288-321 for PTP1B-AD) from a crystal structure without a disordered tail. To quickly thermalize the tail structures, we ran short Monte Carlo (MC) simulations using the ABSINTH implicit-solvent force field84,85, fixing the coordinates of the atoms in the ligand and the protein core.
We performed MD simulations using GROMACS 202086. Briefly, we used the CHARMM36m protein force field87, a CHARMM-modified TIP3P water model88, and ligand parameters generated by CGenFF89,90. We solvated each PTP1B-ligand complex (initialized from the corresponding crystal structure) in a dodecahedral box with edges positioned ≥10 Å from the surface of the complex, and we added six sodium ions to neutralize each system. We used the LINCS algorithm91 to constrain all bonds involving hydrogen atoms, the Verlet leapfrog algorithm to numerically integrate equations of motion with a 2-fs time step, and the particle-mesh Ewald summation92 (cubic interpolation with a grid spacing of 0.16 nm) to calculate long-range electrostatic interactions; we used a cutoff of 1.2 nm, in turn, for short-range electrostatic and Lennard-Jones interactions. We independently coupled the protein-ligand complex and solvent molecules to a temperature bath (300K) using a modified Berendsen thermostat93 with a relaxation time of 0.1 ps, and we fixed pressure coupling to 1 bar using the Parrinello-Rahman algorithm94 with a relaxation time of 2 ps and isothermal compressibility of 4.5×10−5 bar−1.
For each system, we carried out 30 independent MD simulations to reduce sampling bias. For each MD trajectory, we minimized energy using the steepest decent method followed by 100-ps solvent relaxation in the NVT ensemble and 100-ps solvent relaxation in the NPT ensemble. After an additional 5-ns NPT equilibration, we carried out production runs for 5 ns in the NPT ensemble and registered coordinate data every 10 ps.
Analysis of PTP1B inhibition in HEK293TCells. We prepared HEK293T/17 cells for an enzyme-linked immunosorbent assay (ELISA) by growing them in 75 cm2 culture flasks (Corning) with DMEM media supplemented with 10% FBS, 100 units/ml penicillin, and 100 units/ml streptomycin. We replaced the media every day for 3-5 days until the cells reached 80-100% confluency.
We measured the influence of inhibitors on insulin receptor (IR) phosphorylation by using an IR-specific ELISA (
Statistical analysis and reproducibility. We determined statistical significance (
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+This plasmid was a kind gift from Nicholas Tonks of Cold Spring Harbor Laboratory.
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*AG = Addgene accession # (Addgene.com).
All of the features disclosed in this specification may be combined in any combination. Each feature disclosed in this specification may be replaced by an alternative feature serving the same, equivalent, or similar purpose. Thus, unless expressly stated otherwise, each feature disclosed is only an example of a generic series of equivalent or similar features.
From the above description, one skilled in the art can easily ascertain the essential characteristics of the present disclosure, and without departing from the spirit and scope thereof, can make various changes and modifications of the disclosure to adapt it to various usages and conditions. Thus, other embodiments are also within the claims.
While several inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.
All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.
All references, patents and patent applications disclosed herein are incorporated by reference with respect to the subject matter for which each is cited, which in some cases may encompass the entirety of the document.
The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”
The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and/or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and/or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.
As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and
This application is a continuation of International Application No.: PCT/US2021/012621, filed Jan. 8, 2021, which claims the benefit under 35 U.S.C. § 119(e) of U.S. provisional application No. 62/958,368, filed Jan. 8, 2020, each of which is incorporated by reference herein in its entirety.
This invention was made with government support under grant 1750244 awarded by the National Science Foundation. The government has certain rights to this invention.
| Number | Date | Country | |
|---|---|---|---|
| 62958368 | Jan 2020 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2021/012621 | Jan 2021 | US |
| Child | 17859509 | US |
