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Engineering of biosynthetic enzymes is increasingly employed to synthesize structural analogues of antibiotics. Of special interest are non-ribosomal peptide synthetases (NRPSs) responsible for production of important antimicrobial peptides. Here, directed evolution of an adenylation domain of a Pro-specific NRPS module completely switched substrate specificity to the non-standard amino acid piperazic acid (Piz) bearing a labile N-N bond. This success was achieved by LC-MS/MS based screening of small, rationally designed mutant libraries and can presumably be replicated with a larger number of substrates and NRPS modules. The evolved NRPS produces a Piz-derived gramicidin S analog. Thus, we give new impetus to the too-early dismissed idea that widely accessible low-throughput methods can switch the specificity of NRPSs in a biosynthetically useful fashion.

Specificity profiling of a nonribosomal peptide synthetase of an early diverging fungus revealed high substrate flexibility. Feeding studies with click-functionalised amino acids enabled the production of fluorescent peptides targeting macrophages.

Repurposing the enzymes in microbial metabolism such as nonribosomal peptide synthetases (NRPSs) is explored as a route towards better antibiotics. NRPSs are gigantic enzymatic assembly lines that form highly modified peptides from diverse building blocks. A novel hydroxamate assay detects full substrate profiles of NRPSs from cell-like substrate mixtures. Facile recording of substrate profiles has applications in natural product discovery and engineering.

The choanoflagellate Salpingoeca rosetta is an important model system to study the evolution of multicellularity. In this study we developed a new, modular, and scalable synthesis of sulfonolipid IOR-1A (six steps, 27 % overall yield), which acts as bacterial inhibitor of rosette formation in S. rosetta. The synthesis features a decarboxylative cross-coupling reaction of a sulfonic acid-containing tartaric acid derivative with alkyl zinc reagents. Synthesis of 15 modified IOR-1A derivatives, including fluorescent and photoaffinity-based probes, allowed quantification of IOR-1A, localization studies within S. rosetta cells, and evaluation of structure-activity relations. In a proof of concept study, an inhibitory bifunctional probe was employed in proteomic profiling studies, which allowed to deduce binding partners in bacteria and S. rosetta. These results showcase the power of synthetic chemistry to decipher the biochemical basis of cell differentiation processes within S. rosetta.

Nonribosomal peptide synthetases (NRPSs) are a vast source of valuable natural products, and re-engineering them is an attractive path toward structurally diversified active compounds. NRPS engineering often requires heterologous expression, which is hindered by the enormous size of NRPS proteins. Protein splitting and docking domain insertion have been proposed as a strategy to overcome this limitation. Here, we have applied the splitting strategy to the gramicidin S NRPS: Despite better production of the split proteins, gramicidin S production almost ceased. However, the addition of type II thioesterase GrsT boosted production. GrsT is an enzyme encoded in the gramicidin S biosynthetic gene cluster that we have produced and characterized for this purpose. We attribute the activity enhancement to the removal of a stalled intermediate from the split NRPS that is formed due to misinitiation. These results highlight type II thioesterases as useful tools for NRPS engineering.

Pathogenic bacteria of the Burkholderia pseudomallei group cause severe infectious diseases such as glanders and melioidosis. Malleicyprols were identified as important bacterial virulence factors, yet the biosynthetic origin of their cyclopropanol warhead has remained enigmatic. By a combination of mutational analysis and metabolomics we found that sulfonium acids, dimethylsulfoniumpropionate (DMSP) and gonyol, known as osmolytes and as crucial components in the global organosulfur cycle, are key intermediates en route to the cyclopropanol unit. Functional genetics and in vitro analyses uncover a specialized pathway to DMSP involving a rare prokaryotic SET‐domain methyltransferase for a cryptic methylation, and show that DMSP is loaded onto the NRPS‐PKS hybrid assembly line by an adenylation domain dedicated to zwitterionic starter units. Then, the megasynthase transforms DMSP into gonyol, as demonstrated by heterologous pathway reconstitution in E. coli., Sulfur cycle meets pathogen. Sulfonium acids known from global sulfur cycles were elucidated as the biosynthetic origin of the cyclopropanol warhead of malleicyprols, virulence factors of human‐pathogenic bacteria. The pathway involves a specialized S‐methyl transferase to form DMSP, which is activated by a zwitterion‐specific adenylation domain and transformed into the key intermediate gonyol.

Important reactions in biology and biocatalysis involve proton abstraction from carbon. When the resulting anionic charge is delocalized from carbon to an oxygen atom, these deprotonations can be c...

The realm of natural products of early diverging fungi such as

Temperature influences the reaction kinetics and evolvability of all enzymes. To understand how evolution shapes the thermodynamic drivers of catalysis, we optimized the modest activity of a computationally designed enzyme for an elementary proton-transfer reaction by nearly 4 orders of magnitude over 9 rounds of mutagenesis and screening. As theorized for primordial enzymes, the catalytic effects of the original design were almost entirely enthalpic in origin, as were the rate enhancements achieved by laboratory evolution. However, the large reductions in ΔH⧧ were partially offset by a decrease in TΔS⧧ and unexpectedly accompanied by a negative activation heat capacity, signaling strong adaptation to the operating temperature. These findings echo reports of temperature-dependent activation parameters for highly evolved natural enzymes and are relevant to explanations of enzymatic catalysis and adaptation to changing thermal environments.

Nonribosomal peptides are a prolific source of bioactive molecules biosynthesized on large, modular assembly line synthetases. Synthetic biologists seek to obtain tailored peptides with tuned or novel bioactivities by engineering modules and domains of these nonribosomal peptide synthetases. The activation step catalyzed by adenylation domains primarily selects which amino acids are incorporated into nonribosomal peptides. Here, we review experimental protocols for probing the adenylation reaction that are applicable in natural product discovery and engineering. Several alternatives to the established pyrophosphate exchange assay will be compared and potential pitfalls pointed out. Binding pocket mutagenesis of adenylation domains has been successfully conducted to adjust substrate preferences. Novel screening methods relying on yeast surface display, for instance, search a larger sequence space for improved mutants and thus allow more substantial changes in peptide structure.

Adenylation enzymes selecting substrates for ribosomal and nonribosomal protein and peptide biosynthesis have been popular targets of enzyme engineering. Previous standard assays for adenylation specificity have been cumbersome and failed to reflect the competition conditions inside a cell because they measure substrates one at a time. We have developed an adenylation assay based on hydroxamate quenching and LC-MS/MS detection of hydroxamate products testing dozens of competing amino acid substrates in parallel. Streamlined specificity profiling of adenylation enzymes will facilitate engineering and directed evolution of ribosomal and nonribosomal peptide synthesis.

Modular biosynthetic machineries such as polyketide synthases (PKSs) or nonribosomal peptide synthetases (NRPSs) give rise to a vast structural diversity of bioactive metabolites indispensable in the treatment of cancer or infectious diseases. Here, we provide evidence for different evolutionary processes leading to the diversification of modular NRPSs and thus, their respective products. Discovery of a novel lipo-octapeptide family from Pseudomonas, the virginiafactins, and detailed structure elucidation of closely related peptides, the cichofactins and syringafactins, allowed retracing recombinational diversification of the respective NRPS genes. Bioinformatics analyses allowed us to spot an evolutionary snapshot of these processes, where recombination occurred both within the same and between different biosynthetic gene clusters. Our systems feature a recent diversification process, which may represent a typical paradigm to variations in modular biosynthetic machineries.

Engineering of nonribosomal peptide synthetases (NRPS) has faced numerous obstacles despite being an attractive path towards novel bioactive molecules. Specificity filters in the nonribosomal peptide assembly line determine engineering success, but the relative contribution of adenylation (A-) and condensation (C-)domains is under debate. In the engineered, bimodular NRPS sdV-GrsA/GrsB1, the first module is a subdomain-swapped chimera showing substrate promiscuity. On sdV-GrsA and evolved mutants, we have employed kinetic modelling to investigate product specificity under substrate competition. Our model contains one step, in which the A-domain acylates the thiolation (T-)domain, and one condensation step deacylating the T-domain. The simplified model agrees well with experimentally determined acylation preferences and shows that the condensation specificity is mismatched with the engineered acylation specificity. Our model predicts changing product specificity in the course of the reaction due to dynamic T-domain loading, and that A-domain overrules C-domain specificity when T-domain loading reaches a steady-state. Thus, we have established a tool for investigating poorly accessible C-domain specificity through nonlinear kinetic modeling and gained critical insights how the interplay of A- and C-domains determines the product specificity of NRPSs.

Fungi are traditionally considered as reservoir of biologically active natural products. However, an active secondary metabolism has long not been attributed to early diverging fungi such asMortierella spec. Here, we report on the biosynthesis of two series of cyclic pentapeptides, the malpicyclins and malpibaldins, as products ofMortierella alpinaATCC32222. The molecular structures of malpicyclins were elucidated by HR-MS/MS, Marfey’s method, and 1D and 2D NMR spectroscopy. In addition, malpibaldin biosynthesis was confirmed by HR-MS. Genome mining and comparative qRT-PCR expression analysis pointed at two pentamodular nonribosomal peptide synthetases (NRPS), malpicyclin synthetase MpcA and malpibaldin synthetase MpbA, as candidate biosynthetic enzymes. Heterologous production of the respective adenylation domains and substrate specificity assays proved promiscuous substrate selection and confirmed their respective biosynthetic roles. In stark contrast to known fungal NRPSs, MpbA and MpcA contain bacterial-like dual epimerase/condensation domains allowing the racemization of enzyme-tetheredl-amino acids and the subsequent incorporation ofd-amino acids into the metabolites. Phylogenetic analyses of both NRPS genes indicate a bacterial origin and a horizontal gene transfer into the fungal genome. This is the first report of nonribosomal peptide biosynthesis in basal fungi which highlights this paraphylum as novel and underrated resource of natural products.IMPORTANCEFungal natural compounds are industrially produced with application in antibiotic treatment, cancer medications and crop plant protection. Traditionally, higher fungi have been intensively investigated concerning their metabolic potential, but re-identification of already known compounds is frequently observed. Hence, alternative strategies to acquire novel bioactive molecules are required. We present the genusMortierellaas representative of the early diverging fungi as an underestimated resource of natural products.Mortierella alpinaproduces two families of cyclopeptides, denoted malpicyclins and malpibaldins, respectively, via two pentamodular nonribosomal peptide synthetases (NRPSs). These enzymes are much closer related to bacterial than to other fungal NRPSs, suggesting a bacterial origin of these NRPS genes inMortierella. Both enzymes are the first biochemically characterized natural product biosynthesis enzymes of basal fungi. Hence, this report establishes early diverging fungi as prolific natural compound producers and sheds light on the origin of their biosynthetic capacity.

From the evolutionary melting pot of natural product synthetase genes, microorganisms elicit antibiotics, communication tools, and iron scavengers. Chemical biologists manipulate these genes to recreate similarly diverse and potent biological activities not on evolutionary time scales but within months. Enzyme engineering has progressed considerably in recent years and offers new screening, modelling, and design tools for natural product designers. Here, recent advances in enzyme engineering and their application to nonribosomal peptide synthetases are reviewed. Among the nonribosomal peptides that have been subjected to biosynthetic engineering are the antibiotics daptomycin, calcium-dependent antibiotic, and gramicidin S. With these peptides, incorporation of unnatural building blocks and modulation of bioactivities via various structural modifications have been successfully demonstrated. Natural product engineering on the biosynthetic level is not a reliable method yet. However, progress in the understanding and manipulation of biosynthetic pathways may enable the routine production of optimized peptide drugs in the near future. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.

Long sought after [4+2] cyclases have sprouted up in numerous biosynthetic pathways in recent years, raising hopes for biocatalytic solutions to cycloaddition catalysis, an important problem in chemical synthesis. In a few cases, detailed pictures of the inner workings of these catalysts have emerged, but intense efforts to gain deeper understanding are underway by means of crystallography and computational modelling. This Minireview aims to shed light on the catalytic strategies that this highly diverse family of enzymes employs to accelerate and direct the course of [4+2] cycloadditions with reference to small-molecule catalysts and designer enzymes. These catalytic strategies include oxidative or reductive triggers and lid-like movements of enzyme domains. A precise understanding of natural cycloaddition catalysts will be instrumental for customizing them for various synthetic applications.

Biosynthetic modification of nonribosomal peptide backbones represents a potentially powerful strategy to modulate the structure and properties of an important class of therapeutics. Using a high-throughput assay for catalytic activity, we show here that an L-Phe-specific module of an archetypal nonribosomal peptide synthetase can be reprogrammed to accept and process the backbone-modified amino acid (S)-β-Phe with near-native specificity and efficiency. A co-crystal structure with a non-hydrolysable aminoacyl-AMP analogue reveals the origins of the 40,000-fold α/β-specificity switch, illuminating subtle but precise remodelling of the active site. When the engineered catalyst was paired with downstream module(s), (S)-β-Phe-containing peptides were produced at preparative scale in vitro (~1 mmol) and high titres in vivo (~100 mg l

The natural product class of iridoids, found in various species of flowering plants, harbors astonishing chemical complexity. The discovery of iridoid biosynthetic genes in the medicinal plant Catharanthus roseus has provided insight into the biosynthetic origins of this class of natural product. However, not all iridoids share the exact five- to six-bicyclic ring scaffold of the Catharanthus iridoids. For instance, iridoids in the ornamental flower snapdragon (Antirrhinum majus, Plantaginaceae family) are derived from the C7 epimer of this scaffold. Here we have cloned and characterized the iridoid synthase enzyme from A. majus (AmISY), the enzyme that is responsible for converting 8-oxogeranial into the bicyclic iridoid scaffold in a two-step reduction–cyclization sequence. Chiral analysis of the reaction products reveals that AmISY reduces C7 to generate the opposite stereoconfiguration in comparison with the Catharanthus homologue CrISY. The catalytic activity of AmISY thus explains the biosynthesis of 7-epi-iridoids in Antirrhinum and related genera. However, although the stereoselectivity of the reduction step catalyzed by AmISY is clear, in both AmISY and CrISY, the cyclization step produces a diastereomeric mixture. Although the reduction of 8-oxogeranial is clearly enzymatically catalyzed, the cyclization step appears to be subject to less stringent enzyme control.

Nonribosomal peptide synthetases (NRPSs) are multifunctional enzymes that produce a wide array of bioactive peptides. Here we show that a single tryptophan-to-serine mutation in phenylalanine-specific NRPS adenylation domains enables the efficient activation of non-natural aromatic amino acids functionalized with azide and alkyne groups. The resulting 10(5)-fold switch in substrate specificity was achieved without appreciable loss of catalytic efficiency. Moreover, the effective communication of the modified A domains with downstream modules in dipeptide synthetases permitted incorporation of O-propargyl-L-tyrosine into diketopiperazines both in vitro and in vivo, even in the presence of competing phenylalanine. Because azides and alkynes readily undergo bioorthogonal click reactions, reprogramming NRPSs to accept non-natural amino acids that contain these groups provides a potentially powerful means of isolating, labeling, and modifying biologically active peptides.

Plants and microorganisms under phosphorus (P) stress release extracellular phosphatases as a strategy to acquire inorganic phosphate (P i ). These enzymes catalyze the hydrolysis of phosphoesters leading to a release of P i . During the enzymatic hydrolysis an isotopic fractionation (e) occurs leaving an imprint on the oxygen isotope composition of the released P i which might be used to trace phosphorus in the environment. Therefore, enzymatic assays with acid phosphatases from wheat germ and potato tuber and alkaline phosphatase from Escherichia coli were prepared in order to determine the oxygen isotope fractionation caused by these enzymes. Adenosine 5′ monophosphate and glycerol phosphate were used as substrates. The oxygen isotope fractionation caused by acid phosphatases is 20–30‰ smaller than for alkaline phosphatases, resulting in a difference of 5–7.5‰ in δ 18 O of P i depending on the enzyme. We attribute the enzyme dependence of the isotopic fractionation to distinct reaction mechanisms of the two types of phosphatases. The observed difference is large enough to distinguish between the two enzymatic processes in environmental samples. These findings show that the oxygen isotope composition of P i can be used to trace different enzymatic processes, offering an analytical tool that might contribute to a better understanding of the P-cycle in the environment.

The carbon skeleton of ecologically and pharmacologically important iridoid monoterpenes is formed in a reductive cyclization reaction unrelated to canonical terpene cyclization. Here we report the crystal structure of the recently discovered iridoid cyclase (from Catharanthus roseus) bound to a mechanism-inspired inhibitor that illuminates substrate binding and catalytic function of the enzyme. Key features that distinguish iridoid synthase from its close homolog progesterone 5 beta-reductase are highlighted.

Computational enzyme design has emerged as a promising tool for generating made to order biocatalysts. In addition to improving the reliability of the design cycle current efforts in this area are focusing on expanding the set of catalyzed reactions and investigating the structure and mechanism of individual designs. Although the activities of de novo enzymes are typically low they can be significantly increased by directed evolution. Analysis of their evolutionary trajectories provides valuable feedback for the design algorithms and can enhance our understanding of natural protein evolution. © 2013 Elsevier Ltd.

The secoiridoids are the main class of specialized metabolites present in olive (Olea europaea L.) fruit. In particular, the secoiridoid oleuropein strongly influences olive oil quality because of its bitterness, which is a desirable trait. In addition, oleuropein possesses a wide range of pharmacological properties, including antioxidant, anti-inflammatory, and anti-cancer activities. In accordance, obtaining high oleuropein varieties is a main goal of molecular breeding programs. Here we use a transcriptomic approach to identify candidate genes belonging to the secoiridoid pathway in olive. From these candidates, we have functionally characterized the olive homologue of iridoid synthase (OeISY), an unusual terpene cyclase that couples an NAD (P)H-dependent 1,4-reduction step with a subsequent cyclization, and we provide evidence that OeISY likely generates the monoterpene scaffold of oleuropein in olive fruits. OeISY, the first pathway gene characterized for this type of secoiridoid, is a potential target for breeding programs in a high value secoiridoid-accumulating species. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

Split proteins are versatile tools for detecting protein–protein interactions and studying protein folding. Here, we report a new, particularly small split enzyme, engineered from a thermostable chorismate mutase (CM). Upon dissecting the helical-bundle CM from Methanococcus jannaschii into a short N-terminal helix and a 3-helix segment and attaching an antiparallel leucine zipper dimerization domain to the individual fragments, we obtained a weakly active heterodimeric mutase. Using combinatorial mutagenesis and in vivo selection, we optimized the short linker sequences connecting the leucine zipper to the enzyme domain. One of the selected CMs was characterized in detail. It spontaneously assembles from the separately inactive fragments and exhibits wild-type like CM activity. Owing to the availability of a well characterized selection system, the simple 4-helix bundle topology, and the small size of the N-terminal helix, the heterodimeric CM could be a valuable scaffold for enzyme engineering efforts and as a split sensor for specifically oriented protein–protein interactions.

Split proteins are versatile tools for detecting protein–protein interactions and studying protein folding. Here, we report a new, particularly small split enzyme, engineered from a thermostable chorismate mutase (CM). Upon dissecting the helical-bundle CM from Methanococcus jannaschii into a short N-terminal helix and a 3-helix segment and attaching an antiparallel leucine zipper dimerization domain to the individual fragments, we obtained a weakly active heterodimeric mutase. Using combinatorial mutagenesis and in vivo selection, we optimized the short linker sequences connecting the leucine zipper to the enzyme domain. One of the selected CMs was characterized in detail. It spontaneously assembles from the separately inactive fragments and exhibits wild-type like CM activity. Owing to the availability of a well characterized selection system, the simple 4-helix bundle topology, and the small size of the N-terminal helix, the heterodimeric CM could be a valuable scaffold for enzyme engineering efforts and as a split sensor for specifically oriented protein–protein interactions.

The site-specific conjugation of polymers to multiple engineered cysteine residues of a prolyl endopeptidase leads to its stabilization in the gastrointestinal tract of rats, without compromising the activity relative to the native enzyme. The importance of polymer attachment sites is investigated, as well as the significance of polymer structure.

Linus Pauling established the conceptual framework for understanding and mimicking enzymes more than six decades ago. The notion that enzymes selectively stabilize the rate-limiting transition state of the catalysed reaction relative to the bound ground state reduces the problem of design to one of molecular recognition. Nevertheless, past attempts to capitalize on this idea, for example by using transition state analogues to elicit antibodies with catalytic activities, have generally failed to deliver true enzymatic rates. The advent of computational design approaches, combined with directed evolution, has provided an opportunity to revisit this problem. Starting from a computationally designed catalyst for the Kemp elimination--a well-studied model system for proton transfer from carbon – we show that an artificial enzyme can be evolved that accelerates an elementary chemical reaction 6 × 10(8)-fold, approaching the exceptional efficiency of highly optimized natural enzymes such as triosephosphate isomerase. A 1.09 Å resolution crystal structure of the evolved enzyme indicates that familiar catalytic strategies such as shape complementarity and precisely placed catalytic groups can be successfully harnessed to afford such high rate accelerations, making us optimistic about the prospects of designing more sophisticated catalysts.

Harnessing the modular architecture of non-ribosomal peptide synthetases for combinatorial biosynthesis is a longstanding goal in chemical biology. Several recent reports illustrate how computational design and directed evolution can be used to tailor the specificity of these assembly-line enzymes. © 2011 Elsevier Ltd All rights reserved.

SummaryNonribosomal peptide synthetases (NRPSs) protect microorganisms from environmental threats by producing diverse siderophores, antibiotics, and other peptide natural products. Their modular molecular structure is also attractive from the standpoint of biosynthetic engineering. Here we evaluate a methodology for swapping module specificities of these mega-enzymes that takes advantage of flavodoxin-like subdomains involved in substrate recognition. Nine subdomains encoding diverse specificities were transplanted into the Phe-specific GrsA initiation module of gramicidin S synthetase. All chimeras could be purified as soluble protein. One construct based on a Val-specific subdomain showed sizable adenylation activity and functioned as a Val-Pro diketopiperazine synthetase upon addition of the proline-specific GrsB1 module. These results suggest that subdomain swapping could be a viable alternative to previous NRPS design approaches targeting binding pockets, domains, or entire modules. The short length of the swapped sequence stretch may facilitate straightforward exploitation of the wealth of existing NRPS modules for combinatorial biosynthesis.

Metabolic pathways leading to benzylisoquinoline and monoterpene indole alkaloids in plants are revealing remarkable new reactions. Understanding of the enzymes involved in alkaloid biosynthesis provides access to a variety of applications in biocatalysis and bioengineering. In chemo-enzymatic settings, plant biocatalysts can transform medically important scaffolds. Additionally, synthetic biologists are taking alkaloid pathways as templates to assemble pathways in microorganisms that are tailored to the needs of medicinal chemistry. In light of these many recent discoveries, it is expected that plants will continue to be a source of novel biocatalysts for the foreseeable future.