Insights into the biosynthesis of 12-membered resorcylic acid lactones from heterologous production in Saccharomyces cerevisiae

Challenging Aromaticity: Revealing a Thioesterase Domain in a Fungal Nonreducing Polyketide Synthase Governing the Production of 3-Methylene Isochromanone

Thioesterase (TE) domain exerts a great influence over the structure of the final product and TE-released nonreduced polyketides (nrPKs) retain aromaticity. 3-Methylene isochromanones are lactones with a unique olefin at C3 that disrupts the aromaticity, whose biosynthetic details are speculative. Our study unveils the complete biosynthesis of ascochin, in which the construction of the 3-methylene isochromanone backbone is achieved by a nonreducing polyketide synthase (nrPKS) alone and two subsequent oxidations are involved. Intriguingly, the TEAscD serves as a gatekeeper to direct the product release toward formation of nonaromatic 3-methylene isochromanone, rather than the typical aromatic product.

Biosynthesis of Cytosporones in Leotiomycetous Filamentous Fungi

Polyketides with the isochroman-3-one pharmacophore are rare among fungal natural products as their biosynthesis requires an unorthodox S-type aromatic ring cyclization. Genome mining uncovered a conserved gene cluster in select leotiomycetous fungi that encodes the biosynthesis of cytosporones, including isochroman-3-one congeners. Combinatorial biosynthesis in total biosynthetic and biocatalytic formats in Saccharomyces cerevisiae and in vitro reconstitution of key reactions with purified enzymes revealed how cytosporone structural and bioactivity diversity is generated. The S-type acyl dihydroxyphenylacetic acid (ADA) core of cytosporones is assembled by a collaborating polyketide synthase pair. Thioesterase domain-catalyzed transesterification releases ADA esters, some of which are known Nur77 modulators. Alternatively, hydrolytic release allows C6 hydroxylation by a flavin-dependent monooxygenase, yielding a trihydroxybenzene moiety. Reduction of the C9 carbonyl by a short chain dehydrogenase/reductase initiates isochroman-3-one formation, affording cytosporones with cytotoxic and antimicrobial activity. Enoyl di- or trihydroxyphenylacetic acids are generated as shunt products, while isocroman-3,4-diones are formed by autoxidation. The cytosporone pathway offers novel polyketide biosynthetic enzymes for combinatorial synthetic biology to advance the production of "unnatural" natural products for drug discovery.

Non-Native Site-Selective Enzyme Catalysis

The ability to site-selectively modify equivalent functional groups in a molecule has the potential to streamline syntheses and increase product yields by lowering step counts. Enzymes catalyze site-selective transformations throughout primary and secondary metabolism, but leveraging this capability for non-native substrates and reactions requires a detailed understanding of the potential and limitations of enzyme catalysis and how these bounds can be extended by protein engineering. In this review, we discuss representative examples of site-selective enzyme catalysis involving functional group manipulation and C-H bond functionalization. We include illustrative examples of native catalysis, but our focus is on cases involving non-native substrates and reactions often using engineered enzymes. We then discuss the use of these enzymes for chemoenzymatic transformations and target-oriented synthesis and conclude with a survey of tools and techniques that could expand the scope of non-native site-selective enzyme catalysis.

Plasmid Copy Number Engineering Accelerates Fungal Polyketide Discovery upon Unnatural Polyketide Biosynthesis

Saccharomyces cerevisiae has been extensively used as a convenient synthetic biology chassis to reconstitute fungal polyketide biosynthetic pathways. Despite progress in refactoring these pathways for expression and optimization of the yeast production host by metabolic engineering, product yields often remain unsatisfactory. Such problems are especially acute when synthetic biological production is used for bioprospecting via genome mining or when chimeric fungal polyketide synthases (PKSs) are employed to produce novel bioactive compounds. In this work, we demonstrate that empirically balancing the expression levels of the two collaborating PKS subunits that afford benzenediol lactone (BDL)-type fungal polyketides is a facile strategy to improve the product yields. This is accomplished by systematically and independently altering the copy numbers of the two plasmids that express these PKS subunits. We applied this plasmid copy number engineering strategy to two orphan PKSs from genome mining where the yields of the presumed BDL products in S. cerevisiae were far too low for product isolation. This optimization resulted in product yield improvements of up to 10-fold, allowing for the successful isolation and structure elucidation of new BDL analogues. Heterocombinations of these PKS subunits from genome mining with those from previously identified BDL pathways led to the combinatorial biosynthesis of several additional novel BDL-type polyketides.

Methyltransferases, functions and applications

In this review the current state‐of‐the‐art of S‐adenosylmethionine (SAM)‐dependent methyltransferases and SAM are evaluated. Their structural classification and diversity is introduced and key mechanistic aspects presented which are then detailed further. Then, catalytic SAM as a target for drugs, and approaches to utilise SAM as a cofactor in synthesis are introduced with different supply and regeneration approaches evaluated. The use of SAM analogues are also described. Finally O‐, N‐, C‐ and S‐MTs, their synthetic applications and potential for compound diversification is given.

Cloning and Functional Characterization of the Polyketide Synthases Based on Genome Mining of Preussia isomera XL-1326

Fungal polyketides (PKs) are one of the largest families of structurally diverse bioactive natural products biosynthesized by multidomain megasynthases, in which thioesterase (TE) domains act as nonequivalent decision gates determining both the shape and the yield of the polyketide intermediate. The endophytic fungus Preussia isomera XL-1326 was discovered to have an excellent capacity for secreting diverse bioactive PKs, i.e., the hot enantiomers (±)-preuisolactone A with antibacterial activity, the single-spiro minimoidione B with α-glucosidase inhibition activity, and the uncommon heptaketide setosol with antifungal activity, which drive us to illustrate how the unique PKs are biosynthesized. In this study, we first reported the genome sequence information of P. isomera. Based on genome mining, we discovered nine transcriptionally active genes encoding polyketide synthases (PKSs), Preu1–Preu9, of which those of Preu3, Preu4, and Preu6 were cloned and functionally characterized due to possessing complete sets of synthetic and release domains. Through heterologous expression in Saccharomyces cerevisiae, Preu3 and Preu6 could release high yields of orsellinic acid (OA) derivatives [3-methylorsellinic acid (3-MOA) and lecanoric acid, respectively]. Correspondingly, we found that Preu3 and Preu6 were clustered into OA derivative synthase groups by phylogenetic analysis. Next, with TE domain swapping, we constructed a novel “non-native” PKS, Preu6-TE_Preu3, which shared a very low identity with OA synthase, OrsA, from Aspergillus nidulans but could produce a large amount of OA. In addition, with the use of Preu6-TE_Preu3, we synthesized methyl 3-methylorsellinate (synthetic oak moss of great economic value) from 3-MOA as the substrate, and interestingly, 3-MOA exhibited remarkable antibacterial activities, while methyl 3-methylorsellinate displayed broad-spectrum antifungal activity. Taken together, we identified two novel PKSs to biosynthesize 3-MOA and lecanoric acid, respectively, with information on such kinds of PKSs rarely reported, and constructed one novel “non-native” PKS to largely biosynthesize OA. This work is our first step to explore the biosynthesis of the PKs in P. isomera, and it also provides a new platform for high-level environment-friendly production of OA derivatives and the development of new antimicrobial agents.

Biosynthesis of fungal polyketides by collaborating and trans-acting enzymes

Covering: 1999 up to 2021Fungal polyketides encompass a range of structurally diverse molecules with a wide variety of biological activities. The giant multifunctional enzymes that synthesize polyketide backbones remain enigmatic, as do many of the tailoring enzymes involved in functional modifications. Recent advances in elucidating biosynthetic gene clusters (BGCs) have revealed numerous examples of fungal polyketide synthases that require the action of collaborating enzymes to synthesize the carbon backbone. This review will discuss collaborating and trans-acting enzymes involved in loading, extending, and releasing polyketide intermediates from fungal polyketide synthases, and additional modifications introduced by trans-acting enzymes demonstrating the complexity encountered when investigating natural product biosynthesis in fungi.

Natural resorcylic acid lactones: A chemical biology approach for anticancer activity

Resorcylic acid lactones (RALs) are fungal polyketides that consist of a β-resorcylic acid residue (2,4-dihydroxybenzoic acid) embedded in a macrolactone ring. RALs exhibit a broad range of biological activities, including anticancer activities. Following discovery of the selective Hsp90 inhibition activity of radicicol, the kinase inhibition activity of hypothemycin, monocillin II, 5Z-7-oxo-zeaenol, and L-783,277 RALs, and the nuclear factor kappa B (NF-κB) inhibition activity of the RAL zearalenone, have attracted great attention as potential therapeutics for cancer treatment. In this minireview, we focus on natural RALs that possess cytotoxic activities [IC₅₀ values < 10 μM (or 4-5 μg/ml)], discussing their structures, isolation, occurrence, biological activities, and anticancer molecular mechanisms.

Saccharomyces cerevisiae as host for the recombinant production of polyketides and nonribosomal peptides

As a robust, fast growing and genetically tractable organism, the budding yeast Saccharomyces cerevisiae is one of the most widely used hosts in biotechnology. Its applications range from the manufacturing of vaccines and hormones to bulk chemicals and biofuels. In recent years, major efforts have been undertaken to expand this portfolio to include structurally complex natural products, such as polyketides and nonribosomally synthesized peptides. These compounds often have useful pharmacological properties, which make them valuable drugs for the treatment of infectious diseases, cancer, or autoimmune disorders. In nature, polyketides and nonribosomal peptides are generated by consecutive condensation reactions of short chain acyl-CoAs or amino acids, respectively, with the substrates and reaction intermediates being bound to large, multidomain enzymes. For the reconstitution of these multistep catalytic processes, the enzymatic assembly lines need to be functionally expressed and the required substrates must be supplied in reasonable quantities. Furthermore, the production hosts need to be protected from the toxicity of the biosynthetic products. In this review, we will summarize and evaluate the status quo regarding the heterologous production of polyketides and nonribosomal peptides in S. cerevisiae. Based on a comprehensive literature analysis, prerequisites for a successful pathway reconstitution could be deduced, as well as recurring bottlenecks in this microbial host.

β-Resorcylic Acid Derivatives, with Their Phytotoxic Activities, from the Endophytic Fungus Lasiodiplodia theobromae in the Mangrove Plant Xylocarpus granatum

Nine new β-resorcylic acid derivatives, (15S)-de-O-methyllasiodiplodin (1), (13S,15S)-13-hydroxy-de-O-methyllasiodiplodin (2), (14S,15S)-14-hydroxy-de-O-methyllasiodiplodin (3), (13R,14S,15S)-13,14-dihydroxy-de-O-methyllasiodiplodin (4), ethyl (S)-2,4-dihydroxy-6-(8-hydroxynonyl)benzoate (5), ethyl 2,4-dihydroxy-6-(8-hydroxyheptyl)benzoate (6), ethyl 2,4-dihydroxy-6-(4-methoxycarbonylbutyl)benzoate (7), 3-(2-ethoxycarbonyl-3,5-dihydroxyphenyl)propionic acid (8), and isobutyl (S)-2,4-dihydroxy-6-(8-hydroxynonyl)benzoate (9), together with a known ethyl 2,4-dihydroxy-6-(8-oxononyl)benzoate (10) were obtained from Lasiodiplodia theobromae GC-22. The structures of these compounds were elucidated by extensive spectroscopic analyses. Compounds 1, 3, and 6 showed growth inhibitory effects against Digitaria ciliaris. Conversely, treatment with compounds 5, 6, 7, 9, and 10 stimulated elongation activity toward the root of Lactuca sativa. These data expand the repertoire of new β-resorcylic acid derivatives that may function as lead compounds in the synthesis of new agrochemical agents.

Jasmonic acid biosynthesis by fungi: derivatives, first evidence on biochemical pathways and culture conditions for production

Jasmonic acid (JA) and its derivatives called jasmonates (JAs) are lipid-derived signalling molecules that are produced by plants and certain fungi. Beside this function, JAs have a great variety of applications in flavours and fragrances production. In addition, they may have a high potential in agriculture. JAs protect plants against infections. Although there is much information on the biosynthesis and function of JA concerning plants, knowledge on these aspects is still scarce for fungi. Taking into account the practical importance of JAs, the objective of this review is to summarize knowledge on the occurrence of JAs from fungal culture media, their biosynthetic pathways and the culture conditions for optimal JA production as an alternative source for the production of these valuable metabolites.

Chemical mining of heterotrophic Shewanella algae reveals anti-infective potential of macrocyclic polyketides against multidrug-resistant pathogens

Heterotrophic Gamma-proteobacterium Shewanella algae MTCC 12715, associated with an intertidal red algae Hypnea valentiae, presented broad-spectra of antibacterial activities against pathogenic bacteria bringing about nosocomial infection. Bioassay-guided fractionation of the bacterial crude extract resulted in two undescribed macrocyclic polyketide analogs, with anti-infective activities against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis (MIC 3.1-5.0 µg/mL). In order to identify the polyketide biosynthetic machinery termed type-I polyketide synthase (pks-I) encoding biologically active secondary metabolites in this strain, the ketosynthase-coding regions of DNA with ≈700 bp size, were amplified, and the partial sequence was submitted in the GenBank (accession number MH157093). The titled compounds were classified under macrocyclic polyketides bearing dodecahydropyrano-trioxacyclooctadecine-dione and trioxo-octadecahydro-1H-benzo[o]tetraoxacyclopentacosine-carboxylate functionalities. Structure-activity correlation analysis displayed that hydrophobic descriptor of the studied compounds could play a prominent role in its anti-infective property against the opportunistic pathogens. Further, in silico molecular docking studies were performed in the allosteric sites of penicillin-binding protein (PBP2a) coded by mecA genes of MRSA, and the best binding pose for each compound (docking score -8.47 kcal/mol and -9.58 kcal/mol, respectively) could be correlated with their in vitro antibacterial activities. The pks-I assisted biosynthetic pathway of macrocyclic polyketides through step-wise decarboxylative condensation initiated by malonate-acyl carrier protein corroborated their structural attributes. Chemical mining of the studied macroalgae-associated heterotrophic bacterium thus revealed the promising antagonistic properties of macrocyclic polyketides isolated from Shewanella algae MTCC 12715 against multidrug-resistant pathogens.

Combinatorial Biosynthesis of Sulfated Benzenediol Lactones with a Phenolic Sulfotransferase from Fusarium graminearum PH-1

Total biosynthesis or whole-cell biocatalytic production of sulfated small molecules relies on the discovery and implementation of appropriate sulfotransferase enzymes. Although fungi are prominent biocatalysts and have been used to sulfate drug-like phenolics, no gene encoding a sulfotransferase enzyme has been functionally characterized from these organisms. Here, we identify a phenolic sulfotransferase, FgSULT1, by genome mining from the plant-pathogenic fungus Fusarium graminearum PH-1. We expressed FgSULT1 in a Saccharomyces cerevisiae chassis to modify a broad range of benzenediol lactones and their nonmacrocyclic congeners, together with an anthraquinone, with the resulting unnatural natural product (uNP) sulfates displaying increased solubility. FgSULT1 shares low similarity with known animal and plant sulfotransferases. Instead, it forms a sulfotransferase family with putative bacterial and fungal enzymes for phase II detoxification of xenobiotics and allelochemicals. Among fungi, putative FgSULT1 homologues are encoded in the genomes of Fusarium spp. and a few other genera in nonsyntenic regions, some of which may be related to catabolic sulfur recycling. Computational structure modeling combined with site-directed mutagenesis revealed that FgSULT1 retains the key catalytic residues and the typical fold of characterized animal and plant sulfotransferases. Our work opens the way for the discovery of hitherto unknown fungal sulfotransferases and provides a synthetic biological and enzymatic platform that can be adapted to produce bioactive sulfates, together with sulfate ester standards and probes for masked mycotoxins, precarcinogenic toxins, and xenobiotics.IMPORTANCE Sulfation is an expedient strategy to increase the solubility, bioavailability, and bioactivity of nutraceuticals and clinically important drugs. However, chemical or biological synthesis of sulfoconjugates is challenging. Genome mining, heterologous expression, homology structural modeling, and site-directed mutagenesis identified FgSULT1 of Fusarium graminearum PH-1 as a cytosolic sulfotransferase with the typical fold and active site architecture of characterized animal and plant sulfotransferases, despite low sequence similarity. FgSULT1 homologues are sparse in fungi but form a distinct clade with bacterial sulfotransferases. This study extends the functionally characterized sulfotransferase superfamily to the kingdom Fungi and demonstrates total biosynthetic and biocatalytic synthetic biological platforms to produce unnatural natural product (uNP) sulfoconjugates. Such uNP sulfates may be utilized for drug discovery in human and veterinary medicine and crop protection. Our synthetic biological methods may also be adapted to generate masked mycotoxin standards for food safety and environmental monitoring applications and to expose precarcinogenic xenobiotics.

Intrinsic and Extrinsic Programming of Product Chain Length and Release Mode in Fungal Collaborating Iterative Polyketide Synthases

Combinatorial biosynthesis with fungal polyketide synthases (PKSs) promises to produce unprecedented bioactive "unnatural" natural products (uNPs) for drug discovery. Genome mining of the dothideomycete Rhytidhysteron rufulum uncovered a collaborating highly reducing PKS (hrPKS)-nonreducing PKS (nrPKS) pair. These enzymes produce trace amounts of rare S-type benzenediol macrolactone congeners with a phenylacetate core in a heterologous host. However, subunit shuffling and domain swaps with voucher enzymes demonstrated that all PKS domains are highly productive. This contradiction led us to reveal novel programming layers exerted by the starter unit acyltransferase (SAT) and the thioesterase (TE) domains on the PKS system. First, macrocyclic vs linear product formation is dictated by the intrinsic biosynthetic program of the TE domain. Next, the chain length of the hrPKS product is strongly influenced in trans by the off-loading preferences of the nrPKS SAT domain. Last, TE domains are size-selective filters that facilitate or obstruct product formation from certain priming units. Thus, the intrinsic programs of the SAT and TE domains are both part of the extrinsic program of the hrPKS subunit and modulate the observable metaprogram of the whole PKS system. Reconstruction of SAT and TE phylogenies suggests that these domains travel different evolutionary trajectories, with the resulting divergence creating potential conflicts in the PKS metaprogram. Such conflicts often emerge in chimeric PKSs created by combinatorial biosynthesis, reducing biosynthetic efficiency or even incapacitating the system. Understanding the points of failure for such engineered biocatalysts is pivotal to advance the biosynthetic production of uNPs.

Factor XIIIa inhibitors as potential novel drugs for venous thromboembolism

Human factor XIIIa (FXIIIa) is a multifunctional transglutaminase with a significant role in hemostasis. FXIIIa catalyzes the last step in the coagulation process. It stabilizes the blood clot by cross-linking the α- and γ-chains of fibrin. It also protects the newly formed clot from plasmin-mediated fibrinolysis, primarily by cross-linking α2-antiplasmin to fibrin. Furthermore, FXIIIa is a major determinant of clot size and clot's red blood cells content. Therefore, inhibitors targeting FXIIIa have been considered to develop a new generation of anticoagulants to prevent and/or treat venous thromboembolism. Several inhibitors of FXIIIa have been discovered or designed including active site and allosteric site small molecule inhibitors as well as natural and modified polypeptides. This work reviews the structural, biochemical, and pharmacological aspects of FXIIIa inhibitors so as to advance their molecular design to become more clinically relevant.

Stereochemical determination of four 10-membered ring resorcylic acid lactones from the desert plant endophytic fungus Chaetosphaeronema hispidulum

Four 10-membered ring resorcylic acid lactones (RALs) including a new compound hispidulactone F (1) and three known analogs hispidulactone B (2), 2 R, 4R-sonnerlactone (3), and 2 R, 4S-sonnerlactone (4) were isolated from the special bioenvironmental desert plant endophytic fungus Chaetosphaeronema hispidulum. The structure of the new compound hispidulactone F (1) was determined by extensive spectra analysis including HR-ESI-MS, NMR (¹H, ¹³C, ¹H-¹H COSY, HSQC, and HMBC). Hispidulactone F (1) and hispidulactone B (2) were a pair of stereoisomers at C-3, whereas 2 R, 4R-sonnerlactone (3) and 2 R, 4S-sonnerlactone (4) were another pair of stereoisomers at C-4. The stereochemistries of the hydroxyl groups at C-3 in 1 and 2, and at C-4 in 3 and 4 were first determined by modified Mosher's reactions. Thus, the absolute configuration C-3 in hispidulactone B (2) was not right in our previous report, and was rectified to be R. Compounds 1 and 4 were evaluated for their cytotoxic effects on the proliferation of HepG2. The possible biosynthetic pathway of compounds 1-4 was also presented.

Methylglucosylation of Phenolic Compounds by Fungal Glycosyltransferase-Methyltransferase Functional Modules

Glycosylation endows both natural and synthetic small molecules with modulated physicochemical and biological properties. Plant and bacterial glycosyltransferases capable of decorating various privileged scaffolds have been extensively studied, but those from kingdom Fungi still remain underexploited. Here, we use a combination of genome mining and heterologous expression techniques to identify four novel glycosyltransferase-methyltransferase (GT-MT) functional modules from Hypocreales fungi. These GT-MT modules display decent substrate promiscuity and regiospecificity, methylglucosylating a panel of natural products such as flavonoids, stilbenoids, anthraquinones, and benzenediol lactones. Native GT-MT modules can be split up and regrouped into hybrid modules with similar or even improved efficacy as compared with native pairs. Methylglucosylation of kaempferol considerably improves its insecticidal activity against the larvae of oriental armyworm Mythimna separata (Walker). Our work provides a set of efficient biocatalysts for the combinatorial biosynthesis of small molecule glycosides that may have significant importance to the pharmaceutical, agricultural, and food industries.

Rational Reprogramming of O-Methylation Regioselectivity for Combinatorial Biosynthetic Tailoring of Benzenediol Lactone Scaffolds

O-Methylation modulates the pharmacokinetic and pharmacodynamic (PK/PD) properties of small-molecule natural products, affecting their bioavailability, stability, and binding to targets. Diversity-oriented combinatorial biosynthesis of new chemical entities for drug discovery and optimization of known bioactive scaffolds during drug development both demand efficient O-methyltransferase (OMT) biocatalysts with considerable substrate promiscuity and tunable regioselectivity that can be deployed in a scalable and sustainable manner. Here we demonstrate efficient total biosynthetic and biocatalytic platforms that use a pair of fungal OMTs with orthogonal regiospecificity to produce unnatural O-methylated benzenediol lactone polyketides. We show that rational, structure-guided active-site cavity engineering can reprogram the regioselectivity of these enzymes. We also characterize the interplay of engineered regioselectivity with substrate plasticity. These findings will guide combinatorial biosynthetic tailoring of unnatural products toward the generation of diverse chemical matter for drug discovery and the PK/PD optimization of bioactive scaffolds for drug development.

Bioactive Resorcylic Acid Lactones with Different Ring Systems from Desert Plant Chaetosphaeronema hispidulum. [corrected]

Five new resorcylic acid lactones (RALs) hispidulactones A-E (1, 4, 5, 8, and 9), a new natural product (2), and four known ones (3, 6, 7, and 10) with different ring systems were isolated from the desert plant Chaetosphaeronema hispidulum. [corrected]. The new compounds were characterized by NMR data, CD spectra, and X-ray experiment. The new natural product (2) displayed strongly biological effects on the seedlings growth of Arabidopsis thaliana, Digitaria sanguinalis, and Echinochloa crusgalli with a dose-dependent relationship. Compounds 1, 2, and 6 were also tested cytotoxic activities against three cancer cell lines HCT116, Hela, and MCF7 and only did the new natural product (2) display biological activities with IC₅₀ values at 54.86 ± 1.52, 4. 90 ± 0.02, and 20.04 ± 4.00 μM, respectively, whereas the IC₅₀ values of the positive control cis-platinum were 11.36 ± 0.42, 3.54 ± 0.12, and 14.32 ± 1.01 μM, respectively.

Methylglucosylation of aromatic amino and phenolic moieties of drug-like biosynthons by combinatorial biosynthesis

Glycosylation is a prominent strategy to optimize the pharmacokinetic and pharmacodynamic properties of drug-like small-molecule scaffolds by modulating their solubility, stability, bioavailability, and bioactivity. Glycosyltransferases applicable for "sugarcoating" various small-molecule acceptors have been isolated and characterized from plants and bacteria, but remained cryptic from filamentous fungi until recently, despite the frequent use of some fungi for whole-cell biocatalytic glycosylations. Here, we use bioinformatic and genomic tools combined with heterologous expression to identify a glycosyltransferase-methyltransferase (GT-MT) gene pair that encodes a methylglucosylation functional module in the ascomycetous fungus Beauveria bassiana The GT is the founding member of a family nonorthologous to characterized fungal enzymes. Using combinatorial biosynthetic and biocatalytic platforms, we reveal that this GT is a promiscuous enzyme that efficiently modifies a broad range of drug-like substrates, including polyketides, anthraquinones, flavonoids, and naphthalenes. It yields both O- and N-glucosides with remarkable regio- and stereospecificity, a spectrum not demonstrated for other characterized fungal enzymes. These glucosides are faithfully processed by the dedicated MT to afford 4-O-methylglucosides. The resulting "unnatural products" show increased solubility, while representative polyketide methylglucosides also display increased stability against glycoside hydrolysis. Upon methylglucosidation, specific polyketides were found to attain cancer cell line-specific antiproliferative or matrix attachment inhibitory activities. These findings will guide genome mining for fungal GTs with novel substrate and product specificities, and empower the efficient combinatorial biosynthesis of a broad range of natural and unnatural glycosides in total biosynthetic or biocatalytic formats.

Lasiodiplactone A, a novel lactone from the mangrove endophytic fungus Lasiodiplodia theobromae ZJ-HQ1

Lasiodiplactone A (1), an unprecedented lactone, was obtained from the mangrove endophytic fungus Lasiodiplodia theobromae ZJ-HQ1. The structure of 1 was established by analysis of NMR spectroscopic data and electronic circular dichroism (ECD) spectra. Lasiodiplactone A (1) was the first example of lactone that possesses a unique tetracyclic system (12/6/6/5) of RAL₁₂ (12-membered β-resorcylic acid lactone) with a pyran ring and a furan ring. A possible biogenetic pathway for 1 was proposed. Compound 1 showed anti-inflammatory activity by inhibiting nitric oxide (NO) production in lipopolysaccharide activated in RAW264.7 cells with IC₅₀ value of 23.5 μM and exhibited potential α-glucosidase inhibitory activity with IC₅₀ values of 29.4 μM.

Resorcylic acid lactones (RALs) and their structural congeners: recent advances in their biosynthesis, chemical synthesis and biology

Resorcylic acid lactones (RALs) are naturally occurring 14-membered macrolactones that constitute a class of polyketides derived from fungal metabolites and that possess significant and promising biological activity.

Concise synthesis and PTP1B inhibitory activity of (R)- and (S)-dihydroresorcylide

The present study was designed to develop a concise synthetic route for macrolide, with the purpose of confirming the absolute configuration of natural dihydroresorcylide (1) and making it more easily accessible for biological evaluation. The absolute configuration of C-3 in natural 1 was revised to be R by comparison of the rotation sign of synthetic (R)- and (S)-1. The synthetic (R)-1 was found to be a novel highly specific PTP1B inhibitor with an IC₅₀ value of 17.06 μM.

Lactones from the Sponge-Derived Fungus Talaromyces rugulosus

The marine-derived fungus Talaromyces rugulosus isolated from the Mediterranean sponge Axinella cannabina and cultured on solid rice medium yielded seventeen lactone derivatives including five butenolides (1–5), seven (3S)-resorcylide derivatives (6–12), two butenolide-resorcylide dimers (13 and 14), and three dihydroisocoumarins (15–17). Among them, fourteen compounds (1–3, 6–16) are new natural products. The structures of the isolated compounds were elucidated by 1D and 2D NMR (Nuclear Magnetic Resonance) spectroscopy as well as by ESI-HRMS (ElectroSpray Ionization-High Resolution Mass Spectrometry). TDDFT-ECD (Time-Dependent Density Functional Theory-Electronic Circular Dichroism) calculations were performed to determine the absolute configurations of chiral compounds. The butenolide-resorcylide dimers talarodilactones A and B (13 and 14) exhibited potent cytotoxicity against the L5178Y murine lymphoma cell line with IC₅₀ values of 3.9 and 1.3 µM, respectively.

Antifungal and Cytotoxic β-Resorcylic Acid Lactones from a Paecilomyces Species

Eight new β-resorcylic acid lactones (RALs), including the hypothemycin-type compounds paecilomycins N-P (1-3) and the radicicol-type metabolites dechloropochonin I (4), monocillins VI (5) and VII (6), 4'-hydroxymonocillin IV (7), and 4'-methoxymonocillin IV (8), along with nine known RALs (9-17), were isolated from the cultures of Paecilomyces sp. SC0924. Compounds 1 and 2 feature a novel 6/11/5 ring system, and 3 is the first 5'-keto RAL. The structures of 1-8 were elucidated on the basis of extensive spectroscopic analysis, X-ray diffraction analysis, and theoretical calculations of ECD spectra. Compounds 3, 5, and 6 exhibit cytotoxicity against MCF-7, A549, and HeLa cells, and compounds 5 and 7 display antifungal activity against Peronophythora litchii.

Sumalactones A–D, four new curvularin-type macrolides from a marine deep sea fungus Penicillium Sumatrense

Four new curvularin-type macrolides were isolated from a marine fungus Penicillium Sumatrense and their absolute configurations were determined by CD spectra and modified Mosher's methods.

Characterization of Three Tailoring Enzymes in Dutomycin Biosynthesis and Generation of a Potent Antibacterial Analogue

The anthracycline natural product dutomycin and its precursor POK-MD1 were isolated from Streptomyces minoensis NRRL B-5482. The dutomycin biosynthetic gene cluster was identified by genome sequencing and disruption of the ketosynthase gene. Two polyketide synthase (PKS) systems are present in the gene cluster, including a type II PKS and a rare highly reducing iterative type I PKS. The type I PKS DutG repeatedly uses its active sites to create a nine-carbon triketide chain that is subsequently transferred to the α-l-axenose moiety of POK-MD1 at 4″-OH to yield dutomycin. Using a heterologous recombination approach, we disrupted a putative methyltransferase gene (dutMT1) and two glycosyltransferase genes (dutGT1 and dutGT2). Analysis of the metabolites of these mutants revealed the functions of these genes and yielded three dutomycin analogues SW140, SW91, and SW75. The major product SW91 in Streptomyces minoensis NRRL B-5482-ΔDutMT1 was identified as 12-desmethyl-dutomycin, suggesting that DutMT1 is the dedicated 12-methyltransferase. This was confirmed by the in vitro enzymatic assay. DutGT1 and DutGT2 were found to be responsible for the introduction of β-d-amicetose and α-l-axenose, respectively. Dutomycin and SW91 showed strong antibacterial activity against Staphylococcus aureus and methicillin-resistant S. aureus, whereas POK-MD1 and SW75 had no obvious inhibition, which revealed the essential role of the C-4″ triketide chain in antibacterial activity. The minimal inhibitory concentration of SW91 against the two strains was 0.125 μg mL(-1), lower than that of dutomycin (0.25 μg mL(-1)), indicating that the antibacterial activity of dutomycin can be improved through biosynthetic structural modification.

Penicimenolides A-F, Resorcylic Acid Lactones from Penicillium sp., isolated from the Rhizosphere Soil of Panax notoginseng

Five new 12-membered resorcylic acid lactone derivatives, penicimenolides A-E (1-5), one new ring-opened resorcylic acid lactone derivative penicimenolide F (6), and six known biogenetically related derivatives (7-12) were isolated from the culture broth of a strain of Penicillium sp. (NO. SYP-F-7919), a fungus obtained from the rhizosphere soil of Panax notoginseng collected from the Yunnan province of China. Their structures were elucidated by extensive NMR analyses, a modified Mosher's method, chemical derivatization and single crystal X-ray diffraction analysis. Compounds 2-4 exhibited potent cytotoxicity against the U937 and MCF-7 tumour cell lines and showed moderate cytotoxic activity against the SH-SY5Y and SW480 tumour cell lines. The substitution of an acetyloxy or 2-hydroxypropionyloxy group at C-7 significantly increased the cytotoxic activity of the resorcylic acid lactone derivatives. Subsequently, the possible mechanism of compound 2 against MCF-7 cells was preliminarily investigated by in silico analysis and experimental validation, indicating compound 2 may act as a potential MEK/ERK inhibitor. Moreover, proteomics analysis was performed to explore compound 2-regulated concrete mechanism underlying MEK/ERK pathway, which is still need further study in the future. In addition, compounds 2-4 and 7 exhibited a significant inhibitory effect on NO production induced by LPS.

Insights into Adaptations to a Near-Obligate Nematode Endoparasitic Lifestyle from the Finished Genome of Drechmeria coniospora

Nematophagous fungi employ three distinct predatory strategies: nematode trapping, parasitism of females and eggs, and endoparasitism. While endoparasites play key roles in controlling nematode populations in nature, their application for integrated pest management is hindered by the limited understanding of their biology. We present a comparative analysis of a high quality finished genome assembly of Drechmeria coniospora, a model endoparasitic nematophagous fungus, integrated with a transcriptomic study. Adaptation of D. coniospora to its almost completely obligate endoparasitic lifestyle led to the simplification of many orthologous gene families involved in the saprophytic trophic mode, while maintaining orthologs of most known fungal pathogen-host interaction proteins, stress response circuits and putative effectors of the small secreted protein type. The need to adhere to and penetrate the host cuticle led to a selective radiation of surface proteins and hydrolytic enzymes. Although the endoparasite has a simplified secondary metabolome, it produces a novel peptaibiotic family that shows antibacterial, antifungal and nematicidal activities. Our analyses emphasize the basic malleability of the D. coniospora genome: loss of genes advantageous for the saprophytic lifestyle; modulation of elements that its cohort species utilize for entomopathogenesis; and expansion of protein families necessary for the nematode endoparasitic lifestyle.

Diversity-Oriented Combinatorial Biosynthesis of Hybrid Polyketide Scaffolds from Azaphilone and Benzenediol Lactone Biosynthons

Two disparate polyketide families, the benzenediol lactones and the azaphilones, are produced by fungi using iterative polyketide synthase (iPKS) enzymes consisting of collaborating partner subunits. Exploitation of this common biosynthetic logic using iPKS subunit shuffling allowed the diversity-oriented combinatorial biosynthesis of unprecedented polyketide scaffolds new to nature, bearing structural motifs from both of these orthogonal natural product families. Starter unit acyltransferase domain replacements proved necessary but not sufficient to guarantee communication between iPKS subunits.

Reconstitution of Fungal Nonribosomal Peptide Synthetases in Yeast and In Vitro

The emergence of next-generation sequencing has provided new opportunities in the discovery of new nonribosomal peptides (NRPs) and NRP synthethases (NRPSs). However, there remain challenges for the characterization of these megasynthases. While genetic methods in native hosts are critical in elucidation of the function of fungal NRPS, in vitro assays of intact heterologously expressed proteins provide deeper mechanistic insights in NRPS enzymology. Our previous work in the study of NRPS takes advantage of Saccharomyces cerevisiae strain BJ5464-npgA as a robust and versatile platform for characterization of fungal NRPSs. Here we describe the use of yeast recombination strategies in S. cerevisiae for cloning of the NRPS coding sequence in 2μ-based expression vector; the use of affinity chromatography for purification of NRPS from the total S. cerevisiae soluble protein fraction; and strategies for reconstitution of NRPSs activities in vitro.

Polyketide synthase and non-ribosomal peptide synthetase thioesterase selectivity: logic gate or a victim of fate?

Thioesterases (TEs) are product offloading enzymes from FAS, PKS, and NRPS complexes. We review the diversity, structure, and mechanism of PKS and NRPS TEs and analyze TE loading and release steps as possible logic gates with a view to predicting TE function in new pathways.

The Distant Siblings-A Phylogenomic Roadmap Illuminates the Origins of Extant Diversity in Fungal Aromatic Polyketide Biosynthesis

In recent years, the influx of newly sequenced fungal genomes has enabled sampling of secondary metabolite biosynthesis on an unprecedented scale. However, explanations of extant diversity which take into account both large-scale phylogeny reconstructions and knowledge gained from multiple genome projects are still lacking. We analyzed the evolutionary sources of genetic diversity in aromatic polyketide biosynthesis in over 100 model fungal genomes. By reconciling the history of over 400 nonreducing polyketide synthases (NR-PKSs) with corresponding species history, we demonstrate that extant fungal NR-PKSs are clades of distant siblings, originating from a burst of duplications in early Pezizomycotina and thinned by extensive losses. The capability of higher fungi to biosynthesize the simplest precursor molecule (orsellinic acid) is highlighted as an ancestral trait underlying biosynthesis of aromatic compounds. This base activity was modified during early evolution of filamentous fungi, toward divergent reaction schemes associated with biosynthesis of, for example, aflatoxins and fusarubins (C4–C9 cyclization) or various anthraquinone derivatives (C6–C11 cyclization). The functional plasticity is further shown to have been supplemented by modularization of domain architecture into discrete pieces (conserved splice junctions within product template domain), as well as tight linkage of key accessory enzyme families and divergence in employed transcriptional factors. Although the majority of discord between species and gene history is explained by ancient duplications, this landscape has been altered by more recent duplications, as well as multiple horizontal gene transfers. The 25 detected transfers include previously undescribed events leading to emergence of, for example, fusarubin biosynthesis in Fusarium genus. Both the underlying data and the results of present analysis (including alternative scenarios revealed by sampling multiple reconciliation optima) are maintained as a freely available web-based resource: http://cropnet.pl/metasites/sekmet/nrpks_2014.

TAK1 selective inhibition: state of the art and future opportunities

The mitogen activated protein kinase kinase kinase transforming growth factor-β-activated kinase 1 (TAK1) has emerged as an interesting therapeutic target for inflammatory diseases and cancer. TAK1 is a tightly regulated kinase that represents a key signaling node in cellular responses to inflammatory stimuli, modulating both expression of inflammatory mediators and cell death. The first inhibitors described for TAK1 exploit the active site cysteine residue found in this kinase, but more recently both type I ATP hinge-binding inhibitors and type II DFG-out inhibitors have been described. This article will review the emerging role of TAK1 kinase in inflammation, the current state of the art for small molecule inhibitor development and opportunities for chemical biology approaches.

Structure, absolute configuration, and conformational study of resorcylic acid derivatives and related congeners from the fungus Penicillium brocae

A new resorcylic acid derivative (4) and five new loop-opened resorcylic acid-related congeners (5–9), were identified from the marine mangrove-derived endophyte Penicillium brocae MA-192. All compounds were evaluated for the antioxidant activity against DPPH and ABTS radicals.

Modular total syntheses of the marine-derived resorcylic Acid lactones cochliomycins a and B using a late-stage nozaki-hiyama-kishi macrocyclization reaction

The natural products cochliomycin A (1) and cochliomycin B (2), two resorcylic acid lactones obtained from marine sources, have been prepared in a concise and stereocontrolled manner from the readily accessible building blocks 4-6. Olefin cross-metathesis, trans-esterification and Nozaki-Hiyama-Kishi (NHK) macrocyclization reactions were employed in the key steps. Hydrolysis of the immediate precursor to cochliomycin B affords the resorcylic acid lactone zeaenol (24).

Resorcylic acid lactone biosynthesis relies on a stereotolerant macrocyclizing thioesterase

Zearalenone and radicicol are highly related resorcylic acid lactones with the rare property of having opposite stereochemical configurations of the secondary alcohol involved in lactone formation. The ability of the thioesterases from the zearalenone and radicicol biosynthetic pathways to macrocyclize both D and L configured synthetic substrate analogs was biochemically characterized and showed that both enzymes were highly stereotolerant, macrocyclizing both substrates with similar kinetic parameters. This observed stereotolerance is consistent with a proposed evolution of both natural products from a common ancestral resorcylic acid lactone.

Diversity-oriented combinatorial biosynthesis of benzenediol lactone scaffolds by subunit shuffling of fungal polyketide synthases

Combinatorial biosynthesis aspires to exploit the promiscuity of microbial anabolic pathways to engineer the synthesis of new chemical entities. Fungal benzenediol lactone (BDL) polyketides are important pharmacophores with wide-ranging bioactivities, including heat shock response and immune system modulatory effects. Their biosynthesis on a pair of sequentially acting iterative polyketide synthases (iPKSs) offers a test case for the modularization of secondary metabolic pathways into "build-couple-pair" combinatorial synthetic schemes. Expression of random pairs of iPKS subunits from four BDL model systems in a yeast heterologous host created a diverse library of BDL congeners, including a polyketide with an unnatural skeleton and heat shock response-inducing activity. Pairwise heterocombinations of the iPKS subunits also helped to illuminate the innate, idiosyncratic programming of these enzymes. Even in combinatorial contexts, these biosynthetic programs remained largely unchanged, so that the iPKSs built their cognate biosynthons, coupled these building blocks into chimeric polyketide intermediates, and catalyzed intramolecular pairing to release macrocycles or α-pyrones. However, some heterocombinations also provoked stuttering, i.e., the relaxation of iPKSs chain length control to assemble larger homologous products. The success of such a plug and play approach to biosynthesize novel chemical diversity bodes well for bioprospecting unnatural polyketides for drug discovery.