Biosynthetic gene-based secondary metabolite screening: a new diterpene, methyl phomopsenonate, from the fungus Phomopsis amygdali

Mechanistic characterisation of the diterpene synthase for clitopilene and identification of isopentalenene synthase from the fungus Clitopilus passeckerianus

Two terpene synthases from the pleuromutilin producing fungus Clitopilus passeckerianus were functionally characterised. The first enzyme CpTS1 produces the new diterpene clitopilene with a novel 6-6-5-5 tetracyclic skeleton, while the second enzyme CpTS2 makes the new sesquiterpene isopentalenene. The CpTS1 reaction mechanism was studied in depth using experimental and theoretical approaches.

A Functional Switch Between Asperfumene and Fusicoccadiene Synthase and Entrance to Asperfumene Biosynthesis through a Vicinal Deprotonation-Reprotonation Process

The diterpene synthase AfAS was identified from Aspergillus fumigatiaffinis. Its amino acid sequence and-according to a structural model-active site architecture are highly similar to those of the fusicocca-2,10(14)-diene synthase PaFS, but AfAS produces a structurally much more complex diterpene with a novel 6-5-5-5 tetracyclic skeleton called asperfumene. The cyclisation mechanism of AfAS was elucidated through isotopic labelling experiments and DFT calculations. The reaction cascade proceeds in its initial steps through similar intermediates as for the PaFS cascade, but then diverges through an unusual vicinal deprotonation-reprotonation process that triggers a skeletal rearrangement at the entrance to the steps leading to the unique asperfumene skeleton. The structural model revealed only one major difference between the active sites: The PaFS residue F65 is substituted by I65 in AfAS. Intriguingly, site-directed mutagenesis experiments with both diterpene synthases revealed that position 65 serves as a bidirectional functional switch for the biosynthesis of tetracyclic asperfumene versus structurally less complex diterpenes.

Biosynthesis of fungal terpenoids

Covering: up to August 2023Terpenoids, which are widely distributed in animals, plants, and microorganisms, are a large group of natural products with diverse structures and various biological activities. They have made great contributions to human health as therapeutic agents, such as the anti-cancer drug paclitaxel and anti-malarial agent artemisinin. Accordingly, the biosynthesis of this important class of natural products has been extensively studied, which generally involves two major steps: hydrocarbon skeleton construction by terpenoid cyclases and skeleton modification by tailoring enzymes. Additionally, fungi (Ascomycota and Basidiomycota) serve as an important source for the discovery of terpenoids. With the rapid development of sequencing technology and bioinformatics approaches, genome mining has emerged as one of the most effective strategies to discover novel terpenoids from fungi. To date, numerous terpenoid cyclases, including typical class I and class II terpenoid cyclases as well as emerging UbiA-type terpenoid cyclases, have been identified, together with a variety of tailoring enzymes, including cytochrome P450 enzymes, flavin-dependent monooxygenases, and acyltransferases. In this review, our aim is to comprehensively present all fungal terpenoid cyclases identified up to August 2023, with a focus on newly discovered terpenoid cyclases, especially the emerging UbiA-type terpenoid cyclases, and their related tailoring enzymes from 2015 to August 2023.

Isotopic labelings for mechanistic studies

The intricate mechanisms in the biosynthesis of terpenes belong to the most challenging problems in natural product chemistry. Methods to address these problems include the structure-based site-directed mutagenesis of terpene synthases, computational approaches, and isotopic labeling experiments. The latter approach has a long tradition in biosynthesis studies and has recently experienced a revival, after genome sequencing enabled rapid access to biosynthetic genes and enzymes. Today, this allows for a combined approach in which isotopically labeled substrates can be incubated with recombinant terpene synthases. These clearly defined reaction setups can give detailed mechanistic insights into the reactions catalyzed by terpene synthases, and recent developments have substantially deepened our understanding of terpene biosynthesis. This chapter will discuss the state of the art and introduce some of the most important methods that make use of isotopic labelings in mechanistic studies on terpene synthases.

Spiroluchuene A Synthase: A Cyclase from Aspergillus luchuensis Forming a Spirotetracyclic Diterpene

The diterpene synthase AlTS was identified from Aspergillus luchuensis. AlTS catalyses the formation of the diterpene hydrocarbon spiroluchuene A, which exhibits a novel skeleton characterised by a spirocyclic ring system. The cyclisation mechanism towards this compound was elucidated through isotopic labelling experiments in conjunction with DFT calculations and metadynamic simulations. The biosynthetic intermediate luchudiene, besides the derivative spiroluchuene B, was captured from an enzyme variant obtained through site-directed mutagenesis. With its 10-membered ring luchudiene is structurally related to germacrenes and can undergo a Cope rearrangement to luchuelemene.

Total Syntheses of Polycyclic Diterpenes Phomopsene, Methyl Phomopsenonate, and iso-Phomopsene via Reorganization of C-C Single Bonds

The first total syntheses of polycyclic diterpenes phomopsene (1), methyl phomopsenonate (2), and iso-phomopsene (3) have been accomplished through the unusual cascade reorganization of C-C single bonds. This approach features: (i) a synergistic Nazarov cyclization/double ring expansions in one-step, developed by authors, to rapid and stereospecific construction of the 5/5/5/5 tetraquinane scaffold bearing contiguous quaternary centers and (ii) a one-pot strategic ring expansion through Beckmann fragmentation/recombination to efficiently assemble the requisite 5/5/6/5 tetracyclic skeleton of the target molecules 1-3. This work enables us to determine that the correct structure of iso-phomopsene is, in fact, the C7 epimer of the originally assigned structure. Finally, the absolute configurations of three target molecules were confirmed through enantioselective synthesis.

Functional characterisation of twelve terpene synthases from actinobacteria

Fifteen type I terpene synthase homologs from diverse actinobacteria that were selected based on a phylogenetic analysis of more than 4000 amino acid sequences were investigated for their products. For four enzymes with functions not previously reported from bacterial terpene synthases the products were isolated and their structures were elucidated by NMR spectroscopy, resulting in the discovery of the first terpene synthases for (+)-δ-cadinol and (+)-α-cadinene, besides the first two bacterial (-)-amorpha-4,11-diene synthases. For other terpene synthases with functions reported from bacteria before the products were identified by GC-MS. The characterised enzymes include a new epi-isozizaene synthase with monoterpene synthase side activity, a 7-epi-α-eudesmol synthase that also produces hedycaryol and germacrene A, and four more sesquiterpene synthases that produce mixtures of hedycaryol and germacrene A. Three phylogenetically related enzymes were in one case not expressed and in two cases inactive, suggesting pseudogenisation in the respective branch of the phylogenetic tree. Furthermore, a diterpene synthase for allokutznerene and a sesterterpene synthase for sesterviolene were identified.

Norditerpenoids biosynthesized by variediene synthase-associated P450 machinery along with modifications by the host cell Aspergillus oryzae

The chemical diversity of terpenoids is typically established by terpene synthase-catalyzed cyclization and diversified by post-tailoring modifications. Fungal bifunctional terpene synthase (BFTS) associated P450 enzymes have shown significant catalytic potentials through the development of various new terpenoids with different biological activities. This study discovered the BFTS and its related gene cluster from the plant endophytic fungus Didymosphaeria variabile 17020. Heterologous expression of the BFTS in Saccharomyces cerevisiae resulted in the characterization of a major product diterpene variediene (1), along with two new minor products neovariediene and neoflexibilene. Further heterologous expression of the BFTS and one cytochrome P450 enzyme VndE (CYP6138B1) in Aspergillus oryzae NSAR1 led to the identification of seven norditerpenoids (19 carbons) with a structurally unique 5/5 bicyclic ring system. Interestingly, in vivo experiments suggested that the cyclized terpene variediene (1) was modified by VndE along with the endogenous enzymes from the host cell A. oryzae through serial chemical conversions, followed by multi-site hydroxylation via A. oryzae endogenous enzymes. Our work revealed that the two-enzymes biosynthetic system and host cell machinery could produce structurally unique terpenoids.

Identification and Characterization of a Cryptic Bifunctional Type I Diterpene Synthase Involved in Talaronoid Biosynthesis from a Marine-Derived Fungus

We report the identification of the tnd biosynthetic cluster from the marine-derived fungus Aspergillus flavipes and the in vivo characterization of a cryptic type I diterpene synthase. The heterologous expression of the bifunctional terpene synthase led to the discovery of a diterpene backbone, talarodiene, harboring a benzo[a]cyclopenta[d]cyclooctane tricyclic fused ring system. The conversion of geranylgeranyl diphosphate to talarodiene was investigated using ¹³C-labeling studies, and stable isotope tracer experiments showed the biotransformation of talarodiene into talaronoid C.

Enzymatic Synthesis of Variediene Analogs

Five analogs of dimethylallyl diphosphate (DMAPP) with additional or shifted Me groups were converted with isopentenyl diphosphate (IPP) and the fungal variediene synthase from Aspergillus brasiliensis (AbVS). These enzymatic reactions resulted in the formation of several new terpene analogs that were isolated and structurally characterised by NMR spectroscopy. Several DMAPP analogs showed a changed reactivity giving access to compounds with unusual skeletons. Their formation is mechanistically rationalised and the absolute configurations of all obtained compounds were determined through a stereoselective deuteration strategy, revealing absolute configurations that are analogous to that of the natural enzyme product variediene.

Diterpenes Specially Produced by Fungi: Structures, Biological Activities, and Biosynthesis (2010–2020)

Fungi have traditionally been a very rewarding source of biologically active natural products, while diterpenoids from fungi, such as the cyathane-type diterpenoids from Cyathus and Hericium sp., the fusicoccane-type diterpenoids from Fusicoccum and Alternaria sp., the guanacastane-type diterpenoids from Coprinus and Cercospora sp., and the harziene-type diterpenoids from Trichoderma sp., often represent unique carbon skeletons as well as diverse biological functions. The abundances of novel skeletons, biological activities, and biosynthetic pathways present new opportunities for drug discovery, genome mining, and enzymology. In addition, diterpenoids peculiar to fungi also reveal the possibility of differing biological evolution, although they have similar biosynthetic pathways. In this review, we provide an overview about the structures, biological activities, evolution, organic synthesis, and biosynthesis of diterpenoids that have been specially produced by fungi from 2010 to 2020. We hope this review provides timely illumination and beneficial guidance for future research works of scholars who are interested in this area.

DFT Study on the Biosynthesis of Verrucosane Diterpenoids and Mangicol Sesterterpenoids: Involvement of Secondary-Carbocation-Free Reaction Cascades

Some experimental observations indicate that a sequential formation of secondary (2°) carbocations might be involved in some biosynthetic pathways, including those of verrucosane-type diterpenoids and mangicol-type sesterterpenoids, but it remains controversial whether or not such 2° cations are viable intermediates. Here, we performed comprehensive density functional theory calculations of these biosynthetic pathways. The results do not support previously proposed pathways/mechanisms: in particular, we find that none of the putative 2° carbocation intermediates is involved in either of the biosynthetic pathways. In verrucosane biosynthesis, the proposed 2° carbocations (II and IV) in the early stage are bypassed by the formation of the adjacent 3° carbocations and by unusual skeletal rearrangement reactions, and in the later stage, the putative 2° carbocation intermediates (VI, VII, and VIII) are not present as the proposed forms but as nonclassical structures between homoallyl and cyclopropylcarbinyl cations. In the mangicol biosynthesis, one of the two proposed 2° carbocations (X) is bypassed by a C-C bond-breaking reaction to generate a 3° carbocation with a C=C bond, while the other (XI) is bypassed by a strong hyperconjugative interaction leading to a nonclassical carbocation. We propose new biosynthetic pathways/mechanisms for the verrucosane-type diterpenoids and mangicol-type sesterterpenoids. These pathways are in good agreement with the findings of previous biosynthetic studies, including isotope-labeling experiments and byproducts analysis, and moreover can account for the biosynthesis of related terpenes.

Systematic mining of fungal chimeric terpene synthases using an efficient precursor-providing yeast chassis

Chimeric terpene synthases, termed PTTSs, are a unique family of enzymes occurring only in fungi. Characterizing PTTSs is challenging due to the complex reactions they catalyze and the structural complexity of their products. Here, by devising an efficient precursor-providing yeast chassis and incorporating a high-throughput automated platform, we identified 34 active PTTSs, which was considerably more than the number of known functional PTTSs. This effective and rapid pipeline can be employed for the characterization of other PTTSs or related terpenoid biosynthetic enzymes. By systematically analyzing the presence/absence of PTTS genes together with phylogenetic analysis, the ancestral PTTS gene was inferred to have undergone duplication and functional divergence, which led to the development of two distinct cyclization mechanisms.

Chimeric terpene synthases, which consist of C-terminal prenyltransferase (PT) and N-terminal class I terpene synthase (TS) domains (termed PTTSs here), is unique to fungi and produces structurally diverse di- and sesterterpenes. Prior to this study, 20 PTTSs had been functionally characterized. Our understanding of the origin and functional evolution of PTTS genes is limited. Our systematic search of sequenced fungal genomes among diverse taxa revealed that PTTS genes were restricted to Dikarya. Phylogenetic findings indicated different potential models of the origin and evolution of PTTS genes. One was that PTTS genes originated in the common Dikarya ancestor and then underwent frequent gene loss among various subsequent lineages. To understand their functional evolution, we selected 74 PTTS genes for biochemical characterization in an efficient precursor-providing yeast system employing chassis-based, robot-assisted, high-throughput automatic assembly. We found 34 PTTS genes that encoded active enzymes and collectively produced 24 di- and sesterterpenes. About half of these di- and sesterterpenes were also the products of the 20 known PTTSs, indicating functional conservation, whereas the PTTS products included the previously unknown sesterterpenes, sesterevisene (1), and sesterorbiculene (2), suggesting that a diversity of PTTS products awaits discovery. Separating functional PTTSs into two monophyletic groups implied that an early gene duplication event occurred during the evolution of the PTTS family followed by functional divergence with the characteristics of distinct cyclization mechanisms.

An Enzyme-Mediated Aza-Michael Addition Is Involved in the Biosynthesis of an Imidazoyl Hybrid Product of Conidiogenone B

Meleagrin B is a terpene-alkaloid hybrid natural product that contains both the conidiogenone and meleagrin scaffold. Their derivatives show diverse biological activities. We characterized the biosynthesis of (-)-conidiogenone B (1), which involves a diterpene synthase and a P450 monooxygenase. In addition, an α,β-hydrolase (Con-ABH) was shown to catalyze an aza-Michael addition between 1 and imidazole to give 3S-imidazolyl conidiogenone B (6). Compound 6 was more potent than 1 against Staphylococcus aureus strains.

Revision of the Cyclisation Mechanism for the Diterpene Spiroviolene and Investigations of Its Mass Spectrometric Fragmentation

The diterpene spiroviolene, its diterpene synthase from Streptomyces violens and the experimentally determined terpene cyclisation mechanism were reported in 2017. Recently, the structure of spiroviolene was revised based on a total synthesis, with consequences for the cyclisation mechanism. Herein, a reinvestigation of the terpene cyclisation to spiroviolene and the mass spectrometric fragmentation mechanism investigated by 13 C-labelling experiments are presented.

On the mechanism of ophiobolin F synthase and the absolute configuration of its product by isotopic labelling experiments

An ophiobolin F synthase homolog was discovered from Aspergillus calidoustus CBS121601. The cyclisation mechanism of this terpene synthase was investigated by extensive isotopic labelling experiments and the absolute configuration of its product ophiobolin F was elucidated by enantioselective deuteration.

Two Diterpene Synthases from Chryseobacterium: Chryseodiene Synthase and Wanjudiene Synthase

Two bacterial diterpene synthases (DTSs) from Chryseobacterium were characterised. The first enzyme yielded the new compound chryseodiene that closely resembles the known fusicoccane diterpenes from fungi, but its experimentally and computationally studied cyclisation mechanism is fundamentally different to the mechanism of fusicoccadiene synthase. The second enzyme produced wanjudiene, a diterpene hydrocarbon with a new skeleton, besides traces of the enantiomer of bonnadiene that was recently discovered from Allokutzneria albata.

Mechanistic Studies on Trichoacorenol Synthase from Amycolatopsis benzoatilytica

Isotopic labeling experiments performed with a newly identified bacterial trichoacorenol synthase established a 1,5-hydride shift occurring in the cyclization mechanism. During EI-MS analysis, major fragments of the sesquiterpenoid were shown to arise via cryptic hydrogen movements. Therefore, the interpretation of earlier results regarding the cyclization mechanism obtained by feeding experiments in Trichoderma is revised.

Reconstitution of biosynthetic machinery of fungal natural products in heterologous hosts

Ascomycota and basidiomycota fungi are prolific sources of biologically active natural products. Recent genomic data and bioinformatic analysis indicate that fungi possess a large number of biosynthetic gene clusters for bioactive natural products but more than 90% are silent. Heterologous expression in the filamentous fungi as hosts is one of the powerful tools to expression of the silent gene clusters. This review introduces recent studies on the total biosynthesis of representative family members via common platform intermediates, genome mining of novel di- and sesterterpenoids including detailed cyclization pathway, and development of expression host for basidiomycota genes with efficient genome editing method. In addition, this review will discuss the several strategies, for the generation of structural diversity, which are found through these studies.

A Family of Related Fungal and Bacterial Di- and Sesterterpenes: Studies on Fusaterpenol and Variediene

The absolute configuration of fusaterpenol (GJ1012E) has been revised by an enantioselective deuteration strategy. A bifunctional enzyme with a terpene synthase and a prenyltransferase domain from Aspergillus brasiliensis was characterised as variediene synthase, and the absolute configuration of its product was elucidated. The uniform absolute configurations of these and structurally related di- and sesterterpenes together with a common stereochemical course for the geminal methyl groups of GGPP unravel a similar conformational fold of the substrate in the active sites of the terpene synthases. For variediene, a thermal reaction observed during GC/MS analysis was studied in detail for which a surprising mechanism was uncovered.

Bacterial Diterpene Biosynthesis

This Minireview summarises recent developments in the biosynthesis of diterpenes by diterpene synthases in bacteria. It is structured by the class of enzyme involved in the first committed step towards diterpenes, starting with type I diterpene synthases, followed by type II enzymes and the more recently discovered UbiA-related diterpene synthases. A special emphasis lies on the reaction mechanisms of diterpene synthases that convert simple linear precursors through cationic cascades into structurally complex, usually polycyclic carbon skeletons with multiple stereogenic centres. A further main focus of this Minireview is a discussion of how these mechanisms can be unravelled. Downstream modifications to bioactive molecules are also covered.

Diterpene Biosynthesis in Actinomycetes: Studies on Cattleyene Synthase and Phomopsene Synthase

Three diterpene synthases from actinomycetes have been studied. The first enzyme from Streptomyces cattleya produced the novel compound cattleyene. The other two enzymes from Nocardia testacea and Nocardia rhamnosiphila were identified as phomopsene synthases. The cyclisation mechanism of cattleyene synthase and the EIMS fragmentation mechanism of its product were extensively studied by incubation experiments with isotopically labelled precursors. Oxidative transformations expanded the chemical space of these unique diterpenes.

Genome mining for fungal polyketide-diterpenoid hybrids: discovery of key terpene cyclases and multifunctional P450s for structural diversification

The biosynthesis of the fungal meroterpenoid chevalone E and its derivatives has been successfully elucidated and reconstituted.

Biosynthetic study of conidiation-inducing factor conidiogenone: heterologous production and cyclization mechanism of a key bifunctional diterpene synthase

Conidiogenone, a diterpene with a unique structure, is known to induce the conidiation of Penicillium cyclopium. The biosynthetic pathway of (-)-conidiogenone has been fully elucidated by the heterologous expression of biosynthetic genes in Aspergillus oryzae and by in vitro enzyme assay with ¹³C-labeled substrates. After construction of deoxyconidiogenol by the action of bifunctional terpene synthase, one cytochrome P450 catalyzes two rounds of oxidation to furnish conidiogenone. Notably, similar biosynthetic genes are conserved among more than 10 Penicillium sp., suggesting that conidiogenone is a common conidiation inducer in this genus. The cyclization mechanism catalyzed by terpene synthase, which involves successive 1,2-alkyl shifts, was fully elucidated using ¹³C-labeled geranylgeranyl pyrophosphate (GGPP) as substrate. During the structural analysis of deoxyconidiogenol, we observed broadening of some of the ¹³C signals measured at room temperature, which has not been observed with other structurally related compounds. Careful examination using techniques including ¹³C NMR studies at -80 °C, conformational analysis and prediction of the ¹³C chemical shifts using density functional theory gave insights into this intriguing phenomenon.

Crystalline Sponge Method Enabled the Investigation of a Prenyltransferase-terpene Synthase Chimeric Enzyme, Whose Product Exhibits Broadened NMR Signals

By the genome-mining approach, a chimeric enzyme of prenyltransferase-diterpene synthase was discovered from Penicillium chrysogenum MT-12. Since its product exhibited broadened NMR signals, the structural determination by only the NMR analysis was difficult, but the crystalline sponge method successfully revealed the structure with a 6-5-5-5 fused ring system. This demonstrated that the collaboration between the genome-mining and crystalline sponge method has the potential to facilitate rapid inquiries into the unexplored chemical space of small molecules.

Two Bacterial Diterpene Synthases from Allokutzneria albata Produce Bonnadiene, Phomopsene, and Allokutznerene

Two diterpene synthases from Allokutzneria albata were studied for their products, resulting in the identification of the new compound bonnadiene from the first enzyme. Although phylogenetically unrelated to fungal phomopsene synthase, the second enzyme produced a mixture of phomopsene and a biosynthetically linked new compound, allokutznerene, as well as spiroviolene. Both enzymes were subjected to in-depth mechanistic studies involving isotopic labelling experiments, metal-cofactor variation, and site-directed mutagenesis. Oxidation products of phomopsene and allokutznerene are also discussed.

Chimeric Terpene Synthases Possessing both Terpene Cyclization and Prenyltransfer Activities

Prenyltransferase (PT) and terpene synthase (TPS) are key enzymes in the formation of the basic carbon skeletons of terpenoids. The PTs determine the prenyl carbon chain length, whereas TPSs generate the structural complexity of the molecular scaffolds, forming various ring structures. Normally, PTs and TPSs are separate, independent enzymes. However, in 2007, a chimeric enzyme, in which the PT was fused with the TPS, was found in a fungus. Recent studies have revealed that such chimeric TPSs are widely distributed in fungi and function in the biosyntheses of various terpene natural products, including sesterterpenes, which are a relatively rare group of terpenoids. This review summarizes the accumulated knowledge of these recently discovered, unique, chimeric TPSs.

Three xanthone dimers from the Thai mangrove endophytic fungus Phomopsis sp. xy21

Three new xanthone dimers, named phomoxanthones C-E (1-3), were obtained from the Thai mangrove fungus Phomopsis sp. xy21, together with four known ones. The structures of these compounds were elucidated by the analysis of HRESIMS and extensive NMR spectroscopic data. The absolute configuration of 1 was established by the analysis of single-crystal X-ray diffraction with Cu Kα radiation. Phomoxanthones C (1) and D (2) possess a highly oxidized hexahydroxanthone skeleton.

Cyclopentane-forming di/sesterterpene synthases: widely distributed enzymes in bacteria, fungi, and plants

The cyclization mechanisms and structural diversification strategies of novel cyclopentane-forming terpene synthases from various organisms are reviewed.

Unearthing a sesterterpene biosynthetic repertoire in the Brassicaceae through genome mining reveals convergent evolution

Sesterterpenoids are a rare terpene class harboring untapped chemodiversity and bioactivities. Their structural diversity originates primarily from the scaffold-generating sesterterpene synthases (STSs). In fungi, all six known STSs are bifunctional, containing C-terminal trans-prenyltransferase (PT) and N-terminal terpene synthase (TPS) domains. In plants, two colocalized PT and TPS gene pairs from Arabidopsis thaliana were recently reported to synthesize sesterterpenes. However, the landscape of PT and TPS genes in plant genomes is unclear. Here, using a customized algorithm for systematically searching plant genomes, we reveal a suite of physically colocalized pairs of PT and TPS genes for the biosynthesis of a large sesterterpene repertoire in the wider Brassicaceae. Transient expression of seven TPSs from A. thaliana, Capsella rubella, and Brassica oleracea in Nicotiana benthamiana yielded fungal-type sesterterpenes with tri-, tetra-, and pentacyclic scaffolds, and notably (-)-ent-quiannulatene, an enantiomer of the fungal metabolite (+)-quiannulatene. Protein and structural modeling analysis identified an amino acid site implicated in structural diversification. Mutation of this site in one STS (AtTPS19) resulted in premature termination of carbocation intermediates and accumulation of bi-, tri-, and tetracyclic sesterterpenes, revealing the cyclization path for the pentacyclic sesterterpene (-)-retigeranin B. These structural and mechanistic insights, together with phylogenetic analysis, suggest convergent evolution of plant and fungal STSs, and also indicate that the colocalized PT-TPS gene pairs in the Brassicaceae may have originated from a common ancestral gene pair present before speciation. Our findings further provide opportunities for rapid discovery and production of sesterterpenes through metabolic and protein engineering.

Fungal volatiles - a survey from edible mushrooms to moulds

Covering: up to January 2017This review gives a comprehensive overview of the production of fungal volatiles, including the history of the discovery of the first compounds and their distribution in the various investigated strains, species and genera, as unravelled by modern analytical methods. Biosynthetic aspects and the accumulated knowledge about the bioactivity and biological functions of fungal volatiles are also covered. A total number of 325 compounds is presented in this review, with 247 cited references.

Sesterterpene ophiobolin biosynthesis involving multiple gene clusters in Aspergillus ustus

Terpenoids are the most diverse and abundant natural products among which sesterterpenes account for less than 2%, with very few reports on their biosynthesis. Ophiobolins are tricyclic 5–8–5 ring sesterterpenes with potential pharmaceutical application. Aspergillus ustus 094102 from mangrove rizhosphere produces ophiobolin and other terpenes. We obtained five gene cluster knockout mutants, with altered ophiobolin yield using genome sequencing and in silico analysis, combined with in vivo genetic manipulation. Involvement of the five gene clusters in ophiobolin synthesis was confirmed by investigation of the five key terpene synthesis relevant enzymes in each gene cluster, either by gene deletion and complementation or in vitro verification of protein function. The results demonstrate that ophiobolin skeleton biosynthesis involves five gene clusters, which are responsible for C15, C20, C25, and C30 terpenoid biosynthesis.

Identification and manipulation of the pleuromutilin gene cluster from Clitopilus passeckerianus for increased rapid antibiotic production

Semi-synthetic derivatives of the tricyclic diterpene antibiotic pleuromutilin from the basidiomycete Clitopilus passeckerianus are important in combatting bacterial infections in human and veterinary medicine. These compounds belong to the only new class of antibiotics for human applications, with novel mode of action and lack of cross-resistance, representing a class with great potential. Basidiomycete fungi, being dikaryotic, are not generally amenable to strain improvement. We report identification of the seven-gene pleuromutilin gene cluster and verify that using various targeted approaches aimed at increasing antibiotic production in C. passeckerianus, no improvement in yield was achieved. The seven-gene pleuromutilin cluster was reconstructed within Aspergillus oryzae giving production of pleuromutilin in an ascomycete, with a significant increase (2106%) in production. This is the first gene cluster from a basidiomycete to be successfully expressed in an ascomycete, and paves the way for the exploitation of a metabolically rich but traditionally overlooked group of fungi.