Biosynthesis of Cosmosporasides Reveals the Assembly Line for Fungal Hybrid Terpenoid Saccharides

Biosynthesis of (-)-Vinigrol

(-)-Vinigrol is one of the most complex and challenging molecules in total synthesis; however, the parallel biosynthetic strategy employed by nature for the synthesis of this compound has not yet been identified. In this study, we identified a minimal gene cluster encoding a diterpene cyclase (VniA) and a cytochrome P450 (VniB) which enables the synthesis of (-)-vinigrol through three steps. VniA first cyclizes geranylgeranyl diphosphate to generate an unusual vinigrol-type diterpene skeleton, and then VniB catalyzes the allylic C(sp3)-H iterative oxidation. Further genome mining investigation provides new fungal sources for this rare and valuable vinigrol-type diterpene skeleton.

Total biosynthesis of cotylenin diterpene glycosides as 14-3-3 protein-protein interaction stabilizers

Cotylenins (CNs) are bioactive fungal diterpene glycosides that exhibit stabilizing activity on 14-3-3 protein-protein interactions (PPIs), which has significant therapeutic potential. Although CNs were isolated as early as 1970, their biosynthetic pathway has remained unclear, and their limited supply has hindered further research. Here, we report the identification of the biosynthetic gene cluster cty and elucidation of the biosynthetic pathway of CNs. Our investigation reveals the roles of glycosyltransferase, methyltransferase, and prenyltransferase enzymes in the assembly and modification of the saccharide moiety, as well as the multifunctional oxidation activity of the P450 enzyme CtyA. We leveraged this knowledge to achieve the total biosynthesis of not only key intermediates such as CN-C, E, F, and I, but also a novel, unnatural CN derivative using heterologous expression. This showcases the potential of pathway enzymes as catalytic tools to expand the structural diversity of diterpene glycosides. Furthermore, the stabilization effects of pathway intermediates on 14-3-3 PPIs underscore the importance of saccharide modifications in bioactivity. These findings provide a foundation for future rational synthesis of cotylenin A and other structurally diverse derivatives, broadening the scope of diterpene glycoside production.

Developing filamentous fungal chassis for natural product production

The growing demand for green and sustainable production of high-value chemicals has driven the interest in microbial chassis. Recent advances in synthetic biology and metabolic engineering have reinforced filamentous fungi as promising chassis cells to produce bioactive natural products. Compared to the most used model organisms, Escherichia coli and Saccharomyces cerevisiae, most filamentous fungi are natural producers of secondary metabolites and possess an inherent pre-mRNA splicing system and abundant biosynthetic precursors. In this review, we summarize recent advances in the application of filamentous fungi as chassis cells. Emphasis is placed on strategies for developing a filamentous fungal chassis, including the establishment of mature genetic manipulation and efficient genetic tools, the catalogue of regulatory elements, and the optimization of endogenous metabolism. Furthermore, we provide an outlook on the advanced techniques for further engineering and application of filamentous fungal chassis.

Modifications of Prenyl Side Chains in Natural Product Biosynthesis

In recent years, there has been a growing interest in understanding the enzymatic machinery responsible for the modifications of prenyl side chains and elucidating their roles in natural product biosynthesis. This interest stems from the pivotal role such modifications play in shaping the structural and functional diversity of natural products, as well as from their potential applications to synthetic biology and drug discovery. In addition to contributing to the diversity and complexity of natural products, unique modifications of prenyl side chains are represented by several novel biosynthetic mechanisms. Representative unique examples of epoxidation, dehydrogenation, oxidation of methyl groups to carboxyl groups, unusual C-C bond cleavage and oxidative cyclization are summarized and discussed. By revealing the intriguing chemistry and enzymology behind these transformations, this comprehensive and comparative review will guide future efforts in the discovery, characterization and application of modifications of prenyl side chains in natural product biosynthesis.

Biosynthesis and Assembly Logic of Fungal Hybrid Terpenoid Natural Products

In recent decades, fungi have emerged as significant sources of diverse hybrid terpenoid natural products, and their biosynthetic pathways are increasingly unveiled. This review mainly focuses on elucidating the various strategies underlying the biosynthesis and assembly logic of these compounds. These pathways combine terpenoid moieties with diverse building blocks including polyketides, nonribosomal peptides, amino acids, p-hydroxybenzoic acid, saccharides, and adenine, resulting in the formation of plenty of hybrid terpenoid natural products via C-O, C-C, or C-N bond linkages. Subsequent tailoring steps, such as oxidation, cyclization, and rearrangement, further enhance the biological diversity and structural complexity of these hybrid terpenoid natural products. Understanding these biosynthetic mechanisms holds promise for the discovery of novel hybrid terpenoid natural products from fungi, which will promote the development of potential drug candidates in the future.

Cyclo-farnesyl Diphosphate-Dependent Prenylation in Fungi

A conserved two-gene cassette in fungi was discovered by genome mining, which encodes a UbiA family intramembrane prenyltansferase (VviA) and a haloacid dehalogenase-like hydrolase family terpene cyclase (VviB), respectively. A series of in vivo and in vitro investigations revealed that VviA exclusively uses VviB-synthesized drim-8-ene diphosphate (cyclo-farnesyl diphosphate) as the native prenyl donor to catalyze prenylation on d-mannitol, showcasing a previously unidentified function of UbiA-type prenyltransferases and a new prenylation manner in fungi.

Discovery of a polyketide carboxylate phytotoxin from a polyketide glycoside hybrid by β-glucosidase mediated ester bond hydrolysis

Fungal phytotoxins cause significant harm to agricultural production or lead to plant diseases. Discovering new phytotoxins, dissecting their formation mechanism and understanding their action mode are important for controlling the harmful effects of fungal phytopathogens. In this study, a long-term unsolved cluster (polyketide synthase 16, PKS16 cluster) from Fusarium species was thoroughly investigated and a series of new metabolites including both complex α-pyrone-polyketide glycosides and simple polyketide carboxylates were identified from F. proliferatum. The whole pathway reveals an unusual assembly and inactivation process for phytotoxin biosynthesis, with key points as follows: (1) a flavin dependent monooxygenase catalyzes Baeyer-Villiger oxidation on the linear polyketide side chain of α-pyrone-polyketide glycoside 8 to form ester bond compound 1; (2) a β-glucosidase unexpectedly mediates the ester bond hydrolysis of 1 to generate polyketide carboxylate phytotoxin 2; (3) oxidation occurring on the terminal inert carbons of 2 by intracellular oxidase(s) eliminates its phytotoxicity. Our work identifies the chemical basis of the PKS16 cluster in phytotoxicity, shows that polyketide carboxylate is a new structural type of phytotoxin in Fusarium and importantly uncovers a rare ester bond hydrolysis function of β-glucosidase family enzymes.

Genome Mining Reveals a UbiA-Type Prenyltransferase Access to Farnesylation of Diketopiperazines

UbiA-type prenyltransferases (PTases) are significant enzymes that lead to structurally diverse meroterpenoids. Herein, we report the identification and characterization of an undescribed UbiA-type PTase, FtaB, that is responsible for the farnesylation of indole-containing diketopiperazines (DKPs) through genome mining. Heterologous expression of the fta gene cluster and non-native pathways result in the production of a series of new C2-farnesylated DKPs. This study broadens the reaction scope of UbiA-type PTases and expands the chemical diversity of meroterpenoids.

Acremosides A-G, Sugar Alcohol-Conjugated Acyclic Sesquiterpenes from a Sponge-Derived Acremonium Species

Seven new sugar alcohol-conjugated acyclic sesquiterpenes, acremosides A-G (1-7), were isolated from the cultures of the sponge-associated fungus Acremonium sp. IMB18-086 cultivated with heat-killed Pseudomonas aeruginosa. The structures were determined by comprehensive analyses of 1D and 2D NMR spectroscopic data. The relative configurations were established by J-based configuration analysis and acetonide derivatization. The absolute configurations were elucidated by the Mosher ester method and ECD calculations. The structures of acremosides E-G (5-7) featured the linear sesquiterpene skeleton with a tetrahydrofuran moiety attached to a sugar alcohol. Acremosides A (1) and C-E (3-5) showed significant inhibitory activities against hepatitis C virus (EC50 values of 4.8-8.8 μM) with no cytotoxicity (CC50 of >200 μM).

Targeted Discovery of Glycosylated Natural Products by Tailoring Enzyme-Guided Genome Mining and MS-Based Metabolome Analysis

Glycosides make up a biomedically important class of secondary metabolites. Most naturally occurring glycosides were isolated from plants and bacteria; however, the chemical diversity of glycosylated natural products in fungi remains largely unexplored. Herein, we present a paradigm to specifically discover diverse and bioactive glycosylated natural products from fungi by combining tailoring enzyme-guided genome mining with mass spectrometry (MS)-based metabolome analysis. Through in vivo genes deletion and heterologous expression, the first fungal C-glycosyltransferase AuCGT involved in the biosynthesis of stromemycin was identified from Aspergillus ustus. Subsequent homology-based genome mining for fungal glycosyltransferases by using AuCGT as a probe revealed a variety of biosynthetic gene clusters (BGCs) containing its homologues in diverse fungi, of which the glycoside-producing capability was corroborated by high-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis. Consequently, 28 fungal aromatic polyketide C/O-glycosides, including 20 new compounds, were efficiently discovered and isolated from the three selected fungi. Moreover, several novel fungal C/O-glycosyltransferases, especially three novel α-pyrone C-glycosyltransferases, were functionally characterized and verified in the biosynthesis of these glycosides. In addition, a proof of principle for combinatorial biosynthesis was applied to design the production of unnatural glycosides in Aspergillus nidulans. Notably, the newly discovered glycosides exhibited significant antiviral, antibacterial, and antidiabetic activities. Our work demonstrates the promise of tailoring enzyme-guided genome-mining approach for the targeted discovery of fungal glycosides and promotes the exploration of a broader chemical space for natural products with a target structural motif in microbial genomes.

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A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as alscholarine A from Alstonia scholaris.