Genetically-modified activation strategy facilitates the discovery of sesquiterpene-derived metabolites from Penicillium brasilianum

Genome mining has revealed that Penicillium spp. possess numerous down-regulated or cryptic biosynthetic gene clusters (BGCs). This finding hinted that our investigation of fungal secondary metabolomes is limited. Herein, we report a genetically-modified activation strategy to characterize the spectrum of sesquiterpenoids produced by Penicillium brasilianum CGMCC 3.4402. The cryptic or down-regulated pathways were stimulated by constitutive expression of pathway-specific regulator gene berA responsible for berkeleyacetals biosynthesis from Neosartorya glabra. Chemical analysis of the extracts from the mutant strain Pb-OE:berA enabled the isolation of two new compounds including one bisabolene-type arpenibisabolane C (1), one daucane-type arpenicarotane C (4), along with four known sesquiterpenoids including arpenibisabolane A (2), eupenicisirenins A (3), arpenicarotane B (5) and aspterric acid (6). The assignments of their structures were elucidated from detailed analyses of spectroscopic data, electronic circular dichroism calculation, and biogenetic considerations. The bioassay of isolated compounds (1-6) exhibited no cytotoxic activities against three tumor cells including MCF-7, HepG2, and A549. Arpenibisabolane C (1) and A (2) showed weak inhibition bioactivities on aquatic pathogens Vibrio owensii and Vibrio algivorus. Moreover, phylogenetic analysis and sequence alignments of crucial sesquiterpene synthases were performed. Based on the chemical structures and biogenetic investigations, a hypothetic pathway of new compounds (1, 4) was proposed.

Cloning and functional characterization of sesquiterpene synthase genes from Inonotus obliquus using a Saccharomyces cerevisiae expression system

Inonotus obliquus (Chaga mushroom) is a large medicinal and edible fungus that contains a wealth of bioactive terpenoids. However, the detection of certain low-abundance sesquiterpenoids remains a challenge due to limitations in extraction and analytical techniques. Furthermore, the synthase genes responsible for the biosynthesis of the identified terpenoids have not yet been clearly elucidated. To address this, our study combined transcriptome mining with yeast heterologous expression to investigate the synthase genes involved in sesquiterpenoid production in I. obliquus. We successfully identified eight sesquiterpene synthase genes and one farnesyltransferase. Among these, only cis-β-farnesene, synthesized by IoTPS2, had been previously detected before in the sclerotium of I. obliquus, while the other nine sesquiterpenoids-including neoisolongifolene-8-ol, β-longipinene, vetiselinenol, isolongifolene, 7,8-dehydro-8a-hydroxy-, 4a,8b,10b,11a-tetramethylbicyclo[6.3.0]undec-1-en-5-one, 6,11-oxido-acor-4-ene, β-maaliene, neointermedeol, and longifolenaldehyde-were discovered for the first time. This research provides a critical scientific foundation for expanding the known repertoire of sesquiterpenoids and their corresponding synthase genes in I. obliquus.

Genome Mining of the Marine-Derived Fungus Trichoderma erinaceum F1-1 Unearths Bergamotene-Type Sesquiterpenoids

Terpenoids are a vast group of natural products known for their remarkable biological properties and structural diversity. UbiA terpene synthases are increasingly recognized for producing various terpenoids. In this study, we identified a biosynthetic gene cluster (bgt) encoding a UbiA terpene synthase BgtA in the genome of the marine-derived fungus Trichoderma erinaceum F1-1. The gene bgtA was validated to encode the biosynthesis of (-)-α-trans-bergamotene (1). Heterologous expression of the bgt gene cluster in the characterized host Aspergillus nidulans LO8030 activated the biosynthetic pathway, leading to the isolation of eight previously undocumented bergamotene-derived sesquiterpenoids (2-9). Their structures, including the absolute configurations, were elucidated by a combination of spectroscopic analysis, ECD spectra, chemical hydrolysis, single-crystal X-ray diffraction, and biosynthetic considerations. We further demonstrated that the production of these structurally intricate sesquiterpenoids in heterologous expression is attributable to the concerted action of the UbiA terpene synthase BgtA, the cytochrome P450 BgtC, and endogenous enzymes. This study underscores the immense biosynthetic potential of fungal UbiA terpene synthase gene clusters and shows genome mining is a promising strategy for the discovery of novel terpenoids from fungi.

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.

Mechanistic characterisation of a fungal fusicoccane-type diterpene synthase involved in the biosynthesis of talaro-7,13-diene

The cyclisation mechanism of the fungal fusicoccane (FC)-type diterpene synthase (DTS) TadA was investigated by extensive isotopic labelling experiments, and the pH-dependency of the product selectivity of this enzyme was explored. These studies provide new insights into the cyclisation mechanisms of FC-type DTSs.

Exploration of diverse secondary metabolites from Penicillium brasilianum by co-culturing with Armillaria mellea

Bioinformatic analysis revealed that the genomes of ubiquitous Penicillium spp. might carry dozens of biosynthetic gene clusters (BGCs), yet many clusters have remained uncharacterized. In this study, a detailed investigation of co-culture fermentation including the basidiomycete Armillaria mellea CPCC 400891 and the P. brasilianum CGMCC 3.4402 enabled the isolation of five new compounds including two bisabolene-type sesquiterpenes (arpenibisabolanes A and B), two carotane-type sesquiterpenes (arpenicarotanes A and B), and one polyketide (arpenichorismite A) along with seven known compounds. The assignments of their structures were deduced by the extensive analyses of detailed spectroscopic data, electronic circular dichroism spectra, together with delimitation of the biogenesis. Most new compounds were not detected in monocultures under the same fermentation conditions. Arpenibisabolane A represents the first example of a 6/5-fused bicyclic bisabolene. The bioassay of these five new compounds exhibited no cytotoxic activities in vitro against three human cancer cell lines (A549, MCF-7, and HepG2). Moreover, sequence alignments and bioinformatic analysis to other metabolic pathways, two BGCs including Pb-bis and Pb-car, responsible for generating sesquiterpenoids from co-culture were identified, respectively. Furthermore, based on the chemical structures and deduced gene functions of the two clusters, a hypothetic metabolic pathway for biosynthesizing induced sesquiterpenoids was proposed. These results demonstrated that the co-culture approach would facilitate bioprospecting for new metabolites even from the well-studied microbes. Our findings would provide opportunities for further understanding of the biosynthesis of intriguing sesquiterpenoids via metabolic engineering strategies. KEY POINTS: • Penicillium and Armillaria co-culture facilitates the production of diverse secondary metabolites • Arpenibisabolane A represents the first example of 6/5-fused bicyclic bisabolenes • A hypothetic metabolic pathway for biosynthesizing induced sesquiterpenoids was proposed.

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.

Characterization of UbiA terpene synthases with a precursor overproduction system in Escherichia coli

Expression and purification of membrane-bound proteins remains a challenge and limits enzymology efforts, contributing to a substantial knowledge gap in the biochemical functions of many proteins found in nature. Accordingly, the study of bacterial UbiA terpene synthases (TSs) has been limited due to the experimental hurdles required to purify active enzymes for characterization in vitro. Previous work employed the use of microsomes or crude membrane fractions to test enzyme activity; however, these methods can be labor intensive, require access to an ultracentrifuge, or may not be suitable for all membrane-bound TSs. We detail here an alternative strategy for the in vivo expression and biochemical characterization of the membrane associated UbiA TSs by employing a precursor overproduction system in Escherichia coli.

Characterization of a new fusicoccane-type diterpene synthase and an associated P450 enzyme

Fusicoccane-type terpenoids are a subgroup of diterpenoids featured with a unique 5-8-5 ring system. They are widely distributed in nature and possess a variety of biological activities. Up to date, only five fusicoccane-type diterpene synthases have been identified. Here, we identify a two-gene biosynthetic gene cluster containing a new fusicoccane-type diterpene synthase gene tadA and an associated cytochrome P450 gene tadB from Talaromyces wortmannii ATCC 26942. Heterologous expression reveals that TadA catalyzes the formation of a new fusicoccane-type diterpene talaro-7,13-diene. D2O isotope labeling combined with site-directed mutagenesis indicates that TadA might employ a different C2,6 cyclization strategy from the known fusicoccane-type diterpene synthases, in which a neutral intermediate is firstly formed and then protonated by an environmental proton. In addition, we demonstrate that the associated cytochrome P450 enzyme TadB is able to catalyze multiple oxidation of talaro-7,13-diene to yield talaro-6,13-dien-5,8-dione.

Discovery and analysis of a new class of triterpenes derived from hexaprenyl pyrophosphate

Triterpenes are derived from squalene or oxidosqualene. However, a new class of triterpenes derived from hexaprenyl pyrophosphate has been recently discovered, formed by a new family of chimeric class I triterpene synthases. The cyclization mechanisms of triterpenes were elucidated by isotopic labeling and protein structural analyses, which helps understand the biosynthesis of triterpenes in nature.