Aug 2026· Journal of Industrial Microbiology & Biotechnology· Vol 53· 0 citations· 23 references
Medicine
TL;DR
Functional analysis of the condensation domain in vivo demonstrated that it is essential for clavaic acid biosynthesis, and expands the understanding of LovB-like iPKSs and establishes this enzyme family as a promising source of cryptic fungal polyketides.
Abstract
Abstract Fungal iterative type I polyketide synthases (iPKSs) generate structurally diverse natural products. A subset of these assembly line enzymes, exemplified by LovB from Aspergillus terreus, contains a C-terminal condensation domain bearing a noncanonical HRxxxDG motif. While these LovB-like iPKSs are widely distributed in fungi, the majority remain uncharacterized, leaving both their associated polyketide products and the function of their unusual condensation domains largely unexplored. Here, we report the characterization of a LovB-like iPKS from Aspergillus clavatus. Heterologous reconstitution of this PKS system in Aspergillus nidulans led to the discovery of clavaic acid, a previously undescribed polyketide featuring a trimethylated trans-decalin core and an all-E-configured carboxytriene side chain. Functional analysis of the condensation domain in vivo demonstrated that it is essential for clavaic acid biosynthesis. Surprisingly, whereas the conserved arginine residue within the HRxxxDG motif was dispensable for product formation, the conserved aspartate residue was strictly required. These findings expand our understanding of LovB-like iPKSs and establish this enzyme family as a promising source of cryptic fungal polyketides. One-sentence summary Genome-guided discovery of a trans-decalin-containing polyketide encoded by a LovB-like polyketide synthase in Aspergillus clavatus.
Condensation (C) domains in nonribosomal peptide synthetase (NRPS) pathways exhibit versatile functions that drive biosynthetic and chemical novelty. Through genome mining for atypical C domains, we identified a hybrid NRPS/polyketide synthase (PKS) biosynthetic gene cluster (mxg) from Cystobacterineae sp. MCy9003 and discovered myxoglucamides, a family of glycolipopeptides featuring an unprecedented vinyl-substituted γ-amino acid bearing an α-hydroxy/α-ketoamide functionality. Heterologous expression of the promoter-refactored pathway revealed new O-acylated myxoglucamides, and subsequent studies unveiled the C domain-like enzyme MxgH as a promiscuous O-acyltransferase decorating the glucose moiety with short-chain acyl groups. Biosynthetic investigations demonstrated that the unusual γ-amino acid originates from l-glutamate. Completion of the cryptic β-hydroxylation of peptidyl carrier protein-tethered glutamate by the α-ketoglutarate-dependent dioxygenase OxMxgA occurs only concomitantly with upstream chain extension, revealing a bidirectional checkpoint for substrate fidelity. Unexpectedly, the C-domain-like interface domain IMxgB is dispensable for this coupled transformation. Mutational analysis of the FMN-dependent monooxygenase encoded by mxgE, together with characterization of a shunt metabolite, supported its role in α-oxidation for α-hydroxy/α-ketoamide formation during γ-amino acid assembly. Together, these findings uncover an unrecognized biosynthetic logic for generating vinyl-substituted, α-oxidized γ-amino acids and substantially expand the functional repertoire of NRPS/PKS assembly lines.
Tingting Wang, Alexander Popoff, Maja Hunter et al.· Angewandte Chemie· 2 citations
Genome mining of the marine-derived Streptomyces sp. S42 uncovered a type II polyketide synthetase (T2 PKS) biosynthetic gene cluster (BGC) harboring a gene for 3-ketoacyl-ACP synthase III (KAS III), a hallmark of non-acetate starter unit incorporation, suggesting that the BGC may produce previously unidentified aromatic polyketides. Heterologous expression and promoter engineering of this prioritized BGC in host Streptomyces albus J1074 activated the biosynthetic pathway, leading to the isolation of eight new polycyclic aromatic derivatives, verrucones A–H (1–8). Comprehensive structural elucidation via NMR and HRESIMS revealed that these compounds feature either a 2-methylbutyryl or an isobutyryl starter unit and can be classified into three distinct skeletal types. Based on these findings and bioinformatic analysis, a plausible biosynthetic pathway for 1–8 involving divergent spontaneous cyclization from a common nascent polyketide intermediate was proposed. Among the isolated compounds, 1–5 exhibited inhibitory activity against several protein tyrosine phosphatases (PTPs) with IC50 values ranging from 1.84 μM to 24.82 μM. This study presents a successful case study demonstrating that combining KAS III-targeted genome mining with heterologous expression is a viable approach for discovering non-acetate-primed aromatic polyketides.
Xingkun Hao, Ming Yang, Ping Yan et al.· Microorganisms· 0 citations
Enzyme engineering serves as a powerful tool in biocatalysis, enabling the development of enzymes with improved stability, activity, and specificity for a range of academic, industrial, and pharmaceutical applications. However, a limited understanding of sequence-structure-function relationships in terpene synthases, the enzymes that form the complex polycyclic hydrocarbon skeletons of terpenoid natural products, presents a major challenge in predicting and engineering the products of terpene synthases. In this study, we investigated the product profiles of two bacterial variediene synthases, OdVS from Olivibacter domesticus and PsVS from Prauserella shujinwangii, and found that they share some products with the bacterial phomopsene synthase, PmS from Allokutzneria albata, despite low sequence similarity. Thirteen diterpenes were isolated and structurally elucidated including two previously unreported compounds. A series of variants of OdVS, PsVS, and PmS were constructed by targeting conserved residues around the active site and aided in the identification of key residues that control the cyclization pathway. Ultimately, mutation of a single residue, PsVSY86L, was found to switch the major product of PsVS from the tricyclic variediene to the tetracyclic phomopsene, although this switch came at the cost of significantly reduced overall yield indicating a tradeoff between activity and product diversification.
Polyketides are a structurally diverse class of natural products with immense therapeutic potential. However, the biosynthetic output of discrete polyketide synthases (PKSs) has been constrained by a fundamental functional limitation: unlike modular Type I systems, discrete PKS systems typically lack integrated enoyl reductase (ER) activity. This constraint restricts their chemical repertoire primarily to unsaturated polyenes or aromatic scaffolds. Here, we characterize PbrC16, a FabV-family ER from a manumycin-type biosynthetic gene cluster (BGC) in Peterkaempfera bronchialis. This enzyme represents the first experimentally validated ER capable of functioning within discrete PKS architectures. In vitro biochemical reconstitution demonstrates that PbrC16 along with its homologue ScFabV catalyze iterative enoyl reductions in both β-ketoacyl-acyl carrier protein synthase III (KAS III)-dependent and highly reducing (HR) Type II PKS contexts, enabling the complete saturation of long-chain polyketide intermediates. Structural and computational analyses reveal the molecular basis for its exceptional substrate promiscuity and versatile acyl carrier protein (ACP) recognition. These findings resolve a long-standing "reductive gap" in discrete PKS biology and provide a "plug-and-play" module for the rational engineering of saturated polyketide scaffolds.
Yan Gao, Kai Jiang, Yuhan Dai et al.· Journal of the American Chem...· 0 citations
Orcinol synthase (RdORS) from Rhododendron dauricum is a plant type III polyketide synthase involved in the biosynthesis of orsellinic acid-derived metabolites. In contrast to the related Cannabis sativa tetraketide synthase (CsTKS), which preferentially accepts medium-chain acyl-CoAs, RdORS selectively utilizes short-chain starter substrates. Here, we investigated the structural basis underlying this substrate selectivity by combining X-ray crystallography, mutational analysis, and biochemical characterization. The crystal structure of RdORS revealed that its catalytic cavity is substantially smaller than that of CsTKS because of a bulky tryptophan (Trp) 357 residue positioned at the cavity bottom. In vitro enzymatic assays demonstrated that wild-type RdORS efficiently generated tetraketide-derived products from acetyl- and butyryl-CoAs with three malonyl-CoAs, whereas productive tetraketide formation progressively diminished as starter-substrate chain length increased. Structural analysis of the RdORS Trp357S mutant revealed marked cavity expansion without perturbation of the overall catalytic framework. Correspondingly, the Trp357S substitution enabled RdORS to utilize medium-chain acyl-CoAs up to decanoyl-CoA, thereby partially recapitulating the substrate preference of CsTKS. Thus, our results provided direct structural evidence that Trp357 is a key structural determinant underlying the distinct starter-substrate preferences of RdORS.
Y. Nakashima, S. Y. Y. Hnin, Subin Kim et al.· Chemical and pharmaceutical...· 0 citations
Quorum sensing in Gram-positive bacteria commonly relies on posttranslationally modified peptide pheromones. In Bacillus subtilis, the prenyltransferase ComQ catalyzes tryptophan prenylation of the quorum-sensing peptide ComX, but the structural basis of this unique peptide modification has remained unclear. Here we identified a previously uncharacterized ComQ homolog, StheQ, and its cognate peptide substrate, StheX, from Sphaerobacter thermophilus and investigated their structural and functional relationship. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis demonstrated that StheQ catalyzes prenylation of the tryptophan residue located second from the C-terminus of StheX. Crystal structures of apo StheQ and its complexes with a farnesyl pyrophosphate analog revealed that StheQ adopts the all-α-helical fold of the trans-isoprenyl diphosphate synthase (IPPS) superfamily while possessing an active-site architecture adapted for peptide-based indole prenylation. The structures identified a single Mg2+-binding site associated with the first aspartic acid-rich motif and showed no evidence for metal coordination at the pseudo-second aspartic acid-rich motif. Site-directed mutagenesis, complex formation assays, and docking analyses identified a peptide-binding pocket adjacent to the active site and suggested that N215 contributes to productive positioning of the acceptor tryptophan. These findings establish the structural basis for peptide prenylation by a ComQ-family enzyme, providing insight into the evolution of peptide-based indole prenylation within the IPPS superfamily, and support the view that ComQ-family enzymes constitute a distinct functional branch specialized for peptide modification.
