Precursor Supply Increases the Accumulation of 4-Hydroxy-6-(4-hydroxyphenyl)-α-pyrone after NRPS-PKS Gene Expression

Identification and Functional Characterization of Fungal Chalcone Synthase and Chalcone Isomerase

By mining fungal genomic information, a noncanonical iterative type I PKS fused with an N-terminal adenylation-thiolation didomain, which catalyzes the formation of naringenin chalcone, was found. Structural prediction and molecular docking analysis indicated that a C-terminal thioesterase domain was involved in the Claisen-type cyclization. An enzyme responsible for formation of (2S)-flavanone in the biosynthesis of fungal flavonoids was also identified. Collectively, these findings demonstrate unprecedented fungal biosynthetic machinery leading to plant-like metabolites.

Labelling studies in the biosynthesis of polyketides and non-ribosomal peptides

Covering: 2015 to 2022In this review, we discuss the recent advances in the use of isotopically labelled compounds to investigate the biosynthesis of polyketides, non-ribosomally synthesised peptides, and their hybrids. Also, we highlight the use of isotopes in the elucidation of their structures and investigation of enzyme mechanisms. The biosynthetic pathways of selected examples are presented in detail to reveal the principles of the discussed labelling experiments. The presented examples demonstrate that the application of isotopically labelled compounds is still the state of the art and can provide valuable information for the biosynthesis of natural products.

Fungal NRPS-PKS Hybrid Enzymes Biosynthesize New γ-Lactam Compounds, Taslactams A-D, Analogous to Actinomycete Proteasome Inhibitors

Proteasome inhibitors with γ-lactam structure, such as lactacystin and salinosporamide A, have been isolated from actinomycetes and have attracted attention as lead compounds for anticancer drugs. Previously, we identified a unique enzyme TAS1, which is the first reported fungal NRPS-PKS hybrid enzyme, from the filamentous fungus Pyricularia oryzae for the biosynthesis of a mycotoxin tenuazonic acid, a tetramic acid compound without γ-lactam structure. Homologues of TAS1 have been identified in several fungal genomes and classified into four groups (A-D). Here, we show that the group D TAS1 homologues from two filamentous fungi can biosynthesize γ-lactam compounds, taslactams A-D, with high similarity to actinomycete proteasome inhibitors. One of the γ-lactam compounds, taslactam C, showed potent proteasome inhibitory activity. In contrast to actinomycete γ-lactam compounds which require multiple enzymes for biosynthesis, the TAS1 homologue alone was sufficient for the biosynthesis of the fungal γ-lactam compounds.

A fungal NRPS-PKS enzyme catalyses the formation of the flavonoid naringenin

Biosynthesis of the flavonoid naringenin in plants and bacteria is commonly catalysed by a type III polyketide synthase (PKS) using one p-coumaroyl-CoA and three malonyl-CoA molecules as substrates. Here, we report a fungal non-ribosomal peptide synthetase -polyketide synthase (NRPS-PKS) hybrid FnsA for the naringenin formation. Feeding experiments with isotope-labelled precursors demonstrate that FnsA accepts not only p-coumaric acid (p-CA), but also p-hydroxybenzoic acid (p-HBA) as starter units, with three or four malonyl-CoA molecules for elongation, respectively. In vitro assays and MS/MS analysis prove that both p-CA and p-HBA are firstly activated by the adenylation domain of FnsA. Phylogenetic analysis reveals that the PKS portion of FnsA shares high sequence homology with type I PKSs. Refactoring the biosynthetic pathway in yeast with the involvement of fnsA provides an alternative approach for the production of flavonoids such as isorhamnetin and acacetin.

Aspcandine: A Pyrrolobenzazepine Alkaloid Synthesized by a Fungal Nonribosomal Peptide Synthetase-Polyketide Synthase Hybrid

Characterization of an orphan biosynthetic gene cluster found in the fungus Aspergillus candidus CBS 102.13 resulted in the discovery of a pyrrolobenzazepine alkaloid, aspcandine (1). The unique molecular scaffold of 1 is synthesized by the nonribosomal peptide synthetase-polyketide synthase hybrid AcdB, which unusually incorporates 3-hydroxy-l-kynurenine as a building block. AcdB subsequently performs one round of chain elongation using malonyl-CoA, which is followed by the chain release to furnish the tricyclic system of 1.