Polyketide Synthase-Mediated O-Methyloxime Formation in the Biosynthesis of the Oximidine Anticancer Agents.

Bacterial trans-acyltransferase polyketide synthases (trans-AT PKSs) are modular megaenzymes that employ unusual catalytic domains to assemble diverse bioactive natural products. One such PKS is responsible for the biosynthesis of the oximidine anticancer agents, oxime-substituted benzolactone enamides that inhibit vacuolar H+ -ATPases. Here, we describe the identification of the oximidine gene cluster in Pseudomonas baetica and the characterization of four novel oximidine variants, including a structurally simpler intermediate that retains potent anticancer activity. Using a combination of in vivo, in vitro and computational approaches, we experimentally elucidate the oximidine biosynthetic pathway and reveal an unprecedented mechanism for O-methyloxime formation. We show that this process involves a specialized monooxygenase and methyltransferase domain and provide insight into their activity, mechanism and specificity. Our findings expand the catalytic capabilities of trans-AT PKSs and identify potential strategies for the production of novel oximidine analogues.

Beyond peptide bond formation: the versatile role of condensation domains in natural product biosynthesis.

Covering: up to the end of 2020Nonribosomal peptide synthetases are remarkable molecular machines that produce a wide range of structurally complex peptide natural products with important applications in medicine and agriculture. Condensation domains play a central role in these biosynthetic pathways by catalysing amide bond formation between various aminoacyl substrates. In recent years, however, it has become increasingly clear that the catalytic repertoire of C domains extends far beyond conventional peptide bond formation. C domains have been shown to perform highly diverse functions during nonribosomal peptide assembly, such as ß-lactam formation, dehydration, hydrolysis, chain length control, cycloaddition, Pictet-Spengler cyclization, Dieckmann condensation and recruitment of auxiliary enzymes. In this review, a comprehensive overview of the multifaceted role of C domains in the biosynthesis of specialized metabolites in bacteria and fungi is presented. Different perspectives are also offered on how the exceptional functional versatility of C domains may be exploited for bioengineering approaches to expand the chemical diversity of nonribosomal peptides and other natural products.