Analysis of the biosynthetic gene cluster for the polyether antibiotic monensin in Streptomyces cinnamonensis and evidence for the role of monB and monC genes in oxidative cyclization

Abstract

SummaryThe analysis of a candidate biosynthetic gene cluster (97 kbp) for the polyether ionophore monensin from Streptomyces cinnamonensis has revealed a modular polyketide synthase composed of eight separate multienzyme subunits housing a total of 12 extension modules, and flanked by numerous other genes for which a plausible function in monensin biosynthesis can be ascribed. Deletion of essentially all these clustered genes specifically abolished monensin production, while overexpression in S. cinnamonensis of the putative pathway-specific regulatory gene monR led to a fivefold increase in monensin production. Experimental support is presented for a recently-proposed mechanism, for oxidative cyclization of a linear polyketide intermediate, involving four enzymes, the products of monBI , monBII , monCI and monCII . In frame deletion of either of the individual genes monCII (encoding a putative cyclase) or monBII (encoding a putative novel isomerase) specifically abolished monensin production. Also, heterologous expression of monCI , encoding a flavin-linked epoxidase, in S. coelicolor was shown to significantly increase the ability of S. coelicolor to epoxidize linalool, a model substrate for the presumed linear polyketide intermediate in monensin biosynthesis.

Biosynthetic Gene Cluster of the Herbicide Phosphinothricin Tripeptide from Streptomyces viridochromogenes Tü494

“…In contrast to actinorhodin production in S. coelicolor (9) and monensin production in Streptomyces cinnamonensis (25), PTT production in S. viridochromogenes was not significantly affected by overexpression of the pathway-specific regulatory gene; the overexpression of prpA seemed only to increase the expression of PTT biosynthetic genes.…”

The Biosynthesis of Polyketide Metabolites by Dinoflagellates

“…The identification of a putative flavin-linked epoxidase and epoxide hydrolases (for cyclization) in these gene clusters support this hypothesis. In the case of monensin, deletions of these genes abolished production of the polyether (Oliynyk et al, 2003). The carbon backbone of brevetoxin is predicted to be a mostly all trans polyene that is epoxidized and undergoes a similar polyepoxide cyclization (Fig.…”

Identification of a Gene Cluster of Polyether Antibiotic Lasalocid fromStreptomyces lasaliensis

“…However, all efforts to prove this attractive hypothesis failed. 11) In 2001, the gene-cluster of monensin was indentified, 12,13) and several gene disruption experiments on epoxidase (MonCI) and hydrolases (MonBI, BII) established that these three enzymes were responsible for the conversion of all-E triene into monensin via epoxidation and cyclization. 14,15) Yet, the detailed mechanism for the enzymatic polyether formation has remained unconfirmed.…”