Inactivation of the polyketide synthase, 6-methylsalicylic acid synthase, by the specific modification of Cys-204 of the β-ketoacyl synthase by the fungal mycotoxin cerulenin

摘要

pCerulenin, [(2iS,3R)-/i2,3-epoxy-4-oxo-7,10-dodecadienoylamide], a mycotoxin produced by iCephalosporium caerulens,/i irreversibly inactivated 6-methylsalicylic acid synthase from iPenicillium patulum./i A combination of radiolabelling studies with [sup3/supH]cerulenin, proteolytic and chemical digestion and N-terminal sequencing of labelled peptides indicated that the site of cerulenin modification is the highly reactive substrate-binding Cys-204 of the β-ketoacyl synthase enzyme component. The thiol-specific inhibitor, iodoacetamide, was also shown to alkylate this residue. These findings are analogous with those observed for the reaction of cerulenin and iodoacetamide with type-I fatty acid synthases, demonstrating the close similarity between 6-methylsalicylic acid synthase and type-I fatty acid synthases./p