Purification and properties of the Streptomyces peucetius DpsC beta-ketoacyl : acyl carrier protein synthase III that specifies the propionate-starter unit for type II polyketide biosynthesis

Biosynthesis of the polyketide-derived carbon skeleton of daunorubicin (DNR ) begins with propionate rather than acetate, which is the starter unit for most other aromatic polyketides. The dpsC gene has been implicated in spec ifying the unique propionate-starter unit, and it encodes a protein that is very similar to the Escherichia coli beta-ketoacyl:acyl carrier protein (A CP) synthase III (FabH or KS III) enzyme of fatty acid biosynthesis. Purifi ed DpsC was found to use propionyl-coenzyme A as substrate and to be acylat ed by propionate at the Ser-118 residue. DpsC exhibits KS III activity in c atalyzing The condensation of propionyl-CoA and malonyl-ACP, and also funct ions as an acyltransferase in the transfer of propionate to an ACP. The Dps C enzyme has a high-substrate specificity, utilizing only propionyl-CoA, an d not malonyl-CoA, 2-methylmalonyl-CoA or acetyl-CoA, as the starter unit o f DNR biosynthesis.