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■ Starter Unit Specificity of the Asukamycin “Upper” Chain Polyketide Synthase and the Branched-Chain Fatty Acid Synthase of Streptomyces nodosus subsp. asukaensis

Yiding Hu and Heinz G. Floss*

*Department of Chemistry, University of Washington, Seattle, WA 98195-1700, U.S.A.

Abstract

Asukamycin, a member of the manumycin family of antibiotics, obtained from Streptomyces nodosus subsp. asukaensis, contains two amide-linked polyketide chains, one of which, the “upper” chain, is initiated by cyclohexanecarboxylic acid as the starter unit. Analysis of the congeners of asukamycin present in the fermentation and of the fatty acid spectrum of the mycelial lipids revealed that the “upper” chain polyketide synthase (PKS) and the branched-chain fatty acid synthase (FAS) of S. nodosus ssp. asukaensis share qualitatively, although not quantitatively, the same starter unit selectivity for branched chain and alicyclic carboxylic acids. Feeding of various alicyclic carboxylic acids of different ring size resulted in the formation of new asukamycin analogs as well as changes in the fatty acid spectrum. Feeding of various alicyclic carboxylic acids also shut off the endogenous production of cyclohexanecarboxylic acid.