Through an inactivation experiment followed by comple-mentation, the gerGTII gene was previously character-ized as a chalcosyltransferase gene involved in the biosynthesis of dihydochalcomycin. The glycosyltrans-ferase gerGTI was identified as a deoxyallosyltransferase required for the glycosylation of D-mycinose sugar. This 6-deoxyhexose sugar was converted to mycinose, via bis-O-methylation, following attachment to the polyketide lactone during dihydrochalcomycin biosynthesis. Gene sequence alignment of gerGTI to several glycosyltransferases revealed a consensus se-quence motif that appears to be characteristic of the enzymes in this sub-group of the glycosyltransferase family. To characterize its putative function, genetic disruption of gerGTI in the wild-type strain Streptomyces sp. KCTC 0041BP and in the gerGTII-deleted mutant (S. sp. ΔgerGTII), as well as complementation of gerGTII in S. sp. ΔgerGTII-GTI, were carried out, and the products were analyzed by LC/MS. S. sp. ΔgerGTII-GTI mutant produced dihydrochalconolide macrolide. S. sp. ΔgerGTI and S. sp. ΔgerGTII-GTI complementation of gerGTII yielded dihydrochalconolide without the mycinose sugar. The intermediate shows that gerGTI encodes a de-oxyallosyltransferase that acts after gerGTII.

Keywords: biosynthesis, glycosyltransferase, macrolide, Streptomyces