Functional analysis of desVIII homologues involved in glycosylation of macrolide antibiotics by interspecies complementation

The DesVIII is an auxiliary protein which enhances the transfer of TDP-d-desosamine catalyzed by DesVII glycosyltransferase in the biosynthesis of macrolide antibiotics, neomethymycin, methymycin and pikromycin, in Streptomyces venezuelae ATCC 15439. Homologues of the desVIII gene are present in a number of aminosugar-containing antibiotic biosynthetic gene clusters including eryCII from the erythromycin producer Saccharopolyspora erythraea, oleP1 from the oleandomycin producer Streptomyces antibioticus, dnrQ from the doxorubicin producer Streptomyces peucetius, and tylMIII from the tylosin producer Streptomyces fradiae. In order to gain further insight into the function of these DesVIII homologues, interspecies complementation experiments were carried out by expressing each gene in a desVIII deletion mutant strain of S. venezuelae. Complementation by expressing EryCII, OleP1, and DnrQ in this mutant strain restored the production of glycosylated macrolides to an approximate level of 66%, 26% and 26%, respectively, compared to self-complementation by DesVIII. However, expression of TylMIII did not restore the antibiotic production. These results suggest that the DesVIII homologues (except for TylMIII) can functionally replace the native DesVIII for glycosylation to proceed in vivo and their functions are similar in acting as glycosyltransferase auxiliary proteins. The requirement of glycosyltransferase auxiliary protein seems to be more widespread in polyketide biosynthetic pathways than previously known.