Functional Analysis of OleY l -Oleandrosyl 3- O -Methyltransferase of the Oleandomycin Biosynthetic Pathway in Streptomyces antibioticus

Abstract

Oleandomycin, a macrolide antibiotic produced by Streptomyces antibioticus , contains two sugars attached to the aglycon: l -oleandrose and d -desosamine. oleY codes for a methyltransferase involved in the biosynthesis of l -oleandrose. This gene was overexpressed in Escherichia coli to form inclusion bodies and in Streptomyces lividans , producing a soluble protein. S. lividans overexpressing oleY was used as a biotransformation host, and it converted the precursor l -olivosyl-erythronolide B into its 3- O -methylated derivative, l -oleandrosyl-erythronolide B. Two other monoglycosylated derivatives were also substrates for the OleY methyltransferase: l -rhamnosyl- and l -mycarosyl-erythronolide B. OleY methyltransferase was purified yielding a 43-kDa single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The native enzyme showed a molecular mass of 87 kDa by gel filtration chromatography, indicating that the enzyme acts as a dimer. It showed a narrow pH range for optimal activity, and its activity was clearly stimulated by the presence of several divalent cations, being maximal with Co ²⁺ . The S. antibioticus OleG2 glycosyltransferase is proposed to transfer l -olivose to the oleandolide aglycon, which is then converted into l -oleandrose by the OleY methyltransferase. This represents an alternative route for l -oleandrose biosynthesis from that in the avermectin producer Streptomyces avermitilis , in which l -oleandrose is transferred to the aglycon by a glycosyltransferase.