Two glycosyltransferases and a glycosidase are involved in oleandomycin modification during its biosynthesis by Streptomyces antibioticus

A 5.2 kb region from the oleandomycin gene cluster in Streptomyces antibioticus located between the oleandomycin polyketide synthase gene and sugar biosynthetic genes was cloned. Sequence analysis revealed the presence of three open reading frames (designated olel, oleN2 and oleR). The olel gene product resembled glycosyltransferases involved in macrolide inactivation including the oleD product, a previously described glycosyltransferase from S. antibioticus. The oleN2 gene product showed similarities with different aminotransferases involved in the biosynthesis of 6-deoxyhexoses. The oleR gene product was similar to several glucosidases from different origins. The olel, oleR and oleD genes were expressed in Streptomyces lividans. Olel and OleD intracellular proteins were partially purified by affinity chromatography in an UDP-glucuronic acid agarose column and OleR was detected as a major band from the culture supernatant. Olel and OleD showed oleandomycin glycosylating activity but they differ in the pattern of substrate specificity: Olel being much more specific for oleandomycin. OleR showed glycosidase activity converting glycosylated oleandomycin into active oleandomycin. A model is proposed integrating these and previously reported results for intracellular inactivation, secretion and extracellular reactivation of oleandomycin.