Cooperative involvement of glycosyltransferases in the transfer of amino sugars during the biosynthesis of the macrolactam sipanmycin by Streptomyces sp. strain CS149

Abstract

Macrolactams comprise a family of natural compounds with important bioactivities, such as antibiotic, antifungal, and antiproliferative activities. Sipanmycins A and B are two novel members of this family, with two sugar moieties attached to the aglycon. In the related macrolactam vicenistatin, the sugar moiety has been proven to be essential for cytotoxicity. In this work, the gene cluster responsible for the biosynthesis of sipanmycins (sip cluster) in Streptomyces sp. strain CS149 is described and the steps involved in the glycosylation of the final compounds unraveled. Also, the cooperation of two different glycosyltransferases in each glycosylation step is demonstrated. Additionally, the essential role of SipO2 as an auxiliary protein in the incorporation of the second deoxy sugar is addressed. In light of the results obtained by the generation of mutant strains and in silico characterization of the sip cluster, a biosynthetic pathway for sipanmycins and the two deoxy sugars attached is proposed. Finally, the importance of the hydroxyl group at C-10 of the macrolactam ring and the sugar moieties for cytotoxicity and antibiotic activity of sipanmycins is shown.