Divergent evolution of an atypical S -adenosyl- l -methionine–dependent monooxygenase involved in anthracycline biosynthesis

Significance Natural products produced by Streptomyces are widely used in the treatment of various medical conditions. Over the years, thousands of metabolites with complex chemical structures have been isolated from cultures of these soil bacteria. An evolutionary pressure that promotes chemical diversity appears to be critical for generation of this rich source of biologically active compounds. This is reflected in the biosynthetic enzymes, where functions of similar proteins may greatly differ. Here, we have clarified the molecular basis of how a classical methyltransferase has evolved into an unusual hydroxylase on the biosynthetic pathways of two anthracycline anticancer agents. Detailed understanding of enzymes involved in antibiotic biosynthesis will facilitate future protein engineering efforts for generation of improved bioactive natural products.