C-glycosylation of anhydrotetracycline scaffold with SsfS6 from the SF2575 biosynthetic pathway.

Glycosylation with deoxysugar is a common strategy used by nature to introduce structural diversity and biological activities among natural products. In this study, we biochemically confirmed the activities of SsfS6, a C-glycosyltransferase in the SF2575 biosynthetic pathway, as a regioselective D-olivose transferase that acts on the C-9 position of an anhydrotetracycline aglycon. To perform the glycosyl transfer reaction using Escherichia coli as a whole-cell biocatalyst, we reconstituted the biosynthesis of TDP-D-olivose using a heterologous pathway. Under in vivo conditions, SsfS6 transferred multiple endogenous sugar substrates, in addition to D-olivose, to the anhydrotetracycline substrate, demonstrating broad substrate tolerance and potential as a tetracycline-diversifying enzyme.