文摘
The tetracyclic core of anthracycline natural products with antitumor activity such as aclacinomycinA are tailored during biosynthesis by regioselective glycosylation. We report the first synthesis of TDP-L-rhodosamine and demonstrate that the glycosyltransferase AknS transfers L-rhodosamine to the aglyconeto initiate construction of the side-chain trisaccharide. The partner protein AknT accelerates AknS turnoverrate for L-rhodosamine transfer by 200-fold. AknT does not affect the Km but rather affects the kcat. Usingthese data, we propose that AknT causes a conformational change in AknS that stabilizes the transitionstate and ultimately enhances transfer. When the subsequent glycosyltransferase AknK and its substrateTDP-L-fucose are also added to the aglycone, the disaccharide and low levels of a fully reconstitutedtrisaccharide form of aclacinomycin are observed.