Structural dissection of unnatural ginsenoside-biosynthetic UDP-glycosyltransferase Bs-YjiC from Bacillus subtilis for substrate promiscuity.

Glycosylation catalyzed by uridine diphosphate-dependent glycosyltransferases (UGT) contributes to the chemical and functional diversity of a number of natural products. Bacillus subtilis Bs-YjiC is a robust and versatile UGT that holds potentials in the biosynthesis of unnatural bioactive ginsenosides. To understand the molecular mechanism underlying the substrate promiscuity of Bs-YjiC, we solved crystal structures of Bs-YjiC and its binary complex with uridine diphosphate (UDP) at resolution of 2.18 Å and 2.44 Å, respectively. Bs-YjiC adopts the classical GT-B fold containing the N-terminal and C-terminal domains that accommodate the sugar acceptor and UDP-glucose, respectively. Molecular docking indicates that the spacious sugar-acceptor binding pocket of Bs-YjiC might be responsible for its broad substrate spectrum and unique glycosylation patterns toward protopanaxadiol-(PPD) and PPD-type ginsenosides. Our study reveals the structural basis for the aglycone promiscuity of Bs-YjiC and will facilitate the protein engineering of Bs-YjiC to synthesize novel bioactive glycosylated compounds.