Structure of the UDP-Glucosyltransferase GtfB that modifies the heptapeptide aglycone in the biosynthesis of vancomycin group antibiotics

Background: Members of the vancomycin group of glycopeptide antibiotics hav e an oxidatively crosslinked heptapeptide scaffold decorated at the hydroxy l groups of 4-OH-Phegly(4) or beta -OH-Tyr(6) with mono- (residue 6) or dis accharides (residue 4). The disaccharide in vancomycin itself is L-vancosam ine-1,2-glucose, and in chloroeremomycin it is L-4-epi-vancosamine-1,2-gluc ose. The sugars and their substituents play an important role in efficacy, particularly against vancomycin-resistant pathogenic enterococci. Results: The glucosyltransferase, GtfB, that transfers the glucose residue from UDP-glucose to the 4-OH-Phegly(4) residue of the vancomycin aglycone, initiating the glycosylation pathway in chloroeremomycin maturation, has be en crystallized, and its structure has been determined by X-ray analysis at 1.8 Angstrom resolution. The enzyme has a two-domain structure, with a dee p interdomain cleft identified as the likely site of UDP-glucose binding. A hydrophobic patch on the surface of the N-terminal domain is proposed to b e the binding site of the aglycone substrate. Mutagenesis has revealed Asp3 32 as the best candidate for the general base in the glucosyltransfer react ion. Conclusions: The structure of GtfB places it in a growing group of glycosyl transferases, including Escherichia coli MurG and a beta -glucosyltransfera se from T4 phage, which together form a subclass of the glycosyltransferase superfamily and give insights into the recognition of the NDP-sugar and ag lycone cosubstrates. A single major interdomain linker between the N- and C - terminal domains suggests that reprogramming of sugar transfer or aglycon e recognition in the antibiotic glycosyltransferases, including the glycope ptide and also the macrolide antibiotics, will be facilitated by this struc tural information.