Structure of the UDP-Glucosyltransferase GtfB That Modifies the Heptapeptide Aglycone in the Biosynthesis of Vancomycin Group Antibiotics

Abstract

Background: Members of the vancomycin group of glycopeptide antibiotics have an oxidatively crosslinked heptapeptide scaffold decorated at the hydroxyl groups of 4-OH-Phegly 4 or β-OH-Tyr 6 with mono- (residue 6) or disaccharides (residue 4). The disaccharide in vancomycin itself is L-vancosamine-1,2-glucose, and in chloroeremomycin it is L-4- epi-vancosamine-1,2-glucose. 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 been crystallized, and its structure has been determined by X-ray analysis at 1.8 Å resolution. The enzyme has a two-domain structure, with a deep 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 be the binding site of the aglycone substrate. Mutagenesis has revealed Asp332 as the best candidate for the general base in the glucosyltransfer reaction. Conclusions: The structure of GtfB places it in a growing group of glycosyltransferases, including Escherichia coli MurG and a β-glucosyltransferase from T4 phage, which together form a subclass of the glycosyltransferase superfamily and give insights into the recognition of the NDP-sugar and aglycone cosubstrates. A single major interdomain linker between the N- and C- terminal domains suggests that reprogramming of sugar transfer or aglycone recognition in the antibiotic glycosyltransferases, including the glycopeptide and also the macrolide antibiotics, will be facilitated by this structural information.