Crystal structure of the MurG:UDP-GlcNAc complex reveals common structural principles of a superfamily of glycosyltransferases

MurG is an essential glycosyltransferase that forms the glycosidic linkage between N-acetyl muramyl pentapeptide and N-acetyl glucosamine in the biosynthesis of the bacterial cell wall. This enzyme is a member of a major superfamily of NDP-glycosyltransferases for which no x-ray structures containing intact substrates have been reported. Here we present the 2.5-A crystal structure of Escherichia coli MurG in complex with its donor substrate, UDP-GlcNAc. Combined with genomic analysis of other superfamily members and site-specific mutagenesis of E. coli MurG, this structure sheds light on the molecular basis for both donor and acceptor selectivity for the superfamily. This structural analysis suggests that it will be possible to evolve new glycosyltransferases from prototypical superfamily members by varying two key loops while maintaining the overall architecture of the family and preserving key residues.