Crystal structure of the bifunctional N-acetylglucosamine 1-phosphate uridyltransferase from Escherichia coli: a paradigm for the related pyrophosphorylase superfamily

N-acetylglucosamine l-phosphate uridyltransferase (GlmU) is a cytoplasmic b ifunctional enzyme involved in the biosynthesis of the nucleotide-activated UDP-GlcNAc, which is an essential precursor for the biosynthetic pathways of pc peptidoglycan and other components in bacteria. The crystal structure of a truncated form of GlmU has been solved at 2.25 Angstrom resolution us ing the multiwavelength anomalous dispersion technique and its function tes ted with mutagenesis studies. The molecule is composed of two distinct doma ins connected by a long alpha-helical arm: (i) an N-terminal domain which r esembles the dinucleotide-binding Rossmann fold; and (ii) a C-terminal doma in which adopts a left-handed parallel beta-helix structure (L beta H) as f ound in homologous bacterial acetyltransferases. Three GlmU molecules assem ble into a trimeric arl arrangement with tightly packed parallel L beta H d omains, the long alpha-helical linkers being seated on top of the arrangeme nt and the N-terminal domains projected away from the 3-fold axis. In addit ion, the 2.3 Angstrom resolution structure of the GlmU-UDP-GlcNAc complex r eveals the structural bases required for the uridyltransferase activity. Th ese structures exemplify a three-dimensional template for the development o f new antibacterial agents and for studying other members of the large fami ly of XDP-sugar bacterial pyrophosphorylases.