Crystal structure of UDP-N-acetylglucosamine enolpyruvyltransferase, the target of the antibiotic fosfomycin

Abstract

Background: The ever increasing number of antibiotic resistant bacteria has fuelled interest in the development of new antibiotics and other antibacterial agents. The major structural element of the bacterial cell wall is the heteropolymer peptidoglycan and the enzymes of peptidoglycan biosynthesis are potential targets for antibacterial agents. One such enzyme is UDP-N-acetylglucosamine enolpyruvyltransferase (EPT) which catalyzes the first committed step in peptidoglycan biosynthesis: the transfer of the enolpyruvyl moiety of phosphoenolpyruvate (PEP) to the 3-hydroxyl of UDP-N-acetylglucosamine (UDPGlcNAc). EPT is of potential pharmaceutical interest because it is inhibited by the broad spectrum antibiotic fosfomycin.

Results: The crystal structure of substrate-free EPT has been determined at 2.0 A resolution. The structure reveals a two-domain protein with an unusual fold (inside out alpha/beta barrel) which is built up from the sixfold repetition of one folding unit. The only repetitive element in the amino acid sequence is a short motif, Leu-X3-Gly(Ala), which is responsible for the formation of hydrogen-bond interactions between the folding units. An enzyme which catalyzes a similar reaction to EPT, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), has a very similar structure despite an amino acid sequence identity of only 25%. To date, only these two enzymes appear to display this characteristic fold.

Conclusions: The present structure reflects the open conformation of the enzyme which is probably stabilized through two residues, a lysine and an arginine, located in the cleft between the domains. Binding of the negatively charged UDPGlcNAc to these residues could neutralize the repulsive force between the two domains, thereby allowing the movement of a catalytically active cysteine residue towards the cleft.