(1) Max-Planck Unit, c/o DESY, D-22607 Hamburg, Germany
(2) EMBL, c/o DESY, D-22607 Hamburg, Germany
(3) ETH Zuerich, Inst. Plant Sciences, CH-8092 Zuerich, Switzerland
* Current address: NKI, Plesmanlaan 121, NL-1066 CX Amsterdam
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 Enolpyruvyltransferase (EPT) which catalyses the first committed step in the biosynthesis of the bacterial cell wall. EPT is of potential pharmaceutical interest because it is irreversibly inhibited by the broad spectrum antibiotic fosfomycin.
The crystal structure of Enolpyruvyltransferase (EPT) reveals an unusual fold and suggests large conformational changes upon catalysis. The crystal structure of native EPT consists of two distinct globular domains which are connected to each other by a double-stranded hinge. The most striking feature of the structure is the six-fold repetition of one folding unit or subdomain. Although these subdomains are remarkably similar in secondary structure elements and fold, the only repetitive element in the amino acid sequence is a small motif LXXXG(A) which is part of a loop connecting a helix with a beta strand. This motif is responsible for the attachment of the folding units to each other. The core of both domains consists of three alpha-helices which are surrounded by three helices with solvent accessible faces and the three four-stranded beta-sheets. One therefore might characterize this fold as an inside-out alpha/beta barrel. The present structure reflects the open conformation of the enzyme. We assume that large conformational changes upon catalysis are mediated mainly through two residues, a lysin and an arginine, which are located in the cleft between the two domains. These residues assure the open conformation of the native enzyme by the repulsive force between the positive charges of two amino groups. The binding of one of the two substrates probably results in neutralizing the repulsion between the two domains thereby allowing the movement of a catalytically active cystein toward the cleft.