Comparative Structural and Biochemical Studies of Chorismate Binding Enzymes, MenF, EntC and MbtI

Abstract

Bacterial chorismate binding enzymes (CBE¡¯s) are a large family of enzymes, which are structurally and mechanistically similar due to their evolutionarily relationship. The CBE¡¯s are involved in various microbial metabolic pathways including menaquinone, aromatic amino acid and siderophore biosynthesis, and are attractive drug targets since they lack human homologues. Current research is focused on MbtI which catalyzes the initial reaction in the mycobactin biosynthetic pathway from Mycobacterium tuberculosis.. MbtI is a salicylate synthase and the mechanism of this enzyme is being compared with the E. coli MenF enzyme, an isochorismate synthase that catalyzes the first step in menaquinone biosynthesis. MbtI and MenF are Mg2+ dependent, however in the absence of Mg2+ they show chorismate mutase activity despite having no similarity to the AroQ/H chorismate mutase. The crystal structures of MbtI and MenF have been determined and the role of several active site residues are currently being studied using mutagenesis. We propose that MbtI catalyzes pyruvate elimination through an intramolecular mechanism by analogy to a recent study on the isochorismate pyruvate lyase, PchB. Further studies are focused on the synthesis of inhibitors of both these enzymes. *This work was supported by a grant from the National Institutes of Health (AI58785) to P.J.T.