Resistance mechanism to an uncompetitive inhibitor of a single-substrate, single-product enzyme: a study of Helicobacter pylori glutamate racemase

Two independent series of inhibitors of Helicobacter pylori glutamate racemase (MurI) were characterized for their kinetic mechanism, and one was used to generate resistant mutants in vitro. Mutant MurI enzymes from these strains were characterized by structural, genetic, kinetic and biophysical methods. Both inhibitor series, pyrazolopyrimidinediones and benzodiazepines, are uncompetitive with respect to the glutamate substrate, and the resistance mutations were found to act by reducing the affinity of MurI for substrate, thereby reducing the pool of enzyme-substrate complex available for binding inhibitor, while still allowing sufficient glutamate racemase activity for peptidoglycan construction. Uncompetitive inhibitors of a single-substrate, single-product enzyme are rare, and this work gives insight into an remarkable resistance mechanism. This article will discuss the projected clinical impact of H. pylori MurI resistance on these types of inhibitors.