Role of Helicobacter pylori methionine sulfoxide reductase in urease maturation

The persistence of the gastric pathogen Helicobacter pylori is due in part to urease and Msr (methionine sulfoxide reductase). Upon exposure to relatively mild (21 % partial pressure of O-2) oxidative stress, a Delta msr mutant showed both decreased urease specific activity in cell-free extracts and decreased nickel associated with the partially purified urease fraction as compared with the parent strain, yet urease apoprotein levels were the same for the Delta msr and wild-type extracts. Urease activity of the Delta msr mutant was not significantly different from the wild-type upon non-stress microaerobic incubation of strains. Urease maturation occurs through nickel mobilization via a suite of known accessory proteins, one being the GTPase UreG. Treatment of UreG with H2O2 resulted in oxidation of MS-identified methionine residues and loss of up to 70% of its GTPase activity. Incubation of pure H2O2-treated UreG with Msr led to reductive repair of nine methionine residues and recovery of up to full enzyme activity. Binding of Msr to both oxidized and non-oxidized UreG was observed by cross-linking. Therefore we conclude Msr aids the survival of H. pylon in part by ensuring continual UreG-mediated urease maturation under stress conditions.