title: Contribution of dppA to urease activity in Helicobacter pylori 26695.
abstract: BACKGROUND
  The gastric pathogen Helicobacter pylori produces urease in amounts up to 10% of its cell protein. This enzyme, which catalyzes the hydrolysis of urea to ammonia and carbon dioxide, protects the bacterium from gastric acid. Urease, a nickel metalloenzyme, requires active uptake of nickel ions from the environment to maintain its activity. NixA is a nickel transport protein that resides in the cytoplasmic membrane. Mutation of nixA significantly reduces but does not abolish urease activity, strongly suggesting the presence of a second transporter. We postulated that the dipeptide permease (dpp) genes that are homologous to the nik operon of Escherichia coli could be a second nickel transporter. The predicted Dpp polypeptides DppA, DppC, and DppD of H. pylori share approximately 40%, 53%, and 56% amino acid sequence identity with their respective E. coli homologs.
  
  
  METHODS
  A mutation in dppA, constructed by insertional inactivation with a chloramphenicol resistance cassette, was introduced by allelic exchange into H. pylori strain 26695.
  
  
  RESULTS
  When compared to the parental strain, urease activity was not decreased in a dppA mutant.
  
  
  CONCLUSIONS
  DppA does not contribute to the synthesis of catalytically active urease in H. pylori 26695 and is likely not a nickel importer in H. pylori.
authors.affiliation: Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor 48109-0620, USA.
authors.forename: Gregg S
authors.initials: GS
authors.lastname: Davis
authors.forename: Harry L T
authors.initials: HL
authors.lastname: Mobley
mesh_terms: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D016480:Helicobacter pylori / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009532:Nickel / Q000378:metabolism / Q000494:pharmacology; D009876:Operon; D014510:Urease / Q000378:metabolism*
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; C037230:oligopeptide permease, Bacteria; D009532:Nickel; D014510:Urease