title: The role of ExbD in periplasmic pH homeostasis in Helicobacter pylori.
abstract: BACKGROUND
  Helicobacter pylori, a neutralophile, colonizes the acidic environment of the human stomach by employing acid acclimation mechanisms that regulate periplasmic and cytoplasmic pH. The regulation of urease activity is central to acid acclimation. Inactive urease apoenzyme, UreA/B, requires nickel for activation. Accessory proteins UreE, F, G, and H are required for nickel insertion into apoenzyme. The ExbB/ExbD/TonB complex transfers energy from the inner to outer membrane, providing the driving force for nickel uptake. Therefore, the aim of this study was to determine the contribution of ExbD to pH homeostasis.
  
  
  METHODS
  A nonpolar exbD knockout was constructed and survival, growth, urease activity, and membrane potential were determined in comparison with wildtype.
  
  
  RESULTS
  Survival of the ΔexbD strain was significantly reduced at pH 3.0. Urease activity as a function of pH and UreI activation was similar to the wildtype strain, showing normal function of the proton-gated urea channel, UreI. The increase in total urease activity over time in acid seen in the wildtype strain was abolished in the ΔexbD strain, but recovered in the presence of supraphysiologic nickel concentrations, demonstrating that the effect of the ΔexbD mutant is due to loss of a necessary constant supply of nickel. In acid, ΔexbD also decreased its ability to maintain membrane potential and periplasmic buffering in the presence of urea.
  
  
  CONCLUSIONS
  ExbD is essential for maintenance of periplasmic buffering and membrane potential by transferring energy required for nickel uptake, making it a potential nonantibiotic target for H. pylori eradication.
authors.affiliation: Department of Pediatrics, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Marcus
authors.forename: George
authors.initials: G
authors.lastname: Sachs
authors.forename: David R
authors.initials: DR
authors.lastname: Scott
mesh_terms: D000222:Adaptation, Physiological; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology; D055786:Gene Knockout Techniques; D016480:Helicobacter pylori / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D006706:Homeostasis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials; D050296:Microbial Viability / Q000187:drug effects; D014510:Urease / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D014510:Urease
keywords: ExbD; H. pylori; membrane potential; pH homeostasis; periplasm; urease