The Journal of Membrane Biology

, Volume 212, Issue 2, pp 71–82 | Cite as

Urea Transport in Bacteria: Acid Acclimation by Gastric Helicobacter spp

  • G. Sachs
  • J.A. Kraut
  • Y. Wen
  • J. Feng
  • D.R. Scott


Urea transporters in bacteria are relatively rare. There are three classes, the ABC transporters such as those expressed by cyanobacteria and Corynebacterium glutamicum, the Yut protein expressed by Yersinia spp and the UreI expressed by gastric Helicobacter spp. This review focuses largely on the UreI proton-gated channel that is part of the acid acclimation mechanism essential for gastric colonization by the latter. UreI is a six-transmembrane polytopic integral membrane protein, N and C termini periplasmic, and is expressed in all gastric Helicobacter spp that have been studied but also in Helicobacter hepaticus and Streptococcus salivarius. The first two are proton-gated, the latter is pH insensitive. Site-directed mutagenesis and chimeric constructs have identified histidines and dicarboxylic amino acids in the second periplasmic loop of H. pylori and the first loop of H. hepaticus UreI and the C terminus of both as involved in a hydrogen-bonding dependence of proton gating, with the membrane domain in these but not in the UreI of S. salivarius responding to the periplasmic conformational changes. UreI and urease are essential for gastric colonization and urease associates with UreI during acid exposure, facilitating activation of the UreA and UreB apoenzyme complex by Ni2+ insertion by the UreF-UreH and UreE-UreG assembly proteins. Transcriptome analysis of acid responses of H. pylori also identified a cytoplasmic and periplasmic carbonic anhydrase as responding specifically to changes in periplasmic pH and these have been shown to be essential also for acid acclimation. The finding also of upregulation of the two-component histidine kinase HP0165 and its response element HP0166, illustrates the complexity of the acid acclimation processes involved in gastric colonization by this pathogen.


Urea Channel UreI Urease ABC-transporter YUT (Yersinia urea transporter) Carbonic anhydrase Acid acclimation 



Our thanks are due to our long-time collaborators, Drs. David L. Weeks, Elizabeth A. Marcus and Klaus Melchers. Supported in part by U.S. Veterans Administration and NIH grant #’s DK46917, 53462 and 58333


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Copyright information

© Springer Science+Business Media, Inc. 2007

Authors and Affiliations

  • G. Sachs
    • 1
  • J.A. Kraut
    • 2
  • Y. Wen
    • 1
  • J. Feng
    • 1
  • D.R. Scott
    • 1
  1. 1.Department of Physiology, Medicine, David Geffen School of MedicineUniversity of CaliforniaLos AngelesUSA
  2. 2.Department of Nephrology, David Geffen School of MedicineUCLA and VA GLAHSLos AngelesUSA

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