Cytoplasmic histidine kinase (HP0244)-regulated assembly of urease with UreI, a channel for urea and its metabolites, CO2, NH3, and NH4(+), is necessary for acid survival of Helicobacter pylori.
Level 5 - mechanism / opinion, no new human data
Bench mechanistic research on bacterial physiology without human subjects (Oxford CEBM Level 5)
PubMed 19854893 · doi:10.1128/JB.00848-09
What was done
The authors investigated acid survival mechanisms in Helicobacter pylori by testing wild-type and histidine kinase (HP0244) deletion strains exposed to acidic media (pH 4.5 and pH 2.5) with urea, NH4Cl, or CO2. They measured total urease activation kinetics over up to 180 minutes, recruitment of urease subunits (UreA, UreB) and Ni2+ insertion protein (UreE) to the inner membrane urea channel UreI, cytoplasmic and periplasmic pH homeostasis, membrane polarization, metabolite transport, and bacterial survival rates.
What was found
Exposure to pH 4.5 for up to 180 minutes increased total bacterial urease activity threefold. Within 30 minutes at pH 4.5, UreA, UreB, and UreE recruited to UreI at the inner membrane in an HP0244-dependent manner. Deletion of HP0244 completely abolished this assembly and urease activation, impaired cytoplasmic and periplasmic pH homeostasis, caused cell depolarization, and resulted in an approximately 7-log reduction in bacterial survival at pH 2.5 even in the presence of 10 mM urea. UreI was also shown to transport NH3, NH4+, and CO2.
Why it matters
This study defines a cytoplasmic pH-sensing pathway mediated by HP0244 that pairs with periplasmic sensor HP0165 to coordinate urease-channel complex assembly, explaining how H. pylori maintains internal neutrality in gastric acid.
Limits
The findings are derived entirely from in vitro bacterial cultures; no in vivo animal colonization models or human clinical data were tested. The abstract does not report specific sample numbers, replicate counts, or variance metrics.
Cited by
- supports Helicobacter pylori utilizes the urease enzyme to neutralize stomach acid and create a microenvironment of neutral pH in the gastric mucosa.