Effect of the vacuolation of Helicobacter pylori

Transport kinetics and selectivity of HpUreI, the urea channel from Helicobacter pylori

Helicobacter pylori's unique ability to colonize and survive in the acidic environment of the stomach is critically dependent on uptake of urea through the urea channel, HpUreI. Hence, HpUreI may represent a promising target for the development of specific drugs against this human pathogen. To obtain insight into the structure-function relationship of this channel, we developed conditions for the high-yield expression and purification of stable recombinant HpUreI. Detergent-solubilized HpUreI forms a homotrimer, as determined by chemical cross-linking. Urea dissociation kinetics of purified HpUreI were determined by means of the scintillation proximity assay, whereas urea efflux was measured in HpUreI-containing proteoliposomes using stopped-flow spectrometry to determine the kinetics and selectivity of the urea channel. The kinetic analyses revealed that urea conduction in HpUreI is pH-sensitive and saturable with a half-saturation concentration (or K(0.5)) of ~163 mM. The extent of binding of urea by HpUreI was increased at lower pH; however, the apparent affinity of urea binding (~150 mM) was not significantly pH-dependent. The solute selectivity analysis indicated that HpUreI is highly selective for urea and hydroxyurea. Removing either amino group of urea molecules diminishes their permeability through HpUreI. Similar to urea conduction, diffusion of water through HpUreI is pH-dependent with low water permeability at neutral pH.

The expression of VacA in BCF of Helicobacter pylori and its relationship to vacuolated effect

The vacuolated effect of Helicobacter (H. pylori) and its relationship to vacuolated cytotoxin antigen (VacA) were investigated by the method of cytotoxic test and SDS-pobyacrylamide gel electrophoresis (SDS-PAGE). Of the 62 clinical isolates, the broth culture filter (BCF) of 43 strains caused the Vero cell intracytoplasmically vacuolated. H. pylori strains were divided into H. pylori (Toxin+) group with vacuolated effect and H. pylori (Toxin-) group without vacuolated effect. The analysis of the BCF of H. pylori (Toxin+) and that of H. pylori (Toxin-) was studied by SDS-PAGE and Scan reader. A kind of protein with 87 ku molecular weight was recognized in the BCF of 30.23% (13/43) H. pylori (Toxin+) strains but in none of that of H. pylori (Toxin-) strains, the difference was statistically significant (P < 0.05). There was a significant and concordant relationship between OD of the protein band with 87 ku molecular weight and titer of vacuolated activity of H. pylori (Toxin+) (r = 0.67 and P < 0.05 by linear regression analysis). H. pylori strains were divided into H. pylori (Toxin+) group with vacuolated effect and H. pylori (Toxin-) group without vacuolated effect. The vacuolated effect of H. pylori (Toxin+) was caused by the protein with 87 ku molecular weight (VacA).