Helicobacter pylori urease: Significance and mechanism of its surface association

Helicobacter pylori is a microaerophilic, gram-negative, spiral shaped bacteria that causes chronic active gastritis, and is implicated in peptic ulceration and gastric lymphoma. An essential enzyme of H. pylori is a potent multisubunit urease that is crucial for bacterial survival at acidic pH and for colonization of animal models. H. pylori is unique in possessing both cytoplasmic and surface-associated urease.; This dissertation outlines the progress made since its initiation in understanding the importance of surface associated urease and the mechanism of its surface localization in H. pylori.; In vitro H. pylori possessing cytoplasmic and surface-localized urease activity survive when exposed to acid in the presence of 5 mM urea, while H. pylori possessing only cytoplasmic urease show significantly reduced survival, suggesting the requirement of surface-associated urease in acid resistance. In H. pylori surface-associated urease seems to be protected against acid denaturation by the coordinated function of Urel and Hydrogenase proteins.; “Altruistic autolysis” has been proposed as the mechanism of urease surface localization in H. pylori. There are two possible approaches to test this hypothesis (a) Biochemical and (b) Genetic. In the Biochemical approach we have studied the transfer of urease from urease-positive H. pylori on to the surface of urease-negative H. pylori in co-cultures. The results from Immunoelectron microscopy show localization of urease on the surface of urease-negative organisms suggesting transfer of urease from urease-positive bacteria onto the surface of urease negative organisms.; In the genetic approach we proceeded to identify genes that play a role in PG synthesis and degradation in H. pylori, since lysis mechanisms in bacteria would likely involve proteins responsible for the synthesis and/or degradation of PG. The results presented describe the identification of a novel PBP in H. pylori referred to as PBP 4, which exhibits unique features. Attempts to obtain a PBP 4 null mutant of H. pylori have been unsuccessful suggesting that PBP 4 may be essential for the growth and survival of H. pylori.; To study the biochemical activity of PBP 4 we characterized the PG composition of H. pylori as PG is likely to be the substrate for PBP 4. H. pylori PG composition reveals a murein sacculus with a low degree of cross-linking (17%) and a low average glycan chain length.