Discovered in the early 1980's, Helicobacter pylori is a common cause of peptic and duodenal ulcers, gastritis, anemia, and certain gastric cancers. This bacterium is typically acquired during childhood, with crowded living conditions and economic disparities closely correlating with higher infection rates. Urease is an enzyme that is required for infection by H. pylori, and accounts for nearly 10% of the total cellular protein. This enzyme must be active in order for the bacterium to colonize its host, a fact that has been explained by urease's ability to neutralize and buffer against the acidity of the stomach. However, the requirement for urease in colonization is not contingent upon acidic conditions, indicating alternative roles for this enzyme other than simply acid resistance. The primary objective of this research plan is to examine one of these alternative roles for urease-its role in nitrogen metabolism. Over the past fifteen years, two crucial turning points in urease research established this enzyme as player in nitrogen metabolism. First, a set of discoveries led to the current paradigm that urease is an intracellular enzyme, contrary to previously held beliefs. Secondly, urea nitrogen was shown to be incorporated into the cell through tracing studies of 15N-urea. High concentrations of urea have furthermore been shown to kill H. pylori, an effect that was explained by the hydrolysis of urea and subsequent accumulation of ammonium in the cell. The mechanism by which urea nitrogen is assimilated has been scarcely examined through biochemical methods;however, preliminary genome-level comparisons revealed that the pathway of ammonium assimilation in H. pylori is not typical of other proteobacteria. In fact, H. pylori is an anomaly among all other well-studied bacterial taxa with regard to both the structure and the regulation of the enzymes thought to assimilate ammonium in this organism-glutamine synthetase and glutamate dehydrogenase. Furthermore, glutamine synthetase is a putative interacting partner with urease, alluding to a potentially tight relationship between urease and ammonium assimilation. Using molecular techniques such as mutagenesis, in conjunction with biochemical techniques such as enzyme purification and kinetic studies, this study aims to characterize the pathway that takes urea from the gastric mileu directly to the heart of H. pylori primary metabolism.
In some regions of the United States, nearly half of the population is chronically infected with Helicobacter pylori, a Class I carcinogen and causative agent of gastric ulcers. Urease enzyme is required for colonization of H. pylori, yet this enzyme still has not been studied under the lens of bacterial physiology and metabolism. To understand how this bacterium interacts with its host is contingent upon a complete understanding of urease and its role in pathogenesis.
| Miller, Erica F; Maier, Robert J (2014) Ammonium metabolism enzymes aid Helicobacter pylori acid resistance. J Bacteriol 196:3074-81 |
