Structure-Function Studies of the Proton-Gated Urea Channel from H. Pylori

项目摘要 幽门螺杆菌对胃粘膜的感染仍然是一个世界性的问题， 会导致消化性溃疡和胃癌。如果不积极干预，至少20% 在发达国家中，20%的人口将继续受到这种胃病原体的感染。 消灭这种生物将有助于预防疾病。目前根除 需要三联疗法，质子泵抑制剂和两种抗生素，每天两次，持续10到15天。 14天对克拉霉素或甲硝唑的耐药率> 20%，且呈上升趋势。没有 单一疗法有效。胃感染H. pylori依赖于一个通道的表达 这种病原体所特有的尿素酶I UreI是一种质子门控尿素通道， 尿素转化为细菌内尿素酶，对于在酸性环境中维持周质pH 6.1至关重要。 在胃的环境中，低至pH 2.5，从而允许胃的定殖。 通道的表达在胃中增加。该通道具有193个残基，其中6个残基为 跨膜区段和三个周质区。突变研究表明， UreI的质子门控由组氨酸和羧基之间的氢键调节， 酸残基在这三个周质区域。获得高分辨率的三维图像 这一渠道的结构是这项工作的主要目标。这将有助于理解 这种蛋白质独特的质子门控机制，并将提供一种结构， 其中一些已经被发现，可以对接， 关系识别。预期抑制该通道将导致特异性和 有效的单一疗法根除有机体，并迎来一个测试和治疗的时代，而不是 而不仅仅是治疗有症状的病人。这将提供一种预防性办法， 上消化道疾病，特别是胃癌。

Project Summary Infection of the gastric mucosa by Helicobacter pylori remains a worldwide problem and contributes to peptic ulcer disease and gastric cancer. Without active intervention, at least 20% of the population of developed countries will continue to be infected by this gastric pathogen. Eradication of the organism would contribute to prevention of disease. Current eradication requires triple therapy, a proton-pump inhibitor and two antibiotics given twice a day for 10 to 14 days. Resistance to either clarithromycin or metronidazole is > 20% and rising. No monotherapy is effective. Gastric infection by H. pylori depends on the expression of a channel unique to this pathogen, UreI. UreI is a proton-gated urea channel necessary for rapid access of urea to intrabacterial urease, essential for maintaining the periplasm at pH 6.1 in the acidic environment of the stomach, as low as pH 2.5, thus allowing colonization of the stomach. Expression of the channel is increased in the stomach. The channel has 193 residues with six transmembrane segments and three periplasmic regions. Mutagenesis studies have shown that the proton gating of UreI is regulated by hydrogen bonding between histidines and carboxylic acid residues in these three periplasmic regions. Obtaining a high-resolution 3-dimensional structure of this channel is the major goal of this work. This will enable understanding of the unique proton-gating mechanism of this protein and will provide a structure to which inhibitors, some of which have been discovered already, can be docked and their structure-activity relationship identified. Inhibition of this channel would be expected to result in specific and effective monotherapy for eradication of the organism and usher in an era of test and treat, rather than only treating symptomatic patients. This would provide a preventive approach to serious upper gastro-intestinal diseases, particularly gastric cancer.