ANALYSIS OF THE E COLI STB HEAT STABLE ENTEROTOXIN

腹泻病是一个严重的全球性医学和农业问题 意义 引起大肠杆菌感染的大肠杆菌菌株 分泌性中耳炎是通过制造蛋白质毒素来实现的 其干扰肠上皮的正常功能。 一个E. 大肠杆菌肠毒素，热稳定肠毒素（STa和STb）是 肽，虽然共享热稳定性和它们的遗传位置， 在复合细菌转座子上， 彼此相似。 STa介导的分泌机制是 部分理解为，毒素诱导的 刷状缘膜鸟苷酸环化酶随后迅速增加 粘膜cGMP含量与净氯化物分泌有关 可能通过肠上皮细胞cGMP依赖蛋白 激酶。 与我们对STa作用机制的理解相反， 很少有人知道的机制，STb诱导肠道 分泌物 初步研究结果表明，STb诱导产电 离子转运不依赖cAMP或cGMP升高。 在这 应用，我们建议：1）调查的性质和分布 通过标准配体-受体相互作用研究确定STb受体; 2） 检测对STb的第二信使反应， 其在肠上皮中产生生电离子转运。 在这 研究的一部分，我们将调查的潜在作用， 钙离子转运机制，包括 磷脂酶C、活化和水解 磷酸肌醇，蛋白激酶C的潜在作用，或 参与响应毒素作用的类花生酸代谢。 最后，我们将分析STb的结构特征， 受体结合和生物学作用。 我们将通过一个 阿托伐他汀定向诱变和表位作图的组合 的STB。 这些目标的完成将增加我们对 分泌性中耳炎的发病机制，并提供潜在的合理 疾病干预的方法。

Diarrheal disease is a serious medical and agricultural problem of global significance. Strains of enterotoxigenic Escherichia coli which cause secretory diarrheal disease do so by the elaboration of protein toxins which disturb the normal function of the gut epithelium. One class of E. coli enterotoxins, the heat-stable enterotoxins (STa and STb) are peptides which, although share heat-stability and their genetic location on composite bacterial transposons, bear no functional or structural similarity to one another. The mechanism for STa-mediated secretion is partially understood in that, toxin-induced activation of the brush-border membrane guanylate cyclase is followed by a rapid increase in the mucosal cGMP content which is coupled to net chloride secretion probably through the intestinal epithelial cell cGMP dependent protein kinase. In contrast to our understanding of the mechanism of STa action, little is known of the mechanism by which STb induces intestinal secretion. Preliminary findings suggest that STb induces electrogenic ion transport independent of cAMP or cGMP elevation. In this application, we propose to: 1) investigate the nature and distribution of STb receptors by standard ligand-receptor interaction studies; 2) char- acterize the second messenger response to STb and determine the signal which yields electrogenic ion transport in the gut epithelium. In this part of the study we will investigate the potential role of calcium-dependent ion transport mechanisms including the inter-relationship between phospholipase C, activation and hydrolysis of phosphoinositides, the potential role of protein kinase C, or the involvement of eicosanoid metabolism in response to toxin action. Finally, we will analyze the structural features of STb which contribute receptor binding and biological action. We will accomplish this by a combination of oligonucleotide-directed mutagenesis and epitope mapping of STb. The completion of these aims will add to our understanding of secretory diarrheal disease mechanisms and provide potential rational approaches for disease intervention.