ANALYSIS OF THE E COLI STB HEAT STABLE ENTEROTOXIN

腹泻病是一个严重的全球性医疗和农业问题。 意义。引起致病的产肠毒素大肠杆菌 分泌性腹泻病是通过蛋白质毒素的精制来实现的 这会干扰肠道上皮的正常功能。一类E. 大肠杆菌肠毒素，耐热肠毒素(StA和STB)为 具有相同热稳定性的多肽及其遗传定位 在复合细菌转座子上，没有功能或结构 彼此相似。STA介导的分泌机制是 部分理解是，毒素诱导的激活 刷状缘膜鸟苷环化酶迅速升高 在粘膜中cGMP的含量与净氯分泌有关 可能通过肠上皮细胞cGMP依赖蛋白 激活剂。与我们对STA作用机制的理解相反， 目前对STB诱导肠道反应的机制知之甚少 分泌物。初步研究结果表明，STB可诱导产生电 离子转运与cAMP或cGMP升高无关。在这 应用，我们建议：1)调查研究的性质和分布 STB受体的标准配基-受体相互作用研究； 将第二信使响应转换到机顶盒，并确定信号 这会在肠道上皮细胞中产生电生离子传输。在这 作为研究的一部分，我们将调查 钙依赖的离子转运机制，包括 磷脂酶C、磷脂酶C活化与磷脂酶C水解酶活性的相互关系 磷脂酰肌醇、蛋白激酶C的潜在作用 二十烷基类代谢参与毒素作用的反应。 最后，我们将分析机顶盒的结构特征 受体结合和生物学作用。我们将通过一个 寡核苷酸定向突变与表位定位相结合 机顶盒。这些目标的实现将增加我们对 分泌性腹泻的发病机制和潜在的合理性 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.