| Research Abstract |
Heat-stable enterotoxin (STs) produced by enterotoxigenic Escherichia coli are known to cause an acute diarrhea in men and animals. The biological action of ST is initiated by the binding to its receptor proteins on the membrane of intestinal epithelial cell. The formation of a ST-receptor complex leads to stimulation of guanylate cyclase and is followed by increase in cGMP concentration in the cells. Protein kinase is activated by the binding with cGMP and activate Cystic fibrosis transmembrane conductance regulator to result in a fluid secretion from the cells. In a course of study to purify receptor proteins for ST from rat intestine, receptor protein was found to form receptor protein complex. To elucidate the signal transduction mechanism by ST,it is important to know whether ST-receptor complex is the homo-oligomer or the hetero-oligomer with different proteins. Purpose of this study is to elucidate the structure and functions of proteins which forms complex with receptor protein for ST.To accomplish this purpose, ST analogs were designed to have the fluorophore, the functional group for the cross-linking to the receptor protein, and the specific binding ability to the receptor protein corresponding to that of the native ST and were synthesized. Binding characteristics of ST to the membrane prepared from rat intestine were investigated. Results revealed that membrane contained two types of receptor proteins, that is, one binds exchange-ably with ST (Rex) and the other non-echange-ably (Rnex). Rnex existed on membrane in two kinds of receptor complexes ((1) and (2)). (1) and (2) were found to be constructed with common protein components and the different component to each other. Among these proteins, analysis of common components are in progress.
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