Escherichia coli heat-stable enterotoxins and their receptors.

The family of ST has grown to include closely related toxins produced by a number of organisms. The core sequence of these toxins can bind specifically and reversibly to a receptor found in the microvillus membranes of the intestinal cell brush border. As a result of a specific binding event, the ST can stimulate fluid secretion via receptor-mediated stimulation of guanylate cyclase. The structure of the ST molecule has been partially obtained through a variety of techniques. It is apparent that in the near future, key amino acids and sequence regions of these toxins will be found that will identify the requirements for toxicity. The ST are ideal probes to study the secretory system of intestinal cells since they are not cytotoxic. The receptor for ST has been extensively studied and its purification and characterization will yield important insight into the reversal of toxin-mediated diarrheas, and possibly into the nonpathological secretory process. As yet, the nature of the 54,000-57,000 and 68,000-75,000 dalton binding proteins identified by cross-linking studies are not known. When purified ST-binding peptides and other components of the secretory cascade will become available, they will provide better insight into the actual dynamics of the ST receptor-guanylate cyclase complex secretory pathway.