Figure 1.

Bacterial heat-stable enterotoxin, guanylin and uroguanylin. (A) Primary structures of heat-stable enterotoxins produced by various pathogenic bacteria and human homologs, guanylin and uroguanylin. Conserved core regions are highlighted (blue for STs; pink for hormones) with disulfide bridges indicated; (B) Three-dimensional structures of E. coli STa (grey), guanylin (purple) and uroguanylin (pink) conserved regions. Non-conserved regions in uroguanylin are labeled in yellow. Cysteines linked by disulfide bonds conserved among three peptides are colored in cyan. Cysteines linked by the extra-disulfide bond, providing ST greater potency than guanylin and uroguanylin, are colored in blue.