Structural Requirements for the Spatial Structure and Toxicity of Heat-Stable Enterotoxin (STh) of Enterotoxigenic Escherichia coli

The heat-stable enterotoxin (STh) of enterotoxigenic Escherichia coli consists of 19 amino acid residues and is linked intramolecularly by three disulfide bonds between Cys6 and Cys11, Cys7 and Cys15, and Cys10 and Cys18 (Y. Shimonishi et al., FEBS Lett., 215, 165 (1987)). The syntheses and biological assays of various analogs of STh with one or two of the three disulfide bonds showed that a disulfide bond between Cys7 and Cys15 and another between Cys6 and Cys11 or Cys10 and Cys18 are necessary for construction and stabilization of the spatial structure of STh to express its toxicity.