Structure-Activity Relationship of Escherichia coli Heat-Stable Enterotoxin: Role of Ala Residue at Position 14 in Toxin-Receptor Interaction

A heat-stable enterotoxin (STh) produced by a human strain of enterotoxigenic Escherichia coli consists of 19 amino residues including 6 half-cystine residues. Analogs of STh from positions 6 to 19 with replacements of the Ala residue at position 14 by other amino acid residues were synthesized by a solid-phase method and examined by biological and biochemical methods. This Ala residue was demonstrated to be very important for expression of the toxicity of STh and for interaction of the toxin with its receptor protein(s).