Heat-stable Enterotoxin (STh) of Human Enterotoxigenic Escherichia coli (Strain SK-1). Structure-activity Relationship

For examination of the structure-activity relationship of STh, five shorter analogs of STh lacking one to five N-terminal amino acid residues of STh were synthesized. The synthetic peptides were confirmed to have the same intramolecular disulfide linkages as those in native STh. These peptides caused fluid accumulation in the intestine of suckling mice at almost the same molar levels as that of native STh. The toxicities of these peptides were also neutralized by antisera raised against native STh. These results indicated that the toxic and antigenic sites of STh are both located in the amino acid sequence between the Cys residue at the 5th position from the N-terminus and the C-terminal Tyr residue.