Chemical Synthesis of Fully Active and Heat-stable Fragments of Heat-stable Enterotoxin of Enterotoxigenic Escherichia coli Strain 18D

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Abstract
Two shorter peptides of a heat-stable enterotoxin (STp), which is produced by enterotoxigenic Escherichia coli strain 18D, were prepared by two different procedures; i) chemical synthesis and ii) Edman-degradation of STp. These peptides (designated as STp(4–18) and STp(5–18)) corresponded to 15 and 14 amino acid residues in the sequence of STp without three and four residues, respectively, of the N-terminus. Peptides STp(4–18) and STp(5–18) prepared by chemical synthesis had the same biological and physicochemical properties as the peptides obtained by the Edman method. Furthermore, they showed almost the same toxicity as native and synthetic STp, and their toxicity was neutralized by anti-native STp antisera. Synthetic STp(4–18) had similar heat-stability to STp, but synthetic STp(5–18) was much more heat-stable. These findings suggest that the sequence from the Cys residue near the N-terminus to the C-terminal residue is extremely important for the unique characters of toxicity and heat-stability of the toxin.

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