Nicking sites in a subunit of cholera toxin and Escherichia coli heat-labile enterotoxin for Vibrio cholerae hemagglutinin/protease.

We analyzed the nicking site of the A subunit of Escherichia coli heat-labile enterotoxin for hemagglutinin/protease produced by Vibrio cholerae non-O1 (NAG-HA/P). The determined nicking site was the Thr193-Ile194 junction, which was distinct from that for a protease of V. cholerae (Ichinose et al., European Journal of Epidemiology 8, 743-747, 1992). We further analyzed proteolytic cleavage by NAG-HA/P of a synthetic peptide corresponding to the nicking region of cholera toxin A subunit and determined the cleavage site to be preferentially between Ser194 and Met195, and in addition between Ser193 and Ser194.