Vibrio cholerae O1, No. 31, strain, which originally differs from 569B, 86B1, 86B3, 86B6 and 86B10 strains producing nicked toxin, caused mild diarrhea in humans and mainly produced unnicked cholera toxin. As hemagglutinin/protease might nick cholera toxin, its DNA sequence was determined and found to differ by 23 base pairs from that of Vibrio cholerae O1 El Tor 3083. These base pair changes caused 6 amino acid substitutions, none of which are involved in cleavage site of the protease. Its protease activity was neutralized by anti-hemagglutinin/protease serum. Production of its mature or immature form was indistinguishable from other strains. Purified protease could nick the toxin similar to that purified from strain producing nicked toxin.
These data suggest that although the hemagglutinin/protease could nick cholera toxin in vitro, a small amount of cholera toxin is nicked by hemagglutinin/protease in Vibrio cholerae strain, No 31, in vivo. Hemagglutinin /protease is a minor vilurent factor for human diarrhea and other mechanisms, by which toxin is nicked, might exist in Vibrio cholerae.
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