Role of tryptophan-1 in hemolytic and phospholipase C activities of Clostridium perfringens alpha-toxin

Replacement of the Trp-1 in Clostridium perfringens alpha-toxin with tyrosi ne caused no effect on hemolytic and phospholipase C (PLC) activities or on binding to the zinc ion, but that of the residue with alanine, glycine and histidine led to drastic decreases in these activities and a significant r eduction in binding to the zinc ion. The hemolytic and PLC activities of W1 H and W1A were significantly increased by the preincubation of these varian t toxins with zinc ions, but the preincubation of W1G with the metal ion ca used little effect on these activities. Gly-Ile-alpha-toxin, which containe d an additional Gly-Ile linked to the N-terminal amino acid of alpha-toxin, did not show hemolytic activity; but showed about 6% PLC activity of the w ild-type toxin. A mutant toxin, which contained an additional Gly-Ile linke d to the N-terminus of a protein lacking 4 N-terminal residues of alpha-tox in, showed about 1 and 6% hemolytic and PLC activities of the wild-type tox in, respectively. Incubation of the mutant toxin with zinc ions caused a si gnificant increase in PLC activity These observations suggested that Trp-1 is not essential for toxin activity, but plays a role in binding to zinc io ns.