Role of the C-domain in the biological activities of Clostridium perfringens alpha-toxin

Clostridium perfringens alpha-toxin (370 residues) possesses hemolytic and lethal activities as well as the enzymatic activity of phospholipase C (PLC). In this study we examined the role of the C-domain (251-370 residues; CP251=370) in biological activities of the toxin. The N-domain (1-250 residues; CP1-250) of the alpha-toxin as well as the Bacillus cereus phospholipase C (BcPLC) possessed PLC activity, but did not bind to rabbit erythrocytes and lyse them. A hybrid protein (BC-CP251=370) consisting of BePLC and CP251-370 bound to the red cells and lysed them. Incubation of CP1=250 with CP251-370 completely complemented hemolytic and PLC activities. CP251 370 also conferred hemolytic activity on BcPLC. CP251-340 (251-340 residues) significantly stimulated PLC activity of CP1-250, but did not confer hemolytic activity on CP1-250. Kinetic analysis suggested that CP251 370 increased affinity toward the substrate of CP1-250, The results suggested that CP251-370 plays an important role in binding to erythrocytes and the hemolytic and enzymatic activities of CP1-250. Acrylodan-labeled CP251-370 variants (S263C and S365C) bound to liposomes and exhibited a marked blue shift, and in addition, an NN-dimethyl-N-(iodoacetyl)-N'-(7-nitrobenz-2-oxa-1,3-diazolyl)ethylene diamine (NBD)-labeled CP251-370 (S365C) variant also bound to liposomes and the fluorescence intensity significantly increased, suggesting movement Of CP251-370 to a hydrophobic environment. These observations suggest that interaction Of CP251-370 of alpha-toxin with fatty acyl residues of phosphatidylcholine plays an important role in the biological activities Of CP1-250.