MECHANISM OF MEMBRANE DAMAGE BY CLOSTRIDIUM-PERFRINGENS ALPHA-TOXIN

The effect of Clostridium perfringens alpha-toxin on liposomes prepare d from phosphatidylcholine (PC) containing the fatty acyl residues of 18 carbon atoms was investigated. The toxin-induced carboxyfluorescein (CF) leakage and phosphorylcholine release from multilamellar liposom es increased as the phase transition temperature of the phosphatidylch olines containing unsaturated fatty acyl residues decreased. However, there was no difference between the sensitivity of the different phosp hatidylcholines solubilized by deoxycholate to the phospholipase C (PL C) activity of the toxin, However, the toxin did not hydrolyze solubil ized distearoyl-L-alpha-phosphatidylcholine (DSPC) or phosphatidylchol ine containing saturated fatty acyl residue, and caused no effect on l iposomes composed of DSPC. These results suggest that the activity of the toxin is closely related to the membrane fluidity and double bond in PC. The N-terminal domain of alpha-toxin (AT(1.246)) and variant H1 48G did not induce CF leakage from liposomes composed of dioleoyl-L-al pha-phosphatidylcholine (DOPC), H148G bound to the liposomes, but AT(1 .246) did not, However, the C-terminal domain (AT(251.370)) conferred binding to liposomes and the membrane-damaging activity on AT(1.216). These observations suggest that the membrane-damaging action of alpha- toxin is due to the binding of the C-terminal domain of the toxin to t he double bond in the PC in the bilayer and hydrolysis of the PC by th e N-terminal domain.