MEMBRANE-DAMAGING ACTION OF CLOSTRIDIUM-PERFRINGENS ALPHA-TOXIN ON PHOSPHOLIPID LIPOSOMES

The effect of Clostridium perfringens alpha-toxin on multilamellar lip osomes prepared from various phospholipids and cholesterol was investi gated. The toxin induced carboxyfluorescein leakage from liposomes com posed of the choline-containing phospholipids such as egg-yolk phospha tidylcholine and bovine brain sphingomyelin in a dose-dependent manner , but did not induce leakage from those liposomes composed of bovine b rain phosphatidylethanolamine, egg-yolk phosphatidylserine or phosphat idylglycerol. The toxin-induced carboxyfluorescein leakage from egg-yo lk phosphatidylcholine liposomes was increased by addition of divalent cations. The toxin induced carboxyfluorescein release from liposomes composed of phosphatidylcholine containing unsaturated fatty acyl resi dues or shorter chain length saturated fatty acyl residues (12 or 14 c arbon atoms), but did not induce such release from liposomes composed of phosphatidylcholine containing saturated fatty acyl residues of bet ween 16 and 20 carbon atoms. Furthermore. the toxin-induced carboxyflu orescein release decreased with increasing chain length of the acyl re sidues of phosphatidylcholine used. The toxin bound to liposomes compo sed of phospholipids which are hydrolyzed by the toxin, but did not bi nd to those composed of phospholipids which are not attacked by the to xin. The toxin-induced carboxyfluorescein release from liposomes compo sed of dipalmitoleoyl-L-alpha-phosphatidylcholine and cholesterol and the toxin binding to the liposomes decreased with decreasing cholester ol contents. These observations suggest that the specific binding site formed by the choline-containing phospholipids and cholesterol, and m embrane fluidity in liposomes are essential for the membrane-damaging activity of alpha-toxin.