Interaction of Staphylococcal α-Toxin with Artificial and Natural Membranes

Abstract

Comparison of hemolytic activity and chromate-releasing activity of partially purified preparations of staphylococcal α-toxin indicated the presence of a lytic factor other than α-toxin. This lytic release factor (RF) was isolated from the preparations and was shown to be active against both lipid spherules and erythrocytes. Heat-purified α-toxin (HP α-toxin) disrupted spherules, with the formation of fragments which always showed the presence of ring structures similar in dimensions (ca. 90 A) to pure α 12 S -toxin. The interaction of HP α-toxin with spherules was accompanied by loss of hemolytic activity and adsorption of toxic protein. The α 12 S -toxin, although only weakly hemolytic, was shown to be lytic for spherules. An α 12 S -free toxin rapidly disrupted spherules, with formation of fragments with attached rings similar in dimensions to the α 12 S molecule. Lipid monolayer experiments showed that HP α-toxin could penetrate lipid monolayers by virtue of a hydrophobic interaction. Effects of HP α-toxin on rabbit and human erythrocyte ghosts were similar to its effects on spherules, in that rings appeared on membrane fragments. Toxin-lysed rabbit erythrocytes showed similar rings on the resulting membrane fragments. However, rings were not seen on toxin-treated rabbit erythrocytes in the prelytic lag phase; this result and the fact that human erythrocytes are largely insensitive to α-toxin were interpreted as evidence against a lytic mechanism involving ring formation as the primary event. Rings were interpreted as toxin polymers similar to α 12 S molecules, formed from specifically orientated active toxin molecules at the surface of lipid structures. Possible mechanisms for toxin lysis of spherules and erythrocytes are discussed.