Generation of a membrane-bound, oligomerized pre-pore complex is necessary for pore formation by Clostridium septicum alpha toxin

Low-temperature inhibition of the cytolytic activity of alpha toxin has facilitated the identification of an important step in the cytolytic mechanism of this toxin. When alpha toxin-dependent haemolysis was measured on erythrocytes at various temperatures it was clear that at temperatures less than or equal to 15 degrees C the haemolysis rate was significantly inhibited with little or no haemolysis occurring at 4 degrees C. Alpha toxin appeared to bind to and oligomerize on erythrocyte membranes with similar kinetics at 4 degrees C and 37 degrees C, The slight differences in these two processes at 4 degrees C and 37 degrees C could not account for the loss of cytolytic activity at low temperature. At 4 degrees C alpha toxin neither stimulated potassium release from erythrocytes nor formed pores in planar membranes. In contrast, at temperatures greater than or equal to 25 degrees C both processes proceeded rapidly, Pores that were opened in osmotically stabilized erythrocytes could not be closed by low temperature. Therefore, low temperature appeared to prevent the oligomerized complex from forming a pore in the membrane, These data support the hypothesis that alpha toxin oligomerizes into a membrane-bound, pre-pore complex prior to formation of a pore in a lipid bilayer.