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 ha s facilitated the identification of an important step in the cytolytic mechanism of this toxin. When alpha toxin-dependent haemolysis was me asured on erythrocytes at various temperatures it was clear that at te mperatures less than or equal to 15 degrees C the haemolysis rate was significantly inhibited with little or no haemolysis occurring at 4 de grees C. Alpha toxin appeared to bind to and oligomerize on erythrocyt e 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 degre es C could not account for the loss of cytolytic activity at low tempe rature. At 4 degrees C alpha toxin neither stimulated potassium releas e 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 er ythrocytes could not be closed by low temperature. Therefore, low temp erature appeared to prevent the oligomerized complex from forming a po re in the membrane, These data support the hypothesis that alpha toxin oligomerizes into a membrane-bound, pre-pore complex prior to formati on of a pore in a lipid bilayer.