RELEASE OF LIPID VESICLE CONTENTS BY THE BACTERIAL PROTEIN TOXIN ALPHA-HEMOLYSIN

Alpha-Haemolysin is a protein toxin (107 kDa) secreted by some pathoge nic strains of E. coli. It binds to mammalian cell membranes, disrupti ng cellular activities and lysing cells. This paper describes the mech anism of alpha-haemolysin-induced membrane leakage, from experiments i n which extrusion large unilamellar vesicles, loaded with fluorescent solutes, are treated with purified toxin. The results show that the to xin does not require of any membrane receptor to exert its activity, t hat vesicles become leaky following an 'all-or-none' mechanism, and th at leakage occurs through a non-osmotic detergent-like bilayer disrupt ion induced by the protein. Small pores formed by monomeric alpha-haem olysin, as described by other authors, do not appear to be related to the process of membrane disruption. Instead, the experimental data wou ld be in agreement with the idea of oligomeric assemblies being requir ed to produce release of solutes from a single vesicle.