Interaction of the bacterial protein toxin alpha-haemolysin with model membranes: protein binding does not always lead to lytic activity.

alpha-Haemolysin interaction with model membranes has been investigated by a 2-fold procedure. First, protein binding has been measured, by a direct method as well as through changes in the intrinsic fluorescence of the protein when incubated with liposomes and divalent cations. Then, the above results have been correlated with the protein lytic activity. The extent of protein binding is not significantly modified by the presence or absence of Ca2+, or by changes in lipid composition, although these factors influence greatly the membrane lytic activity of the protein. Moreover, Ca2+ binding to the toxin must occur prior to protein binding to the bilayer, for a lytic effect to take place.