Membrane permeabilization induced by cytolytic delta-endotoxin CytA from Bacillus thuringiensis var. israelensis

The mechanism by which cytolytic delta-endotoxin, CytA, from Bacillus thuringiensis var. israelensis permeabilizes membranes and induces the release of self-quenching fluorescence markers from unilamellar vesicles was determined by measuring its reaction kinetics. The rates of release of fluorescence markers were influenced by the concentration of CytA. CytA exhibited a low association constant to lipid membranes. The results also revealed that binding of a large number of toxin molecules to unilamellar vesicles is essential to maintain the integrity of the latter.