Effect of cholesterol on membrane-damaging activity of Naja nigricollis toxin γ toward phospholipid vesicles

Membrane-damaging activity of Naja nigricollis toxin γ on phospholipid vesicles was attenuated by incorporation of cholesterol into phospholipid vesicles. Deprivation of cholesterol from erythrocyte membrane enhanced notably hemolytic activity of toxin γ, while the hemolytic activity of toxin γ on cholesterol-depleted erythrocytes decreased when cholesterol was restored to membrane. Phospholipid-binding capability and oligomeric assembly upon binding with lipid vesicles were modestly affected in the presence of cholesterol. Time-resolved fluorescence and Fourier transform infrared spectra showed that phospholipid-bound toxin γ and cholesterol/phospholipid-bound toxin γ did not adopt the same conformation. Moreover, geometrical arrangement of toxin γ in contact with phospholipid vesicles was different from that with cholesterol/phospholipid vesicles as evidenced by N-(fluorescein-5-thiocarbamoyl)-1, 2-dihexadecanoyl-phosphatidylethanolamine fluorescence enhancement and color transformation of phospholipid/polydiacetylene membrane assay. Taken together, our data show that ordered phospholipid phase arising from incorporation of cholesterol affects conformation and topographical arrangement of toxin γ on water–lipid interface, thus attenuating its membrane-damaging activity against phospholipid vesicles.