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

Membrane-damaging activity of Naja nigricollis toxin gamma on phospholipid vesicles was attenuated by incorporation of cholesterol into phospholipid vesicles. Deprivation of cholesterol from erythrocyte membrane enhanced notably hemolytic activity of toxin gamma, while the hemolytic activity of toxin gamma 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 gamma and cholesterol/phospholipid-bound toxin gamma did not adopt the same conformation. Moreover, geometrical arrangement of toxin gamma 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 gamma on water-lipid interface, thus attenuating its membrane-damaging activity against phospholipid vesicles.