Membrane-bound conformation of Naja nigricollis toxin γ affects its membrane-damaging activity

To address whether the conformational events associated with the absorption of Naja nigricollis toxin γ on water–lipid interface plays a vital role in its membrane-damaging activity, the present study is carried out. Membrane-damaging activity of toxin γ on 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC)/1, 2-dimyristoyl-phosphatidic acid (DMPA) vesicles was approximately 13-fold of that on 1, 2-dipalmitoyl-phosphatidylcholine (DPPC)/DMPA vesicles, while the binding affinity of toxin γ for POPC/DMPA was twofold of that for DPPC/DMPA. Time-resolved fluorescence, acrylamide quenching and Fourier transform infrared spectra showed that POPC/DMPA-bound toxin γ and DPPC/DMPA-bound toxin γ did not adopt the same conformation. Moreover, geometrical arrangement of toxin γ in contact with POPC/DMPA vesicles was different from that with DPPC/DMPA vesicles as evidenced by N-(fluorescein-5-thiocarbamoyl)-1,2-dihexadecanoyl-phosphatidylcholine fluorescence enhancement and cross-linking of membrane-bound toxin γ. Taken together, our data show that different membrane packing densities arising from phospholipid acyl chain affect membrane-bound conformation of toxin γ, thus changing its membrane-damaging activity.