Two mode ion channels induced by interaction of acidic amphipathic alpha-helical peptides with lipid bilayers

In order to investigate the ion permeability and selectivity of ion channel formed by amphipathic alpha-helical peptides, we designed to synthesize an acidic peptide Ac(Leu-Ala-Glu-Leu)3NHCH3 (Glu-4(3)) and its channel property was compared with a basic peptides Arg-4(3) in which Glu in Glu-4(3) was replaced by Arg. Two modes of the conductance change were observed by the interaction of Glu-4(3) with planar lipid bilayers; a steady increase of the conductance with the elapse of time (mode 1) and a spike-like increase of the current (mode 2) appearing with a lag time and overlapping the model current increase. The application of negative membrane potential induced the mode 1 current and the lowering pH decreased it, suggesting that the mode 1 current is caused by slow insertion of Glu-4(3) into the lipid bilayer and then by forming certain unknown bundles like semichannels. Mode 2 was found to be consisted of channel type opened-close current with several different conductances and relatively short opening lifetimes. There was no ion selectivity in the mode 1 current, whereas the mode 2 current was cation selective. The peptide Arg-4(3) has formed a cation-selective ion channel but not shown such two mode current changes. The membrane potential formation experiment in liposomes using DiSC3(5) also showed the cation selectivity for Arg-4(3) and non-ion selectivity for Glu-4(3). The difference between Arg-4(3) and Glu-4(3) was also observed in conformational analysis by CD and in dye-release experiment from liposome. Such difference was discussed in terms of electrostatic interaction between peptides and lipid head groups.