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.
Lee
S
S
Department of Chemistry, Faculty of Science, Fukuoka University, Japan.
Tanaka
T
T
Anzai
K
K
Kirino
Y
Y
Aoyagi
H
H
Sugihara
G
G
D000595:Amino Acid Sequence; D002463:Cell Membrane Permeability; D002942:Circular Dichroism; D005452:Fluoresceins; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000378:metabolism*; D007477:Ions; D008051:Lipid Bilayers; D008564:Membrane Potentials; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000494:pharmacology*; D011487:Protein Conformation
D005452:Fluoresceins; D007473:Ion Channels; D007477:Ions; D008051:Lipid Bilayers; D010455:Peptides; C024098:6-carboxyfluorescein