Synthetic Model Peptides for the Study of Structure-Activity Relationship of Ion Channels Using Planar Lipid Bilayer Technique

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A model peptide for the H5 region,the putative pore-forming region,of voltage dependent potassium channel(H5 peptide)was synthesized and its interaction with lipid bilayer membranes was investigated by fluorescence spectroscopy,CD measurements,and planar bilayer measurements.The fluorescence of the tryptophan residues present in the peptide was only weakly quenched with KI when the peptide was incorporated into the liposomes.The CD spectra showed that beta-structure was induced in the presence of liposomes.The H5 peptide formed ion channels in planar lipid bilayers.These results support the idea that the H5 region penetrates the membrane and forms pore lining of the voltage dependent potassium channel by taking beta-structure.However,the H5 peptide channel was rather anion selective and its conductance was larger than native potassium channel.These deviations from the native channel may reflect the importance of other membrane spanning regions for the function of the potassium channel.Several model peptides with basic amino acids at every three or four residues of their sequences were synthesized.These peptides are models for S4 segment of voltage dependent sodium channel.These peptides formed cation selective ion channels in planar lipid bilayer membranes.The properties of the channels depended on many parameters such as peptide length,amphipathic properties,the size of the side chains of hydrophobic amino acids,the charge of hydrophilic amino acids,etc.Further quantitative studies for the effect of these parameters on the channel properties will contribute to reveal the interaction of channel proteins with lipid bilayers.