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

合成了电压依赖性钾通道H5区（假定的成孔区）的模型肽（H5肽），并通过荧光光谱、CD测量和平面双分子层测量研究了其与脂质双分子层膜的相互作用。当肽被纳入脂质体时，存在于肽中的色氨酸残基的荧光仅被KI微弱猝灭。CD谱分析表明，脂质体的存在诱导了β结构。H5肽在平面脂质双分子层中形成离子通道。这些结果支持了H5区通过β结构穿透膜并形成电压依赖性钾通道的孔衬里的观点。然而，H5肽通道具有较强的阴离子选择性，其电导大于天然钾通道。这些与天然通道的偏离可能反映了其他跨膜区域对钾通道功能的重要性。合成了几个模型肽，每三个或四个残基上都含有碱性氨基酸。这些肽是电压依赖性钠通道S4段的模型。这些多肽在平面脂质双层膜上形成阳离子选择性离子通道。通道的性质取决于许多参数，如肽长度、两亲性、疏水氨基酸侧链的大小、亲水性氨基酸的电荷等。对这些参数对通道性质影响的进一步定量研究将有助于揭示通道蛋白与脂质双分子层的相互作用。

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.