Trans-Bilayer Ion Conduction by Proline Containing Cyclic Hexapeptides and Effects of Amino Acid Substitutions on Ion Conducting Properties
作者:Junichi Taira、Satoshi Osada、Ryo Hayashi、Toshihisa Ueda、Masoud Jelokhani-Niaraki、Haruhiko Aoyagi、Hiroaki Kodama
DOI:10.1246/bcsj.20090272
日期:2010.6.15
Several ion channel forming cyclic peptides have been reported over the past two decades and various ion conducting mechanisms have been proposed. In this article, we report on amino acid substitutions in cyclic hexapeptides and their effects on the ion conducting properties of these peptides. Cyclic hexapeptides, cyclo(Pro–Xxx–Yyy)2, containing two Pro residues, were used as the main framework. The substitution is performed at the Xxx positions with cationic/hydrophilic Lys or hydrophobic Leu. Yyy positions were substituted with d-Phe, d-Ala, or Gly. The peptides which were absent Lys residues showed ion conducting profiles with clear transitions of electric currents, whereas the peptides containing Lys residues tended to exhibit spiky or burst-like profiles. These profiles were altered single state profiles by the protection of ε-amino groups with aromatic protecting groups. The protected analogs exhibited significant decrease in ion conductance. These results indicated that peptides containing Lys conduct ions without forming ring stacked tube-like structure. Ion channel properties were also affected by conformational changes of the cyclic peptides induced by substitution of the Yyy positions. Enhancement of intramolecular β-turn structures of cyclic peptides tended to decrease their ion conductance values.
在过去的二十年里,已经报道了几种形成离子通道的环肽,并提出了各种离子传导机制。在这篇文章中,我们报告了环六肽中的氨基酸取代及其对这些肽离子传导特性的影响。我们以含有两个 Pro 残基的环状六肽 cyclo(Pro-Xxx-Yyy)2 为主要框架。在 Xxx 位置用阳离子/亲水的 Lys 或疏水的 Leu 取代。Yyy 位置被 d-Phe、d-Ala 或 Gly 取代。不含赖氨酸残基的肽呈现出具有清晰电流转换的离子传导曲线,而含有赖氨酸残基的肽则倾向于呈现尖刺状或爆裂状曲线。用芳香族保护基团保护ε-氨基后,这些剖面改变了单态剖面。受保护的类似物的离子传导性明显下降。这些结果表明,含有赖氨酸的肽在传导离子时不会形成环状叠管结构。离子通道特性还受到 Yyy 位置取代引起的环肽构象变化的影响。环肽分子内β-匝结构的增强往往会降低其离子传导值。