Ishida H, Qi Z, Sokabe M, Donowaki K, Inoue Y
Inoue Photochirogenesis Project, ERATO, Japan Science and Technology, 4-6-3 Kamishinden, Toyonaka, Osaka 560-0085, Japan.
J Org Chem. 2001 May 4;66(9):2978-89. doi: 10.1021/jo001079t.
A series of novel cyclic peptides composed of 3 to 5 dipeptide units with alternating natural-unnatural amino acid units, have been designed and synthesized, employing 5-(N-alkanoylamino)-3-aminobenzoic acid with a long alkanoyl chain as the unnatural amino acid. All cyclic peptides with systematically varying pore size, shape, and lipophilicity are found to form ion channels with a conductance of ca. 9 pS in aqueous KCl (500 mM) upon examination by the voltage clamp method. These peptide channels are cation selective with the permeability ratio P(Cl(-))/P(K(+)) of around 0.17. The ion channels formed by the neutral, cationic, and anionic cyclic peptides containing L-alanine, L-lysine, and L-aspartate, respectively, show the monovalent cation selectivity with the permeability ratio P(Na(+))/P(K(+)) of ca. 0.39. On the basis of structural information provided by voltage-dependent blockade of the single channel current of all the tested peptides by Ca(2+), we inferred that each channel is formed from a dimer of the peptide with its peptide ring constructing the channel entrance and its alkanoyl chains lining across the membrane to build up the channel pore. The experimental results are consistent with an idea that the rate of ion conduction is determined by the nature of the hydrophobic alkanoyl chain region, which is common to all the channels.
我们设计并合成了一系列新型环肽，其由3至5个二肽单元组成，这些二肽单元包含天然和非天然氨基酸单元的交替排列，使用带有长链烷酰基的5-(N-烷酰基氨基)-3-氨基苯甲酸作为非天然氨基酸。通过电压钳法检测发现，所有孔径、形状和亲脂性系统变化的环肽在500 mM的氯化钾水溶液中均形成了电导约为9 pS的离子通道。这些肽通道具有阳离子选择性，氯离子与钾离子的渗透率之比P(Cl(-))/P(K(+))约为0.17。分别含有L-丙氨酸、L-赖氨酸和L-天冬氨酸的中性、阳离子和阴离子环肽形成的离子通道，对单价阳离子具有选择性，钠离子与钾离子的渗透率之比P(Na(+))/P(K(+))约为0.39。基于Ca(2+)对所有测试肽单通道电流的电压依赖性阻断所提供的结构信息，我们推断每个通道由肽的二聚体形成，其肽环构成通道入口，烷酰基链跨膜排列形成通道孔。实验结果与离子传导速率由所有通道共有的疏水烷酰基链区域的性质决定这一观点一致。
