A Membrane Protein Model: Polypeptides with Four<i>α</i>-Helix Bundle Structure on 5,10,15,20-Tetrakis[2-(carboxymethoxy)phenyl]porphyrin
作者:Toru Arai、Keisuke Kobata、Hisakazu Mihara、Tsutomu Fujimoto、Norikazu Nishino
DOI:10.1246/bcsj.68.1989
日期:1995.7
A novel template for the polypeptide–porphyrin hybrid, 5,10,15,20-tetrakis[2-(ethoxycarbonylmethoxy)phenyl]porphyrin (2) was synthesized in 17% yield. Four protected carboxyl groups are installed in 2 at the ortho-phenyl groups as the anchoring points, to which the N-termini of the polypeptides can be linked after the hydrolysis. Thus, 2 is a new analog of the porphyrin template tetrakis[2-(methoxycarbonyl)phenyl]porphyrin. The atropisomerization of 2 was much more rapid than that of tetrakis[2-(methoxycarbonyl)phenyl]porphyrin: At 353 K, 2 reached their equilibrium within 15 min. Such atropisomeric flexibility of 2 allows the self-organization of the α-helical peptide segments which are connected to 2. After the hydrolyses of the ethyl ester groups of 2, four α-helical 21-peptides, H–(–Gln–Leu–Leu–Gln–Ala–Leu–Ala–)3–NHCH2CH2OH were combined through the amide bonds to yield a new polypeptide–porphyrin hybrid (12). The polypeptide moieties of 12 showed typical α-helix profiles on circular dichroism measurements in methanol–water (3/1, v/v) and in Tris·HCl buffer solution. Thus, the four α-helix polypeptides are considered to fold into a bundle structure on the porphyrin template through the hydrophobic interaction. The circular dichroism spectrum of 12 in methanol showed an induced Cotton effect at the porphyrin region, and the CD band was symmetrically split. The hybrid (12) was also successfully incorporated into the egg yolk lecithin membrane almost quantitatively. When the molar ratio of egg yolk lecithin/12 was 500/1, the α-helix structure of the peptide segments in 12 was completely retained in the vesicles.
合成了一种新的多肽-卟啉杂化物模板, 5,10,15,20-四[2-(乙氧羰基甲氧基)苯基]卟吩(2),产率为17%。2在邻位苯环基团上装有四个保护羧基作为锚点,在水解后多肽N端可与之相连,因而, 2是一种新的卟啉模板类似物,即四[2-(甲氧羰基)苯基]卟啉。2的轴向旋转异构化比四[2-(甲氧羰基)苯基]卟啉快得多,在353 K温度下2可在15分钟之内达到平衡。这种2的旋转异构的柔性使得连接到2上的α-螺旋多肽片段能够自发地排列。在水解乙酯基团后,四个α-螺旋21肽H-(Gln-Leu-Leu-Gln-Ala-Leu-Ala)3-NHCH2CH2OH通过酰胺键缩合生成新的多肽-卟啉杂化物(12)。12的多肽部在甲醇-水(3/1,体积比)和Tris·HCl缓冲溶液中的圆二色测试显示出典型的α-螺旋轮廓。因而,认为这四种α-螺旋多肽是通过疏水作用折叠成束状结构的卟啉模板。12在甲醇中的圆二色光谱在卟啉区域显示出一个诱导的Cotton效应,并且CD被对称地裂分。杂化物(12)也能够定量地掺入蛋黄卵磷脂膜中。当卵磷脂/12的摩尔比为500/1时,12中的多肽片段的α-螺旋结构能够在小泡中保持不变。