The Ability of an α-Aminoisobutyric Acid Residue to Promote Helical Folding in Oligopeptides
作者:Mitsuaki Narita、Kazunori Ishikawa、Hiroki Sugasawa、Masamitsu Doi
DOI:10.1246/bcsj.58.1731
日期:1985.6
In order to investigate the ability of an Aib residue to promote helical folding in oligopeptides, oligo(Leu)s containing an Aib residue were prepared by stepwise elongation and fragment condensation methods. The peptides prepared were the following: Boc–Aib–Leun–OBzl (n=3–6 and 9), Boc–Leun–Aib–OBzl (n=3–6 and 9), Boc–Leu3–Aib–Leu3–OBzl, Boc–Leu4–Aib–Leu4–OBzl, Boc–Leu8–Aib–Leu4–OBzl, Boc–Leu4–Aib–Leu8–OBzl, and Boc–Leu8–Aib–Leu8–OBzl. The IR absorption conformational analyses of Boc–Aib–Leun–OBzl (n=3–6) in dichloromethane have shown the occurrence of incipient helical structures (α- or 310-helixes) formed by one, two, three, and so forth i→i–4 or i→i–3 hydrogen-bonding patterns. All the peptides except Boc–Aib–Leu9–OBzl and Boc–Leun–Aib–OBzl (n=6 and 9) have also shown helical structures (α- or 310-helixes), indicating the great ability of an Aib residue to promote helical folding in peptides. This is in remarkable contrast with the fact that homologous oligo(Leu) counterparts have β-sheet structures. The solubility properties of the peptides were in good agreement with those speculated from their conformations. The initiation and stabilization mechanism of helical folding in peptides has been illustrated schematically and attributed to the restriction of the values of the backbone dihedral angles φ and ψ of an Aib residue due to steric hindrance, followed by the restriction of the values of φ and ψ of other amino acid residues due to hydrogen bonds initiated by the Aib residue. The great ability of an Aib residue to promote helical folding in peptides also suggests that the restriction of the values of the backbone dihedral angles φ and ψ (right-handed α-helix: φ=−57°, ψ=−47°) of an amino acid residue in peptide chains is one of important initiation mechanisms of α-helical folding in natural proteins. The implication of the new findings for the study of proteins containing Aib residues is presented on the basis of the stabilizing efficacy of Aib residues on helical regions of proteins.
为了研究 Aib 残基促进寡肽螺旋折叠的能力,我们采用分步延伸法和片段缩合法制备了含有 Aib 残基的寡(Leu)肽。制备的肽如下Boc-Aib-Leun-OBzl(n=3-6 和 9)、Boc-Leun-Aib-OBzl(n=3-6 和 9)、Boc-Leu3-Aib-Leu3-OBzl、Boc-Leu4-Aib-Leu4-OBzl、Boc-Leu8-Aib-Leu4-OBzl、Boc-Leu4-Aib-Leu8-OBzl 和 Boc-Leu8-Aib-Leu8-OBzl。在二氯甲烷中对 Boc-Aib-Leun-OBzl(n=3-6)进行的红外吸收构象分析表明,出现了由 1、2、3 等 i→i-4 或 i→i-3 氢键模式形成的初螺旋结构(α- 或 310-螺旋)。除了 Boc-Aib-Leu9-OBzl 和 Boc-Leun-Aib-OBzl(n=6 和 9)外,所有肽也都呈现出螺旋结构(α 螺旋或 310 螺旋),这表明 Aib 残基具有促进肽螺旋折叠的巨大能力。这与同源寡(Leu)对应物的β片状结构形成了鲜明对比。多肽的溶解特性与根据其构象推测的结果十分吻合。多肽螺旋折叠的启动和稳定机制示意图显示,由于立体阻碍,Aib 残基的骨架二面角 φ 和 ψ 值受到限制,随后由于 Aib 残基启动氢键,其他氨基酸残基的 φ 和 ψ 值受到限制。Aib 残基促进肽螺旋折叠的巨大能力还表明,肽链中氨基酸残基的骨架二面角φ 和ψ(右手α-螺旋:φ=-57°,ψ=-47°)值的限制是天然蛋白质中α-螺旋折叠的重要启动机制之一。根据 Aib 残基对蛋白质螺旋区域的稳定作用,介绍了新发现对研究含有 Aib 残基的蛋白质的意义。