Precise side-chain conformation analysis of l-phenylalanine in α-helical polypeptide by quantum-chemical calculation and ¹³C CP-MAS NMR measurement

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• 作者：Subaru Niimura ; Junya Suzuki ; Hiromichi Kurosu ; Takeshi Yamanobe ; Akira Shoji
• 关键词：Quantum-chemical calculation ; l-Phenylalanine ; Side-chain conformation ; α ; -Helix ; CP-MAS NMR
• 刊名：Journal of Molecular Structure
• 出版年：2010
• 出版时间：22 April 2010
• 年：2010
• 卷：969
• 期：1-3
• 页码：40-47
• 全文大小：411 K

文摘

To clarify the positive role of side-chain conformation in the stability of protein secondary structure (main-chain conformation), we successfully calculated the optimization structure of a well-defined α-helical octadecapeptide composed of l-alanine (Ala) and l-phenylalanine (Phe) residues, H–(Ala)₈–Phe–(Ala)₉–OH, based on the molecular orbital calculation with density functional theory (DFT/B3LYP/6-31G(d)). From the total energy and the precise secondary structural parameters such as main-chain dihedral angles and hydrogen-bond parameters of the optimized structure, we confirmed that the conformational stability of an α-helix is affected dominantly by the side-chain conformation (χ₁) of the Phe residue in this system: model A (T form: around 180° of χ₁) is most stable in α-helix and model B (G⁺ form: around −60° of χ₁) is next stable, but model C (G⁻ form: around 60° of χ₁) is less stable. In addition, we demonstrate that the stable conformation of poly(l-phenylalanine) is an α-helix with the side-chain T form, by comparison of the carbonyl ¹³C chemical shift measured by ¹³C CP-MAS NMR and the calculated one.