Senguen F Timur, Lee Naomi R, Gu Xianfeng, Ryan Derek M, Doran Todd M, Anderson Elizabeth A, Nilsson Bradley L
Department of Chemistry, University of Rochester, Rochester, NY 14627-0216, USA.
Mol Biosyst. 2011 Feb;7(2):486-96. doi: 10.1039/c0mb00080a. Epub 2010 Nov 9.
Aromatic amino acids have been shown to promote self-assembly of amyloid peptides, although the basis for this amyloid-inducing behavior is not understood. We adopted the amyloid-β 16-22 peptide (Aβ(16-22), Ac-KLVFFAE-NH(2)) as a model to study the role of aromatic amino acids in peptide self-assembly. Aβ(16-22) contains two consecutive Phe residues (19 and 20) in which Phe 19 side chains form interstrand contacts in fibrils while Phe 20 side chains interact with the side chain of Va l18. The kinetic and thermodynamic effect of varying the hydrophobicity and aromaticity at positions 19 and 20 by mutation with Ala, Tyr, cyclohexylalanine (Cha), and pentafluorophenylalanine (F(5)-Phe) (order of hydrophobicity is Ala < Tyr < Phe < F(5)-Phe < Cha) was characterized. Ala and Tyr position 19 variants failed to undergo fibril formation at the peptide concentrations studied, but Cha and F(5)-Phe variants self-assembled at dramatically enhanced rates relative to wild-type. Cha mutation was thermodynamically stabilizing at position 20 (ΔΔG = -0.2 kcal mol(-1) relative to wild-type) and destabilizing at position 19 (ΔΔG = +0.2 kcal mol(-1)). Conversely, F(5)-Phe mutations were strongly stabilizing at both positions (ΔΔG = -1.3 kcal mol(-1) at 19, ΔΔG = -0.9 kcal mol(-1) at 20). The double Cha and F(5)-Phe mutants showed that the thermodynamic effects were additive (ΔΔG = 0 kcal mol(-1) for Cha 19,20 and -2.1 kcal mol(-1) for F(5)-Phe 19,20). These results indicate that sequence hydrophobicity alone does not dictate amyloid potential, but that aromatic, hydrophobic, and steric considerations collectively influence fibril formation.
芳香族氨基酸已被证明能促进淀粉样肽的自组装，尽管这种诱导淀粉样变行为的基础尚不清楚。我们采用淀粉样β蛋白16 - 22肽（Aβ(16 - 22)，Ac - KLVFFAE - NH₂）作为模型来研究芳香族氨基酸在肽自组装中的作用。Aβ(16 - 22)含有两个连续的苯丙氨酸残基（19位和20位），其中苯丙氨酸19的侧链在纤维中形成链间接触，而苯丙氨酸20的侧链与缬氨酸18的侧链相互作用。通过用丙氨酸、酪氨酸、环己基丙氨酸（Cha）和五氟苯丙氨酸（F(5)-Phe）（疏水性顺序为丙氨酸 < 酪氨酸 < 苯丙氨酸 < F(5)-Phe < Cha）进行突变，研究了改变19位和20位的疏水性和芳香性的动力学和热力学效应。在研究的肽浓度下，19位丙氨酸和酪氨酸变体未能形成纤维，但Cha和F(5)-Phe变体相对于野生型以显著提高的速率自组装。Cha突变在20位是热力学稳定的（相对于野生型，ΔΔG = -0.2 kcal/mol），而在19位是不稳定的（ΔΔG = +0.2 kcal/mol）。相反，F(5)-Phe突变在两个位置都是强烈稳定的（19位时ΔΔG = -1.3 kcal/mol，20位时ΔΔG = -0.9 kcal/mol）。双Cha和F(5)-Phe突变体表明热力学效应是可加的（Cha 19,20时ΔΔG = 0 kcal/mol，F(5)-Phe 19,20时ΔΔG = -2.1 kcal/mol）。这些结果表明，仅序列疏水性并不能决定淀粉样变的潜力，而是芳香性、疏水性和空间因素共同影响纤维的形成。
