Conformational equilibria of terminally blocked single amino acids at the water-hexane interface. A molecular dynamics study
Conformational equilibria of terminally blocked single amino acids at the water-hexane interface. A molecular dynamics study
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DOI：
10.1021/jp970938n
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发表时间：
1998-01-01
影响因子：
3.3
通讯作者：
Pohorille, A
中科院分区：
文献类型：
--
作者：
Chipot, C;Pohorille, A
的乙酰基和甲基酰胺末端封闭的L-丙氨酸，L-亮氨酸和L-谷氨酰胺氨基酸的构象平衡检查在真空中，在散装水，并在水-己烷界面，使用多纳秒分子动力学模拟。在不同二面角的骨干，φ和psi，找到肽的二维概率分布函数进行了计算，并确定不同构象状态之间的自由能差。所有三种肽都是界面活性的，即倾向于在界面处积累，即使它们不是两亲性的。在气相和水中稳定的构象状态在界面环境中也是稳定的。然而，他们的人口，不能简单地预测从本体相的构象平衡的知识，表明界面上的肽施加独特的影响。界面环境中的构象偏好是由静电效应和疏水效应之间的相互作用引起的。如在水溶液中，静电溶质-溶剂相互作用导致更极性的肽构象的稳定化。疏水效应表现在界面处的极性和非极性部分的溶质分离到水相和己烷相，分别的倾向。对于末端封闭的谷氨酰胺，这有利于这样的隔离是兼容的界面的己烷侧上的强，主链侧链分子内氢键的形成的构象。疏水效应的影响也可以注意到在界面处的肽的取向偏好。末端封闭的亮氨酸被定向成使得其非极性侧链被埋在己烷中，而谷氨酰胺的极性侧链被浸没在水中。使肽沿着平行于界面的轴旋转90度以上的自由能是相当大的。这表明肽在界面处的折叠是由采用两亲性结构的趋势强烈驱动的。
The conformational equilibria of the acetyl and methyl amide terminally blocked L-alanine, L-leucine and L-glutamine amino acids are examined in vacuum, in bulk water, and at the water-hexane interface, using multi-nanosecond molecular dynamics simulations. The two-dimensional probability distribution functions of finding the peptides at different dihedral angles of the backbone, phi and psi, are calculated, and free energy differences between different conformational states are determined. All three peptides are interfacially active, i.e. tend to accumulate at the interface even though they are not amphiphilic. Conformational states stable in both gas phase and water are also stable in the interfacial environment. Their populations, however, cannot be simply predicted from the knowledge of conformational equilibria in the bulk phases, indicating that the interface exerts a unique effect on the peptides. Conformational preferences in the interfacial environment arise from the interplay between electrostatic and hydrophobic effects. As in an aqueous solution, electrostatic solute-solvent interactions lead to the stabilization of more polar peptide conformations. The hydrophobic effect is manifested at the interface by a tendency to segregate polar and nonpolar moieties of the solute into the aqueous and the hexane phases, respectively. For the terminally blocked glutamine, this favors conformations for which such a segregation is compatible with the formation of strong, backbone-side chain intramolecular hydrogen bonds on the hexane side of the interface. The influence of the hydrophobic effect can be also noted in the orientational preferences of the peptides at the interface. The terminally blocked leucine is oriented such that its nonpolar side chain is buried in hexane, whereas the polar side chain of glutamine is immersed in water. The free energies of rotating the peptides along the axis parallel to the interface by more than 90 degrees are substantial. This indicates that peptide folding at interfaces is strongly driven by the tendency to adopt amphiphilic structures.