形成α-螺旋的短盐桥的盐特异性稳定性和变性
Salt-specific stability and denaturation of a short salt-bridge forming alpha-helix
摘要：
使用1微秒分子动力学（MD）计算机模拟研究了在大盐浓度（3-4 M）的显式电解质水溶液（NaCl、KCl、NaI和KF）中单个丙氨酸基Ace-AEAAAKEAAAKA-Nme肽的结构。肽显示71 α-螺旋结构无盐和不稳定与NaCl的加入与实验的一个稍微长的版本。它主要通过Lys和Glu侧链之间的直接和间接（i+4）EK盐桥以及伴随的骨架屏蔽机制来稳定。发现NaI是比NaCl更强的变性剂，而钾盐几乎不显示影响。分子结构的研究表明，与最近的实验相一致，Na+对侧链羧酸根和骨架羰基的亲和力比K+强得多，从而削弱了盐桥和二级结构氢键。在同一时间的大I-具有相当大的亲和力的非极性丙氨酸在最近的观察线的一个大的倾向I-吸附到简单的疏水，从而“协助”Na+在其不稳定的行动。在变性状态的肽新的长寿命（10-20 ns）的“环”的配置中观察到单个Na+离子和水分子的氢键结合到多个骨架羰基。在试图分析的优先相互作用形式主义内的变性行为，我们确实发现，对于最强的变性剂，碘化钠，蛋白质是最不水合。此外，蛋白质变性的可能指示可能是肽骨架的第一溶剂化壳被不稳定共溶质（钠）优先溶剂化。
英文摘要：
The structure of a single alanine-based Ace-AEAAAKEAAAKA-Nme peptide in explicit aqueous electrolyte solutions (NaCl, KCl, NaI, and KF) at large salt concentrations (3-4 M) is investigated using 1 microsecond molecular dynamics (MD) computer simulations. The peptide displays 71 alpha-helical structure without salt and destabilizes with the addition of NaCl in agreement with experiments of a somewhat longer version. It is mainly stabilized by direct and indirect (i+4)EK salt bridges between the Lys and Glu side chains and a concomitant backbone shielding mechanism. NaI is found to be a stronger denaturant than NaCl, while the potassium salts hardly show influence. Investigation of the molecular structures reveals that consistent with recent experiments Na+ has a much stronger affinity to side chain carboxylates and backbone carbonyls than K+, thereby weakening salt bridges and secondary structure hydrogen bonds. At the same time the large I- has a considerable affinity to the nonpolar alanine in line with recent observations of a large propensity of I- to adsorb to simple hydrophobes, and thereby 'assists' Na+ in its destabilizing action. In the denatured states of the peptide novel long-lived (10-20 ns) 'loop'-configurations are observed in which single Na+ ions and water molecules are hydrogen-bonded to multiple backbone carbonyls. In an attempt to analyze the denaturation behavior within the preferential interaction formalism, we find indeed that for the strongest denaturant, NaI, the protein is least hydrated. Additionally, a possible indication for protein denaturation might be a preferential solvation of the first solvation shell of the peptide backbone by the destabilizing cosolute (sodium).
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