Institute of Theoretical and Computational Chemistry, College of Chemistry and Molecular Engineering, Beijing National Laboratory for Molecular Sciences, Peking University, Beijing, 100871, China.
Faraday Discuss. 2013;160:191-206; discussion 207-24. doi: 10.1039/c2fd20065a.
Using molecular dynamics simulations, we investigated effects of inorganic salts on the structure and dynamics of a short alpha,beta-polypeptide, BBA5. The simulations showed that three model salts, NaI, NaF, and Na2SO3, have very different effects on the structure of the polypeptide. The addition of NaI to the aqueous solution caused denaturation and significantly weakened hydrogen bonds of the polypeptide. Na2SO3 strengthened the hydrophobic interactions and increased hydrogen bonding of the polypeptide. Preferred binding of Na+ to the backbone carbonyl groups of BBA5 occurred in the NaI solution, consistent with the weakened protein backbone hydrogen bonds, whereas Na+ is excluded more from the vicinity of the protein backbone in the Na2SO3 solution. This difference in Na+ binding correlates well with the different propensities of the counter ions approaching the protein surface: SO3(2-) is much more strongly expelled from the protein apolar surface than I-, and demonstrates the importance of cation-anion cooperativity in affecting protein structures. The binding of the two salts to and their effects on the hydration of the protein surface depends strongly on the polarity of the latter. However, both salts reduce the flexibility of the polypeptide and the fluctuation of its hydration layer. These simulations showed that the chaotropic NaI affects protein structure mainly through a direct binding of Na+ to the backbone and I- to the protein surface. The main effect of Na2SO3 manifests in strengthening the hydrophobic interaction and consequently the hydrogen bonding of the protein, more likely through an "indirect" mechanism. In addition, the simulations showed that NaF has a similar effect as Na2SO3 (but weaker than the latter, consistent with their positions in the Hofmeister series).
使用分子动力学模拟，我们研究了无机盐对短 α,β-多肽 BBA5 的结构和动力学的影响。模拟结果表明，三种模型盐 NaI、NaF 和 Na2SO3 对多肽的结构有非常不同的影响。在水溶液中加入 NaI 会导致变性，并显著削弱多肽的氢键。Na2SO3 增强了疏水力并增加了多肽的氢键。在 NaI 溶液中，Na+优先与 BBA5 的骨架羰基结合，这与蛋白质骨架氢键的削弱一致，而在 Na2SO3 溶液中，Na+更多地被排斥在蛋白质骨架附近。这种 Na+结合的差异与抗衡离子接近蛋白质表面的不同倾向很好地相关：SO3(2-) 比 I- 更强烈地被排斥出蛋白质非极性表面，这表明阳离子-阴离子协同作用在影响蛋白质结构方面的重要性。两种盐对蛋白质表面的结合及其对其水合的影响强烈依赖于后者的极性。然而，两种盐都降低了多肽的灵活性和其水合层的波动。这些模拟表明，具有混乱作用的 NaI 主要通过 Na+与骨架的直接结合以及 I-与蛋白质表面的结合来影响蛋白质结构。Na2SO3 的主要作用在于通过加强疏水力，进而加强蛋白质的氢键，更可能通过一种“间接”机制。此外，模拟结果表明，NaF 与 Na2SO3 具有相似的作用（但比后者弱，这与它们在 Hofmeister 序列中的位置一致）。
