We have performed molecular dynamics (MD) simulations of the protein α-lactalbumin in aqueous solution containing the ionic liquid (IL) 1-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM][BF4]) as the cosolvent at different concentrations. Attempts have been made to obtain quantitative understanding of the effects of the IL on the conformational features of the protein as well as the distributions of the IL and water around it. The calculations revealed enhanced rigidity of the protein with reduced conformational fluctuations and increasingly correlated local motions in the presence of the IL. Nonuniform relative population of the BMIM+ and BF4- ions at the protein surface with respect to that in the bulk solution has been observed. It is demonstrated that exchange of water by the IL around the protein results in rearrangement of the hydrogen bond network at the interface with breaking of protein-water hydrogen bonds and formation of protein-IL hydrogen bonds. Importantly, it is found that the protein forms increased number of stronger salt bridges in the presence of IL. This shows that the formation of a greater number of such stronger salt bridges is the origin behind the enhanced rigidity of the protein in the presence of the IL.

中文翻译：

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从分子模拟研究中微观了解离子液体对蛋白质的影响。

我们已经在包含离子液体（IL）1-丁基-3-甲基咪唑四氟硼酸盐（[BMIM] [BF4]）作为助溶剂的不同浓度的水溶液中进行了蛋白质α-乳清蛋白的分子动力学（MD）模拟。已经尝试获得对IL对蛋白质的构象特征以及IL和其周围水的分布的影响的定量理解。计算结果显示，在IL存在下，蛋白质的刚度增加，构象波动减少，局部运动越来越相关。已经观察到蛋白质表面上的BMIM +和BF4-离子相对于本体溶液的相对不均匀。已经证明，IL周围的蛋白质交换水导致界面处的氢键网络重排，从而破坏了蛋白质-水氢键并形成了蛋白质-IL氢键。重要的是，发现在IL存在下蛋白质形成增加数量的更强的盐桥。这表明在IL存在下，大量这种更强的盐桥的形成是蛋白质刚性增强的原因。