Hydrophobic association is the key contributor behind the formation of well packed core of a protein which is often believed to be an important step for folding from an unfolded chain to its compact functional form. While most of the protein folding/unfolding studies have evaluated the changes in the hydrophobic interactions during chemical denaturation, the role of hydrophilic amino acids in such processes are not discussed in detail. Here we report the role of the hydrophilic amino acids behind ethanol induced unfolding of protein. Using free energy simulations, we show that chicken villin head piece (HP‐36) protein unfolds gradually in presence of water‐ethanol binary mixture with increasing composition of ethanol. However, upon mutation of hydrophilic amino acids by glycine while keeping the hydrophobic amino acids intact, the compact state of the protein is found to be stable at all compositions with gradual flattening of the free energy landscape upon increasing compositions. The local environment around the protein in terms of ethanol/water number significantly differs in wild type protein compared to the mutated protein. The calculated Wyman‐Tanford preferential binding coefficient of ethanol for wild type protein reveals that a greater number of cosolutes (here ethanol) bind to the unfolded state compared to its folded state. However, no significant increase in binding coefficient of ethanol at the unfolded state is found for mutated protein. Local‐bulk partition coefficient calculation also suggests similar scenarios. Our results reveal that the weakening of hydrophobic interactions in aqueous ethanol solution along with larger preferential binding of ethanol to the unfolded state mediated by hydrophilic amino acids combinedly helps unfolding of protein in aqueous ethanol solution.

中文翻译：

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探索亲水性氨基酸在乙醇水溶液中蛋白质去折叠中的作用。

疏水缔合是形成良好包装的蛋白质核心的关键因素，这通常被认为是从未折叠的链折叠到其紧凑的功能形式的重要步骤。虽然大多数蛋白质折叠/展开研究已经评估了化学变性过程中疏水相互作用的变化，但没有详细讨论亲水氨基酸在这些过程中的作用。在这里，我们报告了乙醇诱导蛋白质展开背后的亲水性氨基酸的作用。使用自由能模拟，我们表明鸡绒毛头片 (HP-36) 蛋白在水-乙醇二元混合物存在下随着乙醇组成的增加逐渐展开。然而，当亲水性氨基酸被甘氨酸突变，同时保持疏水性氨基酸完整时，发现蛋白质的紧凑状态在所有组成下都是稳定的，随着组成的增加，自由能景观逐渐变平。与突变的蛋白质相比，野生型蛋白质的乙醇/水数方面的蛋白质周围的局部环境显着不同。计算出的 Wyman-Tanford 乙醇对野生型蛋白质的优先结合系数表明，与其折叠状态相比，更多数量的共溶物（此处为乙醇）与未折叠状态结合。然而，对于突变的蛋白质，未发现未折叠状态下乙醇的结合系数没有显着增加。局部批量分配系数计算也提出了类似的情况。