Urea Impedes the Hydrophobic Collapse of Partially Unfolded Proteins
Urea Impedes the Hydrophobic Collapse of Partially Unfolded Proteins
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DOI：
10.1016/j.bpj.2009.01.051
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发表时间：
2009-05-06
影响因子：
3.4
通讯作者：
Grubmueller, Helmut
中科院分区：
文献类型：
--
作者：
Stumpe, Martin C.;Grubmueller, Helmut
蛋白质在尿素水溶液中发生变性。分子驱动力的性质在过去受到了广泛关注，而尿素在不同展开阶段如何发挥作用的问题在原子水平上尚未得到很好的理解。特别是，尚不清楚尿素是否主动攻击折叠蛋白质或稳定未折叠的构象。在这里，我们通过分子动力学模拟研究了尿素在不同展开阶段的影响，并比较了尿素水溶液和纯水中部分展开状态的行为。虽然水中部分解折叠的蛋白质在初次重折叠事件中表现出疏水性塌陷，但它在尿素水溶液中保持稳定，甚至经历了进一步的解折叠步骤。此外，发现折叠蛋白的初始解折叠步骤不是由尿素触发的，而是稳定的。这种稳定作用的根本机制是尿素与瞬时暴露的极性较小的残基和蛋白质骨架的有利相互作用，从而阻止逆反应。总而言之，这些结果表明，一般来说，尿素诱导的蛋白质解折叠主要不是通过主动攻击进行的。相反，向未折叠状态的热波动是稳定的，并且部分未折叠蛋白质向天然状态的疏水塌陷受到阻碍。结果，平衡向展开状态移动。
Proteins are denatured in aqueous urea solution. The nature of the molecular driving forces has received substantial attention in the past, whereas the question how urea acts at different phases of unfolding is not yet well understood at the atomic level. In particular, it is unclear whether urea actively attacks folded proteins or instead stabilizes unfolded conformations. Here we investigated the effect of urea at different phases of unfolding by molecular dynamics simulations, and the behavior of partially unfolded states in both aqueous urea solution and in pure water was compared. Whereas the partially unfolded protein in water exhibited hydrophobic collapses as primary refolding events, it remained stable or even underwent further unfolding steps in aqueous urea solution. Further, initial unfolding steps of the folded protein were found not to be triggered by urea, but instead, stabilized. The underlying mechanism of this stabilization is a favorable interaction of urea with transiently exposed, less-polar residues and the protein backbone, thereby impeding back-reactions. Taken together, these results suggest that, quite generally, urea-induced protein unfolding proceeds primarily not by active attack. Rather, thermal fluctuations toward the unfolded state are stabilized and the hydrophobic collapse of partially unfolded proteins toward the native state is impeded. As a result, the equilibrium is shifted toward the unfolded state.