Department of Physical Chemistry, Gdansk University of Technology, Gdansk, Poland.
Phys Chem Chem Phys. 2018 Apr 25;20(16):11174-11182. doi: 10.1039/c7cp07436k.
Although osmolytes are known to modulate the folding equilibrium, the molecular mechanism of their effect on thermal denaturation of proteins is still poorly understood. Here, we simulated the thermal denaturation of a small model protein (Trp-cage) in the presence of denaturing (urea) and stabilizing (betaine) osmolytes, using the all-atom replica exchange molecular dynamics simulations. We found that urea destabilizes Trp-cage by enthalpically-driven association with the protein, acting synergistically with temperature to induce unfolding. In contrast, betaine is sterically excluded from the protein surface thereby exerting entropic depletion forces that contribute to the stabilization of the native state. In fact, we find that while at low temperatures betaine slightly increases the folding free energy of Trp-cage by promoting another near-native conformation, it protects the protein against temperature-induced denaturation. This, in turn, can be attributed to enhanced exclusion of betaine at higher temperatures that arises from less attractive interactions with the protein surface.
尽管渗透剂已知可调节折叠平衡，但它们对蛋白质热变性的影响的分子机制仍了解甚少。在这里，我们使用全原子复制交换分子动力学模拟，模拟了变性（尿素）和稳定（甜菜碱）渗透剂存在下，一种小的模型蛋白（色氨酸笼）的热变性。我们发现，尿素通过与蛋白质的焓驱动结合来使色氨酸笼不稳定，与温度协同作用诱导解折叠。相比之下，甜菜碱从蛋白质表面被排斥，从而施加熵耗力，有助于稳定天然状态。事实上，我们发现，虽然在低温下，甜菜碱通过促进另一种近天然构象略微增加了色氨酸笼的折叠自由能，但它可以保护蛋白质免受温度诱导的变性。这反过来又可以归因于与蛋白质表面的相互作用吸引力降低，导致在较高温度下甜菜碱的排除增强。
