Monhemi Hassan, Housaindokht Mohammad Reza, Nakhaei Pour Ali
Research and Technology Center of Biomolecules, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran.
J Phys Chem B. 2015 Aug 20;119(33):10406-16. doi: 10.1021/acs.jpcb.5b03970. Epub 2015 Aug 6.
Protein instability in supercritical CO2 limits the application of this green solvent in enzyme-catalyzed reactions. CO2 molecules act as a protein denaturant at high pressure under supercritical conditions. Here, for the first time, we show that natural osmolytes could stabilize protein conformation in supercritical CO2. Molecular dynamics simulation is used to monitor the effects of adding different natural osmolytes on the conformation and dynamics of chymotrypsin inhibitor 2 (CI2) in supercritical CO2. Simulations showed that CI2 is denatured at 200 bar in supercritical CO2, which is in agreement with experimental observations. Interestingly, the protein conformation remains native after addition of ∼1 M amino acid- and sugar-based osmolyte models. These molecules stabilize protein through the formation of supramolecular self-assemblies resulting from macromolecule-osmolyte hydrogen bonds. Nevertheless, trimethylamine N-oxide, which is known as a potent osmolyte for protein stabilization in aqueous solutions, amplifies protein denaturation in supercritical CO2. On the basis of our structural analysis, we introduce a new mechanism for the osmolyte effect in supercritical CO2, an "inclusion mechanism". To the best of our knowledge, this is the first study that introduces the application of natural osmolytes in a supercritical fluid and describes mechanistic insights into osmolyte action in nonaqueous media.
蛋白质在超临界二氧化碳中的不稳定性限制了这种绿色溶剂在酶催化反应中的应用。在超临界条件下，高压下二氧化碳分子会起到蛋白质变性剂的作用。在此，我们首次表明天然渗透剂能够在超临界二氧化碳中稳定蛋白质构象。分子动力学模拟用于监测添加不同天然渗透剂对超临界二氧化碳中胰凝乳蛋白酶抑制剂2（CI2）构象和动力学的影响。模拟结果表明，CI2在200巴的超临界二氧化碳中会变性，这与实验观察结果一致。有趣的是，添加约1 M基于氨基酸和糖的渗透剂模型后，蛋白质构象保持天然状态。这些分子通过由大分子 - 渗透剂氢键形成的超分子自组装来稳定蛋白质。然而，三甲胺N - 氧化物在水溶液中是一种有效的蛋白质稳定渗透剂，但在超临界二氧化碳中会加剧蛋白质变性。基于我们的结构分析，我们提出了一种超临界二氧化碳中渗透剂效应的新机制——“包合机制”。据我们所知，这是首次介绍天然渗透剂在超临界流体中的应用并描述非水介质中渗透剂作用机理的研究。
