How a protein can remain stable in a solvent with high content of urea: insights from molecular dynamics simulation of Candida antarctica lipase B in urea : choline chloride deep eutectic solvent
How a protein can remain stable in a solvent with high content of urea: insights from molecular dynamics simulation of Candida antarctica lipase B in urea : choline chloride deep eutectic solvent
复制标题
DOI：
10.1039/c4cp00503a
复制
发表时间：
2014-01-01
影响因子：
3.3
通讯作者：
Bozorgmehr, Mohammad Reza
中科院分区：
文献类型：
--
作者：
Monhemi, Hassan;Housaindokht, Mohammad Reza;Bozorgmehr, Mohammad Reza
深共晶溶剂（DESs）是传统离子液体的绿色、廉价的替代品。人们已经知道，一些DESs可以用作酶促反应的溶剂，以获得非常绿色的化学过程。在分子水平上对DESs的了解甚少。此外，我们对这种系统中酶的微观结构了解不多。例如，一些水解酶如何在含有9米尿素的深共熔溶剂中保持活性和稳定性？本研究在分子水平上模拟了DESs作为液体的分子动力学。以尿素-氯化胆碱共晶混合物为模型，研究了脂肪酶作为生物催化剂的行为。为了比较，还模拟了8M尿素中酶的结构。并对酶在DESs、水和8M尿素中的热稳定性进行了评价。该酶在含66%尿素（9 M）的氯化胆碱混合物中，即使在高温下也表现出很好的构象稳定性。这一结果与最近的实验观测结果吻合得很好。相比之下，在8M尿素中，只有12%的尿素在水中发生完全的酶变性。研究发现尿素分子通过阻断链内氢键使酶变性，这是一种“直接变性机制”。但在尿素：氯化胆碱深共晶溶剂中，由于胆碱和氯离子的氢键作用，尿素分子的扩散系数较低，无法到达蛋白质结构域。有趣的是，尿素，胆碱和氯离子与酶的表面残基形成氢键，而不是脂肪酶变性，导致酶更大的稳定性。据我们所知，这是第一次在深共晶溶剂中检测大分子的微观结构特性的研究。
Deep eutectic solvents (DESs) are utilized as green and inexpensive alternatives to classical ionic liquids. It has been known that some of DESs can be used as solvent in the enzymatic reactions to obtain very green chemical processes. DESs are quite poorly understood at the molecular level. Moreover, we do not know much about the enzyme microstructure in such systems. For example, how some hydrolase can remain active and stable in a deep eutectic solvent including 9 M of urea? In this study, the molecular dynamics of DESs as a liquid was simulated at the molecular level. Urea : choline chloride as a well-known eutectic mixture was chosen as a model DES. The behavior of the lipase as a biocatalyst was studied in this system. For comparison, the enzyme structure was also simulated in 8M urea. The thermal stability of the enzyme was also evaluated in DESs, water, and 8M urea. The enzyme showed very good conformational stability in the urea : choline chloride mixture with about 66% urea (9 M) even at high temperatures. The results are in good agreement with recent experimental observations. In contrast, complete enzyme denaturation occurred in 8M urea with only 12% urea in water. It was found that urea molecules denature the enzyme by interrupting the intra-chain hydrogen bonds in a "direct denaturation mechanism''. However, in a urea : choline chloride deep eutectic solvent, as a result of hydrogen bonding with choline and chloride ions, urea molecules have a low diffusion coefficient and cannot reach the protein domains. Interestingly, urea, choline, and chloride ions form hydrogen bonds with the surface residues of the enzyme which, instead of lipase denaturation, leads to greater enzyme stability. To the best of our knowledge, this is the first study in which the microstructural properties of a macromolecule are examined in a deep eutectic solvent.