Tournier Alexander L, Réat Valerie, Dunn Rachel, Daniel Roy, Smith Jeremy C, Finney John
Computational Molecular Biophysics, Interdisciplinary Centre for Scientific Computing (IWR), University of Heidelberg, Heidelberg, Germany.
Phys Chem Chem Phys. 2005 Apr 7;7(7):1388-93. doi: 10.1039/b416103c.
Experimental and computer simulation studies have suggested the presence of a transition in the dynamics of hydrated proteins at around 180-220 K. This transition is manifested by nonlinear behaviour in the temperature dependence of the average atomic mean-square displacement which increases at high temperature. Here, we present results of a dynamic neutron scattering analysis of the transition for a simple enzyme: xylanase in water : methanol solutions of varying methanol concentrations. In order to investigate motions on different timescales, two different instruments were used: one sensitive to approximately 100 ps timescale motions and the other to approximately ns timescale motions. The results reveal distinctly different behaviour on the two timescales examined. On the shorter timescale the dynamics are dictated by the properties of the surrounding solvent: the temperature of the dynamical transition lowers with increasing methanol concentration closely following the melting behaviour of the corresponding water : methanol solution. This contrasts with the longer (ns) timescale results in which the dynamical transition appears at temperatures lower than the corresponding melting point of the cryosolvent. These results are suggested to arise from a collaborative effect between the protein surface and the solvent which lowers the effective melting temperature of the protein hydration layer. Taken together, the results suggest that the protein solvation shell may play a major role in the temperature dependence of protein solution dynamics.
实验和计算机模拟研究表明，水合蛋白质的动力学在180 - 220K左右存在转变。这种转变表现为平均原子均方位移的温度依赖性呈现非线性行为，且在高温下会增加。在此，我们展示了对一种简单酶（木聚糖酶）在不同甲醇浓度的水 - 甲醇溶液中该转变的动态中子散射分析结果。为了研究不同时间尺度上的运动，使用了两种不同的仪器：一种对大约100皮秒时间尺度的运动敏感，另一种对大约纳秒时间尺度的运动敏感。结果显示在所研究的两个时间尺度上行为明显不同。在较短时间尺度上，动力学由周围溶剂的性质决定：随着甲醇浓度增加，动态转变温度降低，这与相应水 - 甲醇溶液的熔化行为密切相关。这与较长（纳秒）时间尺度的结果形成对比，在较长时间尺度结果中，动态转变出现在低于冷冻溶剂相应熔点的温度下。这些结果被认为是由蛋白质表面和溶剂之间的协同效应引起的，这种协同效应降低了蛋白质水化层的有效熔化温度。综合来看，这些结果表明蛋白质溶剂化壳可能在蛋白质溶液动力学的温度依赖性中起主要作用。
