Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA.
J Mol Biol. 2010 Mar 26;397(2):423-35. doi: 10.1016/j.jmb.2010.01.029. Epub 2010 Jan 22.
Neutron spin-echo spectroscopy was used to study structural fluctuations that occur in hemoglobin (Hb) and myoglobin (Mb) in solution. Using neutron spin-echo data up to a very high momentum transfer q ( approximately 0.62 A(-)(1)), we characterized the internal dynamics of these proteins at the levels of dynamic pair correlation function and self-correlation function in the time range of several picoseconds to a few nanoseconds. In the same protein solution, data transition from pair correlation motion to self-correlation motion as the momentum transfer q increases. At low q, coherent scattering dominates; at high q, observations are largely due to incoherent scattering. The low q data were interpreted in terms of an effective diffusion coefficient; on the other hand, the high q data were interpreted in terms of mean square displacements. Comparison of data from the two homologous proteins collected at different temperatures and protein concentrations was used to assess the contributions made by translational and rotational diffusion and internal modes of motion to the data. The temperature dependence of decay times can be attributed to changes in the viscosity and temperature of the solvent, as predicted by the Stokes-Einstein relationship. This is true for contributions from both diffusive and internal modes of motion, indicating an intimate relationship between the internal dynamics of the proteins and the viscosity of the solvent. Viscosity change associated with protein concentration can account for changes in diffusion observed at different concentrations, but is apparently not the only factor involved in the changes in internal dynamics observed with change in protein concentration. Data collected at high q indicate that internal modes in Mb are generally faster than those in Hb, perhaps due to the greater surface-to-volume ratio of Mb and the fact that surface groups tend to exhibit faster motion than buried groups. Comparison of data from Hb and data from Mb at low q indicates an unexpectedly rapid motion of Hb alphabeta dimers relative to one another. Dynamic motion of subunits is increasingly perceived as important to the allosteric behavior of Hb. Our data demonstrate that this motion is highly sensitive to protein concentration, temperature, and solvent viscosity, indicating that great care needs to be exercised in interpreting its effect on protein function.
中子自旋回波谱被用于研究血红蛋白（Hb）和肌红蛋白（Mb）在溶液中的结构波动。通过使用高达非常高的动量传递 q（约 0.62 A(-)(1)）的中子自旋回波数据，我们在几个皮秒到几纳秒的时间范围内，在动态偶联函数和自相关函数的水平上，对这些蛋白质的内部动力学进行了描述。在相同的蛋白质溶液中，随着动量传递 q 的增加，数据从偶联运动转变为自相关运动。在低 q 时，相干散射占主导地位；在高 q 时，观察结果主要归因于非相干散射。低 q 数据用有效扩散系数来解释；另一方面，高 q 数据用均方位移来解释。比较在不同温度和蛋白质浓度下从两种同源蛋白质收集的数据，以评估平移和旋转扩散以及内部运动模式对数据的贡献。衰减时间的温度依赖性可以归因于溶剂粘度和温度的变化，这符合 Stokes-Einstein 关系的预测。这对于来自扩散和内部运动模式的贡献都是如此，这表明蛋白质的内部动力学与溶剂的粘度之间存在密切关系。与蛋白质浓度相关的粘度变化可以解释在不同浓度下观察到的扩散变化，但显然不是与蛋白质浓度变化相关的内部动力学变化所涉及的唯一因素。在高 q 下收集的数据表明，Mb 中的内部模式通常比 Hb 中的快，这可能是由于 Mb 的表面积与体积比更大，并且表面基团往往比埋藏基团表现出更快的运动。在低 q 下比较 Hb 和 Mb 的数据表明，Hb 的 alpha-beta 二聚体之间的相对运动速度快得令人惊讶。亚基的动态运动越来越被认为对 Hb 的变构行为很重要。我们的数据表明，这种运动对蛋白质浓度、温度和溶剂粘度非常敏感，这表明在解释其对蛋白质功能的影响时需要非常小心。
