Experimental and Theoretical Studies on Protein Dynamics and Changes in Dynamics upon Folding

在25K和室温下，观察到葡萄球菌核酸酶在宽能量范围内的非弹性中子散射。所获得的光谱是迄今为止报道的最准确和最精细的。用SNase的简正模分析结果定性地解释了25K下的光谱，并将观测到的峰归属于理论振动模。然而，实验和理论计算之间的定量一致性是如此之差，用于计算的势函数的改进应该是必要的。为了揭示折叠态特有的动力学性质，对野生型SNase（折叠态）和截断型SNase（未折叠态）进行了非弹性和准弹性中子散射实验。在室温下观察到的明显差异与高度水合的样品，表明折叠态的特定运动是非谐运动，这是激活水的玻璃化转变以上。玻色子峰或低能量激发在低温蛋白质的起源进行了研究。我们发现，玻色子峰的位置显示出显着的分子量依赖性。这一事实表明玻色子峰的起源不是二级结构元的局域运动，而是整个分子的扩展运动。提出了用中子非弹性散射评价蛋白质动力学不均匀性的方法。对于细菌视紫红质，这种inhoogenities进行了讨论，其功能。使用氘标记，玻璃化转变温度随蛋白质中的位点而变化。这表明，这种不均匀性是重要的蛋白质功能。

Inelastic neutron scattering over wide energy range was observed for staphylococcal nuclease at 25K and at room temperature. The obtained spectra were the most accurate and the finest reported so far. The observed spectrum at 25K was explained qualitatively with the results of the normal mode analysis for SNase, and the observed peaks were assigned to the theoretical vibrational modes. However, the quantitative agreement between the experiment and the theoretical calculation was so poor that the improvements in potential functions used for the calculation should be required. The obtained spectrum at room temperature was also qualitatively explained with the results of the molecular dynamics simulation.In order to reveal dynamic properties specific to the folded state, inelastic and quasielastic neutron scattering experiments were performed for the wild type SNase (folded) and the truncated SNase (unfolded). The apparent differences were observed at room temperature with highly hydrated specimens, indicating that the specific motions to the folded state is the anharmonic motion which is activated with water above the glass transition.The origin of the boson peak or low energy excitation at low temperature for proteins was investigated. We found that the boson peak position shows significant molecular weight dependency. This fact suggests that the origin of boson peak is not the localized motion to the secondary structure element, but the extended motion over the whole molecule. This property may be common for soft matters including proteins.The method to evaluate inhomogenity of protein dynamics with inelastic neutron scattering was developed. For bacteriorhodopsin, such inhoogenities were discussed in relation to its function. Using deuterium labeling, glass transition temperature varies from site to site in protein. It is suggested that such inhomogenities are important for the protein function.