Yang D, Mok Y K, Forman-Kay J D, Farrow N A, Kay L E
Protein Engineering Network, Centers of Excellence, University of Toronto, Ontario, Canada.
J Mol Biol. 1997 Oct 10;272(5):790-804. doi: 10.1006/jmbi.1997.1285.
The backbone dynamics of both folded and unfolded states of staphylococcal nuclease (SNase) and the N-terminal SH3 domain from drk (drkN SH3) are studied at two different temperatures. A simple method for obtaining order parameters, describing the amplitudes of motion of bond vectors, from NMR relaxation measurements of both folded and unfolded proteins is presented and the data obtained for 15N-NH bond vectors in both the SNase and drkN SH3 systems analyzed with this approach. Using a recently developed theory relating the amplitude of bond vector motions to conformational entropy, the entropy change between the folded and unfolded forms of SNase is calculated on a per residue basis. It is noteworthy that the region of the molecule with the smallest entropy change includes those residues showing native-like structure in the unfolded form of the molecule, as established by NOE-based experiments. Order parameters of backbone 15N-NH bond vectors show significantly larger changes with temperature in the unfolded states of both proteins relative to the corresponding folded forms. The differential temperature dependence is interpreted in terms of differences in the heat capacities of folded and unfolded polypeptide chains. The contribution to the heat capacity of the unfolded chain from rapid 15N-NH bond vector motions is calculated and compared with estimates of the heat capacity of the backbone unit, -CHCONH-, obtained from calorimetric data. Methyl dynamics measured at 14 and 30 degrees C establish that the amplitudes of side-chain motions in the folded SH3 domain are more sensitive to changes in temperature than the backbone dynamics, suggesting that over this temperature range side-chain ps to ns time-scale motions contribute more to the heat capacity than backbone motions for this protein.
在两个不同温度下研究了葡萄球菌核酸酶（SNase）和来自drk的N端SH3结构域（drkN SH3）折叠态与非折叠态的主链动力学。提出了一种从折叠态和非折叠态蛋白质的核磁共振弛豫测量中获取描述键向量运动幅度的序参量的简单方法，并用该方法分析了SNase和drkN SH3系统中15N-NH键向量的数据。利用最近发展的一种将键向量运动幅度与构象熵联系起来的理论，以每个残基为基础计算了SNase折叠态与非折叠态之间的熵变。值得注意的是，熵变最小的分子区域包括那些在基于NOE实验确定的分子非折叠形式中呈现类似天然结构的残基。相对于相应的折叠形式，两种蛋白质非折叠态中主链15N-NH键向量的序参量随温度的变化显著更大。从折叠态和非折叠态多肽链的热容量差异方面解释了这种不同的温度依赖性。计算了快速15N-NH键向量运动对非折叠链热容量的贡献，并与从量热数据获得的主链单元-CHCONH-的热容量估计值进行了比较。在14℃和30℃下测量的甲基动力学表明，折叠的SH3结构域中侧链运动的幅度比主链动力学对温度变化更敏感，这表明在该温度范围内，对于这种蛋白质，侧链皮秒到纳秒时间尺度的运动对热容量的贡献比主链运动更大。
