Lee Andrew L, Sharp Kim A, Kranz James K, Song Xiang-Jin, Wand A Joshua
The Johnson Research Foundation and Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6059, USA.
Biochemistry. 2002 Nov 19;41(46):13814-25. doi: 10.1021/bi026380d.
The temperature dependence of the fast internal dynamics of calcium-saturated calmodulin in complex with a peptide corresponding to the calmodulin-binding domain of the smooth muscle myosin light chain kinase is examined using 15N and 2H NMR relaxation methods. NMR relaxation studies of the complex were carried out at 13 temperatures that span 288-346 K. The dynamics of the backbone and over four dozen methyl-bearing side chains, distributed throughout the calmodulin molecule, were probed. The side chains show a much more variable and often considerably larger response to temperature than the backbone. A significant variation in the temperature dependence of the amplitude of motion of individual side chains is seen. The amplitude of motion of some side chains is essentially temperature-independent while many show a simple roughly linear temperature dependence. In a few cases, angular order increases with temperature, which is interpreted as arising from interactions with neighboring residues. In addition, a number of side chains display a nonlinear temperature dependence. The significance of these and other results is illuminated by several simple interpretative models. Importantly, analysis of these models indicates that changes in generalized order parameters can be robustly related to corresponding changes in residual entropy. A simple cluster model that incorporates features of cooperative or conditional motion reproduces many of the unusual features of the experimentally observed temperature dependence and illustrates that side chain interactions result in a dynamically changing environment that significantly influences the motion of internal side chains. This model also suggests that the intrinsic entropy of interacting clusters of side chains is only modestly reduced from that of independent side chain motion. Finally, estimates of protein heat capacity support the view that the major contribution to the heat capacity of protein solutions largely arises from local bond vibrations and solvent interactions and not from torsional oscillations of side chains.
利用15N和2H NMR弛豫方法，研究了钙饱和钙调蛋白与平滑肌肌球蛋白轻链激酶的钙调蛋白结合结构域对应的肽形成的复合物的快速内部动力学的温度依赖性。在288 - 346 K范围内的13个温度下对该复合物进行了NMR弛豫研究。探测了贯穿钙调蛋白分子的主链以及四十多个含甲基侧链的动力学。侧链对温度的响应比主链更具变化性，且通常大得多。观察到各个侧链运动幅度的温度依赖性存在显著差异。一些侧链的运动幅度基本与温度无关，而许多侧链表现出简单的大致线性温度依赖性。在少数情况下，角序随温度增加，这被解释为与相邻残基的相互作用所致。此外，一些侧链表现出非线性温度依赖性。几个简单的解释模型阐明了这些及其他结果的意义。重要的是，对这些模型的分析表明，广义序参量的变化可以与残余熵的相应变化紧密相关。一个纳入协同或条件运动特征的简单簇模型再现了实验观察到的温度依赖性的许多不寻常特征，并表明侧链相互作用导致动态变化的环境，显著影响内部侧链的运动。该模型还表明，相互作用的侧链簇的固有熵仅比独立侧链运动的固有熵略有降低。最后，蛋白质热容的估计支持这样一种观点，即蛋白质溶液热容的主要贡献很大程度上源于局部键振动和溶剂相互作用，而非侧链的扭转振荡。
