Vijayakumar M, Wong K Y, Schreiber G, Fersht A R, Szabo A, Zhou H X
Department of Biochemistry, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
J Mol Biol. 1998 May 22;278(5):1015-24. doi: 10.1006/jmbi.1998.1747.
The electrostatic enhancement of the association rate of barnase and barstar is calculated using a transition-state theory like expression and atomic-detail modeling of the protein molecules. This expression predicts that the rate enhancement is simply the average Boltzmann factor in the region of configurational space where association occurs instantaneously in the diffusion-controlled limit. Based on experimental evidence, this "transition state" is defined by configurations in which, relative to the stereospecifically bound complex, the two proteins are shifted apart by approximately 8 A (so a layer of water can be accommodated in the interface) and the two binding surfaces are rotated away by 0 degrees to 3 degrees. The values of the average Boltzmann factor, calculated by solving the Poisson-Boltzmann equation, for the wild-type complex and 16 complexes with single mutations are found to correlate well with experimental results for the electrostatic rate enhancement. The predicted rate enhancement is found to be somewhat insensitive to the precise definition of the transition state, due to the long-range nature of electrostatic interactions. The experimental ionic strength dependence of the rate enhancement is also reasonably reproduced.
使用类似过渡态理论的表达式和蛋白质分子的原子细节模型，计算了巴那斯酶和巴丝塔抑制因子缔合速率的静电增强效应。该表达式预测，速率增强仅仅是在扩散控制极限下缔合瞬间发生的构型空间区域中的平均玻尔兹曼因子。基于实验证据，这种“过渡态”由以下构型定义：相对于立体特异性结合的复合物，两种蛋白质彼此错开约8埃（以便在界面中容纳一层水），并且两个结合表面旋转0度至3度。通过求解泊松-玻尔兹曼方程计算得到的野生型复合物和16种单突变复合物的平均玻尔兹曼因子值，与静电速率增强的实验结果具有良好的相关性。由于静电相互作用的长程性质，预测的速率增强对过渡态的精确定义有些不敏感。速率增强的实验离子强度依赖性也得到了合理的再现。
