Ha J H, Spolar R S, Record M T
Department of Chemistry, University of Wisconsin, Madison 53706.
J Mol Biol. 1989 Oct 20;209(4):801-16. doi: 10.1016/0022-2836(89)90608-6.
The site-specific binding interaction of lac repressor with a symmetric operator sequence and of EcoRI endonuclease with its specific recognition site both exhibit a characteristic dependence of equilibrium binding constant (Kobs) on temperature, in which Kobs attains a relative maximum in the physiologically relevant temperature range. This behavior, which appears to be quite general for site-specific protein-DNA interactions, is indicative of a large negative standard heat capacity change (delta C0P,obs) in the association process. By analogy with model compound transfer studies and protein folding data, we propose that this delta C0P,obs results primarily from the removal of non-polar surface from water in the association process. From delta C0P,obs we obtain semiquantitative information regarding the change in water-exposed non-polar surface area (delta Anp) and the corresponding hydrophobic driving force for association (delta G0hyd): delta G0hyd approximately equal to 8(+/- 1) x 10(1) delta C0P,obs approximately equal to -22(+/- 5) delta Anp. We propose that removal of non-polar surface from water (the hydrophobic effect) and release of cations (the polyelectrolyte effect) drive the thermodynamically unfavorable process (e.g. conformational distortions) necessary to achieve mutually complementary recognition surfaces (at a steric and functional-group level) in the specific complex.
乳糖阻遏物与对称操纵序列的位点特异性结合相互作用以及EcoRI核酸内切酶与其特定识别位点的相互作用，均表现出平衡结合常数（Kobs）对温度的特征依赖性，其中Kobs在生理相关温度范围内达到相对最大值。这种行为对于位点特异性蛋白质-DNA相互作用似乎相当普遍，表明在缔合过程中存在较大的负标准热容变化（δC0P,obs）。通过与模型化合物转移研究和蛋白质折叠数据类比，我们提出这种δC0P,obs主要源于缔合过程中从水中去除非极性表面。从δC0P,obs我们获得了关于水暴露非极性表面积变化（δAnp）和相应缔合疏水驱动力（δG0hyd）的半定量信息：δG0hyd约等于8（±1）×10（1）δC0P,obs约等于 -22（±5）δAnp。我们提出从水中去除非极性表面（疏水效应）和阳离子释放（聚电解质效应）驱动了在特定复合物中实现相互互补识别表面（在空间和官能团水平）所需的热力学不利过程（例如构象扭曲）。
