Chong Yuan, Kleinhammes Alfred, Tang Pei, Xu Yan, Wu Yue
†Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599-3255, United States.
J Phys Chem B. 2015 Apr 30;119(17):5367-75. doi: 10.1021/acs.jpcb.5b00378. Epub 2015 Apr 17.
Water plays an important role in weak associations of small drug molecules with proteins. Intense focus has been on binding-induced structural changes in the water network surrounding protein binding sites, especially their contributions to binding thermodynamics. However, water is also tightly coupled to protein conformations and dynamics, and so far little is known about the influence of water-protein interactions on ligand binding. Alcohols are a type of low-affinity drugs, and it remains unclear how water affects alcohol-protein interactions. Here, we present alcohol adsorption isotherms under controlled protein hydration using in situ NMR detection. As functions of hydration level, Gibbs free energy, enthalpy, and entropy of binding were determined from the temperature dependence of isotherms. Two types of alcohol binding were found. The dominant type is low-affinity nonspecific binding, which is strongly dependent on temperature and the level of hydration. At low hydration levels, this nonspecific binding only occurs above a threshold of alcohol vapor pressure. An increased hydration level reduces this threshold, with it finally disappearing at a hydration level of h ≈ 0.2 (g water/g protein), gradually shifting alcohol binding from an entropy-driven to an enthalpy-driven process. Water at charged and polar groups on the protein surface was found to be particularly important in enabling this binding. Although further increase in hydration has smaller effects on the changes of binding enthalpy and entropy, it results in a significant negative change in Gibbs free energy due to unmatched enthalpy-entropy compensation. These results show the crucial role of water-protein interplay in alcohol binding.
水在小药物分子与蛋白质的弱相互作用中起着重要作用。人们一直高度关注蛋白质结合位点周围水网络中结合诱导的结构变化，特别是它们对结合热力学的贡献。然而，水也与蛋白质的构象和动力学紧密相关，到目前为止，关于水 - 蛋白质相互作用对配体结合的影响知之甚少。醇类是一类低亲和力药物，目前尚不清楚水如何影响醇 - 蛋白质相互作用。在此，我们利用原位核磁共振检测技术展示了在可控蛋白质水合作用下的醇吸附等温线。根据等温线的温度依赖性，确定了结合的吉布斯自由能、焓和熵随水合水平的变化关系。发现了两种类型的醇结合。主要类型是低亲和力非特异性结合，它强烈依赖于温度和水合水平。在低水合水平下，这种非特异性结合仅在醇蒸气压的阈值以上发生。水合水平的增加降低了该阈值，最终在水合水平h≈0.2（克水/克蛋白质）时消失，使醇结合逐渐从熵驱动过程转变为焓驱动过程。发现蛋白质表面带电和极性基团上的水对于实现这种结合尤为重要。尽管水合作用的进一步增加对结合焓和熵变化的影响较小，但由于焓 - 熵补偿不匹配，导致吉布斯自由能出现显著的负变化。这些结果表明了水 - 蛋白质相互作用在醇结合中的关键作用。
