Connelly P R, Thomson J A
Vertex Pharmaceuticals Incorporated, Cambridge, MA 02139-4211.
Proc Natl Acad Sci U S A. 1992 Jun 1;89(11):4781-5. doi: 10.1073/pnas.89.11.4781.
Differential interactions among nonpolar moieties at protein/ligand interfaces, and of these nonpolar groups with water, collectively termed hydrophobic interactions, are widely believed to make important energetic contributions to the stability of protein/ligand complexes. Quantitative estimates of hydrophobic interactions, and an evaluation of their structural basis, are essential for obtaining structure-based predictions of the free energies of binding for the purpose of drug design. Two largely nonpolar, immunosuppressive agents, FK506 and rapamycin, each bind with high affinity to a common hydrophobic pocket on a small peptidylproline cis-trans isomerase known as FK506 binding protein (FKBP-12) and inhibit its activity. In an effort to elucidate the structural features of these ligands responsible for the observed energetics, we have undertaken an investigation of the thermodynamics of binding of FK506 and rapamycin to FKBP-12. Enthalpies of binding have been determined by high-precision titration calorimetry over a range of temperature, allowing estimates of heat capacity changes. By analyzing the distribution of changes in solvent-accessible surface area upon binding of FK506 to FKBP-12 from crystallographic data, it is found that 99% of the net surface buried upon binding involves nonpolar groups. This leads to a heat capacity change of FK506 binding, normalized to the amount of nonpolar surface, of -0.40 +/- 0.02 cal.K-1.mol-1.A-2 (1 cal = 4.18 J), a value similar to that obtained for the aqueous dissolution of hydrophobic substances. Our observations are discussed in view of the general nature of hydrophobic interaction processes.
蛋白质/配体界面处非极性部分之间以及这些非极性基团与水之间的差异相互作用，统称为疏水相互作用，人们普遍认为它们对蛋白质/配体复合物的稳定性做出了重要的能量贡献。疏水相互作用的定量估计及其结构基础的评估，对于基于结构预测药物设计中结合自由能至关重要。两种主要为非极性的免疫抑制剂FK506和雷帕霉素，各自以高亲和力结合到一种称为FK506结合蛋白（FKBP - 12）的小肽基脯氨酸顺反异构酶上的一个共同疏水口袋，并抑制其活性。为了阐明这些配体中负责观察到的能量学的结构特征，我们对FK506和雷帕霉素与FKBP - 12结合的热力学进行了研究。通过在一定温度范围内进行高精度滴定热分析测定了结合焓，从而能够估计热容变化。通过分析晶体学数据中FK506与FKBP - 12结合时溶剂可及表面积变化的分布，发现结合时净掩埋的表面99%涉及非极性基团。这导致FK506结合的热容变化（归一化为非极性表面量）为 - 0.40 +/- 0.02 cal.K - 1.mol - 1.A - 2（1 cal = 4.18 J），该值与疏水物质在水中溶解时获得的值相似。我们根据疏水相互作用过程的一般性质对观察结果进行了讨论。
