Protein Interactions and Solvation in Binary Solvents

我们建议继续研究溶剂化对蛋白质构象偏好和相互作用的影响。在要求的预算期间，我们建议开展体积和光谱实验以及分子动力学(MD)模拟，这些实验旨在实现以下具体目标：比较和系统研究N-乙酰氨基酸酰胺在水以及水和水溶性变性和稳定共溶剂的二元混合物中的溶剂化作用；各种共溶剂与单个蛋白质基团结合的热力学表征；天然和未折叠蛋白质在变性和稳定共溶剂中的溶剂化的体积表征，并探索蛋白质溶解的可加性；以及蛋白质在水中的折叠和结合反应以及变性和稳定共溶剂的比较表征。溶剂对蛋白质化学平衡的支配作用得到了一致认可。事实上，任何蛋白质在水溶液中的反应都可以被认为是用溶质-溶质相互作用代替溶质-溶剂相互作用。由此可见，溶质-溶剂和溶质-助溶剂相互作用的热力学是反应热力学的重要组成部分。我们提出的通过统计热力学解释算法放大的低分子模型化合物的体积研究和MD模拟将使我们能够量化蛋白质官能团对水以及稳定和变性渗透分子的不同亲和力。将这些研究扩展到蛋白质，将使我们能够研究折叠和非折叠构象中的非相加溶剂化效应。最后，对蛋白质在二元溶剂中的折叠和结合反应的表征将在真实的生物系统上检验我们的基本结论。

We propose to continue our studies of the effect of solvation on the conformational preferences and interactions of proteins. During the requested budget period, we propose to carry out volumetric and spectroscopic experiments as well as molecular dynamics (MD) simulations which are designed to achieve the following specific aims: comparative and syste¬matic investigation of solvation of the 20 naturally existing amino acid side chains in N-acetyl amino acid amides in water and binary mixtures of water and water-soluble denaturing and stabilizing cosolvents; thermodynamic characterization of the association of various cosolvents with individual protein groups; volumetric characterization of solvation of native and unfolded proteins in denaturing and stabilizing cosolvents and exploration of the ad¬ditivity of protein sol¬vation; and comparative characterization of protein folding and binding reactions in water and denaturing and stabilizing cosolvents. The domineering influence of solvent on chemical equi¬libria involving proteins is unanimously acknowledged. In fact, any protein reaction in an aqu¬eous solution can be considered as replacement of solute-solvent with solute-solute interac¬tions. With this notion, it is clear that the thermodynamics of solute-solvent and solute-cosolvent interactions is an important integral part of the reaction thermodynamics. Our proposed volu¬met¬ric studies on low molecular weight model compounds amplified by the statistical thermo¬dynamic interpretation algorithm and MD simulations will enable us to quantify the differential affinity of protein functional groups for water and stabilizing and denaturing osmolytes. Exten¬ding these studies to proteins will permit us to investigate nonadditive solvation effects in the folded and unfolded conformations. Finally, characterization of protein folding and binding reactions in binary solvents will test our basic conclusions on real biological systems.