DECOMPOSITION OF PROTEIN FOLDING VOLUME CHANGES

拟议工作的长期目标是描述 稳定蛋白质不同构象状态的力。 这些状态被认为主要由以下因素决定： 疏水作用力驱使蛋白质向浓缩致密方向发展 构象和构象熵，有利于扩展、灵活 构象。这个项目主要关注疏水性的各个方面 仍然知之甚少的相互作用。当蛋白质展开时， 非极性氨基酸，最初分离在蛋白质内部，是 暴露在水中。这种暴露的热力学后果可能是 通过将小分子从非极性环境转移到 水。这些研究以及水工构造井的理论分析 解释了观察到的显著的热容变化 蛋白质就会展开。然而，类似的模型并没有考虑到销量 以及在相似条件下观察到的可压缩性变化。这个 后者代表了对热力学的理解上的重大缺陷 它是蛋白质折叠的重要组成部分，也是拟议工作的主要主题。这个 这种方法的基本原理是基于这样的假设，即不同类型的 在褶皱的不同阶段发生的结构变化 运动学。使用实验室开发的仪器，总体上 卷更改将被分解为与 折叠的不同动力学阶段。这将允许部分卷 与不同类型的结构变化相关的变化将是 单独描述的。部分音量变化的测量结果将为 辅以热容变化的测量， 可压缩性和平衡折叠转变。其他内容 主要目的是描述暴露于 在展开过程中与水的相互作用并进一步探索 溶剂迁移测量作为蛋白质体积模型的适用性 以及可压缩性的变化。细胞色素c-HAD的初步测定 论证了许多拟议研究的可行性，并将 在拟议的工作中得到了扩展。

The long range objective of the proposed work is to characterize the forces which stabilize the different conformational states of proteins. These states are thought to be determined mainly by a balance between hydrophobic forces which drive the protein toward condensed compact conformations and conformational entropy which favors extended, flexible conformations. This project focuses on aspects of the hydrophobic interactions which remain poorly understood. When a protein unfolds, nonpolar amino acids, originally segregated in the protein interior, are exposed to water. The thermodynamic consequences of this exposure can be modeled by transfer of small molecules from nonpolar environments to water. These studies and also theoretical analyses of water structure well account for the striking heat capacity changes which are observed when a protein unfolds. Similar models do not, however, account for the volume and compressibility changes observed under analogous conditions. The latter represents a substantial defect in understanding the thermodynamics of protein folding and is the main subject of the proposed work. The rationale of the approach is based on the supposition that different kinds of structural changes occur during the different phases of folding kinetics. Using an instrument developed in the laboratory the overall volume change is to be decomposed into components associated with the different kinetic phases of folding. This will allow partial volume changes associated with different kinds of structural changes to be characterized separately. Measurements of partial volume change will be supplemented with measurements of changes of heat capacity, compressibility and of the equilibrium folding transition. Additional major aims are to characterize the change in protein area exposed to interaction with water during unfolding and to explore further the applicability of solvent transfer measurements as models of protein volume and compressibility changes. Preliminary measurements on cytochrome c have demonstrated the feasibility of many of the proposed studies and will be extended in the proposed work.