DECOMPOSITION OF PROTEIN FOLDING VOLUME CHANGES

拟议工作的长期目标是表征 稳定蛋白质不同构象状态的力。 这些状态被认为主要是由以下因素之间的平衡决定的： 疏水力驱使蛋白质趋向于压缩 构象和构象熵，有利于扩展，灵活， 构象该项目的重点是疏水性的方面， 相互作用仍然知之甚少。当蛋白质展开时， 非极性氨基酸，最初分离在蛋白质内部， 暴露在水中。这种暴露的热力学后果可以是 通过将小分子从非极性环境转移到 水这些研究和水结构的理论分析， 考虑到显着的热容量的变化，这是观察时， 蛋白质展开。然而，类似的模型并不能解释 和在类似条件下观察到的压缩性变化。的 后者代表了理解热力学的一个实质性缺陷 蛋白质折叠，是拟议的工作的主要课题。的 这种方法的基本原理是基于这样一种假设， 在折叠的不同阶段， 动力学使用实验室开发的仪器， 体积变化将被分解为与 折叠的不同动力学阶段。这将允许部分体积 与各种结构变化相关的变化， 分别表征。部分体积变化的测量将 辅以热容变化的测量， 压缩性和平衡折叠过渡。额外 主要目的是表征暴露于以下物质的蛋白质面积的变化： 在展开过程中与水的相互作用， 溶剂转移测量作为蛋白质体积模型的适用性 并且可压缩性改变。对细胞色素c的初步测量表明， 证明了许多拟议研究的可行性，并将 在拟议的工作中。

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.