Thermodynamic Models for Macromolecular Crystallization

[9728240]当前研究的主要目的是建立一个可测试的热力学模型来描述大分子结晶。该项目将使用独特的七核苷酸晶体系统，因为可以使用晶体滴定法研究结晶的热力学。这个实验体系是一系列形成双链的七核苷酸。单个链在晶格中是不同的，并且可以用晶体学或色谱学精确地定量。通过改变结晶溶液中两条链的比例，我们可以确定结晶过程中双链之间的相互作用能量。从最初的研究中观察到晶格类型之间的转换是高度合作的。因此，该分析导致了形成初始种子晶体的DNA双链之间相互作用的能量和协同性的估计。提出的研究是建立一个准确描述这种结晶滴定的模型，准确地确定该模型的参数，然后将该模型扩展到更普遍适用于其他晶体体系。这些模型将通过监测浓度对晶体链组成的影响来验证。x射线晶体学对我们理解大分子的结构和功能，特别是在原子水平上做出了重大贡献。然而，该方法完全依赖于培养衍射质量单晶的能力。尽管最近已经开发了许多工具来促进大分子的结晶，但对结晶的实际过程仍然知之甚少。提出的研究结果将是一个热力学模型，应该是有用的工具，为结晶研究的合理设计。该模型作为核酸和蛋白质结晶的预测工具将普遍有用。该模型将结合mo分子的可测量特性来预测种子形成与晶体生长的概率，以及可能有利于这两个过程的条件。

9728240 Ho The primary objective of the current research is to develop a testable thermodynamic model to describe macromolecular crystallization. This project will use a heptanucleotide crystal system that is unique, in that the thermodynamics of crystallization can be studied using a crystallographic titration assay. This experimental system is a series of heptanucleotides that form duplexes. The individual strands are distinct in the lattice, and can be accurately quantified crystallographically or chromatographically. By varying the ratio of the two strands in the crystallization solutions, we can determine the energies of interaction between duplexes during crystallization. Transitions between lattice types were observed from initial studies to be highly cooperative. Thus, the assay has led to estimates for the energies and cooperativity for interactions between the DNA duplexes that form the initial seed crystal. The proposed studies are to derive a model to accurately describe this crystallization titration, accurately determine the parameters for this model, then extend the model to be more generally applicable to other crystal systems. The models will be validated by monitoring the effects of concentrations on the strand compositions of the crystals. X-ray crystallography has contributed significantly to our understanding of macromolecular structure and function, particularly at the atomic level. However, the method is entirely dependent on the ability to grow diffraction quality single crystals. Although a number of recent tools have been developed to facilitate the crystallization of macromolecules, the actual process of crystallization remains poorly understood. The result of the proposed studies will be a thermodynamic model that should be useful as a tool for the rational design of crystallization studies. The model will be generally useful as a predictive tool for crystallizing nucleic acids and proteins. The model will incorporate measurable properties of mo lecules to predict the probabilities for seed formation versus crystal growth, and conditions that may favor these two processes.