DYNAMIC EXCHANGE IN SLOWLY RELAXING LOCAL STRUCTURE MODEL

这个子项目是许多利用资源的研究子项目之一 由NIH/NCRR资助的中心拨款提供。子项目的主要支持 而子项目的主要调查员可能是由其他来源提供的， 包括其它NIH来源。 列出的子项目总成本可能 代表子项目使用的中心基础设施的估计数量， 而不是由NCRR赠款提供给子项目或子项目工作人员的直接资金。 最近的多频ESR自旋标记的T4-溶菌酶突变体的研究表明，存在两个光谱成分，已暂时归因于存在一个以上的稳定构象的MTSSL自旋标记的氮氧系链。这些多频实验先前已被分析的缓慢松弛的局部结构（SRLS）模型，包括作为不同的实体的整体运动的蛋白质和局部运动感测的自旋标签。在不同的频率的结果表明，可能有一个动态的交换发生在两个构象之间，这样的交换的光谱效应取决于ESR频率的研究。 动态交换现已被纳入SRLS模型，其中每个构象异构体都有自己的整体和局部旋转动力学和定向潜力。交换过程的特征在于每个站点的概率和平均交换率。我们已经研究，特别是，动态交换的两个网站的情况下，其中两个网站表现出非常缓慢的整体翻滚，但网站1表现出相对较快的局部运动和低的局部排序，而网站2表现出缓慢的局部运动和高的局部排序的影响。由于它们的时间尺度不同，在较高（较低）频率下拍摄的ESR光谱对更快（更慢）的交换过程敏感。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Recent multifrequency ESR studies of spin labeled mutants of T4-lysozyme have shown the existence of two spectral components that have been tentatively ascribed to the existence of more than one stable conformer of the nitroxide tether of the MTSSL spin label. These multifrequency experiments have previously been analyzed by the slowly-relaxing local structure (SRLS) model that includes as distinct entities the overall motion of the protein and the local motion sensed by the spin label. Results at the different frequencies have suggested that there may be a dynamic exchange occurring between the two conformers, such that the spectral effects of the exchange depends on the ESR frequency studied. Dynamic exchange has now been incorporated into the SRLS model, wherein each conformer has its own overall and local rotational dynamics and orienting potential. The exchange process is characterized by the probability of each site and the mean exchange rate. We have studied, in particular, the effects of dynamic exchange for the case of two sites, wherein both sites exhibit very slow overall tumbling, but Site 1 exhibits relatively fast local motion and low local ordering, whereas Site 2 exhibits slow local motion and high local ordering. Due to their different time scales, ESR spectra taken at the higher (lower) frequencies are sensitive to faster (slower) exchange processes.