KINETICS OF CAMP-INDUCED STRUCTURAL CHANGES IN PROTEIN KINASE A BY TR-SAXS

这个子项目是许多利用 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 cAMP对蛋白激酶A（PKA）的激活是一个多步骤的过程，涉及cAMP与R亚基中两个不同位点的顺序结合，以及R中产生的一系列结构变化，这些变化将C亚基从抑制状态释放出来。在激活过程中发生的结构变化的性质知之甚少，虽然最近的SAXS数据和X射线晶体结构表明大cAMP诱导的结构变化的R亚基发生之前，C亚基被释放。使用SSRL beamtime授予通过快速访问机制，我们在2007年7月进行了试点时间分辨SAXS实验，以确定混合PKA与cAMP和cAMP类似物后发生的溶液结构变化的近似时间过程。这些研究是与Hiro Tsuruta的小组合作进行的，使用BL 4-2的停流仪器。对这些数据的分析表明，使用TR-SAXS跟踪cAMP诱导的PKA结构变化是可行的，并且这些变化在约750 msec时基本完成。发生的Rg和Dmax的总体变化与我们先前在犹他州大学使用稳态SAXS仪器观察到的变化相当。基于我们成功的中试实验，我们希望使用BL 4-2的TRSAXS功能对PKA结构变化的动力学进行更详细和更广泛的研究。具体而言，我们希望以更高的时间分辨率更详细地分析结构变化（在初步研究中，我们的最短时间积分为255 msec），并将我们的观察结果扩展到包括R和C亚基的解离（我们在初步研究中选择了防止R-C解离的条件，以便仅观察cAMP诱导的构象变化）。这些实验将为PKA的结构动力学提供重要的见解。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Activation of protein kinase A (PKA) by cAMP is a multi-step process involving sequential binding of cAMP to two different sites in the R subunit, and a resultant sequence of structural changes in R that release the C subunit from an inhibited state. The nature of the structural changes that occur during activation are poorly understood, although recent SAXS data and x-ray crystal structures indicate large cAMP-induced structural changes in the R subunit occur before the C subunit is released. Using SSRL beamtime granted through the Rapid Access mechanism, we conducted pilot time-resolved SAXS experiments in July 2007 to determine the approximate time course of solution structural changes that occur after mixing PKA with cAMP and cAMP analogs. These studies were conducted in collaboration with Hiro Tsuruta's group using the stopped-flow instrument on BL 4-2. Analysis of these data indicate that it is feasible to use TR-SAXS to follow the cAMPinduced structural changes in PKA and that these changes are largely complete by ~750 msec. The overall changes in Rg and Dmax that occurred were comparable to what we had previously observed using the steadystate SAXS instrument at the University of Utah. Based on our successful pilot experiments, we would like to follow up with more detailed and extensive studies of the kinetics of PKA structural changes using the TRSAXS capabilities at BL 4-2. Specifically, we would like to analyze in more detail the structural changes with higher temporal resolution (our shortest time integral was 255 msec in the pilot studies), and extend our observations to include the dissociation of R and C subunits (we chose conditions in the pilot studies that prevented R-C dissociation so as to only observe cAMP-induced conformational changes). Such experiments will provide important insights into the structural dynamics of PKA.