CALCIUM ION COORDINATION IN BIOLOGICAL MACROMOLECULES

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 钙是一种重要的第二信使，参与多种生物过程。这些作用是通过钙离子与多种调节蛋白的特异性结合来实现的。真核细胞胞浆中钙的静息水平约为10-100 nM。刺激后，钙离子浓度达到毫米波水平。这导致各种钙结合蛋白的钙依赖构象变化，从而激活酶和其他靶蛋白。我们建议用X射线吸收光谱研究的钙结合蛋白是小蛋白(PV)，它在快速收缩/松弛肌纤维中大量存在。PV是一种延迟的钙库，它在胞质中的钙稳态中起着重要作用，因此通常被称为“钙缓冲器”。PV还存在于不同类型的细胞中，这些细胞的胞浆钙浓度发生快速而巨大的变化，如GABA能抑制内神经元。EXAFS分析发现，在吸收光谱的前40 eV处存在较强的双激发效应。我们发现，只有在原子背景中适当地考虑这些影响，才能可靠地确定第一层钙水化壳层的结构参数。此外，在最近的一项研究中，扩展X射线吸收精细结构光谱(EXAFS)和大角度X射线散射(LAXS)方法都被用来获得关于水合钙离子周围的局部结构的信息。之所以选择PV作为研究案例，是因为它只有两个不同的钙结合部位，而且它的结构已经被核磁共振和X射线结晶学广泛研究。

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. Calcium is an important secondary messenger involved in several biological processes. These effects are mediated through specific binding of the Ca2+ ions to a variety of regulating proteins. The resting level of Ca2+ in the cytosol of an eukaryotic cell is in the order of 10-100 nM. After stimulation, the concentration of calcium reaches mM levels. This leads to a calcium-dependent conformational change of a variety of Ca2+-binding proteins with the consequence of activating enzymes and other target proteins. The calcium binding protein that we propose to investigate by x-ray absorption spectroscopy is Parvalbumin (PV) that is abundantly found in fast contracting/relaxing muscle fibers. PV is a delayed Ca2+ sink, which plays a major role in calcium homeostasis in the cytosol and is, therefore, usually called a "calcium buffer". PV is also found in different cells types, which undergo rapid and large changes in cytosolic calcium concentration such as GABAergic inhibitory intemeurons. From the EXAFS analysis the existence of strong double-excitation effects has been detected in the first 40 eV of the absorption spectrum. It has been found that a reliable determination of the structural parameters of the fist Ca2+ hydration shell can be obtained only if these effects are properly accounted for in the atomic background. Moreover, in a recent study, both the extended X-ray absorption fine structure spectroscopy (EXAFS) and the large-angle X-ray scattering (LAXS) methods have been used to obtain information about the local structure around the hydrated calcium(II) ion. The choice of PV as study case, is related to the fact that it has only two distinct calcium binding sites and that its structure has been extensively studied by NMR and X-ray crystallography.