NMR STUDIES OF C2 DOMAINS OF SYNAPTOTAGMIN I

突触素参与钙离子诱导的神经传递 放手。突触素大约有4个结构域：囊泡内 结构域、跨膜结构域和2个胞质结构域。两个胞质 域被命名为C2a和C2b。第一个领域是要研究的领域 核磁共振仪。C2a结构域是膜上的一种钙离子感受器。 胞吐。根据Ca~(2+)结合试验 磷脂，希尔系数大于3，依次 这意味着C2a至少要与3个钙离子结合。到目前为止，x射线 结构发现了一个钙结合部位，核磁共振数据表明 第二个站点。最近，PLC的X射线结构--1 根据同源性提出了C2结构域的第三结合位点 两个结构中的一个。未能找到第三个结合位点 被推定是由于缺乏脂质造成的，因为 C2a结构域对钙离子的固有亲和力较低。在当前的核磁共振中 对这个C2a结构域的研究，磷脂的一个短版本已经被 使用。核磁共振数据显示了化学位移随存在的变化 钙离子或脂质或两者兼而有之，这强烈地表明 三元复合体。这项研究的目的是解决结构问题 三元络合物：C2a-钙-脂。

The synaptotagmin is involved in the Ca2+-induced neurotrasmitter release. The synaptotagmin has roughly 4 domains: intravesicular domain, transmembrane domain, and 2 cytosolic domains. Two cytosolic domains are named C2A and C2B. The first domain is the one to study by NMR. C2A domain is known to be a Ca2+ sensor in the membrane exocytosis. According to the Ca2+ binding assay in the presence of phospholipids, the Hill coefficient is larger than 3, which in turn means C2A should bind at least 3 Ca2+ ions. So far, the x-ray structure found one Ca2+ binding site, and NMR data suggested the second site. Very recently, the x-ray structure of the PLC-?1 which has a C2 domain proposed the third binding site based on the homology of the two structures. The failure in finding the third binding site is presumed to result from the absence of the lipids since the intrinsic affinity of C2A domain to Ca2+ is low. In the current NMR study of this C2A domain, a short version of the phospholipid has been used. NMR data show changes in the chemical shifts with the presence of Ca2+ or lipid or both, which strongly suggests a existence of a ternary complex. The goal of this study is to solve the structure of the ternary complex: C2A-Ca2+-lipid.