MEMBRANE TARGETING CALCIUM SENSORS IN VISION

细胞内钙离子控制兴奋性和 视网膜视杆细胞和视锥细胞脱敏。恢复和 鸟苷环化酶激活蛋白(GCAP-1和GCAP-2)是 视网膜中介导钙依赖的钙敏感蛋白 在视觉中发出信号。Recoverin和GCAP是 EF-Hand超家族，包括钙调蛋白和肌钙蛋白C。 它们含有肉豆蔻基或相关的脂肪酰基 氨基末端。肉豆蔻甲基化，但不是非肉豆蔻甲基化， 恢复素在高钙浓度下与细胞膜结合， 但在低钙条件下，它不能与膜结合。相反，GCAP 低钙时结合膜，高钙时不结合膜 Ca2+。回收素在溶液中的最新结构测定 表明Ca~(2+)诱导氨基末端挤出 肉豆蔻基到外部，在那里它可以相互作用 膜靶标。哪些结构决定因素促进膜 GCAP的本地化？氨基末端的肉豆蔻基 直接插入到脂质双层中？钙离子的结构 结合GCAP-2、与膜结合的恢复素和结合的恢复素 为了达到其生理靶点，视紫红质激酶将通过 核磁共振(核磁共振)、X射线结晶学和 自旋标记电子自旋共振(ESR)。恢复和GCAP 属于一个快速增长的肉豆蔻酰化钙家族 传感器。发现了十多种恢复素的同源物 中枢神经系统，可能与钙级联和G- 蛋白质层叠而成。Recoverin家族也可以在 无脊椎动物。酵母含有46%的同系物 与哺乳动物的恢复期完全相同。结构和遗传学研究 将进行酵母蛋白的研究，以阐明新的 生理目标。由此决定的结构 研究将揭示肉豆蔻基是如何共价连接的 与钙结合位点协同工作，指导这一家族 蛋白质结合到膜结合的靶标。这些结构还可以 揭示了许多膜靶向机制的洞察力 其他具有重要生物学意义的肉豆蔻酰化蛋白，例如， 致癌RAS，肉豆蔻酰化富含丙氨酸的C-激酶底物 (Marcks)和ADP核糖化因子(ARF)。

Intracellular calcium controls the excitability and desensitization of retinal rod and cone cells. Recoverin and guanylate cyclase activating proteins (GCAP-1 and GCAP-2) are Ca2+ sensing proteins in the retina that mediate Ca2+-dependent signaling in vision. Recoverin and GCAPs are new members of the EF-hand superfamily that includes calmodulin and troponin C. They contain a myristoyl or related fatty acyl group at their amino-terminus. Myristoylated, but not unmyristoylated, recoverin binds to cellular membranes at high Ca2+ concentration, but it does not bind to membranes at low Ca2+. Conversely, GCAPs bind membranes at low Ca2+ but do not bind membranes at high Ca2+. The recently determined structure of recoverin in solution indicates that Ca2+ induces extrusion of the amino-terminal myristoyl group to the exterior where it can interact with membrane targets. What structural determinants promote membrane localization of GCAPs? Does the amino-terminal myristoyl group insert directly into the lipid bilayer? The structures of Ca2+- bound GCAP-2, recoverin bound to membranes, and recoverin bound to its physiological target, rhodopsin kinase will be studied by nuclear magnetic resonance (NMR), x-ray crystallography, and spin-label electron spin resonance (ESR). Recoverin and GCAPs belong to a rapidly growing family of myristoylated calcium sensors. More than ten homologs of recoverin are found in the central nervous system, and may couple calcium cascades and G- protein cascades. The recoverin family is also found in invertebrates. Yeast contains a homolog that is 46 percent identical to mammalian recoverin. Structure and genetic studies of the yeast protein will be carried out to elucidate new physiological targets. The structures determined by this research will reveal how covalently attached myristoyl groups work in concert with Ca2+ binding sites to guide this family of proteins to membrane bound targets. These structures may also reveal insights into the membrane-targeting mechanisms of many other biologically important myristoylated proteins such as Src, oncogenic Ras, myristoylated alanine rich C-kinase substrates (MARCKS) and ADP ribosylation factors (ARFs).