MEMBRANE TARGETING CALCIUM SENSORS IN VISION

细胞内钙控制兴奋性， 视网膜视杆细胞和视锥细胞的脱敏。 恢复和 鸟苷酸环化酶激活蛋白（GCAP-1和GCAP-2）是 视网膜中介导钙依赖性的钙敏感蛋白 视觉信号 恢复和GCAP是新成员， EF-手超家族，包括钙调蛋白和肌钙蛋白C。 它们在它们的侧链上含有肉豆蔻酰基或相关的脂肪酰基。 氨基末端。 豆蔻酰化，但不是未豆蔻酰化， 恢复蛋白在高Ca 2+浓度下与细胞膜结合， 但在低Ca 2+时不与膜结合。 相反，GCAP 在低Ca 2+时结合膜，但在高Ca 2+时不结合膜 Ca2+。 最近确定的溶液中回收蛋白的结构 表明Ca 2+诱导氨基末端的挤出 肉豆蔻酰基基团的外部，在那里它可以与 膜靶。 什么样的结构决定因素促进膜 GCAP的本地化？ 氨基末端的肉豆蔻酰基 直接插入到脂质双层中 Ca 2 +-的结构 结合GCAP-2、与膜结合的恢复素和与膜结合的恢复素 视紫红质激酶的生理靶点，将通过 核磁共振（NMR），X射线晶体学，和 自旋标记电子自旋共振（ESR）。 恢复和GCAP 属于一个迅速增长的肉豆蔻酰化钙家族 传感器. 在大肠杆菌中发现了十多个recoverin的同源物。 中枢神经系统，并可能耦合钙级联和G- 蛋白质级联 recoverin家族也存在于 无脊椎动物 酵母含有一种同源物， 与哺乳动物恢复相同。 结构和遗传研究 将进行酵母蛋白质，以阐明新的 生理目标。 由此决定的结构 研究将揭示共价连接的肉豆蔻酰基 与Ca 2+结合位点协同工作，引导这一家族， 蛋白质与膜结合靶点。 这些结构也可以 揭示了许多细胞膜靶向机制的见解， 其它生物学上重要的豆蔻酰化蛋白质如Src， 致癌Ras，富含豆蔻酰丙氨酸的C激酶底物 （MARCKS）和ADP核糖基化因子（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).