Calcium-dependent protein in photoreceptor light-adaptation

我们最近的工作表明，脊椎动物的光感受器光适应是由钙依赖的调节蛋白S-modulin（敏感性调节蛋白）调节的。在目前的项目中，我发现了以下几点。s -调节蛋白是一种钙结合蛋白。通过钙的结合，疏水部分出现，使s -调节蛋白与盘膜结合，发挥其生理功能。从蛋白水解片段获得的部分氨基酸序列来看，S-modulin与visinin的氨基酸序列一致性约为60%，与recoverin的氨基酸序列一致性约为80%。这三种蛋白质中的每一种都有三种假定的EF手结构。然而，这些蛋白质形成了一个不同于钙调蛋白家族的新家族。s -调节蛋白在光传导级联中的作用位点是视紫红质磷酸化。在暗适应条件下典型的高钙条件下，s -调节蛋白抑制视紫红质的磷酸化，从而延长了活化的视紫红质的寿命。通过这样做，s -调制素延长了光感受器的光反应，并增加了在黑暗中的光敏感性。这些结果可以阐明脊椎动物光感受器适应现象的大部分特征。

Our resent work showed that photoreceptor light-adaptation in vertebrates is regulated by a calcium-dependent regulatory protein, S-modulin (sensitivity-modulating protein). In the present project, I found the followings.1. S-modulin is a calcium-binding protein. By binding of calcium, a hydro-phobic portion emerges so that S-modulin binds to disk membranes to exert its physiologial function.2. According to the partial amino acid sequence obtained from proteolyzed fragments, the amino acid sequence of S-modulin is about 60 % identical to visinin and 80 % to recoverin. Each of these three proteins has three putative EF hand structures. However, these proteins form a new family that is distinct from calmodulin family.3. The site of S-modulin action in the phototransduction cascade is rhodopsin phosphorylation. At high calcium condition which is typical under dark-adapted condition, S-modulin inhibits rhodopsin phosphorylation so that the life time of activated rhodopsin is prolonged. By doing so, S-modulin prolongs photoreceptor light response and increases light-sensitivity in the dark.From these results, one could elucidate most of the characteristics of the adaptation phenomena in vertebrate photoreceptor adaptation.