Аннотация:Recoverin, initially named ‘p26’, belongs to the neuronal calcium sensor protein family and is a Ca2+-binding protein with a predominantly retinal localization. The recoverin molecule consists of 201 amino-acid residues and contains four potential EF-hand Ca2+-binding sites, of which only two — EF-hands 2 and 3 — are capable of binding calcium. The amino (N) terminus of recoverin is acylated, mainly myristoylated. Depending on calcium concentration, compartmentalization of recoverin is changed from a soluble Ca2+-free form to a membrane-bound Ca2+-containing form, and vice versa. This is due to the mechanism of Ca2+-myristoyl switch that operates in recoverin. In the Ca2+-free form, the N-terminal myristoyl moiety of recoverin is buried in the hydrophobic pocket of the protein; on binding of calcium, the myristoylated N terminus is exposed, providing membrane association of recoverin. According to several in vitro experiments, recoverin serves as a Ca2+-dependent regulator of G-protein-coupled receptor kinase 1 (GRK-1), also known as rhodopsin kinase, which is the enzyme that catalyzes phosphorylation and thus desensitization of the visual receptor rhodopsin. At high Ca2+ levels (corresponding to a dark state of photoreceptor cells), rhodopsin kinase is in a complex with recoverin and is inactive. At low Ca2+ levels (corresponding to a bleached state of photoreceptor cells), the complex dissociates and the kinase becomes active. In vivo data, however, are contradictive. On the one hand, recoverin is suggested to be implicated in the light adaptation of photoreceptor cells by Ca2+-dependent prolongation of photoresponse apparently due to (1) regulating the lifetime of photoactivated rhodopsin through feedback on rhodopsin kinase and (2) regulating the speed of light-induced free Ca2+ change through a Ca2+ buffering mechanism. On the other hand, there are data suggesting that the effect of recoverin on the photoresponse could not be explained by its effect on phototransduction. Instead, it is the effect of recoverin occurring downstream of phototransduction in rods that prolongs signal transmission and enhances visual sensitivity. Recoverin is also shown to be a paraneoplastic (or onconeural) antigen in cancer. The aberrant expression of recoverin in malignant tumors can cause an autoimmune response in some cancer patients that is followed by the development of paraneoplastic retina degeneration or cancer-associated retinopathy.