ИСТИНА

Intracellular calcium signaling plays crucial role in regulation of different aspects of neuronal function. The diversity of cellular responses on Ca2+ signals is provided by neuronal Ca2+ sensor (NCS) proteins which are capable of changing conformation upon cation binding thereby transmitting the signals to various target proteins and activating specific signaling pathways. A striking example of NCS-mediated signaling system is a visual transduction cascade in photoreceptor cells of the retina. These cells contain a few NCS proteins including recoverin, guanylyl cyclase activating proteins (GCAPs) and neuronal calcium sensor 1 (NCS1). Retina-specific recoverin and GCAPs are considered to be participants of phototransduction involved in the control of rhodopsin phosphorylation and cGMP synthesis, respectively. In contrast to recoverin and GCAPs, NCS1 is widely distributed in the nervous system but its specific function(s) in photoreceptor neurons remains unknown. In this study we have cloned NCS1 from bovine brain and investigated its regulatory activity in photoreceptor cells. It was found that RNA samples from the brain extracts contain two different NCS1 mRNA, encoding lysine or glutamic acid in the 9th position of the translated protein (isoforms NCS1WT and NCS1K9E). Both isoforms were shown to be almost identical structurally but differed in their ability to bind to photoreceptor membranes. NCS1WT interacted with the membranes in a Ca2+-independent manner, while in the case of NCS1K9E membrane association was slightly decreased in the presence of Ca2+ and significantly impaired in the Ca2+-free state. It was suggested that, being translated in vivo, NCS1WT and NCS1K9E would localize to membranes under different conditions therefore contributing to the regulation of both membrane-associated and cytosolic targets. Further it was demonstrated that NCS1WT is able to recognize rhodopsin kinase in bovine retinal extract and inhibit its activity by interacting with the enzyme specifically. Based on these data NCS1 was considered a potential Ca2+-dependent regulator of rhodopsin kinase in photoreceptor cell, sharing this function with recoverin. Possible role of rhodopsin kinase regulation by both proteins in vivo is discussed. This work was supported by the grant #12-04-01045-а from Russian Foundation for Basic Research.