ИСТИНА

In 1988, Koch an Stryer demonstrated that the effect of calcium upon the activity of photoreceptor guanylyl cyclase is mediated by an unknown protein. This work has stimulated the search for such a protein that finally resulted in the discovery of several photoreceptor Ca2+-binding proteins. These were recoverin and later described GCAPs which confer calcium sensitivity upon rhodopsin kinase (GRK-1) and guanylyl cyclase, respectively. Quite recently, we have found (i) that the well-known Ca2+-binding protein calmodulin can also be involved in the Ca2+-dependent control of phototransduction through the increase of the magnitude and Ca2+-sensitivity of the inhibitory effect of recoverin upon rhodopsin kinase and (ii) that rhodopsin kinase contains separate binding sites for recoverin and calmodulin. Further, we have demonstrated that, in addition to recoverin and calmodulin, GCAP2 and NCS1 are capable of interacting with rhodopsin kinase in a Ca2+-dependent manner. It is yet unclear whether NCS1 can participate in the control of phototransduction as this Ca2+-binding protein is believed to be localized merely in photoreceptor inner segments. Finally, a putative crosstalk between guanylyl cyclase and rhodopsin kinase – via GCAP2 – is discussed. This work was supported by the grants from the Russian Foundation for Basic Research to EYZ (#12-04-01045) and to PPPh (##11-04-00125 and ofi-m-2011 11-04-12108).