Structure and membrane-targeting mechanism of retinal Ca2+-binding proteins, recoverin and GCAP-2.

Recoverin and the guanylate cyclase activating proteins (GCAPs) are calcium-sensing proteins in retinal rod and cone cells that belong to the EF-hand superfamily and serve as important calcium sensors in vision. Recoverin and the OCAP proteins are myristoylated at their amino-terminus and are targeted to retinal disc membranes by a myristoyl switch. Here, we present the three-dimensional, atomic-resolution structures of recombinant myristoylated recoverin containing 0, 1 and 2 calcium ions (Ca2+) bound and unmyristoylated GCAP-2 with 3 Ca2+ bound as determined by nuclear magnetic resonance. The Ca2+-induced structural changes in these proteins are important for elucidating their membrane-targeting mechanisms and for understanding the molecular mechanism of Ca2+-sensitive regulation of phototransduction.