Guanylyl cyclase-activating protein 1 (GUCA1A, also known as GCAP1) regulates the visual photoresponse []. It binds to and regulates RetGC1 (retinal membrane guanylyl cyclase 1), a key enzyme in photoreceptor physiology that produces the second messenger of phototransduction cGMP in rods and cones [, ]. Photoactivated pigment triggers the decay of cGMP and shuts off cGMP-gated channels in the outer segment. The influx of Ca2+ through the channels stops and the free Ca2+ concentration in the outer segment declines rapidly. Recovery of rods and cones from excitation requires the activation of RetGC1 by GCAPs, which occurs at low Ca2+ concentrations [].Mutations in the GCAP1 gene cause congenital retinal diseases in humans, such as cone dystrophy 3 (COD3) [, ].
