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Description

Guanylyl cyclase-activating protein 1 (UniProt: P43081, also known as GCAP 1, Guanylate cyclase activator 1A) is encoded by the Guca1a (also known as Gcap, Gcap1, Guca1) gene (Gene ID: 14913) in murine species. GCAP1 is a membrane bound protein that stimulates retinal guanylyl cyclase when free calcium ions concentration is low and inhibits guanylyl cyclase when free calcium ions concentration is elevated. This Ca2+-sensitive regulation of retinal guanylyl cyclase appears to be a key event in recovery of the dark state of rod photoreceptors following light exposure. GCAP1 is present in rod and cone photoreceptor outer segments where phototransduction occurs. It binds three calcium ions (via EF-hands 2, 3 and 4) when calcium levels are high. Binds Mg2+ when calcium levels are low. Three calcium-binding sites are identified (aa 64-75, 100-111, and 144-155). GCAP1 restores the calcium sensitivity of guanylyl cyclase in a reconstituted system, and it decreases the sensitivity, time-to-peak, and recovery time of the light response following its introduction into intact rod outer segments. (Ref.: Gorczyca WA (1995). J. Biol Chem. 270(37), 22029-36, Schrem A et al. (1999). J Biol Chem. 274(10), 6244-49).