Instead, GCAP1 and GCAP2 bind with the cyclase molecule in a mutually exclusive manner using a common or overlapping binding site(s) in the Arg(488)-Arg(851) portion of RetGC1, and mutations in that region causing Leber congenital amaurosis blindness disrupt activation of the cyclase by both GCAP1 and GCAP2.
They play a fundamental role in light adaptation by coupling the rate of cGMP synthesis to the intracellular concentration of calcium.Mutations in GCAPs lead to blindness.