Ca2+-modulated vision-linked ROS-GC guanylate cyclase transduction machinery

Vertebrate phototransduction depends on the reciprocal relationship between two-second messengers, cyclic GMP and Ca²⁺. The concentration of both is reciprocally regulated including the dynamic synthesis of cyclic GMP by a membrane bound guanylate cyclase. Different from hormone receptor guanylate cyclases, the cyclases operating in phototransduction are regulated by the intracellular Ca²⁺-concentration via small Ca²⁺-binding proteins. Based on the site of their expression and their Ca²⁺ modulation, this sub-branch of the cyclase family was named sensory guanylate cyclases, of which the retina specific forms are named ROS-GCs (rod outer segment guanylate cyclases). This review focuses on the structure and function of the ROS-GC subfamily present in the mammalian retinal neurons: photoreceptors and inner layers of the retinal neurons. Portions and excerpts of the review are from a previous chapter (Curr Top Biochem Res 6:111–144, 2004).