Vertebrate and Invertebrate Rhodopsins: Light Control of G-Protein Signaling

Vertebrate and invertebrate rhodopsins are G-protein-coupled receptors that are involved in sensing light. Light activation of these receptors leads to intracellular responses via activation of G-proteins. Both receptor types belong to the Class A (rhodopsin-like) family of seven transmembrane domain receptors. Differences between vertebrate and invertebrate rhodopsins exist according to their light cycles and the G-proteins utilized to sense and transduce light into a cellular response. While vertebrate rhodopsin uses 11-cis- retinal as the light-sensing compound coupled to an extrinsic photocycle to activate a G-protein of the Gi family, invertebrate rhodopsin uses all-trans- retinal coupled to an intrinsic photocycle to activate a G-protein of the Gq family. We will now discuss the difference between the two receptor types, their applications and expression outside of the vertebrate and invertebrate eye in regard to the control of cellular signaling.