Opsin 3 (OPN3)

Opsins, including OPN3, are members of the superfamily of guanine nucleotide-binding protein (G protein)-coupled receptors, which function through the activation of a G protein and an effector enzyme. Opsin proteins consist of a single polypeptide chain of 340 to 500 amino acids that form 7 alpha-helical transmembrane regions connected by cytoplasmic and extracellular loops.

The predicted 403-amino acid human OPN3 protein shares 85.5% identity with the mouse protein. Northern blot analysis of mouse tissues revealed strong expression of Opn3 in cortex, cerebellum, and testes only, with faint expression in heart, liver, and kidney. In situ hybridization localized Opn3 to pachytene spermatids in testes.