OPN4 is a symbol for the gene, Opsin 4, in humans. Other names include: Melanopsin; Opsin-4; MOP. The encoded protein has an amino acid length of 478 and a mass of 52.6 kDa. OPN4 is a member of the G-protein coupled receptor 1 family, Opsin subfamily. This gene shares homology with other species, including: Frog.