OPN4 Membrane Protein Introduction

Introduction of OPN4

OPN4 is a type of photopigment belonging to a larger family of light-sensitive retinal proteins called opsins and encoded by the gene Opn4. In the mammalian retina, there are two additional opsins, both involved in the formation of visual images: rhodopsin and photopsin (types I, II, and III) in the rod and cone photoreceptor cells, respectively. OPN4, like all other animal opsins (e.g. rhodopsin), is a member of the G-protein coupled receptor (GPCR) family. The OPN4 protein has seven alpha helices integrated into the plasma membrane, an N-terminal domain, and a C-terminal domain.

Basic Information of OPN4
Protein Name	Melanopsin
Gene Name	OPN4
Aliases	Melanopsin, Opsin-4
Organism	Homo sapiens (Human)
UniProt ID	Q9UHM6
Transmembrane Times	7
Length (aa)	478
Sequence	MNPPSGPRVPPSPTQEPSCMATPAPPSWWDSSQSSISSLGRLPSISPTAPGTWAAAWVPLPTVD VPDHAHYTLGTVILLVGLTGMLGNLTVIYTFCRSRSLRTPANMFIINLAVSDFLMSFTQAPVFF TSSLYKQWLFGETGCEFYAFCGALFGISSMITLTAIALDRYLVITRPLATFGVASKRRAAFVLL GVWLYALAWSLPPFFGWSAYVPEGLLTSCSWDYMSFTPAVRAYTMLLCCFVFFLPLLIIIYCYI FIFRAIRETGRALQTFGACKGNGESLWQRQRLQSECKMAKIMLLVILLFVLSWAPYSAVALVAF AGYAHVLTPYMSSVPAVIAKASAIHNPIIYAITHPKYRVAIAQHLPCLGVLLGVSRRHSRPYPS YRSTHRSTLTSHTSNLSWISIRRRQESLGSESEVGWTHMEAAAVWGAAQQANGRSLYGQGLEDL EAKAPPRPQGHEAETPGKTKGLIPSQDPRM

Function of OPN4 Membrane Protein

OPN4 plays an important non-image-forming role in the setting of circadian rhythms as well as other functions. Mutations in the Opn4 gene can lead to clinical disorders, such as seasonal affective disorder (SAD). Studies have shown that 5% of patients with SAD are associated with missense mutations in Opn4 and P10L. Besides, OPN4 serves an important role in the photoentrainment of circadian rhythms in mammals. The discovery of the role of OPN4 in non-image forming vision has led to a growth in optogenetics. Additionally, an OPN4 based receptor has been reported to link to migraine pain.

OPN4 Membrane Protein Introduction Fig.1 Structure of OPN4 membrane protein.

Application of OPN4 Membrane Protein in Literature

Panda S., et al. Melanopsin (Opn4) requirement for normal light-induced circadian phase shifting. Science. 2002, 298(5601): 2213-2216. PubMed: 12481141

This article reports that OPN4-knockout mice display reduced photoentrainment. In comparison to wild-type mice that expressed OPN4 normally, deficits in light-induced phase shifts in locomotion activity were noted in melanopsin-null mice (Opn4 -/-).
Panda S., et al. Melanopsin is required for non-image-forming photic responses in blind mice. Science. 2003, 301(5632): 525-527. PubMed: 12829787.

This article reveals that mice with both outer-retinal degeneration and a deficiency in OPN4 exhibited complete loss of photoentrainment of the circadian oscillator, pupillary light responses, photic suppression of arylalkylamine-N-acetyltransferase transcript, and acute suppression of locomotor activity by light.
Hattar S., et al. Melanopsin-containing retinal ganglion cells: architecture, projections, and intrinsic photosensitivity. Science. 2002, 295(5557): 1065-1070. PubMed: 11834834.

Authors show that OPN4 is present in cell bodies, dendrites, and proximal axonal segments of a subset of rat RGCs. Rat RGCs that exhibited intrinsic photosensitivity invariably expressed OPN4. Hence, OPN4 is most likely the visual pigment of phototransducing RGCs that set the circadian clock and initiate other non-image-forming visual functions.
Sakamoto K., et al. Dopamine regulates melanopsin mRNA expression in intrinsically photosensitive retinal ganglion cells. The European Journal of Neuroscience. 2005, 22(12): 3129-3136. PubMed: 16367779

This article reports that the mechanisms that control OPN4 expression in the rat retina. They discover that dopamine (DA) is involved in the regulation of OPN4 mRNA, possibly via dopamine D2 receptors that are located on these ipRGCs.
Rollag M.D., et al. Melanopsin, ganglion-cell photoreceptors, and mammalian photoentrainment. Journal of Biological Rhythms. 2003, 18(3): 227-234. PubMed: 12828280

This article summarizes recent findings related to OPN4 and OPN4 ganglion cells and lists other retinal proteins that might serve as photopigments in the mammalian photoentrainment input pathway.

OPN4 Preparation Options

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