Rhodopsin (RHO, Opsin-2, OPN2)

Rhodopsin is the protein in the mammalian retina responsible for the light sensitivity of rod cells, which are responsible for vision in low light levels. Somewhat surprisingly, the rhodopsin protein turned out to be a typical member of the seven transmembrane G protein-coupled receptor (GPCR) superfamily. Whereas other GPCRs initiate signaling on binding a specific ligand, rhodopsin exists with a ligand already bound, specifically the vitamin A related substance retinal. Retinal can exist in two isomeric forms, 11-cis and 11-trans retinal. In the dark rhodopsin is associated with 11-cis retinal, but photons cause the 11-cis form to flip to the 11-trans form, and this causes an alteration in the structure of the rhodopsin making it catalytically active. Activated rhodopsin in turn activates the GTP binding protein transducin by favoring the loss of GDP and the addition of GTP. Transducin is a typical member of the family of heterotrimeric G proteins, and consists of an a and a bg subunit. The a subunit is responsible for the GTP binding and the GTP bound form activates a phosphodiesterase (PDE) enzyme which hydrolyses cyclic GMP. This in turn results in the closure of cyclic nucleotide gated ion channels in the rod cell membrane, which prevent the influx of sodium and calcium ions. This results in an increase in the membrane potential of the rod cell and so reduces the rate of synaptic signaling. So light stimulation results in a reduced rate of photoreceptor synaptic release. This information is transmitted through neurons of the retina to the visual centers of the brain (1,2). Rhodopsin activity is shut off by phosphorylation under the influence of rhodopsin kinase, the activity of which results in binding of visual arrestin, which prevents rhodopsin from interacting with and activating more transducin molecules (3,4). This basic signaling paradigm proved to be a prototype for understanding how other GPCRs function, as proteins similar to transducin, arrestin and rhodopsin kinase are found in these pathways. The protein is concentrated in rod outer segments. The HGNC name for this protein is RHO.\n\nApplications:\nSuitable for use in Immunofluorescence and Western Blot. A suitable control tissue is retinal extracts. Rhodopsin run at 35kD on SDS-PAGE gels. Other applications not tested.\n\nRecommended Dilution:\nImmunofluorescence: ~1:1000\nWestern Blot: 1:5000\nOptimal dilutions to be determined by the researcher.\n\nStorage and Stability:\nMay be stored at 4 degrees C for short-term only. Aliquot to avoid repeated freezing and thawing. Store at -20 degrees C. Aliquots are stable for 12 months. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap.

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