Interaction of 11-cis-retinol dehydrogenase with the chromophore of retinal g protein-coupled receptor opsin.
Vertebrate opsins in both photoreceptors and the retinal pigment epithelium (RPE) have fundamental roles in the visual process. The visual pigments in photoreceptors are bound to 11-cis-retinal and are responsible for the initiation of visual excitation. Retinochrome-like opsins in the RPE are bound to all-trans-retinal and play an important role in chromophore metabolism. The retinal G protein-coupled receptor (RGR) of the RPE and Müller cells is an abundant opsin that generates 11-cis-retinal by stereospecific photoisomerization of its bound all-trans-retinal chromophore. We have analyzed a 32-kDa protein (p32) that co-purifies with bovine RGR from RPE microsomes. The co-purified p32 was identified by mass spectrometric analysis as 11-cis-retinol dehydrogenase (cRDH), and enzymatic assays have confirmed the isolation of an active cRDH. The co-purified cRDH showed marked substrate preference to 11-cis-retinal and preferred NADH rather than NADPH as the cofactor in reduction reactions. cRDH did not react with endogenous all-trans-retinal bound to RGR but reacted specifically with 11-cis-retinal that was generated by photoisomerization after irradiation of RGR. The reduction of 11-cis-retinal to 11-cis-retinol by cRDH enhanced the net photoisomerization of all-trans-retinal bound to RGR. These results indicate that cRDH is involved in the processing of 11-cis-retinal after irradiation of RGR opsin and suggest that cRDH has a novel role in the visual cycle.
Center for Craniofacial Molecular Biology, University of Southern California School of Dentistry, Department of Ophthalmology, Los Angeles, California 90033, USA.
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Fong
D000429:Alcohol Oxidoreductases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D003624:Darkness; D005136:Eye Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008027:Light; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry; D010857:Pigment Epithelium of Eye / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled; D012160:Retina / Q000166:cytology / Q000378:metabolism*; D012172:Retinaldehyde / Q000378:metabolism; D017299:Rod Opsins / Q000737:chemistry* / Q000378:metabolism*; D013379:Substrate Specificity; D014357:Trypsin; D014801:Vitamin A / Q000378:metabolism
D005136:Eye Proteins; C089754:G protein-coupled receptor RGR; D010446:Peptide Fragments; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D017299:Rod Opsins; D009243:NAD; D014801:Vitamin A; D009249:NADP; D000429:Alcohol Oxidoreductases; C022520:retinol dehydrogenase; D014357:Trypsin; D012172:Retinaldehyde