RGR Membrane Protein Introduction

Introduction of RGR

RGR is a membrane-bound opsin with seven transmembrane domains and is expressed in the RPE. It is closely related in amino acid sequence to invertebrate visual pigments and retinochrome, a photoisomerase that catalyzes the conversion of all-trans- to 11-cis-retinal in squid photoreceptors. The RGR opsin is bound in the dark to all-trans-retinal and has absorption maxima at 469 and 370 nm. Illumination in vitro results in the stereospecific conversion of the bound all-trans-retinal to the 11-cis isomer. RGR is involved in the formation of 11-cis-retinal in mice and is necessary for maintaining normal steady-state levels of both 11-cis-retinal and rhodopsin in a light-adapted eye. It indicates that RGR functions to generate 11-cis-retinal in vivo and participates in a light-dependent visual cycle. Mutations in human RGR, which is located on chromosome 10q23, are associated with cases of recessive and dominant retinitis pigmentosa.

Function of RGR Membrane Protein

RGR-opsin is a member of the rhodopsin-like receptor subfamily of GPCR. Like other opsins bound retinaldehyde, it has a conserved lysine residue in the seventh transmembrane domain. RGR-opsin preferentially binds all-trans-retinal, which is the dominant form in the dark adapted retina, upon light exposure it is isomerized to 11-cis-retinal. Therefore, RGR-opsin acts as a photoisomerase to transfer all-trans-retinal to 11-cis-retina. 11-cis-retinal will be isomerized back within rhodopsin and the iodopsins in the rods and cones of the retina. RGR-opsin may be associated with autosomal recessive and autosomal dominant retinitis pigmentosa (arRP and adRP, respectively). RGR-opsin comes in different isoforms produced by alternative splicing.

Fig.1 Proposed model of the photic visual cycle and interaction of retinol dehydrogenases with the chromophore of RGR. (Yang, 2002)

Application of RGR Membrane Protein in Literature

1. Maeda T., et al. Evaluation of the role of the retinal G protein-coupled receptor (RGR) in the vertebrate retina in vivo. J Neurochem. 2003, 85(4):944-56. PubMed ID: 12716426
   
   

   The authors find that RGR and RDH5 are likely to function in the retinoid cycle, although their role is not essential and regeneration of visual pigment is only mildly affected by the absence of both proteins in rod-dominated mice.

2. Wenzel A., et al. The retinal G protein-coupled receptor (RGR) enhances isomerohydrolase activity independent of light. J Biol Chem. 2005, 280(33):29874-84. PubMed ID: 15961402
   
   

   This article suggests RGR accelerates the conversion of retinyl esters to 11-cis-retinal by positively modulating isomerohydrolase activity, which is a key step in the "classical" visual cycle. The authors also find that light accelerates rhodopsin regeneration, independent of RGR.

3. Chen P., et al. Interaction of 11-cis-retinol dehydrogenase with the chromophore of retinal g protein-coupled receptor opsin. J Biol Chem. 2001, 276(24):21098-104. PubMed ID: 11274198
   
   

   Their results suggest that the reduction of 11-cis-retinal to 11-cis-retinol by cRDH will enhance the net photoisomerization of all-trans-retinal bound to RGR. It also indicates that cRDH is involved in the processing of 11-cis-retinal after irradiation of RGR opsin and suggests that cRDH has a novel role in the visual cycle.

4. Radu R.A., et al. Retinal pigment epithelium-retinal G protein receptor-opsin mediates light-dependent translocation of all-trans-retinyl esters for synthesis of visual chromophore in retinal pigment epithelial cells. J Biol Chem. 2008, 283(28):19730-8. PubMed ID: 18474598
   
   

   The results of this study suggest that RGR-opsin mediates light-dependent translocation of all-trans-retinyl esters from a storage pool in lipid droplets to an "isomerase pool" in membranes of the endoplasmic reticulum.

5. Hao W., et al. Analysis of chromophore of RGR: retinal G-protein-coupled receptor from pigment epithelium. Methods Enzymol. 2000, 316:413-22. PubMed ID: 10800691
   
   

   This chapter presents procedures used to analyze the chromophore of RGR to elude various limitations in accessibility, abundance, and biochemical properties. The reaction of RGR and hydroxylamine may be followed by measurement of the absorbance of RGR at various times after the addition of hydroxylamine.

RGR Preparation Options

We keep in a leading position of membrane protein studies over the past few years. Based on our versatile Magic™ membrane protein production platform, we can provide a series of advanced membrane protein preparation services in reconstitution forms as well as multiple active formats for worldwide customers. Aided by our versatile Magic™ anti-membrane protein antibody discovery platform, we also provide customized anti-RGR antibody development services.

• Magic™ Membrane Protein Production Platform
• Magic™ Anti-Membrane Protein Antibody Discovery Platform

During the past years, Creative Biolabs has successfully generated many functional membrane proteins for our global customers. It’s our responsibility to boost the development of our clients’ programs with our experienced service. For more details, please feel free to contact us.

Reference

1. Yang M and Fong H K. (2002). Synthesis of the all-trans-retinal chromophore of retinal G protein-coupled receptor opsin in cultured pigment epithelial cells. J Biol Chem. 277(5), 3318-3324.

All listed services and products are For Research Use Only. Do Not use in any diagnostic or therapeutic applications.