The retinal G protein-coupled receptor (RGR) enhances isomerohydrolase activity independent of light

J Biol Chem. 2005 Aug 19;280(33):29874-84. doi: 10.1074/jbc.M503603200. Epub 2005 Jun 16.

Abstract

Rod and cone visual pigments use 11-cis-retinal, a vitamin A derivative, as their chromophore. Light isomerizes 11-cis- into all-trans-retinal, triggering a conformational transition of the opsin molecule that initiates phototransduction. After bleaching all-trans-retinal leaves the opsin, and light sensitivity must be restored by regeneration of 11-cis-retinal. Under bright light conditions the retinal G protein-coupled receptor (RGR) was reported to support this regeneration by acting as a photoisomerase in a proposed photic visual cycle. We analyzed the contribution of RGR to rhodopsin regeneration under different light regimes and show that regeneration, during light exposure and in darkness, is slowed about 3-fold in Rgr(-/-) mice. These findings are not in line with the proposed function of RGR as a photoisomerase. Instead, RGR, independent of light, accelerates the conversion of retinyl esters to 11-cis-retinal by positively modulating isomerohydrolase activity, a key step in the "classical" visual cycle. Furthermore, we find that light accelerates rhodopsin regeneration, independent of RGR.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Carrier Proteins
  • Eye Proteins / analysis
  • Eye Proteins / physiology
  • Light*
  • Mice
  • Mice, Inbred BALB C
  • Mice, Inbred C57BL
  • Photoreceptor Cells / physiology
  • Receptors, G-Protein-Coupled / physiology*
  • Regeneration
  • Retina / physiology*
  • Retinaldehyde / chemistry*
  • Stereoisomerism
  • cis-trans-Isomerases / metabolism*

Substances

  • Carrier Proteins
  • Eye Proteins
  • Receptors, G-Protein-Coupled
  • retinoid isomerohydrolase
  • cis-trans-Isomerases
  • Retinaldehyde