Crystal structure of rhodopsin: implications for vision and beyond.
A heptahelical transmembrane bundle is a common structural feature of G-protein-coupled receptors (GPCRs) and bacterial retinal-binding proteins, two functionally distinct groups of membrane proteins. Rhodopsin, a photoreceptor protein involved in photopic (rod) vision, is a prototypical GPCR that contains 11-cis-retinal as its intrinsic chromophore ligand. Therefore, uniquely, rhodopsin is a GPCR and also a retinal-binding protein, but is not found in bacteria. Rhodopsin functions as a typical GPCR in processes that are triggered by light and photoisomerization of its ligand. Bacteriorhodopsin is a light-driven proton pump with an all-trans-retinal chromophore that photoisomerizes to 13-cis-retinal. The recent crystal structure determination of bovine rhodopsin revealed a structure that is not similar to previously established bacteriorhodopsin structures. Both groups of proteins have a heptahelical transmembrane bundle structure, but the helices are arranged differently. The activation of rhodopsin involves rapid cis-trans photoisomerization of the chromophore, followed by slower and incompletely defined structural rearrangements. For rhodopsin and related receptors, a common mechanism is predicted for the formation of an active state intermediate that is capable of interacting with G proteins.
Okada
T
T
Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan. okada@photo2.biophys.kyoto-u.ac.jp
Palczewski
K
K
D000818:Animals; D001436:Bacteriorhodopsins / Q000737:chemistry; D002417:Cattle; D018360:Crystallography, X-Ray; D019204:GTP-Binding Proteins / Q000737:chemistry*; D007536:Isomerism; D008024:Ligands; D008565:Membrane Proteins / Q000737:chemistry* / Q000502:physiology; D020419:Photoreceptor Cells, Vertebrate / Q000737:chemistry*; D011487:Protein Conformation; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000378:metabolism; D012172:Retinaldehyde / Q000737:chemistry / Q000378:metabolism*; D012243:Rhodopsin / Q000737:chemistry* / Q000378:metabolism
D008024:Ligands; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; D001436:Bacteriorhodopsins; D012243:Rhodopsin; D019204:GTP-Binding Proteins; D012172:Retinaldehyde