title: Retinal orientation and interactions in rhodopsin reveal a two-stage trigger mechanism for activation.
abstract: The 11-cis retinal chromophore is tightly packed within the interior of the visual receptor rhodopsin and isomerizes to the all-trans configuration following absorption of light. The mechanism by which this isomerization event drives the outward rotation of transmembrane helix H6, a hallmark of activated G protein-coupled receptors, is not well established. To address this question, we use solid-state NMR and FTIR spectroscopy to define the orientation and interactions of the retinal chromophore in the active metarhodopsin II intermediate. Here we show that isomerization of the 11-cis retinal chromophore generates strong steric interactions between its β-ionone ring and transmembrane helices H5 and H6, while deprotonation of its protonated Schiff's base triggers the rearrangement of the hydrogen-bonding network involving residues on H6 and within the second extracellular loop. We integrate these observations with previous structural and functional studies to propose a two-stage mechanism for rhodopsin activation.
authors: Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, New York 11794-5215, USA.
authors: Naoki
authors: N
authors: Kimata
authors: Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, New York 11794-5215, USA.
authors: Andreyah
authors: A
authors: Pope
authors: Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, New York 11794-5215, USA.
authors: Markus
authors: M
authors: Eilers
authors: School of Biological Sciences, University of Essex, Wivenhoe Park, Essex CO4 3SQ, UK.
authors: Chikwado A
authors: CA
authors: Opefi
authors: Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, New York 11794-5215, USA.
authors: Martine
authors: M
authors: Ziliox
authors: Department of Organic Chemistry, Weizmann Institute, Rehovot 76100 Israel.
authors: Amiram
authors: A
authors: Hirshfeld
authors: University of Freiburg, Institute of Physiology II, D79104 Freiburg Germany.
authors: Ekaterina
authors: E
authors: Zaitseva
authors: Biophysics Section, Institute of Molecular Medicine and Cell Research, Albert-Ludwigs-University, D-79104 Freiburg, Germany.
authors: Reiner
authors: R
authors: Vogel
authors: Department of Organic Chemistry, Weizmann Institute, Rehovot 76100 Israel.
authors: Mordechai
authors: M
authors: Sheves
authors: School of Biological Sciences, University of Essex, Wivenhoe Park, Essex CO4 3SQ, UK.
authors: Philip J
authors: PJ
authors: Reeves
authors: Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, New York 11794-5215, USA.
authors: Steven O
authors: 0000-0003-1861-7159
authors: SO
authors: Smith
mesh_terms: D002460:Cell Line; D057809:HEK293 Cells; D006801:Humans; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D017434:Protein Structure, Tertiary; D012160:Retina / Q000502:physiology*; D012172:Retinaldehyde / Q000737:chemistry*; D012243:Rhodopsin / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: C013110:metarhodopsins; D012243:Rhodopsin; D012172:Retinaldehyde