TY - JOUR

T1 - Deuterium NMR structure of retinal in the ground state of rhodopsin

AU - Salgado, Gilmar F.J.

AU - Struts, Andrey V.

AU - Tanaka, Katsunori

AU - Fujioka, Naoko

AU - Nakanishi, Koji

AU - Brown, Michael F.

N1 - Copyright: Copyright 2008 Elsevier B.V., All rights reserved.

PY - 2004/10/12

Y1 - 2004/10/12

N2 - The conformation of retinal bound to the G protein-coupled receptor rhodopsin is intimately linked to its photochemistry, which initiates the visual process. Site-directed deuterium (2H) NMR spectroscopy was used to investigate the structure of retinal within the binding pocket of bovine rhodopsin. Aligned recombinant membranes were studied containing rhodopsin that was regenerated with retinal 2H-labeled at the C5, C 9, or C13 methyl groups by total synthesis. Studies were conducted at temperatures below the gel to liquid-crystalline phase transition of the membrane lipid bilayer, where rotational and translational diffusion of rhodopsin is effectively quenched. The experimental tilt series of 2H NMR spectra were fit to a theoretical line shape analysis [Nevzorov, A. A., Moltke, S., Heyn, M. P., and Brown, M. F. (1999) J. Am. Chem. Soc. 121, 7636-7643] giving the retinylidene bond orientations with respect to the membrane normal in the dark state. Moreover, the relative orientations of pairs of methyl groups were used to calculate effective torsional angles between different planes of unsaturation of the retinal chromophore. Our results are consistent with significant conformational distortion of retinal, and they have important implications for quantum mechanical calculations of its electronic spectral properties. In particular, we find that the β-ionone ring has a twisted 6-s-cis conformation, whereas the polyene chain is twisted 12-s-trans. The conformational strain of retinal as revealed by solid-state 2H NMR is significant for explaining the quantum yields and mechanism of its ultrafast photoisomerization in visual pigments. This work provides a consensus view of the retinal conformation in rhodopsin as seen by X-ray diffraction, solid-state NMR spectroscopy, and quantum chemical calculations.

AB - The conformation of retinal bound to the G protein-coupled receptor rhodopsin is intimately linked to its photochemistry, which initiates the visual process. Site-directed deuterium (2H) NMR spectroscopy was used to investigate the structure of retinal within the binding pocket of bovine rhodopsin. Aligned recombinant membranes were studied containing rhodopsin that was regenerated with retinal 2H-labeled at the C5, C 9, or C13 methyl groups by total synthesis. Studies were conducted at temperatures below the gel to liquid-crystalline phase transition of the membrane lipid bilayer, where rotational and translational diffusion of rhodopsin is effectively quenched. The experimental tilt series of 2H NMR spectra were fit to a theoretical line shape analysis [Nevzorov, A. A., Moltke, S., Heyn, M. P., and Brown, M. F. (1999) J. Am. Chem. Soc. 121, 7636-7643] giving the retinylidene bond orientations with respect to the membrane normal in the dark state. Moreover, the relative orientations of pairs of methyl groups were used to calculate effective torsional angles between different planes of unsaturation of the retinal chromophore. Our results are consistent with significant conformational distortion of retinal, and they have important implications for quantum mechanical calculations of its electronic spectral properties. In particular, we find that the β-ionone ring has a twisted 6-s-cis conformation, whereas the polyene chain is twisted 12-s-trans. The conformational strain of retinal as revealed by solid-state 2H NMR is significant for explaining the quantum yields and mechanism of its ultrafast photoisomerization in visual pigments. This work provides a consensus view of the retinal conformation in rhodopsin as seen by X-ray diffraction, solid-state NMR spectroscopy, and quantum chemical calculations.

UR - http://www.scopus.com/inward/record.url?scp=4944234024&partnerID=8YFLogxK

U2 - 10.1021/bi0491191

DO - 10.1021/bi0491191

M3 - Article

C2 - 15461454

VL - 43

SP - 12819

EP - 12828

JO - Biochemistry

JF - Biochemistry

SN - 0006-2960

IS - 40

ER -