TY - JOUR

T1 - Solid-State 2H NMR spectroscopy of retinal proteins in aligned membranes

AU - Brown, Michael F.

AU - Heyn, Maarten P.

AU - Job, Constantin

AU - Kim, Suhkmann

AU - Moltke, Stephan

AU - Nakanishi, Koji

AU - Nevzorov, Alexander A.

AU - Struts, Andrey V.

AU - Salgado, Gilmar F.J.

AU - Wallat, Ingrid

N1 - Funding Information: Research described in this article was supported by NIH grants EY 12049 (M. F. B.) and GM 36564 (K. N.), NSF grant CHE-607917 (M.F.B.), and by Deutsche Forschungsgemeinschaft grant Sfb 498 (M. P. H.). We are especially grateful to our colleagues and laboratory members for their many contributions to this work. Organic synthesis of retinal benefited from the collaboration of S. Krane, N. Fujioka, N. Sakai, and K. Tanaka whose efforts are warmly acknowledged. We also express our appreciation to R. Bogomolni and W. L. Hubbell for stimulating discussions. Copyright: Copyright 2008 Elsevier B.V., All rights reserved.

PY - 2007/12

Y1 - 2007/12

N2 - Solid-state 2H NMR spectroscopy gives a powerful avenue to investigating the structures of ligands and cofactors bound to integral membrane proteins. For bacteriorhodopsin (bR) and rhodopsin, retinal was site-specifically labeled by deuteration of the methyl groups followed by regeneration of the apoprotein. 2H NMR studies of aligned membrane samples were conducted under conditions where rotational and translational diffusion of the protein were absent on the NMR time scale. The theoretical lineshape treatment involved a static axial distribution of rotating C-C2H3 groups about the local membrane frame, together with the static axial distribution of the local normal relative to the average normal. Simulation of solid-state 2H NMR lineshapes gave both the methyl group orientations and the alignment disorder (mosaic spread) of the membrane stack. The methyl bond orientations provided the angular restraints for structural analysis. In the case of bR the retinal chromophore is nearly planar in the dark- and all-trans light-adapted states, as well upon isomerization to 13-cis in the M state. The C13-methyl group at the "business end" of the chromophore changes its orientation to the membrane upon photon absorption, moving towards W182 and thus driving the proton pump in energy conservation. Moreover, rhodopsin was studied as a prototype for G protein-coupled receptors (GPCRs) implicated in many biological responses in humans. In contrast to bR, the retinal chromophore of rhodopsin has an 11-cis conformation and is highly twisted in the dark state. Three sites of interaction affect the torsional deformation of retinal, viz. the protonated Schiff base with its carboxylate counterion; the C9-methyl group of the polyene; and the β-ionone ring within its hydrophobic pocket. For rhodopsin, the strain energy and dynamics of retinal as established by 2H NMR are implicated in substituent control of activation. Retinal is locked in a conformation that is twisted in the direction of the photoisomerization, which explains the dark stability of rhodopsin and allows for ultra-fast isomerization upon absorption of a photon. Torsional strain is relaxed in the meta I state that precedes subsequent receptor activation. Comparison of the two retinal proteins using solid-state 2H NMR is thus illuminating in terms of their different biological functions.

AB - Solid-state 2H NMR spectroscopy gives a powerful avenue to investigating the structures of ligands and cofactors bound to integral membrane proteins. For bacteriorhodopsin (bR) and rhodopsin, retinal was site-specifically labeled by deuteration of the methyl groups followed by regeneration of the apoprotein. 2H NMR studies of aligned membrane samples were conducted under conditions where rotational and translational diffusion of the protein were absent on the NMR time scale. The theoretical lineshape treatment involved a static axial distribution of rotating C-C2H3 groups about the local membrane frame, together with the static axial distribution of the local normal relative to the average normal. Simulation of solid-state 2H NMR lineshapes gave both the methyl group orientations and the alignment disorder (mosaic spread) of the membrane stack. The methyl bond orientations provided the angular restraints for structural analysis. In the case of bR the retinal chromophore is nearly planar in the dark- and all-trans light-adapted states, as well upon isomerization to 13-cis in the M state. The C13-methyl group at the "business end" of the chromophore changes its orientation to the membrane upon photon absorption, moving towards W182 and thus driving the proton pump in energy conservation. Moreover, rhodopsin was studied as a prototype for G protein-coupled receptors (GPCRs) implicated in many biological responses in humans. In contrast to bR, the retinal chromophore of rhodopsin has an 11-cis conformation and is highly twisted in the dark state. Three sites of interaction affect the torsional deformation of retinal, viz. the protonated Schiff base with its carboxylate counterion; the C9-methyl group of the polyene; and the β-ionone ring within its hydrophobic pocket. For rhodopsin, the strain energy and dynamics of retinal as established by 2H NMR are implicated in substituent control of activation. Retinal is locked in a conformation that is twisted in the direction of the photoisomerization, which explains the dark stability of rhodopsin and allows for ultra-fast isomerization upon absorption of a photon. Torsional strain is relaxed in the meta I state that precedes subsequent receptor activation. Comparison of the two retinal proteins using solid-state 2H NMR is thus illuminating in terms of their different biological functions.

KW - Bacteriorhodopsin

KW - G protein-coupled receptor

KW - Membrane

KW - Proton pump

KW - Retinal

KW - Rhodopsin

KW - Solid-state NMR

KW - Vision

UR - http://www.scopus.com/inward/record.url?scp=36849045169&partnerID=8YFLogxK

U2 - 10.1016/j.bbamem.2007.10.014

DO - 10.1016/j.bbamem.2007.10.014

M3 - Review article

C2 - 18021739

VL - 1768

SP - 2979

EP - 3000

JO - Biochimica et Biophysica Acta - Biomembranes

JF - Biochimica et Biophysica Acta - Biomembranes

SN - 0005-2736

IS - 12

ER -