101
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Crystal structure of the ligand-free G-protein-coupled receptor opsin. Nature 2008; 454:183-7. [PMID: 18563085 DOI: 10.1038/nature07063] [Citation(s) in RCA: 719] [Impact Index Per Article: 44.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2008] [Accepted: 05/09/2008] [Indexed: 01/02/2023]
Abstract
In the G-protein-coupled receptor (GPCR) rhodopsin, the inactivating ligand 11-cis-retinal is bound in the seven-transmembrane helix (TM) bundle and is cis/trans isomerized by light to form active metarhodopsin II. With metarhodopsin II decay, all-trans-retinal is released, and opsin is reloaded with new 11-cis-retinal. Here we present the crystal structure of ligand-free native opsin from bovine retinal rod cells at 2.9 ångström (A) resolution. Compared to rhodopsin, opsin shows prominent structural changes in the conserved E(D)RY and NPxxY(x)(5,6)F regions and in TM5-TM7. At the cytoplasmic side, TM6 is tilted outwards by 6-7 A, whereas the helix structure of TM5 is more elongated and close to TM6. These structural changes, some of which were attributed to an active GPCR state, reorganize the empty retinal-binding pocket to disclose two openings that may serve the entry and exit of retinal. The opsin structure sheds new light on ligand binding to GPCRs and on GPCR activation.
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102
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Mechanism of signal propagation upon retinal isomerization: insights from molecular dynamics simulations of rhodopsin restrained by normal modes. Biophys J 2008; 95:789-803. [PMID: 18390613 DOI: 10.1529/biophysj.107.120691] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
As one of the best studied members of the pharmaceutically relevant family of G-protein-coupled receptors, rhodopsin serves as a prototype for understanding the mechanism of G-protein-coupled receptor activation. Here, we aim at exploring functionally relevant conformational changes and signal transmission mechanisms involved in its photoactivation brought about through a cis-trans photoisomerization of retinal. For this exploration, we propose a molecular dynamics simulation protocol that utilizes normal modes derived from the anisotropic network model for proteins. Deformations along multiple low-frequency modes of motion are used to efficiently sample collective conformational changes in the presence of explicit membrane and water environment, consistent with interresidue interactions. We identify two highly stable regions in rhodopsin, one clustered near the chromophore, the other near the cytoplasmic ends of transmembrane helices H1, H2, and H7. Due to redistribution of interactions in the neighborhood of retinal upon stabilization of the trans form, local structural rearrangements in the adjoining H3-H6 residues are efficiently propagated to the cytoplasmic end of these particular helices. In the structures obtained by our simulations, all-trans retinal interacts with Cys(167) on H4 and Phe(203) on H5, which were not accessible in the dark state, and exhibits stronger interactions with H5, while some of the contacts made (in the cis form) with H6 are lost.
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103
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Rapid incorporation of functional rhodopsin into nanoscale apolipoprotein bound bilayer (NABB) particles. J Mol Biol 2008; 377:1067-81. [PMID: 18313692 DOI: 10.1016/j.jmb.2008.01.066] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2007] [Revised: 01/18/2008] [Accepted: 01/22/2008] [Indexed: 11/23/2022]
Abstract
Human apolipoprotein A-I (apo A-I) and its engineered constructs form discoidal lipid bilayers upon interaction with lipids in vitro. We now report the cloning, expression, and purification of apo A-I derived from zebrafish (Danio rerio), which combines with phospholipids to form similar discoidal bilayers and may prove to be superior to human apo A-I constructs for rapid reconstitution of seven-transmembrane helix receptors into nanoscale apolipoprotein bound bilayers (NABBs). We characterized NABBs by gel-filtration chromatography, native polyacrylamide gradient gel electrophoresis, UV-visible photobleaching difference spectroscopy, and fluorescence spectroscopy. We used electron microscopy to determine the stoichiometry and orientation of rhodopsin (rho)-containing NABBs prepared under various conditions and correlated stability and signaling efficiency of rho in NABBs with either one or two receptors. We discovered that the specific activity of G protein coupling for single rhos sequestered in individual NABBs was nearly identical with that of two rhos per NABB under conditions where stoichiometry and orientation could be inferred by electron microscopy imaging. Thermal stability of rho in NABBs was superior to that of rho in various commonly used detergents. We conclude that the NABB system using engineered zebrafish apo A-I is a native-like membrane mimetic system for G-protein-coupled receptors and discuss strategies for rapid incorporation of expressed membrane proteins into NABBs.
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104
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McKibbin C, Toye AM, Reeves PJ, Khorana HG, Edwards PC, Villa C, Booth PJ. Opsin Stability and Folding: The Role of Cys185 and Abnormal Disulfide Bond Formation in the Intradiscal Domain. J Mol Biol 2007; 374:1309-18. [DOI: 10.1016/j.jmb.2007.10.013] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2007] [Revised: 09/11/2007] [Accepted: 10/01/2007] [Indexed: 10/22/2022]
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105
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Whorton MR, Jastrzebska B, Park PSH, Fotiadis D, Engel A, Palczewski K, Sunahara RK. Efficient coupling of transducin to monomeric rhodopsin in a phospholipid bilayer. J Biol Chem 2007; 283:4387-94. [PMID: 18033822 DOI: 10.1074/jbc.m703346200] [Citation(s) in RCA: 218] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
G protein-coupled receptors (GPCRs) are seven transmembrane domain proteins that transduce extracellular signals across the plasma membrane and couple to the heterotrimeric family of G proteins. Like most intrinsic membrane proteins, GPCRs are capable of oligomerization, the function of which has only been established for a few different receptor systems. One challenge in understanding the function of oligomers relates to the inability to separate monomeric and oligomeric receptor complexes in membrane environments. Here we report the reconstitution of bovine rhodopsin, a GPCR expressed in the retina, into an apolipoprotein A-I phospholipid particle, derived from high density lipoprotein (HDL). We demonstrate that rhodopsin, when incorporated into these 10 nm reconstituted HDL (rHDL) particles, is monomeric and functional. Rhodopsin.rHDL maintains the appropriate spectral properties with respect to photoactivation and formation of the active form, metarhodopsin II. Additionally, the kinetics of metarhodopsin II decay is similar between rhodopsin in native membranes and rhodopsin in rHDL particles. Photoactivation of monomeric rhodopsin.rHDL also results in the rapid activation of transducin, at a rate that is comparable with that found in native rod outer segments and 20-fold faster than rhodopsin in detergent micelles. These data suggest that monomeric rhodopsin is the minimal functional unit in G protein activation and that oligomerization is not absolutely required for this process.
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Affiliation(s)
- Matthew R Whorton
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0632, USA
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106
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Tastan O, Yu E, Ganapathiraju M, Aref A, Rader AJ, Klein-Seetharaman J. Comparison of stability predictions and simulated unfolding of rhodopsin structures. Photochem Photobiol 2007; 83:351-62. [PMID: 17576347 DOI: 10.1562/2006-06-20-ra-942] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Developing a better mechanistic understanding of membrane protein folding is urgently needed because of the discovery of an increasing number of human diseases, where membrane protein instability and misfolding is involved. Towards this goal, we investigated folding and stability of 7-transmembrane (TM) helical bundles by computational methods. We compared the results of three different algorithms for predicting changes in stability of proteins against an experimental mutation dataset obtained for bacteriorhodopsin (BR) and mammalian rhodopsin and find that 61.6% and 70.6% of the mutation results can potentially be explained by known local contributors to the stability of the folded state of BR and mammalian rhodopsin, respectively. To obtain further information on the predicted folding pathway of 7-TM proteins, we conducted simulated thermal unfolding experiments of all available rhodopsin structures with resolution better than 3 angstroms using the Floppy Inclusions and Rigid Substructure Topography (FIRST) method (Jacobs, D. J., A. J. Rader, L. A. Kuhn and M. F. Thorpe [2001] Proteins 44, 150) described previously for a single mammalian rhodopsin structure (Rader et al. [2004] PNAS 101, 7246). In statistical comparison we found that structures of mammalian rhodopsin have a stability core that is characterized by long-range interactions involving amino acids close in space but distant in sequence comprising positions from both extracellular loop and TM regions. In contrast, BR-simulated unfolding does not reveal such a core but is dominated by interactions within individual and groups of TM helices, consistent with the two-stage hypothesis of membrane protein folding. Similar results were obtained for halo- and sensory rhodopsins as for BRs. However, the average folding core energies of sensory rhodopsins were in between those observed for mammalian rhodopsins and BRs hinting at a possible evolution of these structures toward a rhodopsin-like behavior. These results support the conclusion that although the two-stage model can explain the mechanisms of folding and stability of BR, it fails to account for the folding and stability of mammalian rhodopsin, even though the two proteins are structurally related.
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Affiliation(s)
- Oznur Tastan
- Language Technologies Institute, School of Computer Science, Carnegie Mellon University, Pittsburgh, PA, USA
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107
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Wu Q, Blakeley LR, Cornwall MC, Crouch RK, Wiggert BN, Koutalos Y. Interphotoreceptor retinoid-binding protein is the physiologically relevant carrier that removes retinol from rod photoreceptor outer segments. Biochemistry 2007; 46:8669-79. [PMID: 17602665 PMCID: PMC2568998 DOI: 10.1021/bi7004619] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Light detection by vertebrate rod photoreceptor outer segments results in the destruction of the visual pigment, rhodopsin, as its retinyl moiety is photoisomerized from 11-cis to all-trans. The regeneration of rhodopsin is necessary for vision and begins with the release of the all-trans retinal and its reduction to all-trans retinol. Retinol is then transported out of the rod outer segment for further processing. We used fluorescence imaging to monitor retinol fluorescence and quantify the kinetics of its formation and clearance after rhodopsin bleaching in the outer segments of living isolated frog (Rana pipiens) rod photoreceptors. We independently measured the release of all-trans retinal from bleached rhodopsin in frog rod outer segment membranes and the rate of all-trans retinol removal by the lipophilic carriers interphotoreceptor retinoid binding protein (IRBP) and serum albumin. We find that the kinetics of all-trans retinol formation in frog rod outer segments after rhodopsin bleaching are to a good first approximation determined by the kinetics of all-trans retinal release from the bleached pigment. For the physiological concentrations of carriers, the rate of retinol removal from the outer segment is determined by IRBP concentration, whereas the effect of serum albumin is negligible. The results indicate the presence of a specific interaction between IRBP and the rod outer segment, probably mediated by a receptor. The effect of different concentrations of IRBP on the rate of retinol removal shows no cooperativity and has an EC50 of 40 micromol/L.
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Affiliation(s)
| | | | | | | | | | - Yiannis Koutalos
- * Corresponding author, Tel: (843)-792-9180, Fax: (843)-792-1723, e-mail:
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108
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Isin B, Rader AJ, Dhiman HK, Klein-Seetharaman J, Bahar I. Predisposition of the dark state of rhodopsin to functional changes in structure. Proteins 2007; 65:970-83. [PMID: 17009319 DOI: 10.1002/prot.21158] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
As the only member of the family of G-protein-coupled receptors for which atomic coordinates are available, rhodopsin is widely studied for insight into the molecular mechanism of G-protein-coupled receptor activation. The currently available structures refer to the inactive, dark state, of rhodopsin, rather than the light-activated metarhodopsin II (Meta II) state. A model for the Meta II state is proposed here by analyzing elastic network normal modes in conjunction with experimental data. Key mechanical features and interactions broken/formed in the proposed model are found to be consistent with the experimental data. The model is further tested by using a set of Meta II fluorescence decay rates measured to empirically characterize the deactivation of rhodopsin mutants. The model is found to correctly predict 93% of the experimentally observed effects in 119 rhodopsin mutants for which the decay rates and misfolding data have been measured, including a systematic analysis of Cys-->Ser replacements reported here. Based on the detailed comparison between model and experiments, a cooperative activation mechanism is deduced that couples retinal isomerization to concerted changes in conformation, facilitated by the intrinsic dynamics of rhodopsin. A global hinge site is identified near the retinal-binding pocket that ensures the efficient propagation of signals from the central transmembrane region to both cytoplasmic and extracellular ends. The predicted activation mechanism opens the transmembrane helices at the critical G-protein binding cytoplasmic domain. This model provides a detailed, mechanistic description of the activation process, extending experimental observations and yielding new insights for further tests.
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Affiliation(s)
- Basak Isin
- Department of Computational Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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109
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Bartl FJ, Vogel R. Structural and functional properties of metarhodopsin III: recent spectroscopic studies on deactivation pathways of rhodopsin. Phys Chem Chem Phys 2007; 9:1648-58. [PMID: 17396175 DOI: 10.1039/b616365c] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The activation of rhodopsin has been the focus of researchers over the past decades, revealing many aspects of the activation pathways of this prototypical G protein-coupled receptor on a molecular level, starting with the light-dependent isomerization of its retinal chromophore from 11-cis to all-trans and leading eventually to the large scale helix movements in the transition to the active receptor state, Meta II. Comparatively little is known, however, on the deactivation pathways of the light receptor, which represent essential steps in maintaining a functional photoreceptor cell. Rhodopsin's active receptor species, Meta II, decays by two fundamentally different pathways, either forming the apoprotein opsin by release of the activating all-trans retinal ligand from its binding pocket, or by a thermal isomerization of this ligand to a less activating species in the transition to metarhodopsin III (Meta III). Both decay products, opsin and Meta III, are largely inactive under physiological conditions, yet they do not restore the complete inactivity of the dark state. Although some properties of Meta III have been described already in the 1960s, its molecular nature and the pathways of its formation have remained rather obscure. In this review, we focus on recent studies from our laboratories, which have provided a major progress in our understanding of the Meta III deactivation pathway and its potential physiological roles. Using Fourier-transform infrared (FTIR) difference spectroscopy in combination with a variety of other spectroscopic and biochemical techniques and quantum chemical calculations, we have developed a general picture of the interplay between the retinal ligand and the receptor protein, which is compared to similar reaction mechanisms in invertebrate photoreceptors and microbial retinal proteins.
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Affiliation(s)
- Franz J Bartl
- Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, Campus Charité Mitte, Schumannstrasse 20-21, 10015, Berlin, Germany.
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110
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Abdulaev NG, Ngo T, Ramon E, Brabazon DM, Marino JP, Ridge KD. The receptor-bound "empty pocket" state of the heterotrimeric G-protein alpha-subunit is conformationally dynamic. Biochemistry 2006; 45:12986-97. [PMID: 17059215 DOI: 10.1021/bi061088h] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Heterotrimeric G-protein activation by a G-protein-coupled receptor (GPCR) requires the propagation of structural signals from the receptor-interacting surfaces to the guanine nucleotide-binding pocket. To probe conformational changes in the G-protein alpha-subunit (G(alpha)) associated with activated GPCR (R*) interactions and guanine nucleotide exchange, high-resolution solution NMR methods are being applied in studying signaling of the G-protein, transducin, by light-activated rhodopsin. Using these methods, we recently demonstrated that an isotope-labeled G(alpha) reconstituted heterotrimer forms functional complexes under NMR experimental conditions with light-activated, detergent-solubilized rhodopsin and a soluble mimic of R*, both of which trigger guanine nucleotide exchange [Ridge, K. D., et al. (2006) J. Biol. Chem. 281, 7635-7648]. Here, it is shown that both light-activated rhodopsin and the soluble mimic of R form trapped intermediate complexes with a GDP-released "empty pocket" state of the heterotrimer in the absence of GTP (or GTPgammaS). In contrast to guanine nucleotide-bound forms of G(alpha), the NMR spectra of the GDP-released, R-bound empty pocket state of G(alpha) display severe line broadening suggestive of a dynamic intermediate state. Interestingly, the conformation of a GDP-depleted, Mg(2+)-bound state of G(alpha) generated in a manner independent of R* does not exhibit a similar degree of line broadening but rather appears structurally similar to the GDP/Mg(2+)-bound form of the protein. Taken together, these results suggest that R*-mediated changes in the receptor-interacting regions of G(alpha), and not the absence of bound guanine nucleotide, are the predominant factors which dictate G(alpha) conformation and dynamics in this R*-bound state of the heterotrimer.
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Affiliation(s)
- Najmoutin G Abdulaev
- Center for Advanced Research in Biotechnology, University of Maryland Biotechnology Institute and National Institute of Standards and Technology, Rockville, Maryland 20850, USA
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111
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Salom D, Lodowski DT, Stenkamp RE, Trong IL, Golczak M, Jastrzebska B, Harris T, Ballesteros JA, Palczewski K. Crystal structure of a photoactivated deprotonated intermediate of rhodopsin. Proc Natl Acad Sci U S A 2006; 103:16123-8. [PMID: 17060607 PMCID: PMC1637547 DOI: 10.1073/pnas.0608022103] [Citation(s) in RCA: 372] [Impact Index Per Article: 20.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2006] [Indexed: 11/18/2022] Open
Abstract
The changes that lead to activation of G protein-coupled receptors have not been elucidated at the structural level. In this work we report the crystal structures of both ground state and a photoactivated deprotonated intermediate of bovine rhodopsin at a resolution of 4.15 A. In the photoactivated state, the Schiff base linking the chromophore and Lys-296 becomes deprotonated, reminiscent of the G protein-activating state, metarhodopsin II. The structures reveal that the changes that accompany photoactivation are smaller than previously predicted for the metarhodopsin II state and include changes on the cytoplasmic surface of rhodopsin that possibly enable the coupling to its cognate G protein, transducin. Furthermore, rhodopsin forms a potentially physiologically relevant dimer interface that involves helices I, II, and 8, and when taken with the prior work that implicates helices IV and V as the physiological dimer interface may account for one of the interfaces of the oligomeric structure of rhodopsin seen in the membrane by atomic force microscopy. The activation and oligomerization models likely extend to the majority of other G protein-coupled receptors.
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Affiliation(s)
- David Salom
- *Novasite Pharmaceuticals, Inc., San Diego, CA 92121
| | - David T. Lodowski
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106; and
| | - Ronald E. Stenkamp
- Departments of Biological Structure and Biochemistry and Biomolecular Structure Center, University of Washington, Seattle, WA 98195
| | - Isolde Le Trong
- Departments of Biological Structure and Biochemistry and Biomolecular Structure Center, University of Washington, Seattle, WA 98195
| | - Marcin Golczak
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106; and
| | - Beata Jastrzebska
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106; and
| | - Tim Harris
- *Novasite Pharmaceuticals, Inc., San Diego, CA 92121
| | | | - Krzysztof Palczewski
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106; and
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112
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Sommer ME, Farrens DL. Arrestin can act as a regulator of rhodopsin photochemistry. Vision Res 2006; 46:4532-46. [PMID: 17069872 PMCID: PMC2877124 DOI: 10.1016/j.visres.2006.08.031] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2006] [Revised: 08/11/2006] [Accepted: 08/16/2006] [Indexed: 11/24/2022]
Abstract
We report that visual arrestin can regulate retinal release and late photoproduct formation in rhodopsin. Our experiments, which employ a fluorescently labeled arrestin and rhodopsin solubilized in detergent/phospholipid micelles, indicate that arrestin can trap a population of retinal in the binding pocket with an absorbance characteristic of Meta II with the retinal Schiff-base intact. Furthermore, arrestin can convert Metarhodopsin III (formed either by thermal decay or blue-light irradiation) to a Meta II-like absorbing species. Together, our results suggest arrestin may be able to play a more complex role in the rod cell besides simply quenching transducin activity. This possibility may help explain why arrestin deficiency leads to problems like stationary night blindness (Oguchi disease) and retinal degeneration.
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Affiliation(s)
| | - David L. Farrens
- Corresponding author. Fax: +1 503 494 8393. E-mail address: (D.L. Farrens)
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113
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Zhu L, Imanishi Y, Filipek S, Alekseev A, Jastrzebska B, Sun W, Saperstein DA, Palczewski K. Autosomal recessive retinitis pigmentosa and E150K mutation in the opsin gene. J Biol Chem 2006; 281:22289-22298. [PMID: 16737970 PMCID: PMC1618956 DOI: 10.1074/jbc.m602664200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Retinitis pigmentosa (RP) is a heterogeneous group of hereditary disorders of the retina caused by mutation in genes of the photoreceptor proteins with an autosomal dominant (adRP), autosomal recessive (arRP), or X-linked pattern of inheritance. Although there are over 100 identified mutations in the opsin gene associated with RP, only a few of them are inherited with the arRP pattern. E150K is the first reported missense mutation associated with arRP. This opsin mutation is located in the second cytoplasmic loop of this G protein-coupled receptor. E150K opsin expressed in HEK293 cells and reconstituted with 11-cis-retinal displayed an absorption spectrum similar to the wild type (WT) counterpart and activated G protein transducin slightly faster than WT receptor. However, the majority of E150K opsin showed a higher apparent molecular mass in SDS-PAGE and was resistant to endoglycosidase H deglycosidase. Instead of being transported to the plasma membrane, E150K opsin is partially colocalized with the cis/medial Golgi compartment markers such as GM130 and Vti1b but not with the trans-Golgi network. In contrast to the endoplasmic reticulum-retained adRP mutant, P23H opsin, Golgi-retained E150K opsin did not influence the proper transport of the WT opsin when coexpressed in HEK293 cells. This result is consistent with the recessive pattern of inheritance of this mutation. Thus, our study reveals a novel molecular mechanism for retinal degeneration that results from deficient export of opsin from the Golgi apparatus.
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Affiliation(s)
- Li Zhu
- Department of Chemistry, University of Washington, Seattle, Washington 98195
| | - Yoshikazu Imanishi
- Department of Pharmacology, Case School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
| | - Sławomir Filipek
- International Institute of Molecular and Cell Biology, 02-109 Warsaw, Poland
| | - Andrei Alekseev
- Department of Ophthalmology, University of Washington, Seattle, Washington 98195
| | - Beata Jastrzebska
- Department of Pharmacology, Case School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
| | - Wenyu Sun
- Department of Pharmacology, Case School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
| | - David A Saperstein
- Department of Ophthalmology, University of Washington, Seattle, Washington 98195
| | - Krzysztof Palczewski
- Department of Pharmacology, Case School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106.
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114
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Jastrzebska B, Fotiadis D, Jang GF, Stenkamp RE, Engel A, Palczewski K. Functional and structural characterization of rhodopsin oligomers. J Biol Chem 2006; 281:11917-22. [PMID: 16495215 PMCID: PMC1618955 DOI: 10.1074/jbc.m600422200] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A major question in G protein-coupled receptor signaling concerns the quaternary structure required for signal transduction. Do these transmembrane receptors function as monomers, dimers, or larger oligomers? We have investigated the oligomeric state of the model G protein-coupled receptor rhodopsin (Rho), which absorbs light and initiates a phototransduction-signaling cascade that forms the basis of vision. In this study, different forms of Rho were isolated using gel filtration techniques in mild detergents, including n-dodecyl-beta-D-maltoside, n-tetradecyl-beta-D-maltoside, and n-hexadecyl-beta-D-maltoside. The quaternary structure of isolated Rho was determined by transmission electron microscopy, demonstrating that in micelles containing n-dodecyl-beta-D-maltoside, Rho exists as a mixture of monomers and dimers whereas in n-tetradecyl-beta-D-maltoside and n-hexadecyl-beta-D-maltoside Rho forms higher ordered structures. Especially in n-hexadecyl-beta-D-maltoside, most of the particles are present in tightly packed rows of dimers. The oligomerization of Rho seems to be important for interaction with its cognate G protein, transducin. Although the activated Rho (Meta II) monomer or dimers are capable of activating the G protein, transducin, the activation process is much faster when Rho exists as organized dimers. Our studies provide direct comparisons between signaling properties of Meta II in different quaternary complexes.
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Affiliation(s)
- Beata Jastrzebska
- From the Department of Pharmacology, Case School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
| | - Dimitrios Fotiadis
- M. E. Müller Institute for Microscopy, Biozentrum, University of Basel, CH-4056 Basel, Switzerland, and Departments of
| | | | - Ronald E. Stenkamp
- Biological Structure, and
- Biochemistry and the
- Biomolecular Structure Center, University of Washington, Seattle, Washington 98195
| | - Andreas Engel
- M. E. Müller Institute for Microscopy, Biozentrum, University of Basel, CH-4056 Basel, Switzerland, and Departments of
| | - Krzysztof Palczewski
- From the Department of Pharmacology, Case School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
- To whom correspondence should be addressed: Dept. of Pharmacology, School of Medicine, Case Western Reserve University, BRB Bldg., 10900 Euclid Ave, Cleveland, OH 44106-4965. E-mail:
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115
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Sommer ME, Smith WC, Farrens DL. Dynamics of arrestin-rhodopsin interactions: acidic phospholipids enable binding of arrestin to purified rhodopsin in detergent. J Biol Chem 2006; 281:9407-17. [PMID: 16428804 DOI: 10.1074/jbc.m510037200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We report that acidic phospholipids can restore the binding of visual arrestin to purified rhodopsin solubilized in n-dodecyl-beta-d-maltopyranoside. We used this finding to investigate the interplay between arrestin binding and the status of the retinal chromophore ligand in the receptor binding pocket. Our results showed that arrestin can interact with the late photoproduct Meta III and convert it to a Meta II-like species. Interestingly in these mixed micelles, the release of retinal and arrestin was no longer directly coupled as it is in the native rod disk membrane. For example, up to approximately 50% of the retinal could be released even though arrestin remains bound to the receptor in a long lived complex. We anticipate that this new ability to study these proteins in a defined, purified system will facilitate further structural and dynamic studies of arrestin-rhodopsin interactions.
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Affiliation(s)
- Martha E Sommer
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239-3098, USA
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116
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Ridge KD, Abdulaev NG, Zhang C, Ngo T, Brabazon DM, Marino JP. Conformational changes associated with receptor-stimulated guanine nucleotide exchange in a heterotrimeric G-protein alpha-subunit: NMR analysis of GTPgammaS-bound states. J Biol Chem 2006; 281:7635-48. [PMID: 16407225 DOI: 10.1074/jbc.m509851200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Solution NMR studies of a (15)N-labeled G-protein alpha-subunit (G(alpha)) chimera ((15)N-ChiT)-reconstituted heterotrimer have shown previously that G-protein betagamma-subunit (G(betagamma)) association induces a "pre-activated" conformation that likely facilitates interaction with the agonist-activated form of a G-protein-coupled receptor (R*) and guanine nucleotide exchange (Abdulaev, N. G., Ngo, T., Zhang, C., Dinh, A., Brabazon, D. M., Ridge, K. D., and Marino, J. P. (2005) J. Biol. Chem. 280, 38071-38080). Here we demonstrated that the (15)N-ChiT-reconstituted heterotrimer can form functional complexes under NMR experimental conditions with light-activated, detergent-solubilized rhodopsin (R*), as well as a soluble mimic of R*. NMR methods were used to track R*-triggered guanine nucleotide exchange and release of guanosine 5'-O-3-thiotriphosphate (GTPgammaS)/Mg(2+)-bound ChiT. A heteronuclear single quantum correlation (HSQC) spectrum of R*-generated GTPgammaS/Mg(2+)-bound ChiT revealed (1)HN, (15)N chemical shift changes relative to GDP/Mg(2+)-bound ChiT that were similar, but not identical, to those observed for the GDP.AlF(4)(-)/Mg(2+)-bound state. Line widths observed for R*-generated GTPgammaS/Mg(2+)-bound (15)N-ChiT, however, indicated that it is more conformationally dynamic relative to the GDP/Mg(2+)- and GDP.AlF(4)(-)/Mg(2+)-bound states. The increased dynamics appeared to be correlated with G(betagamma) and R* interactions because they are not observed for GTPgammaS/Mg(2+)-bound ChiT generated independently of R*. In contrast to R*, a soluble mimic that does not catalytically interact with G-protein (Abdulaev, N. G., Ngo, T., Chen, R., Lu, Z., and Ridge, K. D. (2000) J. Biol. Chem. 275, 39354-39363) is found to form a stable complex with the GTPgammaS/Mg(2+)-exchanged heterotrimer. The HSQC spectrum of (15)N-ChiT in this complex displays a unique chemical shift pattern that nonetheless shares similarities with the heterotrimer and GTPgammaS/Mg(2+)-bound ChiT. Overall, these results demonstrated that R*-induced changes in G(alpha) can be followed by NMR and that guanine nucleotide exchange can be uncoupled from heterotrimer dissociation.
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Affiliation(s)
- Kevin D Ridge
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center, Houston, TX 77030, USA.
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117
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Maiti P, Gollapalli D, Rando RR. Specificity of Binding of all-trans-Retinyl Ester to RPE65. Biochemistry 2005; 44:14463-9. [PMID: 16262246 DOI: 10.1021/bi0510779] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Membrane-bound RPE65 (mRPE65) is a binding protein for all-trans-retinyl esters, which are the substrates for the isomerization reaction that completes the visual cycle. RPE65 is essential for rhodopsin regeneration and, hence, for vision. As RPE65 appears to be part of the rate-limiting pathway in the visual cycle, specific antagonists of the molecule will be important in evaluating its full physiological role. The protein is known to stereoselectively bind all-trans-retinyl esters (tREs), with dissociation constants in the 50 nM range. This study explores the overall binding specificity of RPE65 with respect to both retinoids and other isoprenoids in an effort to define the specificity of binding, and to begin the process of designing specific antagonists for it. The nature of the specificity directed toward the three main structural elements (retinoid, linker, and acyl moieties) in the tRE molecule is reported. In the all-trans-retinyl ester series, binding affinity increased as a function of the hydrophobicity of the fatty acyl group. In the linker region, binding affinities were little affected by amide, ketone, and ether replacements for the carboxy ester moiety of the naturally occurring tRE ligand. Finally, modifications in the all-trans-retinoid moiety are also tolerated. For example, E,E-farnesyl palmitate binds with approximately the same affinity as does all-trans-retinyl palmitate. Other isoprenoid analogues also bind, as do truncated retinoids in the beta-ionone series. Therefore, mRPE65 is a moderately specific retinoid binding protein directed at long chain all-trans-retinyl esters.
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Affiliation(s)
- Pranab Maiti
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 45 Shattuck Street, Boston, Massachusetts 02115, USA
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118
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Fanelli F, De Benedetti PG. Computational Modeling Approaches to Structure−Function Analysis of G Protein-Coupled Receptors. Chem Rev 2005; 105:3297-351. [PMID: 16159154 DOI: 10.1021/cr000095n] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Francesca Fanelli
- Dulbecco Telethon Institute and Department of Chemistry, University of Modena and Reggio Emilia, via Campi 183, 41100 Modena, Italy.
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119
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Bartl FJ, Fritze O, Ritter E, Herrmann R, Kuksa V, Palczewski K, Hofmann KP, Ernst OP. Partial agonism in a G Protein-coupled receptor: role of the retinal ring structure in rhodopsin activation. J Biol Chem 2005; 280:34259-67. [PMID: 16027155 DOI: 10.1074/jbc.m505260200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The visual process in rod cells is initiated by absorption of a photon in the rhodopsin retinal chromophore and consequent retinal cis/trans-isomerization. The ring structure of retinal is thought to be needed to transmit the photonic energy into conformational changes culminating in the active metarhodopsin II (Meta II) intermediate. Here, we demonstrate that cis-acyclic retinals, lacking four carbon atoms of the ring, can activate rhodopsin. Detailed analysis of the activation pathway showed that, although the photoproduct pathway is more complex, Meta II formed with almost normal kinetics. However, lack of the ring structure resulted in a low amount of Meta II and a fast decay of activity. We conclude that the main role of the ring structure is to maintain the active state, thus specifying a mechanism of activation by a partial agonist of the G protein-coupled receptor rhodopsin.
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Affiliation(s)
- Franz J Bartl
- Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, Schumannstrasse 20/21, D-10098 Berlin, Germany.
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120
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Tsukamoto H, Terakita A, Shichida Y. A rhodopsin exhibiting binding ability to agonist all-trans-retinal. Proc Natl Acad Sci U S A 2005; 102:6303-8. [PMID: 15851682 PMCID: PMC1088369 DOI: 10.1073/pnas.0500378102] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Rhodopsins are the members of the family of G protein-coupled receptors that have diverged from ligand-binding receptors into photoreceptive pigments. Vertebrate rhodopsins are able to bind the inverse agonist 11-cis-retinal but are unable to bind the agonist all-trans-retinal, indicating that vertebrate rhodopsin changed its binding ability during the course of molecular evolution. Here, we show that unlike vertebrate rhodopsin, amphioxus rhodopsin is still able to bind the agonist all-trans-retinal. The opsin of amphioxus rhodopsin can also bind 11-cis-retinal to form a photoreceptive pigment that can convert to a red-shifted photoproduct through cis-trans isomerization of the chromophore upon photon absorption. The red-shifted photoproduct is the stable G protein activating state. Incubation of the opsin with all-trans-retinal produces a G protein activating state that is spectroscopically and biochemically indistinguishable from the red-shifted photoproduct, indicating that the opsin possesses agonist-binding ability. The opsin exhibits an approximately 50-fold higher affinity for 11-cis-retinal than for all-trans-retinal, and mutational analyses revealed that Trp-265 situated in helix VI is important for the increase in binding affinity to 11-cis-retinal. These properties of amphioxus rhodopsin suggest that an ancestral rhodopsin increased the affinity for 11-cis-retinal by rearrangement of a structure including Trp-265 to act as a photoreceptor. In addition, an additional mechanism was acquired in vertebrate rhodopsin to prevent completely the binding of exogenous all-trans-retinal during molecular evolution.
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Affiliation(s)
- Hisao Tsukamoto
- Department of Biophysics, Graduate School of Science, Kyoto University and Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Kyoto 606-8502, Japan
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121
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Kim JM, Hwa J, Garriga P, Reeves PJ, RajBhandary UL, Khorana HG. Light-driven activation of beta 2-adrenergic receptor signaling by a chimeric rhodopsin containing the beta 2-adrenergic receptor cytoplasmic loops. Biochemistry 2005; 44:2284-92. [PMID: 15709741 DOI: 10.1021/bi048328i] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Structure-function studies of rhodopsin indicate that both intradiscal and transmembrane (TM) domains are required for retinal binding and subsequent light-induced structural changes in the cytoplasmic domain. Further, a hypothesis involving a common mechanism for activation of G-protein-coupled receptor (GPCR) has been proposed. To test this hypothesis, chimeric receptors were required in which the cytoplasmic domains of rhodopsin were replaced with those of the beta(2)-adrenergic receptor (beta(2)-AR). Their preparation required identification of the boundaries between the TM domain of rhodopsin and the cytoplasmic domain of the beta(2)-AR necessary for formation of the rhodopsin chromophore and its activation by light and subsequent optimal activation of beta(2)-AR signaling. Chimeric receptors were constructed in which the cytoplasmic loops of rhodopsin were replaced one at a time and in combination. In these replacements, size of the third cytoplasmic (EF) loop critically determined the extent of chromophore formation, its stability, and subsequent signal transduction specificity. All the EF loop replacements showed significant decreases in transducin activation, while only minor effects were observed by replacements of the CD and AB loops. Light-dependent activation of beta(2)-AR leading to Galphas signaling was observed only for the EF2 chimera, and its activation was further enhanced by replacements of the other loops. The results demonstrate coupling between light-induced conformational changes occurring in the transmembrane domain of rhodopsin and the cytoplasmic domain of the beta(2)-AR.
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Affiliation(s)
- Jong-Myoung Kim
- Department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
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122
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Maeda A, Maeda T, Imanishi Y, Kuksa V, Alekseev A, Bronson JD, Zhang H, Zhu L, Sun W, Saperstein DA, Rieke F, Baehr W, Palczewski K. Role of photoreceptor-specific retinol dehydrogenase in the retinoid cycle in vivo. J Biol Chem 2005; 280:18822-32. [PMID: 15755727 PMCID: PMC1283069 DOI: 10.1074/jbc.m501757200] [Citation(s) in RCA: 127] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The retinoid cycle is a recycling system that replenishes the 11-cis-retinal chromophore of rhodopsin and cone pigments. Photoreceptor-specific retinol dehydrogenase (prRDH) catalyzes reduction of all-trans-retinal to all-trans-retinol and is thought to be a key enzyme in the retinoid cycle. We disrupted mouse prRDH (human gene symbol RDH8) gene expression by targeted recombination and generated a homozygous prRDH knock-out (prRDH-/-) mouse. Histological analysis and electron microscopy of retinas from 6- to 8-week-old prRDH-/- mice revealed no structural differences of the photoreceptors or inner retina. For brief light exposure, absence of prRDH did not affect the rate of 11-cis-retinal regeneration or the decay of Meta II, the activated form of rhodopsin. Absence of prRDH, however, caused significant accumulation of all-trans-retinal following exposure to bright lights and delayed recovery of rod function as measured by electroretinograms and single cell recordings. Retention of all-trans-retinal resulted in slight overproduction of A2E, a condensation product of all-trans-retinal and phosphatidylethanolamine. We conclude that prRDH is an enzyme that catalyzes reduction of all-trans-retinal in the rod outer segment, most noticeably at higher light intensities and prolonged illumination, but is not an essential enzyme of the retinoid cycle.
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MESH Headings
- Alcohol Oxidoreductases/metabolism
- Alcohol Oxidoreductases/physiology
- Animals
- Blotting, Southern
- Catalysis
- Cell Line
- Cell Line, Tumor
- Chromatography, High Pressure Liquid
- DNA, Complementary/metabolism
- Electrophoresis, Polyacrylamide Gel
- Electroretinography
- Eye/metabolism
- Genetic Vectors
- Genotype
- Humans
- Immunoblotting
- Immunohistochemistry
- Insecta
- Kinetics
- Light
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Mice, Transgenic
- Microscopy, Electron, Transmission
- Models, Chemical
- Models, Genetic
- Mutation
- Phosphatidylethanolamines/metabolism
- Photoreceptor Cells, Vertebrate/metabolism
- Polymerase Chain Reaction
- RNA, Messenger/metabolism
- Recombination, Genetic
- Retina/metabolism
- Retinaldehyde/chemistry
- Retinoids/chemistry
- Retinoids/metabolism
- Rhodopsin/chemistry
- Rhodopsin/metabolism
- Time Factors
- Transgenes
- Vitamin A/metabolism
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Affiliation(s)
| | | | | | | | | | | | - Houbin Zhang
- Departments of Ophthalmology and Visual Sciences
- Neurobiology and Anatomy, University of Utah, Salt Lake City, Utah 84112
| | - Li Zhu
- From the Departments of Ophthalmology
| | - Wenyu Sun
- From the Departments of Ophthalmology
| | | | | | - Wolfgang Baehr
- Departments of Ophthalmology and Visual Sciences
- Biology, and
- Neurobiology and Anatomy, University of Utah, Salt Lake City, Utah 84112
| | - Krzysztof Palczewski
- From the Departments of Ophthalmology
- Pharmacology, and
- Chemistry, University of Washington, Seattle, Washington 98195 and the
- To whom correspondence should be addressed: Dept. of Ophthalmology, University of Washington, Box 356485, Seattle, WA 98195-6485. Tel.: 206-543-9074; Fax: 206-221-6784; E-mail:
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123
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Chen C, Tsina E, Cornwall MC, Crouch RK, Vijayaraghavan S, Koutalos Y. Reduction of all-trans retinal to all-trans retinol in the outer segments of frog and mouse rod photoreceptors. Biophys J 2004; 88:2278-87. [PMID: 15626704 PMCID: PMC1305277 DOI: 10.1529/biophysj.104.054254] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The first step in the Visual Cycle, the series of reactions that regenerate the vertebrate visual pigment rhodopsin, is the reduction of all-trans retinal to all-trans retinol, a reaction that requires NADPH. We have used the fluorescence of all-trans retinol to study this reduction in living rod photoreceptors. After the bleaching of rhodopsin, fluorescence (excitation, 360 nm; emission, 457 or 540 nm) appears in frog and wild-type mouse rod outer segments reaching a maximum in 30-60 min at room temperature. With this excitation and emission, the mitochondrial-rich ellipsoid region of the cells shows strong fluorescence as well. Fluorescence measurements at different emission wavelengths establish that the outer segment and ellipsoid signals originate from all-trans retinol and reduced pyridine nucleotides, respectively. Using outer segment fluorescence as a measure of all-trans retinol formation, we find that in frog rod photoreceptors the NADPH necessary for the reduction of all-trans retinal can be supplied by both cytoplasmic and mitochondrial metabolic pathways. Inhibition of the reduction reaction, either by retinoic acid or through suppression of metabolic activity, reduced the formation of retinol. Finally, there are no significant fluorescence changes after bleaching in the rod outer segments of Rpe65(-/-) mice, which lack 11-cis retinal.
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Affiliation(s)
- Chunhe Chen
- Department of Physiology and Biophysics, University of Colorado School of Medicine, Denver, Colorado, USA
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124
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Sommer ME, Smith WC, Farrens DL. Dynamics of arrestin-rhodopsin interactions: arrestin and retinal release are directly linked events. J Biol Chem 2004; 280:6861-71. [PMID: 15591052 DOI: 10.1074/jbc.m411341200] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In this study, we address the mechanism of visual arrestin release from light-activated rhodopsin using fluorescently labeled arrestin mutants. We find that two mutants, I72C and S251C, when labeled with the small, solvent-sensitive fluorophore monobromobimane, exhibit spectral changes only upon binding light-activated, phosphorylated rhodopsin. Our analysis indicates that these changes are probably due to a burying of the probes at these sites in the rhodopsin-arrestin or phospholipid-arrestin interface. Using a fluorescence approach based on this observation, we demonstrate that arrestin and retinal release are linked and are described by similar activation energies. However, at physiological temperatures, we find that arrestin slows the rate of retinal release approximately 2-fold and abolishes the pH dependence of retinal release. Using fluorescence, EPR, and biochemical approaches, we also find intriguing evidence that arrestin binds to a post-Meta II photodecay product, possibly Meta III. We speculate that arrestin regulates levels of free retinal in the rod cell to help limit the formation of damaging oxidative retinal adducts. Such adducts may contribute to diseases like atrophic age-related macular degeneration (AMD). Thus, arrestin may serve to both attenuate rhodopsin signaling and protect the cell from excessive retinal levels under bright light conditions.
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Affiliation(s)
- Martha E Sommer
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239-3098, USA
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125
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Janz JM, Farrens DL. Role of the Retinal Hydrogen Bond Network in Rhodopsin Schiff Base Stability and Hydrolysis. J Biol Chem 2004; 279:55886-94. [PMID: 15475355 DOI: 10.1074/jbc.m408766200] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Little is known about the molecular mechanism of Schiff base hydrolysis in rhodopsin. We report here our investigation into this process focusing on the role of amino acids involved in a hydrogen bond network around the retinal Schiff base. We find conservative mutations in this network (T94I, E113Q, S186A, E181Q, Y192F, and Y268F) increase the activation energy (E(a)) and abolish the concave Arrhenius plot normally seen for Schiff base hydrolysis in dark state rhodopsin. Interestingly, two mutants (T94I and E113Q) show dramatically faster rates of Schiff base hydrolysis in dark state rhodopsin, yet slower hydrolysis rates in the active MII form. We find deuterium affects the hydrolysis process in wild-type rhodopsin, exhibiting a specific isotope effect of approximately 2.5, and proton inventory studies indicate that multiple proton transfer events occur during the process of Schiff base hydrolysis for both dark state and MII forms. Taken together, our study demonstrates the importance of the retinal hydrogen bond network both in maintaining Schiff base integrity in dark state rhodopsin, as well as in catalyzing the hydrolysis and release of retinal from the MII form. Finally, we note that the dramatic alteration of Schiff base stability caused by mutation T94I may play a causative role in congenital night blindness as has been suggested by the Oprian and Garriga laboratories.
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Affiliation(s)
- Jay M Janz
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA
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126
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Jastrzebska B, Maeda T, Zhu L, Fotiadis D, Filipek S, Engel A, Stenkamp RE, Palczewski K. Functional characterization of rhodopsin monomers and dimers in detergents. J Biol Chem 2004; 279:54663-75. [PMID: 15489507 PMCID: PMC1351296 DOI: 10.1074/jbc.m408691200] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Rhodopsin (Rho) is a G protein-coupled receptor that initiates phototransduction in rod photoreceptors. High expression levels of Rho in the disc membranes of rod outer segments and the propensity of Rho to form higher oligomeric structures are evident from atomic force microscopy, transmission electron microscopy, and chemical cross-linking experiments. To explore the structural and functional properties of Rho in n-dodecyl-beta-maltoside, frequently used to purify heterologously expressed Rho and its mutants, we used gel filtration techniques, blue native gel electrophoresis, and functional assays. Here, we show that in micelles containing n-dodecyl-beta-maltoside at concentrations greater than 3 mM, Rho is present as a single monomer per detergent micelle. In contrast, in 12 mM 3-[(3-cholamidopropyl)dimethyl-ammonio]-1-propanesulfonate (CHAPS), micelles contain mostly dimeric Rho. The cognate G protein transducin (Gt) appears to have a preference for binding to the Rho dimer, and the complexes fall apart in the presence of guanosine 5'-3-O-(thio)triphosphate. Cross-linked Rho dimers release the chromophore at a slower rate than monomers and are much more resistant to heat denaturation. Both Rho(*) monomers and dimers are capable of activating Gt, and both of them are phosphorylated by Rho kinase. Rho expressed in HEK293 cells is also readily cross-linked by a bifunctional reagent. These studies provide an explanation of how detergent influences the oligomer-dimermonomer equilibrium of Rho and describe the functional characterization of Rho monomers and dimers in detergent.
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Affiliation(s)
- Beata Jastrzebska
- Department of Ophthalmology, University of Washington, Seattle, Washington 98195, USA
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127
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Zhu L, Jang GF, Jastrzebska B, Filipek S, Pearce-Kelling SE, Aguirre GD, Stenkamp RE, Acland GM, Palczewski K. A naturally occurring mutation of the opsin gene (T4R) in dogs affects glycosylation and stability of the G protein-coupled receptor. J Biol Chem 2004; 279:53828-39. [PMID: 15459196 PMCID: PMC1351288 DOI: 10.1074/jbc.m408472200] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Rho (rhodopsin; opsin plus 11-cis-retinal) is a prototypical G protein-coupled receptor responsible for the capture of a photon in retinal photoreceptor cells. A large number of mutations in the opsin gene associated with autosomal dominant retinitis pigmentosa have been identified. The naturally occurring T4R opsin mutation in the English mastiff dog leads to a progressive retinal degeneration that closely resembles human retinitis pigmentosa caused by the T4K mutation in the opsin gene. Using genetic approaches and biochemical assays, we explored the properties of the T4R mutant protein. Employing immunoaffinity-purified Rho from affected RHO(T4R/T4R) dog retina, we found that the mutation abolished glycosylation at Asn(2), whereas glycosylation at Asn(15) was unaffected, and the mutant opsin localized normally to the rod outer segments. Moreover, we found that T4R Rho(*) lost its chromophore faster as measured by the decay of meta-rhodopsin II and that it was less resistant to heat denaturation. Detergent-solubilized T4R opsin regenerated poorly and interacted abnormally with the G protein transducin (G(t)). Structurally, the mutation affected mainly the "plug" at the intradiscal (extracellular) side of Rho, which is possibly responsible for protecting the chromophore from the access of bulk water. The T4R mutation may represent a novel molecular mechanism of degeneration where the unliganded form of the mutant opsin exerts a detrimental effect by losing its structural integrity.
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Affiliation(s)
- Li Zhu
- Department of Ophthalmology, University of Washington, 1957 NE Pacific St., Seattle, WA 98195-6485, USA
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128
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Patel AB, Crocker E, Eilers M, Hirshfeld A, Sheves M, Smith SO. Coupling of retinal isomerization to the activation of rhodopsin. Proc Natl Acad Sci U S A 2004; 101:10048-53. [PMID: 15220479 PMCID: PMC454162 DOI: 10.1073/pnas.0402848101] [Citation(s) in RCA: 119] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Activation of the visual pigment rhodopsin is caused by 11-cis to -trans isomerization of its retinal chromophore. High-resolution solid-state NMR measurements on both rhodopsin and the metarhodopsin II intermediate show how retinal isomerization disrupts helix interactions that lock the receptor off in the dark. We made 2D dipolar-assisted rotational resonance NMR measurements between (13)C-labels on the retinal chromophore and specific (13)C-labels on tyrosine, glycine, serine, and threonine in the retinal binding site of rhodopsin. The essential aspects of the isomerization trajectory are a large rotation of the C20 methyl group toward extracellular loop 2 and a 4- to 5-A translation of the retinal chromophore toward transmembrane helix 5. The retinal-protein contacts observed in the active metarhodopsin II intermediate suggest a general activation mechanism for class A G protein-coupled receptors involving coupled motion of transmembrane helices 5, 6, and 7.
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Affiliation(s)
- Ashish B Patel
- Department of Physiology and Biophysics, Center for Structural Biology, Stony Brook University, NY 11794-5215, USA
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129
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Getmanova E, Patel AB, Klein-Seetharaman J, Loewen MC, Reeves PJ, Friedman N, Sheves M, Smith SO, Khorana HG. NMR spectroscopy of phosphorylated wild-type rhodopsin: mobility of the phosphorylated C-terminus of rhodopsin in the dark and upon light activation. Biochemistry 2004; 43:1126-33. [PMID: 14744159 DOI: 10.1021/bi030120u] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Binding of arrestin to light-activated rhodopsin involves recognition of the phosphorylated C-terminus and several residues on the cytoplasmic surface of the receptor. These sites are in close proximity in dark, unphosphorylated rhodopsin. To address the position and mobility of the phosphorylated C-terminus in the active and inactive receptor, we combined high-resolution solution and solid state NMR spectroscopy of the intact mammalian photoreceptor rhodopsin in detergent micelles as a function of temperature. The (31)P NMR resonance of rhodopsin phosphorylated by rhodopsin kinase at the C-terminal tail was observable with single pulse excitation using magic angle spinning until the sample temperature reached -40 degrees C. Below this temperature, the (31)P resonance broadened and was only observable using cross polarization. These results indicate that the phosphorylated C-terminus is highly mobile above -40 degrees C and immobilized at lower temperature. To probe the relative position of the immobilized phosphorylated C-terminus with respect to the cytoplasmic domain of rhodopsin, (19)F labels were introduced at positions 140 and 316 by the reaction of rhodopsin with 2,2,2-trifluoroethanethiol (TET). Solid state rotational-echo double-resonance (REDOR) NMR was used to probe the internuclear distance between the (19)F and the (31)P-labels. The REDOR technique allows (19)F...(31)P distances to be measured out to approximately 12 A with high resolution, but no significant dephasing was observed in the REDOR experiment in the dark or upon light activation. This result indicates that the distances between the phosphorylated sites on the C-terminus and the (19)F sites on helix 8 (Cys 316) and in the second cytoplasmic loop (Cys140) are greater than 12 A in phosphorylated rhodopsin.
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Affiliation(s)
- Elena Getmanova
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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130
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Janz JM, Farrens DL. Rhodopsin activation exposes a key hydrophobic binding site for the transducin alpha-subunit C terminus. J Biol Chem 2004; 279:29767-73. [PMID: 15070895 DOI: 10.1074/jbc.m402567200] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Conformational changes enable the photoreceptor rhodopsin to couple with and activate the G-protein transducin. Here we demonstrate a key interaction between these proteins occurs between the C terminus of the transducin alpha-subunit (G(Talpha)) and a hydrophobic cleft in the rhodopsin cytoplasmic face exposed during receptor activation. We mapped this interaction by labeling rhodopsin mutants with the fluorescent probe bimane and then assessed how binding of a peptide analogue of the G(Talpha) C terminus (containing a tryptophan quenching group) affected their fluorescence. From these and other assays, we conclude that the G(Talpha) C-terminal tail binds to the inner face of helix 6 in a retinal-linked manner. Further, we find that a "hydrophobic patch" comprising key residues in the exposed cleft is required for transducin binding/activation because it enhances the binding affinity for the G(Talpha) C-terminal tail, contributing up to 3 kcal/mol for this interaction. We speculate the hydrophobic interactions identified here may be important in other GPCR signaling systems, and our Trp/bimane fluorescence methodology may be generally useful for mapping sites of protein-protein interaction.
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Affiliation(s)
- Jay M Janz
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239, USA
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131
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Janz JM, Farrens DL. Assessing structural elements that influence Schiff base stability: mutants E113Q and D190N destabilize rhodopsin through different mechanisms. Vision Res 2003; 43:2991-3002. [PMID: 14611935 DOI: 10.1016/j.visres.2003.08.010] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The stability of the retinal chromophore attachment varies between different visual pigments and may factor in some retinal disease states. Opsin appears to stabilize this Schiff base linkage by: (i) affecting the hydrolysis chemistry, (ii) shielding the retinal linkage from solvent, or (iii) acting as a kinetic trap to slow retinal release. Here we describe methods to determine Schiff base stability in rhodopsin, present examples of dark state and MII rhodopsin stability differences, and show that studies of mutants E113Q and D190N demonstrate different parts of rhodopsin influence Schiff base stability in different ways.
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Affiliation(s)
- Jay M Janz
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Mail Code L224 3181 S.W. Sam Jackson Park Road, Portland, OR 97239, USA
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132
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Heck M, Schädel SA, Maretzki D, Hofmann KP. Secondary binding sites of retinoids in opsin: characterization and role in regeneration. Vision Res 2003; 43:3003-10. [PMID: 14611936 DOI: 10.1016/j.visres.2003.08.011] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
To regenerate light-sensitive rhodopsin in rods from active metarhodopsin II (Meta II), all-trans-retinal must be removed from the retinal binding pocket and metabolically supplied 11-cis-retinal has to form a new retinylidene bond in the active site. Recent work from this laboratory has focused on Meta II decay and release and uptake of retinals in opsin employing intrinsic protein fluorescence. Here we summarize the results in the retinal channeling hypothesis, which describes a passage of the chromophore through the protein. 11-cis-retinal is taken up into an entrance site, and photolyzed all-trans-retinal is released from the active site into an exit site.
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Affiliation(s)
- Martin Heck
- Institut für Medizinische Physik und Biophysik, Universitätsklinikum Charité, Humboldt Universität zu Berlin, Schumannstr. 20-21, 10098 Berlin, Germany
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133
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Schädel SA, Heck M, Maretzki D, Filipek S, Teller DC, Palczewski K, Hofmann KP. Ligand channeling within a G-protein-coupled receptor. The entry and exit of retinals in native opsin. J Biol Chem 2003; 278:24896-24903. [PMID: 12707280 PMCID: PMC1360283 DOI: 10.1074/jbc.m302115200] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Deactivation of light-activated rhodopsin (metarhodopsin II) involves, after rhodopsin kinase and arrestin interactions, the hydrolysis of the covalent bond of all-trans-retinal to the apoprotein. Although the long-lived storage form metarhodopsin III is transiently formed, all-trans-retinal is eventually released from the active site. Here we address the question of whether the release results in a retinal that is freely diffusible in the lipid phase of the photoreceptor membrane. The release reaction is accompanied by an increase in intrinsic protein fluorescence (release signal), which arises from the relief of the fluorescence quenching imposed by the retinal in the active site. An analogous fluorescence decrease (uptake signal) was evoked by exogenous retinoids when they non-covalently bound to native opsin membranes. Uptake of 11-cis-retinal was faster than formation of the retinylidene linkage to the apoprotein. Endogenous all-trans-retinal released from the active site during metarhodopsin II decay did not generate the uptake signal. The data show that in addition to the retinylidene pocket (site I) there are two other retinoidbinding sites within opsin. Site II involved in the uptake signal is an entrance site, while the exit site (site III) is occupied when retinal remains bound after its release from site I. Support for a retinal channeling mechanism comes from the rhodopsin crystal structure, which unveiled two putative hydrophobic binding sites. This mechanism enables a unidirectional process for the release of photoisomerized chromophore and the uptake of newly synthesized 11-cis-retinal for the regeneration of rhodopsin.
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Affiliation(s)
- Sandra A Schädel
- Institut für Medizinische Physik und Biophysik, Universitätsklinikum Charité, Humboldt Universität zu Berlin, Schumannstrasse 20-21, 10098 Berlin, Germany
| | - Martin Heck
- Institut für Medizinische Physik und Biophysik, Universitätsklinikum Charité, Humboldt Universität zu Berlin, Schumannstrasse 20-21, 10098 Berlin, Germany
| | - Dieter Maretzki
- Institut für Medizinische Physik und Biophysik, Universitätsklinikum Charité, Humboldt Universität zu Berlin, Schumannstrasse 20-21, 10098 Berlin, Germany
| | - Slawomir Filipek
- International Institute of Molecular and Cell Biology and the Department of Chemistry, University of Warsaw, 1 Pasteur St, PL-02109 Warsaw, Poland
| | - David C Teller
- Departments of Biological Structure, Biochemistry, and Biomolecular Structure Center, University of Washington, Seattle, Washington 98195
| | - Krzysztof Palczewski
- Departments of Ophthalmology, Pharmacology, and Chemistry, University of Washington, Seattle, Washington 98195
| | - Klaus Peter Hofmann
- Institut für Medizinische Physik und Biophysik, Universitätsklinikum Charité, Humboldt Universität zu Berlin, Schumannstrasse 20-21, 10098 Berlin, Germany
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134
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Bosch L, Ramon E, Del Valle LJ, Garriga P. Structural and functional role of helices I and II in rhodopsin. A novel interplay evidenced by mutations at Gly-51 and Gly-89 in the transmembrane domain. J Biol Chem 2003; 278:20203-9. [PMID: 12660238 DOI: 10.1074/jbc.m301319200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The naturally occurring mutations G51A and G51V in transmembrane helix I and G89D in the transmembrane helix II of rhodopsin are associated with the retinal degenerative disease autosomal dominant retinitis pigmentosa. To probe the orientation and packing of helices I and II a number of replacements at positions 51 and 89 were prepared by using site-directed mutagenesis, and the corresponding proteins expressed in COS-1 cells were characterized. Mutations at position 51 (G51V and G51L) bound retinal like wild-type rhodopsin but had thermally destabilized structures in the dark, altered photobleaching behavior, destabilized metarhodopsin II active conformations, and were severely defective in signal transduction. The effects observed can be correlated with the size of the mutated side chains that would interfere with specific interhelical interaction with Val-300 in helix VII. Mutations at position 89 had sensitivity to charge, as in G89K and G89D mutants, which showed reduced transducin activation. G89K showed a second absorbing species in the UV region at 350 nm, suggesting a charge effect of the introduced lysine. Increased formation of non-active forms of rhodopsin, like metarhodopsin III, may have some influence in the molecular defect underlying retinitis pigmentosa in the mutants studied. At the structural level, the effect of the mutations analyzed can be rationalized assuming a very specific set of tertiary interactions in the interhelical packing of the transmembrane segments of rhodopsin.
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Affiliation(s)
- Laia Bosch
- Centre de Biotecnologia Molecular, Departament d'Enginyeria Química, Universitat Politècnica de Catalunya, Colom 1, 08222 Terrassa, Catalonia, Spain
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135
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Janz JM, Fay JF, Farrens DL. Stability of dark state rhodopsin is mediated by a conserved ion pair in intradiscal loop E-2. J Biol Chem 2003; 278:16982-91. [PMID: 12547830 DOI: 10.1074/jbc.m210567200] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The rhodopsin crystal structure reveals that intradiscal loop E-2 covers the 11-cis-retinal, creating a "retinal plug." Recently, we noticed the ends of loop E-2 are linked by an ion pair between residues Arg-177 and Asp-190, near the highly conserved disulfide bond. This ion pair appears biologically significant; it is conserved in almost all vertebrate opsins and may occur in other G-protein-coupled receptors. We report here that the Arg-177/Asp-190 ion pair is critical for the folding and stability of dark state rhodopsin. We find ion pair mutants that regenerate with retinal are functionally and spectrally wild-type-like yet thermally unstable in their dark state because of rapid hydrolysis of the retinal Schiff base linkage. Surprisingly, Arrhenius analysis indicates that the activation energies for the hydrolysis process are similar between the ion pair mutants and wild-type rhodopsin. Furthermore, the ion pair mutants do not show increased reactivity toward hydroxylamine, suggesting that their instability is not caused by an increased exposure to bulk solvent. Our results indicate that the loop E-2 ion pair is important for rhodopsin stability and thus suggest that retinitis pigmentosa observed in patients with Asp-190 mutations may in part be the result of thermally unstable rhodopsin proteins.
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Affiliation(s)
- Jay M Janz
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97201, USA
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136
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Abstract
This report describes the biochemical characterization of a double mutant of rhodopsin (N2C,D282C) in which Cys residues engineered into the protein at positions 2 (in the amino-terminal extracellular domain) and 282 (in the extracellular loop between transmembrane helices 6 and 7) are shown to form a disulfide bond and increase the thermal stability of the unliganded or opsin form of the protein. Wild-type opsin does not survive detergent solubilization and purification at pH 7.5 and 25 degrees C. In contrast, the N2C,D282C mutant opsin survives the purification protocol and loses less than 50% activity after incubation for 20 days under the same conditions. Less than 5% is lost after 20 days at 4 degrees C. While the disulfide bond clearly has a dramatic effect on protein stability, it has a minor impact on the activity of the pigment. The MII lifetime of the mutant (6.6 min) is similar to that of the wild type (7.9 min), and the specific activity of the light-activated mutant for activation of transducin is within 20% of the wild-type activity. Therefore, it seems likely that the disulfide bond does not perturb greatly the structure of the protein. For these reasons, we anticipate that the mutant may be of use in detailed kinetic and mechanistic investigations of the ligand binding reaction and for crystallization trials involving recombinant rhodopsin, especially the unliganded opsin form of the protein.
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Affiliation(s)
- Guifu Xie
- Department of Biochemistry, Brandeis University, Waltham, Massachusetts 02454, USA
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137
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Gross AK, Rao VR, Oprian DD. Characterization of rhodopsin congenital night blindness mutant T94I. Biochemistry 2003; 42:2009-15. [PMID: 12590588 DOI: 10.1021/bi020613j] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The Thr94 --> Ile mutation in the second transmembrane segment of rhodopsin has been reported to be associated with a congenital night blindness phenotype in a large Irish pedigree. Previously, two other known rhodopsin mutants that cause congenital night blindness, A292E and G90D, have been shown in vitro to constitutively activate the G protein transducin in the absence of a chromophore. The proposed mechanism of constitutive activation of these two mutants is an electrostatic disruption of the active site salt bridge between Glu113 and Lys296 that contributes to stabilization of the protein in the inactive state. Here, the T94I rhodopsin mutant is characterized and compared to the two other known rhodopsin night blindness mutants. The T94I mutant opsin is shown also to constitutively activate transducin. The T94I mutant pigment (with a bound 11-cis-retinal chromophore), like the other known rhodopsin night blindness mutants, is not active in the dark and has wild-type activity upon exposure to light. Similar to the Gly90 --> Asp substitution, position 94 is close enough to the Schiff base nitrogen that an Asp at this position can functionally substitute for the Glu113 counterion. However, in contrast to the other night blindness mutants, the T94I MII intermediate decays with a half-life that is approximately 8-fold slower than in the wild-type MII intermediate. Thus, the one phenotype shared by all congenital night blindness mutants that is different from the wild-type protein is constitutive activation of the apoprotein.
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Affiliation(s)
- Alecia K Gross
- Department of Biochemistry, Brandeis University, Waltham, Massachusetts 02454, USA
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138
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Ramon E, del Valle LJ, Garriga P. Unusual thermal and conformational properties of the rhodopsin congenital night blindness mutant Thr-94 --> Ile. J Biol Chem 2003; 278:6427-32. [PMID: 12466267 DOI: 10.1074/jbc.m210929200] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Naturally occurring point mutations in the opsin gene cause the retinal diseases retinitis pigmentosa and congenital night blindness. Although these diseases involve similar mutations in very close locations in rhodopsin, their progression is very different, with retinitis pigmentosa being severe and causing retinal degeneration. We report on the expression and characterization of the recently found T94I mutation associated with congenital night blindness, in the second transmembrane helix or rhodopsin, and mutations at the same site. T94I mutant rhodopsin folded properly and was able to bind 11-cis-retinal to form chromophore, but it showed a blue-shifted visible band at 478 nm and reduced molar extinction coefficient. Furthermore, T94I showed dramatically reduced thermal stability, extremely long lived metarhodopsin II intermediate, and highly increased reactivity toward hydroxylamine in the dark, when compared with wild type rhodopsin. The results are consistent with the location of Thr-94 in close proximity to Glu-113 counterion in the vicinity of the Schiff base linkage and suggest a role for this residue in maintaining the correct dark inactive conformation of the receptor. The reported results, together with previously published data on the other two known congenital night blindness mutants, suggest that the molecular mechanism underlying this disease may not be structural misfolding, as proposed for retinitis pigmentosa mutants, but abnormal functioning of the receptor by decreased thermal stability and/or constitutive activity.
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Affiliation(s)
- Eva Ramon
- Centre de Biotecnologia Molecular (CEBIM), Departament d'Enginyeria Quimica, Universitat Politècnica de Catalunya, Colom 1, 08222 Terrassa, Catalonia, Spain
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139
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Heck M, Schädel SA, Maretzki D, Bartl FJ, Ritter E, Palczewski K, Hofmann KP. Signaling states of rhodopsin. Formation of the storage form, metarhodopsin III, from active metarhodopsin II. J Biol Chem 2003; 278:3162-9. [PMID: 12427735 PMCID: PMC1364529 DOI: 10.1074/jbc.m209675200] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Vertebrate rhodopsin consists of the apoprotein opsin and the chromophore 11-cis-retinal covalently linked via a protonated Schiff base. Upon photoisomerization of the chromophore to all-trans-retinal, the retinylidene linkage hydrolyzes, and all-trans-retinal dissociates from opsin. The pigment is eventually restored by recombining with enzymatically produced 11-cis-retinal. All-trans-retinal release occurs in parallel with decay of the active form, metarhodopsin (Meta) II, in which the original Schiff base is intact but deprotonated. The intermediates formed during Meta II decay include Meta III, with the original Schiff base reprotonated, and Meta III-like pseudo-photoproducts. Using an intrinsic fluorescence assay, Fourier transform infrared spectroscopy, and UV-visible spectroscopy, we investigated Meta II decay in native rod disk membranes. Up to 40% of Meta III is formed without changes in the intrinsic Trp fluorescence and thus without all-trans-retinal release. NADPH, a cofactor for the reduction of all-trans-retinal to all-trans-retinol, does not accelerate Meta II decay nor does it change the amount of Meta III formed. However, Meta III can be photoconverted back to the Meta II signaling state. The data are described by two quasi-irreversible pathways, leading in parallel into Meta III or into release of all-trans-retinal. Therefore, Meta III could be a form of rhodopsin that is stored away, thus regulating photoreceptor regeneration.
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Affiliation(s)
- Martin Heck
- Institut für Medizinische Physik und Biophysik, Universitätsklinikum Charité, Humboldt Universität zu Berlin, Schumannstrasse 20-21, 10098 Berlin, Germany.
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140
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Niu L, Kim JM, Khorana HG. Structure and function in rhodopsin: asymmetric reconstitution of rhodopsin in liposomes. Proc Natl Acad Sci U S A 2002; 99:13409-12. [PMID: 12370420 PMCID: PMC129686 DOI: 10.1073/pnas.212518899] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We report on preparation of rhodopsin proteoliposomes with the cytoplasmic domain of rhodopsin facing the exterior of the proteoliposomes. Rhodopsin purified from rod outer segments of bovine retinae by immunoaffinity chromatography in octyl glucoside was reconstituted into liposomes prepared from soybean phospholipids by detergent dialysis. The orientation of rhodopsin in the liposomes was determined by susceptibility of its C terminus to papain and the endoproteinase, Asp-N, followed by SDS/PAGE, which showed that the cytoplasmic domain in at least 90% of rhodopsin faced the exterior of the proteoliposomes. By using escape of (32)P-KP(i) encapsulated in the proteoliposomes as the assay, the half-life of the proteasomes was approximately 8 days. After light activation, rhodopsin in proteoliposomes showed the rate of decay of metarhodopsin II and the initial rate of transducin activation comparable with the rates of rhodopsin in rod outer segment membranes. This finding demonstrates the functional capability of rhodopsin in proteoliposomes for kinetic studies of protein-protein interactions.
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Affiliation(s)
- Li Niu
- Departments of Biology and Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
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141
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Vogel R, Siebert F. Conformation and stability of alpha-helical membrane proteins. 2. Influence of pH and salts on stability and unfolding of rhodopsin. Biochemistry 2002; 41:3536-45. [PMID: 11888269 DOI: 10.1021/bi016024f] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We studied the stability and pH-induced denaturation of rhodopsin and its photoproducts as a model for alpha-helical membrane proteins. The increased stability of the dark state of rhodopsin as compared to its photoproduct states allows the initiation of unfolding of the protein by light-dependent isomerization of the chromophore. We could therefore characterize the transition from the native to either acid or alkaline denatured states by light-induced Fourier transform infrared difference spectroscopy, UV-visible spectroscopy, and intrinsic tryptophan fluorescence spectroscopy. The results indicate a loss of important tertiary interactions within the protein and between the protein and the retinal chromophore in the denatured state, despite that the secondary structure of the protein is almost fully retained during the transition. We therefore propose that in this denatured state the protein adopts the conformation of a loose bundle of preserved, but only weakly interacting, transmembrane helices with a largely des-oriented and partly solvent-exposed chromophore. We further characterized the influence of salts on the stability of the rhodopsin helix bundle, which was found to follow the Hofmeister series. We found that the effect of sodium chloride may be stabilizing or destabilizing, depending on the intrinsic stability of the examined protein conformation and on salt concentration. In particular, sodium chloride is shown to counteract the formation of the denatured loose bundle state presumably by increasing the lateral pressure on the helix bundle, thereby stabilizing native-like tertiary contacts within the protein.
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Affiliation(s)
- Reiner Vogel
- Biophysics Group, Institut für Molekulare Medizin und Zellforschung, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Strasse 9, D-79104 Freiburg, Germany.
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142
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Yan ECY, Kazmi MA, De S, Chang BSW, Seibert C, Marin EP, Mathies RA, Sakmar TP. Function of extracellular loop 2 in rhodopsin: glutamic acid 181 modulates stability and absorption wavelength of metarhodopsin II. Biochemistry 2002; 41:3620-7. [PMID: 11888278 PMCID: PMC1404524 DOI: 10.1021/bi0160011] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The second extracellular loop of rhodopsin folds back into the membrane-embedded domain of the receptor to form part of the binding pocket for the 11-cis-retinylidene chromophore. A carboxylic acid side chain from this loop, Glu181, points toward the center of the retinal polyene chain. We studied the role of Glu181 in bovine rhodopsin by characterizing a set of site-directed mutants. Sixteen of the 19 single-site mutants expressed and bound 11-cis-retinal to form pigments. The lambda(max) value of mutant pigment E181Q showed a significant spectral red shift to 508 nm only in the absence of NaCl. Other substitutions did not significantly affect the spectral features of the mutant pigments in the dark. Thus, Glu181 does not contribute significantly to spectral tuning of the ground state of rhodopsin. The most likely interpretation of these data is that Glu181 is protonated and uncharged in the dark state of rhodopsin. The Glu181 mutants displayed significantly increased reactivity toward hydroxylamine in the dark. The mutants formed metarhodopsin II-like photoproducts upon illumination but many of the photoproducts displayed shifted lambda(max) values. In addition, the metarhodopsin II-like photoproducts of the mutant pigments had significant alterations in their decay rates. The increased reactivity of the mutants to hydroxylamine supports the notion that the second extracellular loop prevents solvent access to the chromophore-binding pocket. In addition, Glu181 strongly affects the environment of the retinylidene Schiff base in the active metarhodopsin II photoproduct.
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Affiliation(s)
- Elsa C Y Yan
- Department of Chemistry, University of California, Berkeley, California 94720, USA
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143
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Babu KR, Dukkipati A, Birge RR, Knox BE. Regulation of phototransduction in short-wavelength cone visual pigments via the retinylidene Schiff base counterion. Biochemistry 2001; 40:13760-6. [PMID: 11705364 DOI: 10.1021/bi015584b] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Short-wavelength visual pigments (SWS1) have lambda(max) values that range from the ultraviolet to the blue. Like all visual pigments, this class has an 11-cis-retinal chromophore attached through a Schiff base linkage to a lysine residue of opsin apoprotein. We have characterized a series of site-specific mutants at a conserved acidic residue in transmembrane helix 3 in the Xenopus short-wavelength sensitive cone opsin (VCOP, lambda(max) approximately 427 nm). We report the identification of D108 as the counterion to the protonated retinylidene Schiff base. This residue regulates the pK(a) of the Schiff base and, neutralizing this charge, converts the violet sensitive pigment into one that absorbs maximally in the ultraviolet region. Changes to this position cause the pigment to exhibit two chromophore absorbance bands, a major band with a lambda(max) of approximately 352-372 nm and a minor, broad shoulder centered around 480 nm. The behavior of these two absorbance bands suggests that these represent unprotonated and protonated Schiff base forms of the pigment. The D108A mutant does not activate bovine rod transducin in the dark but has a significantly prolonged lifetime of the active MetaII state. The data suggest that in short-wavelength sensitive cone visual pigments, the counterion is necessary for the characteristic rapid production and decay of the active MetaII state.
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Affiliation(s)
- K R Babu
- Department of Biochemistry and Molecular Biology, State University of New York Upstate Medical University, 766 Irving Avenue, Syracuse, New York 13210, USA
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144
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Klein-Seetharaman J, Hwa J, Cai K, Altenbach C, Hubbell WL, Khorana HG. Probing the dark state tertiary structure in the cytoplasmic domain of rhodopsin: proximities between amino acids deduced from spontaneous disulfide bond formation between Cys316 and engineered cysteines in cytoplasmic loop 1. Biochemistry 2001; 40:12472-8. [PMID: 11601970 DOI: 10.1021/bi010746p] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A dark state tertiary structure in the cytoplasmic domain of rhodopsin is presumed to be the key to the restriction of binding of transducin and rhodopsin kinase to rhodopsin. Upon light-activation, this tertiary structure undergoes a conformational change to form a new structure, which is recognized by the above proteins and signal transduction is initiated. In this and the following paper in this issue [Cai, K., Klein-Seetharaman, J., Altenbach, C., Hubbell, W. L., and Khorana, H. G. (2001) Biochemistry 40, 12479-12485], we probe the dark state cytoplasmic domain structure in rhodopsin by investigating proximity between amino acids in different regions of the cytoplasmic face. The approach uses engineered pairs of cysteines at predetermined positions, which are tested for spontaneous formation of disulfide bonds between them, indicative of proximity between the original amino acids. Focusing here on proximity between the native cysteine at position 316 and engineered cysteines at amino acid positions 55-75 in the cytoplasmic sequence connecting helices I-II, disulfide bond formation was studied under strictly defined conditions and plotted as a function of the position of the variable cysteines. An absolute maximum was observed for position 65 with two additional relative maxima for cysteines at positions 61 and 68. The observed disulfide bond formation rates correlate well with proximity of these residues found in the crystal structure of rhodopsin in the dark. Modeling of the engineered cysteines in the crystal structure indicates that small but significant motions are required for productive disulfide bond formation. During these motions, secondary structure elements are retained as indicated by the lack of disulfide bond formation in cysteines that do not face toward Cys316 in the crystal structure model. Such motions may be important in light-induced conformational changes.
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Affiliation(s)
- J Klein-Seetharaman
- Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
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145
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Cai K, Klein-Seetharaman J, Altenbach C, Hubbell WL, Khorana HG. Probing the dark state tertiary structure in the cytoplasmic domain of rhodopsin: proximities between amino acids deduced from spontaneous disulfide bond formation between cysteine pairs engineered in cytoplasmic loops 1, 3, and 4. Biochemistry 2001; 40:12479-85. [PMID: 11601971 DOI: 10.1021/bi010747h] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
To probe proximities between amino acids in the cytoplasmic domain by using mutants containing engineered cysteine pairs, three sets of rhodopsin mutants have been prepared. In the first two sets, a cysteine was placed, one at a time, at positions 311-314 in helix VIII, while the second cysteine was fixed at position 246 (set I) and at position 250 (set II) at the cytoplasmic end of helix VI. In the third set, one cysteine was fixed at position 65 while the second cysteine was varied between amino acid positions 306 and 321 located at the cytoplasmic end of helix VII and throughout in helix VIII. Rapid disulfide bond formation in the dark was found between the cysteine pairs in mutants A246C/Q312C,A246C/K311C and in mutants H65C/C316, H65C/315C and H65C/312C. Disulfide bond formation at much lower rates was found in mutants A246C/F313C, V250C/Q312C, H65C/N310C, H65C/K311C, H65C/F313C, and H65C/R314C; the remaining mutants showed no significant disulfide bond formation. Comparisons of the results from disulfide bond formation in solution with the distances observed in the rhodopsin crystal structure showed that the rates of disulfide bond formation in most cases were consistent with the amino acid proximities as revealed in crystal structure. However, deviations were also found, in particular, in the set containing fixed cysteine at position Cys246 and cysteines at positions 311-314. The results implicate significant effects of structural dynamics on disulfide bond formation in solution.
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Affiliation(s)
- K Cai
- Department of Biology and Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 68-680, Cambridge, Massachusetts 02139, USA
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146
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Abstract
We report an effort to engineer a functional, maximally blue-wavelength-shifted version of rhodopsin. Toward this goal, we first constructed and assayed a number of previously described mutations in the retinal binding pocket of rhodopsin, G90S, E122D, A292S, and A295S. Of these mutants, we found that only mutants E122D and A292S were like the wild type (WT). In contrast, mutant G90S exhibited a perturbed photobleaching spectrum, and mutant A295S exhibited decreased ability to activate transducin. We also identified and characterized a new blue-wavelength-shifting mutation (at site T118), a residue conserved in most opsin proteins. Interestingly, although residue T118 contacts the critically important C9-methyl group of the retinal chromophore, the T118A mutant exhibited no significant perturbation other than the blue-wavelength shift. In analyzing these mutants, we found that although several mutants exhibited different rates of retinal release, the activation energies of the retinal release were all approximately 20 kcal/mol, almost identical to the value found for WT rhodopsin. These latter results support the theory that chemical hydrolysis of the Schiff base is the rate-limiting step of the retinal release pathway. A combination of the functional blue-wavelength-shifting mutations was then used to generate a triple mutant (T118A/E122D/A292S) which exhibited a large blue-wavelength shift (absorption lambda(max) = 453 nm) while exhibiting minimal functional perturbation. Mutant T118A/E122D/A292S thus offers the possibility of a rhodopsin protein that can be worked with and studied using more ambient lighting conditions, and facilitates further study by fluorescence spectroscopy.
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Affiliation(s)
- J M Janz
- Department of Biochemistry and Molecular Biology, Oregon Health Sciences University, 3181 Southwest Sam Jackson Park Drive, Portland, Oregon 97201-3098, USA
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147
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Ernst OP, Bieri C, Vogel H, Hofmann KP. Intrinsic biophysical monitors of transducin activation: fluorescence, UV-visible spectroscopy, light scattering, and evanescent field techniques. Methods Enzymol 2000; 315:471-89. [PMID: 10736721 DOI: 10.1016/s0076-6879(00)15862-8] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- O P Ernst
- Institut für Medizinische Physik und Biophysik, Universitätsklinikum Charité, Humboldt Universität zu Berlin, Germany
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148
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Abstract
G protein-coupled, seven-transmembrane segment receptors (GPCRs or 7TM receptors), with more than 1000 different members, comprise the largest superfamily of proteins in the body. Since the cloning of the first receptors more than a decade ago, extensive experimental work has uncovered multiple aspects of their function and challenged many traditional paradigms. However, it is only recently that we are beginning to gain insight into some of the most fundamental questions in the molecular function of this class of receptors. How can, for example, so many chemically diverse hormones, neurotransmitters, and other signaling molecules activate receptors believed to share a similar overall tertiary structure? What is the nature of the physical changes linking agonist binding to receptor activation and subsequent transduction of the signal to the associated G protein on the cytoplasmic side of the membrane and to other putative signaling pathways? The goal of the present review is to specifically address these questions as well as to depict the current awareness about GPCR structure-function relationships in general.
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Affiliation(s)
- U Gether
- Department of Medical Physiology, Panum Institute, University of Copenhagen, Denmark.
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149
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Klein-Seetharaman J, Getmanova EV, Loewen MC, Reeves PJ, Khorana HG. NMR spectroscopy in studies of light-induced structural changes in mammalian rhodopsin: applicability of solution (19)F NMR. Proc Natl Acad Sci U S A 1999; 96:13744-9. [PMID: 10570143 PMCID: PMC24135 DOI: 10.1073/pnas.96.24.13744] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We report high resolution solution (19)F NMR spectra of fluorine-labeled rhodopsin mutants in detergent micelles. Single cysteine substitution mutants in the cytoplasmic face of rhodopsin were labeled by attachment of the trifluoroethylthio (TET), CF(3)-CH(2)-S, group through a disulfide linkage. TET-labeled cysteine mutants at amino acid positions 67, 140, 245, 248, 311, and 316 in rhodopsin were thus prepared. Purified mutant rhodopsins (6-10 mg), in dodecylmaltoside, were analyzed at 20 degrees C by solution (19)F NMR spectroscopy. The spectra recorded in the dark showed the following chemical shifts relative to trifluoroacetate: Cys-67, 9.8 ppm; Cys-140, 10.6 ppm; Cys-245, 9.9 ppm; Cys-248, 9.5 ppm; Cys-311, 9.9 ppm; and Cys-316, 10.0 ppm. Thus, all mutants showed chemical shifts downfield that of free TET (6.5 ppm). On illumination to form metarhodopsin II, upfield changes in chemical shift were observed for (19)F labels at positions 67 (-0.2 ppm) and 140 (-0.4 ppm) and downfield changes for positions 248 (+0.1 ppm) and 316 (+0.1 ppm) whereas little or no change was observed at positions 311 and 245. On decay of metarhodopsin II, the chemical shifts reverted largely to those originally observed in the dark. The results demonstrate the applicability of solution (19)F NMR spectroscopy to studies of the tertiary structures in the cytoplasmic face of intact rhodopsin in the dark and on light activation.
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Affiliation(s)
- J Klein-Seetharaman
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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150
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Bieri C, Ernst OP, Heyse S, Hofmann KP, Vogel H. Micropatterned immobilization of a G protein-coupled receptor and direct detection of G protein activation. Nat Biotechnol 1999; 17:1105-8. [PMID: 10545918 DOI: 10.1038/15090] [Citation(s) in RCA: 240] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
G protein-coupled receptors (GPCRs) constitute an abundant family of membrane receptors of high pharmacological interest. Cell-based assays are the predominant means of assessing GPCR activation, but are limited by their inherent complexity. Functional molecular assays that directly and specifically report G protein activation by receptors could offer substantial advantages. We present an approach to immobilize receptors stably and with defined orientation to substrates. By surface plasmon resonance (SPR), we were able to follow ligand binding, G protein activation, and receptor deactivation of a representative GPCR, bovine rhodopsin. Microcontact printing was used to produce micrometer-sized patterns with high contrast in receptor activity. These patterns can be used for local referencing to enhance the sensitivity of chip-based assays. The immobilized receptor was stable both for hours and during several activation cycles. A ligand dose-response curve with the photoactivatable agonist 11-cis-retinal showed a half-maximal signal at 120 nM. Our findings may be useful to develop novel assay formats for GPCRs based on receptor immobilization to solid supports, particularly to sensor surfaces.
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Affiliation(s)
- C Bieri
- Swiss Federal Institute of Technology, Institute of Physical Chemistry, Laboratory for Physical Chemistry of Polymers and Membranes, CH-1015 Lausanne, Switzerland
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