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Hofmann KP, Lamb TD. Rhodopsin, light-sensor of vision. Prog Retin Eye Res 2023; 93:101116. [PMID: 36273969 DOI: 10.1016/j.preteyeres.2022.101116] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2022] [Revised: 08/20/2022] [Accepted: 08/22/2022] [Indexed: 11/06/2022]
Abstract
The light sensor of vertebrate scotopic (low-light) vision, rhodopsin, is a G-protein-coupled receptor comprising a polypeptide chain with bound chromophore, 11-cis-retinal, that exhibits remarkable physicochemical properties. This photopigment is extremely stable in the dark, yet its chromophore isomerises upon photon absorption with 70% efficiency, enabling the activation of its G-protein, transducin, with high efficiency. Rhodopsin's photochemical and biochemical activities occur over very different time-scales: the energy of retinaldehyde's excited state is stored in <1 ps in retinal-protein interactions, but it takes milliseconds for the catalytically active state to form, and many tens of minutes for the resting state to be restored. In this review, we describe the properties of rhodopsin and its role in rod phototransduction. We first introduce rhodopsin's gross structural features, its evolution, and the basic mechanisms of its activation. We then discuss light absorption and spectral sensitivity, photoreceptor electrical responses that result from the activity of individual rhodopsin molecules, and recovery of rhodopsin and the visual system from intense bleaching exposures. We then provide a detailed examination of rhodopsin's molecular structure and function, first in its dark state, and then in the active Meta states that govern its interactions with transducin, rhodopsin kinase and arrestin. While it is clear that rhodopsin's molecular properties are exquisitely honed for phototransduction, from starlight to dawn/dusk intensity levels, our understanding of how its molecular interactions determine the properties of scotopic vision remains incomplete. We describe potential future directions of research, and outline several major problems that remain to be solved.
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Affiliation(s)
- Klaus Peter Hofmann
- Institut für Medizinische Physik und Biophysik (CC2), Charité, and, Zentrum für Biophysik und Bioinformatik, Humboldt-Unversität zu Berlin, Berlin, 10117, Germany.
| | - Trevor D Lamb
- Eccles Institute of Neuroscience, John Curtin School of Medical Research, The Australian National University, Canberra, ACT 2600, Australia.
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2
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Guo X, Cui Y, Irwin DM, Liu Y. Accelerated evolution of dim-light vision-related arrestin in deep-diving amniotes. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.1069088] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Arrestins are key molecules involved in the signaling of light-sensation initiated by visual pigments in retinal photoreceptor cells. Vertebrate photoreceptor cells have two types of arrestins, rod arrestin, which is encoded by SAG and is expressed in both rods and cones, and cone arrestin, encoded by ARR3 in cones. The arrestins can bind to visual pigments, and thus regulate either dim-light vision via interactions with rhodopsin or bright-light vision together with cone visual pigments. After adapting to terrestrial life, several amniote lineages independently went back to the sea and evolved deep-diving habits. Interestingly, the rhodopsins in these species exhibit specialized phenotypes responding to rapidly changing dim-light environments. However, little is known about whether their rod arrestin also experienced adaptive evolution associated with rhodopsin. Here, we collected SAG coding sequences from >250 amniote species, and examined changes in selective pressure experienced by the sequences from deep-diving taxa. Divergent patterns of evolution of SAG were observed in the penguin, pinniped and cetacean clades, suggesting possible co-adaptation with rhodopsin. After verifying pseudogenes, the same analyses were performed for cone arrestin (ARR3) in deep-diving species and only sequences from cetacean species, and not pinnipeds or penguins, have experienced changed selection pressure compared to other species. Taken together, this evidence for changes in selective pressures acting upon arrestin genes strengthens the suggestion that rapid dim-light adaptation for deep-diving amniotes require SAG, but not ARR3.
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3
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Pitch SG, Yao W, Szundi I, Fay J, Chen E, Shumate A, Kliger DS, Farrens DL. Functional integrity of membrane protein rhodopsin solubilized by styrene-maleic acid copolymer. Biophys J 2021; 120:3508-3515. [PMID: 34022241 DOI: 10.1016/j.bpj.2021.05.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2020] [Revised: 04/18/2021] [Accepted: 05/13/2021] [Indexed: 11/25/2022] Open
Abstract
Membrane proteins often require solubilization to study their structure or define the mechanisms underlying their function. In this study, the functional properties of the membrane protein rhodopsin in its native lipid environment were investigated after being solubilized with styrene-maleic acid (SMA) copolymer. The static absorption spectra of rhodopsin before and after the addition of SMA were recorded at room temperature to quantify the amount of membrane protein solubilized. The samples were then photobleached to analyze the functionality of rhodopsin upon solubilization. Samples with low or high SMA/rhodopsin ratios were compared to find a threshold in which the maximal amount of active rhodopsin was solubilized from membrane suspensions. Interestingly, whereas the highest SMA/rhodopsin ratios yielded the most solubilized rhodopsin, the rhodopsin produced under these conditions could not reach the active (Meta II) state upon photoactivation. The results confirm that SMA is a useful tool for membrane protein research, but SMA added in excess can interfere with the dynamics of protein activation.
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Affiliation(s)
- Stephanie G Pitch
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, Santa Cruz, California
| | - Weekie Yao
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Portland, Oregon
| | - Istvan Szundi
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, Santa Cruz, California
| | - Jonathan Fay
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Portland, Oregon
| | - Eefei Chen
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, Santa Cruz, California
| | - Anthony Shumate
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Portland, Oregon
| | - David S Kliger
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, Santa Cruz, California
| | - David L Farrens
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Portland, Oregon.
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4
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Site-directed labeling of β-arrestin with monobromobimane for measuring their interaction with G protein-coupled receptors. Methods Enzymol 2020; 633:271-280. [PMID: 32046850 PMCID: PMC7217711 DOI: 10.1016/bs.mie.2019.11.009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
β-arrestins (βarrs) are multifunctional proteins that interact with activated and phosphorylated G protein-coupled receptors (GPCRs) to regulate their signaling and trafficking. Understanding the intricate details of GPCR-βarr interaction continues to be a key research area in the field of GPCR biology. Bimane fluorescence spectroscopy has been one of the key approaches among a broad range of methods employed to study GPCR-βarr interaction using purified and reconstituted system. Here, we present a step-by-step protocol for labeling βarrs with monobromobimane (mBBr) in a site-directed fashion for measuring their interaction with GPCRs and the resulting conformational changes. This simple protocol can be directly applied to other protein-protein interaction modules as well for measuring interactions and conformational changes in reconstituted systems in vitro.
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5
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Sahin K, Gencoglu H, Akdemir F, Orhan C, Tuzcu M, Sahin N, Yilmaz I, Juturu V. Lutein and zeaxanthin isomers may attenuate photo-oxidative retinal damage via modulation of G protein-coupled receptors and growth factors in rats. Biochem Biophys Res Commun 2019; 516:163-170. [PMID: 31204054 DOI: 10.1016/j.bbrc.2019.06.032] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2019] [Accepted: 06/07/2019] [Indexed: 01/05/2023]
Abstract
BACKGROUND Retina photoreceptor cells are specially adapted for functioning over comprehensive ambient light conditions. Lutein and Zeaxanthin isomers (L/Zi) can protect photoreceptor cells against excessive light degeneration. Efficacy of L/Zi has been assessed on some G protein-coupled receptors (GPCRs), transcription and neurotrophic factors in the retina of rats exposed to incremental intense light emitting diode (LED) illumination conditions. METHODS Forty-two male rats (age: 8 weeks) were randomly assigned to six treatment groups, 7 rats each. The rats with a 3x2 factorial design were kept under 3 intense light conditions (12hL/12hD, 16hL/8hD, 24hL/0hD) and received two levels of L/Zi (0 or 100 mg/kg BW) for two months. Increased nuclear factor-kappa B (NF-κB), glial fibrillary acid protein (GFAP), and decreased Rhodopsin (Rho), Rod arrestin (Sag), G Protein Subunit Alpha Transducin1 (Gnat1), neural cell adhesion molecule (NCAM), growth-associated protein-43 (GAP43), nuclear factor (erythroid-derived 2)-like 2 (Nrf2), and heme oxygenase 1 (HO-1) were observed in 24 h light intensity adaptation followed by 16 h IL and 8 h D. RESULTS L/Zi administration significantly improved antioxidant capacity and retinal Rho, Rod-arrestin (Sag), Gnat1, NCAM, GAP43, BDNF, NGF, IGF1, Nrf2, and HO-1 levels. However, the levels of NF-κB and GFAP levels were decreased by administration of L/Zi. CONCLUSIONS According to these results, L/Zi may be assumed as an adjunct therapy to prevent early photoreceptor cell degeneration and neutralize free radicals derived from oxidative stress.
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Affiliation(s)
- Kazim Sahin
- Department of Nutrition, Faculty of Veterinary Medicine, Firat University, Elazig, Turkey.
| | - Hasan Gencoglu
- Department of Biology, Faculty of Science, Firat University, Elazig, Turkey
| | - Fatih Akdemir
- Faculty of Fisheries, Inonu University, Malatya, Turkey
| | - Cemal Orhan
- Department of Nutrition, Faculty of Veterinary Medicine, Firat University, Elazig, Turkey
| | - Mehmet Tuzcu
- Department of Biology, Faculty of Science, Firat University, Elazig, Turkey
| | - Nurhan Sahin
- Department of Nutrition, Faculty of Veterinary Medicine, Firat University, Elazig, Turkey
| | - Ismet Yilmaz
- Department of Pharmacology, Faculty of Pharmacy, Inonu University, Malatya, Turkey
| | - Vijaya Juturu
- Research and Development, OmniActive Health Technologies Inc., Morristown, NJ, United States
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Sahin K, Akdemir F, Orhan C, Tuzcu M, Gencoglu H, Sahin N, Ozercan IH, Ali S, Yilmaz I, Juturu V. (3R, 3'R)-zeaxanthin protects the retina from photo-oxidative damage via modulating the inflammation and visual health molecular markers. Cutan Ocul Toxicol 2019; 38:161-168. [PMID: 30513212 DOI: 10.1080/15569527.2018.1554667] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
PURPOSE Zeaxanthin protects the macula from ocular damage due to light or radiation by scavenging harmful reactive oxygen species. In the present study, zeaxanthin product (OmniXan®; OMX), derived from paprika pods (Capsicum annum; Family-Solanaceae), was tested for its efficacy in the rat retina against photooxidation. METHODS Forty-two male 8-week-old Wistar rats exposed to 12L/12D, 16L/8D and 24L/0D hours of intense light conditions were orally administrated either 0 or 100 mg/kg BW of zeaxanthin concentration. Retinal morphology was analyzed by histopathology, and target gene expressions were detected with real-time polymerase chain reaction methods. RESULTS OMX treatment significantly increased the serum zeaxanthin concentration (p < 0.001) and ameliorated oxidative damage by increasing the antioxidant enzyme activities in the retina induced by light (p < 0.001). OMX administration significantly upregulated the expression of genes, including Rhodopsin (Rho), Rod arrestin (SAG), Gα Transducin 1 (GNAT-1), neural cell adhesion molecule (NCAM), growth-associated protein 43 (GAP43), nuclear factor-(erythroid-derived 2)-like 2 (Nrf2) and heme oxygenase (HO-1) and decreased the expression of nuclear factor-κB (NF- κB) and GFAP by OMX treatment rats. The histologic findings confirmed the antioxidant and gene expression data. CONCLUSIONS This study suggests that OMX is a potent substance that can be used to protect photoreceptor cell degeneration in the retina exposed to intense light.
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Affiliation(s)
- Kazim Sahin
- a Department of Animal Nutrition, Faculty of Veterinary Science , Firat University , Elazig , Turkey.,b Department of Nutrition, Faculty of Fisheries , Inonu University , Malatya , Turkey
| | - Fatih Akdemir
- b Department of Nutrition, Faculty of Fisheries , Inonu University , Malatya , Turkey
| | - Cemal Orhan
- a Department of Animal Nutrition, Faculty of Veterinary Science , Firat University , Elazig , Turkey
| | - Mehmet Tuzcu
- c Division of Biology, Faculty of Science , Firat University , Elazig , Turkey
| | - Hasan Gencoglu
- c Division of Biology, Faculty of Science , Firat University , Elazig , Turkey
| | - Nurhan Sahin
- a Department of Animal Nutrition, Faculty of Veterinary Science , Firat University , Elazig , Turkey
| | - Ibrahim H Ozercan
- d Department of Pathology, Faculty of Medicine , Firat University , Elazig , Turkey
| | - Shakir Ali
- e Department of Biochemistry, Faculty of Science , Jamia Hamdard , New Delhi , India
| | - Ismet Yilmaz
- f Department of Pharmacology, Faculty of Pharmacy , Inonu University , Malatya , Turkey
| | - Vijaya Juturu
- g Research and Development, OmniActive Health Technologies Inc , Morristown , NJ , USA
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7
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Castiglione GM, Chang BS. Functional trade-offs and environmental variation shaped ancient trajectories in the evolution of dim-light vision. eLife 2018; 7:35957. [PMID: 30362942 PMCID: PMC6203435 DOI: 10.7554/elife.35957] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2018] [Accepted: 09/09/2018] [Indexed: 12/11/2022] Open
Abstract
Trade-offs between protein stability and activity can restrict access to evolutionary trajectories, but widespread epistasis may facilitate indirect routes to adaptation. This may be enhanced by natural environmental variation, but in multicellular organisms this process is poorly understood. We investigated a paradoxical trajectory taken during the evolution of tetrapod dim-light vision, where in the rod visual pigment rhodopsin, E122 was fixed 350 million years ago, a residue associated with increased active-state (MII) stability but greatly diminished rod photosensitivity. Here, we demonstrate that high MII stability could have likely evolved without E122, but instead, selection appears to have entrenched E122 in tetrapods via epistatic interactions with nearby coevolving sites. In fishes by contrast, selection may have exploited these epistatic effects to explore alternative trajectories, but via indirect routes with low MII stability. Our results suggest that within tetrapods, E122 and high MII stability cannot be sacrificed-not even for improvements to rod photosensitivity.
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Affiliation(s)
- Gianni M Castiglione
- Department of Cell and Systems Biology, University of Toronto, Toronto, Canada.,Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Canada
| | - Belinda Sw Chang
- Department of Cell and Systems Biology, University of Toronto, Toronto, Canada.,Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Canada.,Centre for the Analysis of Genome Evolution and Function, University of Toronto, Toronto, Canada
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8
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Frederiksen R, Nymark S, Kolesnikov AV, Berry JD, Adler L, Koutalos Y, Kefalov VJ, Cornwall MC. Rhodopsin kinase and arrestin binding control the decay of photoactivated rhodopsin and dark adaptation of mouse rods. J Gen Physiol 2017; 148:1-11. [PMID: 27353443 PMCID: PMC4924931 DOI: 10.1085/jgp.201511538] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Accepted: 06/06/2016] [Indexed: 12/22/2022] Open
Abstract
G-protein receptor kinase and arrestin 1 are required for inactivation of photoactivated vertebrate rhodopsin. Frederiksen et al. show that they additionally regulate the subsequent decay of inactive rhodopsin into opsin and all-trans retinal and therefore dark adaptation. Photoactivation of vertebrate rhodopsin converts it to the physiologically active Meta II (R*) state, which triggers the rod light response. Meta II is rapidly inactivated by the phosphorylation of C-terminal serine and threonine residues by G-protein receptor kinase (Grk1) and subsequent binding of arrestin 1 (Arr1). Meta II exists in equilibrium with the more stable inactive form of rhodopsin, Meta III. Dark adaptation of rods requires the complete thermal decay of Meta II/Meta III into opsin and all-trans retinal and the subsequent regeneration of rhodopsin with 11-cis retinal chromophore. In this study, we examine the regulation of Meta III decay by Grk1 and Arr1 in intact mouse rods and their effect on rod dark adaptation. We measure the rates of Meta III decay in isolated retinas of wild-type (WT), Grk1-deficient (Grk1−/−), Arr1-deficient (Arr1−/−), and Arr1-overexpressing (Arr1ox) mice. We find that in WT mouse rods, Meta III peaks ∼6 min after rhodopsin activation and decays with a time constant (τ) of 17 min. Meta III decay slows in Arr1−/− rods (τ of ∼27 min), whereas it accelerates in Arr1ox rods (τ of ∼8 min) and Grk1−/− rods (τ of ∼13 min). In all cases, regeneration of rhodopsin with exogenous 11-cis retinal is rate limited by the decay of Meta III. Notably, the kinetics of rod dark adaptation in vivo is also modulated by the levels of Arr1 and Grk1. We conclude that, in addition to their well-established roles in Meta II inactivation, Grk1 and Arr1 can modulate the kinetics of Meta III decay and rod dark adaptation in vivo.
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Affiliation(s)
- Rikard Frederiksen
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118
| | - Soile Nymark
- Department of Electronics and Communications Engineering, BioMediTech, Tampere University of Technology, 33720 Tampere, Finland
| | - Alexander V Kolesnikov
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO 63110
| | - Justin D Berry
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118
| | - Leopold Adler
- Department of Ophthalmology, Medical University of South Carolina, Charleston, SC 29425
| | - Yiannis Koutalos
- Department of Ophthalmology, Medical University of South Carolina, Charleston, SC 29425
| | - Vladimir J Kefalov
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO 63110
| | - M Carter Cornwall
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118
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9
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Bailes HJ, Milosavljevic N, Zhuang LY, Gerrard EJ, Nishiguchi T, Ozawa T, Lucas RJ. Optogenetic interrogation reveals separable G-protein-dependent and -independent signalling linking G-protein-coupled receptors to the circadian oscillator. BMC Biol 2017; 15:40. [PMID: 28506231 PMCID: PMC5430609 DOI: 10.1186/s12915-017-0380-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2017] [Accepted: 04/26/2017] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Endogenous circadian oscillators distributed across the mammalian body are synchronised among themselves and with external time via a variety of signalling molecules, some of which interact with G-protein-coupled receptors (GPCRs). GPCRs can regulate cell physiology via pathways originating with heterotrimeric G-proteins or β-arrestins. We applied an optogenetic approach to determine the contribution of these two signalling modes on circadian phase. RESULTS We employed a photopigment (JellyOp) that activates Gαs signalling with better selectivity and higher sensitivity than available alternatives, and a point mutant of this pigment (F112A) biased towards β-arrestin signalling. When expressed in fibroblasts, both native JellyOp and the F112A arrestin-biased mutant drove light-dependent phase resetting in the circadian clock. Shifts induced by the two opsins differed in their circadian phase dependence and the degree to which they were associated with clock gene induction. CONCLUSIONS Our data imply separable G-protein and arrestin inputs to the mammalian circadian clock and establish a pair of optogenetic tools suitable for manipulating Gαs- and β-arrestin-biased signalling in live cells.
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Affiliation(s)
- Helena J Bailes
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK
| | - Nina Milosavljevic
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK.
| | - Ling-Yu Zhuang
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK
| | - Elliot J Gerrard
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK
| | | | - Takeaki Ozawa
- Department of Chemistry, The University of Tokyo, Tokyo, Japan
| | - Robert J Lucas
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK
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10
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Peterhans C, Lally CCM, Ostermaier MK, Sommer ME, Standfuss J. Functional map of arrestin binding to phosphorylated opsin, with and without agonist. Sci Rep 2016; 6:28686. [PMID: 27350090 PMCID: PMC4923902 DOI: 10.1038/srep28686] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Accepted: 06/01/2016] [Indexed: 01/06/2023] Open
Abstract
Arrestins desensitize G protein-coupled receptors (GPCRs) and act as mediators of signalling. Here we investigated the interactions of arrestin-1 with two functionally distinct forms of the dim-light photoreceptor rhodopsin. Using unbiased scanning mutagenesis we probed the individual contribution of each arrestin residue to the interaction with the phosphorylated apo-receptor (Ops-P) and the agonist-bound form (Meta II-P). Disruption of the polar core or displacement of the C-tail strengthened binding to both receptor forms. In contrast, mutations of phosphate-binding residues (phosphosensors) suggest the phosphorylated receptor C-terminus binds arrestin differently for Meta II-P and Ops-P. Likewise, mutations within the inter-domain interface, variations in the receptor-binding loops and the C-edge of arrestin reveal different binding modes. In summary, our results indicate that arrestin-1 binding to Meta II-P and Ops-P is similarly dependent on arrestin activation, although the complexes formed with these two receptor forms are structurally distinct.
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Affiliation(s)
- Christian Peterhans
- Paul Scherrer Institute, Laboratory for Biomolecular Research, CH-5323, Villigen, Switzerland
| | - Ciara C M Lally
- Institut für Medizinische Physik und Biophysik (CC2), Charité-Universitätsmedizin Berlin, Charitéplatz 1, D-10117, Berlin, Germany
| | - Martin K Ostermaier
- Institut für Medizinische Physik und Biophysik (CC2), Charité-Universitätsmedizin Berlin, Charitéplatz 1, D-10117, Berlin, Germany
| | - Martha E Sommer
- Institut für Medizinische Physik und Biophysik (CC2), Charité-Universitätsmedizin Berlin, Charitéplatz 1, D-10117, Berlin, Germany
| | - Jörg Standfuss
- Paul Scherrer Institute, Laboratory for Biomolecular Research, CH-5323, Villigen, Switzerland
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11
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Jones Brunette AM, Sinha A, David L, Farrens DL. Evidence that the Rhodopsin Kinase (GRK1) N-Terminus and the Transducin Gα C-Terminus Interact with the Same "Hydrophobic Patch" on Rhodopsin TM5. Biochemistry 2016; 55:3123-35. [PMID: 27078130 DOI: 10.1021/acs.biochem.6b00328] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Phosphorylation of G protein-coupled receptors (GPCRs) terminates their ability to couple with and activate G proteins by increasing their affinity for arrestins. Unfortunately, detailed information regarding how GPCRs interact with the kinases responsible for their phosphorylation is still limited. Here, we purified fully functional GPCR kinase 1 (GRK1) using a rapid method and used it to gain insights into how this important kinase interacts with the GPCR rhodopsin. Specifically, we find that GRK1 uses the same site on rhodopsin as the transducin (Gt) Gtα C-terminal tail and the arrestin "finger loop", a cleft formed in the cytoplasmic face of the receptor upon activation. Our studies also show GRK1 requires two conserved residues located in this cleft (L226 and V230) that have been shown to be required for Gt activation due to their direct interactions with hydrophobic residues on the Gα C-terminal tail. Our data and modeling studies are consistent with the idea that all three proteins (Gt, GRK1, and visual arrestin) bind, at least in part, in the same site on rhodopsin and interact with the receptor through a similar hydrophobic contact-driven mechanism.
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Affiliation(s)
- Amber M Jones Brunette
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University , Portland, Oregon 97239-3098, United States
| | - Abhinav Sinha
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University , Portland, Oregon 97239-3098, United States
| | - Larry David
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University , Portland, Oregon 97239-3098, United States
| | - David L Farrens
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University , Portland, Oregon 97239-3098, United States
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12
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Jones BW, Pfeiffer RL, Ferrell WD, Watt CB, Marmor M, Marc RE. Retinal remodeling in human retinitis pigmentosa. Exp Eye Res 2016; 150:149-65. [PMID: 27020758 DOI: 10.1016/j.exer.2016.03.018] [Citation(s) in RCA: 208] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2015] [Revised: 02/23/2016] [Accepted: 03/18/2016] [Indexed: 12/11/2022]
Abstract
Retinitis Pigmentosa (RP) in the human is a progressive, currently irreversible neural degenerative disease usually caused by gene defects that disrupt the function or architecture of the photoreceptors. While RP can initially be a disease of photoreceptors, there is increasing evidence that the inner retina becomes progressively disorganized as the outer retina degenerates. These alterations have been extensively described in animal models, but remodeling in humans has not been as well characterized. This study, using computational molecular phenotyping (CMP) seeks to advance our understanding of the retinal remodeling process in humans. We describe cone mediated preservation of overall topology, retinal reprogramming in the earliest stages of the disease in retinal bipolar cells, and alterations in both small molecule and protein signatures of neurons and glia. Furthermore, while Müller glia appear to be some of the last cells left in the degenerate retina, they are also one of the first cell classes in the neural retina to respond to stress which may reveal mechanisms related to remodeling and cell death in other retinal cell classes. Also fundamentally important is the finding that retinal network topologies are altered. Our results suggest interventions that presume substantial preservation of the neural retina will likely fail in late stages of the disease. Even early intervention offers no guarantee that the interventions will be immune to progressive remodeling. Fundamental work in the biology and mechanisms of disease progression are needed to support vision rescue strategies.
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Affiliation(s)
- B W Jones
- Dept. Ophthalmology, Moran Eye Center, University of Utah, USA.
| | - R L Pfeiffer
- Dept. Ophthalmology, Moran Eye Center, University of Utah, USA
| | - W D Ferrell
- Dept. Ophthalmology, Moran Eye Center, University of Utah, USA
| | - C B Watt
- Dept. Ophthalmology, Moran Eye Center, University of Utah, USA
| | - M Marmor
- Dept. Ophthalmology, Stanford University, USA
| | - R E Marc
- Dept. Ophthalmology, Moran Eye Center, University of Utah, USA
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13
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van Hazel I, Dungan SZ, Hauser FE, Morrow JM, Endler JA, Chang BSW. A comparative study of rhodopsin function in the great bowerbird (Ptilonorhynchus nuchalis): Spectral tuning and light-activated kinetics. Protein Sci 2016; 25:1308-18. [PMID: 26889650 DOI: 10.1002/pro.2902] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2016] [Revised: 02/16/2016] [Accepted: 02/16/2016] [Indexed: 12/18/2022]
Abstract
Rhodopsin is the visual pigment responsible for initiating the phototransduction cascade in vertebrate rod photoreceptors. Although well-characterized in a few model systems, comparative studies of rhodopsin function, particularly for nonmammalian vertebrates are comparatively lacking. Bowerbirds are rare among passerines in possessing a key substitution, D83N, at a site that is otherwise highly conserved among G protein-coupled receptors. While this substitution is present in some dim-light adapted vertebrates, often accompanying another unusual substitution, A292S, its functional relevance in birds is uncertain. To investigate functional effects associated with these two substitutions, we use the rhodopsin gene from the great bowerbird (Ptilonorhynchus nuchalis) as a background for site-directed mutagenesis, in vitro expression and functional characterization. We also mutated these sites in two additional rhodopsins that do not naturally possess N83, chicken and bovine, for comparison. Both sites were found to contribute to spectral blue-shifts, but had opposing effects on kinetic rates. Substitutions at site 83 were found to primarily affect the kinetics of light-activated rhodopsin, while substitutions at site 292 had a larger impact on spectral tuning. The contribution of substitutions at site 83 to spectral tuning in particular depended on genetic background, but overall, the effects of substitutions were otherwise surprisingly additive, and the magnitudes of functional shifts were roughly similar across all three genetic backgrounds. By employing a comparative approach with multiple species, our study provides new insight into the joint impact of sites 83 and 292 on rhodopsin structure-function as well as their evolutionary significance for dim-light vision across vertebrates.
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Affiliation(s)
- Ilke van Hazel
- Department of Ecology and Evolutionary Biology, University of Toronto, Canada
| | - Sarah Z Dungan
- Department of Ecology and Evolutionary Biology, University of Toronto, Canada
| | - Frances E Hauser
- Department of Ecology and Evolutionary Biology, University of Toronto, Canada
| | - James M Morrow
- Department of Cell and Systems Biology, University of Toronto, Canada
| | - John A Endler
- Centre for Integrative Ecology, Deakin University, Australia
| | - Belinda S W Chang
- Department of Ecology and Evolutionary Biology, University of Toronto, Canada.,Department of Cell and Systems Biology, University of Toronto, Canada.,Centre for the Analysis of Genome Evolution and Function, University of Toronto, Canada
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14
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Chatterjee D, Eckert CE, Slavov C, Saxena K, Fürtig B, Sanders CR, Gurevich VV, Wachtveitl J, Schwalbe H. Influence of Arrestin on the Photodecay of Bovine Rhodopsin. Angew Chem Int Ed Engl 2015; 54:13555-60. [PMID: 26383645 PMCID: PMC4685475 DOI: 10.1002/anie.201505798] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2015] [Revised: 08/11/2015] [Indexed: 11/07/2022]
Abstract
Continued activation of the photocycle of the dim-light receptor rhodopsin leads to the accumulation of all-trans-retinal in the rod outer segments (ROS). This accumulation can damage the photoreceptor cell. For retinal homeostasis, deactivation processes are initiated in which the release of retinal is delayed. One of these processes involves the binding of arrestin to rhodopsin. Here, the interaction of pre-activated truncated bovine visual arrestin (Arr(Tr)) with rhodopsin in 1,2-diheptanoyl-sn-glycero-3-phosphocholine (DHPC) micelles is investigated by solution NMR techniques and flash photolysis spectroscopy. Our results show that formation of the rhodopsin-arrestin complex markedly influences partitioning in the decay kinetics of rhodopsin, which involves the simultaneous formation of a meta II and a meta III state from the meta I state. Binding of Arr(Tr) leads to an increase in the population of the meta III state and consequently to an approximately twofold slower release of all-trans-retinal from rhodopsin.
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Affiliation(s)
- Deep Chatterjee
- Institute of Organic Chemistry and Chemical Biology, Center of Biomolecular Magnetic Resonance (BMRZ), Goethe University Frankfurt/Main, Max-von-Laue-Strasse 7, 60438 Frankfurt am Main (Germany)
| | - Carl Elias Eckert
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt/Main, Max-von-Laue-Strasse 7, 60438 Frankfurt am Main (Germany)
| | - Chavdar Slavov
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt/Main, Max-von-Laue-Strasse 7, 60438 Frankfurt am Main (Germany)
| | - Krishna Saxena
- Institute of Organic Chemistry and Chemical Biology, Center of Biomolecular Magnetic Resonance (BMRZ), Goethe University Frankfurt/Main, Max-von-Laue-Strasse 7, 60438 Frankfurt am Main (Germany)
| | - Boris Fürtig
- Institute of Organic Chemistry and Chemical Biology, Center of Biomolecular Magnetic Resonance (BMRZ), Goethe University Frankfurt/Main, Max-von-Laue-Strasse 7, 60438 Frankfurt am Main (Germany)
| | - Charles R Sanders
- Department of Biochemistry, Center for Structural Biology, Institute of Chemical Biology, Vanderbilt University School of Medicine, Nashville, TN 37232 (USA)
| | - Vsevolod V Gurevich
- Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN 37232 (USA)
| | - Josef Wachtveitl
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt/Main, Max-von-Laue-Strasse 7, 60438 Frankfurt am Main (Germany).
| | - Harald Schwalbe
- Institute of Organic Chemistry and Chemical Biology, Center of Biomolecular Magnetic Resonance (BMRZ), Goethe University Frankfurt/Main, Max-von-Laue-Strasse 7, 60438 Frankfurt am Main (Germany).
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15
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Chatterjee D, Eckert CE, Slavov C, Saxena K, Fürtig B, Sanders CR, Gurevich VV, Wachtveitl J, Schwalbe H. Influence of Arrestin on the Photodecay of Bovine Rhodopsin. Angew Chem Int Ed Engl 2015. [DOI: 10.1002/ange.201505798] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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16
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Beyrière F, Sommer ME, Szczepek M, Bartl FJ, Hofmann KP, Heck M, Ritter E. Formation and decay of the arrestin·rhodopsin complex in native disc membranes. J Biol Chem 2015; 290:12919-28. [PMID: 25847250 DOI: 10.1074/jbc.m114.620898] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2014] [Indexed: 01/05/2023] Open
Abstract
In the G protein-coupled receptor rhodopsin, light-induced cis/trans isomerization of the retinal ligand triggers a series of distinct receptor states culminating in the active Metarhodopsin II (Meta II) state, which binds and activates the G protein transducin (Gt). Long before Meta II decays into the aporeceptor opsin and free all-trans-retinal, its signaling is quenched by receptor phosphorylation and binding of the protein arrestin-1, which blocks further access of Gt to Meta II. Although recent crystal structures of arrestin indicate how it might look in a precomplex with the phosphorylated receptor, the transition into the high affinity complex is not understood. Here we applied Fourier transform infrared spectroscopy to monitor the interaction of arrestin-1 and phosphorylated rhodopsin in native disc membranes. By isolating the unique infrared signature of arrestin binding, we directly observed the structural alterations in both reaction partners. In the high affinity complex, rhodopsin adopts a structure similar to Gt-bound Meta II. In arrestin, a modest loss of β-sheet structure indicates an increase in flexibility but is inconsistent with a large scale structural change. During Meta II decay, the arrestin-rhodopsin stoichiometry shifts from 1:1 to 1:2. Arrestin stabilizes half of the receptor population in a specific Meta II protein conformation, whereas the other half decays to inactive opsin. Altogether these results illustrate the distinct binding modes used by arrestin to interact with different functional forms of the receptor.
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Affiliation(s)
- Florent Beyrière
- From the Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany and
| | - Martha E Sommer
- From the Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany and
| | - Michal Szczepek
- From the Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany and
| | - Franz J Bartl
- From the Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany and Zentrum für Biophysik und Bioinformatik (BPI) and
| | - Klaus Peter Hofmann
- From the Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany and Zentrum für Biophysik und Bioinformatik (BPI) and
| | - Martin Heck
- From the Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany and
| | - Eglof Ritter
- Institut für Biologie, Experimentelle Biophysik, Humboldt-Universität zu Berlin, 10115 Berlin, Germany
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17
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Schafer CT, Farrens DL. Conformational selection and equilibrium governs the ability of retinals to bind opsin. J Biol Chem 2014; 290:4304-18. [PMID: 25451936 DOI: 10.1074/jbc.m114.603134] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Despite extensive study, how retinal enters and exits the visual G protein-coupled receptor rhodopsin remains unclear. One clue may lie in two openings between transmembrane helix 1 (TM1) and TM7 and between TM5 and TM6 in the active receptor structure. Recently, retinal has been proposed to enter the inactive apoprotein opsin (ops) through these holes when the receptor transiently adopts the active opsin conformation (ops*). Here, we directly test this "transient activation" hypothesis using a fluorescence-based approach to measure rates of retinal binding to samples containing differing relative fractions of ops and ops*. In contrast to what the transient activation hypothesis model would predict, we found that binding for the inverse agonist, 11-cis-retinal (11CR), slowed when the sample contained more ops* (produced using M257Y, a constitutively activating mutation). Interestingly, the increased presence of ops* allowed for binding of the agonist, all-trans-retinal (ATR), whereas WT opsin showed no binding. Shifting the conformational equilibrium toward even more ops* using a G protein peptide mimic (either free in solution or fused to the receptor) accelerated the rate of ATR binding and slowed 11CR binding. An arrestin peptide mimic showed little effect on 11CR binding; however, it stabilized opsin · ATR complexes. The TM5/TM6 hole is apparently not involved in this conformational selection. Increasing its size by mutagenesis did not enable ATR binding but instead slowed 11CR binding, suggesting that it may play a role in trapping 11CR. In summary, our results indicate that conformational selection dictates stable retinal binding, which we propose involves ATR and 11CR binding to different states, the latter a previously unidentified, open-but-inactive conformation.
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Affiliation(s)
- Christopher T Schafer
- From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239-3098
| | - David L Farrens
- From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239-3098
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18
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Hauser FE, van Hazel I, Chang BSW. Spectral tuning in vertebrate short wavelength-sensitive 1 (SWS1) visual pigments: Can wavelength sensitivity be inferred from sequence data? JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2014; 322:529-39. [DOI: 10.1002/jez.b.22576] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2013] [Revised: 03/05/2014] [Accepted: 05/06/2014] [Indexed: 01/12/2023]
Affiliation(s)
- Frances E. Hauser
- Department of Ecology & Evolutionary Biology; University of Toronto; Toronto Ontario Canada
| | - Ilke van Hazel
- Department of Ecology & Evolutionary Biology; University of Toronto; Toronto Ontario Canada
| | - Belinda S. W. Chang
- Department of Ecology & Evolutionary Biology; University of Toronto; Toronto Ontario Canada
- Department of Cell & Systems Biology; University of Toronto; Toronto Ontario Canada
- Centre for the Analysis of Genome Evolution & Function; University of Toronto; Toronto Ontario Canada
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19
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Sinha A, Jones Brunette AM, Fay JF, Schafer CT, Farrens DL. Rhodopsin TM6 can interact with two separate and distinct sites on arrestin: evidence for structural plasticity and multiple docking modes in arrestin-rhodopsin binding. Biochemistry 2014; 53:3294-307. [PMID: 24724832 PMCID: PMC4039336 DOI: 10.1021/bi401534y] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
![]()
Various studies have implicated the
concave surface of arrestin
in the binding of the cytosolic surface of rhodopsin. However, specific
sites of contact between the two proteins have not previously been
defined in detail. Here, we report that arrestin shares part of the
same binding site on rhodopsin as does the transducin Gα subunit C-terminal tail, suggesting binding of both proteins to
rhodopsin may share some similar underlying mechanisms. We also identify
two areas of contact between the proteins near this region. Both sites
lie in the arrestin N-domain, one in the so-called “finger”
loop (residues 67–79) and the other in the 160 loop (residues
155–165). We mapped these sites using a novel tryptophan-induced
quenching method, in which we introduced Trp residues into arrestin
and measured their ability to quench the fluorescence of bimane probes
attached to cysteine residues on TM6 of rhodopsin (T242C and T243C).
The involvement of finger loop binding to rhodopsin was expected,
but the evidence of the arrestin 160 loop contacting rhodopsin was
not. Remarkably, our data indicate one site on rhodopsin can interact
with multiple structurally separate sites on arrestin that are almost
30 Å apart. Although this observation at first seems paradoxical,
in fact, it provides strong support for recent hypotheses that structural
plasticity and conformational changes are involved in the arrestin–rhodopsin
binding interface and that the two proteins may be able to interact
through multiple docking modes, with arrestin binding to both monomeric
and dimeric rhodopsin.
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Affiliation(s)
- Abhinav Sinha
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University , Portland, Oregon 97239-3098, United States
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20
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Vishnivetskiy SA, Ostermaier MK, Singhal A, Panneels V, Homan KT, Glukhova A, Sligar SG, Tesmer JJG, Schertler GF, Standfuss J, Gurevich VV. Constitutively active rhodopsin mutants causing night blindness are effectively phosphorylated by GRKs but differ in arrestin-1 binding. Cell Signal 2013; 25:2155-62. [PMID: 23872075 PMCID: PMC3774132 DOI: 10.1016/j.cellsig.2013.07.009] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Accepted: 07/11/2013] [Indexed: 11/24/2022]
Abstract
The effects of activating mutations associated with night blindness on the stoichiometry of rhodopsin interactions with G protein-coupled receptor kinase 1 (GRK1) and arrestin-1 have not been reported. Here we show that the monomeric form of WT rhodopsin and its constitutively active mutants M257Y, G90D, and T94I, reconstituted into HDL particles are effectively phosphorylated by GRK1, as well as two more ubiquitously expressed subtypes, GRK2 and GRK5. All versions of arrestin-1 tested (WT, pre-activated, and constitutively monomeric mutants) bind to monomeric rhodopsin and show the same selectivity for different functional forms of rhodopsin as in native disc membranes. Rhodopsin phosphorylation by GRK1 and GRK2 promotes arrestin-1 binding to a comparable extent, whereas similar phosphorylation by GRK5 is less effective, suggesting that not all phosphorylation sites on rhodopsin are equivalent in promoting arrestin-1 binding. The binding of WT arrestin-1 to phospho-opsin is comparable to the binding to its preferred target, P-Rh*, suggesting that in photoreceptors arrestin-1 only dissociates after opsin regeneration with 11-cis-retinal, which converts phospho-opsin into inactive phospho-rhodopsin that has lower affinity for arrestin-1. Reduced binding of arrestin-1 to the phospho-opsin form of G90D mutant likely contributes to night blindness caused by this mutation in humans.
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Affiliation(s)
| | - Martin K. Ostermaier
- Laboratory of Biomolecular Research, Paul Scherrer Institut, Villigen 5232, Switzerland
| | - Ankita Singhal
- Laboratory of Biomolecular Research, Paul Scherrer Institut, Villigen 5232, Switzerland
| | - Valerie Panneels
- Laboratory of Biomolecular Research, Paul Scherrer Institut, Villigen 5232, Switzerland
| | - Kristoff T. Homan
- Life Sciences Institute, Departments of Pharmacology and Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109-2216, USA
| | - Alisa Glukhova
- Life Sciences Institute, Departments of Pharmacology and Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109-2216, USA
| | - Stephen G. Sligar
- Department of Biochemistry, University of Illinois, Urbana, IL 61801, USA
| | - John J. G. Tesmer
- Life Sciences Institute, Departments of Pharmacology and Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109-2216, USA
| | - Gebhard F.X. Schertler
- Laboratory of Biomolecular Research, Paul Scherrer Institut, Villigen 5232, Switzerland
- Department of Biology, ETH Zurich, Zurich, 8093, Switzerland
| | - Joerg Standfuss
- Laboratory of Biomolecular Research, Paul Scherrer Institut, Villigen 5232, Switzerland
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21
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Alexiev U, Farrens DL. Fluorescence spectroscopy of rhodopsins: insights and approaches. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2013; 1837:694-709. [PMID: 24183695 DOI: 10.1016/j.bbabio.2013.10.008] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Revised: 10/11/2013] [Accepted: 10/16/2013] [Indexed: 01/30/2023]
Abstract
Fluorescence spectroscopy has become an established tool at the interface of biology, chemistry and physics because of its exquisite sensitivity and recent technical advancements. However, rhodopsin proteins present the fluorescence spectroscopist with a unique set of challenges and opportunities due to the presence of the light-sensitive retinal chromophore. This review briefly summarizes some approaches that have successfully met these challenges and the novel insights they have yielded about rhodopsin structure and function. We start with a brief overview of fluorescence fundamentals and experimental methodologies, followed by more specific discussions of technical challenges rhodopsin proteins present to fluorescence studies. Finally, we end by discussing some of the unique insights that have been gained specifically about visual rhodopsin and its interactions with affiliate proteins through the use of fluorescence spectroscopy. This article is part of a Special Issue entitled: Retinal Proteins - You can teach an old dog new tricks.
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Affiliation(s)
- Ulrike Alexiev
- Physics Department, Freie Universität Berlin, Berlin, Germany.
| | - David L Farrens
- Departments of Biochemistry and Molecular Biology, Oregon Health Sciences University, USA
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22
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Smith WC. The role of arrestins in visual and disease processes of the eye. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2013; 118:243-65. [PMID: 23764057 DOI: 10.1016/b978-0-12-394440-5.00010-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Visual arrestins are well known for their function in quenching the phototransduction process in rods and cones. Perhaps not as well known is their participation in multiple other processes in the normal and disease states of the eye. This chapter covers the range of the known functions of the visual arrestins, beginning with their classical role in quenching light-activated visual pigments. The role of visual arrestins is also reviewed from the perspective of their dynamic mobility whereby they redistribute significantly between the compartments of highly polarized photoreceptor cells. Additional roles of the visual arrestins are also reviewed based on new interacting partners that have been discovered over the past decade. Finally, the contribution of the visual arrestins to diseases of the visual system is explored.
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Affiliation(s)
- W Clay Smith
- Department of Ophthalmology, University of Florida, Gainesville, Florida, USA
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23
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Functional characterization of the rod visual pigment of the echidna (Tachyglossus aculeatus), a basal mammal. Vis Neurosci 2012; 29:211-7. [PMID: 22874131 DOI: 10.1017/s0952523812000223] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Monotremes are the most basal egg-laying mammals comprised of two extant genera, which are largely nocturnal. Visual pigments, the first step in the sensory transduction cascade in photoreceptors of the eye, have been examined in a variety of vertebrates, but little work has been done to study the rhodopsin of monotremes. We isolated the rhodopsin gene of the nocturnal short-beaked echidna (Tachyglossus aculeatus) and expressed and functionally characterized the protein in vitro. Three mutants were also expressed and characterized: N83D, an important site for spectral tuning and metarhodopsin kinetics, and two sites with amino acids unique to the echidna (T158A and F169A). The λ(max) of echidna rhodopsin (497.9 ± 1.1 nm) did not vary significantly in either T158A (498.0 ± 1.3 nm) or F169A (499.4 ± 0.1 nm) but was redshifted in N83D (503.8 ± 1.5 nm). Unlike other mammalian rhodopsins, echidna rhodopsin did react when exposed to hydroxylamine, although not as fast as cone opsins. The retinal release rate of light-activated echidna rhodopsin, as measured by fluorescence spectroscopy, had a half-life of 9.5 ± 2.6 min-1, which is significantly shorter than that of bovine rhodopsin. The half-life of the N83D mutant was 5.1 ± 0.1 min-1, even shorter than wild type. Our results show that with respect to hydroxylamine sensitivity and retinal release, the wild-type echidna rhodopsin displays major differences to all previously characterized mammalian rhodopsins and appears more similar to other nonmammalian vertebrate rhodopsins such as chicken and anole. However, our N83D mutagenesis results suggest that this site may mediate adaptation in the echidna to dim light environments, possibly via increased stability of light-activated intermediates. This study is the first characterization of a rhodopsin from a most basal mammal and indicates that there might be more functional variation in mammalian rhodopsins than previously assumed.
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Abstract
Retinal photoreceptor degeneration takes many forms. Mutations in rhodopsin genes or disorders of the retinal pigment epithelium, defects in the adenosine triphosphate binding cassette transporter, ABCR gene defects, receptor tyrosine kinase defects, ciliopathies and transport defects, defects in both transducin and arrestin, defects in rod cyclic guanosine 3',5'-monophosphate phosphodiesterase, peripherin defects, defects in metabotropic glutamate receptors, synthetic enzymatic defects, defects in genes associated with signaling, and many more can all result in retinal degenerative disease like retinitis pigmentosa (RP) or RP-like disorders. Age-related macular degeneration (AMD) and AMD-like disorders are possibly due to a constellation of potential gene targets and gene/gene interactions, while other defects result in diabetic retinopathy or glaucoma. However, all of these insults as well as traumatic insults to the retina result in retinal remodeling. Retinal remodeling is a universal finding subsequent to retinal degenerative disease that results in deafferentation of the neural retina from photoreceptor input as downstream neuronal elements respond to loss of input with negative plasticity. This negative plasticity is not passive in the face of photoreceptor degeneration, with a phased revision of retinal structure and function found at the molecular, synaptic, cell, and tissue levels involving all cell classes in the retina, including neurons and glia. Retinal remodeling has direct implications for the rescue of vision loss through bionic or biological approaches, as circuit revision in the retina corrupts any potential surrogate photoreceptor input to a remnant neural retina. However, there are a number of potential opportunities for intervention that are revealed through the study of retinal remodeling, including therapies that are designed to slow down photoreceptor loss, interventions that are designed to limit or arrest remodeling events, and optogenetic approaches that target appropriate classes of neurons in the remnant neural retina.
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25
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Nymark S, Frederiksen R, Woodruff ML, Cornwall MC, Fain GL. Bleaching of mouse rods: microspectrophotometry and suction-electrode recording. J Physiol 2012; 590:2353-64. [PMID: 22451436 DOI: 10.1113/jphysiol.2012.228627] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
When a substantial fraction of rhodopsin in a rod photoreceptor is exposed to bright light, the rod is desensitized by a process known as bleaching adaptation. Experiments on isolated photoreceptors in amphibians have revealed many of the features of bleaching adaptation, but such experiments have not so far been possible in mammals. We now describe a method for making microspectrophotometric measurements of pigment concentration and suction-electrode recording of electrical responses over a wide range of bleaching exposures from isolated mouse rods or pieces of mouse retina. We show that if pigment is bleached at a low rate in the presence of bovine serum albumin (BSA), and intermediate photoproducts are allowed to decay, mouse rods are stably desensitized; subsequent treatment with exogenous 11-cis retinal results in pigment regeneration and substantial recovery of sensitivity to the dark-adapted value. Stably bleached wild-type (WT) rods show a decrease in circulating current and acceleration of the time course of decay, much as in steady background light; similar effects are seen in guanylyl cyclase-activating protein knockout (GCAPs(-/-)) rods, indicating that regulation of guanylyl cyclase is not necessary for at least a part of the adaptation produced by bleaching. Our experiments demonstrate that in mammalian rods, as in amphibian rods, steady-state desensitization after bleaching is produced by two components: (1) a reduction in the probability of photon absorption produced by a decrease in rhodopsin concentration; and (2) an equivalent background light whose intensity is proportional to the fraction of bleached pigment, and which adapts the rod like real background light. These two mechanisms together fully account for the ‘log-linear' relationship in mammalian retina between sensitivity and per cent bleach, which can be measured in the steady state following exposure to bright light. Our methods will now make possible an examination of bleaching adaptation and pigment regeneration in mouse animal lines with mutations or other alterations in the proteins of transduction.
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Affiliation(s)
- S Nymark
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118-2526, USA
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26
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Yanamala N, Gardner E, Riciutti A, Klein-Seetharaman J. The cytoplasmic rhodopsin-protein interface: potential for drug discovery. Curr Drug Targets 2012; 13:3-14. [PMID: 21777183 PMCID: PMC3275648 DOI: 10.2174/138945012798868461] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2010] [Revised: 02/08/2011] [Accepted: 02/10/2011] [Indexed: 01/20/2023]
Abstract
The mammalian dim-light photoreceptor rhodopsin is a prototypic G protein coupled receptor (GPCR), interacting with the G protein, transducin, rhodopsin kinase, and arrestin. All of these proteins interact with rhodopsin at its cytoplasmic surface. Structural and modeling studies have provided in-depth descriptions of the respective interfaces. Overlap and thus competition for binding surfaces is a major regulatory mechanism for signal processing. Recently, it was found that the same surface is also targeted by small molecules. These ligands can directly interfere with the binding and activation of the proteins of the signal transduction cascade, but they can also allosterically modulate the retinal ligand binding pocket. Because the pocket that is targeted contains residues that are highly conserved across Class A GPCRs, these findings imply that it may be possible to target multiple GPCRs with the same ligand(s). This is desirable for example in complex diseases such as cancer where multiple GPCRs participate in the disease networks.
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Affiliation(s)
- Naveena Yanamala
- Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
| | - Eric Gardner
- Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
| | - Alec Riciutti
- Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
| | - Judith Klein-Seetharaman
- Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
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Reuter T. Fifty years of dark adaptation 1961–2011. Vision Res 2011; 51:2243-62. [DOI: 10.1016/j.visres.2011.08.021] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2010] [Revised: 08/24/2011] [Accepted: 08/24/2011] [Indexed: 02/07/2023]
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Huang CC, Orban T, Jastrzebska B, Palczewski K, Tesmer JJG. Activation of G protein-coupled receptor kinase 1 involves interactions between its N-terminal region and its kinase domain. Biochemistry 2011; 50:1940-9. [PMID: 21265573 PMCID: PMC3069497 DOI: 10.1021/bi101606e] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
G protein-coupled receptor kinases (GRKs) phosphorylate activated G protein-coupled receptors (GPCRs) to initiate receptor desensitization. In addition to the canonical phosphoacceptor site of the kinase domain, activated receptors bind to a distinct docking site that confers higher affinity and activates GRKs allosterically. Recent mutagenesis and structural studies support a model in which receptor docking activates a GRK by stabilizing the interaction of its ∼20-amino acid N-terminal region with the kinase domain. This interaction in turn stabilizes a closed, more active conformation of the enzyme. To investigate the importance of this interaction for the process of GRK activation, we first validated the functionality of the N-terminal region in rhodopsin kinase (GRK1) by site-directed mutagenesis and then introduced a disulfide bond to cross-link the N-terminal region of GRK1 with its specific binding site on the kinase domain. Characterization of the kinetic and biophysical properties of the cross-linked protein showed that disulfide bond formation greatly enhances the catalytic efficiency of the peptide phosphorylation, but receptor-dependent phosphorylation, Meta II stabilization, and inhibition of transducin activation were unaffected. These data indicate that the interaction of the N-terminal region with the kinase domain is important for GRK activation but does not dictate the affinity of GRKs for activated receptors.
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Affiliation(s)
- Chih-chin Huang
- Life Sciences Institute, 210 Washtenaw Avenue, University of Michigan, Ann Arbor, Michigan 48109-2216, United States
| | - Tivadar Orban
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965, United States
| | - Beata Jastrzebska
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965, United States
| | - Krzysztof Palczewski
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965, United States
| | - John J. G. Tesmer
- Life Sciences Institute, 210 Washtenaw Avenue, University of Michigan, Ann Arbor, Michigan 48109-2216, United States
- Department of Pharmacology, 210 Washtenaw Avenue, University of Michigan, Ann Arbor, Michigan 48109-2216, United States
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Tsukamoto H, Sinha A, DeWitt M, Farrens DL. Monomeric rhodopsin is the minimal functional unit required for arrestin binding. J Mol Biol 2010; 399:501-11. [PMID: 20417217 DOI: 10.1016/j.jmb.2010.04.029] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2010] [Revised: 04/13/2010] [Accepted: 04/16/2010] [Indexed: 11/19/2022]
Abstract
We have tested whether arrestin binding requires the G-protein-coupled receptor be a dimer or a multimer. To do this, we encapsulated single-rhodopsin molecules into nanoscale phospholipid particles (so-called nanodiscs) and measured their ability to bind arrestin. Our data clearly show that both visual arrestin and beta-arrestin 1 can bind to monomeric rhodopsin and stabilize the active metarhodopsin II form. Interestingly, we find that the monomeric rhodopsin in nanodiscs has a higher affinity for wild-type arrestin binding than does oligomeric rhodopsin in liposomes or nanodiscs, as assessed by stabilization of metarhodopsin II. Together, these results establish that rhodopsin self-association is not required to enable arrestin binding.
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Affiliation(s)
- Hisao Tsukamoto
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239-3098, USA
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Abstract
By its action on rhodopsin, light triggers the well-known visual transduction cascade, but can also induce cell damage and death through phototoxic mechanisms - a comprehensive understanding of which is still elusive despite more than 40 years of research. Herein, we integrate recent experimental findings to address several hypotheses of retinal light damage, premised in part on the close anatomical and metabolic relationships between the photoreceptors and the retinal pigment epithelium. We begin by reviewing the salient features of light damage, recently joined by evidence for retinal remodeling which has implications for the prognosis of recovery of function in retinal degenerations. We then consider select factors that influence the progression of the damage process and the extent of visual cell loss. Traditional, genetically modified, and emerging animal models are discussed, with particular emphasis on cone visual cells. Exogenous and endogenous retinal protective factors are explored, with implications for light damage mechanisms and some suggested avenues for future research. Synergies are known to exist between our long term light environment and photoreceptor cell death in retinal disease. Understanding the molecular mechanisms of light damage in a variety of animal models can provide valuable insights into the effects of light in clinical disorders and may form the basis of future therapies to prevent or delay visual cell loss.
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Krebs MP, Holden DC, Joshi P, Clark CL, Lee AH, Kaushal S. Molecular mechanisms of rhodopsin retinitis pigmentosa and the efficacy of pharmacological rescue. J Mol Biol 2009; 395:1063-78. [PMID: 19913029 DOI: 10.1016/j.jmb.2009.11.015] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2009] [Revised: 11/05/2009] [Accepted: 11/05/2009] [Indexed: 11/24/2022]
Abstract
Variants of rhodopsin, a complex of 11-cis retinal and opsin, cause retinitis pigmentosa (RP), a degenerative disease of the retina. Trafficking defects due to rhodopsin misfolding have been proposed as the most likely basis of the disease, but other potentially overlapping mechanisms may also apply. Pharmacological therapies for RP must target the major disease mechanism and contend with overlap, if it occurs. To this end, we have explored the molecular basis of rhodopsin RP in the context of pharmacological rescue with 11-cis retinal. Stable inducible cell lines were constructed to express wild-type opsin; the pathogenic variants T4R, T17M, P23A, P23H, P23L, and C110Y; or the nonpathogenic variants F220L and A299S. Pharmacological rescue was measured as the fold increase in rhodopsin or opsin levels upon addition of 11-cis retinal during opsin expression. Only Pro23 and T17M variants were rescued significantly. C110Y opsin was produced at low levels and did not yield rhodopsin, whereas the T4R, F220L, and A299S proteins reached near-wild-type levels and changed little with 11-cis retinal. All of the mutant rhodopsins exhibited misfolding, which increased over a broad range in the order F220L, A299S, T4R, T17M, P23A, P23H, P23L, as determined by decreased thermal stability in the dark and increased hydroxylamine sensitivity. Pharmacological rescue increased as misfolding decreased, but was limited for the least misfolded variants. Significantly, pathogenic variants also showed abnormal photobleaching behavior, including an increased ratio of metarhodopsin-I-like species to metarhodopsin-II-like species and aberrant photoproduct accumulation with prolonged illumination. These results, combined with an analysis of published biochemical and clinical studies, suggest that many rhodopsin variants cause disease by affecting both biosynthesis and photoactivity. We conclude that pharmacological rescue is promising as a broadly effective therapy for rhodopsin RP, particularly if implemented in a way that minimizes the photoactivity of the mutant proteins.
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Affiliation(s)
- Mark P Krebs
- Department of Ophthalmology and the Charlie Mack Overstreet Laboratories for Retinal Diseases, College of Medicine, University of Florida, Gainesville, FL 32610, USA
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Imai H, Kefalov V, Sakurai K, Chisaka O, Ueda Y, Onishi A, Morizumi T, Fu Y, Ichikawa K, Nakatani K, Honda Y, Chen J, Yau KW, Shichida Y. Molecular properties of rhodopsin and rod function. J Biol Chem 2007; 282:6677-84. [PMID: 17194706 PMCID: PMC2885910 DOI: 10.1074/jbc.m610086200] [Citation(s) in RCA: 54] [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
Signal transduction in rod cells begins with photon absorption by rhodopsin and leads to the generation of an electrical response. The response profile is determined by the molecular properties of the phototransduction components. To examine how the molecular properties of rhodopsin correlate with the rod-response profile, we have generated a knock-in mouse with rhodopsin replaced by its E122Q mutant, which exhibits properties different from those of wild-type (WT) rhodopsin. Knock-in mouse rods with E122Q rhodopsin exhibited a photosensitivity about 70% of WT. Correspondingly, their single-photon response had an amplitude about 80% of WT, and a rate of decline from peak about 1.3 times of WT. The overall 30% lower photosensitivity of mutant rods can be explained by a lower pigment photosensitivity (0.9) and the smaller single-photon response (0.8). The slower decline of the response, however, did not correlate with the 10-fold shorter lifetime of the meta-II state of E122Q rhodopsin. This shorter lifetime became evident in the recovery phase of rod cells only when arrestin was absent. Simulation analysis of the photoresponse profile indicated that the slower decline and the smaller amplitude of the single-photon response can both be explained by the shift in the meta-I/meta-II equilibrium of E122Q rhodopsin toward meta-I. The difference in meta-III lifetime between WT and E122Q mutant became obvious in the recovery phase of the dark current after moderate photobleaching of rod cells. Thus, the present study clearly reveals how the molecular properties of rhodopsin affect the amplitude, shape, and kinetics of the rod response.
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Affiliation(s)
- Hiroo Imai
- 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
| | - Vladimir Kefalov
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Keisuke Sakurai
- 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
| | - Osamu Chisaka
- Department of Cell and Developmental Biology, Graduate School of Biostudies, Kyoto University, Kyoto 606-8507, Japan
| | - Yoshiki Ueda
- Department of Ophthalmology and Visual Science, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan
| | - Akishi Onishi
- 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
| | - Takefumi Morizumi
- 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
| | - Yingbin Fu
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Kazuhisa Ichikawa
- Department of Brain and Bioinformation Science, Kanazawa Institute of Technology, Ishikawa 924-0838, Japan
| | - Kei Nakatani
- Graduate School of Life and Environmental Sciences, University of Tsukuba and Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Ibaraki 305-8572, Japan
| | - Yoshihito Honda
- Department of Ophthalmology and Visual Science, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan
| | - Jeannie Chen
- The Mary D. Allen Laboratory for Vision Research, Doheny Eye Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033
| | - King-Wai Yau
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Yoshinori Shichida
- 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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Ritter E, Elgeti M, Hofmann KP, Bartl FJ. Deactivation and proton transfer in light-induced metarhodopsin II/metarhodopsin III conversion: a time-resolved fourier transform infrared spectroscopic study. J Biol Chem 2007; 282:10720-30. [PMID: 17287211 DOI: 10.1074/jbc.m610658200] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Vertebrate rhodopsin shares with other retinal proteins the 11-cis-retinal chromophore and the light-induced 11-cis/trans isomerization triggering its activation pathway. However, only in rhodopsin the retinylidene Schiff base bond to the apoprotein is eventually hydrolyzed, making a complex regeneration pathway necessary. Metabolic regeneration cannot be short-cut, and light absorption in the active metarhodopsin (Meta) II intermediate causes anti/syn isomerization around the retinylidene linkage rather than reversed trans/cis isomerization. A new deactivating pathway is thereby triggered, which ends in the Meta III "retinal storage" product. Using time-resolved Fourier transform infrared spectroscopy, we show that the identified steps of receptor activation, including Schiff base deprotonation, protein structural changes, and proton uptake by the apoprotein, are all reversed. However, Schiff base reprotonation is much faster than the activating deprotonation, whereas the protein structural changes are slower. The final proton release occurs with pK approximately 4.5, similar to the pK of a free Glu residue and to the pK at which the isolated opsin apoprotein becomes active. A forced deprotonation, equivalent to the forced protonation in the activating pathway, which occurs against the unfavorable pH of the medium, is not observed. This explains properties of the final Meta III product, which displays much higher residual activity and is less stable than rhodopsin arising from regeneration with 11-cis-retinal. We propose that the anti/syn conversion can only induce a fast reorientation and distance change of the Schiff base but fails to build up the full set of dark ground state constraints, presumably involving the Glu(134)/Arg(135) cluster.
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Affiliation(s)
- Eglof Ritter
- Institut für Medizinische Physik und Biophysik, Charité, Universitätsmedizin Berlin, Charitéplatz 1, D-10098 Berlin
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