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Batebi H, Pérez-Hernández G, Rahman SN, Lan B, Kamprad A, Shi M, Speck D, Tiemann JKS, Guixà-González R, Reinhardt F, Stadler PF, Papasergi-Scott MM, Skiniotis G, Scheerer P, Kobilka BK, Mathiesen JM, Liu X, Hildebrand PW. Mechanistic insights into G-protein coupling with an agonist-bound G-protein-coupled receptor. Nat Struct Mol Biol 2024:10.1038/s41594-024-01334-2. [PMID: 38867113 DOI: 10.1038/s41594-024-01334-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2024] [Accepted: 05/14/2024] [Indexed: 06/14/2024]
Abstract
G-protein-coupled receptors (GPCRs) activate heterotrimeric G proteins by promoting guanine nucleotide exchange. Here, we investigate the coupling of G proteins with GPCRs and describe the events that ultimately lead to the ejection of GDP from its binding pocket in the Gα subunit, the rate-limiting step during G-protein activation. Using molecular dynamics simulations, we investigate the temporal progression of structural rearrangements of GDP-bound Gs protein (Gs·GDP; hereafter GsGDP) upon coupling to the β2-adrenergic receptor (β2AR) in atomic detail. The binding of GsGDP to the β2AR is followed by long-range allosteric effects that significantly reduce the energy needed for GDP release: the opening of α1-αF helices, the displacement of the αG helix and the opening of the α-helical domain. Signal propagation to the Gs occurs through an extended receptor interface, including a lysine-rich motif at the intracellular end of a kinked transmembrane helix 6, which was confirmed by site-directed mutagenesis and functional assays. From this β2AR-GsGDP intermediate, Gs undergoes an in-plane rotation along the receptor axis to approach the β2AR-Gsempty state. The simulations shed light on how the structural elements at the receptor-G-protein interface may interact to transmit the signal over 30 Å to the nucleotide-binding site. Our analysis extends the current limited view of nucleotide-free snapshots to include additional states and structural features responsible for signaling and G-protein coupling specificity.
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Affiliation(s)
- Hossein Batebi
- Universität Leipzig, Medizinische Fakultät, Institut für Medizinische Physik und Biophysik, Leipzig, Germany
- Freie Universität Berlin, Fachbereich Physik, Berlin, Germany
| | - Guillermo Pérez-Hernández
- Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Medical Physics and Biophysics, Berlin, Germany
| | - Sabrina N Rahman
- University of Copenhagen, Department of Drug Design and Pharmacology, Copenhagen, Denmark
| | - Baoliang Lan
- State Key Laboratory of Membrane Biology, Tsinghua-Peking Center for Life Sciences, Beijing Frontier Research Center for Biological Structure, School of Pharmaceutical Sciences, Tsinghua University, Beijing, China
| | - Antje Kamprad
- Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Medical Physics and Biophysics, Group Structural Biology of Cellular Signaling, Berlin, Germany
| | - Mingyu Shi
- State Key Laboratory of Membrane Biology, Tsinghua-Peking Center for Life Sciences, Beijing Frontier Research Center for Biological Structure, School of Pharmaceutical Sciences, Tsinghua University, Beijing, China
| | - David Speck
- Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Medical Physics and Biophysics, Group Structural Biology of Cellular Signaling, Berlin, Germany
| | - Johanna K S Tiemann
- Universität Leipzig, Medizinische Fakultät, Institut für Medizinische Physik und Biophysik, Leipzig, Germany
- Novozymes A/S, Lyngby, Denmark
| | - Ramon Guixà-González
- Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Medical Physics and Biophysics, Berlin, Germany
- Department of Biological Chemistry, Institute for Advanced Chemistry of Catalonia (IQAC-CSIC), Barcelona, Spain
| | - Franziska Reinhardt
- Universität Leipzig, Department of Computer Science, Bioinformatics, Leipzig, Germany
| | - Peter F Stadler
- Universität Leipzig, Department of Computer Science, Bioinformatics, Leipzig, Germany
| | - Makaía M Papasergi-Scott
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA
| | - Georgios Skiniotis
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA
- Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Patrick Scheerer
- Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Medical Physics and Biophysics, Group Structural Biology of Cellular Signaling, Berlin, Germany
| | - Brian K Kobilka
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA
| | - Jesper M Mathiesen
- University of Copenhagen, Department of Drug Design and Pharmacology, Copenhagen, Denmark
| | - Xiangyu Liu
- State Key Laboratory of Membrane Biology, Tsinghua-Peking Center for Life Sciences, Beijing Frontier Research Center for Biological Structure, School of Pharmaceutical Sciences, Tsinghua University, Beijing, China
| | - Peter W Hildebrand
- Universität Leipzig, Medizinische Fakultät, Institut für Medizinische Physik und Biophysik, Leipzig, Germany.
- Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Medical Physics and Biophysics, Berlin, Germany.
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2
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Seufert F, Chung YK, Hildebrand PW, Langenhan T. 7TM domain structures of adhesion GPCRs: what's new and what's missing? Trends Biochem Sci 2023; 48:726-739. [PMID: 37349240 DOI: 10.1016/j.tibs.2023.05.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2023] [Revised: 05/05/2023] [Accepted: 05/19/2023] [Indexed: 06/24/2023]
Abstract
Adhesion-type G protein-coupled receptors (aGPCRs) have long resisted approaches to resolve the structural details of their heptahelical transmembrane (7TM) domains. Single-particle cryogenic electron microscopy (cryo-EM) has recently produced aGPCR 7TM domain structures for ADGRD1, ADGRG1, ADGRG2, ADGRG3, ADGRG4, ADGRG5, ADGRF1, and ADGRL3. We review the unique properties, including the position and conformation of their activating tethered agonist (TA) and signaling motifs within the 7TM bundle, that the novel structures have helped to identify. We also discuss questions that the kaleidoscope of novel aGPCR 7TM domain structures have left unanswered. These concern the relative positions, orientations, and interactions of the 7TM and GPCR autoproteolysis-inducing (GAIN) domains with one another. Clarifying their interplay remains an important goal of future structural studies on aGPCRs.
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Affiliation(s)
- Florian Seufert
- Institute of Medical Physics and Biophysics, Medical Faculty, Leipzig University, Härtelstrasse 16-18, 04107 Leipzig, Germany
| | - Yin Kwan Chung
- Rudolf Schönheimer Institute of Biochemistry, Division of General Biochemistry, Medical Faculty, Leipzig University, Johannisallee 30, 04103 Leipzig, Germany
| | - Peter W Hildebrand
- Institute of Medical Physics and Biophysics, Medical Faculty, Leipzig University, Härtelstrasse 16-18, 04107 Leipzig, Germany; Institute of Medical Physics and Biophysics, Charité - Universitätsmedizin Berlin, Berlin, Germany.
| | - Tobias Langenhan
- Rudolf Schönheimer Institute of Biochemistry, Division of General Biochemistry, Medical Faculty, Leipzig University, Johannisallee 30, 04103 Leipzig, Germany.
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3
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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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Hanna J, David LA, Touahri Y, Fleming T, Screaton RA, Schuurmans C. Beyond Genetics: The Role of Metabolism in Photoreceptor Survival, Development and Repair. Front Cell Dev Biol 2022; 10:887764. [PMID: 35663397 PMCID: PMC9157592 DOI: 10.3389/fcell.2022.887764] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2022] [Accepted: 04/19/2022] [Indexed: 12/11/2022] Open
Abstract
Vision commences in the retina with rod and cone photoreceptors that detect and convert light to electrical signals. The irreversible loss of photoreceptors due to neurodegenerative disease leads to visual impairment and blindness. Interventions now in development include transplanting photoreceptors, committed photoreceptor precursors, or retinal pigment epithelial (RPE) cells, with the latter protecting photoreceptors from dying. However, introducing exogenous human cells in a clinical setting faces both regulatory and supply chain hurdles. Recent work has shown that abnormalities in central cell metabolism pathways are an underlying feature of most neurodegenerative disorders, including those in the retina. Reversal of key metabolic alterations to drive retinal repair thus represents a novel strategy to treat vision loss based on cell regeneration. Here, we review the connection between photoreceptor degeneration and alterations in cell metabolism, along with new insights into how metabolic reprogramming drives both retinal development and repair following damage. The potential impact of metabolic reprogramming on retinal regeneration is also discussed, specifically in the context of how metabolic switches drive both retinal development and the activation of retinal glial cells known as Müller glia. Müller glia display latent regenerative properties in teleost fish, however, their capacity to regenerate new photoreceptors has been lost in mammals. Thus, re-activating the regenerative properties of Müller glia in mammals represents an exciting new area that integrates research into developmental cues, central metabolism, disease mechanisms, and glial cell biology. In addition, we discuss this work in relation to the latest insights gleaned from other tissues (brain, muscle) and regenerative species (zebrafish).
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Affiliation(s)
- Joseph Hanna
- Sunnybrook Research Institute, Biological Sciences, Toronto, ON, Canada
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada
- Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, ON, Canada
| | - Luke Ajay David
- Sunnybrook Research Institute, Biological Sciences, Toronto, ON, Canada
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada
- Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, ON, Canada
| | - Yacine Touahri
- Sunnybrook Research Institute, Biological Sciences, Toronto, ON, Canada
- Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, ON, Canada
- Department of Biochemistry, University of Toronto, Toronto, ON, Canada
| | - Taylor Fleming
- Sunnybrook Research Institute, Biological Sciences, Toronto, ON, Canada
| | - Robert A. Screaton
- Sunnybrook Research Institute, Biological Sciences, Toronto, ON, Canada
- Department of Biochemistry, University of Toronto, Toronto, ON, Canada
| | - Carol Schuurmans
- Sunnybrook Research Institute, Biological Sciences, Toronto, ON, Canada
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada
- Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, ON, Canada
- Department of Biochemistry, University of Toronto, Toronto, ON, Canada
- *Correspondence: Carol Schuurmans,
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5
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Millette MA, Roy S, Salesse C. Farnesylation and lipid unsaturation are critical for the membrane binding of the C-terminal segment of G-Protein Receptor Kinase 1. Colloids Surf B Biointerfaces 2022; 211:112315. [PMID: 35026543 DOI: 10.1016/j.colsurfb.2021.112315] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 12/15/2021] [Accepted: 12/30/2021] [Indexed: 10/19/2022]
Abstract
Many proteins are modified by the covalent addition of different types of lipids, such as myristoylation, palmitoylation and prenylation. Lipidation is expected to promote membrane association of proteins. Visual phototransduction involves many lipid-modified proteins. The G-Protein-coupled receptor of rod photoreceptors, rhodopsin, is inactivated by G-Protein-coupled Receptor Kinase 1 (GRK1). The C-terminus of GRK1 is farnesylated and its truncation has been shown to result in a very high decrease of its enzymatic activity, most likely because of the loss of its membrane localization. Little information is available on the membrane binding of GRK1 as well as of most prenylated proteins. Measurements of the membrane binding of the non-farnesylated and farnesylated C-terminal segment of GRK1 were thus performed using lipids typical of those found in rod outer segment disk membranes. Their random coil secondary structure was determined using circular dichroism and infrared spectroscopy. The non-farnesylated C-terminal segment of GRK1 has no surface activity. In contrast, the farnesylated C-terminal segment of GRK1 shows a particularly strong binding to lipid monolayers bearing at least one unsaturated fatty acyl chain. No binding is observed in the presence of monolayers of saturated phospholipids, in agreement with the low affinity of farnesylated Ras proteins for lipids in the liquid-ordered state. Altogether, these data demonstrate that the farnesyl group of the C-terminal segment of GRK1 is mandatory for its membrane binding, which is favored by particular lipids or lipid mixtures. This information will also be useful for the understanding of the membrane binding of other prenylated proteins.
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Affiliation(s)
- Marc-Antoine Millette
- CUO-Recherche, Centre de recherche du CHU de Québec and Département d'ophtalmologie, Faculté de médecine, and Regroupement stratégique PROTEO, Université Laval, Québec, Québec, Canada
| | - Sarah Roy
- CUO-Recherche, Centre de recherche du CHU de Québec and Département d'ophtalmologie, Faculté de médecine, and Regroupement stratégique PROTEO, Université Laval, Québec, Québec, Canada
| | - Christian Salesse
- CUO-Recherche, Centre de recherche du CHU de Québec and Département d'ophtalmologie, Faculté de médecine, and Regroupement stratégique PROTEO, Université Laval, Québec, Québec, Canada.
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6
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Guérin DMA, Digilio A, Branda MM. Dimeric Rhodopsin R135L Mutant-Transducin-like Complex Sheds Light on Retinitis Pigmentosa Misfunctions. J Phys Chem B 2021; 125:12958-12971. [PMID: 34793169 DOI: 10.1021/acs.jpcb.1c06348] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Rhodopsin (RHO) is a light-sensitive pigment in the retina and the main prototypical protein of the G-protein-coupled receptor (GCPR) family. After receiving a light stimulus, RHO and its cofactor retinylidene undergo a series of structural changes that initiate an intricate transduction mechanism. Along with RHO, other partner proteins play key roles in the signaling pathway. These include transducin, a GTPase, kinases that phosphorylate RHO, and arrestin (Arr), which ultimately stops the signaling process and promotes RHO regeneration. A large number of RHO genetic mutations may lead to very severe retinal dysfunction and eventually to impaired dark adaptation disease called autosomal dominant retinitis pigmentosa (adRP). In this study, we used molecular dynamics (MD) simulations to evaluate the different behaviors of the dimeric form of wild-type RHO (WT dRHO) and its mutant at position 135 of arginine to leucine (dR135L), both in the free (noncomplexed) and in complex with the transducin-like protein (Gtl). Gtl is a heterotrimeric model composed of a mixture of human and bovine G proteins. Our calculations allow us to explain how the mutation causes structural changes in the RHO dimer and how this can affect the signal that transducin generates when it is bound to RHO. Moreover, the structural modifications induced by the R135L mutation can also account for other misfunctions observed in the up- and downstream signaling pathways. The mechanism of these dysfunctions, together with the transducin activity reduction, provides structure-based explanations of the impairment of some key processes that lead to adRP.
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Affiliation(s)
- Diego M A Guérin
- Department of Biochemistry and Molecular Biology, University of the Basque Country (EHU) and Instituto Biofisika (CSIC, UPV/EHU), Barrio Sarriena S/N, 48940 Leioa, Vizcaya, Spain
| | - Ayelen Digilio
- Department of Physics, National University of San Luis (UNSL), Av. Ejército de los Andes 950, 5700 San Luis, Argentina
| | - María Marta Branda
- Institute of Applied Physics (CONICET-UNSL), Av. Ejercito de los Andes 950, 5700 San Luis, Argentina
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7
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Kojima K, Matsutani Y, Yanagawa M, Imamoto Y, Yamano Y, Wada A, Shichida Y, Yamashita T. Evolutionary adaptation of visual pigments in geckos for their photic environment. SCIENCE ADVANCES 2021; 7:eabj1316. [PMID: 34597144 PMCID: PMC10938493 DOI: 10.1126/sciadv.abj1316] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2021] [Accepted: 08/11/2021] [Indexed: 06/13/2023]
Abstract
Vertebrates generally have a single type of rod for scotopic vision and multiple types of cones for photopic vision. Noteworthily, nocturnal geckos transmuted ancestral photoreceptor cells into rods containing not rhodopsin but cone pigments, and, subsequently, diurnal geckos retransmuted these rods into cones containing cone pigments. High sensitivity of scotopic vision is underlain by the rod’s low background noise, which originated from a much lower spontaneous activation rate of rhodopsin than of cone pigments. Here, we revealed that nocturnal gecko cone pigments decreased their spontaneous activation rates to mimic rhodopsin, whereas diurnal gecko cone pigments recovered high rates similar to those of typical cone pigments. We also identified amino acid residues responsible for the alterations of the spontaneous activation rates. Therefore, we concluded that the switch between diurnality and nocturnality in geckos required not only morphological transmutation of photoreceptors but also adjustment of the spontaneous activation rates of visual pigments.
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Affiliation(s)
- Keiichi Kojima
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
- Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama 700-8530, Japan
| | - Yuki Matsutani
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - Masataka Yanagawa
- Cellular Informatics Laboratory, RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako 351-0198, Japan
| | - Yasushi Imamoto
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - Yumiko Yamano
- Laboratory of Organic Chemistry for Life Science, Kobe Pharmaceutical University, Kobe 658-8558, Japan
| | - Akimori Wada
- Laboratory of Organic Chemistry for Life Science, Kobe Pharmaceutical University, Kobe 658-8558, Japan
| | - Yoshinori Shichida
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
- Research Organization for Science and Technology, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan
| | - Takahiro Yamashita
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
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Sander CL, Sears AE, Pinto AF, Choi EH, Kahremany S, Gao F, Salom D, Jin H, Pardon E, Suh S, Dong Z, Steyaert J, Saghatelian A, Skowronska-Krawczyk D, Kiser PD, Palczewski K. Nano-scale resolution of native retinal rod disk membranes reveals differences in lipid composition. J Cell Biol 2021; 220:e202101063. [PMID: 34132745 PMCID: PMC8240855 DOI: 10.1083/jcb.202101063] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Revised: 04/26/2021] [Accepted: 05/18/2021] [Indexed: 02/07/2023] Open
Abstract
Photoreceptors rely on distinct membrane compartments to support their specialized function. Unlike protein localization, identification of critical differences in membrane content has not yet been expanded to lipids, due to the difficulty of isolating domain-specific samples. We have overcome this by using SMA to coimmunopurify membrane proteins and their native lipids from two regions of photoreceptor ROS disks. Each sample's copurified lipids were subjected to untargeted lipidomic and fatty acid analysis. Extensive differences between center (rhodopsin) and rim (ABCA4 and PRPH2/ROM1) samples included a lower PC to PE ratio and increased LC- and VLC-PUFAs in the center relative to the rim region, which was enriched in shorter, saturated FAs. The comparatively few differences between the two rim samples likely reflect specific protein-lipid interactions. High-resolution profiling of the ROS disk lipid composition gives new insights into how intricate membrane structure and protein activity are balanced within the ROS, and provides a model for future studies of other complex cellular structures.
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Affiliation(s)
- Christopher L. Sander
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
| | - Avery E. Sears
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
| | - Antonio F.M. Pinto
- Clayton Foundation Laboratories for Peptide Biology, Salk Institute for Biological Studies, La Jolla, CA
| | - Elliot H. Choi
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
| | - Shirin Kahremany
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
| | - Fangyuan Gao
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
| | - David Salom
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
| | - Hui Jin
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH
| | - Els Pardon
- Vlaams Instituut voor Biotechnologie–Vrije Universiteit Brussel Center for Structural Biology, Vlaams Instituut voor Biotechnologie, Brussels, Belgium
- Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium
| | - Susie Suh
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
| | - Zhiqian Dong
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
| | - Jan Steyaert
- Vlaams Instituut voor Biotechnologie–Vrije Universiteit Brussel Center for Structural Biology, Vlaams Instituut voor Biotechnologie, Brussels, Belgium
- Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium
| | - Alan Saghatelian
- Clayton Foundation Laboratories for Peptide Biology, Salk Institute for Biological Studies, La Jolla, CA
| | - Dorota Skowronska-Krawczyk
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
- Department of Physiology and Biophysics, University of California, Irvine, Irvine, CA
| | - Philip D. Kiser
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
- Department of Physiology and Biophysics, University of California, Irvine, Irvine, CA
- Research Service, VA Long Beach Healthcare System, Long Beach, CA
| | - Krzysztof Palczewski
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
- Department of Physiology and Biophysics, University of California, Irvine, Irvine, CA
- Department of Chemistry, University of California, Irvine, Irvine, CA
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9
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Abtout A, Fain G, Reingruber J. Analysis of waveform and amplitude of mouse rod and cone flash responses. J Physiol 2021; 599:3295-3312. [PMID: 33977528 DOI: 10.1113/jp281225] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Accepted: 04/28/2021] [Indexed: 12/14/2022] Open
Abstract
KEY POINTS Most vertebrate eyes have rod and cone photoreceptors, which use a signal transduction pathway consisting of many biological processes to transform light into an electrical response. We dissect and quantify the contribution of each of these processes to the photoreceptor light response by using a novel method of analysis that provides an analytical solution for the entire time course of the dim-flash light response. We find that the shape of the light response is exclusively controlled by deactivation parameters. Activation parameters scale this shape and alter the response amplitude. We show that the rising phase of the response depends on Ca2+ feedback, and we identify the deactivation parameters that control the recovery phase of the response. We devise new methods to extract values for deactivation and activation parameters from a separate analysis of response shape and response amplitude. ABSTRACT Vertebrate eyes have rod and cone photoreceptors, which use a complex transduction pathway comprising many biological processes to transform the absorption of light into an electrical response. A fundamental question in sensory transduction is how these processes contribute to the response. To study this question, we use a well-accepted phototransduction model, which we analyse with a novel method based on the log transform of the current. We derive an analytical solution that describes the entire time course of the photoreceptor response to dim flashes of light. We use this solution to dissect and quantify the contribution of each process to the response. We find that the entire dim-flash response is proportional to the flash intensity. By normalizing responses to unit amplitude, we define a waveform that is independent of the light intensity and characterizes the invariant shape of dim-flash responses. We show that this waveform is exclusively determined by deactivation rates; activation rates only scale the waveform and affect the amplitude. This analysis corrects a previous assumption that the rising phase is determined entirely by activation rates. We further show that the rising phase depends on Ca2+ feedback to the cyclase, contrary to current belief. We identify the deactivation rates that control the recovery phase of the response, and we devise new methods to extract activation and deactivation rates from an analysis of response shape and response amplitude. In summary, we provide a comprehensive understanding of how the various transduction processes produce the cellular response.
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Affiliation(s)
- Annia Abtout
- Institut de Biologie de l'École Normale Supérieure, Paris, France
| | - Gordon Fain
- Department of Integrative Biology and Physiology, University of California, Los Angeles, California, USA.,Department of Ophthalmology and Stein Eye Institute, University of California, Los Angeles, California, USA
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10
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Gulati S, Palczewski K. New focus on regulation of the rod photoreceptor phosphodiesterase. Curr Opin Struct Biol 2021; 69:99-107. [PMID: 33945959 DOI: 10.1016/j.sbi.2021.03.016] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2020] [Revised: 02/18/2021] [Accepted: 03/25/2021] [Indexed: 02/03/2023]
Abstract
Rod photoreceptor phosphodiesterase (PDE6) is the key catalytic enzyme of visual phototransduction. PDE6 is the only member of the phosphodiesterase family that consists of a heterodimeric catalytic core composed of PDE6α and PDE6β subunits and two inhibitory PDE6γ subunits. Both PDE6α and PDE6β contain two regulatory GAF domains and one catalytic domain. GAF domains and the tightly bound PDE6γ subunits allosterically regulate the activity of the catalytic domain in association with the GTP-bound transducin alpha subunit (Gtα-GTP). Recent cryo-electron microscopy structures of the PDE6αγβγ and PDE6αγβγ-(Gtα-GTP)2 complexes have provided valuable knowledge shedding additional light on the allosteric activation of PDE6 by Gtα-GTP. Here we discuss recent developments in our understanding of the mechanism of PDE6 activation.
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Affiliation(s)
| | - Krzysztof Palczewski
- Gavin Herbert Eye Institute and the Department of Ophthalmology, Center for Translational Vision Research, University of California, 829 Health Sciences Road, Irvine, CA 92617, USA; The Department of Physiology & Biophysics, University of California, Irvine, CA 92697, USA; The Department of Chemistry, University of California, Irvine, CA 92697, USA.
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11
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Calebiro D, Koszegi Z, Lanoiselée Y, Miljus T, O'Brien S. G protein-coupled receptor-G protein interactions: a single-molecule perspective. Physiol Rev 2020; 101:857-906. [PMID: 33331229 DOI: 10.1152/physrev.00021.2020] [Citation(s) in RCA: 45] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
G protein-coupled receptors (GPCRs) regulate many cellular and physiological processes, responding to a diverse range of extracellular stimuli including hormones, neurotransmitters, odorants, and light. Decades of biochemical and pharmacological studies have provided fundamental insights into the mechanisms of GPCR signaling. Thanks to recent advances in structural biology, we now possess an atomistic understanding of receptor activation and G protein coupling. However, how GPCRs and G proteins interact in living cells to confer signaling efficiency and specificity remains insufficiently understood. The development of advanced optical methods, including single-molecule microscopy, has provided the means to study receptors and G proteins in living cells with unprecedented spatio-temporal resolution. The results of these studies reveal an unexpected level of complexity, whereby GPCRs undergo transient interactions among themselves as well as with G proteins and structural elements of the plasma membrane to form short-lived signaling nanodomains that likely confer both rapidity and specificity to GPCR signaling. These findings may provide new strategies to pharmaceutically modulate GPCR function, which might eventually pave the way to innovative drugs for common diseases such as diabetes or heart failure.
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Affiliation(s)
- Davide Calebiro
- Institute of Metabolism and Systems Research, University of Birmingham, Birmingham, United Kingdom; Centre of Membrane Proteins and Receptors (COMPARE), Universities of Nottingham and Birmingham, Birmingham, United Kingdom
| | - Zsombor Koszegi
- Institute of Metabolism and Systems Research, University of Birmingham, Birmingham, United Kingdom; Centre of Membrane Proteins and Receptors (COMPARE), Universities of Nottingham and Birmingham, Birmingham, United Kingdom
| | - Yann Lanoiselée
- Institute of Metabolism and Systems Research, University of Birmingham, Birmingham, United Kingdom; Centre of Membrane Proteins and Receptors (COMPARE), Universities of Nottingham and Birmingham, Birmingham, United Kingdom
| | - Tamara Miljus
- Institute of Metabolism and Systems Research, University of Birmingham, Birmingham, United Kingdom; Centre of Membrane Proteins and Receptors (COMPARE), Universities of Nottingham and Birmingham, Birmingham, United Kingdom
| | - Shannon O'Brien
- Institute of Metabolism and Systems Research, University of Birmingham, Birmingham, United Kingdom; Centre of Membrane Proteins and Receptors (COMPARE), Universities of Nottingham and Birmingham, Birmingham, United Kingdom
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12
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Biased GPCR signaling: Possible mechanisms and inherent limitations. Pharmacol Ther 2020; 211:107540. [PMID: 32201315 DOI: 10.1016/j.pharmthera.2020.107540] [Citation(s) in RCA: 60] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2020] [Accepted: 03/17/2020] [Indexed: 02/06/2023]
Abstract
G protein-coupled receptors (GPCRs) are targeted by about a third of clinically used drugs. Many GPCRs couple to more than one type of heterotrimeric G proteins, become phosphorylated by any of several different GRKs, and then bind one or more types of arrestin. Thus, classical therapeutically active drugs simultaneously initiate several branches of signaling, some of which are beneficial, whereas others result in unwanted on-target side effects. The development of novel compounds to selectively channel the signaling into the desired direction has the potential to become a breakthrough in health care. However, there are natural and technological hurdles that must be overcome. The fact that most GPCRs are subject to homologous desensitization, where the active receptor couples to G proteins, is phosphorylated by GRKs, and then binds arrestins, suggest that in most cases the GPCR conformations that facilitate their interactions with these three classes of binding partners significantly overlap. Thus, while partner-specific conformations might exist, they are likely low-probability states. GPCRs are inherently flexible, which suggests that complete bias is highly unlikely to be feasible: in the conformational ensemble induced by any ligand, there would be some conformations facilitating receptor coupling to unwanted partners. Things are further complicated by the fact that virtually every cell expresses numerous G proteins, several GRK subtypes, and two non-visual arrestins with distinct signaling capabilities. Finally, novel screening methods for measuring ligand bias must be devised, as the existing methods are not specific for one particular branch of signaling.
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13
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Phototransduction gain at the G-protein, transducin, and effector protein, phosphodiesterase-6, stages in retinal rods. Proc Natl Acad Sci U S A 2020; 116:8653-8654. [PMID: 31040258 DOI: 10.1073/pnas.1904017116] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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14
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Lamb TD, Kraft TW. A quantitative account of mammalian rod phototransduction with PDE6 dimeric activation: responses to bright flashes. Open Biol 2020; 10:190241. [PMID: 31910741 PMCID: PMC7014685 DOI: 10.1098/rsob.190241] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
We develop an improved quantitative model of mammalian rod phototransduction, and we apply it to the prediction of responses to bright flashes of light. We take account of the recently characterized dimeric nature of PDE6 activation, where the configuration of primary importance has two transducin molecules bound. We simulate the stochastic nature of the activation and shut-off reactions to generate the predicted kinetics of the active molecular species on the disc membrane surfaces, and then we integrate the differential equations for the downstream cytoplasmic reactions to obtain the predicted electrical responses. The simulated responses recover the qualitative form of bright-flash response families recorded from mammalian rod photoreceptors. Furthermore, they provide an accurate description of the relationship between the time spent in saturation and flash intensity, predicting the transition between first and second ‘dominant time constants’ to occur at an intensity around 5000 isomerizations per flash, when the rate of transducin activation is taken to be 1250 transducins s−1 per activated rhodopsin. This rate is consistent with estimates from light-scattering experiments, but is around fourfold higher than has typically been assumed in other studies. We conclude that our model and parameters provide a compelling description of rod photoreceptor bright-flash responses.
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Affiliation(s)
- Trevor D Lamb
- Eccles Institute of Neuroscience, John Curtin School of Medical Research, The Australian National University, Canberra, ACT 2600, Australia
| | - Timothy W Kraft
- Department of Optometry and Vision Science, University of Alabama at Birmingham, Birmingham, AL, USA
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15
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Draper-Joyce C, Furness SGB. Conformational Transitions and the Activation of Heterotrimeric G Proteins by G Protein-Coupled Receptors. ACS Pharmacol Transl Sci 2019; 2:285-290. [PMID: 32259062 PMCID: PMC7088962 DOI: 10.1021/acsptsci.9b00054] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Indexed: 01/10/2023]
Abstract
G protein-coupled receptors (GPCRs) are particularly attractive targets for therapeutic pharmaceuticals. This is because they are involved in almost all facets of physiology, in many pathophysiological processes, they are tractable due to their cell surface location, and can exhibit highly textured pharmacology. While the development of new drugs does not require the molecular details of the mechanism of activity for a particular target, there has been increasing interest in the GPCR field in these details. In part, this has come with the recognition that differential activity at a particular target might be a way in which to leverage drug activity, either through manipulation of efficacy or through differential coupling (signaling bias). To this end, the past few years have seen a number of publications that have specifically attempted to address one or more aspects of the molecular reaction pathway, leading to activation of heterotrimeric G proteins by GPCRs.
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16
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Getter T, Gulati S, Zimmerman R, Chen Y, Vinberg F, Palczewski K. Stereospecific modulation of dimeric rhodopsin. FASEB J 2019; 33:9526-9539. [PMID: 31121099 PMCID: PMC6662988 DOI: 10.1096/fj.201900443rr] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Accepted: 04/23/2019] [Indexed: 11/11/2022]
Abstract
The classic concept that GPCRs function as monomers has been challenged by the emerging evidence of GPCR dimerization and oligomerization. Rhodopsin (Rh) is the only GPCR whose native oligomeric arrangement was revealed by atomic force microscopy demonstrating that Rh exists as a dimer. However, the role of Rh dimerization in retinal physiology is currently unknown. In this study, we identified econazole and sulconazole, two small molecules that disrupt Rh dimer contacts, by implementing a cell-based high-throughput screening assay. Racemic mixtures of identified lead compounds were separated and tested for their stereospecific binding to Rh using UV-visible spectroscopy and intrinsic fluorescence of tryptophan (Trp) 265 after illumination. By following the changes in UV-visible spectra and Trp265 fluorescence in vitro, we found that binding of R-econazole modulates the formation of Meta III and quenches the intrinsic fluorescence of Trp265. In addition, electrophysiological ex vivo recording revealed that R-econazole slows photoresponse kinetics, whereas S-econazole decreased the sensitivity of rods without effecting the kinetics. Thus, this study contributes new methodology to identify compounds that disrupt the dimerization of GPCRs in general and validates the first active compounds that disrupt the Rh dimer specifically.-Getter, T., Gulati, S., Zimmerman, R., Chen, Y., Vinberg, F., Palczewski, K. Stereospecific modulation of dimeric rhodopsin.
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Affiliation(s)
- Tamar Getter
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California–Irvine, California, USA
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio, USA
| | - Sahil Gulati
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California–Irvine, California, USA
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio, USA
- Department of Physiology and Biophysics, University of California–Irvine, Irvine, California, USA
| | - Remy Zimmerman
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California–Irvine, California, USA
| | - Yuanyuan Chen
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
- McGowan Institute of Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Frans Vinberg
- Department of Ophthalmology and Visual Sciences, University of Utah, Salt Lake City, Utah, USA
| | - Krzysztof Palczewski
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California–Irvine, California, USA
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio, USA
- Department of Physiology and Biophysics, University of California–Irvine, Irvine, California, USA
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17
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Ortega JT, Parmar T, Jastrzebska B. Flavonoids enhance rod opsin stability, folding, and self-association by directly binding to ligand-free opsin and modulating its conformation. J Biol Chem 2019; 294:8101-8122. [PMID: 30944172 DOI: 10.1074/jbc.ra119.007808] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2019] [Revised: 03/27/2019] [Indexed: 12/29/2022] Open
Abstract
Rhodopsin (Rho) is a visual G protein-coupled receptor expressed in the rod photoreceptors of the eye, where it mediates transmission of a light signal into a cell and converts this signal into a nerve impulse. More than 100 mutations in Rho are linked to various ocular impairments, including retinitis pigmentosa (RP). Accordingly, much effort has been directed toward developing ligands that target Rho and improve its folding and stability. Natural compounds may provide another viable approach to such drug discovery efforts. The dietary polyphenol compounds, ubiquitously present in fruits and vegetables, have beneficial effects in several eye diseases. However, the underlying mechanism of their activity is not fully understood. In this study, we used a combination of computational methods, biochemical and biophysical approaches, including bioluminescence resonance energy transfer, and mammalian cell expression systems to clarify the effects of four common bioactive flavonoids (quercetin, myricetin, and their mono-glycosylated forms quercetin-3-rhamnoside and myricetrin) on rod opsin stability, function, and membrane organization. We observed that by directly interacting with ligand-free opsin, flavonoids modulate its conformation, thereby causing faster entry of the retinal chromophore into its binding pocket. Moreover, flavonoids significantly increased opsin stability, most likely by introducing structural rigidity and promoting receptor self-association within the biological membranes. Of note, the binding of flavonoids to an RP-linked P23H opsin variant partially restored its normal cellular trafficking. Together, our results suggest that flavonoids could be utilized as lead compounds in the development of effective nonretinoid therapeutics for managing RP-related retinopathies.
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Affiliation(s)
- Joseph T Ortega
- Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
| | - Tanu Parmar
- Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
| | - Beata Jastrzebska
- Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106.
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18
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Lamb TD, Heck M, Kraft TW. Implications of dimeric activation of PDE6 for rod phototransduction. Open Biol 2019; 8:rsob.180076. [PMID: 30068567 PMCID: PMC6119862 DOI: 10.1098/rsob.180076] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2018] [Accepted: 07/06/2018] [Indexed: 01/14/2023] Open
Abstract
We examine the implications of a recent report providing evidence that two transducins must bind to the rod phosphodiesterase to elicit significant hydrolytic activity. To predict the rod photoreceptor's electrical response, we use numerical simulation of the two-dimensional diffusional contact of interacting molecules at the surface of the disc membrane, and then we use the simulated PDE activity as the driving function for the downstream reaction cascade. The results account for a number of aspects of rod phototransduction that have previously been puzzling. For example, they explain the existence of a greater initial delay in rods than in cones. Furthermore, our analysis suggests that the 'continuous' noise recorded in rods in darkness is likely to arise from spontaneous activation of individual molecules of PDE at a rate of a few tens per second per rod, probably as a consequence of spontaneous activation of transducins at a rate of thousands per second per rod. Hence, the dimeric activation of PDE in rods provides immunity against spontaneous transducin activation, thereby reducing the continuous noise. Our analysis also provides a coherent quantitative explanation of the amplification underlying the single photon response. Overall, numerical analysis of the dimeric activation of PDE places rod phototransduction in a new light.
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Affiliation(s)
- Trevor D Lamb
- Eccles Institute of Neuroscience, John Curtin School of Medical Research, The Australian National University, Australian Capital Territory 2600, Australia
| | - Martin Heck
- Institut für Medizinische Physik und Biophysik der Charité, Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Timothy W Kraft
- Department of Optometry and Vision Science, University of Alabama at Birmingham, Birmingham, AL, USA
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19
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Roushar FJ, Gruenhagen TC, Penn WD, Li B, Meiler J, Jastrzebska B, Schlebach JP. Contribution of Cotranslational Folding Defects to Membrane Protein Homeostasis. J Am Chem Soc 2018; 141:204-215. [PMID: 30537820 DOI: 10.1021/jacs.8b08243] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Membrane proteins are prone to misfolding and degradation within the cell, yet the nature of the conformational defects involved in this process remain poorly understood. The earliest stages of membrane protein folding are mediated by the Sec61 translocon, a molecular machine that facilitates the lateral partitioning of the polypeptide into the membrane. Proper membrane integration is an essential prerequisite for folding of the nascent chain. However, the marginal energetic drivers of this reaction suggest the translocon may operate with modest fidelity. In this work, we employed biophysical modeling in conjunction with quantitative biochemical measurements in order to evaluate the extent to which cotranslational folding defects influence membrane protein homeostasis. Protein engineering was employed to selectively perturb the topological energetics of human rhodopsin, and the expression and cellular trafficking of engineered variants were quantitatively compared. Our results reveal clear relationships between topological energetics and the efficiency of rhodopsin biogenesis, which appears to be limited by the propensity of a polar transmembrane domain to achieve its correct topological orientation. Though the polarity of this segment is functionally constrained, we find that its topology can be stabilized in a manner that enhances biogenesis without compromising the functional properties of rhodopsin. Furthermore, sequence alignments reveal this topological instability has been conserved throughout the course of evolution. These results suggest that topological defects significantly contribute to the inefficiency of membrane protein folding in the cell. Additionally, our findings suggest that the marginal stability of rhodopsin may represent an evolved trait.
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Affiliation(s)
- Francis J Roushar
- Department of Chemistry , Indiana University , Bloomington , Indiana 47405 , United States
| | - Timothy C Gruenhagen
- Department of Chemistry , Indiana University , Bloomington , Indiana 47405 , United States
| | - Wesley D Penn
- Department of Chemistry , Indiana University , Bloomington , Indiana 47405 , United States
| | - Bian Li
- Department of Chemistry , Vanderbilt University , Nashville , Tennessee 37235 , United States
| | - Jens Meiler
- Department of Chemistry , Vanderbilt University , Nashville , Tennessee 37235 , United States
| | - Beata Jastrzebska
- Department of Pharmacology , Case Western Reserve University , Cleveland , Ohio 44106 , United States
| | - Jonathan P Schlebach
- Department of Chemistry , Indiana University , Bloomington , Indiana 47405 , United States
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20
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Apo-Opsin Exists in Equilibrium Between a Predominant Inactive and a Rare Highly Active State. J Neurosci 2018; 39:212-223. [PMID: 30459230 DOI: 10.1523/jneurosci.1980-18.2018] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Revised: 10/30/2018] [Accepted: 11/04/2018] [Indexed: 12/17/2022] Open
Abstract
Bleaching adaptation in rod photoreceptors is mediated by apo-opsin, which activates phototransduction with effective activity 105- to 106-fold lower than that of photoactivated rhodopsin (meta II). However, the mechanism that produces such low opsin activity is unknown. To address this question, we sought to record single opsin responses in mouse rods. We used mutant mice lacking efficient calcium feedback to boosts rod responses and generated a small fraction of opsin by photobleaching ∼1% of rhodopsin. The bleach produced a dramatic increase in the frequency of discrete photoresponse-like events. This activity persisted for hours, was quenched by 11-cis-retinal, and was blocked by uncoupling opsin from phototransduction, all indicating opsin as its source. Opsin-driven discrete activity was also observed in rods containing non-activatable rhodopsin, ruling out transactivation of rhodopsin by opsin. We conclude that bleaching adaptation is mediated by opsin that exists in equilibrium between a predominant inactive and a rare meta II-like state.SIGNIFICANCE STATEMENT Electrophysiological analysis is used to show that the G-protein-coupled receptor opsin exists in equilibrium between a predominant inactive and a rare highly active state that mediates bleaching adaptation in photoreceptors.
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21
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Tsai CJ, Pamula F, Nehmé R, Mühle J, Weinert T, Flock T, Nogly P, Edwards PC, Carpenter B, Gruhl T, Ma P, Deupi X, Standfuss J, Tate CG, Schertler GFX. Crystal structure of rhodopsin in complex with a mini-G o sheds light on the principles of G protein selectivity. SCIENCE ADVANCES 2018; 4:eaat7052. [PMID: 30255144 PMCID: PMC6154990 DOI: 10.1126/sciadv.aat7052] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Accepted: 08/10/2018] [Indexed: 05/20/2023]
Abstract
Selective coupling of G protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptors (GPCRs) to specific Gα-protein subtypes is critical to transform extracellular signals, carried by natural ligands and clinical drugs, into cellular responses. At the center of this transduction event lies the formation of a signaling complex between the receptor and G protein. We report the crystal structure of light-sensitive GPCR rhodopsin bound to an engineered mini-Go protein. The conformation of the receptor is identical to all previous structures of active rhodopsin, including the complex with arrestin. Thus, rhodopsin seems to adopt predominantly one thermodynamically stable active conformation, effectively acting like a "structural switch," allowing for maximum efficiency in the visual system. Furthermore, our analysis of the well-defined GPCR-G protein interface suggests that the precise position of the carboxyl-terminal "hook-like" element of the G protein (its four last residues) relative to the TM7/helix 8 (H8) joint of the receptor is a significant determinant in selective G protein activation.
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Affiliation(s)
- Ching-Ju Tsai
- Laboratory of Biomolecular Research, Paul Scherrer Institute (PSI), 5232 Villigen PSI, Switzerland
- Corresponding author. (C.-J.T.); (G.F.X.S.)
| | - Filip Pamula
- Laboratory of Biomolecular Research, Paul Scherrer Institute (PSI), 5232 Villigen PSI, Switzerland
- Department of Biology, ETH Zürich, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland
| | - Rony Nehmé
- Medical Research Council Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Jonas Mühle
- Laboratory of Biomolecular Research, Paul Scherrer Institute (PSI), 5232 Villigen PSI, Switzerland
| | - Tobias Weinert
- Laboratory of Biomolecular Research, Paul Scherrer Institute (PSI), 5232 Villigen PSI, Switzerland
| | - Tilman Flock
- Laboratory of Biomolecular Research, Paul Scherrer Institute (PSI), 5232 Villigen PSI, Switzerland
- Department of Biology, ETH Zürich, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland
- Fitzwilliam College, University of Cambridge, Cambridge, UK
| | - Przemyslaw Nogly
- Laboratory of Biomolecular Research, Paul Scherrer Institute (PSI), 5232 Villigen PSI, Switzerland
- Department of Biology, ETH Zürich, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland
| | - Patricia C. Edwards
- Medical Research Council Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Byron Carpenter
- Medical Research Council Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Thomas Gruhl
- Laboratory of Biomolecular Research, Paul Scherrer Institute (PSI), 5232 Villigen PSI, Switzerland
- Department of Biology, ETH Zürich, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland
| | - Pikyee Ma
- Laboratory of Biomolecular Research, Paul Scherrer Institute (PSI), 5232 Villigen PSI, Switzerland
| | - Xavier Deupi
- Laboratory of Biomolecular Research, Paul Scherrer Institute (PSI), 5232 Villigen PSI, Switzerland
- Condensed Matter Theory Group, PSI, 5232 Villigen PSI, Switzerland
| | - Jörg Standfuss
- Laboratory of Biomolecular Research, Paul Scherrer Institute (PSI), 5232 Villigen PSI, Switzerland
| | - Christopher G. Tate
- Medical Research Council Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Gebhard F. X. Schertler
- Laboratory of Biomolecular Research, Paul Scherrer Institute (PSI), 5232 Villigen PSI, Switzerland
- Department of Biology, ETH Zürich, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland
- Corresponding author. (C.-J.T.); (G.F.X.S.)
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22
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Mallory DP, Gutierrez E, Pinkevitch M, Klinginsmith C, Comar WD, Roushar FJ, Schlebach JP, Smith AW, Jastrzebska B. The Retinitis Pigmentosa-Linked Mutations in Transmembrane Helix 5 of Rhodopsin Disrupt Cellular Trafficking Regardless of Oligomerization State. Biochemistry 2018; 57:5188-5201. [PMID: 30085663 DOI: 10.1021/acs.biochem.8b00403] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
G protein-coupled receptors can exist as dimers and higher-order oligomers in biological membranes. The specific oligomeric assembly of these receptors is believed to play a major role in their function, and the disruption of native oligomers has been implicated in specific human pathologies. Computational predictions and biochemical analyses suggest that two molecules of rhodopsin (Rho) associate through the interactions involving its fifth transmembrane helix (TM5). Interestingly, there are several pathogenic loss-of-function mutations within TM5 that face the lipid bilayer in a manner that could potentially influence the dimerization of Rho. Though several of these mutations are known to induce misfolding, the pathogenic defects associated with V209M and F220C Rho remain unclear. In this work, we utilized a variety of biochemical and biophysical approaches to elucidate the effects of these mutations on the dimerization, folding, trafficking, and function of Rho in relation to other pathogenic TM5 variants. Chemical cross-linking, bioluminescence energy transfer, and pulsed-interleaved excitation fluorescence cross-correlation spectroscopy experiments revealed that each of these mutants exhibits a wild type-like propensity to self-associate within the plasma membrane. However, V209M and F220C each exhibit subtle defects in cellular trafficking. Together, our results suggest that the RP pathology associated with the expression of the V209M and F220C mutants could arise from defects in folding and cellular trafficking rather than the disruption of dimerization, as has been previously proposed.
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Affiliation(s)
- D Paul Mallory
- Department of Chemistry , University of Akron , 190 Buchtel Common , Akron , Ohio 44325 , United States
| | - Elizabeth Gutierrez
- Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine , Case Western Reserve University , 10900 Euclid Avenue , Cleveland , Ohio 44106 , United States
| | - Margaret Pinkevitch
- Department of Chemistry , University of Akron , 190 Buchtel Common , Akron , Ohio 44325 , United States
| | - Christie Klinginsmith
- Department of Chemistry , University of Akron , 190 Buchtel Common , Akron , Ohio 44325 , United States
| | - William D Comar
- Department of Chemistry , University of Akron , 190 Buchtel Common , Akron , Ohio 44325 , United States
| | - Francis J Roushar
- Department of Chemistry , Indiana University , 800 East Kirkwood Avenue , Bloomington , Indiana 47405-7102 , United States
| | - Jonathan P Schlebach
- Department of Chemistry , Indiana University , 800 East Kirkwood Avenue , Bloomington , Indiana 47405-7102 , United States
| | - Adam W Smith
- Department of Chemistry , University of Akron , 190 Buchtel Common , Akron , Ohio 44325 , United States
| | - Beata Jastrzebska
- Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine , Case Western Reserve University , 10900 Euclid Avenue , Cleveland , Ohio 44106 , United States
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23
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Qureshi BM, Behrmann E, Schöneberg J, Loerke J, Bürger J, Mielke T, Giesebrecht J, Noé F, Lamb TD, Hofmann KP, Spahn CMT, Heck M. It takes two transducins to activate the cGMP-phosphodiesterase 6 in retinal rods. Open Biol 2018; 8:180075. [PMID: 30068566 PMCID: PMC6119865 DOI: 10.1098/rsob.180075] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2018] [Accepted: 07/06/2018] [Indexed: 12/21/2022] Open
Abstract
Among cyclic nucleotide phosphodiesterases (PDEs), PDE6 is unique in serving as an effector enzyme in G protein-coupled signal transduction. In retinal rods and cones, PDE6 is membrane-bound and activated to hydrolyse its substrate, cGMP, by binding of two active G protein α-subunits (Gα*). To investigate the activation mechanism of mammalian rod PDE6, we have collected functional and structural data, and analysed them by reaction-diffusion simulations. Gα* titration of membrane-bound PDE6 reveals a strong functional asymmetry of the enzyme with respect to the affinity of Gα* for its two binding sites on membrane-bound PDE6 and the enzymatic activity of the intermediary 1 : 1 Gα* · PDE6 complex. Employing cGMP and its 8-bromo analogue as substrates, we find that Gα* · PDE6 forms with high affinity but has virtually no cGMP hydrolytic activity. To fully activate PDE6, it takes a second copy of Gα* which binds with lower affinity, forming Gα* · PDE6 · Gα*. Reaction-diffusion simulations show that the functional asymmetry of membrane-bound PDE6 constitutes a coincidence switch and explains the lack of G protein-related noise in visual signal transduction. The high local concentration of Gα* generated by a light-activated rhodopsin molecule efficiently activates PDE6, whereas the low density of spontaneously activated Gα* fails to activate the effector enzyme.
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Affiliation(s)
- Bilal M Qureshi
- Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Elmar Behrmann
- Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Johannes Schöneberg
- Department of Mathematics, Computer Science and Bioinformatics, Freie Universität Berlin, Berlin, Germany
| | - Justus Loerke
- Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Jörg Bürger
- Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Thorsten Mielke
- Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
- Microscopy and Cryo Electron Microscopy Group, Max-Planck Institut für Molekulare Genetik, Berlin, Germany
| | - Jan Giesebrecht
- Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Frank Noé
- Department of Mathematics, Computer Science and Bioinformatics, Freie Universität Berlin, Berlin, Germany
| | - Trevor D Lamb
- Eccles Institute of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital Territory 2600, Australia
| | - Klaus Peter Hofmann
- Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
- Zentrum für Biophysik und Bioinformatik, Humboldt-Universität zu Berlin, Berlin, Germany
| | - Christian M T Spahn
- Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Martin Heck
- Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
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Transducin β-Subunit Can Interact with Multiple G-Protein γ-Subunits to Enable Light Detection by Rod Photoreceptors. eNeuro 2018; 5:eN-NWR-0144-18. [PMID: 29911170 PMCID: PMC6001135 DOI: 10.1523/eneuro.0144-18.2018] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2018] [Revised: 05/07/2018] [Accepted: 05/10/2018] [Indexed: 11/21/2022] Open
Abstract
The heterotrimeric G-protein transducin mediates visual signaling in vertebrate photoreceptor cells. Many aspects of the function of transducin were learned from knock-out mice lacking its individual subunits. Of particular interest is the knockout of its rod-specific γ-subunit (Gγ1). Two studies using independently generated mice documented that this knockout results in a considerable >60-fold reduction in the light sensitivity of affected rods, but provided different interpretations of how the remaining α-subunit (Gαt) mediates phototransduction without its cognate Gβ1γ1-subunit partner. One study found that the light sensitivity reduction matched a corresponding reduction in Gαt content in the light-sensing rod outer segments and proposed that Gαt activation is supported by remaining Gβ1 associating with other Gγ subunits naturally expressed in photoreceptors. In contrast, the second study reported the same light sensitivity loss but a much lower, only approximately sixfold, reduction of Gαt and proposed that the light responses of these rods do not require Gβγ at all. To resolve this controversy and elucidate the mechanism driving visual signaling in Gγ1 knock-out rods, we analyzed both mouse lines side by side. We first determined that the outer segments of both mice have identical Gαt content, which is reduced ∼65-fold from the wild-type (WT) level. We further demonstrated that the remaining Gβ1 is present in a complex with endogenous Gγ2 and Gγ3 subunits and that these complexes exist in wild-type rods as well. Together, these results argue against the idea that Gαt alone supports light responses of Gγ1 knock-out rods and suggest that Gβ1γ1 is not unique in its ability to mediate vertebrate phototransduction.
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25
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Targeting G protein-coupled receptor signaling at the G protein level with a selective nanobody inhibitor. Nat Commun 2018; 9:1996. [PMID: 29777099 PMCID: PMC5959942 DOI: 10.1038/s41467-018-04432-0] [Citation(s) in RCA: 57] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2017] [Accepted: 04/25/2018] [Indexed: 01/06/2023] Open
Abstract
G protein-coupled receptors (GPCRs) activate heterotrimeric G proteins by mediating a GDP to GTP exchange in the Gα subunit. This leads to dissociation of the heterotrimer into Gα-GTP and Gβγ dimer. The Gα-GTP and Gβγ dimer each regulate a variety of downstream pathways to control various aspects of human physiology. Dysregulated Gβγ-signaling is a central element of various neurological and cancer-related anomalies. However, Gβγ also serves as a negative regulator of Gα that is essential for G protein inactivation, and thus has the potential for numerous side effects when targeted therapeutically. Here we report a llama-derived nanobody (Nb5) that binds tightly to the Gβγ dimer. Nb5 responds to all combinations of β-subtypes and γ-subtypes and competes with other Gβγ-regulatory proteins for a common binding site on the Gβγ dimer. Despite its inhibitory effect on Gβγ-mediated signaling, Nb5 has no effect on Gαq-mediated and Gαs-mediated signaling events in living cells.
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26
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Qureshi BM, Schmidt A, Behrmann E, Bürger J, Mielke T, Spahn CMT, Heck M, Scheerer P. Mechanistic insights into the role of prenyl-binding protein PrBP/δ in membrane dissociation of phosphodiesterase 6. Nat Commun 2018; 9:90. [PMID: 29311697 PMCID: PMC5758567 DOI: 10.1038/s41467-017-02569-y] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2017] [Accepted: 12/11/2017] [Indexed: 01/01/2023] Open
Abstract
Isoprenylated proteins are associated with membranes and their inter-compartmental distribution is regulated by solubilization factors, which incorporate lipid moieties in hydrophobic cavities and thereby facilitate free diffusion during trafficking. Here we report the crystal structure of a solubilization factor, the prenyl-binding protein (PrBP/δ), at 1.81 Å resolution in its ligand-free apo-form. Apo-PrBP/δ harbors a preshaped, deep hydrophobic cavity, capacitating apo-PrBP/δ to readily bind its prenylated cargo. To investigate the molecular mechanism of cargo solubilization we analyzed the PrBP/δ-induced membrane dissociation of rod photoreceptor phosphodiesterase (PDE6). The results suggest that PrBP/δ exclusively interacts with the soluble fraction of PDE6. Depletion of soluble species in turn leads to dissociation of membrane-bound PDE6, as both are in equilibrium. This “solubilization by depletion” mechanism of PrBP/δ differs from the extraction of prenylated proteins by the similar folded solubilization factor RhoGDI, which interacts with membrane bound cargo via an N-terminal structural element lacking in PrBP/δ. The prenyl-binding protein PrBP/δ is a solubilization factor involved in trafficking of prenylated proteins. Here the authors present the ligand-free apo-PrBP/δ structure and propose a "solubilization by depletion" mechanism, where PrBP/δ sequesters only soluble rod photoreceptor phosphodiesterase (PDE6), leading to a dissociation of membrane-bound PDE6.
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Affiliation(s)
- Bilal M Qureshi
- Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Charitéplatz 1, D-10117, Berlin, Germany.,Charité - Universitätsmedizin Berlin, Institut für Medizinische Physik und Biophysik (CC2), Group Protein X-ray Crystallography and Signal Transduction, Charitéplatz 1, D-10117, Berlin, Germany.,Charité - Universitätsmedizin Berlin, Institut für Medizinische Physik und Biophysik (CC2), Group Cryo Electron Microscopy, Charitéplatz 1, D-10117, Berlin, Germany.,Charité - Universitätsmedizin Berlin, Institut für Medizinische Physik und Biophysik (CC2), Group Enzyme Kinetics, Charitéplatz 1, D-10117, Berlin, Germany.,Division of Biological & Environmental Sciences & Engineering, King Abdullah University of Science and Technology (KAUST), 23955-6900, Thuwal, Saudi Arabia
| | - Andrea Schmidt
- Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Charitéplatz 1, D-10117, Berlin, Germany.,Charité - Universitätsmedizin Berlin, Institut für Medizinische Physik und Biophysik (CC2), Group Protein X-ray Crystallography and Signal Transduction, Charitéplatz 1, D-10117, Berlin, Germany
| | - Elmar Behrmann
- Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Charitéplatz 1, D-10117, Berlin, Germany.,Charité - Universitätsmedizin Berlin, Institut für Medizinische Physik und Biophysik (CC2), Group Cryo Electron Microscopy, Charitéplatz 1, D-10117, Berlin, Germany.,Research Group Structural Dynamics of Proteins, Center of Advanced European Studies and Research (Caesar), Ludwig-Erhard-Allee 2, D-53175, Bonn, Germany.,Institute of Biochemistry-Structural Biochemistry, University of Cologne, Zuelpicher Straße 47, D-50674, Cologne, Germany
| | - Jörg Bürger
- Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Charitéplatz 1, D-10117, Berlin, Germany.,Charité - Universitätsmedizin Berlin, Institut für Medizinische Physik und Biophysik (CC2), Group Cryo Electron Microscopy, Charitéplatz 1, D-10117, Berlin, Germany.,UltraStrukturNetzwerk, Max Planck Institute for Molecular Genetics, Ihnestrasse 73, D-14195, Berlin, Germany
| | - Thorsten Mielke
- UltraStrukturNetzwerk, Max Planck Institute for Molecular Genetics, Ihnestrasse 73, D-14195, Berlin, Germany
| | - Christian M T Spahn
- Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Charitéplatz 1, D-10117, Berlin, Germany.,Charité - Universitätsmedizin Berlin, Institut für Medizinische Physik und Biophysik (CC2), Group Cryo Electron Microscopy, Charitéplatz 1, D-10117, Berlin, Germany
| | - Martin Heck
- Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Charitéplatz 1, D-10117, Berlin, Germany.,Charité - Universitätsmedizin Berlin, Institut für Medizinische Physik und Biophysik (CC2), Group Enzyme Kinetics, Charitéplatz 1, D-10117, Berlin, Germany
| | - Patrick Scheerer
- Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Charitéplatz 1, D-10117, Berlin, Germany. .,Charité - Universitätsmedizin Berlin, Institut für Medizinische Physik und Biophysik (CC2), Group Protein X-ray Crystallography and Signal Transduction, Charitéplatz 1, D-10117, Berlin, Germany.
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27
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Abstract
High-altitude environments present a range of biochemical and physiological challenges for organisms through decreases in oxygen, pressure, and temperature relative to lowland habitats. Protein-level adaptations to hypoxic high-altitude conditions have been identified in multiple terrestrial endotherms; however, comparable adaptations in aquatic ectotherms, such as fishes, have not been as extensively characterized. In enzyme proteins, cold adaptation is attained through functional trade-offs between stability and activity, often mediated by substitutions outside the active site. Little is known whether signaling proteins [e.g., G protein-coupled receptors (GPCRs)] exhibit natural variation in response to cold temperatures. Rhodopsin (RH1), the temperature-sensitive visual pigment mediating dim-light vision, offers an opportunity to enhance our understanding of thermal adaptation in a model GPCR. Here, we investigate the evolution of rhodopsin function in an Andean mountain catfish system spanning a range of elevations. Using molecular evolutionary analyses and site-directed mutagenesis experiments, we provide evidence for cold adaptation in RH1. We find that unique amino acid substitutions occur at sites under positive selection in high-altitude catfishes, located at opposite ends of the RH1 intramolecular hydrogen-bonding network. Natural high-altitude variants introduced into these sites via mutagenesis have limited effects on spectral tuning, yet decrease the stability of dark-state and light-activated rhodopsin, accelerating the decay of ligand-bound forms. As found in cold-adapted enzymes, this phenotype likely compensates for a cold-induced decrease in kinetic rates-properties of rhodopsin that mediate rod sensitivity and visual performance. Our results support a role for natural variation in enhancing the performance of GPCRs in response to cold temperatures.
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In vivo optophysiology reveals that G-protein activation triggers osmotic swelling and increased light scattering of rod photoreceptors. Proc Natl Acad Sci U S A 2017; 114:E2937-E2946. [PMID: 28320964 DOI: 10.1073/pnas.1620572114] [Citation(s) in RCA: 77] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The light responses of rod and cone photoreceptors have been studied electrophysiologically for decades, largely with ex vivo approaches that disrupt the photoreceptors' subretinal microenvironment. Here we report the use of optical coherence tomography (OCT) to measure light-driven signals of rod photoreceptors in vivo. Visible light stimulation over a 200-fold intensity range caused correlated rod outer segment (OS) elongation and increased light scattering in wild-type mice, but not in mice lacking the rod G-protein alpha subunit, transducin (Gαt), revealing these responses to be triggered by phototransduction. For stimuli that photoactivated one rhodopsin per Gαt the rod OS swelling response reached a saturated elongation of 10.0 ± 2.1%, at a maximum rate of 0.11% s-1 Analyzing swelling as osmotically driven water influx, we find the H2O membrane permeability of the rod OS to be (2.6 ± 0.4) × 10-5 cm⋅s-1, comparable to that of other cells lacking aquaporin expression. Application of Van't Hoff's law reveals that complete activation of phototransduction generates a potentially harmful 20% increase in OS osmotic pressure. The increased backscattering from the base of the OS is explained by a model combining cytoplasmic swelling, translocation of dissociated G-protein subunits from the disc membranes into the cytoplasm, and a relatively higher H2O permeability of nascent discs in the basal rod OS. Translocation of phototransduction components out of the OS may protect rods from osmotic stress, which could be especially harmful in disease conditions that affect rod OS structural integrity.
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29
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Photocyclic behavior of rhodopsin induced by an atypical isomerization mechanism. Proc Natl Acad Sci U S A 2017; 114:E2608-E2615. [PMID: 28289214 DOI: 10.1073/pnas.1617446114] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Vertebrate rhodopsin (Rh) contains 11-cis-retinal as a chromophore to convert light energy into visual signals. On absorption of light, 11-cis-retinal is isomerized to all-trans-retinal, constituting a one-way reaction that activates transducin (Gt) followed by chromophore release. Here we report that bovine Rh, regenerated instead with a six-carbon-ring retinal chromophore featuring a C11=C12 double bond locked in its cis conformation (Rh6mr), employs an atypical isomerization mechanism by converting 11-cis to an 11,13-dicis configuration for prolonged Gt activation. Time-dependent UV-vis spectroscopy, HPLC, and molecular mechanics analyses revealed an atypical thermal reisomerization of the 11,13-dicis to the 11-cis configuration on a slow timescale, which enables Rh6mr to function in a photocyclic manner similar to that of microbial Rhs. With this photocyclic behavior, Rh6mr repeatedly recruits and activates Gt in response to light stimuli, making it an excellent candidate for optogenetic tools based on retinal analog-bound vertebrate Rhs. Overall, these comprehensive structure-function studies unveil a unique photocyclic mechanism of Rh activation by an 11-cis-to-11,13-dicis isomerization.
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Salesse C. Physiologie du signal visuel rétinien : de la phototransduction jusqu’au cycle visuel. J Fr Ophtalmol 2017; 40:239-250. [DOI: 10.1016/j.jfo.2016.12.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2016] [Accepted: 12/16/2016] [Indexed: 11/28/2022]
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Rose AS, Zachariae U, Grubmüller H, Hofmann KP, Scheerer P, Hildebrand PW. Role of Structural Dynamics at the Receptor G Protein Interface for Signal Transduction. PLoS One 2015; 10:e0143399. [PMID: 26606751 PMCID: PMC4659624 DOI: 10.1371/journal.pone.0143399] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Accepted: 11/04/2015] [Indexed: 11/19/2022] Open
Abstract
GPCRs catalyze GDP/GTP exchange in the α-subunit of heterotrimeric G proteins (Gαßγ) through displacement of the Gα C-terminal α5 helix, which directly connects the interface of the active receptor (R*) to the nucleotide binding pocket of G. Hydrogen-deuterium exchange mass spectrometry and kinetic analysis of R* catalysed G protein activation have suggested that displacement of α5 starts from an intermediate GDP bound complex (R*•GGDP). To elucidate the structural basis of receptor-catalysed displacement of α5, we modelled the structure of R*•GGDP. A flexible docking protocol yielded an intermediate R*•GGDP complex, with a similar overall arrangement as in the X-ray structure of the nucleotide free complex (R*•Gempty), however with the α5 C-terminus (GαCT) forming different polar contacts with R*. Starting molecular dynamics simulations of GαCT bound to R* in the intermediate position, we observe a screw-like motion, which restores the specific interactions of α5 with R* in R*•Gempty. The observed rotation of α5 by 60° is in line with experimental data. Reformation of hydrogen bonds, water expulsion and formation of hydrophobic interactions are driving forces of the α5 displacement. We conclude that the identified interactions between R* and G protein define a structural framework in which the α5 displacement promotes direct transmission of the signal from R* to the GDP binding pocket.
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Affiliation(s)
- Alexander S. Rose
- Institute of Medical Physics and Biophysics (CC2), Universitätsmedizin Berlin, Charitéplatz 1, 10098, Berlin, Germany
- Team ProteiInformatics, Universitätsmedizin Berlin, Charitéplatz 1, 10098, Berlin, Germany
| | - Ulrich Zachariae
- Dep. of Theoretical and Computational Biophysics, Max-Planck-Institute for Biophysical Chemistry, 37077, Göttingen, Germany
- Computational Biology, School of Life Sciences, and Physics, School of Science and Engineering, University of Dundee, Dow Street, Dundee, DD1 5EH, United Kingdom
| | - Helmut Grubmüller
- Dep. of Theoretical and Computational Biophysics, Max-Planck-Institute for Biophysical Chemistry, 37077, Göttingen, Germany
| | - Klaus Peter Hofmann
- Institute of Medical Physics and Biophysics (CC2), Universitätsmedizin Berlin, Charitéplatz 1, 10098, Berlin, Germany
- Centre of Biophysics and Bioinformatics, Humboldt-Universität zu Berlin, Invalidenstrasse 42, 10115, Berlin, Germany
| | - Patrick Scheerer
- Institute of Medical Physics and Biophysics (CC2), Universitätsmedizin Berlin, Charitéplatz 1, 10098, Berlin, Germany
- Team Protein X-ray Crystallography and Signal Transduction, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10098, Berlin, Germany
| | - Peter W. Hildebrand
- Institute of Medical Physics and Biophysics (CC2), Universitätsmedizin Berlin, Charitéplatz 1, 10098, Berlin, Germany
- Team ProteiInformatics, Universitätsmedizin Berlin, Charitéplatz 1, 10098, Berlin, Germany
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Rhodopsin Forms Nanodomains in Rod Outer Segment Disc Membranes of the Cold-Blooded Xenopus laevis. PLoS One 2015; 10:e0141114. [PMID: 26492040 PMCID: PMC4619631 DOI: 10.1371/journal.pone.0141114] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Accepted: 10/04/2015] [Indexed: 11/19/2022] Open
Abstract
Rhodopsin forms nanoscale domains (i.e., nanodomains) in rod outer segment disc membranes from mammalian species. It is unclear whether rhodopsin arranges in a similar manner in amphibian species, which are often used as a model system to investigate the function of rhodopsin and the structure of photoreceptor cells. Moreover, since samples are routinely prepared at low temperatures, it is unclear whether lipid phase separation effects in the membrane promote the observed nanodomain organization of rhodopsin from mammalian species. Rod outer segment disc membranes prepared from the cold-blooded frog Xenopus laevis were investigated by atomic force microscopy to visualize the organization of rhodopsin in the absence of lipid phase separation effects. Atomic force microscopy revealed that rhodopsin nanodomains form similarly as that observed previously in mammalian membranes. Formation of nanodomains in ROS disc membranes is independent of lipid phase separation and conserved among vertebrates.
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Dell'Orco D, Koch KW. Transient complexes between dark rhodopsin and transducin: circumstantial evidence or physiological necessity? Biophys J 2015; 108:775-7. [PMID: 25650944 DOI: 10.1016/j.bpj.2014.12.031] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2014] [Revised: 12/01/2014] [Accepted: 12/05/2014] [Indexed: 01/08/2023] Open
Affiliation(s)
- Daniele Dell'Orco
- Department of Life Sciences and Reproduction, Section of Biological Chemistry and Centre for BioMedical Computing, University of Verona, Verona, Italy.
| | - Karl-Wilhelm Koch
- Department of Neurosciences, Biochemistry Group, University of Oldenburg, Oldenburg, Germany.
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34
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Schöneberg J, Hofmann KP, Heck M, Noé F. Response to comment "Transient complexes between dark rhodopsin and transducin: circumstantial evidence or physiological necessity?" by D. Dell'Orco and K.-W. Koch. Biophys J 2015; 108:778-9. [PMID: 25650945 DOI: 10.1016/j.bpj.2014.12.030] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Accepted: 12/18/2014] [Indexed: 01/13/2023] Open
Affiliation(s)
| | | | - Martin Heck
- Institute for Medical Physics and Biophysics, Berlin, Germany.
| | - Frank Noé
- Department of Mathematics, Computer Science and Bioinformatics, Free University of Berlin, Berlin, Germany.
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35
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Schöneberg J, Heck M, Hofmann KP, Noé F. Explicit spatiotemporal simulation of receptor-G protein coupling in rod cell disk membranes. Biophys J 2015; 107:1042-1053. [PMID: 25185540 DOI: 10.1016/j.bpj.2014.05.050] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2014] [Revised: 05/13/2014] [Accepted: 05/19/2014] [Indexed: 12/11/2022] Open
Abstract
Dim-light vision is mediated by retinal rod cells. Rhodopsin (R), a G-protein-coupled receptor, switches to its active form (R(∗)) in response to absorbing a single photon and activates multiple copies of the G-protein transducin (G) that trigger further downstream reactions of the phototransduction cascade. The classical assumption is that R and G are uniformly distributed and freely diffusing on disk membranes. Recent experimental findings have challenged this view by showing specific R architectures, including RG precomplexes, nonuniform R density, specific R arrangements, and immobile fractions of R. Here, we derive a physical model that describes the first steps of the photoactivation cascade in spatiotemporal detail and single-molecule resolution. The model was implemented in the ReaDDy software for particle-based reaction-diffusion simulations. Detailed kinetic in vitro experiments are used to parametrize the reaction rates and diffusion constants of R and G. Particle diffusion and G activation are then studied under different conditions of R-R interaction. It is found that the classical free-diffusion model is consistent with the available kinetic data. The existence of precomplexes between inactive R and G is only consistent with the data if these precomplexes are weak, with much larger dissociation rates than suggested elsewhere. Microarchitectures of R, such as dimer racks, would effectively immobilize R but have little impact on the diffusivity of G and on the overall amplification of the cascade at the level of the G protein.
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Affiliation(s)
- Johannes Schöneberg
- Department of Mathematics, Computer Science and Bioinformatics, Freie Universität Berlin, Berlin, Germany
| | - Martin Heck
- Institut für Medizinische Physik und Biophysik, Charité, Universitätsmedizin Berlin, Berlin, Germany.
| | - Klaus Peter Hofmann
- Institut für Medizinische Physik und Biophysik, Charité, Universitätsmedizin Berlin, Berlin, Germany
| | - Frank Noé
- Department of Mathematics, Computer Science and Bioinformatics, Freie Universität Berlin, Berlin, Germany.
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Jastrzebska B, Chen Y, Orban T, Jin H, Hofmann L, Palczewski K. Disruption of Rhodopsin Dimerization with Synthetic Peptides Targeting an Interaction Interface. J Biol Chem 2015; 290:25728-44. [PMID: 26330551 DOI: 10.1074/jbc.m115.662684] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2015] [Indexed: 11/06/2022] Open
Abstract
Although homo- and heterodimerizations of G protein-coupled receptors (GPCRs) are well documented, GPCR monomers are able to assemble in different ways, thus causing variations in the interactive interface between receptor monomers among different GPCRs. Moreover, the functional consequences of this phenomenon, which remain to be clarified, could be specific for different GPCRs. Synthetic peptides derived from transmembrane (TM) domains can interact with a full-length GPCR, blocking dimer formation and affecting its function. Here we used peptides corresponding to TM helices of bovine rhodopsin (Rho) to investigate the Rho dimer interface and functional consequences of its disruption. Incubation of Rho with TM1, TM2, TM4, and TM5 peptides in rod outer segment (ROS) membranes shifted the resulting detergent-solubilized protein migration through a gel filtration column toward smaller molecular masses with a reduced propensity for dimer formation in a cross-linking reaction. Binding of these TM peptides to Rho was characterized by both mass spectrometry and a label-free assay from which dissociation constants were calculated. A BRET (bioluminescence resonance energy transfer) assay revealed that the physical interaction between Rho molecules expressed in membranes of living cells was blocked by the same four TM peptides identified in our in vitro experiments. Although disruption of the Rho dimer/oligomer had no effect on the rates of G protein activation, binding of Gt to the activated receptor stabilized the dimer. However, TM peptide-induced disruption of dimer/oligomer decreased receptor stability, suggesting that Rho supramolecular organization could be essential for ROS stabilization and receptor trafficking.
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Affiliation(s)
- Beata Jastrzebska
- From the Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965
| | - Yuanyuan Chen
- From the Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965
| | - Tivadar Orban
- From the Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965
| | - Hui Jin
- From the Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965
| | - Lukas Hofmann
- From the Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965
| | - Krzysztof Palczewski
- From the Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965
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37
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Soubias O, Teague WE, Hines KG, Gawrisch K. The role of membrane curvature elastic stress for function of rhodopsin-like G protein-coupled receptors. Biochimie 2015; 107 Pt A:28-32. [PMID: 25447139 DOI: 10.1016/j.biochi.2014.10.011] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2014] [Accepted: 10/16/2014] [Indexed: 10/24/2022]
Abstract
The human genome encodes about 800 different G protein-coupled receptors (GPCR). They are key molecules in signal transduction pathways that transmit signals of a variety of ligands such as hormones and neurotransmitters to the cell interior. Upon ligand binding, the receptors undergo structural transitions that either enhance or inhibit transmission of a specific signal to the cell interior. Here we discuss results which indicate that transmission of such signals can be strongly modulated by the composition of the lipid matrix into which GPCR are imbedded. Experimental results have been obtained on rhodopsin, a prototype GPCR whose structure and function is representative for the great majority of GPCR in humans. The data shed light on the importance of curvature elastic stress in the lipid domain for function of GPCR.
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38
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Lohse MJ, Hofmann KP. Spatial and Temporal Aspects of Signaling by G-Protein-Coupled Receptors. Mol Pharmacol 2015; 88:572-8. [PMID: 26184590 DOI: 10.1124/mol.115.100248] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2015] [Accepted: 07/10/2015] [Indexed: 01/07/2023] Open
Abstract
Signaling by G-protein-coupled receptors is often considered a uniform process, whereby a homogeneously activated proportion of randomly distributed receptors are activated under equilibrium conditions and produce homogeneous, steady-state intracellular signals. While this may be the case in some biologic systems, the example of rhodopsin with its strictly local single-quantum mode of function shows that homogeneity in space and time cannot be a general property of G-protein-coupled systems. Recent work has now revealed many other systems where such simplicity does not prevail. Instead, a plethora of mechanisms allows much more complex patterns of receptor activation and signaling: different mechanisms of protein-protein interaction; temporal changes under nonequilibrium conditions; localized receptor activation; and localized second messenger generation and degradation-all of which shape receptor-generated signals and permit the creation of multiple signal types. Here, we review the evidence for such pleiotropic receptor signaling in space and time.
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Affiliation(s)
- Martin J Lohse
- Institute of Pharmacology and Toxicology, Rudolf Virchow Center, and Comprehensive Heart Failure Center, University of Würzburg, Würzburg, Germany (M.J.L.); Institut für Medizinische Physik und Biophysik (CC2), Charité-Universitätsmedizin Berlin, Berlin, Germany (K.P.H.); and Zentrum für Biophysik und Bioinformatik, Humboldt-Universität zu Berlin, Berlin, Germany (K.P.H.)
| | - Klaus Peter Hofmann
- Institute of Pharmacology and Toxicology, Rudolf Virchow Center, and Comprehensive Heart Failure Center, University of Würzburg, Würzburg, Germany (M.J.L.); Institut für Medizinische Physik und Biophysik (CC2), Charité-Universitätsmedizin Berlin, Berlin, Germany (K.P.H.); and Zentrum für Biophysik und Bioinformatik, Humboldt-Universität zu Berlin, Berlin, Germany (K.P.H.)
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39
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Kazmin R, Rose A, Szczepek M, Elgeti M, Ritter E, Piechnick R, Hofmann KP, Scheerer P, Hildebrand PW, Bartl FJ. The Activation Pathway of Human Rhodopsin in Comparison to Bovine Rhodopsin. J Biol Chem 2015; 290:20117-27. [PMID: 26105054 DOI: 10.1074/jbc.m115.652172] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Indexed: 11/06/2022] Open
Abstract
Rhodopsin, the photoreceptor of rod cells, absorbs light to mediate the first step of vision by activating the G protein transducin (Gt). Several human diseases, such as retinitis pigmentosa or congenital night blindness, are linked to rhodopsin malfunctions. Most of the corresponding in vivo studies and structure-function analyses (e.g. based on protein x-ray crystallography or spectroscopy) have been carried out on murine or bovine rhodopsin. Because these rhodopsins differ at several amino acid positions from human rhodopsin, we conducted a comprehensive spectroscopic characterization of human rhodopsin in combination with molecular dynamics simulations. We show by FTIR and UV-visible difference spectroscopy that the light-induced transformations of the early photointermediates are very similar. Significant differences between the pigments appear with formation of the still inactive Meta I state and the transition to active Meta II. However, the conformation of Meta II and its activity toward the G protein are essentially the same, presumably reflecting the evolutionary pressure under which the active state has developed. Altogether, our results show that although the basic activation pathways of human and bovine rhodopsin are similar, structural deviations exist in the inactive conformation and during receptor activation, even between closely related rhodopsins. These differences between the well studied bovine or murine rhodopsins and human rhodopsin have to be taken into account when the influence of point mutations on the activation pathway of human rhodopsin are investigated using the bovine or murine rhodopsin template sequences.
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Affiliation(s)
- Roman Kazmin
- From the Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, Institut für Biologie, Experimentelle Biophysik, Humboldt-Universität zu Berlin, 10115 Berlin, Germany, and
| | - Alexander Rose
- From the Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, AG ProteInformatics, Charitéplatz 1, 10117 Berlin, Germany
| | - Michal Szczepek
- From the Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, AG Protein X-ray Crystallography and Signal Transduction, and
| | - Matthias Elgeti
- From the Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin
| | - Eglof Ritter
- Institut für Biologie, Experimentelle Biophysik, Humboldt-Universität zu Berlin, 10115 Berlin, Germany, and
| | - Ronny Piechnick
- From the Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin
| | - Klaus Peter Hofmann
- From the Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, Zentrum für Biophysik und Bioinformatik (BPI), Humboldt-Universität zu Berlin, 10115 Berlin, Germany
| | - Patrick Scheerer
- From the Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, AG Protein X-ray Crystallography and Signal Transduction, and
| | - Peter W Hildebrand
- From the Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, AG ProteInformatics, Charitéplatz 1, 10117 Berlin, Germany
| | - Franz J Bartl
- From the Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin,
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40
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Gross OP, Pugh EN, Burns ME. cGMP in mouse rods: the spatiotemporal dynamics underlying single photon responses. Front Mol Neurosci 2015; 8:6. [PMID: 25788876 PMCID: PMC4349151 DOI: 10.3389/fnmol.2015.00006] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2014] [Accepted: 02/12/2015] [Indexed: 02/04/2023] Open
Abstract
Vertebrate vision begins when retinal photoreceptors transduce photons into electrical signals that are then relayed to other neurons in the eye, and ultimately to the brain. In rod photoreceptors, transduction of single photons is achieved by a well-understood G-protein cascade that modulates cGMP levels, and in turn, cGMP-sensitive inward current. The spatial extent and depth of the decline in cGMP during the single photon response (SPR) have been major issues in phototransduction research since the discovery that single photons elicit substantial and reproducible changes in membrane current. The spatial profile of cGMP decline during the SPR affects signal gain, and thus may contribute to reduction of trial-to-trial fluctuations in the SPR. Here we summarize the general principles of rod phototransduction, emphasizing recent advances in resolving the spatiotemporal dynamics of cGMP during the SPR.
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Affiliation(s)
- Owen P Gross
- Center for Neuroscience, University of California Davis Davis, CA, USA
| | - Edward N Pugh
- Departments of Ophthalmology and Vision Science, University of California Davis Davis, CA, USA ; Physiology and Membrane Biology, University of California Davis Davis, CA, USA ; Cell Biology and Human Anatomy, University of California Davis Davis, CA, USA
| | - Marie E Burns
- Center for Neuroscience, University of California Davis Davis, CA, USA ; Departments of Ophthalmology and Vision Science, University of California Davis Davis, CA, USA ; Cell Biology and Human Anatomy, University of California Davis Davis, CA, USA
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41
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Gunkel M, Schöneberg J, Alkhaldi W, Irsen S, Noé F, Kaupp UB, Al-Amoudi A. Higher-order architecture of rhodopsin in intact photoreceptors and its implication for phototransduction kinetics. Structure 2015; 23:628-38. [PMID: 25728926 DOI: 10.1016/j.str.2015.01.015] [Citation(s) in RCA: 85] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2014] [Revised: 01/16/2015] [Accepted: 01/22/2015] [Indexed: 12/23/2022]
Abstract
The visual pigment rhodopsin belongs to the family of G protein-coupled receptors that can form higher oligomers. It is controversial whether rhodopsin forms oligomers and whether oligomers are functionally relevant. Here, we study rhodopsin organization in cryosections of dark-adapted mouse rod photoreceptors by cryoelectron tomography. We identify four hierarchical levels of organization. Rhodopsin forms dimers; at least ten dimers form a row. Rows form pairs (tracks) that are aligned parallel to the disk incisures. Particle-based simulation shows that the combination of tracks with fast precomplex formation, i.e. rapid association and dissociation between inactive rhodopsin and the G protein transducin, leads to kinetic trapping: rhodopsin first activates transducin from its own track, whereas recruitment of transducin from other tracks proceeds more slowly. The trap mechanism could produce uniform single-photon responses independent of rhodopsin lifetime. In general, tracks might provide a platform that coordinates the spatiotemporal interaction of signaling molecules.
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Affiliation(s)
- Monika Gunkel
- Department of Molecular Sensory Systems, Center of Advanced European Studies and Research (caesar), Ludwig-Erhard-Allee 2, 53175 Bonn, Germany
| | - Johannes Schöneberg
- Computational Molecular Biology Group, Freie Universität Berlin, Arnimallee 6, 14195 Berlin, Germany
| | - Weaam Alkhaldi
- German Center of Neurodegenerative Diseases, Ludwig-Erhard-Allee 2, 53175 Bonn, Germany
| | - Stephan Irsen
- Department of Molecular Sensory Systems, Center of Advanced European Studies and Research (caesar), Ludwig-Erhard-Allee 2, 53175 Bonn, Germany
| | - Frank Noé
- Computational Molecular Biology Group, Freie Universität Berlin, Arnimallee 6, 14195 Berlin, Germany
| | - U Benjamin Kaupp
- Department of Molecular Sensory Systems, Center of Advanced European Studies and Research (caesar), Ludwig-Erhard-Allee 2, 53175 Bonn, Germany.
| | - Ashraf Al-Amoudi
- German Center of Neurodegenerative Diseases, Ludwig-Erhard-Allee 2, 53175 Bonn, Germany.
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42
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Structure-Based Biophysical Analysis of the Interaction of Rhodopsin with G Protein and Arrestin. Methods Enzymol 2015; 556:563-608. [DOI: 10.1016/bs.mie.2014.12.014] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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43
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Palczewski K. Chemistry and biology of the initial steps in vision: the Friedenwald lecture. Invest Ophthalmol Vis Sci 2014; 55:6651-72. [PMID: 25338686 DOI: 10.1167/iovs.14-15502] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Visual transduction is the process in the eye whereby absorption of light in the retina is translated into electrical signals that ultimately reach the brain. The first challenge presented by visual transduction is to understand its molecular basis. We know that maintenance of vision is a continuous process requiring the activation and subsequent restoration of a vitamin A-derived chromophore through a series of chemical reactions catalyzed by enzymes in the retina and retinal pigment epithelium (RPE). Diverse biochemical approaches that identified key proteins and reactions were essential to achieve a mechanistic understanding of these visual processes. The three-dimensional arrangements of these enzymes' polypeptide chains provide invaluable insights into their mechanisms of action. A wealth of information has already been obtained by solving high-resolution crystal structures of both rhodopsin and the retinoid isomerase from pigment RPE (RPE65). Rhodopsin, which is activated by photoisomerization of its 11-cis-retinylidene chromophore, is a prototypical member of a large family of membrane-bound proteins called G protein-coupled receptors (GPCRs). RPE65 is a retinoid isomerase critical for regeneration of the chromophore. Electron microscopy (EM) and atomic force microscopy have provided insights into how certain proteins are assembled to form much larger structures such as rod photoreceptor cell outer segment membranes. A second challenge of visual transduction is to use this knowledge to devise therapeutic approaches that can prevent or reverse conditions leading to blindness. Imaging modalities like optical coherence tomography (OCT) and scanning laser ophthalmoscopy (SLO) applied to appropriate animal models as well as human retinal imaging have been employed to characterize blinding diseases, monitor their progression, and evaluate the success of therapeutic agents. Lately two-photon (2-PO) imaging, together with biochemical assays, are revealing functional aspects of vision at a new molecular level. These multidisciplinary approaches combined with suitable animal models and inbred mutant species can be especially helpful in translating provocative cell and tissue culture findings into therapeutic options for further development in animals and eventually in humans. A host of different approaches and techniques is required for substantial progress in understanding fundamental properties of the visual system.
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Affiliation(s)
- Krzysztof Palczewski
- Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio, United States
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44
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Wang T, Chen J. Induction of the unfolded protein response by constitutive G-protein signaling in rod photoreceptor cells. J Biol Chem 2014; 289:29310-21. [PMID: 25183010 DOI: 10.1074/jbc.m114.595207] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phototransduction is a G-protein signal transduction cascade that converts photon absorption to a change in current at the plasma membrane. Certain genetic mutations affecting the proteins in the phototransduction cascade cause blinding disorders in humans. Some of these mutations serve as a genetic source of "equivalent light" that activates the cascade, whereas other mutations lead to amplification of the light response. How constitutive phototransduction causes photoreceptor cell death is poorly understood. We showed that persistent G-protein signaling, which occurs in rod arrestin and rhodopsin kinase knock-out mice, caused a rapid and specific induction of the PERK pathway of the unfolded protein response. These changes were not observed in the cGMP-gated channel knock-out rods, an equivalent light condition that mimics light-stimulated channel closure. Thus transducin signaling, but not channel closure, triggers rapid cell death in light damage caused by constitutive phototransduction. Additionally, we show that in the albino light damage model cell death was not associated with increase in global protein ubiquitination or unfolded protein response induction. Taken together, these observations provide novel mechanistic insights into the cell death pathway caused by constitutive phototransduction and identify the unfolded protein response as a potential target for therapeutic intervention.
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Affiliation(s)
- Tian Wang
- From the Program in Genetic, Molecular and Cellular Biology and the Zilkha Neurogenetic Institute, Department of Cell & Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, California 90089
| | - Jeannie Chen
- the Zilkha Neurogenetic Institute, Department of Cell & Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, California 90089
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45
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Arshavsky VY, Burns ME. Current understanding of signal amplification in phototransduction. CELLULAR LOGISTICS 2014; 4:e29390. [PMID: 25279249 PMCID: PMC4160332 DOI: 10.4161/cl.29390] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Accepted: 05/28/2014] [Indexed: 11/30/2022]
Abstract
The studies of visual signal transduction, or phototransduction, have played a pivotal role in elucidating the most general principles of G protein signaling, particularly in regards to the concept of signal amplification, i.e., the process by which activation of a relatively small number of G protein coupled receptors is transformed into a robust downstream signaling event. In this essay, we summarize our current quantitative understanding of this process in living rods of lower and higher vertebrate animals. An integration of biochemical experiments in vitro with electrophysiological recordings from intact rod photoreceptors indicates that the total number of G protein molecules activated in the course of a light response to a single photon is ~16 in the mouse and ~60 in the frog. This further translates into hydrolysis of ~2000 and ~72 000 molecules of cGMP downstream of G protein, respectively, which represents the total degree of biochemical amplification in the phototransduction cascade.
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Affiliation(s)
- Vadim Y Arshavsky
- Departments of Ophthalmology and Pharmacology; Duke University; Durham NC USA
| | - Marie E Burns
- Departments of Cell Biology and Human Anatomy and Ophthalmology and Vision Science; University of California; Davis, CA USA
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46
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Linser R, Sarkar R, Krushelnitzky A, Mainz A, Reif B. Dynamics in the solid-state: perspectives for the investigation of amyloid aggregates, membrane proteins and soluble protein complexes. JOURNAL OF BIOMOLECULAR NMR 2014; 59:1-14. [PMID: 24595988 DOI: 10.1007/s10858-014-9822-6] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Accepted: 02/26/2014] [Indexed: 06/03/2023]
Abstract
Aggregates formed by amyloidogenic peptides and proteins and reconstituted membrane protein preparations differ significantly in terms of the spectral quality that they display in solid-state NMR experiments. Structural heterogeneity and dynamics can both in principle account for that observation. This perspectives article aims to point out challenges and limitations, but also potential opportunities in the investigation of these systems.
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Affiliation(s)
- Rasmus Linser
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Ave, Boston, MA, 02115, USA
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47
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Chen Y, Jastrzebska B, Cao P, Zhang J, Wang B, Sun W, Yuan Y, Feng Z, Palczewski K. Inherent instability of the retinitis pigmentosa P23H mutant opsin. J Biol Chem 2014; 289:9288-303. [PMID: 24515108 PMCID: PMC3979360 DOI: 10.1074/jbc.m114.551713] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2014] [Revised: 02/05/2014] [Indexed: 11/06/2022] Open
Abstract
The P23H opsin mutation is the most common cause of autosomal dominant retinitis pigmentosa. Even though the pathobiology of the resulting retinal degeneration has been characterized in several animal models, its complex molecular mechanism is not well understood. Here, we expressed P23H bovine rod opsin in the nervous system of Caenorhabditis elegans. Expression was low due to enhanced protein degradation. The mutant opsin was glycosylated, but the polysaccharide size differed from that of the normal protein. Although P23H opsin aggregated in the nervous system of C. elegans, the pharmacological chaperone 9-cis-retinal stabilized it during biogenesis, producing a variant of rhodopsin called P23H isorhodopsin. In vitro, P23H isorhodopsin folded correctly, formed the appropriate disulfide bond, could be photoactivated but with reduced sensitivity, and underwent Meta II decay at a rate similar to wild type isorhodopsin. In worm neurons, P23H isorhodopsin initiated phototransduction by coupling with the endogenous Gi/o signaling cascade that induced loss of locomotion. Using pharmacological interventions affecting protein synthesis and degradation, we showed that the chromophore could be incorporated either during or after mutant protein translation. However, regeneration of P23H isorhodopsin with chromophore was significantly slower than that of wild type isorhodopsin. This effect, combined with the inherent instability of P23H rhodopsin, could lead to the structural cellular changes and photoreceptor death found in autosomal dominant retinitis pigmentosa. These results also suggest that slow regeneration of P23H rhodopsin could prevent endogenous chromophore-mediated stabilization of rhodopsin in the retina.
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Affiliation(s)
| | | | | | | | - Benlian Wang
- Center for Proteomics and Bioinformatics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965 and
| | - Wenyu Sun
- Polgenix Inc., Cleveland, Ohio 44106
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48
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Invergo BM, Dell'Orco D, Montanucci L, Koch KW, Bertranpetit J. A comprehensive model of the phototransduction cascade in mouse rod cells. MOLECULAR BIOSYSTEMS 2014; 10:1481-9. [PMID: 24675755 DOI: 10.1039/c3mb70584f] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Vertebrate visual phototransduction is perhaps the most well-studied G-protein signaling pathway. A wealth of available biochemical and electrophysiological data has resulted in a rich history of mathematical modeling of the system. However, while the most comprehensive models have relied upon amphibian biochemical and electrophysiological data, modern research typically employs mammalian species, particularly mice, which exhibit significantly faster signaling dynamics. In this work, we present an adaptation of a previously published, comprehensive model of amphibian phototransduction that can produce quantitatively accurate simulations of the murine photoresponse. We demonstrate the ability of the model to predict responses to a wide range of stimuli and under a variety of mutant conditions. Finally, we employ the model to highlight a likely unknown mechanism related to the interaction between rhodopsin and rhodopsin kinase.
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Affiliation(s)
- Brandon M Invergo
- IBE - Institute of Evolutionary Biology (CSIC-Universitat Pompeu Fabra), CEXS-UPF-PRBB, Barcelona, Catalonia, Spain
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49
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Ernst OP, Lodowski DT, Elstner M, Hegemann P, Brown L, Kandori H. Microbial and animal rhodopsins: structures, functions, and molecular mechanisms. Chem Rev 2014; 114:126-63. [PMID: 24364740 PMCID: PMC3979449 DOI: 10.1021/cr4003769] [Citation(s) in RCA: 759] [Impact Index Per Article: 75.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2013] [Indexed: 12/31/2022]
Affiliation(s)
- Oliver P. Ernst
- Departments
of Biochemistry and Molecular Genetics, University of Toronto, 1 King’s College Circle, Medical Sciences Building, Toronto, Ontario M5S 1A8, Canada
| | - David T. Lodowski
- Center
for Proteomics and Bioinformatics, Case
Western Reserve University School of Medicine, 10900 Euclid Avenue, Cleveland, Ohio 44106, United States
| | - Marcus Elstner
- Institute
for Physical Chemistry, Karlsruhe Institute
of Technology, Kaiserstrasse
12, 76131 Karlsruhe, Germany
| | - Peter Hegemann
- Institute
of Biology, Experimental Biophysics, Humboldt-Universität
zu Berlin, Invalidenstrasse
42, 10115 Berlin, Germany
| | - Leonid
S. Brown
- Department
of Physics and Biophysics Interdepartmental Group, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G 2W1, Canada
| | - Hideki Kandori
- Department
of Frontier Materials, Nagoya Institute
of Technology, Showa-ku, Nagoya 466-8555, Japan
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50
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Sommer ME, Hofmann KP, Heck M. Not just signal shutoff: the protective role of arrestin-1 in rod cells. Handb Exp Pharmacol 2014; 219:101-16. [PMID: 24292826 DOI: 10.1007/978-3-642-41199-1_5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The retinal rod cell is an exquisitely sensitive single-photon detector that primarily functions in dim light (e.g., moonlight). However, rod cells must routinely survive light intensities more than a billion times greater (e.g., bright daylight). One serious challenge to rod cell survival in daylight is the massive amount of all-trans-retinal that is released by Meta II, the light-activated form of the photoreceptor rhodopsin. All-trans-retinal is toxic, and its condensation products have been implicated in disease. Our recent work has developed the concept that rod arrestin (arrestin-1), which terminates Meta II signaling, has an additional role in protecting rod cells from the consequences of bright light by limiting free all-trans-retinal. In this chapter we will elaborate upon the molecular mechanisms by which arrestin-1 serves as both a single-photon response quencher as well as an instrument of rod cell survival in bright light. This discussion will take place within the framework of three distinct functional modules of vision: signal transduction, the retinoid cycle, and protein translocation.
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Affiliation(s)
- Martha E Sommer
- Institut für Medizinische Physik und Biophysik (CC2), Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117, Berlin, Germany,
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