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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: 21] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2022] [Revised: 08/20/2022] [Accepted: 08/22/2022] [Indexed: 11/06/2022]
Abstract
The light sensor of vertebrate scotopic (low-light) vision, rhodopsin, is a G-protein-coupled receptor comprising a polypeptide chain with bound chromophore, 11-cis-retinal, that exhibits remarkable physicochemical properties. This photopigment is extremely stable in the dark, yet its chromophore isomerises upon photon absorption with 70% efficiency, enabling the activation of its G-protein, transducin, with high efficiency. Rhodopsin's photochemical and biochemical activities occur over very different time-scales: the energy of retinaldehyde's excited state is stored in <1 ps in retinal-protein interactions, but it takes milliseconds for the catalytically active state to form, and many tens of minutes for the resting state to be restored. In this review, we describe the properties of rhodopsin and its role in rod phototransduction. We first introduce rhodopsin's gross structural features, its evolution, and the basic mechanisms of its activation. We then discuss light absorption and spectral sensitivity, photoreceptor electrical responses that result from the activity of individual rhodopsin molecules, and recovery of rhodopsin and the visual system from intense bleaching exposures. We then provide a detailed examination of rhodopsin's molecular structure and function, first in its dark state, and then in the active Meta states that govern its interactions with transducin, rhodopsin kinase and arrestin. While it is clear that rhodopsin's molecular properties are exquisitely honed for phototransduction, from starlight to dawn/dusk intensity levels, our understanding of how its molecular interactions determine the properties of scotopic vision remains incomplete. We describe potential future directions of research, and outline several major problems that remain to be solved.
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Affiliation(s)
- Klaus Peter Hofmann
- Institut für Medizinische Physik und Biophysik (CC2), Charité, and, Zentrum für Biophysik und Bioinformatik, Humboldt-Unversität zu Berlin, Berlin, 10117, Germany.
| | - Trevor D Lamb
- Eccles Institute of Neuroscience, John Curtin School of Medical Research, The Australian National University, Canberra, ACT 2600, Australia.
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2
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Delgado J, Lara-Astiaso M, González-Vázquez J, Decleva P, Palacios A, Martín F. Molecular fragmentation as a way to reveal early electron dynamics induced by attosecond pulses. Faraday Discuss 2021; 228:349-377. [PMID: 33571330 DOI: 10.1039/d0fd00121j] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
We present a theoretical study of the electron and nuclear dynamics that would arise in an attosecond two-color XUV-pump/XUV-probe experiment in glycine. In this scheme, the broadband pump pulse suddenly ionizes the molecule and creates an electronic wave packet that subsequently evolves under the influence of the nuclear motion until it is finally probed by the second XUV pulse. To describe the different steps of such an experiment, we have combined a multi-reference static-exchange scattering method with a trajectory surface hopping approach. We show that by changing the central frequency of the pump pulse, i.e., by engineering the initial electronic wave packet with the pump pulse, one can drive the cation dynamics into a specific fragmentation pathway. Reminiscence of this early electron dynamics can be observed in specific fragmentation channels (not all of them) as a function of the pump-probe delay and in time-resolved photoelectron spectra at specific photoelectron energies. The optimum conditions to visualize the initial electronic coherence in photoelectron and photo-ion spectra depend very much on the characteristics of the pump pulse as well as on the electronic structure of the molecule under study.
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Affiliation(s)
- Jorge Delgado
- Instituto Madrileño de Estudios Avanzados en Nanociencia, 28049 Madrid, Spain
| | - Manuel Lara-Astiaso
- Departamento de Química, Modulo 13, Universidad Autónoma de Madrid, 28049 Madrid, Spain.
| | - Jesús González-Vázquez
- Departamento de Química, Modulo 13, Universidad Autónoma de Madrid, 28049 Madrid, Spain.
| | - Piero Decleva
- CNR IOM, Dipartimento di Scienze Chimiche e Farmaceutiche, Universitá di Trieste, 34127 Trieste, Italy
| | - Alicia Palacios
- Departamento de Química, Modulo 13, Universidad Autónoma de Madrid, 28049 Madrid, Spain. and Institute for Advanced Research in Chemical Sciences (IAdChem), Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - Fernando Martín
- Instituto Madrileño de Estudios Avanzados en Nanociencia, 28049 Madrid, Spain and Departamento de Química, Modulo 13, Universidad Autónoma de Madrid, 28049 Madrid, Spain. and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, 28049 Madrid, Spain
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3
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Boyle KC, Chen ZC, Ling T, Pandiyan VP, Kuchenbecker J, Sabesan R, Palanker D. Mechanisms of Light-Induced Deformations in Photoreceptors. Biophys J 2020; 119:1481-1488. [PMID: 33031739 PMCID: PMC7642315 DOI: 10.1016/j.bpj.2020.09.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2020] [Revised: 09/02/2020] [Accepted: 09/08/2020] [Indexed: 01/11/2023] Open
Abstract
Biological cells deform on a nanometer scale when their transmembrane voltage changes, an effect that has been visualized during the action potential using quantitative phase imaging. Similar changes in the optical path length have been observed in photoreceptor outer segments after a flash stimulus via phase-resolved optical coherence tomography. These optoretinograms reveal a fast, millisecond-scale contraction of the outer segments by tens of nanometers, followed by a slow (hundreds of milliseconds) elongation reaching hundreds of nanometers. Ultrafast measurements of the contractile response using line-field phase-resolved optical coherence tomography show a logarithmic increase in amplitude and a decreasing time to peak with increasing stimulus intensity. We present a model that relates the early receptor potential to these deformations based on the voltage-dependent membrane tension-the mechanism observed earlier in neurons and other electrogenic cells. The early receptor potential is caused by conformational changes in opsins after photoisomerization, resulting in the fractional shift of the charge across the disk membrane. Lateral repulsion of the ions on both sides of the membrane affects its surface tension and leads to its lateral expansion. Because the volume of the disks does not change on a millisecond timescale, their lateral expansion leads to an axial contraction of the outer segment. With increasing stimulus intensity and the resulting tension, the area expansion coefficient of the disk membrane also increases as thermally induced fluctuations are pulled flat, resisting further expansion. This leads to the logarithmic saturation observed in measurements as well as the peak shift in time. This imaging technique therefore relates the structural changes in the photoreceptor to the underlying neurological function of transducing light into electrical signals. Such label-free optical monitoring of neural activity using fast interferometry may be applicable not only to optoretinography but also to neuroscience in general.
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Affiliation(s)
- K C Boyle
- Department of Electrical Engineering, Stanford University, Stanford, California; Hansen Experimental Physics Laboratory, Stanford University, Stanford, California.
| | - Z C Chen
- Department of Electrical Engineering, Stanford University, Stanford, California; Hansen Experimental Physics Laboratory, Stanford University, Stanford, California
| | - T Ling
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, California; Department of Ophthalmology, Stanford University, Stanford, California
| | - V P Pandiyan
- Department of Ophthalmology, University of Washington, Seattle, Washington
| | - J Kuchenbecker
- Department of Ophthalmology, University of Washington, Seattle, Washington
| | - R Sabesan
- Department of Ophthalmology, University of Washington, Seattle, Washington.
| | - D Palanker
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, California; Department of Ophthalmology, Stanford University, Stanford, California.
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Park B, Yang H, Ha TH, Park HS, Oh SJ, Ryu YS, Cho Y, Kim HS, Oh J, Lee DK, Kim C, Lee T, Seo M, Choi J, Jhon YM, Woo DH, Lee S, Kim SH, Lee HJ, Jun SC, Song HS, Park TH, Kim JH. Artificial Rod and Cone Photoreceptors with Human-Like Spectral Sensitivities. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1706764. [PMID: 29775503 DOI: 10.1002/adma.201706764] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2017] [Revised: 03/21/2018] [Indexed: 06/08/2023]
Abstract
Photosensitive materials contain biologically engineered elements and are constructed using delicate techniques, with special attention devoted to efficiency, stability, and biocompatibility. However, to date, no photosensitive material has been developed to replace damaged visual-systems to detect light and transmit the signal to a neuron in the human body. In the current study, artificial nanovesicle-based photosensitive materials are observed to possess the characteristics of photoreceptors similar to the human eye. The materials exhibit considerably effective spectral characteristics according to each pigment. Four photoreceptors originating from the human eye with color-distinguishability are produced in human embryonic kidney (HEK)-293 cells and partially purified in the form of nanovesicles. Under various wavelengths of visible light, electrochemical measurements are performed to analyze the physiological behavior and kinetics of the photoreceptors, with graphene, performing as an electrode, playing an important role in the lipid bilayer deposition and oxygen reduction processes. Four nanovesicles with different photoreceptors, namely, rhodopsin (Rho), short-, medium-, and longwave sensitive opsin 1 (1SW, 1MW, 1LW), show remarkable color-dependent characteristics, consistent with those of natural human retina. With four different light-emitting diodes for functional verification, the photoreceptors embedded in nanovesicles show remarkably specific color sensitivity. This study demonstrates the potential applications of light-activated platforms in biological optoelectronic industries.
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Affiliation(s)
- Byeongho Park
- Korean Institute of Science and Technology, Seoul, 02792, Republic of Korea
- Department of Mechanical Engineering, Yonsei University, Seoul, 03722, Republic of Korea
| | - Heehong Yang
- School of Chemical and Biological Engineering, Seoul National University, Seoul, 08826, Republic of Korea
- Protein Engineering Laboratory, Recombinants Unit, MOGAM Institute for Biomedical Research, Yongin, 16924, Republic of Korea
| | - Tai Hwan Ha
- Hazards Monitoring Bionanotechnology Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon, 34134, Republic of Korea
| | - Hyun Seo Park
- Korean Institute of Science and Technology, Seoul, 02792, Republic of Korea
| | - Seung Ja Oh
- Korean Institute of Science and Technology, Seoul, 02792, Republic of Korea
| | - Yong-Sang Ryu
- Korean Institute of Science and Technology, Seoul, 02792, Republic of Korea
| | - Youngho Cho
- Korean Institute of Science and Technology, Seoul, 02792, Republic of Korea
- College of Science and Technology, Kookmin University, Seoul, 02707, Republic of Korea
| | - Hyo-Suk Kim
- Korean Institute of Science and Technology, Seoul, 02792, Republic of Korea
- Department of Electronics and Communications Engineering, Kwang-woon University, Seoul, 01890, Republic of Korea
| | - Juyeong Oh
- Korean Institute of Science and Technology, Seoul, 02792, Republic of Korea
- Department of Mechanical Engineering, Yonsei University, Seoul, 03722, Republic of Korea
| | - Dong Kyu Lee
- Korean Institute of Science and Technology, Seoul, 02792, Republic of Korea
| | - Chulki Kim
- Korean Institute of Science and Technology, Seoul, 02792, Republic of Korea
| | - Taikjin Lee
- Korean Institute of Science and Technology, Seoul, 02792, Republic of Korea
| | - Minah Seo
- Korean Institute of Science and Technology, Seoul, 02792, Republic of Korea
| | - Jaebin Choi
- Korean Institute of Science and Technology, Seoul, 02792, Republic of Korea
| | - Young Min Jhon
- Korean Institute of Science and Technology, Seoul, 02792, Republic of Korea
| | - Deok Ha Woo
- Korean Institute of Science and Technology, Seoul, 02792, Republic of Korea
| | - Seok Lee
- Korean Institute of Science and Technology, Seoul, 02792, Republic of Korea
| | - Seok Hwan Kim
- Department of Ophthalmology, Seoul National University Boramae Hospital, Seoul, 07061, Republic of Korea
| | - Hyuk-Jae Lee
- College of Science and Technology, Kookmin University, Seoul, 02707, Republic of Korea
| | - Seong Chan Jun
- Department of Mechanical Engineering, Yonsei University, Seoul, 03722, Republic of Korea
| | - Hyun Seok Song
- Korea Basic Science Institute (KBSI), Republic of Korea
- Center for Convergent Research of Emerging Virus Infection, Korea Research Institute of Chemical Technology, Daejeon, 34114, Republic of Korea
- Department of Bio-Analytical Science, University of Science and Technology (UST), Daejeon, 34113, Republic of Korea
| | - Tai Hyun Park
- School of Chemical and Biological Engineering, Seoul National University, Seoul, 08826, Republic of Korea
| | - Jae Hun Kim
- Korean Institute of Science and Technology, Seoul, 02792, Republic of Korea
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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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Kessler C, Tillman M, Burns ME, Pugh EN. Rhodopsin in the rod surface membrane regenerates more rapidly than bulk rhodopsin in the disc membranes in vivo. J Physiol 2014; 592:2785-97. [PMID: 24801306 DOI: 10.1113/jphysiol.2014.272518] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Sustained vertebrate vision requires that opsin chromophores isomerized by light to the all-trans form be replaced with 11-cis retinal to regenerate the visual pigment. We have characterized the early receptor potential (ERP), a component of the electroretinogram arising from photoisomerization-induced charge displacements in plasma membrane visual pigment, and used it to measure pigment bleaching and regeneration in living mice. The mouse ERP was characterized by an outward 'R2' charge displacement with a time constant of 215 μs that discharged through a membrane with an apparent time constant of ∼0.6 ms. After complete bleaching of rhodopsin, the ERP recovered in two phases. The initial, faster phase had a time constant of ∼1 min, accounted for ∼20% of the total, and was not dependent on the level of expression of the retinal pigment epithelium isomerase, Rpe65. The slower, complementary phase had a time constant of 23 min in wild-type (WT) mice (C57Bl/6) and was substantially slowed in Rpe65(+/-) mice. Comparison of the ERPs of a mouse line expressing 150% of the normal level of cone M-opsin with those of WT mice revealed that M-opsin contributed 26% of the total WT ERP in these experiments, with the remaining 74% arising from rhodopsin. Thus, the fast regenerating fraction (20%) corresponds approximately to the fraction of the total ERP independently estimated to arise from M-opsin. Because both phases of the ERP recover substantially faster than previous measurements of bulk rhodopsin regeneration in living mice, we conclude that delivery of the highly hydrophobic 11-cis retinal to the interior of rod photoreceptors appears to be retarded by transit across the cytoplasmic gap between plasma and disc membranes.
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Affiliation(s)
| | - Megan Tillman
- Center for Neuroscience, University of California, Davis, Davis, CA, USA
| | - Marie E Burns
- Department of Ophthalmology and Vision Science, University of California, Davis, Davis, CA, USA Department of Cell Biology and Human Anatomy, University of California, Davis, Davis, CA, USA
| | - Edward N Pugh
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, USA Department of Cell Biology and Human Anatomy, University of California, Davis, Davis, CA, USA
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Möller M, Alexiev U. Surface Charge Changes upon Formation of the Signaling State in Visual Rhodopsin. Photochem Photobiol 2009; 85:501-8. [DOI: 10.1111/j.1751-1097.2008.00528.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Development of lead hammerhead ribozyme candidates against human rod opsin mRNA for retinal degeneration therapy. Exp Eye Res 2008; 88:859-79. [PMID: 19094986 DOI: 10.1016/j.exer.2008.11.018] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2008] [Revised: 11/08/2008] [Accepted: 11/11/2008] [Indexed: 11/22/2022]
Abstract
To identify lead candidate allele-independent hammerhead ribozymes (hhRz) for the treatment of autosomal dominant mutations in the human rod opsin (RHO) gene, we tested a series of hhRzs for potential to significantly knockdown human RHO gene expression in a human cell expression system. Multiple computational criteria were used to select target mRNA regions likely to be single stranded and accessible to hhRz annealing and cleavage. Target regions are tested for accessibility in a human cell culture expression system where the hhRz RNA and target mRNA and protein are coexpressed. The hhRz RNA is embedded in an adenoviral VAI RNA chimeric RNA of established structure and properties which are critical to the experimental paradigm. The chimeric hhRz-VAI RNA is abundantly transcribed so that the hhRzs are expected to be in great excess over substrate mRNA. HhRz-VAI traffics predominantly to the cytoplasm to colocalize with the RHO mRNA target. Colocalization is essential for second-order annealing reactions. The VAI chimera protects the hhRz RNA from degradation and provides for a long half-life. With cell lines chosen for high transfection efficiency and a molar excess of hhRz plasmid over target plasmid, the conditions of this experimental paradigm are specifically designed to evaluate for regions of accessibility of the target mRNA in cellulo. Western analysis was used to measure the impact of hhRz expression on RHO protein expression. Three lead candidate hhRz designs were identified that significantly knockdown target protein expression relative to control (p<0.05). Successful lead candidates (hhRz CUC [see in text downward arrow] 266, hhRz CUC [see in text downward arrow] 1411, hhRz AUA [see in text downward arrow] 1414) targeted regions of human RHO mRNA that were predicted to be accessible by a bioinformatics approach, whereas regions predicted to be inaccessible supported no knockdown. The maximum opsin protein level knockdown is approximately 30% over a 48h paradigm of testing. These results validate a rigorous computational bioinformatics approach to detect accessible regions of target mRNAs in cellulo. The opsin knockdown effect could prove to be clinically significant when integrated over longer periods in photoreceptors. Further optimization and animal testing are the next step in this stratified RNA drug discovery program. A recently developed novel and efficient screening assay based upon expression of a dicistronic mRNA (RHO-IRES-SEAP) containing both RHO and reporter (SEAP) cDNAs was used to compare the hhRz 266 lead candidate to another agent (Rz525/hhRz485) already known to partially rescue retinal degeneration in a rodent model. Lead hhRz 266 CUC [see in text downward arrow] proved more efficacious than Rz525/hhRz485 which infers viability for rescue of retinal degeneration in appropriate preclinical models of disease.
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Mahaut-Smith MP, Martinez-Pinna J, Gurung IS. A role for membrane potential in regulating GPCRs? Trends Pharmacol Sci 2008; 29:421-9. [PMID: 18621424 DOI: 10.1016/j.tips.2008.05.007] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2007] [Revised: 05/16/2008] [Accepted: 05/28/2008] [Indexed: 10/21/2022]
Abstract
G-protein-coupled receptors (GPCRs) have ubiquitous roles in transducing extracellular signals into cellular responses. Therefore, the concept that members of this superfamily of surface proteins are directly modulated by changes in membrane voltage could have widespread consequences for cell signalling. Although several studies have indicated that GPCRs can be voltage dependent, particularly P2Y(1) receptors in the non-excitable megakaryocyte, the evidence has been mostly indirect. Recent work on muscarinic receptors has stimulated substantial interest in this field by reporting the first voltage-dependent charge movements for a GPCR. An underlying mechanism is proposed whereby a voltage-induced conformational change in the receptor alters its ability to couple to the G protein and thereby influences its affinity for an agonist. We discuss the strength of the evidence behind this hypothesis and include suggestions for future work. We also describe other examples in which direct voltage control of GPCRs can account for effects of membrane potential on downstream signals and highlight the possible physiological consequences of this phenomenon.
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Affiliation(s)
- Martyn P Mahaut-Smith
- Department of Cell Physiology and Pharmacology, University of Leicester, LE1 9HN, UK.
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Gurung IS, Martinez-Pinna J, Mahaut-Smith MP. Novel consequences of voltage-dependence to G-protein-coupled P2Y1 receptors. Br J Pharmacol 2008; 154:882-9. [PMID: 18414379 DOI: 10.1038/bjp.2008.97] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
BACKGROUND AND PURPOSE Emerging evidence suggests that activation of G-protein-coupled receptors (GPCRs) can be directly regulated by membrane voltage. However, the physiological and pharmacological relevance of this effect remains unclear. We have further examined this phenomenon for P2Y1 receptors in the non-excitable megakaryocyte using a range of agonists and antagonists. EXPERIMENTAL APPROACH Simultaneous whole-cell patch clamp and fura-2 fluorescence recordings of rat megakaryocytes, which lack voltage-gated Ca2+ influx, were used to examine the voltage-dependence of P2Y1 receptor-evoked IP3-dependent Ca2+ mobilization. RESULTS Depolarization transiently and repeatedly enhanced P2Y1 receptor-evoked Ca2+ mobilization across a wide concentration range of both weak, partial and full, potent agonists. Moreover, the amplitude of the depolarization-evoked [Ca2+]i increase displayed an inverse relationship with agonist concentration, such that the greatest potentiating effect of voltage was observed at near-threshold levels of agonist. Unexpectedly, depolarization also stimulated an [Ca2+]i increase in the absence of agonist during exposure to the competitive antagonists A3P5PS and MRS2179, or the allosteric enhancer 2,2'-pyridylisatogen tosylate. A further effect of some antagonists, particularly suramin, was to enhance the depolarization-evoked Ca2+ responses during co-application of an agonist. Of several P2Y1 receptor inhibitors, only SCH202676, which has a proposed allosteric mechanism of action, could block ADP-induced voltage-dependent Ca2+ release. CONCLUSIONS AND IMPLICATIONS The ability of depolarization to potentiate GPCRs at near-threshold agonist concentrations represents a novel mechanism for coincidence detection. Furthermore, the induction and enhancement of voltage-dependent GPCR responses by antagonists has implications for the design of therapeutic compounds.
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Affiliation(s)
- I S Gurung
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, UK
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11
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Molecular and Cellular Regulation of Pineal Organ Responses. ACTA ACUST UNITED AC 2006. [DOI: 10.1016/s1546-5098(06)25006-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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12
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Chen Y, Moiseyev G, Wu BX, Ma JX, Crouch RK. Visual cycle retinoid processing proteins are present in HEK293S cells. Vision Res 2004; 43:3037-44. [PMID: 14611939 DOI: 10.1016/j.visres.2003.08.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In HEK293S cells expressing opsin, rhodopsin regenerates on addition of all-trans retinol. This study was to determine if key proteins in the retinal pigment epithelium (RPE) are present in these cells. Cellular retinoid binding protein, cellular retinoic-acid binding protein, RPE65, caveolin-1-alpha- and -beta-isoforms, interphotoreceptor retinoid binding protein, and 11-cis retinol dehydrogenase, but not lecithin:retinol acyltransferase (LRAT), were identified by Western blot analysis. LRAT transcripts were found by RT-PCR and Southern blot analysis. Small interference RNA specific to LRAT reduced ester formation, confirming that the enzyme is present. Therefore, HEK293S cells contain the functional components of the retinoid cycle found in the RPE.
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Affiliation(s)
- Yumei Chen
- Department of Ophthalmology, Medical University of South Carolina, 167 Ashley Avenue, 29425, Charleston, SC, USA
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13
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Martinez-Pinna J, Tolhurst G, Gurung IS, Vandenberg JI, Mahaut-Smith MP. Sensitivity limits for voltage control of P2Y receptor-evoked Ca2+ mobilization in the rat megakaryocyte. J Physiol 2003; 555:61-70. [PMID: 14645457 PMCID: PMC1664815 DOI: 10.1113/jphysiol.2003.056846] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
G-protein-coupled receptor signalling has been suggested to be voltage dependent in a number of cell types; however, the limits of sensitivity of this potentially important phenomenon are unknown. Using the non-excitable rat megakaryocyte as a model system, we now show that P2Y receptor-evoked Ca2+ mobilization is controlled by membrane voltage in a graded and bipolar manner without evidence for a discrete threshold potential. Throughout the range of potentials studied, the peak increase in intracellular Ca2+ concentration ([Ca2+]i) in response to depolarization was always larger than the maximal reduction in [Ca2+]i following an equivalent amplitude hyperpolarization. Significant [Ca2+]i increases were observed in response to small amplitude (< 5 mV, 5 s duration) or short duration (25 ms, 135 mV) depolarizations. Individual cardiac action potential waveforms were also able to repeatedly potentiate P2Y receptor-evoked Ca2+ release and the response to trains of normally paced stimuli fused to generate prolonged [Ca2+]i increases. Furthermore, elevation of the temperature to physiological levels (36 degrees C) resulted in a more sustained depolarization-evoked Ca2+ increase compared with more transient or oscillatory responses at 20-24 degrees C. The ability of signalling via a G-protein-coupled receptor to be potentiated by action potential waveforms and small amplitude depolarizations has broad implications in excitable and non-excitable tissues.
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Affiliation(s)
- Juan Martinez-Pinna
- Department of Physiology, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK
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Brueggemann LI, Sullivan JM. HEK293S cells have functional retinoid processing machinery. J Gen Physiol 2002; 119:593-612. [PMID: 12034766 PMCID: PMC2233870 DOI: 10.1085/jgp.20018495] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2001] [Revised: 04/16/2002] [Accepted: 04/22/2002] [Indexed: 01/01/2023] Open
Abstract
Rhodopsin activation is measured by the early receptor current (ERC), a conformation-associated charge motion, in human embryonic kidney cells (HEK293S) expressing opsins. After rhodopsin bleaching in cells loaded with 11-cis-retinal, ERC signals recover in minutes and recurrently over a period of hours by simple dark adaptation, with no added chromophore. The purpose of this study is to investigate the source of ERC signal recovery in these cells. Giant HEK293S cells expressing normal wild-type (WT)-human rod opsin (HEK293S) were regenerated by solubilized 11-cis-retinal, all-trans-retinal, or Vitamin A in darkness. ERCs were elicited by flash photolysis and measured by whole-cell recording. Visible flashes initially elicit bimodal (R(1), R(2)) ERC signals in WT-HEK293S cells loaded with 11-cis-retinal for 40 min or overnight. In contrast, cells regenerated for 40 min with all-trans-retinal or Vitamin A had negative ERCs (R(1)-like) or none at all. After these were placed in the dark overnight, ERCs with outward R(2) signals were recorded the following day. This indicates conversion of loaded Vitamin A or all-trans-retinal into cis-retinaldehyde that regenerated ground-state pigment. 4-butylaniline, an inhibitor of the mammalian retinoid cycle, reversibly suppressed recovery of the outward R(2) component from Vitamin A and 11-cis-retinal-loaded cells. These physiological findings are evidence for the presence of intrinsic retinoid processing machinery in WT-HEK293S cells similar to what occurs in the mammalian eye.
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Affiliation(s)
- Lioubov I Brueggemann
- Department of Ophthalmology, Institute for Human Performance, State University of New York, Upstate Medical University, 750 East Adams Street, Syracuse, NY 13210, USA
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Abstract
The crystal structure of rod cell visual pigment rhodopsin was recently solved at 2.8-A resolution. A critical evaluation of a decade of structure-function studies is now possible. It is also possible to begin to explain the structural basis for several unique physiological properties of the vertebrate visual system, including extremely low dark noise levels as well as high gain and color detection. The ligand-binding pocket of rhodopsin is remarkably compact, and several apparent chromophore-protein interactions were not predicted from extensive mutagenesis or spectroscopic studies. The transmembrane helices are interrupted or kinked at multiple sites. An extensive network of interhelical interactions stabilizes the ground state of the receptor. The helix movement model of receptor activation, which might apply to all G protein-coupled receptors (GPCRs) of the rhodopsin family, is supported by several structural elements that suggest how light-induced conformational changes in the ligand-binding pocket are transmitted to the cytoplasmic surface. The cytoplasmic domain of the receptor is remarkable for a carboxy-terminal helical domain extending from the seventh transmembrane segment parallel to the bilayer surface. Thus the cytoplasmic surface appears to be approximately the right size to bind to the transducin heterotrimer in a one-to-one complex. Future high-resolution structural studies of rhodopsin and other GPCRs will form a basis to elucidate the detailed molecular mechanism of GPCR-mediated signal transduction.
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Affiliation(s)
- S T Menon
- Howard Hughes Medical Institute, Laboratory of Molecular Biology and Biochemistry, The Rockefeller University, New York, New York 10021, USA
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16
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Hessel E, Müller P, Herrmann A, Hofmann KP. Light-induced reorganization of phospholipids in rod disc membranes. J Biol Chem 2001; 276:2538-43. [PMID: 11062249 DOI: 10.1074/jbc.m009061200] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The transbilayer redistribution of spin-labeled phospholipid analogues (SL-PL) with choline, serine, and ethanolamine head groups (PC, PS, and PE, respectively) was studied on intact disc vesicles of bovine rod outer segment membranes in the dark and after illumination. Redistribution was measured by the extraction of spin-labeled lipid analogues from the outer leaflet of membrane using the bovine serum albumin back-exchange assay. In the dark, PS was distributed asymmetrically, favoring the outer leaflet, whereas PC and PE showed small if any asymmetry. Green illumination for 1 min caused lipid head group-specific reorganization of SL-PL. Extraction of SL-PS by bovine serum albumin showed a fast transient (<10 min) enhancement, which was further augmented by a peptide stabilizing the active metarhodopsin II conformation. The data suggest a direct release of 1 molecule of bound PS per rhodopsin into the outer leaflet and subsequent redistribution between the two leaflets. SL-PE and SL-PC showed more complex kinetics, in both cases consistent with a prolonged period of reduced extraction (2 phospholipids per rhodopsin in each case). The different phases of SL-PL reorganization after illumination may be related to the formation and decay of the active rhodopsin species and to their subsequent regeneration process.
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Affiliation(s)
- E Hessel
- Institut für Medizinische Physik und Biophysik, Universitätsklinikum Charité, Humboldt Universität zu Berlin, Ziegelstrabetae 5-9, Berlin D-10098, Germany.
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Sullivan JM, Brueggemann L, Shukla P. Electrical approach to study rhodopsin activation in single cells with early receptor current assay. Methods Enzymol 2000; 315:268-93. [PMID: 10736708 DOI: 10.1016/s0076-6879(00)15849-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Abstract
The ERC is a conformation-dependent charge motion similar to the gating currents of ionic channels. Both the waveforms and bandwidth of ERCs and ionic channel gating currents are similar, providing support to the initial suggestion that the ERP was a kind of gating current. In ionic channels the electrostatic field promotes motion of alpha-helical elements that stimulate large-scale molecular events that promote opening of the ionic pore. In ionic channels gating currents of expressed channel mutants has contributed significantly to understanding the mechanism of activation. Given the known role of electrical processes to rhodopsin activation, the ERC approach applied to mutant and wild-type visual pigments is likely to lead to a fuller understanding of the mechanism of conformational activation. This method is currently well suited to investigate the later phases of rhodopsin activation that are thought to be electrostatic in nature. We anticipate that ERC studies will make significant contributions to understanding how the breakdown of the electrostatic interaction between the PSB and its counterion is initiated and propagated to induce the proton uptake on the cytoplasmic surface of the pigment and the shaping of the transducin docking domain. We encourage collaboration to apply the ERC methodology to interesting mutant pigments and retinal analogs. We expect that the ERC methodology can soon be applied to understand rapid charge displacements associated with photochemistry (i.e., R1), the effects of transduction proteins on R2, and the measurement of electrical processes during cone visual pigment activation.
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Affiliation(s)
- J M Sullivan
- Department of Ophthalmology, State University of New York Health Science Center, Syracuse 13210, USA
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Sullivan JM, Satchwell MF. Development of stable cell lines expressing high levels of point mutants of human opsin for biochemical and biophysical studies. Methods Enzymol 2000; 315:30-58. [PMID: 10736692 DOI: 10.1016/s0076-6879(00)15833-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Abstract
Stable HEK293S cell lines expressing high levels of normal and mutant human rod opsins were generated. Cellular expression is uniform across a population. Secondary overexpression of the same opsin transgene linked to a different drug selection marker (hygro(R)) yielded expression clones with increased opsin levels compared to the neo(R) parent strain. Wild-type and mutant human opsins regenerate with native chromophore and demonstrate spectroscopic properties consistent with previous reports of bovine opsin mutants. HEK293S cells can be grown in larger scale suspension culture (10(9) cells/liter) or in roller bottles (10(8) cells/bottle) to facilitate milligram-order preparations of purified pigments. These cell lines should be useful in any time-resolved spectroscopic or biophysical experiments that require either uniform cellular levels of opsin protein or regenerable pigment, or large amounts of purified visual pigment. They should also be useful in experiments where uniform constitutive levels of a given mutant human visual pigment are needed in each cell. These and similar types of constitutive or inducible cell lines may also be useful for studying mechanisms of human cell death that occur by mutations in the human rod opsin gene.
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Affiliation(s)
- J M Sullivan
- Department of Ophthalmology, State University of New York Health Science Center, Syracuse 13210, USA
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Chapter 3 Late photoproducts and signaling states of bovine rhodopsin. ACTA ACUST UNITED AC 2000. [DOI: 10.1016/s1383-8121(00)80006-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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20
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Shukla P, Sullivan JM. Normal and mutant rhodopsin activation measured with the early receptor current in a unicellular expression system. J Gen Physiol 1999; 114:609-36. [PMID: 10532961 PMCID: PMC2230543 DOI: 10.1085/jgp.114.5.609] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The early receptor current (ERC) represents molecular charge movement during rhodopsin conformational dynamics. To determine whether this time-resolved assay can probe various aspects of structure-function relationships in rhodopsin, we first measured properties of expressed normal human rhodopsin with ERC recordings. These studies were conducted in single fused giant cells containing on the order of a picogram of regenerated pigment. The action spectrum of the ERC of normal human opsin regenerated with 11-cis-retinal was fit by the human rhodopsin absorbance spectrum. Successive flashes extinguished ERC signals consistent with bleaching of a rhodopsin photopigment with a normal range of photosensitivity. ERC signals followed the univariance principle since millisecond-order relaxation kinetics were independent of the wavelength of the flash stimulus. After signal extinction, dark adaptation without added 11-cis-retinal resulted in spontaneous pigment regeneration from an intracellular store of chromophore remaining from earlier loading. After the ERC was extinguished, 350-nm flashes overlapping metarhodopsin-II absorption promoted immediate recovery of ERC charge motions identified by subsequent 500-nm flashes. Small inverted R(2) signals were seen in response to some 350-nm flashes. These results indicate that the ERC can be photoregenerated from the metarhodopsin-II state. Regeneration with 9-cis-retinal permits recording of ERC signals consistent with flash activation of isorhodopsin. We initiated structure-function studies by measuring ERC signals in cells expressing the D83N and E134Q mutant human rhodopsin pigments. D83N ERCs were simplified in comparison with normal rhodopsin, while E134Q ERCs had only the early phase of charge motion. This study demonstrates that properties of normal rhodopsin can be accurately measured with the ERC assay and that a structure-function investigation of rapid activation processes in analogue and mutant visual pigments is feasible in a live unicellular environment.
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Affiliation(s)
- Pragati Shukla
- From the Department of Ophthalmology, State University of New York, Health Science Center at Syracuse, Syracuse, New York 13210
| | - Jack M. Sullivan
- From the Department of Ophthalmology, State University of New York, Health Science Center at Syracuse, Syracuse, New York 13210
- From the Department of Biochemistry, State University of New York, Health Science Center at Syracuse, Syracuse, New York 13210
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Affiliation(s)
- T P Sakmar
- Department of Molecular Biology and Biochemistry, Howard Hughes Medical Institute, Rockefeller University, New York, New York 10021 USA
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