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Abstract
Rhodopsin is the photoreceptor in human rod cells responsible for dim-light vision. The visual receptors are part of the large superfamily of G protein-coupled receptors (GPCRs) that mediate signal transduction in response to diverse diffusible ligands. The high level of sequence conservation within the transmembrane helices of the visual receptors and the family A GPCRs has long been considered evidence for a common pathway for signal transduction. I review recent studies that reveal a comprehensive mechanism for how light absorption by the retinylidene chromophore drives rhodopsin activation and highlight those features of the mechanism that are conserved across the ligand-activated GPCRs.
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Affiliation(s)
- Steven O Smith
- Department of Biochemistry and Cell Biology, Center for Structural Biology, Stony Brook University, Stony Brook, New York, USA;
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Chandler B, Todd L, Smith SO. Magic angle spinning NMR of G protein-coupled receptors. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2022; 128:25-43. [PMID: 35282868 PMCID: PMC10718405 DOI: 10.1016/j.pnmrs.2021.10.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2021] [Revised: 10/26/2021] [Accepted: 10/27/2021] [Indexed: 06/14/2023]
Abstract
G protein-coupled receptors (GPCRs) have a simple seven transmembrane helix architecture which has evolved to recognize a diverse number of chemical signals. The more than 800 GPCRs encoded in the human genome function as receptors for vision, smell and taste, and mediate key physiological processes. Consequently, these receptors are a major target for pharmaceuticals. Protein crystallography and electron cryo-microscopy have provided high resolution structures of many GPCRs in both active and inactive conformations. However, these structures have not sparked a surge in rational drug design, in part because GPCRs are inherently dynamic and the structural changes induced by ligand or drug binding to stabilize inactive or active conformations are often subtle rearrangements in packing or hydrogen-bonding interactions. NMR spectroscopy provides a sensitive probe of local structure and dynamics at specific sites within these receptors as well as global changes in receptor structure and dynamics. These methods can also capture intermediate states and conformations with low populations that provide insights into the activation pathways. We review the use of solid-state magic angle spinning NMR to address the structure and activation mechanisms of GPCRs. The focus is on the large and diverse class A family of receptors. We highlight three specific class A GPCRs in order to illustrate how solid-state, as well as solution-state, NMR spectroscopy can answer questions in the field involving how different GPCR classes and subfamilies are activated by their associated ligands, and how small molecule drugs can modulate GPCR activation.
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Affiliation(s)
- Bianca Chandler
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794, United States.
| | - Lauren Todd
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794, United States.
| | - Steven O Smith
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794, United States.
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Retinal orientation and interactions in rhodopsin reveal a two-stage trigger mechanism for activation. Nat Commun 2016; 7:12683. [PMID: 27585742 PMCID: PMC5025775 DOI: 10.1038/ncomms12683] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2016] [Accepted: 07/22/2016] [Indexed: 01/28/2023] Open
Abstract
The 11-cis retinal chromophore is tightly packed within the interior of the visual receptor rhodopsin and isomerizes to the all-trans configuration following absorption of light. The mechanism by which this isomerization event drives the outward rotation of transmembrane helix H6, a hallmark of activated G protein-coupled receptors, is not well established. To address this question, we use solid-state NMR and FTIR spectroscopy to define the orientation and interactions of the retinal chromophore in the active metarhodopsin II intermediate. Here we show that isomerization of the 11-cis retinal chromophore generates strong steric interactions between its β-ionone ring and transmembrane helices H5 and H6, while deprotonation of its protonated Schiff's base triggers the rearrangement of the hydrogen-bonding network involving residues on H6 and within the second extracellular loop. We integrate these observations with previous structural and functional studies to propose a two-stage mechanism for rhodopsin activation.
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Kimata N, Reeves PJ, Smith SO. Uncovering the triggers for GPCR activation using solid-state NMR spectroscopy. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2015; 253:111-118. [PMID: 25797010 PMCID: PMC4391883 DOI: 10.1016/j.jmr.2014.12.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2014] [Revised: 12/16/2014] [Accepted: 12/23/2014] [Indexed: 06/04/2023]
Abstract
G protein-coupled receptors (GPCRs) span cell membranes with seven transmembrane helices and respond to a diverse array of extracellular signals. Crystal structures of GPCRs have provided key insights into the architecture of these receptors and the role of conserved residues. However, the question of how ligand binding induces the conformational changes that are essential for activation remains largely unanswered. Since the extracellular sequences and structures of GPCRs are not conserved between receptor subfamilies, it is likely that the initial molecular triggers for activation vary depending on the specific type of ligand and receptor. In this article, we describe NMR studies on the rhodopsin subfamily of GPCRs and propose a mechanism for how retinal isomerization switches the receptor to the active conformation. These results suggest a general approach for determining the triggers for activation in other GPCR subfamilies using NMR spectroscopy.
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Affiliation(s)
- Naoki Kimata
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794-5215, United States
| | - Philip J Reeves
- School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, United Kingdom
| | - Steven O Smith
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794-5215, United States.
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Nakanishi K, Crouch R. Application of Artificial Pigments to Structure Determination and Study of Photoinduced Transformations of Retinal Proteins. Isr J Chem 2013. [DOI: 10.1002/ijch.199500030] [Citation(s) in RCA: 102] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Pope A, Eilers M, Reeves PJ, Smith SO. Amino acid conservation and interactions in rhodopsin: probing receptor activation by NMR spectroscopy. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2013; 1837:683-93. [PMID: 24183693 DOI: 10.1016/j.bbabio.2013.10.007] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Revised: 10/15/2013] [Accepted: 10/18/2013] [Indexed: 11/30/2022]
Abstract
Rhodopsin is a classical two-state G protein-coupled receptor (GPCR). In the dark, its 11-cis retinal chromophore serves as an inverse agonist to lock the receptor in an inactive state. Retinal-protein and protein-protein interactions have evolved to reduce the basal activity of the receptor in order to achieve low dark noise in the visual system. In contrast, absorption of light triggers rapid isomerization of the retinal, which drives the conversion of the receptor to a fully active conformation. Several specific protein-protein interactions have evolved that maintain the lifetime of the active state in order to increase the sensitivity of this receptor for dim-light vision in vertebrates. In this article, we review the molecular interactions that stabilize rhodopsin in the dark-state and describe the use of solid-state NMR spectroscopy for probing the structural changes that occur upon light-activation. Amino acid conservation provides a guide for those interactions that are common in the class A GPCRs as well as those that are unique to the visual system. This article is part of a Special Issue entitled: Retinal Proteins - You can teach an old dog new tricks.
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Affiliation(s)
- Andreyah Pope
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794-5215, USA
| | - Markus Eilers
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794-5215, USA
| | - Philip J Reeves
- School of Biological Sciences, University of Essex, Wivenhoe Park, Essex CO4 3SQ, UK
| | - Steven O Smith
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794-5215, USA.
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7
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Abstract
Recent advances in the structural biology of GPCRs (G-protein-coupled receptors) have provided insights into their structure and function. Comparisons of the visual and ligand-activated receptors highlight the unique elements of rhodopsin that allow it to function as a highly sensitive dim-light photoreceptor in vertebrates, as well as the common elements that it shares with the large class A GPCR family. However, despite progress, a number of questions remain unanswered about how these receptors are activated.
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Goncalves JA, Ahuja S, Erfani S, Eilers M, Smith SO. Structure and function of G protein-coupled receptors using NMR spectroscopy. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2010; 57:159-80. [PMID: 20633362 PMCID: PMC2907352 DOI: 10.1016/j.pnmrs.2010.04.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2010] [Accepted: 04/08/2010] [Indexed: 05/15/2023]
Affiliation(s)
- Joseph A Goncalves
- Department of Biochemistry and Cell Biology, Center for Structural Biology, Stony Brook University, Stony Brook, NY 11794-5215, USA
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9
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Abstract
Rhodopsin is a specialized G protein-coupled receptor (GPCR) found in vertebrate rod cells. Absorption of light by its 11-cis retinal chromophore leads to rapid photochemical isomerization and receptor activation. Recent results from protein crystallography and NMR spectroscopy show how structural changes on the extracellular side of rhodopsin induced by retinal isomerization are coupled to the motion of membrane-spanning helices to create a G protein binding pocket on the intracellular side of the receptor. The signaling pathway provides a comprehensive explanation for the conservation of specific amino acids and structural motifs across the class A family of GPCRs, as well as for the conservation of selected residues within the visual receptor subfamily. The emerging model of activation indicates that, rather than being unique, the visual receptors provide a basis for understanding the common structural and dynamic elements in the class A GPCRs.
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Affiliation(s)
- Steven O Smith
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, New York 11794-5215, USA.
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Is the lifetime of light-stimulated cGMP phosphodiesterase regulated by recoverin through its regulation of rhodopsin phosphorylation? Behav Brain Sci 2010. [DOI: 10.1017/s0140525x00039522] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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13
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Kefalov VJ, Cornwall MC, Fain GL. Physiological studies of the interaction between opsin and chromophore in rod and cone visual pigments. Methods Mol Biol 2010; 652:95-114. [PMID: 20552424 DOI: 10.1007/978-1-60327-325-1_5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The visual pigment in vertebrate photoreceptors is a G protein-coupled receptor that consists of a protein, opsin, covalently attached to a chromophore, 11-cis-retinal. Activation of the visual pigment by light triggers a transduction cascade that produces experimentally measurable electrical responses in photoreceptors. The interactions between opsin and chromophore can be investigated with electrophysiologial recordings in intact amphibian and mouse rod and cone photoreceptor cells. Here we describe methods for substituting the native chromophore with various chromophore analogs to investigate how specific parts of the chromophore affect the signaling properties of the visual pigment and the function of photoreceptors. We also describe methods for genetically substituting the native rod opsin gene with cone opsins or with mutant rod opsins to investigate and compare their signaling properties. These methods are useful not only for understanding the relation between the properties of visual pigments and the function of photoreceptors but also for understanding the mechanisms by which mutations in rod opsin produce night blindness and other visual disorders.
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Affiliation(s)
- Vladimir J Kefalov
- Department of Ophthalmology and Visual Sciences and Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO, USA
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Light activation of rhodopsin: insights from molecular dynamics simulations guided by solid-state NMR distance restraints. J Mol Biol 2009; 396:510-27. [PMID: 20004206 DOI: 10.1016/j.jmb.2009.12.003] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2009] [Revised: 10/09/2009] [Accepted: 12/02/2009] [Indexed: 11/20/2022]
Abstract
Structural restraints provided by solid-state NMR measurements of the metarhodopsin II intermediate are combined with molecular dynamics simulations to help visualize structural changes in the light activation of rhodopsin. Since the timescale for the formation of the metarhodopsin II intermediate (>1 ms) is beyond that readily accessible by molecular dynamics, we use NMR distance restraints derived from 13C dipolar recoupling measurements to guide the simulations. The simulations yield a working model for how photoisomerization of the 11-cis retinylidene chromophore bound within the interior of rhodopsin is coupled to transmembrane helix motion and receptor activation. The mechanism of activation that emerges is that multiple switches on the extracellular (or intradiscal) side of rhodopsin trigger structural changes that converge to disrupt the ionic lock between helices H3 and H6 on the intracellular side of the receptor.
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Estevez ME, Ala-Laurila P, Crouch RK, Cornwall MC. Turning cones off: the role of the 9-methyl group of retinal in red cones. ACTA ACUST UNITED AC 2006; 128:671-85. [PMID: 17101818 PMCID: PMC2151603 DOI: 10.1085/jgp.200609630] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Our ability to see in bright light depends critically on the rapid rate at which cone photoreceptors detect and adapt to changes in illumination. This is achieved, in part, by their rapid response termination. In this study, we investigate the hypothesis that this rapid termination of the response in red cones is dependent on interactions between the 9-methyl group of retinal and red cone opsin, which are required for timely metarhodopsin (Meta) II decay. We used single-cell electrical recordings of flash responses to assess the kinetics of response termination and to calculate guanylyl cyclase (GC) rates in salamander red cones containing native visual pigment as well as visual pigment regenerated with 11-cis 9-demethyl retinal, an analogue of retinal in which the 9-methyl group is missing. After exposure to bright light that photoactivated more than ∼0.2% of the pigment, red cones containing the analogue pigment had a slower recovery of both flash response amplitudes and GC rates (up to 10 times slower at high bleaches) than red cones containing 11-cis retinal. This finding is consistent with previously published biochemical data demonstrating that red cone opsin regenerated in vitro with 11-cis 9-demethyl retinal exhibited prolonged activation as a result of slowed Meta II decay. Our results suggest that two different mechanisms regulate the recovery of responsiveness in red cones after exposure to light. We propose a model in which the response recovery in red cones can be regulated (particularly at high light intensities) by the Meta II decay rate if that rate has been inhibited. In red cones, the interaction of the 9-methyl group of retinal with opsin promotes efficient Meta II decay and, thus, the rapid rate of recovery.
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Affiliation(s)
- Maureen E Estevez
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118, USA.
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Verhoeven MA, Bovee-Geurts PHM, de Groot HJM, Lugtenburg J, DeGrip WJ. Methyl Substituents at the 11 or 12 Position of Retinal Profoundly and Differentially Affect Photochemistry and Signalling Activity of Rhodopsin. J Mol Biol 2006; 363:98-113. [PMID: 16962138 DOI: 10.1016/j.jmb.2006.07.039] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2006] [Revised: 07/12/2006] [Accepted: 07/19/2006] [Indexed: 11/18/2022]
Abstract
The C-11=C-12 double bond of the retinylidene chromophore of rhodopsin holds a central position in its light-induced photoisomerization and hence the photosensory function of this visual pigment. To probe the local environment of the HC-11=C-12H element we have prepared the 11-methyl and 12-methyl derivatives of 11-Z retinal and incorporated these into opsin to generate the rhodopsin analogs 11-methyl and 12-methyl rhodopsin. These analog pigments form with much slower kinetics and lower efficiency than the native pigment. The initial photochemistry and the signaling activity of the analog pigments were investigated by UV-vis and FTIR spectroscopy, and by a G protein activation assay. Our data indicate that the ultrafast formation of the first photointermediate is strongly perturbed by the presence of an 11-methyl substituent, but much less by a 12-methyl substituent. These results support the current concept of the mechanism of the primary photoisomerization event in rhodopsin. An important stronghold of this concept is an out-of-plane movement of the C-12H element, which is facilitated by torsion as well as extended positive charge delocalization into the C-10-C-13 segment of the chromophore. We argue that this mechanism is maintained principally with a methyl substituent at C-12. In addition, we show that both an 11-methyl and a 12-methyl substitutent perturb the photointermediate cascade and finally yield a low-activity state of the receptor. The 11-methyl pigment retains about 30% of the G protein activation rate of native rhodopsin, while the 12-methyl chromophore behaves like an inverse agonist up to at least 20 degrees C, trapping the protein in a perturbed Meta-I-like conformation. We conclude that the isomerization region of the chromophore and the spatial structure of the binding site are finely tuned, in order to achieve a high photosensory potential with an efficient pathway to a high-activity state.
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Govorunova EG, Sineshchekov OA, Gärtner W, Chunaev AS, Hegemann P. Photoreceptor current and photoorientation in chlamydomonas mediated by 9-demethylchlamyrhodopsin. Biophys J 2001; 81:2897-907. [PMID: 11606300 PMCID: PMC1301754 DOI: 10.1016/s0006-3495(01)75930-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
Green flagellates possess rhodopsin-like photoreceptors involved in control of their behavior via generation of photocurrents across the plasma membrane. Chlamydomonas mutants blocked in retinal biosynthesis are "blind," but they can be rescued by the addition of exogenous retinoids. Photosignaling by chlamyrhodopsin regenerated with 9-demethylretinal was investigated by recording photocurrents from single cells and cell suspensions, and by measuring phototactic orientation. The addition of a saturating concentration of this analog led to reconstitution of all receptor molecules. However, sensitivity of the photoreceptor current in cells reconstituted with the analog was smaller compared with retinal-reconstituted cells, indicating a decreased signaling efficiency of the analog receptor protein. Suppression of the photoreceptor current in double-flash experiments was smaller and its recovery faster with 9-demethylretinal than with retinal, as it would be expected from a decreased PC amplitude in the analog-reconstituted cells. Cells reconstituted with either retinal or the analog displayed negative phototaxis at low light and switched to positive one upon an increase in stimulus intensity, as opposed to the wild type. The reversal of the phototaxis direction in analog-reconstituted cells was shifted to a higher fluence rate compared with cells reconstituted with retinal, which corresponded to the decreased signaling efficiency of 9-demethylchlamyrhodopsin.
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Affiliation(s)
- E G Govorunova
- Biology Faculty, Moscow State University, 119899 Moscow, Russia.
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Matthews HR, Cornwall M, Crouch R. Prolongation of actions of Ca2+ early in phototransduction by 9-demethylretinal. J Gen Physiol 2001; 118:377-90. [PMID: 11585850 PMCID: PMC2233701 DOI: 10.1085/jgp.118.4.377] [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
During adaptation Ca2+ acts on a step early in phototransduction, which is normally available for only a brief period after excitation. To investigate the identity of this step, we studied the effect of the light-induced decline in intracellular Ca2+ concentration on the response to a bright flash in normal rods, and in rods bleached and regenerated with 11-cis 9-demethylretinal, which forms a photopigment with a prolonged photoactivated lifetime. Changes in cytoplasmic Ca2+ were opposed by rapid superfusion of the outer segment with a 0Na+/0Ca2+ solution designed to minimize Ca2+ fluxes across the surface membrane. After regeneration of a bleached rod with 9-demethlyretinal, the response in Ringer's to a 440-nm bright flash was prolonged in comparison with the unbleached control, and the response remained in saturation for 10-15s. If the dynamic fall in Ca2+i induced by the flash was delayed by stepping the outer segment to 0Na+/0Ca2+ solution just before the flash and returning it to Ringer's shortly before recovery, then the response saturation was prolonged further, increasing linearly by 0.41 +/- 0.01 of the time spent in this solution. In contrast, even long exposures to 0Na+/0Ca2+ solution of rods containing native photopigment evoked only a modest response prolongation on the return to Ringer's. Furthermore, if the rod was preexposed to steady subsaturating light, thereby reducing the cytoplasmic calcium concentration, then the prolongation of the bright flash response evoked by 0Na+/0Ca2+ solution was reduced in a graded manner with increasing background intensity. These results indicate that altering the chromophore of rhodopsin prolongs the time course of the Ca2+-dependent step early in the transduction cascade so that it dominates response recovery, and suggest that it is associated with photopigment quenching by phosphorylation.
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Affiliation(s)
- Hugh R. Matthews
- Physiological Laboratory, University of Cambridge, Downing Street, Cambridge CB2 3EG, United Kingdom
| | - M.C. Cornwall
- Department of Physiology, Boston University Medical School, Boston, MA 02215
| | - R.K. Crouch
- Department of Ophthalmology, Medical University of South Carolina, Charleston, SC 29401
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23
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Abstract
The basis of the duplex theory of vision is examined in view of the dazzling array of data on visual pigment sequences and the pigments they form, on the microspectrophotometry measurements of single photoreceptor cells, on the kinds of photoreceptor cascade enzymes, and on the electrophysiological properties of photoreceptors. The implications of the existence of five distinct visual pigment families are explored, especially with regard to what pigments are in what types of photoreceptors, if there are different phototransduction enzymes associated with different types of photoreceptors, and if there are electrophysiological differences between different types of cones.
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Affiliation(s)
- T Ebrey
- University of Washington, Seattle 98195, USA
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Corson D, Kefalov VJ, Cornwall MC, Crouch RK. Effect of 11-cis 13-demethylretinal on phototransduction in bleach-adapted rod and cone photoreceptors. J Gen Physiol 2000; 116:283-97. [PMID: 10919871 PMCID: PMC2229494 DOI: 10.1085/jgp.116.2.283] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We used 11-cis 13-demethylretinal to examine the physiological consequences of retinal's noncovalent interaction with opsin in intact rod and cone photoreceptors during visual pigment regeneration. 11-Cis 13-demethylretinal is an analog of 11-cis retinal in which the 13 position methyl group has been removed. Biochemical experiments have shown that it is capable of binding in the chromophore pocket of opsin, forming a Schiff-base linkage with the protein to produce a pigment, but at a much slower rate than the native 11-cis retinal (Nelson, R., J. Kim deReil, and A. Kropf. 1970. Proc. Nat. Acad. Sci. USA. 66:531-538). Experimentally, this slow rate of pigment formation should allow separate physiological examination of the effects of the initial binding of retinal in the pocket and the subsequent formation of the protonated Schiff-base linkage. Currents from solitary rods and cones from the tiger salamander were recorded in darkness before and after bleaching and then after exposure to 11-cis 13-demethylretinal. In bleach-adapted rods, 11-cis 13-demethylretinal caused transient activation of phototransduction, as evidenced by a decrease of the dark current and sensitivity, acceleration of the dim flash responses, and activation of cGMP phosphodiesterase and guanylyl cyclase. The steady state of phototransduction activity was still higher than that of the bleach-adapted rod. In contrast, exposure of bleach-adapted cones to 11-cis 13-demethylretinal resulted in an immediate deactivation of transduction as measured by the same parameters. These results extend the validity of a model for the effects of the noncovalent binding of a retinoid in the chromophore pockets of rod and cone opsins to analogs capable of forming a Schiff-base and imply that the noncovalent binding by itself may play a role for the dark adaptation of photoreceptors.
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Affiliation(s)
- D.Wesley Corson
- Department of Pathology & Laboratory Medicine, Medical University of South Carolina, Charleston, South Carolina 29425
- Department of Ophthalmology, Medical University of South Carolina, Charleston, South Carolina 29425
| | - Vladimir J. Kefalov
- Department of Physiology, Boston University School of Medicine, Boston, Massachusetts 02118
| | - M. Carter Cornwall
- Department of Physiology, Boston University School of Medicine, Boston, Massachusetts 02118
| | - Rosalie K. Crouch
- Department of Pathology & Laboratory Medicine, Medical University of South Carolina, Charleston, South Carolina 29425
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Li Z, Zhuang J, Corson DW. Delivery of 9-Cis Retinal to Photoreceptors from Bovine Serum Albumin. Photochem Photobiol 1999. [DOI: 10.1111/j.1751-1097.1999.tb03319.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Tan Q, Nakanishi K, Crouch RK. Mechanism of Transient Dark Activity of 13-Desmethylretinal/Rod Opsin Complex. J Am Chem Soc 1998. [DOI: 10.1021/ja9827752] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Qiang Tan
- Department of Chemistry Columbia University New York, New York 10027
| | - Koji Nakanishi
- Department of Chemistry Columbia University New York, New York 10027
| | - Rosalie K. Crouch
- Department of Ophthalmology Medical University of South Carolina Charleston, South Carolina 29425
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Affiliation(s)
- R K Crouch
- Department of Ophthalmology, Medical University of South Carolina, Charleston 29425, USA.
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28
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Abstract
Rhodopsin is constrained in an inactive conformation by interactions with 11-cis-retinal including formation of a protonated Schiff base with Lys296. Upon photoisomerization, major structural rearrangements that involve protonation of the active site Glu113 and cytoplasmic acidic residues, including Glu134, lead to the formation of the active form of the receptor, metarhodopsin II b, which decays to opsin. However, an activated receptor may be generated without illumination by addition of all-trans-retinal or its analogues to opsin, as measured in this study by the increased phosphorylation of opsin by rhodopsin kinase. The potency of stimulation depended on the chemical and isomeric nature of the analogues and the length of the polyene chain with all-trans-C17 aldehyde and all-trans-retinal being the most active and trans-C12 aldehyde being the least active. Certain cis-isomers, 11-cis-13-demethyl-retinal and 9-cis-C17 aldehyde, were also active. Most of the retinal analogues tested did not regenerate a spectrally identifiable pigment, and many were incapable of Schiff base formation (ketone, stable oximes, and Schiff base-derivatives of retinal). Thus, receptor activation resulted from formation of non-covalent complexes with opsin. pH titrations suggested that an equilibrium exists between partially active (protonated) and inactive (deprotonated) forms of opsin. These findings are consistent with a model in which protonation of one or more cytoplasmic carboxyl groups of opsin is essential for activity. Upon addition of retinoids, the partially active conformation of opsin is converted to a more active intermediate similar to metarhodopsin II b. The model provides an understanding of the structural requirements for opsin activation and an interpretation of the observed activities of natural and experimental opsin mutants.
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Affiliation(s)
- J Buczyłko
- Department of Ophthalmology, School of Medicine, University of Washington, Seattle, Washington 98195, USA
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29
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Corson DW, Crouch RK. Physiological activity of retinoids in natural and artificial visual pigments. Photochem Photobiol 1996; 63:595-600. [PMID: 8628750 DOI: 10.1111/j.1751-1097.1996.tb05661.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- D W Corson
- Department of Pathology, Medical University of South Carolina, Charleston 29425, USA.
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30
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Abstract
AbstractRecoverin is a Ca2+-binding protein found primarily in vertebrate photoreceptors. The proposed physiological function of recoverin is based on the finding that recoverin inhibits light-stimulated phosphorylation of rhodopsin. Recoverin interacts with rod outer segment membranes in a Ca2+-dependent manner. This interaction requires N-terminal acylation of recoverin. Four types of fatty acids have been detected on the N-terminus of recoverin, but the functional significance of this heterogeneous acylation is not yet clear.
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31
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Future directions for rhodopsin structure and function studies. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039534] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
AbstractNMR (nuclear magnetic resonance) may be useful for determining the structure of retinal and its environment in rhodopsin, but not for determining the complete protein structure. Aggregation and low yield of fragments of rhodopsin may make them difficult to study by NMR. A long-term multidisciplinary attack on rhodopsin structure is required.
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32
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More answers about cGMP-gated channels pose more questions. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039509] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractOur understanding of the molecular properties and cellular role of cGMP-gated channels in outer segments of vertebrate photo-receptors has come from over a decade of studies which have continuously altered and refined ideas about these channels. Further examination of this current view may lead to future surprises and further refine the understanding of cGMP-gated channels.
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33
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Cyclic nucleotides as regulators of light-adaptation in photoreceptors. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039510] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractCyclic nucleotides can regulate the sensitivity of retinal rods to light through phosducin. The phosphorylation state of phosducin determines the amount of G available for activation by Rho*. Phosducin phosphorylation is regulated by cyclic nucleotides through their activation of cAMP-dependent protein kinase. The regulation of phosphodiesterase activity by the noncatalytic cGMP binding sites as well as Ca2+/calmodulin dependent regulation of cGMP binding to the cation channel are also discussed.
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34
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Long term potentiation and CaM-sensitive adenylyl cyclase: Long-term prospects. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039327] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractThe type I CaM-sensitive adenylyl cyclase is in a position to integrate signals from multiple inputs, consistent with the requirements for mediating long term potentiation (LTP). Biochemical and genetic evidence supports the idea that this enzyme plays an important role inc LTP. However, more work is needed before we will be certain of the role that CaM-sensitive adenylyl cyclases play in LTP.
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35
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Modulation of the cGMP-gated channel by calcium. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractCalcium acting through calmodulin has been shown to regulate the affinity of cyclic nucleotide-gated channels expressed in cell lines. But is calmodulin the Ca-sensor that normally regulates these channels?
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36
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How many light adaptation mechanisms are there? Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039546] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractThe generally positive response to our target article indicates that most of the commentators accept our contention that light adaptation consists of multiple and possibly redundant mechanisms. The commentaries fall into three general categories. The first deals with putative mechanisms that we chose not to emphasize. The second is a more extended discussion of the role of calcium in adaptation. Finally, additional aspects of cGMP involvement in adaptation are considered. We discuss each of these points in turn.
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37
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Gene therapy, regulatory mechanisms, and protein function in vision. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039388] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractHereditary retinal degeneration due to mutations in visual genes may be amenable to therapeutic interventions that modulate, either positively or negatively, the amount of protein product. Some of the proteins involved in phototransduction are rapidly moved by a lightdependent mechanism between the inner segment and the outer segment in rod photoreceptor cells, and this phenomenon is important in phototransduction.
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38
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A novel protein family of neuronal modulators. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039479] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractA number of proteins homologous to recoverin have been identified in the brains of the several vertebrate species. The brainderived members originally contain four EF-hand domains, but NH2- terminal domain is aberrant. Many of these proteins inhibited light-induced rhodopsin phosphorylation at high [Ca2+], suggesting that the brain-derived members may act as a Ca2+-sensitive modulator of receptor phosphorylation, as recoverin does.
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39
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The structure of rhodopsin and mechanisms of visual adaptation. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039273] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
AbstractRapidly advancing studies on rhodopsin have focused on new strategies for crystallization of this integral membrane protein for x-ray analysis and on alternative methods for structural determination from nuclear magnetic resonance data. Functional studies of the interactions between the apoprotein and its chromophore have clarified the role of the chromophore in deactivation of opsin and in photoactivation of the pigment.
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40
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Crucial steps in photoreceptor adaptation: Regulation of phosphodiesterase and guanylate cyclase activities and Ca 2+-buffering. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039364] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractThis commentary discusses the balance of phosphodiesterase and guanylate cyclase activities in vertebrate photoreceptors at moderate light intensities. The rate of cGMP hydrolysis and synthesis seem to equal each other. Ca2+ as regulator of both enzyme activities is also effectively buffered in photoreceptor cells by cytoplasmic buffer components.
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41
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The atomic structure of visual rhodopsin: How and when? Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039297] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractStrong arguments are presented by Hargrave suggesting that the crystallization of visual rhodopsin for high resolution analysis by X-ray crystallography or electron microscopy is feasible. However, the effort needed to achieve this goal will most likely exceed the resources of a single laboratory and a concerted approach to the research is necessary.
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42
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Molecular insights gained from covalently tethering cGMP to the ligand-binding sites of retinal rod cGMP-gated channels. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039261] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractA photoaffinity analog of cGMP has been used to biochemically identify a new ligand-binding subunit of the retinal rod cGMP-activated ion channel, as well as amino acids in contact with cGMP in the original subunit. Covalent tethering of this probe to channels in excised menbrane patches has revealed a functional heteogeneity in the ligand-binding sites that may arise from the two biochemically identified subunits.
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Abstract
AbstractRecent findings emphasize the complexity, both genetic and functional, of the manifold genes and mutations causing inherited retinal degeneration in humans. Knowledge of the genetic bases of these diseases can contribute to design of rational therapy, as well as elucidating the function of each gene product in normal visual processes.
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Channel structure and divalent cation regulation of phototransduction. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039339] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractThe identification of additional subunits of the cGMP-gated cation channel suggests exciting questions about their regulatory roles and about structure/functional relationships. How do the different subunits interact? How is the complex assembled into the plasma membrane? Divalent cations have been implicated in the regulation of adaptation. One often overlooked cation is magnesium. Could this ion play a role in phototransduction?
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45
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Structure of the cGMP-gated channel. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x0003939x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractThe subunit structure of the cGMP-gated cation channel of rod photoreceptors is rapidly being defined, and in the process the mode of regulation by Ca2+-calmodulin unraveled. Intriguingly, early results suggest that additional subunits of unknown function are associated with the channel and remain to be identified.
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46
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Linking genotypes with phenotypes in human retinal degenerations: Implications for future research and treatment. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039340] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractAlthough undoubtedly it will be incomplete by the time it is published, the target article by Daiger et al. organizes mutations in genes that produce retinal degenerations in humans into categories of clinically relevant phenotypes. Such classifications should help us understand the link between altered photoreceptor cell proteins and subsequent cell death, and they may yield insight into methods for preventing consequent blindness.
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47
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Genetic and clinical heterogeneity in tapetal retinal dystrophies. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x0003925x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
AbstractLarge scale DNA-mutation screening in patients with hereditary retinal diseases greatly enhances our knowledge about retinal function and diseases. Scientists, clinicians, patients, and families involved with retinal disorders may directly benefit from these developments. However, certain aspects of this expanding knowledge, such as the correlation between genotype and phenotype, may be much more complicated than we expect at present.
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48
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The determination of rhodopsin structure may require alternative approaches. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039236] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
AbstractThe structure of rhodopsin is a subject of intense interest. Solving the structure by traditional methods has proved exceedingly challenging. It may therefore be useful to confront the problem by a combination of alternate techniques. These include FTIR (Fourier transform infrared spectroscopy) and AFM (atomic force microscopy) on the intact protein. Furthermore, additional insights may be gained through structural investigations of discrete rhodopsin domains.
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Na-Ca + K exchanger and Ca 2+ homeostasis in retinal rod outer segments: Inactivation of the Ca 2+ efflux mode and possible involvement of intracellular Ca 2+ stores in Ca 2+ homeostasis. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039455] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
AbstractInactivation of the Ca2+ extrusion mode of the retinal rod Na- Ca + K exchanger is suggested to be the mechanism that prevents lowering of cytosolic free Ca2+ to < 1 nM when rod cells are saturated for a prolonged time under bright light conditions. Under these conditions, Ca2+ fluxes across disk membranes can contribute significantly to Ca2+ homeostasis in rods.
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50
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Nuclear magnetic resonance studies on the structure and function of rhodopsin. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039467] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractMagic angle spinning (MAS) NMR methods provide a means of obtaining high resolution structural data on rhodopsin and its photoin termediates. Current work has focused on the structure of the retinal chromophore and its interactions with surrounding protein charges. The recent development of MAS NMR methods for measuring internuclear distances with a resolution of ∼0.2 will complement diffraction methods for addressing key mechanistic questions.
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