1
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Hofmann KP, Lamb TD. Rhodopsin, light-sensor of vision. Prog Retin Eye Res 2023; 93:101116. [PMID: 36273969 DOI: 10.1016/j.preteyeres.2022.101116] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2022] [Revised: 08/20/2022] [Accepted: 08/22/2022] [Indexed: 11/06/2022]
Abstract
The light sensor of vertebrate scotopic (low-light) vision, rhodopsin, is a G-protein-coupled receptor comprising a polypeptide chain with bound chromophore, 11-cis-retinal, that exhibits remarkable physicochemical properties. This photopigment is extremely stable in the dark, yet its chromophore isomerises upon photon absorption with 70% efficiency, enabling the activation of its G-protein, transducin, with high efficiency. Rhodopsin's photochemical and biochemical activities occur over very different time-scales: the energy of retinaldehyde's excited state is stored in <1 ps in retinal-protein interactions, but it takes milliseconds for the catalytically active state to form, and many tens of minutes for the resting state to be restored. In this review, we describe the properties of rhodopsin and its role in rod phototransduction. We first introduce rhodopsin's gross structural features, its evolution, and the basic mechanisms of its activation. We then discuss light absorption and spectral sensitivity, photoreceptor electrical responses that result from the activity of individual rhodopsin molecules, and recovery of rhodopsin and the visual system from intense bleaching exposures. We then provide a detailed examination of rhodopsin's molecular structure and function, first in its dark state, and then in the active Meta states that govern its interactions with transducin, rhodopsin kinase and arrestin. While it is clear that rhodopsin's molecular properties are exquisitely honed for phototransduction, from starlight to dawn/dusk intensity levels, our understanding of how its molecular interactions determine the properties of scotopic vision remains incomplete. We describe potential future directions of research, and outline several major problems that remain to be solved.
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Affiliation(s)
- Klaus Peter Hofmann
- Institut für Medizinische Physik und Biophysik (CC2), Charité, and, Zentrum für Biophysik und Bioinformatik, Humboldt-Unversität zu Berlin, Berlin, 10117, Germany.
| | - Trevor D Lamb
- Eccles Institute of Neuroscience, John Curtin School of Medical Research, The Australian National University, Canberra, ACT 2600, Australia.
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2
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Getter T, Gulati S, Zimmerman R, Chen Y, Vinberg F, Palczewski K. Stereospecific modulation of dimeric rhodopsin. FASEB J 2019; 33:9526-9539. [PMID: 31121099 PMCID: PMC6662988 DOI: 10.1096/fj.201900443rr] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Accepted: 04/23/2019] [Indexed: 11/11/2022]
Abstract
The classic concept that GPCRs function as monomers has been challenged by the emerging evidence of GPCR dimerization and oligomerization. Rhodopsin (Rh) is the only GPCR whose native oligomeric arrangement was revealed by atomic force microscopy demonstrating that Rh exists as a dimer. However, the role of Rh dimerization in retinal physiology is currently unknown. In this study, we identified econazole and sulconazole, two small molecules that disrupt Rh dimer contacts, by implementing a cell-based high-throughput screening assay. Racemic mixtures of identified lead compounds were separated and tested for their stereospecific binding to Rh using UV-visible spectroscopy and intrinsic fluorescence of tryptophan (Trp) 265 after illumination. By following the changes in UV-visible spectra and Trp265 fluorescence in vitro, we found that binding of R-econazole modulates the formation of Meta III and quenches the intrinsic fluorescence of Trp265. In addition, electrophysiological ex vivo recording revealed that R-econazole slows photoresponse kinetics, whereas S-econazole decreased the sensitivity of rods without effecting the kinetics. Thus, this study contributes new methodology to identify compounds that disrupt the dimerization of GPCRs in general and validates the first active compounds that disrupt the Rh dimer specifically.-Getter, T., Gulati, S., Zimmerman, R., Chen, Y., Vinberg, F., Palczewski, K. Stereospecific modulation of dimeric rhodopsin.
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Affiliation(s)
- Tamar Getter
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California–Irvine, California, USA
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio, USA
| | - Sahil Gulati
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California–Irvine, California, USA
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio, USA
- Department of Physiology and Biophysics, University of California–Irvine, Irvine, California, USA
| | - Remy Zimmerman
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California–Irvine, California, USA
| | - Yuanyuan Chen
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
- McGowan Institute of Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Frans Vinberg
- Department of Ophthalmology and Visual Sciences, University of Utah, Salt Lake City, Utah, USA
| | - Krzysztof Palczewski
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California–Irvine, California, USA
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio, USA
- Department of Physiology and Biophysics, University of California–Irvine, Irvine, California, USA
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3
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Ortega JT, Parmar T, Jastrzebska B. Flavonoids enhance rod opsin stability, folding, and self-association by directly binding to ligand-free opsin and modulating its conformation. J Biol Chem 2019; 294:8101-8122. [PMID: 30944172 DOI: 10.1074/jbc.ra119.007808] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2019] [Revised: 03/27/2019] [Indexed: 12/29/2022] Open
Abstract
Rhodopsin (Rho) is a visual G protein-coupled receptor expressed in the rod photoreceptors of the eye, where it mediates transmission of a light signal into a cell and converts this signal into a nerve impulse. More than 100 mutations in Rho are linked to various ocular impairments, including retinitis pigmentosa (RP). Accordingly, much effort has been directed toward developing ligands that target Rho and improve its folding and stability. Natural compounds may provide another viable approach to such drug discovery efforts. The dietary polyphenol compounds, ubiquitously present in fruits and vegetables, have beneficial effects in several eye diseases. However, the underlying mechanism of their activity is not fully understood. In this study, we used a combination of computational methods, biochemical and biophysical approaches, including bioluminescence resonance energy transfer, and mammalian cell expression systems to clarify the effects of four common bioactive flavonoids (quercetin, myricetin, and their mono-glycosylated forms quercetin-3-rhamnoside and myricetrin) on rod opsin stability, function, and membrane organization. We observed that by directly interacting with ligand-free opsin, flavonoids modulate its conformation, thereby causing faster entry of the retinal chromophore into its binding pocket. Moreover, flavonoids significantly increased opsin stability, most likely by introducing structural rigidity and promoting receptor self-association within the biological membranes. Of note, the binding of flavonoids to an RP-linked P23H opsin variant partially restored its normal cellular trafficking. Together, our results suggest that flavonoids could be utilized as lead compounds in the development of effective nonretinoid therapeutics for managing RP-related retinopathies.
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Affiliation(s)
- Joseph T Ortega
- Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
| | - Tanu Parmar
- Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
| | - Beata Jastrzebska
- Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106.
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4
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Roushar FJ, Gruenhagen TC, Penn WD, Li B, Meiler J, Jastrzebska B, Schlebach JP. Contribution of Cotranslational Folding Defects to Membrane Protein Homeostasis. J Am Chem Soc 2018; 141:204-215. [PMID: 30537820 DOI: 10.1021/jacs.8b08243] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Membrane proteins are prone to misfolding and degradation within the cell, yet the nature of the conformational defects involved in this process remain poorly understood. The earliest stages of membrane protein folding are mediated by the Sec61 translocon, a molecular machine that facilitates the lateral partitioning of the polypeptide into the membrane. Proper membrane integration is an essential prerequisite for folding of the nascent chain. However, the marginal energetic drivers of this reaction suggest the translocon may operate with modest fidelity. In this work, we employed biophysical modeling in conjunction with quantitative biochemical measurements in order to evaluate the extent to which cotranslational folding defects influence membrane protein homeostasis. Protein engineering was employed to selectively perturb the topological energetics of human rhodopsin, and the expression and cellular trafficking of engineered variants were quantitatively compared. Our results reveal clear relationships between topological energetics and the efficiency of rhodopsin biogenesis, which appears to be limited by the propensity of a polar transmembrane domain to achieve its correct topological orientation. Though the polarity of this segment is functionally constrained, we find that its topology can be stabilized in a manner that enhances biogenesis without compromising the functional properties of rhodopsin. Furthermore, sequence alignments reveal this topological instability has been conserved throughout the course of evolution. These results suggest that topological defects significantly contribute to the inefficiency of membrane protein folding in the cell. Additionally, our findings suggest that the marginal stability of rhodopsin may represent an evolved trait.
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Affiliation(s)
- Francis J Roushar
- Department of Chemistry , Indiana University , Bloomington , Indiana 47405 , United States
| | - Timothy C Gruenhagen
- Department of Chemistry , Indiana University , Bloomington , Indiana 47405 , United States
| | - Wesley D Penn
- Department of Chemistry , Indiana University , Bloomington , Indiana 47405 , United States
| | - Bian Li
- Department of Chemistry , Vanderbilt University , Nashville , Tennessee 37235 , United States
| | - Jens Meiler
- Department of Chemistry , Vanderbilt University , Nashville , Tennessee 37235 , United States
| | - Beata Jastrzebska
- Department of Pharmacology , Case Western Reserve University , Cleveland , Ohio 44106 , United States
| | - Jonathan P Schlebach
- Department of Chemistry , Indiana University , Bloomington , Indiana 47405 , United States
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5
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Apo-Opsin Exists in Equilibrium Between a Predominant Inactive and a Rare Highly Active State. J Neurosci 2018; 39:212-223. [PMID: 30459230 DOI: 10.1523/jneurosci.1980-18.2018] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Revised: 10/30/2018] [Accepted: 11/04/2018] [Indexed: 12/17/2022] Open
Abstract
Bleaching adaptation in rod photoreceptors is mediated by apo-opsin, which activates phototransduction with effective activity 105- to 106-fold lower than that of photoactivated rhodopsin (meta II). However, the mechanism that produces such low opsin activity is unknown. To address this question, we sought to record single opsin responses in mouse rods. We used mutant mice lacking efficient calcium feedback to boosts rod responses and generated a small fraction of opsin by photobleaching ∼1% of rhodopsin. The bleach produced a dramatic increase in the frequency of discrete photoresponse-like events. This activity persisted for hours, was quenched by 11-cis-retinal, and was blocked by uncoupling opsin from phototransduction, all indicating opsin as its source. Opsin-driven discrete activity was also observed in rods containing non-activatable rhodopsin, ruling out transactivation of rhodopsin by opsin. We conclude that bleaching adaptation is mediated by opsin that exists in equilibrium between a predominant inactive and a rare meta II-like state.SIGNIFICANCE STATEMENT Electrophysiological analysis is used to show that the G-protein-coupled receptor opsin exists in equilibrium between a predominant inactive and a rare highly active state that mediates bleaching adaptation in photoreceptors.
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6
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Milano SK, Wang C, Erickson JW, Cerione RA, Ramachandran S. Gain-of-function screen of α-transducin identifies an essential phenylalanine residue necessary for full effector activation. J Biol Chem 2018; 293:17941-17952. [PMID: 30266806 DOI: 10.1074/jbc.ra118.003746] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2018] [Revised: 09/21/2018] [Indexed: 11/06/2022] Open
Abstract
Two regions on the α subunits of heterotrimeric GTP-binding proteins (G-proteins), the Switch II/α2 helix (which changes conformation upon GDP-GTP exchange) and the α3 helix, have been shown to contain the binding sites for their effector proteins. However, how the binding of Gα subunits to their effector proteins is translated into the stimulation of effector activity is still poorly understood. Here, we took advantage of a reconstituted rhodopsin-coupled phototransduction system to address this question and identified a distinct surface and an essential residue on the α subunit of the G-protein transducin (αT) that is necessary to fully activate its effector enzyme, the cGMP phosphodiesterase (PDE). We started with a chimeric G-protein α subunit (αT*) comprising residues mainly from αT and a short stretch of residues from the Gi1 α subunit (αi1), which only weakly stimulates PDE activity. We then reinstated the αT residues by systematically replacing the corresponding αi1 residues within αT* with the aim of fully restoring PDE stimulatory activity. These experiments revealed that the αG/α4 loop and a phenylalanine residue at position 283 are essential for conferring the αT* subunit with full PDE stimulatory capability. We further demonstrated that this same region and amino acid within the α subunit of the Gs protein (αs) are necessary for full adenylyl cyclase activation. These findings highlight the importance of the αG/α4 loop and of an essential phenylalanine residue within this region on Gα subunits αT and αs as being pivotal for their selective and optimal stimulation of effector activity.
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Affiliation(s)
- Shawn K Milano
- From the Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301
| | - Chenyue Wang
- From the Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301
| | - Jon W Erickson
- From the Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301
| | - Richard A Cerione
- From the Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301; Department of Molecular Medicine, Cornell University, Ithaca, New York 14853-6401.
| | - Sekar Ramachandran
- From the Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301
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7
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Mallory DP, Gutierrez E, Pinkevitch M, Klinginsmith C, Comar WD, Roushar FJ, Schlebach JP, Smith AW, Jastrzebska B. The Retinitis Pigmentosa-Linked Mutations in Transmembrane Helix 5 of Rhodopsin Disrupt Cellular Trafficking Regardless of Oligomerization State. Biochemistry 2018; 57:5188-5201. [PMID: 30085663 DOI: 10.1021/acs.biochem.8b00403] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
G protein-coupled receptors can exist as dimers and higher-order oligomers in biological membranes. The specific oligomeric assembly of these receptors is believed to play a major role in their function, and the disruption of native oligomers has been implicated in specific human pathologies. Computational predictions and biochemical analyses suggest that two molecules of rhodopsin (Rho) associate through the interactions involving its fifth transmembrane helix (TM5). Interestingly, there are several pathogenic loss-of-function mutations within TM5 that face the lipid bilayer in a manner that could potentially influence the dimerization of Rho. Though several of these mutations are known to induce misfolding, the pathogenic defects associated with V209M and F220C Rho remain unclear. In this work, we utilized a variety of biochemical and biophysical approaches to elucidate the effects of these mutations on the dimerization, folding, trafficking, and function of Rho in relation to other pathogenic TM5 variants. Chemical cross-linking, bioluminescence energy transfer, and pulsed-interleaved excitation fluorescence cross-correlation spectroscopy experiments revealed that each of these mutants exhibits a wild type-like propensity to self-associate within the plasma membrane. However, V209M and F220C each exhibit subtle defects in cellular trafficking. Together, our results suggest that the RP pathology associated with the expression of the V209M and F220C mutants could arise from defects in folding and cellular trafficking rather than the disruption of dimerization, as has been previously proposed.
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Affiliation(s)
- D Paul Mallory
- Department of Chemistry , University of Akron , 190 Buchtel Common , Akron , Ohio 44325 , United States
| | - Elizabeth Gutierrez
- Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine , Case Western Reserve University , 10900 Euclid Avenue , Cleveland , Ohio 44106 , United States
| | - Margaret Pinkevitch
- Department of Chemistry , University of Akron , 190 Buchtel Common , Akron , Ohio 44325 , United States
| | - Christie Klinginsmith
- Department of Chemistry , University of Akron , 190 Buchtel Common , Akron , Ohio 44325 , United States
| | - William D Comar
- Department of Chemistry , University of Akron , 190 Buchtel Common , Akron , Ohio 44325 , United States
| | - Francis J Roushar
- Department of Chemistry , Indiana University , 800 East Kirkwood Avenue , Bloomington , Indiana 47405-7102 , United States
| | - Jonathan P Schlebach
- Department of Chemistry , Indiana University , 800 East Kirkwood Avenue , Bloomington , Indiana 47405-7102 , United States
| | - Adam W Smith
- Department of Chemistry , University of Akron , 190 Buchtel Common , Akron , Ohio 44325 , United States
| | - Beata Jastrzebska
- Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine , Case Western Reserve University , 10900 Euclid Avenue , Cleveland , Ohio 44106 , United States
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8
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Targeting G protein-coupled receptor signaling at the G protein level with a selective nanobody inhibitor. Nat Commun 2018; 9:1996. [PMID: 29777099 PMCID: PMC5959942 DOI: 10.1038/s41467-018-04432-0] [Citation(s) in RCA: 57] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2017] [Accepted: 04/25/2018] [Indexed: 01/06/2023] Open
Abstract
G protein-coupled receptors (GPCRs) activate heterotrimeric G proteins by mediating a GDP to GTP exchange in the Gα subunit. This leads to dissociation of the heterotrimer into Gα-GTP and Gβγ dimer. The Gα-GTP and Gβγ dimer each regulate a variety of downstream pathways to control various aspects of human physiology. Dysregulated Gβγ-signaling is a central element of various neurological and cancer-related anomalies. However, Gβγ also serves as a negative regulator of Gα that is essential for G protein inactivation, and thus has the potential for numerous side effects when targeted therapeutically. Here we report a llama-derived nanobody (Nb5) that binds tightly to the Gβγ dimer. Nb5 responds to all combinations of β-subtypes and γ-subtypes and competes with other Gβγ-regulatory proteins for a common binding site on the Gβγ dimer. Despite its inhibitory effect on Gβγ-mediated signaling, Nb5 has no effect on Gαq-mediated and Gαs-mediated signaling events in living cells.
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9
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Chen Y, Chen Y, Jastrzebska B, Golczak M, Gulati S, Tang H, Seibel W, Li X, Jin H, Han Y, Gao S, Zhang J, Liu X, Heidari-Torkabadi H, Stewart PL, Harte WE, Tochtrop GP, Palczewski K. A novel small molecule chaperone of rod opsin and its potential therapy for retinal degeneration. Nat Commun 2018; 9:1976. [PMID: 29773803 PMCID: PMC5958115 DOI: 10.1038/s41467-018-04261-1] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2017] [Accepted: 04/13/2018] [Indexed: 12/21/2022] Open
Abstract
Rhodopsin homeostasis is tightly coupled to rod photoreceptor cell survival and vision. Mutations resulting in the misfolding of rhodopsin can lead to autosomal dominant retinitis pigmentosa (adRP), a progressive retinal degeneration that currently is untreatable. Using a cell-based high-throughput screen (HTS) to identify small molecules that can stabilize the P23H-opsin mutant, which causes most cases of adRP, we identified a novel pharmacological chaperone of rod photoreceptor opsin, YC-001. As a non-retinoid molecule, YC-001 demonstrates micromolar potency and efficacy greater than 9-cis-retinal with lower cytotoxicity. YC-001 binds to bovine rod opsin with an EC50 similar to 9-cis-retinal. The chaperone activity of YC-001 is evidenced by its ability to rescue the transport of multiple rod opsin mutants in mammalian cells. YC-001 is also an inverse agonist that non-competitively antagonizes rod opsin signaling. Significantly, a single dose of YC-001 protects Abca4 -/- Rdh8 -/- mice from bright light-induced retinal degeneration, suggesting its broad therapeutic potential.
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Affiliation(s)
- Yuanyuan Chen
- Department of Pharmacology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA.
- The McGowan Institute for Regenerative Medicine, University of Pittsburgh, 450 Technology Drive Suite 300, Pittsburgh, PA, 15219, USA.
- Department of Ophthalmology, University of Pittsburgh, 3501 Fifth Avenue, Pittsburgh, PA, 15260, USA.
| | - Yu Chen
- Department of Pharmacology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA
- Yueyang Hospital and Clinical Research Institute of Integrative Medicine, Shanghai University of Traditional Chinese Medicine, 200437, Shanghai, China
| | - Beata Jastrzebska
- Department of Pharmacology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA
- Cleveland Center for Membrane and Structural Biology, Case Western Reserve University, 1819 E. 101st Street, Cleveland, OH, 44106, USA
| | - Marcin Golczak
- Department of Pharmacology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA
- Cleveland Center for Membrane and Structural Biology, Case Western Reserve University, 1819 E. 101st Street, Cleveland, OH, 44106, USA
| | - Sahil Gulati
- Department of Pharmacology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA
- Cleveland Center for Membrane and Structural Biology, Case Western Reserve University, 1819 E. 101st Street, Cleveland, OH, 44106, USA
| | - Hong Tang
- Drug Discovery Center, University of Cincinnati, 2180 E. Galbraith Road, Cincinnati, OH, 45237, USA
| | - William Seibel
- Drug Discovery Center, University of Cincinnati, 2180 E. Galbraith Road, Cincinnati, OH, 45237, USA
| | - Xiaoyu Li
- Department of Pharmacology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA
| | - Hui Jin
- Department of Pharmacology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA
| | - Yong Han
- Department of Chemistry, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA
| | - Songqi Gao
- Department of Pharmacology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA
| | - Jianye Zhang
- Department of Pharmacology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA
| | - Xujie Liu
- Department of Ophthalmology, University of Pittsburgh, 3501 Fifth Avenue, Pittsburgh, PA, 15260, USA
| | - Hossein Heidari-Torkabadi
- Department of Pharmacology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA
| | - Phoebe L Stewart
- Department of Pharmacology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA
- Cleveland Center for Membrane and Structural Biology, Case Western Reserve University, 1819 E. 101st Street, Cleveland, OH, 44106, USA
| | - William E Harte
- Office of Translation and Innovation, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA
| | - Gregory P Tochtrop
- Department of Chemistry, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA
| | - Krzysztof Palczewski
- Department of Pharmacology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA.
- Cleveland Center for Membrane and Structural Biology, Case Western Reserve University, 1819 E. 101st Street, Cleveland, OH, 44106, USA.
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10
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Elgeti M, Kazmin R, Rose AS, Szczepek M, Hildebrand PW, Bartl FJ, Scheerer P, Hofmann KP. The arrestin-1 finger loop interacts with two distinct conformations of active rhodopsin. J Biol Chem 2018; 293:4403-4410. [PMID: 29363577 DOI: 10.1074/jbc.m117.817890] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2017] [Revised: 01/17/2018] [Indexed: 11/06/2022] Open
Abstract
Signaling of the prototypical G protein-coupled receptor (GPCR) rhodopsin through its cognate G protein transducin (Gt) is quenched when arrestin binds to the activated receptor. Although the overall architecture of the rhodopsin/arrestin complex is known, many questions regarding its specificity remain unresolved. Here, using FTIR difference spectroscopy and a dual pH/peptide titration assay, we show that rhodopsin maintains certain flexibility upon binding the "finger loop" of visual arrestin (prepared as synthetic peptide ArrFL-1). We found that two distinct complexes can be stabilized depending on the protonation state of E3.49 in the conserved (D)ERY motif. Both complexes exhibit different interaction modes and affinities of ArrFL-1 binding. The plasticity of the receptor within the rhodopsin/ArrFL-1 complex stands in contrast to the complex with the C terminus of the Gt α-subunit (GαCT), which stabilizes only one specific substate out of the conformational ensemble. However, Gt α-subunit binding and both ArrFL-1-binding modes involve a direct interaction to conserved R3.50, as determined by site-directed mutagenesis. Our findings highlight the importance of receptor conformational flexibility and cytoplasmic proton uptake for modulation of rhodopsin signaling and thereby extend the picture provided by crystal structures of the rhodopsin/arrestin and rhodopsin/ArrFL-1 complexes. Furthermore, the two binding modes of ArrFL-1 identified here involve motifs of conserved amino acids, which indicates that our results may have elucidated a common modulation mechanism of class A GPCR-G protein/-arrestin signaling.
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Affiliation(s)
- Matthias Elgeti
- From the Institut für Medizinische Physik und Biophysik (CC2), Charité-Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany,
| | - Roman Kazmin
- From the Institut für Medizinische Physik und Biophysik (CC2), Charité-Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany
| | - Alexander S Rose
- From the Institut für Medizinische Physik und Biophysik (CC2), Charité-Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany.,Group ProteInformatics
| | - Michal Szczepek
- From the Institut für Medizinische Physik und Biophysik (CC2), Charité-Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany.,Group Protein X-ray Crystallography and Signal Transduction
| | - Peter W Hildebrand
- From the Institut für Medizinische Physik und Biophysik (CC2), Charité-Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany.,Institut für Medizinische Physik und Biophysik, Universität Leipzig, Härtelstrasse 16-18, 04107 Leipzig, Germany
| | - Franz J Bartl
- From the Institut für Medizinische Physik und Biophysik (CC2), Charité-Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany.,Institut für Biologie, Biophysikalische Chemie, Humboldt-Universität zu Berlin, Invalidenstrasse 42, 10115 Berlin, Germany
| | - Patrick Scheerer
- From the Institut für Medizinische Physik und Biophysik (CC2), Charité-Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany.,Group Protein X-ray Crystallography and Signal Transduction
| | - Klaus Peter Hofmann
- From the Institut für Medizinische Physik und Biophysik (CC2), Charité-Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany
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11
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Andhirka SK, Vignesh R, Aradhyam GK. The nucleotide-free state of heterotrimeric G proteins α-subunit adopts a highly stable conformation. FEBS J 2017. [PMID: 28627018 DOI: 10.1111/febs.14143] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Deciphering the mechanism of activation of heterotrimeric G proteins by their cognate receptors continues to be an intriguing area of research. The recently solved crystal structure of the ternary complex captured the receptor-bound α-subunit in an open conformation, without bound nucleotide has improved our understanding of the activation process. Despite these advancements, the mechanism by which the receptor causes GDP release from the α-subunit remains elusive. To elucidate the mechanism of activation, we studied guanine nucleotide-induced structural stability of the α-subunit (in response to thermal/chaotrope-mediated stress). Inherent stabilities of the inactive (GDP-bound) and active (GTP-bound) forms contribute antagonistically to the difference in conformational stability whereas the GDP-bound protein is able to switch to a stable intermediate state, GTP-bound protein loses this ability. Partial perturbation of the protein fold reveals the underlying influence of the bound nucleotide providing an insight into the mechanism of activation. An extra stable, pretransition intermediate, 'empty pocket' state (conformationally active-state like) in the unfolding pathway of GDP-bound protein mimics a gating system - the activation process having to overcome this stable intermediate state. We demonstrate that a relatively more complex conformational fold of the GDP-bound protein is at the core of the gating system. We report capturing this threshold, 'metastable empty pocket' conformation (the gate) of α-subunit of G protein and hypothesize that the receptor activates the G protein by enabling it to achieve this structure through mild structural perturbation.
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Affiliation(s)
- Sai Krishna Andhirka
- Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India
| | - Ravichandran Vignesh
- Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India
| | - Gopala Krishna Aradhyam
- Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India
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12
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Abstract
Conformational equilibria of G-protein-coupled receptors (GPCRs) are intimately involved in intracellular signaling. Here conformational substates of the GPCR rhodopsin are investigated in micelles of dodecyl maltoside (DDM) and in phospholipid nanodiscs by monitoring the spatial positions of transmembrane helices 6 and 7 at the cytoplasmic surface using site-directed spin labeling and double electron-electron resonance spectroscopy. The photoactivated receptor in DDM is dominated by one conformation with weak pH dependence. In nanodiscs, however, an ensemble of pH-dependent conformational substates is observed, even at pH 6.0 where the MIIbH+ form defined by proton uptake and optical spectroscopic methods is reported to be the sole species present in native disk membranes. In nanodiscs, the ensemble of substates in the photoactivated receptor spontaneously decays to that characteristic of the inactive state with a lifetime of ∼16 min at 20 °C. Importantly, transducin binding to the activated receptor selects a subset of the ensemble in which multiple substates are apparently retained. The results indicate that in a native-like lipid environment rhodopsin activation is not analogous to a simple binary switch between two defined conformations, but the activated receptor is in equilibrium between multiple conformers that in principle could recognize different binding partners.
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13
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Photocyclic behavior of rhodopsin induced by an atypical isomerization mechanism. Proc Natl Acad Sci U S A 2017; 114:E2608-E2615. [PMID: 28289214 DOI: 10.1073/pnas.1617446114] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Vertebrate rhodopsin (Rh) contains 11-cis-retinal as a chromophore to convert light energy into visual signals. On absorption of light, 11-cis-retinal is isomerized to all-trans-retinal, constituting a one-way reaction that activates transducin (Gt) followed by chromophore release. Here we report that bovine Rh, regenerated instead with a six-carbon-ring retinal chromophore featuring a C11=C12 double bond locked in its cis conformation (Rh6mr), employs an atypical isomerization mechanism by converting 11-cis to an 11,13-dicis configuration for prolonged Gt activation. Time-dependent UV-vis spectroscopy, HPLC, and molecular mechanics analyses revealed an atypical thermal reisomerization of the 11,13-dicis to the 11-cis configuration on a slow timescale, which enables Rh6mr to function in a photocyclic manner similar to that of microbial Rhs. With this photocyclic behavior, Rh6mr repeatedly recruits and activates Gt in response to light stimuli, making it an excellent candidate for optogenetic tools based on retinal analog-bound vertebrate Rhs. Overall, these comprehensive structure-function studies unveil a unique photocyclic mechanism of Rh activation by an 11-cis-to-11,13-dicis isomerization.
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14
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Ploier B, Caro LN, Morizumi T, Pandey K, Pearring JN, Goren MA, Finnemann SC, Graumann J, Arshavsky VY, Dittman JS, Ernst OP, Menon AK. Dimerization deficiency of enigmatic retinitis pigmentosa-linked rhodopsin mutants. Nat Commun 2016; 7:12832. [PMID: 27694816 PMCID: PMC5059438 DOI: 10.1038/ncomms12832] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2015] [Accepted: 08/03/2016] [Indexed: 02/05/2023] Open
Abstract
Retinitis pigmentosa (RP) is a blinding disease often associated with mutations in rhodopsin, a light-sensing G protein-coupled receptor and phospholipid scramblase. Most RP-associated mutations affect rhodopsin's activity or transport to disc membranes. Intriguingly, some mutations produce apparently normal rhodopsins that nevertheless cause disease. Here we show that three such enigmatic mutations—F45L, V209M and F220C—yield fully functional visual pigments that bind the 11-cis retinal chromophore, activate the G protein transducin, traffic to the light-sensitive photoreceptor compartment and scramble phospholipids. However, tests of scramblase activity show that unlike wild-type rhodopsin that functionally reconstitutes into liposomes as dimers or multimers, F45L, V209M and F220C rhodopsins behave as monomers. This result was confirmed in pull-down experiments. Our data suggest that the photoreceptor pathology associated with expression of these enigmatic RP-associated pigments arises from their unexpected inability to dimerize via transmembrane helices 1 and 5. Retinitis pigmentosa is often caused by mutations that affect the activity or transport of rhodopsin, but some mutations cause disease even though an apparently functional protein is produced. Here the authors show that three such enigmatic mutants retain scramblase activity but are unable to dimerize.
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Affiliation(s)
- Birgit Ploier
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, New York 10065, USA
| | - Lydia N Caro
- Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Takefumi Morizumi
- Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Kalpana Pandey
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, New York 10065, USA
| | - Jillian N Pearring
- Department of Ophthalmology, Duke University Medical Center, Durham, North Carolina 27710, USA
| | - Michael A Goren
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, New York 10065, USA
| | - Silvia C Finnemann
- Department of Biological Sciences, Center for Cancer, Genetic Diseases and Gene Regulation, Fordham University, Bronx, New York 10458, USA
| | - Johannes Graumann
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, New York 10065, USA.,Weill Cornell Medicine-Qatar, Qatar Foundation, Education City P.O.Box 24144, Doha, State of Qatar
| | - Vadim Y Arshavsky
- Department of Ophthalmology, Duke University Medical Center, Durham, North Carolina 27710, USA.,Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA
| | - Jeremy S Dittman
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, New York 10065, USA
| | - Oliver P Ernst
- Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada M5S 1A8.,Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Anant K Menon
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, New York 10065, USA
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15
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Szundi I, Funatogawa C, Kliger DS. Complexity of Bovine Rhodopsin Activation Revealed at Low Temperature and Alkaline pH. Biochemistry 2016; 55:5095-105. [DOI: 10.1021/acs.biochem.6b00687] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Istvan Szundi
- Department
of Chemistry and
Biochemistry, University of California, Santa Cruz, Santa Cruz, California 95064, United States
| | - Chie Funatogawa
- Department
of Chemistry and
Biochemistry, University of California, Santa Cruz, Santa Cruz, California 95064, United States
| | - David S. Kliger
- Department
of Chemistry and
Biochemistry, University of California, Santa Cruz, Santa Cruz, California 95064, United States
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16
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Jastrzebska B, Chen Y, Orban T, Jin H, Hofmann L, Palczewski K. Disruption of Rhodopsin Dimerization with Synthetic Peptides Targeting an Interaction Interface. J Biol Chem 2015; 290:25728-44. [PMID: 26330551 DOI: 10.1074/jbc.m115.662684] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2015] [Indexed: 11/06/2022] Open
Abstract
Although homo- and heterodimerizations of G protein-coupled receptors (GPCRs) are well documented, GPCR monomers are able to assemble in different ways, thus causing variations in the interactive interface between receptor monomers among different GPCRs. Moreover, the functional consequences of this phenomenon, which remain to be clarified, could be specific for different GPCRs. Synthetic peptides derived from transmembrane (TM) domains can interact with a full-length GPCR, blocking dimer formation and affecting its function. Here we used peptides corresponding to TM helices of bovine rhodopsin (Rho) to investigate the Rho dimer interface and functional consequences of its disruption. Incubation of Rho with TM1, TM2, TM4, and TM5 peptides in rod outer segment (ROS) membranes shifted the resulting detergent-solubilized protein migration through a gel filtration column toward smaller molecular masses with a reduced propensity for dimer formation in a cross-linking reaction. Binding of these TM peptides to Rho was characterized by both mass spectrometry and a label-free assay from which dissociation constants were calculated. A BRET (bioluminescence resonance energy transfer) assay revealed that the physical interaction between Rho molecules expressed in membranes of living cells was blocked by the same four TM peptides identified in our in vitro experiments. Although disruption of the Rho dimer/oligomer had no effect on the rates of G protein activation, binding of Gt to the activated receptor stabilized the dimer. However, TM peptide-induced disruption of dimer/oligomer decreased receptor stability, suggesting that Rho supramolecular organization could be essential for ROS stabilization and receptor trafficking.
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Affiliation(s)
- Beata Jastrzebska
- From the Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965
| | - Yuanyuan Chen
- From the Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965
| | - Tivadar Orban
- From the Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965
| | - Hui Jin
- From the Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965
| | - Lukas Hofmann
- From the Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965
| | - Krzysztof Palczewski
- From the Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965
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17
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Yamazaki Y, Nagata T, Terakita A, Kandori H, Shichida Y, Imamoto Y. Intramolecular interactions that induce helical rearrangement upon rhodopsin activation: light-induced structural changes in metarhodopsin IIa probed by cysteine S-H stretching vibrations. J Biol Chem 2014; 289:13792-800. [PMID: 24692562 DOI: 10.1074/jbc.m113.527606] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Rhodopsin undergoes rearrangements of its transmembrane helices after photon absorption to transfer a light signal to the G-protein transducin. To investigate the mechanism by which rhodopsin adopts the transducin-activating conformation, the local environmental changes in the transmembrane region were probed using the cysteine S-H group, whose stretching frequency is well isolated from the other protein vibrational modes. The S-H stretching modes of cysteine residues introduced into Helix III, which contains several key residues for the helical movements, and of native cysteine residues were measured by Fourier transform infrared spectroscopy. This method was applied to metarhodopsin IIa, a precursor of the transducin-activating state in which the intramolecular interactions are likely to produce a state ready for helical movements. No environmental change was observed near the ionic lock between Arg-135 in Helix III and Glu-247 in Helix VI that maintains the inactive conformation. Rather, the cysteine residues that showed environmental changes were located around the chromophore, Ala-164, His-211, and Phe-261. These findings imply that the hydrogen bond between Helix III and Helix V involving Glu-122 and His-211 and the hydrophobic packing between Helix III and Helix VI involving Gly-121, Leu-125, Phe-261, and Trp-265 are altered before the helical rearrangement leading toward the active conformation.
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Affiliation(s)
- Yoichi Yamazaki
- From the Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan, the Graduate School of Materials Science, Nara Institute of Science and Technology, Nara, 630-0192, Japan
| | - Tomoko Nagata
- From the Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - Akihisa Terakita
- From the Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan, the Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Osaka 558-8585, Japan, and
| | - Hideki Kandori
- From the Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan, the Department of Frontier Materials, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan
| | - Yoshinori Shichida
- From the Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - Yasushi Imamoto
- From the Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan,
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18
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Chen Y, Jastrzebska B, Cao P, Zhang J, Wang B, Sun W, Yuan Y, Feng Z, Palczewski K. Inherent instability of the retinitis pigmentosa P23H mutant opsin. J Biol Chem 2014; 289:9288-303. [PMID: 24515108 PMCID: PMC3979360 DOI: 10.1074/jbc.m114.551713] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2014] [Revised: 02/05/2014] [Indexed: 11/06/2022] Open
Abstract
The P23H opsin mutation is the most common cause of autosomal dominant retinitis pigmentosa. Even though the pathobiology of the resulting retinal degeneration has been characterized in several animal models, its complex molecular mechanism is not well understood. Here, we expressed P23H bovine rod opsin in the nervous system of Caenorhabditis elegans. Expression was low due to enhanced protein degradation. The mutant opsin was glycosylated, but the polysaccharide size differed from that of the normal protein. Although P23H opsin aggregated in the nervous system of C. elegans, the pharmacological chaperone 9-cis-retinal stabilized it during biogenesis, producing a variant of rhodopsin called P23H isorhodopsin. In vitro, P23H isorhodopsin folded correctly, formed the appropriate disulfide bond, could be photoactivated but with reduced sensitivity, and underwent Meta II decay at a rate similar to wild type isorhodopsin. In worm neurons, P23H isorhodopsin initiated phototransduction by coupling with the endogenous Gi/o signaling cascade that induced loss of locomotion. Using pharmacological interventions affecting protein synthesis and degradation, we showed that the chromophore could be incorporated either during or after mutant protein translation. However, regeneration of P23H isorhodopsin with chromophore was significantly slower than that of wild type isorhodopsin. This effect, combined with the inherent instability of P23H rhodopsin, could lead to the structural cellular changes and photoreceptor death found in autosomal dominant retinitis pigmentosa. These results also suggest that slow regeneration of P23H rhodopsin could prevent endogenous chromophore-mediated stabilization of rhodopsin in the retina.
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Affiliation(s)
| | | | | | | | - Benlian Wang
- Center for Proteomics and Bioinformatics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965 and
| | - Wenyu Sun
- Polgenix Inc., Cleveland, Ohio 44106
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19
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Yamazaki Y, Nagata T, Terakita A, Kandori H, Shichida Y, Imamoto Y. Mapping of the local environmental changes in proteins by cysteine scanning. Biophysics (Nagoya-shi) 2014; 10:1-7. [PMID: 27493492 PMCID: PMC4629666 DOI: 10.2142/biophysics.10.1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2013] [Accepted: 12/18/2013] [Indexed: 12/01/2022] Open
Abstract
Protein conformational changes, which regulate the activity of proteins, are induced by the alternation of intramolecular interactions. Therefore, the detection of the local environmental changes around the key amino acid residues is essential to understand the activation mechanisms of functional proteins. Here we developed the methods to scan the local environmental changes using the vibrational band of cysteine S-H group. We validated the sensitivity of this method using bathorhodopsin, a photoproduct of rhodopsin trapped at liquid nitrogen temperature, which undergoes little conformational changes from the dark state as shown by the X-ray crystallography. The cysteine residues were individually introduced into 15 positions of Helix III, which contains several key amino acid residues for the light-induced conformational changes of rhodopsin. The shifts of S-H stretching modes of these cysteine residues and native cysteine residues upon the formation of bathorhodopsin were measured by Fourier transform infrared spectroscopy. While most of cysteine residues demonstrated no shift of S-H stretching mode, cysteine residues introduced at positions 117, 118, and 122, which are in the vicinity of the chromophore, demonstrated the significant changes. The current results are consistent with the crystal structure of bathorhodopsin, implying that the cysteine scanning is sensitive enough to detect the tiny conformational changes.
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Affiliation(s)
- Yoichi Yamazaki
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan; Graduate School of Materials Science, Nara Institute of Science and Technology, Nara 630-0192, Japan
| | - Tomoko Nagata
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - Akihisa Terakita
- Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Osaka 558-8585, Japan
| | - Hideki Kandori
- Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan
| | - Yoshinori Shichida
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - Yasushi Imamoto
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
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21
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22
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Goncalves J, Eilers M, South K, Opefi CA, Laissue P, Reeves PJ, Smith SO. Magic angle spinning nuclear magnetic resonance spectroscopy of G protein-coupled receptors. Methods Enzymol 2013; 522:365-89. [PMID: 23374193 DOI: 10.1016/b978-0-12-407865-9.00017-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/08/2022]
Abstract
G protein-coupled receptors (GPCRs) represent the largest family of membrane receptors and mediate a diversity of cellular processes. These receptors have a common seven-transmembrane helix structure, yet have evolved to respond to literally thousands of different ligands. In this chapter, we describe the use of magic angle spinning solid-state NMR spectroscopy for characterizing the structure and dynamics of GPCRs. Solid-state NMR spectroscopy is well suited for structural measurements in both detergent micelles and membrane bilayer environments. We first outline the methods for large-scale production of stable, functional receptors containing (13)C- and (15)N-labeled amino acids. The expression methods make use of eukaryotic HEK293S cell lines that produce correctly folded, fully functional receptors. We subsequently describe the basic methods used for magic angle spinning solid-state NMR measurements of chemical shifts and dipolar couplings, which reveal detailed information on GPCR structure and dynamics.
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Affiliation(s)
- Joseph Goncalves
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, New York, USA
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23
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Kanuru M, Raman R, Aradhyam GK. Serine protease activity of calnuc: regulation by Zn2+ and G proteins. J Biol Chem 2012. [PMID: 23195954 DOI: 10.1074/jbc.m112.382846] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The functions of calnuc, a novel Ca(2+)-binding protein with multiple structural domains and diverse interacting partners, are yet unknown. We demonstrate unknown facets of calnuc, which is a serine protease in which Ser-378 of GXSXG motif, Asp-328 of DTG motif, and His-339 form the "catalytic triad," locating the enzyme active site in the C-terminal region. Analogous to the active site of Zn(2+) carboxypeptidases, calnuc has two high affinity (K(d) ∼ 20 nm), well conserved Zn(2+)-binding sites near its N terminus, although it is inactive as a peptidase. Zn(2+) binding allosterically and negatively regulates the serine protease activity of calnuc, inhibition being caused by an "open to close" change in its conformation not seen upon Ca(2+) binding. Most strikingly, interaction with G protein α subunit completely inhibits the enzymatic activity of calnuc. We thus illustrate that G proteins and Zn(2+) act as two "keys" that control enzymatic activity of calnuc, arresting it in "locked" state. Calnuc, therefore, exists dynamically in two different forms, (i) as a Ca(2+)-binding protein in Zn(2+)-bound form and (ii) as a protease in Zn(2+)-free form, commissioning it to perform multiple functions.
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Affiliation(s)
- Madhavi Kanuru
- Department of Biotechnology, Indian Institute of Technology Madras, Chennai 600 036, India
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24
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Salom D, Cao P, Sun W, Kramp K, Jastrzebska B, Jin H, Feng Z, Palczewski K. Heterologous expression of functional G-protein-coupled receptors in Caenorhabditis elegans. FASEB J 2011; 26:492-502. [PMID: 22090314 DOI: 10.1096/fj.11-197780] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
New strategies for expression, purification, functional characterization, and structural determination of membrane-spanning G-protein-coupled receptors (GPCRs) are constantly being developed because of their importance to human health. Here, we report a Caenorhabditis elegans heterologous expression system able to produce milligram amounts of functional native and engineered GPCRs. Both bovine opsin [(b)opsin] and human adenosine A(2A) subtype receptor [(h)A(2A)R] expressed in neurons or muscles of C. elegans were localized to cell membranes. Worms expressing these GPCRs manifested changes in motor behavior in response to light and ligands, respectively. With a newly devised protocol, 0.6-1 mg of purified homogenous 9-cis-retinal-bound bovine isorhodopsin [(b)isoRho] and ligand-bound (h)A(2A)R were obtained from C. elegans from one 10-L fermentation at low cost. Purified recombinant (b)isoRho exhibited its signature absorbance spectrum and activated its cognate G-protein transducin in vitro at a rate similar to native rhodopsin (Rho) obtained from bovine retina. Generally high expression levels of 11 native and mutant GPCRs demonstrated the potential of this C. elegans system to produce milligram quantities of high-quality GPCRs and possibly other membrane proteins suitable for detailed characterization.
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Cao P, Sun W, Kramp K, Zheng M, Salom D, Jastrzebska B, Jin H, Palczewski K, Feng Z. Light-sensitive coupling of rhodopsin and melanopsin to G(i/o) and G(q) signal transduction in Caenorhabditis elegans. FASEB J 2011; 26:480-91. [PMID: 22090313 DOI: 10.1096/fj.11-197798] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Activation of G-protein-coupled receptors (GPCRs) initiates signal transduction cascades that affect many physiological responses. The worm Caenorhabditis elegans expresses >1000 of these receptors along with their cognate heterotrimeric G proteins. Here, we report properties of 9-cis-retinal regenerated bovine opsin [(b)isoRho] and human melanopsin [(h)Mo], two light-activated, heterologously expressed GPCRs in the nervous system of C. elegans with various genetically engineered alterations. Profound transient photoactivation of G(i/o) signaling by (b)isoRho led to a sudden and transient loss of worm motility dependent on cyclic adenosine monophosphate, whereas transient photoactivation of G(q) signaling by (h)Mo enhanced worm locomotion dependent on phospholipase Cβ. These transgenic C. elegans models provide a unique way to study the consequences of G(i/o) and G(q) signaling in vivo with temporal and spatial precision and, by analogy, their relationship to human neuromotor function.
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Affiliation(s)
- Pengxiu Cao
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106-4965, USA
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26
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Elgeti M, Kazmin R, Heck M, Morizumi T, Ritter E, Scheerer P, Ernst OP, Siebert F, Hofmann KP, Bartl FJ. Conserved Tyr223(5.58) plays different roles in the activation and G-protein interaction of rhodopsin. J Am Chem Soc 2011; 133:7159-65. [PMID: 21506561 DOI: 10.1021/ja200545n] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Rhodopsin, a seven transmembrane helix (TM) receptor, binds its ligand 11-cis-retinal via a protonated Schiff base. Coupling to the G-protein transducin (G(t)) occurs after light-induced cis/trans-retinal isomerization, which leads through photoproducts into a sequence of metarhodopsin (Meta) states: Meta I ⇌ Meta IIa ⇌ Meta IIb ⇌ Meta IIbH(+). The structural changes behind this three-step activation scheme are mediated by microswitch domains consisting of conserved amino acids. Here we focus on Tyr223(5.58) as part of the Y(5.58)X(7)K(R)(5.66) motif. Mutation to Ala, Phe, or Glu results in specific impairments of G(t)-activation measured by intrinsic G(t) fluorescence. UV-vis/FTIR spectroscopy of rhodopsin and its complex with a C-terminal G(t)α peptide allows the assignment of these deficiencies to specific steps in the activation path. Effects of mutation occur already in Meta I but do not directly influence deprotonation of the Schiff base during formation of Meta IIa. Absence of the whole phenol ring (Y223A) allows the activating motion of TM6 in Meta IIb but impairs the coupling to G(t). When only the hydroxyl group is lacking (Y223F), Meta IIb does not accumulate, but the activity toward G(t) remains substantial. From the FTIR features of Meta IIbH(+) we conclude that proton uptake to Glu134(3.49) is mandatory for Tyr223(5.58) to engage in the interaction with the key player Arg135(3.50) predicted by X-ray analysis. This polar interaction is partially recovered in Y223E, explaining its relatively high activity. Only the phenol side chain of tyrosine provides all characteristics for accumulation of the active state and G-protein activation.
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Affiliation(s)
- Matthias Elgeti
- Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, Berlin, Germany.
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deGrip WJ, Bovee-Geurts PHM, Wang Y, Verhoeven MA, Lugtenburg J. Cyclopropyl and isopropyl derivatives of 11-cis and 9-cis retinals at C-9 and C-13: subtle steric differences with major effects on ligand efficacy in rhodopsin. JOURNAL OF NATURAL PRODUCTS 2011; 74:383-390. [PMID: 21309593 DOI: 10.1021/np100744v] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Retinal is the natural ligand (chromophore) of the vertebrate rod visual pigment. It occurs in either the 11-cis (rhodopsin) or the 9-cis (isorhodopsin) configuration. In its evolution to a G protein coupled photoreceptor, rhodopsin has acquired exceptional photochemical properties. Illumination isomerizes the chromophore to the all-trans isomer, which acts as a full agonist. This process is extremely efficient, and there is abundant evidence that the C-9 and C-13 methyl groups of retinal play a pivotal role in this process. To examine the steric limits of the C-9 and C-13 methyl binding pocket of the binding site, we have prepared C-9 and C-13 cyclopropyl and isopropyl derivatives of its native ligands and of α-retinal at C-9. Most isopropyl analogues show very poor binding, except for 9-cis-13-isopropylretinal. Most cyclopropyl derivatives exhibit intermediate binding activity, except for 9-cis-13-cyclopropylretinal, which presents good binding activity. In general, the binding site shows preference for the 9-cis analogues over the 11-cis analogues. In fact, 13-isopropyl-9-cis-retinal acts as a superagonist after illumination. Another surprising finding was that 9-cyclopropylisorhodopsin is more like native rhodopsin with respect to spectral and photochemical properties, whereas 9-cyclopropylrhodopsin behaves more like native isorhodopsin in these aspects.
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Affiliation(s)
- Willem J deGrip
- Department of Biochemistry, UMCN 286, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
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Huang CC, Orban T, Jastrzebska B, Palczewski K, Tesmer JJG. Activation of G protein-coupled receptor kinase 1 involves interactions between its N-terminal region and its kinase domain. Biochemistry 2011; 50:1940-9. [PMID: 21265573 PMCID: PMC3069497 DOI: 10.1021/bi101606e] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
G protein-coupled receptor kinases (GRKs) phosphorylate activated G protein-coupled receptors (GPCRs) to initiate receptor desensitization. In addition to the canonical phosphoacceptor site of the kinase domain, activated receptors bind to a distinct docking site that confers higher affinity and activates GRKs allosterically. Recent mutagenesis and structural studies support a model in which receptor docking activates a GRK by stabilizing the interaction of its ∼20-amino acid N-terminal region with the kinase domain. This interaction in turn stabilizes a closed, more active conformation of the enzyme. To investigate the importance of this interaction for the process of GRK activation, we first validated the functionality of the N-terminal region in rhodopsin kinase (GRK1) by site-directed mutagenesis and then introduced a disulfide bond to cross-link the N-terminal region of GRK1 with its specific binding site on the kinase domain. Characterization of the kinetic and biophysical properties of the cross-linked protein showed that disulfide bond formation greatly enhances the catalytic efficiency of the peptide phosphorylation, but receptor-dependent phosphorylation, Meta II stabilization, and inhibition of transducin activation were unaffected. These data indicate that the interaction of the N-terminal region with the kinase domain is important for GRK activation but does not dictate the affinity of GRKs for activated receptors.
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Affiliation(s)
- Chih-chin Huang
- Life Sciences Institute, 210 Washtenaw Avenue, University of Michigan, Ann Arbor, Michigan 48109-2216, United States
| | - Tivadar Orban
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965, United States
| | - Beata Jastrzebska
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965, United States
| | - Krzysztof Palczewski
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965, United States
| | - John J. G. Tesmer
- Life Sciences Institute, 210 Washtenaw Avenue, University of Michigan, Ann Arbor, Michigan 48109-2216, United States
- Department of Pharmacology, 210 Washtenaw Avenue, University of Michigan, Ann Arbor, Michigan 48109-2216, United States
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Abstract
G-protein-coupled receptors (GPCRs) are seven transmembrane helix (TM) proteins that transduce signals into living cells by binding extracellular ligands and coupling to intracellular heterotrimeric G proteins (Gαβγ). The photoreceptor rhodopsin couples to transducin and bears its ligand 11-cis-retinal covalently bound via a protonated Schiff base to the opsin apoprotein. Absorption of a photon causes retinal cis/trans isomerization and generates the agonist all-trans-retinal in situ. After early photoproducts, the active G-protein-binding intermediate metarhodopsin II (Meta II) is formed, in which the retinal Schiff base is still intact but deprotonated. Dissociation of the proton from the Schiff base breaks a major constraint in the protein and enables further activating steps, including an outward tilt of TM6 and formation of a large cytoplasmic crevice for uptake of the interacting C terminus of the Gα subunit. Owing to Schiff base hydrolysis, Meta II is short-lived and notoriously difficult to crystallize. We therefore soaked opsin crystals with all-trans-retinal to form Meta II, presuming that the crystal's high concentration of opsin in an active conformation (Ops*) may facilitate all-trans-retinal uptake and Schiff base formation. Here we present the 3.0 Å and 2.85 Å crystal structures, respectively, of Meta II alone or in complex with an 11-amino-acid C-terminal fragment derived from Gα (GαCT2). GαCT2 binds in a large crevice at the cytoplasmic side, akin to the binding of a similar Gα-derived peptide to Ops* (ref. 7). In the Meta II structures, the electron density from the retinal ligand seamlessly continues into the Lys 296 side chain, reflecting proper formation of the Schiff base linkage. The retinal is in a relaxed conformation and almost undistorted compared with pure crystalline all-trans-retinal. By comparison with early photoproducts we propose how retinal translocation and rotation induce the gross conformational changes characteristic for Meta II. The structures can now serve as models for the large GPCR family.
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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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Bovee-Geurts PHM, Fernández Fernández I, Liu RSH, Mathies RA, Lugtenburg J, DeGrip WJ. Fluoro Derivatives of Retinal Illuminate the Decisive Role of the C12-H Element in Photoisomerization and Rhodopsin Activation. J Am Chem Soc 2009; 131:17933-42. [DOI: 10.1021/ja907577p] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Petra H. M. Bovee-Geurts
- Department of Biochemistry, UMCN 286, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands, Department of BioOrganic Photochemistry, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands, Department of Chemistry, University of Hawaii at Manao, 2545 The Mall, Honolulu, Hawaii 96822, and Department of Chemistry, University of California, Berkeley, California 94720
| | - Isabelle Fernández Fernández
- Department of Biochemistry, UMCN 286, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands, Department of BioOrganic Photochemistry, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands, Department of Chemistry, University of Hawaii at Manao, 2545 The Mall, Honolulu, Hawaii 96822, and Department of Chemistry, University of California, Berkeley, California 94720
| | - Robert S. H. Liu
- Department of Biochemistry, UMCN 286, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands, Department of BioOrganic Photochemistry, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands, Department of Chemistry, University of Hawaii at Manao, 2545 The Mall, Honolulu, Hawaii 96822, and Department of Chemistry, University of California, Berkeley, California 94720
| | - Richard A. Mathies
- Department of Biochemistry, UMCN 286, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands, Department of BioOrganic Photochemistry, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands, Department of Chemistry, University of Hawaii at Manao, 2545 The Mall, Honolulu, Hawaii 96822, and Department of Chemistry, University of California, Berkeley, California 94720
| | - Johan Lugtenburg
- Department of Biochemistry, UMCN 286, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands, Department of BioOrganic Photochemistry, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands, Department of Chemistry, University of Hawaii at Manao, 2545 The Mall, Honolulu, Hawaii 96822, and Department of Chemistry, University of California, Berkeley, California 94720
| | - Willem J. DeGrip
- Department of Biochemistry, UMCN 286, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands, Department of BioOrganic Photochemistry, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands, Department of Chemistry, University of Hawaii at Manao, 2545 The Mall, Honolulu, Hawaii 96822, and Department of Chemistry, University of California, Berkeley, California 94720
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Madathil S, Fahmy K. Lipid protein interactions couple protonation to conformation in a conserved cytosolic domain of G protein-coupled receptors. J Biol Chem 2009; 284:28801-9. [PMID: 19706606 DOI: 10.1074/jbc.m109.002030] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The visual photoreceptor rhodopsin is a prototypical class I (rhodopsin-like) G protein-coupled receptor. Photoisomerization of the covalently bound ligand 11-cis-retinal leads to restructuring of the cytosolic face of rhodopsin. The ensuing protonation of Glu-134 in the class-conserved D(E)RY motif at the C-terminal end of transmembrane helix-3 promotes the formation of the G protein-activating state. Using transmembrane segments derived from helix-3 of bovine rhodopsin, we show that lipid protein interactions play a key role in this cytosolic "proton switch." Infrared and fluorescence spectroscopic pK(a) determinations reveal that the D(E)RY motif is an autonomous functional module coupling side chain neutralization to conformation and helix positioning as evidenced by side chain to lipid headgroup Foerster resonance energy transfer. The free enthalpies of helix stabilization and hydrophobic burial of the neutral carboxyl shift the side chain pK(a) into the range typical of Glu-134 in photoactivated rhodopsin. The lipid-mediated coupling mechanism is independent of interhelical contacts allowing its conservation without interference with the diversity of ligand-specific interactions in class I G protein-coupled receptors.
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Affiliation(s)
- Sineej Madathil
- Division of Biophysics, Institute of Radiochemistry, Forschungszentrum Dresden-Rossendorf, PF 510119, D-01314 Dresden, Germany
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Lüdeke S, Mahalingam M, Vogel R. Rhodopsin activation switches in a native membrane environment. Photochem Photobiol 2009; 85:437-41. [PMID: 19267869 DOI: 10.1111/j.1751-1097.2008.00490.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The elucidation of structure-function relationships of membrane proteins still poses a considerable challenge due to the sometimes profound influence of the lipid bilayer on the functional properties of the protein. The visual pigment rhodopsin is a prototype of the family of G protein-coupled transmembrane receptors and a considerable part of our knowledge on its activation mechanisms has been derived from studies on detergent-solubilized proteins. This includes in particular the events associated with the conformational transitions of the receptor from the still inactive Meta I to the Meta II photoproduct states, which are involved in signaling. These events involve disruption of an internal salt bridge of the retinal protonated Schiff base, movement of helices and proton uptake from the solvent by the conserved cytoplasmic E(D)RY network around Glu134. As the equilibria associated with these events are considerably altered by the detergent environment, we set out to investigate these equilibria in the native membrane environment and to develop a coherent thermodynamic model of these activating steps using UV-visible and Fourier-transform infrared spectroscopy as complementary techniques. Particular emphasis is put on the role of protonation of Glu134 from the solvent, which is a thermodynamic prerequisite for full receptor activation in membranes, but not in detergent. In view of the conservation of this carboxylate group in family A G protein-coupled receptors, it may also play a similar role in the activation of other family members.
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Affiliation(s)
- Steffen Lüdeke
- Institute of Molecular Medicine and Cell Research, Albert-Ludwigs-University Freiburg, Freiburg, Germany
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Park PSH, Sapra KT, Jastrzebska B, Maeda T, Maeda A, Pulawski W, Kono M, Lem J, Crouch RK, Filipek S, Müller DJ, Palczewski K. Modulation of molecular interactions and function by rhodopsin palmitylation. Biochemistry 2009; 48:4294-304. [PMID: 19348429 DOI: 10.1021/bi900417b] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Rhodopsin is palmitylated at two cysteine residues in its carboxyl terminal region. We have looked at the effects of palmitylation on the molecular interactions formed by rhodopsin using single-molecule force spectroscopy and the function of rhodopsin using both in vitro and in vivo approaches. A knockin mouse model expressing palmitate-deficient rhodopsin was used for live animal in vivo studies and to obtain native tissue samples for in vitro assays. We specifically looked at the effects of palmitylation on the chromophore-binding pocket, interactions of rhodopsin with transducin, and molecular interactions stabilizing the receptor structure. The structure of rhodopsin is largely unperturbed by the absence of palmitate linkage. The binding pocket for the chromophore 11-cis-retinal is minimally altered as palmitate-deficient rhodopsin exhibited the same absorbance spectrum as wild-type rhodopsin. Similarly, the rate of release of all-trans-retinal after light activation was the same both in the presence and absence of palmitylation. Significant differences were observed in the rate of transducin activation by rhodopsin and in the force required to unfold the last stable structural segment in rhodopsin at its carboxyl terminal end. A 1.3-fold reduction in the rate of transducin activation by rhodopsin was observed in the absence of palmitylation. Single-molecule force spectroscopy revealed a 2.1-fold reduction in the normalized force required to unfold the carboxyl terminal end of rhodopsin. The absence of palmitylation in rhodopsin therefore destabilizes the molecular interactions formed in the carboxyl terminal end of the receptor, which appears to hinder the activation of transducin by light-activated rhodopsin.
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Affiliation(s)
- Paul S-H Park
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, Ohio 44106, USA.
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Goc A, Angel TE, Jastrzebska B, Wang B, Wintrode PL, Palczewski K. Different properties of the native and reconstituted heterotrimeric G protein transducin. Biochemistry 2009; 47:12409-19. [PMID: 18975915 DOI: 10.1021/bi8015444] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Visual signal transduction serves as one of the best understood G protein-coupled receptor signaling systems. Signaling is initiated when a photon strikes rhodopsin (Rho) causing a conformational change leading to productive interaction of this G protein-coupled receptor with the heterotrimeric G protein, transducin (Gt). Here we describe a new method for Gt purification from native bovine rod photoreceptor membranes without subunit dissociation caused by exposure to photoactivated rhodopsin (Rho*). Native electrophoresis followed by immunoblotting revealed that Gt purified by this method formed more stable heterotrimers and interacted more efficiently with membranes containing Rho* or its target, phosphodiesterase 6, than did Gt purified by a traditional method involving subunit dissociation and reconstitution in solution without membranes. Because these differences could result from selective extraction, we characterized the type and amount of posttranslational modifications on both purified native and reconstituted Gt preparations. Similar N-terminal acylation of the Gtalpha subunit was observed for both proteins as was farnesylation and methylation of the terminal Gtgamma subunit Cys residue. However, hydrogen/deuterium exchange experiments revealed less incorporation of deuterium into the Gtalpha and Gtbeta subunits of native Gt as compared to reconstituted Gt. These findings may indicate differences in conformation and heterotrimer complex formation between the two preparations or altered stability of the reconstituted Gt that assembles differently than the native protein. Therefore, Gt extracted and purified without subunit dissociation appears to be more appropriate for future studies.
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Affiliation(s)
- Anna Goc
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965, USA
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Morizumi T, Kimata N, Terakita A, Imamoto Y, Yamashita T, Shichida Y. G Protein Subtype Specificity of Rhodopsin Intermediates Metarhodopsin Ib and Metarhodopsin II. Photochem Photobiol 2009; 85:57-62. [DOI: 10.1111/j.1751-1097.2008.00396.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Two protonation switches control rhodopsin activation in membranes. Proc Natl Acad Sci U S A 2008; 105:17795-800. [PMID: 18997017 DOI: 10.1073/pnas.0804541105] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Activation of the G protein-coupled receptor (GPCR) rhodopsin is initiated by light-induced isomerization of the retinal ligand, which triggers 2 protonation switches in the conformational transition to the active receptor state Meta II. The first switch involves disruption of an interhelical salt bridge by internal proton transfer from the retinal protonated Schiff base (PSB) to its counterion, Glu-113, in the transmembrane domain. The second switch consists of uptake of a proton from the solvent by Glu-134 of the conserved E(D)RY motif at the cytoplasmic terminus of helix 3, leading to pH-dependent receptor activation. By using a combination of UV-visible and FTIR spectroscopy, we study the activation mechanism of rhodopsin in different membrane environments and show that these 2 protonation switches become partially uncoupled at physiological temperature. This partial uncoupling leads to approximately 50% population of an entropy-stabilized Meta II state in which the interhelical PSB salt bridge is broken and activating helix movements have taken place but in which Glu-134 remains unprotonated. This partial activation is converted to full activation only by coupling to the pH-dependent protonation of Glu-134 from the solvent, which stabilizes the active receptor conformation by lowering its enthalpy. In a membrane environment, protonation of Glu-134 is therefore a thermodynamic rather than a structural prerequisite for activating helix movements. In light of the conservation of the E(D)RY motif in rhodopsin-like GPCRs, protonation of this carboxylate also may serve a similar function in signal transduction of other members of this receptor family.
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Scheerer P, Park JH, Hildebrand PW, Kim YJ, Krauss N, Choe HW, Hofmann KP, Ernst OP. Crystal structure of opsin in its G-protein-interacting conformation. Nature 2008; 455:497-502. [PMID: 18818650 DOI: 10.1038/nature07330] [Citation(s) in RCA: 854] [Impact Index Per Article: 53.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2008] [Accepted: 08/08/2008] [Indexed: 12/14/2022]
Abstract
Opsin, the ligand-free form of the G-protein-coupled receptor rhodopsin, at low pH adopts a conformationally distinct, active G-protein-binding state known as Ops*. A synthetic peptide derived from the main binding site of the heterotrimeric G protein-the carboxy terminus of the alpha-subunit (GalphaCT)-stabilizes Ops*. Here we present the 3.2 A crystal structure of the bovine Ops*-GalphaCT peptide complex. GalphaCT binds to a site in opsin that is opened by an outward tilt of transmembrane helix (TM) 6, a pairing of TM5 and TM6, and a restructured TM7-helix 8 kink. Contacts along the inner surface of TM5 and TM6 induce an alpha-helical conformation in GalphaCT with a C-terminal reverse turn. Main-chain carbonyl groups in the reverse turn constitute the centre of a hydrogen-bonded network, which links the two receptor regions containing the conserved E(D)RY and NPxxY(x)(5,6)F motifs. On the basis of the Ops*-GalphaCT structure and known conformational changes in Galpha, we discuss signal transfer from the receptor to the G protein nucleotide-binding site.
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Affiliation(s)
- Patrick Scheerer
- Institut für Medizinische Physik und Biophysik (CC2), Charité - Universitätsmedizin Berlin, Charitéplatz 1, D-10117 Berlin, Germany
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Functional role of the "ionic lock"--an interhelical hydrogen-bond network in family A heptahelical receptors. J Mol Biol 2008; 380:648-55. [PMID: 18554610 DOI: 10.1016/j.jmb.2008.05.022] [Citation(s) in RCA: 132] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2008] [Revised: 05/06/2008] [Accepted: 05/09/2008] [Indexed: 11/23/2022]
Abstract
Activation of family A G-protein-coupled receptors involves a rearrangement of a conserved interhelical cytoplasmic hydrogen bond network between the E(D)RY motif on transmembrane helix 3 (H3) and residues on H6, which is commonly termed the cytoplasmic "ionic lock." Glu134(3.49) of the E(D)RY motif also forms an intrahelical salt bridge with neighboring Arg135(3.50) in the dark-state crystal structure of rhodopsin. We examined the roles of Glu134(3.49) and Arg135(3.50) on H3 and Glu247(6.30) and Glu249(6.32) on H6 on the activation of rhodopsin using Fourier transform infrared spectroscopy of wild-type and mutant pigments reconstituted into lipid membranes. Activation of rhodopsin is pH-dependent with proton uptake during the transition from the inactive Meta I to the active Meta II state. Glu134(3.49) of the ERY motif is identified as the proton-accepting group, using the Fourier transform infrared protonation signature and the absence of a pH dependence of activation in the E134Q mutant. Neutralization of Arg135(3.50) similarly leads to pH-independent receptor activation, but with structural alterations in the Meta II state. Neutralization of Glu247(6.30) and Glu249(6.32) on H6, which are involved in interhelical interactions with H3 and H7, respectively, led to a shift toward Meta II in the E247Q and E249Q mutants while retaining the pH sensitivity of the equilibrium. Disruption of the interhelical interaction of Glu247(6.30) and Glu249(6.32) on H6 with H3 and H7 plays its role during receptor activation, but neutralization of the intrahelical salt bridge between Glu134(3.49) and Arg135(3.50) is considerably more critical for shifting the photoproduct equilibrium to the active conformation. These conclusions are discussed in the context of recent structural data of the beta(2)-adrenergic receptor.
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Marin VL, Bayburt TH, Sligar SG, Mrksich M. Functional assays of membrane-bound proteins with SAMDI-TOF mass spectrometry. Angew Chem Int Ed Engl 2008; 46:8796-8. [PMID: 17943935 PMCID: PMC2790068 DOI: 10.1002/anie.200702694] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Violeta L Marin
- Department of Chemistry and Howard Hughes Medical Institute, University of Chicago, 929 East 57th Street, Chicago, IL 60637, USA
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47
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Marin V, Bayburt T, Sligar S, Mrksich M. Functional Assays of Membrane-Bound Proteins with SAMDI-TOF Mass Spectrometry. Angew Chem Int Ed Engl 2007. [DOI: 10.1002/ange.200702694] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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48
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Whorton MR, Jastrzebska B, Park PSH, Fotiadis D, Engel A, Palczewski K, Sunahara RK. Efficient coupling of transducin to monomeric rhodopsin in a phospholipid bilayer. J Biol Chem 2007; 283:4387-94. [PMID: 18033822 DOI: 10.1074/jbc.m703346200] [Citation(s) in RCA: 218] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
G protein-coupled receptors (GPCRs) are seven transmembrane domain proteins that transduce extracellular signals across the plasma membrane and couple to the heterotrimeric family of G proteins. Like most intrinsic membrane proteins, GPCRs are capable of oligomerization, the function of which has only been established for a few different receptor systems. One challenge in understanding the function of oligomers relates to the inability to separate monomeric and oligomeric receptor complexes in membrane environments. Here we report the reconstitution of bovine rhodopsin, a GPCR expressed in the retina, into an apolipoprotein A-I phospholipid particle, derived from high density lipoprotein (HDL). We demonstrate that rhodopsin, when incorporated into these 10 nm reconstituted HDL (rHDL) particles, is monomeric and functional. Rhodopsin.rHDL maintains the appropriate spectral properties with respect to photoactivation and formation of the active form, metarhodopsin II. Additionally, the kinetics of metarhodopsin II decay is similar between rhodopsin in native membranes and rhodopsin in rHDL particles. Photoactivation of monomeric rhodopsin.rHDL also results in the rapid activation of transducin, at a rate that is comparable with that found in native rod outer segments and 20-fold faster than rhodopsin in detergent micelles. These data suggest that monomeric rhodopsin is the minimal functional unit in G protein activation and that oligomerization is not absolutely required for this process.
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Affiliation(s)
- Matthew R Whorton
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0632, USA
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Bayburt TH, Leitz AJ, Xie G, Oprian DD, Sligar SG. Transducin activation by nanoscale lipid bilayers containing one and two rhodopsins. J Biol Chem 2007; 282:14875-81. [PMID: 17395586 DOI: 10.1074/jbc.m701433200] [Citation(s) in RCA: 296] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nanodiscs are nanometer scale planar membranes of controlled size that are rendered soluble in aqueous solution via an encircling amphipathic membrane scaffold protein "belt" (Bayburt, T. H., Grinkova, Y. V., and Sligar, S. G. (2002) Nano. Lett. 2, 853-856). Integral membrane proteins can be self-assembled into the Nanodisc bilayer with defined stoichiometry, which allows an unprecedented opportunity to investigate the nature of the oligomerization state of a G-protein-coupled receptor and its coupling to heterotrimeric G-proteins. We generated Nanodiscs having one and two rhodopsins present in the 10-nm-diameter lipid bilayer domain. Efficient transducin activation and isolation of a high affinity transducin-metarhodopsin II complex was demonstrated for a monodisperse and monomeric receptor. A population of Nanodiscs containing two rhodopsins was generated using an increased ratio of receptor to membrane scaffold protein in the self-assembly mixture. The two-rhodopsin population was isolated and purified by density gradient centrifugation. Interestingly, in this case, only one of the two receptors present in the Nanodisc was able to form a stable metarhodopsin II-G-protein complex. Thus there is clear evidence that a monomeric rhodopsin is capable of full coupling to transducin. Importantly, presumably due to steric interactions, it appears that only a single receptor in the Nanodiscs containing two rhodopsins can interact with G-protein. These results have important implications for the stoichiometry of receptor-G-protein coupling and cross talk in signaling pathways.
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Affiliation(s)
- Timothy H Bayburt
- Department of Biochemistry, University of Illinois, Urbana, Illinois 61801, USA
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Crozier PS, Stevens MJ, Woolf TB. How a small change in retinal leads to G-protein activation: initial events suggested by molecular dynamics calculations. Proteins 2007; 66:559-74. [PMID: 17109408 PMCID: PMC2848121 DOI: 10.1002/prot.21175] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Rhodopsin is the prototypical G-protein coupled receptor, coupling light activation with high efficiency to signaling molecules. The dark-state X-ray structures of the protein provide a starting point for consideration of the relaxation from initial light activation to conformational changes that may lead to signaling. In this study we create an energetically unstable retinal in the light activated state and then use molecular dynamics simulations to examine the types of compensation, relaxation, and conformational changes that occur following the cis-trans light activation. The results suggest that changes occur throughout the protein, with changes in the orientation of Helices 5 and 6, a closer interaction between Ala 169 on Helix 4 and retinal, and a shift in the Schiff base counterion that also reflects changes in sidechain interactions with the retinal. Taken together, the simulation is suggestive of the types of changes that lead from local conformational change to light-activated signaling in this prototypical system.
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Affiliation(s)
- Paul S Crozier
- Sandia National Laboratories, MS 1322, Albuquerque, New Mexico 87185-1322, USA.
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