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Mukhaleva E, Yang T, Sadler F, Sivaramakrishnan S, Ma N, Vaidehi N. Cellular lipids regulate the conformational ensembles of the disordered intracellular loop 3 in β2-adrenergic receptor. iScience 2024; 27:110086. [PMID: 38947516 PMCID: PMC11214514 DOI: 10.1016/j.isci.2024.110086] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2023] [Revised: 03/19/2024] [Accepted: 05/20/2024] [Indexed: 07/02/2024] Open
Abstract
The intracellular loops of G protein-coupled receptors (GPCRs) have been shown to play a key role in G protein coupling and selectivity. We recently showed that the intrinsically disordered third intracellular loop (ICL3) of β2-adrenergic receptor is dynamic and equilibrates between open and closed conformations to regulate the G protein coupling. In this study, using the extensive molecular dynamics simulations in multi-lipid bilayer models, we show that the lipid phosphatidylinositol 4,5-bisphosphate (PIP2) stabilizes the active state of β2-adrenergic receptor by keeping ICL3 in an open conformation. This stabilization results in a tilt of the receptor within the membrane. Additionally, the ganglioside lipid, GM3 interacts with extracellular loops, impacting the ligand binding site allosterically. This demonstrates the active role of the chemistry of lipids in stabilizing specific GPCR conformations.
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Affiliation(s)
- Elizaveta Mukhaleva
- Irell and Manella Graduate School of Biological Sciences, Beckman Research Institute of the City of Hope, Duarte, CA, USA
- Department of Computational and Quantitative Medicine, Beckman Research Institute of the City of Hope, Duarte, CA, USA
| | - Tianyi Yang
- Irell and Manella Graduate School of Biological Sciences, Beckman Research Institute of the City of Hope, Duarte, CA, USA
| | - Fredrik Sadler
- Biochemistry, Molecular Biology and Biophysics Graduate Program, University of Minnesota, Minneapolis, MN, USA
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN, USA
| | - Sivaraj Sivaramakrishnan
- Biochemistry, Molecular Biology and Biophysics Graduate Program, University of Minnesota, Minneapolis, MN, USA
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN, USA
| | - Ning Ma
- Irell and Manella Graduate School of Biological Sciences, Beckman Research Institute of the City of Hope, Duarte, CA, USA
| | - Nagarajan Vaidehi
- Irell and Manella Graduate School of Biological Sciences, Beckman Research Institute of the City of Hope, Duarte, CA, USA
- Department of Computational and Quantitative Medicine, Beckman Research Institute of the City of Hope, Duarte, CA, USA
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Schafer CT, Pauszek RF, Gustavsson M, Handel TM, Millar DP. Distinct Activation Mechanisms of CXCR4 and ACKR3 Revealed by Single-Molecule Analysis of their Conformational Landscapes. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.10.31.564925. [PMID: 37961571 PMCID: PMC10635023 DOI: 10.1101/2023.10.31.564925] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2023]
Abstract
The canonical chemokine receptor CXCR4 and atypical receptor ACKR3 both respond to CXCL12 but induce different effector responses to regulate cell migration. While CXCR4 couples to G proteins and directly promotes cell migration, ACKR3 is G protein-independent and scavenges CXCL12 to regulate extracellular chemokine levels and maintain CXCR4 responsiveness, thereby indirectly influencing migration. The receptors also have distinct activation requirements. CXCR4 only responds to wild-type CXCL12 and is sensitive to mutation of the chemokine. By contrast, ACKR3 recruits GPCR kinases (GRKs) and β-arrestins and promiscuously responds to CXCL12, CXCL12 variants, other peptides and proteins, and is relatively insensitive to mutation. To investigate the role of conformational dynamics in the distinct pharmacological behaviors of CXCR4 and ACKR3, we employed single-molecule FRET to track discrete conformational states of the receptors in real-time. The data revealed that apo-CXCR4 preferentially populates a high-FRET inactive state, while apo-ACKR3 shows little conformational preference and high transition probabilities among multiple inactive, intermediate and active conformations, consistent with its propensity for activation. Multiple active-like ACKR3 conformations are populated in response to agonists, compared to the single CXCR4 active-state. This and the markedly different conformational landscapes of the receptors suggest that activation of ACKR3 may be achieved by a broader distribution of conformational states than CXCR4. Much of the conformational heterogeneity of ACKR3 is linked to a single residue that differs between ACKR3 and CXCR4. The dynamic properties of ACKR3 may underly its inability to form productive interactions with G proteins that would drive canonical GPCR signaling.
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Affiliation(s)
- Christopher T. Schafer
- Skaggs School of Pharmacy and Pharmaceutical Sciences, Department of Pharmacology, University of California San Diego, La Jolla, CA 92037
| | - Raymond F. Pauszek
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037
| | - Martin Gustavsson
- Skaggs School of Pharmacy and Pharmaceutical Sciences, Department of Pharmacology, University of California San Diego, La Jolla, CA 92037
| | - Tracy M. Handel
- Skaggs School of Pharmacy and Pharmaceutical Sciences, Department of Pharmacology, University of California San Diego, La Jolla, CA 92037
| | - David P. Millar
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037
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3
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Shumate AD, Farrens DL. A rapid, tag-free way to purify functional GPCRs. J Biol Chem 2024; 300:105558. [PMID: 38097184 PMCID: PMC10820827 DOI: 10.1016/j.jbc.2023.105558] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2023] [Revised: 12/01/2023] [Accepted: 12/05/2023] [Indexed: 01/14/2024] Open
Abstract
G protein-coupled receptors (GPCRs) play diverse signaling roles and represent major pharmaceutical targets. Consequently, they are the focus of intense study, and numerous advances have been made in their handling and analysis. However, a universal way to purify GPCRs has remained elusive, in part because of their inherent instability when isolated from cells. To address this, we have developed a general, rapid, and tag-free way to purify GPCRs. The method uses short peptide analogs of the Gα subunit C terminus (Gα-CT) that are attached to chromatography beads (Gα-CT resin). Because the Gα-CT peptides bind active GPCRs with high affinity, the Gα-CT resin selectively purifies only active functional receptors. We use this method to purify both rhodopsin and the β2-adrenergic receptor and show they can be purified in either active conformations or inactive conformations, simply by varying elution conditions. While simple in concept-leveraging the conserved GPCR-Gα-CT binding interaction for the purpose of GPCR purification-we think this approach holds excellent potential to isolate functional receptors for a myriad of uses, from structural biology to proteomics.
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Affiliation(s)
- Anthony D Shumate
- Department of Chemical Biology and Physiology, Oregon Health and Science University, Portland, Oregon, USA
| | - David L Farrens
- Department of Chemical Biology and Physiology, Oregon Health and Science University, Portland, Oregon, USA.
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4
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Mukhaleva E, Yang T, Sadler F, Sivaramakrishnan S, Ma N, Vaidehi N. Cellular Lipids Regulate the Conformational Ensembles of the Disordered Intracellular Loop 3 in β2 Adrenergic Receptor. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.11.28.569080. [PMID: 38077083 PMCID: PMC10705491 DOI: 10.1101/2023.11.28.569080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/21/2023]
Abstract
The structurally disordered intracellular loops (ICLs) of G protein-coupled receptors (GPCRs) play a critical role in G protein coupling. In our previous work, we used a combination of FRET-based and computational methodologies to show that the third intracellular loop (ICL3) modulates the activity and G protein coupling selectivity in GPCRs. In the current study, we have uncovered the role of several lipid components in modulating the conformational ensemble of ICL3 of the β2-adrenergic receptor (β2AR). Our findings indicate that phosphatidylinositol 4,5-bisphosphate (PIP2) in the inner leaflet of the membrane bilayer acts as a stabilizing anchor for ICL3, opening the intracellular cavity to facilitate G protein coupling. This interaction between PIP2 and ICL3 causes tilting of β2AR within the cellular membrane. Notably, this tilting of the receptor is supported by ganglioside GM3 stabilizing the extracellular loops on the outer leaflet of the bilayer, thereby exerting an allosteric effect on the orthosteric ligand binding pocket. Our results underscore the significance of lipids in modulating GPCR activity, proposing an allosteric mechanism that occurs through the receptor's orientation within the membrane.
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Affiliation(s)
- Elizaveta Mukhaleva
- Irell and Manella Graduate School of Biological Sciences, Beckman Research Institute of the City of Hope, Duarte, CA, USA
- Department of Computational and Quantitative Medicine, Beckman Research Institute of the City of Hope, Duarte, CA, USA
| | - Tianyi Yang
- Irell and Manella Graduate School of Biological Sciences, Beckman Research Institute of the City of Hope, Duarte, CA, USA
| | - Fredrik Sadler
- Biochemistry, Molecular Biology and Biophysics Graduate Program, University of Minnesota, Minneapolis, MN, USA
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN, USA
| | - Sivaraj Sivaramakrishnan
- Biochemistry, Molecular Biology and Biophysics Graduate Program, University of Minnesota, Minneapolis, MN, USA
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN, USA
| | - Ning Ma
- Irell and Manella Graduate School of Biological Sciences, Beckman Research Institute of the City of Hope, Duarte, CA, USA
| | - Nagarajan Vaidehi
- Irell and Manella Graduate School of Biological Sciences, Beckman Research Institute of the City of Hope, Duarte, CA, USA
- Department of Computational and Quantitative Medicine, Beckman Research Institute of the City of Hope, Duarte, CA, USA
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5
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Sadee W. Ligand-Free Signaling of G-Protein-Coupled Receptors: Physiology, Pharmacology, and Genetics. Molecules 2023; 28:6375. [PMID: 37687205 PMCID: PMC10489045 DOI: 10.3390/molecules28176375] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2023] [Revised: 08/28/2023] [Accepted: 08/30/2023] [Indexed: 09/10/2023] Open
Abstract
G-protein-coupled receptors (GPCRs) are ubiquitous sensors and regulators of cellular functions. Each GPCR exists in complex aggregates with multiple resting and active conformations. Designed to detect weak stimuli, GPCRs can also activate spontaneously, resulting in basal ligand-free signaling. Agonists trigger a cascade of events leading to an activated agonist-receptor G-protein complex with high agonist affinity. However, the ensuing signaling process can further remodel the receptor complex to reduce agonist affinity, causing rapid ligand dissociation. The acutely activated ligand-free receptor can continue signaling, as proposed for rhodopsin and μ opioid receptors, resulting in robust receptor activation at low agonist occupancy with enhanced agonist potency. Continued receptor stimulation can further modify the receptor complex, regulating sustained ligand-free signaling-proposed to play a role in opioid dependence. Basal, acutely agonist-triggered, and sustained elevated ligand-free signaling could each have distinct functions, reflecting multi-state conformations of GPCRs. This review addresses basal and stimulus-activated ligand-free signaling, its regulation, genetic factors, and pharmacological implications, focusing on opioid and serotonin receptors, and the growth hormone secretagogue receptor (GHSR). The hypothesis is proposed that ligand-free signaling of 5-HT2A receptors mediate therapeutic effects of psychedelic drugs. Research avenues are suggested to close the gaps in our knowledge of ligand-free GPCR signaling.
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Affiliation(s)
- Wolfgang Sadee
- Cancer Biology and Genetics, College of Medicine, The Ohio State University, Columbus, OH 43210, USA;
- Bioengineering and Therapeutic Sciences, University of California, San Francisco, CA 94158, USA
- Aether Therapeutics Inc., Austin, TX 78756, USA
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Tian H, Gunnison KM, Kazmi MA, Sakmar TP, Huber T. FRET sensors reveal the retinal entry pathway in the G protein-coupled receptor rhodopsin. iScience 2022; 25:104060. [PMID: 35355518 PMCID: PMC8958324 DOI: 10.1016/j.isci.2022.104060] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2021] [Revised: 01/11/2022] [Accepted: 03/04/2022] [Indexed: 11/26/2022] Open
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Brahma R, Raghuraman H. Measuring Membrane Penetration Depths and Conformational Changes in Membrane Peptides and Proteins. J Membr Biol 2022; 255:469-483. [PMID: 35274157 DOI: 10.1007/s00232-022-00224-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2022] [Accepted: 02/23/2022] [Indexed: 10/18/2022]
Abstract
The structural organization and dynamic nature of the biomembrane components are important determinants for numerous cellular functions. Particularly, membrane proteins are critically important for various physiological functions and are important drug targets. The mechanistic insights on the complex functionality of membrane lipids and proteins can be elucidated by understanding the interplay between structure and dynamics. In this regard, membrane penetration depth represents an important parameter to obtain the precise depth of membrane-embedded molecules that often define the conformation and topology of membrane probes and proteins. In this review, we discuss about the widely used fluorescence quenching-based methods (parallax method, distribution analysis, and dual-quencher analysis) to accurately determine the membrane penetration depths of fluorescent probes that are either membrane-embedded or attached to lipids and proteins. Further, we also discuss a relatively novel fluorescence quenching method that utilizes tryptophan residue as the quencher, namely the tryptophan-induced quenching, which is sensitive to monitor small-scale conformational changes (short distances of < 15 Å) and useful in mapping distances in proteins. We have provided numerous examples for the benefit of readers to appreciate the importance and applicability of these simple yet powerful methods to study membrane proteins.
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Affiliation(s)
- Rupasree Brahma
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, A CI of Homi Bhabha National Institute, 1/AF, Bidhannagar, Kolkata, 700 064, India
| | - H Raghuraman
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, A CI of Homi Bhabha National Institute, 1/AF, Bidhannagar, Kolkata, 700 064, India.
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Schafer CT, Shumate A, Farrens DL. Novel fluorescent GPCR biosensor detects retinal equilibrium binding to opsin and active G protein and arrestin signaling conformations. J Biol Chem 2020; 295:17486-17496. [PMID: 33453993 DOI: 10.1074/jbc.ra120.014631] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Revised: 09/25/2020] [Indexed: 01/14/2023] Open
Abstract
Rhodopsin is a canonical class A photosensitive G protein-coupled receptor (GPCR), yet relatively few pharmaceutical agents targeting this visual receptor have been identified, in part due to the unique characteristics of its light-sensitive, covalently bound retinal ligands. Rhodopsin becomes activated when light isomerizes 11-cis-retinal into an agonist, all-trans-retinal (ATR), which enables the receptor to activate its G protein. We have previously demonstrated that, despite being covalently bound, ATR can display properties of equilibrium binding, yet how this is accomplished is unknown. Here, we describe a new approach for both identifying compounds that can activate and attenuate rhodopsin and testing the hypothesis that opsin binds retinal in equilibrium. Our method uses opsin-based fluorescent sensors, which directly report the formation of active receptor conformations by detecting the binding of G protein or arrestin fragments that have been fused onto the receptor's C terminus. We show that these biosensors can be used to monitor equilibrium binding of the agonist, ATR, as well as the noncovalent binding of β-ionone, an antagonist for G protein activation. Finally, we use these novel biosensors to observe ATR release from an activated, unlabeled receptor and its subsequent transfer to the sensor in real time. Taken together, these data support the retinal equilibrium binding hypothesis. The approach we describe should prove directly translatable to other GPCRs, providing a new tool for ligand discovery and mutant characterization.
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Affiliation(s)
- Christopher T Schafer
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Portland, Oregon, USA
| | - Anthony Shumate
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Portland, Oregon, USA
| | - David L Farrens
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Portland, Oregon, USA.
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9
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Ma N, Lee S, Vaidehi N. Activation Microswitches in Adenosine Receptor A 2A Function as Rheostats in the Cell Membrane. Biochemistry 2020; 59:4059-4071. [PMID: 33054162 PMCID: PMC8526178 DOI: 10.1021/acs.biochem.0c00626] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Although multiple components of the cell membrane modulate the stability and activation of G protein-coupled receptors (GPCRs), insights into the dynamics of GPCR structures come from biophysical studies conducted in detergents. This is because of the challenges of studying activation in a multicomponent lipid bilayer. To understand the role of cellular membrane lipids and cations in GPCR activation, we performed multiscale molecular dynamics simulations (56 μs) on three different conformational states of adenosine receptor A2AR, in both the cell membrane-like lipid bilayer and in detergent micelles. Molecular dynamics (MD) simulations show that the phosphatidylinositol bisphosphate (PIP2) interacts with the basic residues in the intracellular regions of A2AR, thereby reducing the flexibility of the receptor in the inactive state and limiting the transition to the active-intermediate state. In the G protein-coupled fully active state, PIP2 stabilizes the GPCR:G protein complex. Such stiffening effects are absent in non-ionic detergent micelles, and therefore, more transitions have been observed in detergents. The inter-residue distances that change significantly upon GPCR activation are known as activation microswitches. The activation microswitches show different levels of activation in the cell membrane, in the pure POPC bilayer, and in detergents. Thus, the temporal heat map of different activation microswitches calculated from the MD simulations suggests a rheostat model of GPCR activation microswitches rather than the binary switch model. These simulation results connect the chemistry of cell membrane lipids to receptor activity, which is useful for the design of detergents mimicking the cell membrane.
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Affiliation(s)
- Ning Ma
- Department of Computational and Quantitative Medicine, Beckman Research Institute of the City of Hope, 1500 E Duarte Road, Duarte, CA-91010
| | - Sangbae Lee
- Department of Computational and Quantitative Medicine, Beckman Research Institute of the City of Hope, 1500 E Duarte Road, Duarte, CA-91010
| | - Nagarajan Vaidehi
- Department of Computational and Quantitative Medicine, Beckman Research Institute of the City of Hope, 1500 E Duarte Road, Duarte, CA-91010
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10
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From extraocular photoreception to pigment movement regulation: a new control mechanism of the lanternshark luminescence. Sci Rep 2020; 10:10195. [PMID: 32576969 PMCID: PMC7311519 DOI: 10.1038/s41598-020-67287-w] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2020] [Accepted: 05/28/2020] [Indexed: 11/08/2022] Open
Abstract
The velvet belly lanternshark, Etmopterus spinax, uses counterillumination to disappear in the surrounding blue light of its marine environment. This shark displays hormonally controlled bioluminescence in which melatonin (MT) and prolactin (PRL) trigger light emission, while α-melanocyte-stimulating hormone (α-MSH) and adrenocorticotropic hormone (ACTH) play an inhibitory role. The extraocular encephalopsin (Es-Opn3) was also hypothesized to act as a luminescence regulator. The majority of these compounds (MT, α-MSH, ACTH, opsin) are members of the rapid physiological colour change that regulates the pigment motion within chromatophores in metazoans. Interestingly, the lanternshark photophore comprises a specific iris-like structure (ILS), partially composed of melanophore-like cells, serving as a photophore shutter. Here, we investigated the role of (i) Es-Opn3 and (ii) actors involved in both MT and α-MSH/ACTH pathways on the shark bioluminescence and ILS cell pigment motions. Our results reveal the implication of Es-Opn3, MT, inositol triphosphate (IP3), intracellular calcium, calcium-dependent calmodulin and dynein in the ILS cell pigment aggregation. Conversely, our results highlighted the implication of the α-MSH/ACTH pathway, involving kinesin, in the dispersion of the ILS cell pigment. The lanternshark luminescence then appears to be controlled by the balanced bidirectional motion of ILS cell pigments within the photophore. This suggests a functional link between photoreception and photoemission in the photogenic tissue of lanternsharks and gives precious insights into the bioluminescence control of these organisms.
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11
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Raghuraman H, Chatterjee S, Das A. Site-Directed Fluorescence Approaches for Dynamic Structural Biology of Membrane Peptides and Proteins. Front Mol Biosci 2019; 6:96. [PMID: 31608290 PMCID: PMC6774292 DOI: 10.3389/fmolb.2019.00096] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Accepted: 09/11/2019] [Indexed: 12/31/2022] Open
Abstract
Membrane proteins mediate a number of cellular functions and are associated with several diseases and also play a crucial role in pathogenicity. Due to their importance in cellular structure and function, they are important drug targets for ~60% of drugs available in the market. Despite the technological advancement and recent successful outcomes in determining the high-resolution structural snapshot of membrane proteins, the mechanistic details underlining the complex functionalities of membrane proteins is least understood. This is largely due to lack of structural dynamics information pertaining to different functional states of membrane proteins in a membrane environment. Fluorescence spectroscopy is a widely used technique in the analysis of functionally-relevant structure and dynamics of membrane protein. This review is focused on various site-directed fluorescence (SDFL) approaches and their applications to explore structural information, conformational changes, hydration dynamics, and lipid-protein interactions of important classes of membrane proteins that include the pore-forming peptides/proteins, ion channels/transporters and G-protein coupled receptors.
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Affiliation(s)
- H. Raghuraman
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, Kolkata, India
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12
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Rosenberg EM, Harrison RES, Tsou LK, Drucker N, Humphries B, Rajasekaran D, Luker KE, Wu CH, Song JS, Wang CJ, Murphy JW, Cheng YC, Shia KS, Luker GD, Morikis D, Lolis EJ. Characterization, Dynamics, and Mechanism of CXCR4 Antagonists on a Constitutively Active Mutant. Cell Chem Biol 2019; 26:662-673.e7. [PMID: 30827936 PMCID: PMC6736600 DOI: 10.1016/j.chembiol.2019.01.012] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Revised: 11/21/2018] [Accepted: 01/24/2019] [Indexed: 12/11/2022]
Abstract
The G protein-coupled receptor (GPCR) CXCR4 is a co-receptor for HIV and is involved in cancers and autoimmune diseases. We characterized five purine or quinazoline core polyamine pharmacophores used for targeting CXCR4 dysregulation in diseases. All were neutral antagonists for wild-type CXCR4 and two were biased antagonists with effects on β-arrestin-2 only at high concentrations. These compounds displayed various activities for a constitutively active mutant (CAM). We use the IT1t-CXCR4 crystal structure and molecular dynamics (MD) simulations to develop two hypotheses for the activation of the N1193.35A CAM. The N1193.35A mutation facilitates increased coupling of TM helices III and VI. IT1t deactivates the CAM by disrupting the coupling between TM helices III and VI, mediated primarily by residue F872.53. Mutants of F872.53 in N1193.35A CXCR4 precluded constitutive signaling and prevented inverse agonism. This work characterizes CXCR4 ligands and provides a mechanism for N1193.35A constitutive activation.
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Affiliation(s)
- Eric M Rosenberg
- Department of Pharmacology, Yale School of Medicine, New Haven, CT 06510, USA
| | - Reed E S Harrison
- Department of Bioengineering, Bourns College of Engineering, University of California, Riverside, CA 92507, USA
| | - Lun Kelvin Tsou
- Institute of Biotechnology and Pharmaceutical Research, National Health Research Institutes, Zhunan Town, Miaoli County 35053, Taiwan, R.O.C
| | - Natalie Drucker
- Department of Pharmacology, Yale School of Medicine, New Haven, CT 06510, USA
| | - Brock Humphries
- University of Michigan Center for Molecular Imaging, Department of Radiology, University of Michigan Medical School and College of Engineering, Ann Arbor, MI 48109, USA
| | - Deepa Rajasekaran
- Department of Pharmacology, Yale School of Medicine, New Haven, CT 06510, USA
| | - Kathryn E Luker
- University of Michigan Center for Molecular Imaging, Department of Radiology, University of Michigan Medical School and College of Engineering, Ann Arbor, MI 48109, USA
| | - Chien-Huang Wu
- Institute of Biotechnology and Pharmaceutical Research, National Health Research Institutes, Zhunan Town, Miaoli County 35053, Taiwan, R.O.C
| | - Jen-Shin Song
- Institute of Biotechnology and Pharmaceutical Research, National Health Research Institutes, Zhunan Town, Miaoli County 35053, Taiwan, R.O.C
| | - Chuan-Jen Wang
- Department of Pharmacology, Yale School of Medicine, New Haven, CT 06510, USA
| | - James W Murphy
- Department of Pharmacology, Yale School of Medicine, New Haven, CT 06510, USA
| | - Yung-Chi Cheng
- Department of Pharmacology, Yale School of Medicine, New Haven, CT 06510, USA
| | - Kak-Shan Shia
- Institute of Biotechnology and Pharmaceutical Research, National Health Research Institutes, Zhunan Town, Miaoli County 35053, Taiwan, R.O.C
| | - Gary D Luker
- University of Michigan Center for Molecular Imaging, Department of Radiology, University of Michigan Medical School and College of Engineering, Ann Arbor, MI 48109, USA
| | - Dimitrios Morikis
- Department of Bioengineering, Bourns College of Engineering, University of California, Riverside, CA 92507, USA
| | - Elias J Lolis
- Department of Pharmacology, Yale School of Medicine, New Haven, CT 06510, USA.
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13
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Computational Approaches to Prioritize Cancer Driver Missense Mutations. Int J Mol Sci 2018; 19:ijms19072113. [PMID: 30037003 PMCID: PMC6073793 DOI: 10.3390/ijms19072113] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Revised: 07/02/2018] [Accepted: 07/05/2018] [Indexed: 12/31/2022] Open
Abstract
Cancer is a complex disease that is driven by genetic alterations. There has been a rapid development of genome-wide techniques during the last decade along with a significant lowering of the cost of gene sequencing, which has generated widely available cancer genomic data. However, the interpretation of genomic data and the prediction of the association of genetic variations with cancer and disease phenotypes still requires significant improvement. Missense mutations, which can render proteins non-functional and provide a selective growth advantage to cancer cells, are frequently detected in cancer. Effects caused by missense mutations can be pinpointed by in silico modeling, which makes it more feasible to find a treatment and reverse the effect. Specific human phenotypes are largely determined by stability, activity, and interactions between proteins and other biomolecules that work together to execute specific cellular functions. Therefore, analysis of missense mutations’ effects on proteins and their complexes would provide important clues for identifying functionally important missense mutations, understanding the molecular mechanisms of cancer progression and facilitating treatment and prevention. Herein, we summarize the major computational approaches and tools that provide not only the classification of missense mutations as cancer drivers or passengers but also the molecular mechanisms induced by driver mutations. This review focuses on the discussion of annotation and prediction methods based on structural and biophysical data, analysis of somatic cancer missense mutations in 3D structures of proteins and their complexes, predictions of the effects of missense mutations on protein stability, protein-protein and protein-nucleic acid interactions, and assessment of conformational changes in protein conformations induced by mutations.
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14
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Maeda R, Hiroshima M, Yamashita T, Wada A, Sako Y, Shichida Y, Imamoto Y. Shift in Conformational Equilibrium Induces Constitutive Activity of G-Protein-Coupled Receptor, Rhodopsin. J Phys Chem B 2018; 122:4838-4843. [DOI: 10.1021/acs.jpcb.8b02819] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Ryo Maeda
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan
- Cellular Informatics Laboratory, RIKEN, Wako, Saitama, Japan
| | - Michio Hiroshima
- Cellular Informatics Laboratory, RIKEN, Wako, Saitama, Japan
- Laboratory for Cell Signaling Dynamics, RIKEN Quantitative Biology Center, Suita, Osaka, Japan
| | - Takahiro Yamashita
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan
| | - Akimori Wada
- Laboratory of Organic Chemistry for Life Science, Kobe Pharmaceutical University, Kobe, Hyogo, Japan
| | - Yasushi Sako
- Cellular Informatics Laboratory, RIKEN, Wako, Saitama, Japan
| | - Yoshinori Shichida
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan
- Research Organization for Science and Technology, Ritsumeikan University, Kusatsu, Shiga, Japan
| | - Yasushi Imamoto
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan
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15
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Tsukamoto H, Higashi M, Motoki H, Watanabe H, Ganser C, Nakajo K, Kubo Y, Uchihashi T, Furutani Y. Structural properties determining low K + affinity of the selectivity filter in the TWIK1 K + channel. J Biol Chem 2018; 293:6969-6984. [PMID: 29545310 DOI: 10.1074/jbc.ra118.001817] [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: 01/10/2018] [Revised: 03/14/2018] [Indexed: 11/06/2022] Open
Abstract
Canonical K+ channels are tetrameric and highly K+-selective, whereas two-pore-domain K+ (K2P) channels form dimers, but with a similar pore architecture. A two-pore-domain potassium channel TWIK1 (KCNK1 or K2P1) allows permeation of Na+ and other monovalent ions, resulting mainly from the presence of Thr-118 in the P1 domain. However, the mechanistic basis for this reduced selectivity is unclear. Using ion-exchange-induced difference IR spectroscopy, we analyzed WT TWIK1 and T118I (highly K+-selective) and L228F (substitution in the P2 domain) TWIK1 variants and found that in the presence of K+ ions, WT and both variants exhibit an amide-I band at 1680 cm-1 This band corresponds to interactions of the backbone carbonyls in the selectivity filter with K+, a feature very similar to that of the canonical K+ channel KcsA. Computational analysis indicated that the relatively high frequency for the amide-I band is well explained by impairment of hydrogen bond formation with water molecules. Moreover, concentration-dependent spectral changes indicated that the K+ affinity of the WT selectivity filter was much lower than those of the variants. Furthermore, only the variants displayed a higher frequency shift of the 1680-cm-1 band upon changes from K+ to Rb+ or Cs+ conditions. High-speed atomic force microscopy disclosed that TWIK1's surface morphology largely does not change in K+ and Na+ solutions. Our results reveal the local conformational changes of the TWIK1 selectivity filter and suggest that the amide-I bands may be useful "molecular fingerprints" for assessing the properties of other K+ channels.
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Affiliation(s)
- Hisao Tsukamoto
- From the Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, and.,Departments of Structural Molecular Science and
| | - Masahiro Higashi
- the Department of Chemistry, Biology and Marine Science, University of the Ryukyus, 1 Senbaru, Nishihara, Nakagami, Okinawa 903-0213
| | - Hideyoshi Motoki
- the Department of Chemistry, Biology and Marine Science, University of the Ryukyus, 1 Senbaru, Nishihara, Nakagami, Okinawa 903-0213
| | - Hiroki Watanabe
- the Department of Physics and Structural Biology Research Center, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, and
| | - Christian Ganser
- the Department of Physics and Structural Biology Research Center, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, and
| | - Koichi Nakajo
- the Division of Biophysics and Neurobiology, Department of Molecular and Cellular Physiology, National Institute for Physiological Sciences, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan.,Physiological Sciences, SOKENDAI (Graduate University for Advanced Studies), 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585
| | - Yoshihiro Kubo
- the Division of Biophysics and Neurobiology, Department of Molecular and Cellular Physiology, National Institute for Physiological Sciences, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan.,Physiological Sciences, SOKENDAI (Graduate University for Advanced Studies), 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585
| | - Takayuki Uchihashi
- the Department of Physics and Structural Biology Research Center, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, and
| | - Yuji Furutani
- From the Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, and .,Departments of Structural Molecular Science and
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16
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Purification of Functional CB 1 and Analysis by Site-Directed Fluorescence Labeling Methods. Methods Enzymol 2017; 593:343-370. [PMID: 28750810 DOI: 10.1016/bs.mie.2017.06.026] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The human cannabinoid receptor, CB1, has been difficult to purify in a functional form, hampering structural and biophysical studies. Here, we present our approaches for obtaining pure, detergent solubilized, functional CB1. We also discuss our site-directed fluorescence labeling (SDFL) methods for identifying different structural changes that CB1 can undergo upon binding different cannabinoid ligands. To identify optimal CB1 constructs for these studies (those with the best expression levels, solubility in detergent and function), we first screened various CB1-green fluorescent protein chimeras in a mammalian expression system. Once identified, we then tagged the best candidates with the 1D4 epitope (the C-terminus of rhodopsin) and purified them using a single-step immunoaffinity process. The resulting, highly pure proteins retain their ability to activate G-protein, and are ~85% functional, as assessed by radioligand binding studies. The SDFL studies involve introducing single cysteine residues at key places in the receptor, then labeling them with a small fluorophore, bimane. The spectral properties of the bimane probe are then monitored before and after addition of cannabinoid ligands. Changes in fluorescence of the attached probe indicate regions of the receptor undergoing conformational changes upon ligand binding. Together, these approaches set the stage for a deeper understanding of the structure and function of CB1. Access to pure, functional CB1 makes subsequent structural studies possible (such as crystallography and single-particle EM analysis), and the SDFL studies enable a better structural and mechanistic understanding of this key receptor and the dynamic changes it undergoes during activation and attenuation.
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17
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Tsukamoto H, Chen IS, Kubo Y, Furutani Y. A ciliary opsin in the brain of a marine annelid zooplankton is ultraviolet-sensitive, and the sensitivity is tuned by a single amino acid residue. J Biol Chem 2017. [PMID: 28623234 DOI: 10.1074/jbc.m117.793539] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ciliary opsins were classically thought to function only in vertebrates for vision, but they have also been identified recently in invertebrates for non-visual photoreception. Larvae of the annelid Platynereis dumerilii are used as a zooplankton model, and this zooplankton species possesses a "vertebrate-type" ciliary opsin (named c-opsin) in the brain. Platynereis c-opsin is suggested to relay light signals for melatonin production and circadian behaviors. Thus, the spectral and biochemical characteristics of this c-opsin would be directly related to non-visual photoreception in this zooplankton model. Here we demonstrate that the c-opsin can sense UV to activate intracellular signaling cascades and that it can directly bind exogenous all-trans-retinal. These results suggest that this c-opsin regulates circadian signaling in a UV-dependent manner and that it does not require a supply of 11-cis-retinal for photoreception. Avoidance of damaging UV irradiation is a major cause of large-scale daily zooplankton movement, and the observed capability of the c-opsin to transmit UV signals and bind all-trans-retinal is ideally suited for sensing UV radiation in the brain, which presumably lacks enzymes producing 11-cis-retinal. Mutagenesis analyses indicated that a unique amino acid residue (Lys-94) is responsible for c-opsin-mediated UV sensing in the Platynereis brain. We therefore propose that acquisition of the lysine residue in the c-opsin would be a critical event in the evolution of Platynereis to enable detection of ambient UV light. In summary, our findings indicate that the c-opsin possesses spectral and biochemical properties suitable for UV sensing by the zooplankton model.
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Affiliation(s)
- Hisao Tsukamoto
- Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan; Department of Structural Molecular Science, Graduate University for Advanced Studies, Hayama, Kanagawa 240-0193, Japan.
| | - I-Shan Chen
- Division of Biophysics and Neurobiology, Department of Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Aichi 444-8585, Japan; Physiological Sciences, SOKENDAI, Graduate University for Advanced Studies, Hayama, Kanagawa 240-0193, Japan
| | - Yoshihiro Kubo
- Division of Biophysics and Neurobiology, Department of Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Aichi 444-8585, Japan; Physiological Sciences, SOKENDAI, Graduate University for Advanced Studies, Hayama, Kanagawa 240-0193, Japan
| | - Yuji Furutani
- Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan; Department of Structural Molecular Science, Graduate University for Advanced Studies, Hayama, Kanagawa 240-0193, Japan
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18
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Abstract
Membrane proteins play a most important part in metabolism, signaling, cell motility, transport, development, and many other biochemical and biophysical processes which constitute fundamentals of life on the molecular level. Detailed understanding of these processes is necessary for the progress of life sciences and biomedical applications. Nanodiscs provide a new and powerful tool for a broad spectrum of biochemical and biophysical studies of membrane proteins and are commonly acknowledged as an optimal membrane mimetic system that provides control over size, composition, and specific functional modifications on the nanometer scale. In this review we attempted to combine a comprehensive list of various applications of nanodisc technology with systematic analysis of the most attractive features of this system and advantages provided by nanodiscs for structural and mechanistic studies of membrane proteins.
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Affiliation(s)
- Ilia G Denisov
- Department of Biochemistry and Department of Chemistry, University of Illinois , Urbana, Illinois 61801, United States
| | - Stephen G Sligar
- Department of Biochemistry and Department of Chemistry, University of Illinois , Urbana, Illinois 61801, United States
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19
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Decay of an active GPCR: Conformational dynamics govern agonist rebinding and persistence of an active, yet empty, receptor state. Proc Natl Acad Sci U S A 2016; 113:11961-11966. [PMID: 27702898 DOI: 10.1073/pnas.1606347113] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Here, we describe two insights into the role of receptor conformational dynamics during agonist release (all-trans retinal, ATR) from the visual G protein-coupled receptor (GPCR) rhodopsin. First, we show that, after light activation, ATR can continually release and rebind to any receptor remaining in an active-like conformation. As with other GPCRs, we observe that this equilibrium can be shifted by either promoting the active-like population or increasing the agonist concentration. Second, we find that during decay of the signaling state an active-like, yet empty, receptor conformation can transiently persist after retinal release, before the receptor ultimately collapses into an inactive conformation. The latter conclusion is based on time-resolved, site-directed fluorescence labeling experiments that show a small, but reproducible, lag between the retinal leaving the protein and return of transmembrane helix 6 (TM6) to the inactive conformation, as determined from tryptophan-induced quenching studies. Accelerating Schiff base hydrolysis and subsequent ATR dissociation, either by addition of hydroxylamine or introduction of mutations, further increased the time lag between ATR release and TM6 movement. These observations show that rhodopsin can bind its agonist in equilibrium like a traditional GPCR, provide evidence that an active GPCR conformation can persist even after agonist release, and raise the possibility of targeting this key photoreceptor protein by traditional pharmaceutical-based treatments.
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20
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Sugihara T, Nagata T, Mason B, Koyanagi M, Terakita A. Absorption Characteristics of Vertebrate Non-Visual Opsin, Opn3. PLoS One 2016; 11:e0161215. [PMID: 27532629 PMCID: PMC4988782 DOI: 10.1371/journal.pone.0161215] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2016] [Accepted: 08/02/2016] [Indexed: 11/18/2022] Open
Abstract
Most animals possess multiple opsins which sense light for visual and non-visual functions. Here, we show spectral characteristics of non-visual opsins, vertebrate Opn3s, which are widely distributed among vertebrates. We successfully expressed zebrafish Opn3 in mammalian cultured cells and measured its absorption spectrum spectroscopically. When incubated with 11-cis retinal, zebrafish Opn3 formed a blue-sensitive photopigment with an absorption maximum around 465 nm. The Opn3 converts to an all-trans retinal-bearing photoproduct with an absorption spectrum similar to the dark state following brief blue-light irradiation. The photoproduct experienced a remarkable blue-shift, with changes in position of the isosbestic point, during further irradiation. We then used a cAMP-dependent luciferase reporter assay to investigate light-dependent cAMP responses in cultured cells expressing zebrafish, pufferfish, anole and chicken Opn3. The wild type opsins did not produce responses, but cells expressing chimera mutants (WT Opn3s in which the third intracellular loops were replaced with the third intracellular loop of a Gs-coupled jellyfish opsin) displayed light-dependent changes in cAMP. The results suggest that Opn3 is capable of activating G protein(s) in a light-dependent manner. Finally, we used this assay to measure the relative wavelength-dependent response of cells expressing Opn3 chimeras to multiple quantally-matched stimuli. The inferred spectral sensitivity curve of zebrafish Opn3 accurately matched the measured absorption spectrum. We were unable to estimate the spectral sensitivity curve of mouse or anole Opn3, but, like zebrafish Opn3, the chicken and pufferfish Opn3-JiL3 chimeras also formed blue-sensitive pigments. These findings suggest that vertebrate Opn3s may form blue-sensitive G protein-coupled pigments. Further, we suggest that the method described here, combining a cAMP-dependent luciferase reporter assay with chimeric opsins possessing the third intracellular loop of jellyfish opsin, is a versatile approach for estimating absorption spectra of opsins with unknown signaling cascades or for which absorption spectra are difficult to obtain.
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Affiliation(s)
- Tomohiro Sugihara
- Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Sugimoto, Sumiyoshi-ku, Osaka, Japan
| | - Takashi Nagata
- Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Sugimoto, Sumiyoshi-ku, Osaka, Japan
| | - Benjamin Mason
- Department of Genetics, Stanford School of Medicine, Stanford University, Stanford, California, United States of America
| | - Mitsumasa Koyanagi
- Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Sugimoto, Sumiyoshi-ku, Osaka, Japan
- Japan Science and Technology Agency (JST), Precursory Research for Embryonic Science and Technology (PRESTO), Kawaguchi, Saitama, Japan
- * E-mail: (AT); (MK)
| | - Akihisa Terakita
- Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Sugimoto, Sumiyoshi-ku, Osaka, Japan
- * E-mail: (AT); (MK)
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21
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Tian H, Fürstenberg A, Huber T. Labeling and Single-Molecule Methods To Monitor G Protein-Coupled Receptor Dynamics. Chem Rev 2016; 117:186-245. [DOI: 10.1021/acs.chemrev.6b00084] [Citation(s) in RCA: 84] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Affiliation(s)
- He Tian
- Laboratory of Chemical Biology
and Signal Transduction, The Rockefeller University, 1230 York
Avenue, New York, New York 10065, United States
| | - Alexandre Fürstenberg
- Laboratory of Chemical Biology
and Signal Transduction, The Rockefeller University, 1230 York
Avenue, New York, New York 10065, United States
| | - Thomas Huber
- Laboratory of Chemical Biology
and Signal Transduction, The Rockefeller University, 1230 York
Avenue, New York, New York 10065, United States
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22
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Use of Fluorescence Indicators in Receptor Ligands. Methods Mol Biol 2016; 1335:115-30. [PMID: 26260598 DOI: 10.1007/978-1-4939-2914-6_9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Fluorescence techniques can provide insights into the environment of fluorescence indicators incorporated within a ligand as it is bound to its receptor. Fluorescence indicators of different sizes and chemical characteristics can provide insights into the nature of the binding environment, the surrounding structures, and even into conformational changes associated with receptor activation. Methods for determining fluorescence spectral analysis, fluorescence quenching, fluorescence anisotropy, fluorescence lifetimes, and red edge excitation shifts of the ligand probes are described. The applications of these techniques to the CCK1 receptor occupied by alexa(488)-CCK and aladan-CCK, as examples of probes developed (1) by derivatization of an existing peptide and (2) by incorporation during peptide synthesis, are utilized as examples. These methods represent powerful tools to expand our understanding of the structure and molecular basis of ligand activation of G protein-coupled receptors.
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23
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Tsukamoto H, Kubo Y, Farrens DL, Koyanagi M, Terakita A, Furutani Y. Retinal Attachment Instability Is Diversified among Mammalian Melanopsins. J Biol Chem 2015; 290:27176-27187. [PMID: 26416885 DOI: 10.1074/jbc.m115.666305] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Indexed: 01/12/2023] Open
Abstract
Melanopsins play a key role in non-visual photoreception in mammals. Their close phylogenetic relationship to the photopigments in invertebrate visual cells suggests they have evolved to acquire molecular characteristics that are more suited for their non-visual functions. Here we set out to identify such characteristics by comparing the molecular properties of mammalian melanopsin to those of invertebrate melanopsin and visual pigment. Our data show that the Schiff base linking the chromophore retinal to the protein is more susceptive to spontaneous cleavage in mammalian melanopsins. We also find this stability is highly diversified between mammalian species, being particularly unstable for human melanopsin. Through mutagenesis analyses, we find that this diversified stability is mainly due to parallel amino acid substitutions in extracellular regions. We propose that the different stability of the retinal attachment in melanopsins may contribute to functional tuning of non-visual photoreception in mammals.
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Affiliation(s)
- Hisao Tsukamoto
- Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, Okazaki, 444-8585, Japan,; Department of Structural Molecular Science, SOKENDAI (The Graduate University for Advanced Studies), Hayama, Kanagawa 240-0193, Japan,.
| | - Yoshihiro Kubo
- Division of Biophysics and Neurobiology, Department of Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Aichi 444-8585, Japan,; Department of Physiological Sciences, SOKENDAI (The Graduate University for Advanced Studies), Hayama, Kanagawa 240-0193, Japan
| | - David L Farrens
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239-3098
| | - Mitsumasa Koyanagi
- Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Osaka 558-8585, Japan
| | - Akihisa Terakita
- Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Osaka 558-8585, Japan
| | - Yuji Furutani
- Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, Okazaki, 444-8585, Japan,; Department of Structural Molecular Science, SOKENDAI (The Graduate University for Advanced Studies), Hayama, Kanagawa 240-0193, Japan
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24
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Structural dynamics and energetics underlying allosteric inactivation of the cannabinoid receptor CB1. Proc Natl Acad Sci U S A 2015; 112:8469-74. [PMID: 26100912 DOI: 10.1073/pnas.1500895112] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
G protein-coupled receptors (GPCRs) are surprisingly flexible molecules that can do much more than simply turn on G proteins. Some even exhibit biased signaling, wherein the same receptor preferentially activates different G-protein or arrestin signaling pathways depending on the type of ligand bound. Why this behavior occurs is still unclear, but it can happen with both traditional ligands and ligands that bind allosterically outside the orthosteric receptor binding pocket. Here, we looked for structural mechanisms underlying these phenomena in the marijuana receptor CB1. Our work focused on the allosteric ligand Org 27569, which has an unusual effect on CB1-it simultaneously increases agonist binding, decreases G--protein activation, and induces biased signaling. Using classical pharmacological binding studies, we find that Org 27569 binds to a unique allosteric site on CB1 and show that it can act alone (without need for agonist cobinding). Through mutagenesis studies, we find that the ability of Org 27569 to bind is related to how much receptor is in an active conformation that can couple with G protein. Using these data, we estimated the energy differences between the inactive and active states. Finally, site-directed fluorescence labeling studies show the CB1 structure stabilized by Org 27569 is different and unique from that stabilized by antagonist or agonist. Specifically, transmembrane helix 6 (TM6) movements associated with G-protein activation are blocked, but at the same time, helix 8/TM7 movements are enhanced, suggesting a possible mechanism for the ability of Org 27569 to induce biased signaling.
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25
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Inaguma A, Tsukamoto H, Kato HE, Kimura T, Ishizuka T, Oishi S, Yawo H, Nureki O, Furutani Y. Chimeras of channelrhodopsin-1 and -2 from Chlamydomonas reinhardtii exhibit distinctive light-induced structural changes from channelrhodopsin-2. J Biol Chem 2015; 290:11623-34. [PMID: 25796616 DOI: 10.1074/jbc.m115.642256] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2015] [Indexed: 01/18/2023] Open
Abstract
Channelrhodopsin-2 (ChR2) from the green alga Chlamydomonas reinhardtii functions as a light-gated cation channel that has been developed as an optogenetic tool to stimulate specific nerve cells in animals and control their behavior by illumination. The molecular mechanism of ChR2 has been extensively studied by a variety of spectroscopic methods, including light-induced difference Fourier transform infrared (FTIR) spectroscopy, which is sensitive to structural changes in the protein upon light activation. An atomic structure of channelrhodopsin was recently determined by x-ray crystallography using a chimera of channelrhodopsin-1 (ChR1) and ChR2. Electrophysiological studies have shown that ChR1/ChR2 chimeras are less desensitized upon continuous illumination than native ChR2, implying that there are some structural differences between ChR2 and chimeras. In this study, we applied light-induced difference FTIR spectroscopy to ChR2 and ChR1/ChR2 chimeras to determine the molecular basis underlying these functional differences. Upon continuous illumination, ChR1/ChR2 chimeras exhibited structural changes distinct from those in ChR2. In particular, the protonation state of a glutamate residue, Glu-129 (Glu-90 in ChR2 numbering), in the ChR chimeras is not changed as dramatically as in ChR2. Moreover, using mutants stabilizing particular photointermediates as well as time-resolved measurements, we identified some differences between the major photointermediates of ChR2 and ChR1/ChR2 chimeras. Taken together, our data indicate that the gating and desensitizing processes in ChR1/ChR2 chimeras are different from those in ChR2 and that these differences should be considered in the rational design of new optogenetic tools based on channelrhodopsins.
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Affiliation(s)
- Asumi Inaguma
- From the Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan, PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan, Department of Structural Molecular Science, Graduate University for Advanced Studies (SOKENDAI), 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan
| | - Hisao Tsukamoto
- From the Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan, Department of Structural Molecular Science, Graduate University for Advanced Studies (SOKENDAI), 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan
| | - Hideaki E Kato
- Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
| | - Tetsunari Kimura
- From the Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan, Department of Structural Molecular Science, Graduate University for Advanced Studies (SOKENDAI), 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan
| | - Toru Ishizuka
- CREST, Japan Science and Technology Agency (JST), 5 Sanbancho, Chiyoda-ku, Tokyo 102-0075, and Department of Developmental Biology and Neuroscience, Tohoku University Graduate School of Life Sciences, Sendai 980-8577, Japan
| | - Satomi Oishi
- Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
| | - Hiromu Yawo
- CREST, Japan Science and Technology Agency (JST), 5 Sanbancho, Chiyoda-ku, Tokyo 102-0075, and Department of Developmental Biology and Neuroscience, Tohoku University Graduate School of Life Sciences, Sendai 980-8577, Japan
| | - Osamu Nureki
- Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
| | - Yuji Furutani
- From the Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan, PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan, Department of Structural Molecular Science, Graduate University for Advanced Studies (SOKENDAI), 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan,
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26
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Vihinen M. Types and effects of protein variations. Hum Genet 2015; 134:405-21. [DOI: 10.1007/s00439-015-1529-6] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2014] [Accepted: 01/09/2015] [Indexed: 12/12/2022]
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27
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Naganathan S, Ray-Saha S, Park M, Tian H, Sakmar TP, Huber T. Multiplex detection of functional G protein-coupled receptors harboring site-specifically modified unnatural amino acids. Biochemistry 2015; 54:776-86. [PMID: 25524496 PMCID: PMC4310623 DOI: 10.1021/bi501267x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
![]()
We developed a strategy for identifying
positions in G protein-coupled
receptors that are amenable to bioorthogonal modification with a peptide
epitope tag under cell culturing conditions. We introduced the unnatural
amino acid p-azido-l-phenylalanine (azF)
into human CC chemokine receptor 5 (CCR5) at site-specific amber codon
mutations. We then used strain-promoted azide–alkyne [3+2]
cycloaddition to label the azF-CCR5 variants with a FLAG peptide epitope-conjugated
aza-dibenzocyclooctyne (DBCO) reagent. A microtiter plate-based sandwich
fluorophore-linked immunosorbent assay was used to probe simultaneously
the FLAG epitope and the receptor using infrared dye-conjugated antibodies
so that the extent of DBCO incorporation, corresponding nominally
to labeling efficiency, could be quantified ratiometrically. The extent
of incorporation of DBCO at the various sites was evaluated in the
context of a recent crystal structure of maraviroc-bound CCR5. We
observed that labeling efficiency varied dramatically depending on
the topological location of the azF in CCR5. Interestingly, position
109 in transmembrane helix 3, located in a hydrophobic cavity on the
extracellular side of the receptor, was labeled most efficiently.
Because the bioorthogonal labeling and detection strategy described
might be used to introduce a variety of different peptide epitopes
or fluorophores into engineered expressed receptors, it might prove
to be useful for a wide range of applications, including single-molecule
detection studies of receptor trafficking and signaling mechanism.
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Affiliation(s)
- Saranga Naganathan
- Laboratory of Chemical Biology & Signal Transduction, The Rockefeller University , New York, New York 10065, United States
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Schafer CT, Farrens DL. Conformational selection and equilibrium governs the ability of retinals to bind opsin. J Biol Chem 2014; 290:4304-18. [PMID: 25451936 DOI: 10.1074/jbc.m114.603134] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Despite extensive study, how retinal enters and exits the visual G protein-coupled receptor rhodopsin remains unclear. One clue may lie in two openings between transmembrane helix 1 (TM1) and TM7 and between TM5 and TM6 in the active receptor structure. Recently, retinal has been proposed to enter the inactive apoprotein opsin (ops) through these holes when the receptor transiently adopts the active opsin conformation (ops*). Here, we directly test this "transient activation" hypothesis using a fluorescence-based approach to measure rates of retinal binding to samples containing differing relative fractions of ops and ops*. In contrast to what the transient activation hypothesis model would predict, we found that binding for the inverse agonist, 11-cis-retinal (11CR), slowed when the sample contained more ops* (produced using M257Y, a constitutively activating mutation). Interestingly, the increased presence of ops* allowed for binding of the agonist, all-trans-retinal (ATR), whereas WT opsin showed no binding. Shifting the conformational equilibrium toward even more ops* using a G protein peptide mimic (either free in solution or fused to the receptor) accelerated the rate of ATR binding and slowed 11CR binding. An arrestin peptide mimic showed little effect on 11CR binding; however, it stabilized opsin · ATR complexes. The TM5/TM6 hole is apparently not involved in this conformational selection. Increasing its size by mutagenesis did not enable ATR binding but instead slowed 11CR binding, suggesting that it may play a role in trapping 11CR. In summary, our results indicate that conformational selection dictates stable retinal binding, which we propose involves ATR and 11CR binding to different states, the latter a previously unidentified, open-but-inactive conformation.
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Affiliation(s)
- Christopher T Schafer
- From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239-3098
| | - David L Farrens
- From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239-3098
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29
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Goren MA, Morizumi T, Menon I, Joseph JS, Dittman JS, Cherezov V, Stevens RC, Ernst OP, Menon AK. Constitutive phospholipid scramblase activity of a G protein-coupled receptor. Nat Commun 2014; 5:5115. [PMID: 25296113 PMCID: PMC4198942 DOI: 10.1038/ncomms6115] [Citation(s) in RCA: 90] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2014] [Accepted: 09/01/2014] [Indexed: 12/26/2022] Open
Abstract
Opsin, the rhodopsin apoprotein, was recently shown to be an ATP-independent flippase (or scramblase) that equilibrates phospholipids across photoreceptor disc membranes in mammalian retina, a process required for disc homeostasis. Here we show that scrambling is a constitutive activity of rhodopsin, distinct from its light-sensing function. Upon reconstitution into vesicles, discrete conformational states of the protein (rhodopsin, a metarhodopsin II-mimic, and two forms of opsin) facilitated rapid (>10,000 phospholipids per protein per second) scrambling of phospholipid probes. Our results indicate that the large conformational changes involved in converting rhodopsin to metarhodopsin II are not required for scrambling, and that the lipid translocation pathway either lies near the protein surface or involves membrane packing defects in the vicinity of the protein. Additionally, we demonstrate that β2-adrenergic and adenosine A2A receptors scramble lipids, suggesting that rhodopsin-like G protein-coupled receptors may play an unexpected moonlighting role in re-modeling cell membranes.
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Affiliation(s)
- Michael A Goren
- Department of Biochemistry, Weill Cornell Medical College, New York, New York 10065, USA
| | - Takefumi Morizumi
- Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Indu Menon
- Department of Biochemistry, Weill Cornell Medical College, New York, New York 10065, USA
| | - Jeremiah S Joseph
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, California 92037, USA
| | - Jeremy S Dittman
- Department of Biochemistry, Weill Cornell Medical College, New York, New York 10065, USA
| | - Vadim Cherezov
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, California 92037, USA
| | - Raymond C Stevens
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, California 92037, USA
| | - Oliver P Ernst
- 1] Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada M5S 1A8 [2] Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Anant K Menon
- Department of Biochemistry, Weill Cornell Medical College, New York, New York 10065, USA
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30
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Jones Brunette AM, Farrens DL. Distance mapping in proteins using fluorescence spectroscopy: tyrosine, like tryptophan, quenches bimane fluorescence in a distance-dependent manner. Biochemistry 2014; 53:6290-301. [PMID: 25144569 PMCID: PMC4196733 DOI: 10.1021/bi500493r] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
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Tryptophan-induced quenching of fluorophores
(TrIQ) uses intramolecular
fluorescence quenching to assess distances in proteins too small (<15
Å) to be easily probed by traditional Forster resonance energy
transfer methods. A powerful aspect of TrIQ is its ability to obtain
an ultrafast snapshot of a protein conformation, by identifying “static
quenching” (contact between the Trp and probe at the moment
of light excitation). Here we report new advances in this site-directed
fluorescence labeling (SDFL) approach, gleaned from recent studies
of T4 lysozyme (T4L). First, we show that like TrIQ, tyrosine-induced
quenching (TyrIQ) occurs for the fluorophore bimane in a distance-dependent
fashion, although with some key differences. The Tyr “sphere
of quenching” for bimane (≤10 Å) is smaller than
for Trp (≤15 Å, Cα–Cα distance), and
the size difference between the quenching residue (Tyr) and control
(Phe) differs by only a hydroxyl group. Second, we show how TrIQ and
TyrIQ can be used together to assess the magnitude and energetics
of a protein movement. In these studies, we placed a bimane (probe)
and Trp or Tyr (quencher) on opposite ends of a “hinge”
in T4L and conducted TrIQ and TyrIQ measurements. Our results are
consistent with an ∼5 Å change in Cα–Cα
distances between these sites upon substrate binding, in agreement
with the crystal structures. Subsequent Arrhenius analysis suggests
the activation energy barrier (Ea) to
this movement is relatively low (∼1.5–2.5 kcal/mol).
Together, these results demonstrate that TyrIQ, used together with
TrIQ, significantly expands the power of quenching-based distance
mapping SDFL studies.
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Affiliation(s)
- Amber M Jones Brunette
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University , Portland, Oregon 97239-3098, United States
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31
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Sun L, Kawano-Yamashita E, Nagata T, Tsukamoto H, Furutani Y, Koyanagi M, Terakita A. Distribution of mammalian-like melanopsin in cyclostome retinas exhibiting a different extent of visual functions. PLoS One 2014; 9:e108209. [PMID: 25251771 PMCID: PMC4177573 DOI: 10.1371/journal.pone.0108209] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2014] [Accepted: 08/20/2014] [Indexed: 11/18/2022] Open
Abstract
Mammals contain 1 melanopsin (Opn4) gene that is expressed in a subset of retinal ganglion cells to serve as a photopigment involved in non-image-forming vision such as photoentrainment of circadian rhythms. In contrast, most nonmammalian vertebrates possess multiple melanopsins that are distributed in various types of retinal cells; however, their functions remain unclear. We previously found that the lamprey has only 1 type of mammalian-like melanopsin gene, which is similar to that observed in mammals. Here we investigated the molecular properties and localization of melanopsin in the lamprey and other cyclostome hagfish retinas, which contribute to visual functions including image-forming vision and mainly to non-image-forming vision, respectively. We isolated 1 type of mammalian-like melanopsin cDNA from the eyes of each species. We showed that the recombinant lamprey melanopsin was a blue light-sensitive pigment and that both the lamprey and hagfish melanopsins caused light-dependent increases in calcium ion concentration in cultured cells in a manner that was similar to that observed for mammalian melanopsins. We observed that melanopsin was distributed in several types of retinal cells, including horizontal cells and ganglion cells, in the lamprey retina, despite the existence of only 1 melanopsin gene in the lamprey. In contrast, melanopsin was almost specifically distributed to retinal ganglion cells in the hagfish retina. Furthermore, we found that the melanopsin-expressing horizontal cells connected to the rhodopsin-containing short photoreceptor cells in the lamprey. Taken together, our findings suggest that in cyclostomes, the global distribution of melanopsin in retinal cells might not be related to the melanopsin gene number but to the extent of retinal contribution to visual function.
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Affiliation(s)
- Lanfang Sun
- Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Osaka, Japan
| | - Emi Kawano-Yamashita
- Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Osaka, Japan
| | - Takashi Nagata
- Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Osaka, Japan
| | - Hisao Tsukamoto
- Department of life and Coordination-Complex Molecular Science, Institute for Molecular Science, Okazaki, Japan
- Department of Structural Molecular Science, The Graduate University for Advanced Studies (SOKENDAI), Okazaki, Japan
| | - Yuji Furutani
- Department of life and Coordination-Complex Molecular Science, Institute for Molecular Science, Okazaki, Japan
- Department of Structural Molecular Science, The Graduate University for Advanced Studies (SOKENDAI), Okazaki, Japan
| | - Mitsumasa Koyanagi
- Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Osaka, Japan
- PRESTO, Japan Science and Technology Agency, Saitama, Japan
| | - Akihisa Terakita
- Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Osaka, Japan
- * E-mail:
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32
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Advances in Human Biology: Combining Genetics and Molecular Biophysics to Pave the Way for Personalized Diagnostics and Medicine. ACTA ACUST UNITED AC 2014. [DOI: 10.1155/2014/471836] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Advances in several biology-oriented initiatives such as genome sequencing and structural genomics, along with the progress made through traditional biological and biochemical research, have opened up a unique opportunity to better understand the molecular effects of human diseases. Human DNA can vary significantly from person to person and determines an individual’s physical characteristics and their susceptibility to diseases. Armed with an individual’s DNA sequence, researchers and physicians can check for defects known to be associated with certain diseases by utilizing various databases. However, for unclassified DNA mutations or in order to reveal molecular mechanism behind the effects, the mutations have to be mapped onto the corresponding networks and macromolecular structures and then analyzed to reveal their effect on the wild type properties of biological processes involved. Predicting the effect of DNA mutations on individual’s health is typically referred to as personalized or companion diagnostics. Furthermore, once the molecular mechanism of the mutations is revealed, the patient should be given drugs which are the most appropriate for the individual genome, referred to as pharmacogenomics. Altogether, the shift in focus in medicine towards more genomic-oriented practices is the foundation of personalized medicine. The progress made in these rapidly developing fields is outlined.
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33
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Park PSH. Constitutively active rhodopsin and retinal disease. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2014; 70:1-36. [PMID: 24931191 DOI: 10.1016/b978-0-12-417197-8.00001-8] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Rhodopsin is the light receptor in rod photoreceptor cells of the retina that initiates scotopic vision. In the dark, rhodopsin is bound to the chromophore 11-cis retinal, which locks the receptor in an inactive state. The maintenance of an inactive rhodopsin in the dark is critical for rod photoreceptor cells to remain highly sensitive. Perturbations by mutation or the absence of 11-cis retinal can cause rhodopsin to become constitutively active, which leads to the desensitization of photoreceptor cells and, in some instances, retinal degeneration. Constitutive activity can arise in rhodopsin by various mechanisms and can cause a variety of inherited retinal diseases including Leber congenital amaurosis, congenital night blindness, and retinitis pigmentosa. In this review, the molecular and structural properties of different constitutively active forms of rhodopsin are overviewed, and the possibility that constitutive activity can arise from different active-state conformations is discussed.
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Affiliation(s)
- Paul Shin-Hyun Park
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, Ohio, USA.
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34
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Alexiev U, Farrens DL. Fluorescence spectroscopy of rhodopsins: insights and approaches. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2013; 1837:694-709. [PMID: 24183695 DOI: 10.1016/j.bbabio.2013.10.008] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Revised: 10/11/2013] [Accepted: 10/16/2013] [Indexed: 01/30/2023]
Abstract
Fluorescence spectroscopy has become an established tool at the interface of biology, chemistry and physics because of its exquisite sensitivity and recent technical advancements. However, rhodopsin proteins present the fluorescence spectroscopist with a unique set of challenges and opportunities due to the presence of the light-sensitive retinal chromophore. This review briefly summarizes some approaches that have successfully met these challenges and the novel insights they have yielded about rhodopsin structure and function. We start with a brief overview of fluorescence fundamentals and experimental methodologies, followed by more specific discussions of technical challenges rhodopsin proteins present to fluorescence studies. Finally, we end by discussing some of the unique insights that have been gained specifically about visual rhodopsin and its interactions with affiliate proteins through the use of fluorescence spectroscopy. This article is part of a Special Issue entitled: Retinal Proteins - You can teach an old dog new tricks.
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Affiliation(s)
- Ulrike Alexiev
- Physics Department, Freie Universität Berlin, Berlin, Germany.
| | - David L Farrens
- Departments of Biochemistry and Molecular Biology, Oregon Health Sciences University, USA
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