1
|
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.
Collapse
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.
| |
Collapse
|
2
|
Martinecz A, Niitsuma M. Fractional integral-like processing in retinal cones reduces noise and improves adaptation. PLoS One 2018; 13:e0205099. [PMID: 30286168 PMCID: PMC6171915 DOI: 10.1371/journal.pone.0205099] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2018] [Accepted: 08/21/2018] [Indexed: 11/17/2022] Open
Abstract
In the human retina, rod and cone cells detect incoming light with a molecule called rhodopsin. After rhodopsin molecules are activated (by photon impact), these molecules activate the rest of the signalling process for a brief period of time until they are deactivated by a multistage process. First, active rhodopsin is phosphorylated multiple times. Following this, they are further inhibited by the binding of molecules called arrestins. Finally, they decay into opsins. The time required for each of these stages becomes progressively longer, and each stage further reduces the activity of rhodopsin. However, while this deactivation process itself is well researched, the roles of the above stages in signal (and image) processing are poorly understood. In this paper, we will show that the activity of rhodopsin molecules during the deactivation process can be described as the fractional integration of an incoming signal. Furthermore, we show how this affects an image; specifically, the effect of fractional integration in video and signal processing and how it reduces noise and the improves adaptability under different lighting conditions. Our experimental results provide a better understanding of vertebrate and human vision, and why the rods and cones of the retina differ from the light detectors in cameras.
Collapse
Affiliation(s)
- Antal Martinecz
- Department of Precision Mechanics, Chuo University, Tokyo, Japan
| | - Mihoko Niitsuma
- Department of Precision Mechanics, Chuo University, Tokyo, Japan
| |
Collapse
|
3
|
Chen Q, Perry NA, Vishnivetskiy SA, Berndt S, Gilbert NC, Zhuo Y, Singh PK, Tholen J, Ohi MD, Gurevich EV, Brautigam CA, Klug CS, Gurevich VV, Iverson TM. Structural basis of arrestin-3 activation and signaling. Nat Commun 2017; 8:1427. [PMID: 29127291 PMCID: PMC5681653 DOI: 10.1038/s41467-017-01218-8] [Citation(s) in RCA: 76] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2017] [Accepted: 08/29/2017] [Indexed: 02/06/2023] Open
Abstract
A unique aspect of arrestin-3 is its ability to support both receptor-dependent and receptor-independent signaling. Here, we show that inositol hexakisphosphate (IP6) is a non-receptor activator of arrestin-3 and report the structure of IP6-activated arrestin-3 at 2.4-Å resolution. IP6-activated arrestin-3 exhibits an inter-domain twist and a displaced C-tail, hallmarks of active arrestin. IP6 binds to the arrestin phosphate sensor, and is stabilized by trimerization. Analysis of the trimerization surface, which is also the receptor-binding surface, suggests a feature called the finger loop as a key region of the activation sensor. We show that finger loop helicity and flexibility may underlie coupling to hundreds of diverse receptors and also promote arrestin-3 activation by IP6. Importantly, we show that effector-binding sites on arrestins have distinct conformations in the basal and activated states, acting as switch regions. These switch regions may work with the inter-domain twist to initiate and direct arrestin-mediated signaling. While arrestins are mainly associated with GPCR signaling, arrestin-3 can signal independently of receptor interaction. Here the authors present the structure of arrestin-3 bound to inositol hexakisphosphate (IP6) and propose a model for arrestin-3 activation.
Collapse
Affiliation(s)
- Qiuyan Chen
- Department of Pharmacology, Vanderbilt University, Nashville, TN, 37232, USA
| | - Nicole A Perry
- Department of Pharmacology, Vanderbilt University, Nashville, TN, 37232, USA
| | | | - Sandra Berndt
- Department of Pharmacology, Vanderbilt University, Nashville, TN, 37232, USA
| | - Nathaniel C Gilbert
- Department of Pharmacology, Vanderbilt University, Nashville, TN, 37232, USA.,Louisiana State University, Baton Rouge, LA, 70803, USA
| | - Ya Zhuo
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, 53226, USA
| | - Prashant K Singh
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN, 37232, USA
| | - Jonas Tholen
- University of Applied Sciences Emden/Leer, Emden, 26723, Germany
| | - Melanie D Ohi
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN, 37232, USA.,Department of Biochemistry, Vanderbilt University, Nashville, TN, 37232, USA.,Center for Structural Biology, Vanderbilt University, Nashville, TN, 37232, USA
| | - Eugenia V Gurevich
- Department of Pharmacology, Vanderbilt University, Nashville, TN, 37232, USA
| | - Chad A Brautigam
- Departments of Biophysics and Microbiology, The University of Texas Southwestern Medical Center, Dallas, TX, 75390, USA
| | - Candice S Klug
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, 53226, USA
| | - Vsevolod V Gurevich
- Department of Pharmacology, Vanderbilt University, Nashville, TN, 37232, USA.
| | - T M Iverson
- Department of Pharmacology, Vanderbilt University, Nashville, TN, 37232, USA. .,Department of Biochemistry, Vanderbilt University, Nashville, TN, 37232, USA. .,Center for Structural Biology, Vanderbilt University, Nashville, TN, 37232, USA. .,Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, TN, 37232, USA.
| |
Collapse
|
4
|
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.
Collapse
|
5
|
Kumari P, Srivastava A, Ghosh E, Ranjan R, Dogra S, Yadav PN, Shukla AK. Core engagement with β-arrestin is dispensable for agonist-induced vasopressin receptor endocytosis and ERK activation. Mol Biol Cell 2017; 28:1003-1010. [PMID: 28228552 PMCID: PMC5391177 DOI: 10.1091/mbc.e16-12-0818] [Citation(s) in RCA: 71] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2016] [Revised: 02/13/2017] [Accepted: 02/14/2017] [Indexed: 01/14/2023] Open
Abstract
G protein-coupled receptors (GPCRs) exhibit highly conserved activation and signaling mechanisms by which agonist stimulation leads to coupling of heterotrimeric G proteins and generation of second messenger response. This is followed by receptor phosphorylation, primarily in the carboxyl terminus but also in the cytoplasmic loops, and subsequent binding of arrestins. GPCRs typically recruit arrestins through two different sets of interactions, one involving phosphorylated receptor tail and the other mediated by the receptor core. The engagement of both set of interactions (tail and core) is generally believed to be necessary for arrestin-dependent functional outcomes such as receptor desensitization, endocytosis, and G protein-independent signaling. Here we demonstrate that a vasopressin receptor (V2R) mutant with truncated third intracellular loop (V2RΔICL3) can interact with β-arrestin 1 (βarr1) only through the phosphorylated tail without engaging the core interaction. Of interest, such a partially engaged V2RΔICL3-βarr1 complex can efficiently interact with clathrin terminal domain and ERK2 MAPK in vitro. Furthermore, this core interaction-deficient V2R mutant exhibits efficient endocytosis and ERK activation upon agonist stimulation. Our data suggest that core interaction with βarr is dispensable for V2R endocytosis and ERK activation and therefore provide novel insights into refining the current understanding of functional requirements in biphasic GPCR-βarr interaction.
Collapse
Affiliation(s)
- Punita Kumari
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur 208016, India
| | - Ashish Srivastava
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur 208016, India
| | - Eshan Ghosh
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur 208016, India
| | - Ravi Ranjan
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur 208016, India
| | - Shalini Dogra
- Division of Pharmacology, CSIR-Central Drug Research Institute, Lucknow, UP 226031, India
| | - Prem N Yadav
- Division of Pharmacology, CSIR-Central Drug Research Institute, Lucknow, UP 226031, India
| | - Arun K Shukla
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur 208016, India
| |
Collapse
|
6
|
Kumari P, Srivastava A, Banerjee R, Ghosh E, Gupta P, Ranjan R, Chen X, Gupta B, Gupta C, Jaiman D, Shukla AK. Functional competence of a partially engaged GPCR-β-arrestin complex. Nat Commun 2016; 7:13416. [PMID: 27827372 PMCID: PMC5105198 DOI: 10.1038/ncomms13416] [Citation(s) in RCA: 114] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2016] [Accepted: 09/30/2016] [Indexed: 12/28/2022] Open
Abstract
G Protein-coupled receptors (GPCRs) constitute the largest family of cell surface receptors and drug targets. GPCR signalling and desensitization is critically regulated by β-arrestins (βarr). GPCR–βarr interaction is biphasic where the phosphorylated carboxyl terminus of GPCRs docks to the N-domain of βarr first and then seven transmembrane core of the receptor engages with βarr. It is currently unknown whether fully engaged GPCR–βarr complex is essential for functional outcomes or partially engaged complex can also be functionally competent. Here we assemble partially and fully engaged complexes of a chimeric β2V2R with βarr1, and discover that the core interaction is dispensable for receptor endocytosis, ERK MAP kinase binding and activation. Furthermore, we observe that carvedilol, a βarr biased ligand, does not promote detectable engagement between βarr1 and the receptor core. These findings uncover a previously unknown aspect of GPCR-βarr interaction and provide novel insights into GPCR signalling and regulatory paradigms. β-arrestins initially contact with the phosphorylated carboxyl-terminus of GPCRs before engaging with the GPCR core. Here, the authors use a chimeric GPCR partially and fully engaged with β-arrestin1 and show that the core interaction is dispensable for receptor endocytosis and signalling.
Collapse
Affiliation(s)
- Punita Kumari
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur 208016, India
| | - Ashish Srivastava
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur 208016, India
| | - Ramanuj Banerjee
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur 208016, India
| | - Eshan Ghosh
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur 208016, India
| | - Pragya Gupta
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur 208016, India
| | - Ravi Ranjan
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur 208016, India
| | - Xin Chen
- School of Pharmaceutical Engineering and Life Sciences, Changzhou University, Changzhou, Jiangsu 213164, China
| | - Bhagyashri Gupta
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur 208016, India
| | - Charu Gupta
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur 208016, India
| | - Deepika Jaiman
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur 208016, India
| | - Arun K Shukla
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur 208016, India
| |
Collapse
|
7
|
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.
Collapse
|
8
|
Jones Brunette AM, Sinha A, David L, Farrens DL. Evidence that the Rhodopsin Kinase (GRK1) N-Terminus and the Transducin Gα C-Terminus Interact with the Same "Hydrophobic Patch" on Rhodopsin TM5. Biochemistry 2016; 55:3123-35. [PMID: 27078130 DOI: 10.1021/acs.biochem.6b00328] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Phosphorylation of G protein-coupled receptors (GPCRs) terminates their ability to couple with and activate G proteins by increasing their affinity for arrestins. Unfortunately, detailed information regarding how GPCRs interact with the kinases responsible for their phosphorylation is still limited. Here, we purified fully functional GPCR kinase 1 (GRK1) using a rapid method and used it to gain insights into how this important kinase interacts with the GPCR rhodopsin. Specifically, we find that GRK1 uses the same site on rhodopsin as the transducin (Gt) Gtα C-terminal tail and the arrestin "finger loop", a cleft formed in the cytoplasmic face of the receptor upon activation. Our studies also show GRK1 requires two conserved residues located in this cleft (L226 and V230) that have been shown to be required for Gt activation due to their direct interactions with hydrophobic residues on the Gα C-terminal tail. Our data and modeling studies are consistent with the idea that all three proteins (Gt, GRK1, and visual arrestin) bind, at least in part, in the same site on rhodopsin and interact with the receptor through a similar hydrophobic contact-driven mechanism.
Collapse
Affiliation(s)
- Amber M Jones Brunette
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University , Portland, Oregon 97239-3098, United States
| | - Abhinav Sinha
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University , Portland, Oregon 97239-3098, United States
| | - Larry David
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University , Portland, Oregon 97239-3098, United States
| | - David L Farrens
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University , Portland, Oregon 97239-3098, United States
| |
Collapse
|
9
|
Structural mechanism of GPCR-arrestin interaction: recent breakthroughs. Arch Pharm Res 2016; 39:293-301. [DOI: 10.1007/s12272-016-0712-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2015] [Accepted: 01/22/2016] [Indexed: 01/14/2023]
|
10
|
Madziva MT, Mkhize NN, Flanagan CA, Katz AA. The carboxy-terminal tail or the intracellular loop 3 is required for β-arrestin-dependent internalization of a mammalian type II GnRH receptor. Mol Cell Endocrinol 2015; 411:187-97. [PMID: 25957085 DOI: 10.1016/j.mce.2015.04.029] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/31/2014] [Revised: 04/08/2015] [Accepted: 04/29/2015] [Indexed: 10/23/2022]
Abstract
The type II GnRH receptor (GnRH-R2) in contrast to mammalian type I GnRH receptor (GnRH-R1) has a cytosolic carboxy-terminal tail. We investigated the role of β-arrestin 1 in GnRH-R2-mediated signalling and mapped the regions in GnRH-R2 required for recruitment of β-arrestin, employing internalization assays. We show that GnRH-R2 activation of ERK is dependent on β-arrestin and protein kinase C. Appending the tail of GnRH-R2 to GnRH-R1 enabled GRK- and β-arrestin-dependent internalization of the chimaeric receptor. Surprisingly, carboxy-terminally truncated GnRH-R2 retained β-arrestin and GRK-dependent internalization, suggesting that β-arrestin interacts with additional elements of GnRH-R2. Mutating serine and threonine or basic residues of intracellular loop 3 did not abolish β-arrestin 1-dependent internalization but a receptor lacking these basic residues and the carboxy-terminus showed no β-arrestin 1-dependent internalization. Our results suggest that basic residues at the amino-terminal end of intracellular loop 3 or the carboxy-terminal tail are required for β-arrestin dependent internalization.
Collapse
Affiliation(s)
- Michael T Madziva
- Medical Research Council Research Unit for Receptor Biology, Institute of Infectious Disease and Molecular Medicine and Division of Medical Biochemistry, Faculty of Health Sciences, University of Cape Town, Observatory, 7925 Cape Town, South Africa; School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Medical School, 7 York Road, Parktown 2193, Johannesburg, South Africa
| | - Nonhlanhla N Mkhize
- Medical Research Council Research Unit for Receptor Biology, Institute of Infectious Disease and Molecular Medicine and Division of Medical Biochemistry, Faculty of Health Sciences, University of Cape Town, Observatory, 7925 Cape Town, South Africa
| | - Colleen A Flanagan
- Medical Research Council Research Unit for Receptor Biology, Institute of Infectious Disease and Molecular Medicine and Division of Medical Biochemistry, Faculty of Health Sciences, University of Cape Town, Observatory, 7925 Cape Town, South Africa; School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Medical School, 7 York Road, Parktown 2193, Johannesburg, South Africa
| | - Arieh A Katz
- Medical Research Council Research Unit for Receptor Biology, Institute of Infectious Disease and Molecular Medicine and Division of Medical Biochemistry, Faculty of Health Sciences, University of Cape Town, Observatory, 7925 Cape Town, South Africa.
| |
Collapse
|
11
|
Ostermaier MK, Schertler GFX, Standfuss J. Molecular mechanism of phosphorylation-dependent arrestin activation. Curr Opin Struct Biol 2014; 29:143-51. [PMID: 25484000 DOI: 10.1016/j.sbi.2014.07.006] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2014] [Revised: 07/16/2014] [Accepted: 07/18/2014] [Indexed: 12/31/2022]
Abstract
The past years have seen tremendous progress towards understanding how arrestins recognize phosphorylated G protein-coupled receptors (GPCRs). Two arrestin crystal structures, one of a pre-activated splice variant and one bound to a GPCR phosphopeptide, provided insights into the conformational changes upon phosphate recognition. Scanning mutagenesis and spectroscopic studies complete the picture of arrestin activation and receptor binding. Most perspicuous is the C-tail exchange mechanism, by which the C-tail of arrestin is released from its basal conformation and replaced by the phosphorylated GPCR C-terminus. Three positively charged clusters could act as conserved arrestin phosphosensors. Variations in the pattern of phosphorylation in a GPCR and variations within the C-terminus of different GPCRs may encode specificity to arrestin subtypes and particular physiological responses.
Collapse
Affiliation(s)
- Martin K Ostermaier
- Laboratory of Biomolecular Research, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Gebhard F X Schertler
- Laboratory of Biomolecular Research, Paul Scherrer Institute, 5232 Villigen, Switzerland; Deparment of Biology, ETH Zurich, Wolfgang-Pauli-Str. 27, 8093 Zürich, Switzerland
| | - Joerg Standfuss
- Laboratory of Biomolecular Research, Paul Scherrer Institute, 5232 Villigen, Switzerland.
| |
Collapse
|
12
|
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.
Collapse
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
| |
Collapse
|
13
|
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
![]()
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.
Collapse
Affiliation(s)
- Amber M Jones Brunette
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University , Portland, Oregon 97239-3098, United States
| | | |
Collapse
|
14
|
Crystal structure of a common GPCR-binding interface for G protein and arrestin. Nat Commun 2014; 5:4801. [PMID: 25205354 PMCID: PMC4199108 DOI: 10.1038/ncomms5801] [Citation(s) in RCA: 124] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2014] [Accepted: 07/24/2014] [Indexed: 01/18/2023] Open
Abstract
G-protein-coupled receptors (GPCRs) transmit extracellular signals to activate intracellular heterotrimeric G proteins (Gαβγ) and arrestins. For G protein signalling, the Gα C-terminus (GαCT) binds to a cytoplasmic crevice of the receptor that opens upon activation. A consensus motif is shared among GαCT from the Gi/Gt family and the ‘finger loop’ region (ArrFL1–4) of all four arrestins. Here we present a 2.75 Å crystal structure of ArrFL-1, a peptide analogue of the finger loop of rod photoreceptor arrestin, in complex with the prototypical GPCR rhodopsin. Functional binding of ArrFL to the receptor was confirmed by ultraviolet-visible absorption spectroscopy, competitive binding assays and Fourier transform infrared spectroscopy. For both GαCT and ArrFL, binding to the receptor crevice induces a similar reverse turn structure, although significant structural differences are seen at the rim of the binding crevice. Our results reflect both the common receptor-binding interface and the divergent biological functions of G proteins and arrestins. G-protein-coupled receptors (GPCRs) transmit signals through intracellular heterotrimeric G proteins and arrestins. Here, Szczepek et al. present the structure of a common binding interface for Gα and arrestin on rhodopsin to shed light on key interactions that mediate transduction of specific signals through a single GPCR.
Collapse
|