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Szolomajer J, Stráner P, Kele Z, Tóth GK, Perczel A. Synthesis of the extracellular domain of GLP-1R by chemical and biotechnological approaches. RSC Adv 2022; 12:24278-24287. [PMID: 36128537 PMCID: PMC9412715 DOI: 10.1039/d2ra02784d] [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: 05/02/2022] [Accepted: 08/07/2022] [Indexed: 11/21/2022] Open
Abstract
A 10–15 kDa, 3-disulfide-bridges containing protein domain is obtained by SPPS and is expressed in E. coli.
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Affiliation(s)
- János Szolomajer
- Department of Medical Chemistry, Albert Szent-Györgyi Medical School, University of Szeged, H-6720 Szeged, Hungary
| | - Pál Stráner
- MTA-ELTE Protein Model. Res. Group and Laboratory of Structural Chemistry and Biology, Pázmány P. stny. 1/A, 1117 Budapest, Hungary
- Laboratory of Structural Chemistry and Biology, Institute of Chemistry, ELTE Eötvös Loránd University, Pázmány P. stny. 1/A, 1117 Budapest, Hungary
| | - Zoltán Kele
- Department of Medical Chemistry, Albert Szent-Györgyi Medical School, University of Szeged, H-6720 Szeged, Hungary
| | - Gábor K. Tóth
- Department of Medical Chemistry, Albert Szent-Györgyi Medical School, University of Szeged, H-6720 Szeged, Hungary
- MTA-SZTE Biomimetic Research Group, University of Szeged, H-6720 Szeged, Hungary
| | - András Perczel
- MTA-ELTE Protein Model. Res. Group and Laboratory of Structural Chemistry and Biology, Pázmány P. stny. 1/A, 1117 Budapest, Hungary
- Laboratory of Structural Chemistry and Biology, Institute of Chemistry, ELTE Eötvös Loránd University, Pázmány P. stny. 1/A, 1117 Budapest, Hungary
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2
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Isozaki Y, Tsumoto K, Tomita M. Conformation-specific monoclonal antibodies recognizing the native structure of G protein-coupled receptor (GPCR). Int Immunopharmacol 2021; 98:107872. [PMID: 34182241 DOI: 10.1016/j.intimp.2021.107872] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Revised: 06/01/2021] [Accepted: 06/08/2021] [Indexed: 01/03/2023]
Abstract
It is quite difficult to generate monoclonal antibodies that recognize the three-dimensional structures of the antigens of interest. To address this limitation, we developed a new hybridoma technology termed "optimized stereospecific targeting (SST)". Here we aimed at generating stereospecific monoclonal antibodies against a G protein-coupled receptor (GPCR). The optimized SST technique enabled the efficient production of conformation-specific monoclonal antibodies against human corticotropin-releasing hormone receptor 1 (huCRHR1). Hybridoma cells secreting stereospecific monoclonal antibodies were selectively cloned by a limiting dilution method and the target monoclonal antibodies were purified by protein A column chromatography. They specifically cross-reacted with native huCRHR1 expressed on the surface of CHO cells, whereas they showed no affinity for MDA-MB-231 cancer cells, which abundantly express EphA2 on the cell surface. Furthermore, immunofluorescence analysis revealed that treatment of huCRHR1-expressing CHO cells with 4% paraformaldehyde led to a decrease in the affinity of purified monoclonal antibodies for intact huCRHR1 on the cell surface. In addition, purified monoclonal antibodies showed no cross-reactivity with huCRHR1 expressed on Sf9 insect cells. These results strongly suggest that monoclonal antibodies generated by the optimized SST technique feature specific binding to the intact form of the target GPCR on mammalian cells.
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Affiliation(s)
- Yushi Isozaki
- Division of Chemistry for Materials, Graduate School of Engineering, Mie University, 1577 Kurimamachiya-cho, Tsu, Mie 514-8507, Japan.
| | - Kanta Tsumoto
- Division of Chemistry for Materials, Graduate School of Engineering, Mie University, 1577 Kurimamachiya-cho, Tsu, Mie 514-8507, Japan
| | - Masahiro Tomita
- Division of Chemistry for Materials, Graduate School of Engineering, Mie University, 1577 Kurimamachiya-cho, Tsu, Mie 514-8507, Japan.
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3
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Liao C, Remington JM, May V, Li J. Molecular Basis of Class B GPCR Selectivity for the Neuropeptides PACAP and VIP. Front Mol Biosci 2021; 8:644644. [PMID: 33842547 PMCID: PMC8027070 DOI: 10.3389/fmolb.2021.644644] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Accepted: 02/16/2021] [Indexed: 11/13/2022] Open
Abstract
The related neuropeptides PACAP and VIP, and their shared PAC1, VPAC1 and VPAC2 receptors, regulate a large array of physiological activities in the central and peripheral nervous systems. However, the lack of comparative and molecular mechanistic investigations hinder further understanding of their preferred binding selectivity and function. PACAP and VIP have comparable affinity at the VPAC1 and VPAC2 receptor, but PACAP is 400-1,000 fold more potent than VIP at the PAC1 receptor. A molecular understanding of the differing neuropeptide-receptor interactions and the details underlying the receptor transitions leading to receptor activation are much needed for the rational design of selective ligands. To these ends, we have combined structural information and advanced simulation techniques to study PACAP/VIP binding selectivity, full-length receptor conformation ensembles and transitions of the PACAP/VIP receptor variants and subtypes, and a few key interactions in the orthosteric-binding pocket. Our results reveal differential peptide-receptor interactions (at the atomistic detail) important for PAC1, VPAC1 and VPAC2 receptor ligand selectivity. Using microsecond-long molecular dynamics simulations and the Markov State Models, we have also identified diverse receptor conformational ensembles and microstate transition paths for each receptor, the potential mechanisms underlying receptor open and closed states, and the interactions and dynamics at the transmembrane orthosteric pocket for receptor activation. These analyses reveal important features in class B GPCR structure-dynamics-function relationships, which provide novel insights for structure-based drug discovery.
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Affiliation(s)
- Chenyi Liao
- Department of Chemistry, University of Vermont, Burlington, VT, United States.,State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Dalian, China
| | - Jacob M Remington
- Department of Chemistry, University of Vermont, Burlington, VT, United States
| | - Victor May
- Department of Neuroscience, University of Vermont, Burlington, VT, United States
| | - Jianing Li
- Department of Chemistry, University of Vermont, Burlington, VT, United States
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4
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Discovery of a stable tripeptide targeting the N-domain of CRF1 receptor. Amino Acids 2020; 52:1337-1351. [PMID: 32996057 DOI: 10.1007/s00726-020-02895-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2019] [Accepted: 09/19/2020] [Indexed: 10/23/2022]
Abstract
The corticotropin-releasing factor (CRF) and its CRF1 receptor (CRF1R) play a central role in the maintenance of homeostasis. Malfunctioning of the CRF/CRF1R unit is associated with several disorders, such as anxiety and depression. Non-peptide CRF1R-selective antagonists have been shown to exert anxiolytic and antidepressant effects on experimental animals. However, none of them is in clinical use today because of several side effects, thus demonstrating the need for the development of other more suitable CRF1R antagonists. In an effort to develop novel CRF1R antagonists we designed, synthesized and chemically characterized two tripeptide analogues of CRF, namely (R)-LMI and (S)-LMI, having their Leu either in R (or D) or in S (or L) configuration, respectively. Their design was based on the crystal structure of the N-extracellular domain (N-domain) of CRF1R/CRF complex, using a relevant array of computational methods. Experimental evaluation of the stability of synthetic peptides in human plasma has revealed that (R)-LMI is proteolytically more stable than (S)-LMI. Based on this finding, (R)-LMI was selected for pharmacological characterization. We have found that (R)-LMI is a CRF antagonist, inhibiting (1) the CRF-stimulated accumulation of cAMP in HEK 293 cells expressing the CRF1R, (2) the production of interleukins by adipocytes and (3) the proliferation rate of RAW 264.7 cells. (R)-LMI likely blocked agonist actions by interacting with the N-domain of CRF1R as suggested by data using a constitutively active chimera of CRF1R. We propose that (R)-LMI can be used as an optimal lead compound in the rational design of novel CRF antagonists.
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Fonin AV, Darling AL, Kuznetsova IM, Turoverov KK, Uversky VN. Multi-functionality of proteins involved in GPCR and G protein signaling: making sense of structure-function continuum with intrinsic disorder-based proteoforms. Cell Mol Life Sci 2019; 76:4461-4492. [PMID: 31428838 PMCID: PMC11105632 DOI: 10.1007/s00018-019-03276-1] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Revised: 08/05/2019] [Accepted: 08/12/2019] [Indexed: 12/21/2022]
Abstract
GPCR-G protein signaling system recognizes a multitude of extracellular ligands and triggers a variety of intracellular signaling cascades in response. In humans, this system includes more than 800 various GPCRs and a large set of heterotrimeric G proteins. Complexity of this system goes far beyond a multitude of pair-wise ligand-GPCR and GPCR-G protein interactions. In fact, one GPCR can recognize more than one extracellular signal and interact with more than one G protein. Furthermore, one ligand can activate more than one GPCR, and multiple GPCRs can couple to the same G protein. This defines an intricate multifunctionality of this important signaling system. Here, we show that the multifunctionality of GPCR-G protein system represents an illustrative example of the protein structure-function continuum, where structures of the involved proteins represent a complex mosaic of differently folded regions (foldons, non-foldons, unfoldons, semi-foldons, and inducible foldons). The functionality of resulting highly dynamic conformational ensembles is fine-tuned by various post-translational modifications and alternative splicing, and such ensembles can undergo dramatic changes at interaction with their specific partners. In other words, GPCRs and G proteins exist as sets of conformational/basic, inducible/modified, and functioning proteoforms characterized by a broad spectrum of structural features and possessing various functional potentials.
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Affiliation(s)
- Alexander V Fonin
- Laboratory of structural Dynamics, Stability and Folding of Proteins, Institute of Cytology, Russian Academy of Sciences, St. Petersburg, 194064, Russian Federation
| | - April L Darling
- Department of Molecular Medicine and USF Health Byrd Alzheimer's Research Institute, Morsani College of Medicine, University of South Florida, Tampa, FL, USA
| | - Irina M Kuznetsova
- Laboratory of structural Dynamics, Stability and Folding of Proteins, Institute of Cytology, Russian Academy of Sciences, St. Petersburg, 194064, Russian Federation
| | - Konstantin K Turoverov
- Laboratory of structural Dynamics, Stability and Folding of Proteins, Institute of Cytology, Russian Academy of Sciences, St. Petersburg, 194064, Russian Federation
- Department of Biophysics, Peter the Great St. Petersburg Polytechnic University, Polytechnicheskaya av. 29, St. Petersburg, 195251, Russian Federation
| | - Vladimir N Uversky
- Department of Molecular Medicine and USF Health Byrd Alzheimer's Research Institute, Morsani College of Medicine, University of South Florida, Tampa, FL, USA.
- Institute for Biological Instrumentation, Russian Academy of Sciences, Pushchino, Moscow, Russian Federation.
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6
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Liao C, de Molliens MP, Schneebeli ST, Brewer M, Song G, Chatenet D, Braas KM, May V, Li J. Targeting the PAC1 Receptor for Neurological and Metabolic Disorders. Curr Top Med Chem 2019; 19:1399-1417. [PMID: 31284862 PMCID: PMC6761004 DOI: 10.2174/1568026619666190709092647] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Revised: 12/23/2018] [Accepted: 12/26/2018] [Indexed: 12/16/2022]
Abstract
The pituitary adenylate cyclase-activating polypeptide (PACAP)-selective PAC1 receptor (PAC1R, ADCYAP1R1) is a member of the vasoactive intestinal peptide (VIP)/secretin/glucagon family of G protein-coupled receptors (GPCRs). PAC1R has been shown to play crucial roles in the central and peripheral nervous systems. The activation of PAC1R initiates diverse downstream signal transduction pathways, including adenylyl cyclase, phospholipase C, MEK/ERK, and Akt pathways that regulate a number of physiological systems to maintain functional homeostasis. Accordingly, at times of tissue injury or insult, PACAP/PAC1R activation of these pathways can be trophic to blunt or delay apoptotic events and enhance cell survival. Enhancing PAC1R signaling under these conditions has the potential to mitigate cellular damages associated with cerebrovascular trauma (including stroke), neurodegeneration (such as Parkinson's and Alzheimer's disease), or peripheral organ insults. Conversely, maladaptive PACAP/PAC1R signaling has been implicated in a number of disorders, including stressrelated psychopathologies (i.e., depression, posttraumatic stress disorder, and related abnormalities), chronic pain and migraine, and metabolic diseases; abrogating PAC1R signaling under these pathological conditions represent opportunities for therapeutic intervention. Given the diverse PAC1R-mediated biological activities, the receptor has emerged as a relevant pharmaceutical target. In this review, we first describe the current knowledge regarding the molecular structure, dynamics, and function of PAC1R. Then, we discuss the roles of PACAP and PAC1R in the activation of a variety of signaling cascades related to the physiology and diseases of the nervous system. Lastly, we examine current drug design and development of peptides and small molecules targeting PAC1R based on a number of structure- activity relationship studies and key pharmacophore elements. At present, the rational design of PAC1R-selective peptide or small-molecule therapeutics is largely hindered by the lack of structural information regarding PAC1R activation mechanisms, the PACAP-PAC1R interface, and the core segments involved in receptor activation. Understanding the molecular basis governing the PACAP interactions with its different cognate receptors will undoubtedly provide a basis for the development and/or refinement of receptor-selective therapeutics.
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Affiliation(s)
- Chenyi Liao
- Department of Chemistry, University of Vermont, Burlington, VT 05405, United States
| | | | - Severin T Schneebeli
- Department of Chemistry, University of Vermont, Burlington, VT 05405, United States
| | - Matthias Brewer
- Department of Chemistry, University of Vermont, Burlington, VT 05405, United States
| | - Gaojie Song
- Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, 200241, China
| | - David Chatenet
- INRS - Institut Armand-Frappier, 531 boul. des Prairies, Laval, QC H7V 1B7, Canada
| | - Karen M Braas
- Department of Neurological Sciences, University of Vermont, Larner College of Medicine, 149 Beaumont Avenue, Burlington, VT 05405, United States
| | - Victor May
- Department of Neurological Sciences, University of Vermont, Larner College of Medicine, 149 Beaumont Avenue, Burlington, VT 05405, United States
| | - Jianing Li
- Department of Chemistry, University of Vermont, Burlington, VT 05405, United States
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Husić M, Barsyte-Lovejoy D, Lovejoy DA. Teneurin C-Terminal Associated Peptide (TCAP)-1 and Latrophilin Interaction in HEK293 Cells: Evidence for Modulation of Intercellular Adhesion. Front Endocrinol (Lausanne) 2019; 10:22. [PMID: 30774623 PMCID: PMC6367273 DOI: 10.3389/fendo.2019.00022] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/13/2018] [Accepted: 01/14/2019] [Indexed: 11/24/2022] Open
Abstract
The teneurins are a family of four transmembrane proteins essential to intercellular adhesion processes, and are required for the development and maintenance of tissues. The Adhesion G protein-coupled receptor (GPCR) subclass latrophilins (ADGRL), or simply the latrophilins (LPHN), are putative receptors of the teneurins and act, in part, to mediate intercellular adhesion via binding with the teneurin extracellular region. At the distal tip of the extracellular region of each teneurin lies a peptide sequence termed the teneurin C-terminal associated peptide (TCAP). TCAP-1, associated with teneurin-1, is itself bioactive, suggesting that TCAP is a critical functional region of teneurin. However, the role of TCAP-1 has not been established with respect to its ability to interact with LPHN to induce downstream effects. To establish that TCAP-1 binds to LPHN1, a FLAG-tagged hormone binding domain (HBD) of LPHN1 and a GFP-tagged TCAP-1 peptide were co-expressed in HEK293 cells. Both immunoreactive epitopes were co-localized as a single band after immunoprecipitation, indicating an association between the two proteins. Moreover, fluorescent co-labeling occurred at the plasma membrane of LPHN1 over-expressing cells when treated with a FITC-tagged TCAP-1 variant. Expression of LPHN1 and treatment with TCAP-1 modulated the actin-based cytoskeleton in these cells in a manner consistent with previously reported actions of TCAP-1 and affected the overall morphology and aggregation of the cells. This study indicates that TCAP-1 may associate directly with LPHN1 and could play a role in the modulation of cytoskeletal organization and intercellular adhesion and aggregation via this interaction.
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Affiliation(s)
- Mia Husić
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada
| | | | - David A. Lovejoy
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada
- *Correspondence: David A. Lovejoy
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Deussing JM, Chen A. The Corticotropin-Releasing Factor Family: Physiology of the Stress Response. Physiol Rev 2018; 98:2225-2286. [DOI: 10.1152/physrev.00042.2017] [Citation(s) in RCA: 127] [Impact Index Per Article: 21.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The physiological stress response is responsible for the maintenance of homeostasis in the presence of real or perceived challenges. In this function, the brain activates adaptive responses that involve numerous neural circuits and effector molecules to adapt to the current and future demands. A maladaptive stress response has been linked to the etiology of a variety of disorders, such as anxiety and mood disorders, eating disorders, and the metabolic syndrome. The neuropeptide corticotropin-releasing factor (CRF) and its relatives, the urocortins 1–3, in concert with their receptors (CRFR1, CRFR2), have emerged as central components of the physiological stress response. This central peptidergic system impinges on a broad spectrum of physiological processes that are the basis for successful adaptation and concomitantly integrate autonomic, neuroendocrine, and behavioral stress responses. This review focuses on the physiology of CRF-related peptides and their cognate receptors with the aim of providing a comprehensive up-to-date overview of the field. We describe the major molecular features covering aspects of gene expression and regulation, structural properties, and molecular interactions, as well as mechanisms of signal transduction and their surveillance. In addition, we discuss the large body of published experimental studies focusing on state-of-the-art genetic approaches with high temporal and spatial precision, which collectively aimed to dissect the contribution of CRF-related ligands and receptors to different levels of the stress response. We discuss the controversies in the field and unravel knowledge gaps that might pave the way for future research directions and open up novel opportunities for therapeutic intervention.
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Affiliation(s)
- Jan M. Deussing
- Department of Stress Neurobiology and Neurogenetics, Max Planck Institute of Psychiatry, Munich, Germany; and Department of Neurobiology, Weizmann Institute of Science, Rehovot, Israel
| | - Alon Chen
- Department of Stress Neurobiology and Neurogenetics, Max Planck Institute of Psychiatry, Munich, Germany; and Department of Neurobiology, Weizmann Institute of Science, Rehovot, Israel
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Karageorgos V, Venihaki M, Sakellaris S, Pardalos M, Kontakis G, Matsoukas MT, Gravanis A, Margioris A, Liapakis G. Current understanding of the structure and function of family B GPCRs to design novel drugs. Hormones (Athens) 2018; 17:45-59. [PMID: 29858864 DOI: 10.1007/s42000-018-0009-5] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/03/2017] [Accepted: 01/25/2018] [Indexed: 01/10/2023]
Abstract
Family B of G-protein-coupled receptors (GPCRs) and their ligands play a central role in a number of homeostatic mechanisms in the endocrine, gastrointestinal, skeletal, immune, cardiovascular and central nervous systems. Alterations in family B GPCR-regulated homeostatic mechanisms may cause a variety of potentially life-threatening conditions, signifying the necessity to develop novel ligands targeting these receptors. Obtaining structural and functional information on family B GPCRs will accelerate the development of novel drugs to target these receptors. Family B GPCRs are proteins that span the plasma membrane seven times, thus forming seven transmembrane domains (TM1-TM7) which are connected to each other by three extracellular (EL) and three intracellular (IL) loops. In addition, these receptors have a long extracellular N-domain and an intracellular C-tail. The upper parts of the TMs and ELs form the J-domain of receptors. The C-terminal region of peptides first binds to the N-domain of receptors. This 'first-step' interaction orients the N-terminal region of peptides towards the J-domain of receptors, thus resulting in a 'second-step' of ligand-receptor interaction that activates the receptor. Activation-associated structural changes of receptors are transmitted through TMs to their intracellular regions and are responsible for their interaction with the G proteins and activation of the latter, thus resulting in a biological effect. This review summarizes the current information regarding the structure and function of family B GPCRs and their physiological and pathophysiological roles.
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Affiliation(s)
- Vlasios Karageorgos
- Department of Pharmacology, School of Medicine, University of Crete, Voutes, 71003, Heraklion, Crete, Greece
| | - Maria Venihaki
- Department of Clinical Chemistry, School of Medicine, University of Crete, Heraklion, Crete, Greece
| | - Stelios Sakellaris
- Department of Pharmacology, School of Medicine, University of Crete, Voutes, 71003, Heraklion, Crete, Greece
| | - Michail Pardalos
- Department of Pharmacology, School of Medicine, University of Crete, Voutes, 71003, Heraklion, Crete, Greece
| | - George Kontakis
- Department of Orthopedics, University Hospital of Heraklion, Crete, Greece
| | | | - Achille Gravanis
- Department of Pharmacology, School of Medicine, University of Crete, Voutes, 71003, Heraklion, Crete, Greece
| | - Andreas Margioris
- Department of Clinical Chemistry, School of Medicine, University of Crete, Heraklion, Crete, Greece
| | - George Liapakis
- Department of Pharmacology, School of Medicine, University of Crete, Voutes, 71003, Heraklion, Crete, Greece.
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Extending the Structural View of Class B GPCRs. Trends Biochem Sci 2017; 42:946-960. [PMID: 29132948 DOI: 10.1016/j.tibs.2017.10.003] [Citation(s) in RCA: 94] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2017] [Revised: 10/02/2017] [Accepted: 10/09/2017] [Indexed: 01/27/2023]
Abstract
The secretin-like class B family of G protein-coupled receptors (GPCRs) are key players in hormonal homeostasis. Recent structures of various receptors in complex with a variety of orthosteric and allosteric ligands provide fundamental new insights into the function and mechanism of class B GPCRs, including: (i) ligand-induced changes in the relative orientation of the extracellular and transmembrane receptor domains; (ii) intramolecular interaction networks that stabilize conformational changes to accommodate intracellular G protein binding; and (iii) allosteric modulation of receptor activation. This review provides a comprehensive analysis of the structural, biochemical, and pharmacological data on class B GPCRs for understanding ligand-receptor interaction and modulation mechanisms and assessing the potential implications for drug discovery for the secretin-like GPCR family.
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Seidel L, Zarzycka B, Zaidi SA, Katritch V, Coin I. Structural insight into the activation of a class B G-protein-coupled receptor by peptide hormones in live human cells. eLife 2017; 6. [PMID: 28771403 PMCID: PMC5542768 DOI: 10.7554/elife.27711] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2017] [Accepted: 07/17/2017] [Indexed: 12/22/2022] Open
Abstract
The activation mechanism of class B G-protein-coupled receptors (GPCRs) remains largely unknown. To characterize conformational changes induced by peptide hormones, we investigated interactions of the class B corticotropin-releasing factor receptor type 1 (CRF1R) with two peptide agonists and three peptide antagonists obtained by N-truncation of the agonists. Surface mapping with genetically encoded photo-crosslinkers and pair-wise crosslinking revealed distinct footprints of agonists and antagonists on the transmembrane domain (TMD) of CRF1R and identified numerous ligand-receptor contact sites, directly from the intact receptor in live human cells. The data enabled generating atomistic models of CRF- and CRF(12-41)-bound CRF1R, further explored by molecular dynamics simulations. We show that bound agonist and antagonist adopt different folds and stabilize distinct TMD conformations, which involves bending of helices VI and VII around flexible glycine hinges. Conservation of these glycine hinges among all class B GPCRs suggests their general role in activation of these receptors. DOI:http://dx.doi.org/10.7554/eLife.27711.001
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Affiliation(s)
- Lisa Seidel
- Institute of Biochemistry, Leipzig University, Leipzig, Germany
| | - Barbara Zarzycka
- Department of Biological Sciences, Bridge Institute, University of Southern California, Los Angeles, United States
| | - Saheem A Zaidi
- Department of Biological Sciences, Bridge Institute, University of Southern California, Los Angeles, United States
| | - Vsevolod Katritch
- Department of Biological Sciences, Bridge Institute, University of Southern California, Los Angeles, United States.,Department of Chemistry, Bridge Institute, University of Southern California, Los Angeles, United States
| | - Irene Coin
- Institute of Biochemistry, Leipzig University, Leipzig, Germany
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12
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Inda C, Armando NG, Dos Santos Claro PA, Silberstein S. Endocrinology and the brain: corticotropin-releasing hormone signaling. Endocr Connect 2017; 6:R99-R120. [PMID: 28710078 PMCID: PMC5551434 DOI: 10.1530/ec-17-0111] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/11/2017] [Accepted: 07/14/2017] [Indexed: 01/01/2023]
Abstract
Corticotropin-releasing hormone (CRH) is a key player of basal and stress-activated responses in the hypothalamic-pituitary-adrenal axis (HPA) and in extrahypothalamic circuits, where it functions as a neuromodulator to orchestrate humoral and behavioral adaptive responses to stress. This review describes molecular components and cellular mechanisms involved in CRH signaling downstream of its G protein-coupled receptors (GPCRs) CRHR1 and CRHR2 and summarizes recent findings that challenge the classical view of GPCR signaling and impact on our understanding of CRHRs function. Special emphasis is placed on recent studies of CRH signaling that revealed new mechanistic aspects of cAMP generation and ERK1/2 activation in physiologically relevant contexts of the neurohormone action. In addition, we present an overview of the pathophysiological role of the CRH system, which highlights the need for a precise definition of CRHRs signaling at molecular level to identify novel targets for pharmacological intervention in neuroendocrine tissues and specific brain areas involved in CRH-related disorders.
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Affiliation(s)
- Carolina Inda
- Instituto de Investigación en Biomedicina de Buenos Aires (IBioBA)-CONICET-Partner Institute of the Max Planck SocietyBuenos Aires, Argentina
- DFBMCFacultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Natalia G Armando
- Instituto de Investigación en Biomedicina de Buenos Aires (IBioBA)-CONICET-Partner Institute of the Max Planck SocietyBuenos Aires, Argentina
| | - Paula A Dos Santos Claro
- Instituto de Investigación en Biomedicina de Buenos Aires (IBioBA)-CONICET-Partner Institute of the Max Planck SocietyBuenos Aires, Argentina
| | - Susana Silberstein
- Instituto de Investigación en Biomedicina de Buenos Aires (IBioBA)-CONICET-Partner Institute of the Max Planck SocietyBuenos Aires, Argentina
- DFBMCFacultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina
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13
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Sekar R, Singh K, Arokiaraj AWR, Chow BKC. Pharmacological Actions of Glucagon-Like Peptide-1, Gastric Inhibitory Polypeptide, and Glucagon. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2016; 326:279-341. [PMID: 27572131 DOI: 10.1016/bs.ircmb.2016.05.002] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Glucagon family of peptide hormones is a group of structurally related brain-gut peptides that exert their pleiotropic actions through interactions with unique members of class B1 G protein-coupled receptors (GPCRs). They are key regulators of hormonal homeostasis and are important drug targets for metabolic disorders such as type-2 diabetes mellitus (T2DM), obesity, and dysregulations of the nervous systems such as migraine, anxiety, depression, neurodegeneration, psychiatric disorders, and cardiovascular diseases. The current review aims to provide a detailed overview of the current understanding of the pharmacological actions and therapeutic advances of three members within this family including glucagon-like peptide-1 (GLP-1), gastric inhibitory polypeptide (GIP), and glucagon.
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Affiliation(s)
- R Sekar
- School of Biological Sciences, University of Hong Kong, Hong Kong, China
| | - K Singh
- School of Biological Sciences, University of Hong Kong, Hong Kong, China
| | - A W R Arokiaraj
- School of Biological Sciences, University of Hong Kong, Hong Kong, China
| | - B K C Chow
- School of Biological Sciences, University of Hong Kong, Hong Kong, China.
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14
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Zhao LH, Yin Y, Yang D, Liu B, Hou L, Wang X, Pal K, Jiang Y, Feng Y, Cai X, Dai A, Liu M, Wang MW, Melcher K, Xu HE. Differential Requirement of the Extracellular Domain in Activation of Class B G Protein-coupled Receptors. J Biol Chem 2016; 291:15119-30. [PMID: 27226600 DOI: 10.1074/jbc.m116.726620] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2016] [Indexed: 12/16/2022] Open
Abstract
G protein-coupled receptors (GPCRs) from the secretin-like (class B) family are key players in hormonal homeostasis and are important drug targets for the treatment of metabolic disorders and neuronal diseases. They consist of a large N-terminal extracellular domain (ECD) and a transmembrane domain (TMD) with the GPCR signature of seven transmembrane helices. Class B GPCRs are activated by peptide hormones with their C termini bound to the receptor ECD and their N termini bound to the TMD. It is thought that the ECD functions as an affinity trap to bind and localize the hormone to the receptor. This in turn would allow the hormone N terminus to insert into the TMD and induce conformational changes of the TMD to activate downstream signaling. In contrast to this prevailing model, we demonstrate that human class B GPCRs vary widely in their requirement of the ECD for activation. In one group, represented by corticotrophin-releasing factor receptor 1 (CRF1R), parathyroid hormone receptor (PTH1R), and pituitary adenylate cyclase activating polypeptide type 1 receptor (PAC1R), the ECD requirement for high affinity hormone binding can be bypassed by induced proximity and mass action effects, whereas in the other group, represented by glucagon receptor (GCGR) and glucagon-like peptide-1 receptor (GLP-1R), the ECD is required for signaling even when the hormone is covalently linked to the TMD. Furthermore, the activation of GLP-1R by small molecules that interact with the intracellular side of the receptor is dependent on the presence of its ECD, suggesting a direct role of the ECD in GLP-1R activation.
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Affiliation(s)
- Li-Hua Zhao
- From the Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai 200241, China, VARI-SIMM Center for Structure and Function of Drug Targets and the CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Yanting Yin
- VARI-SIMM Center for Structure and Function of Drug Targets and the CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China, Laboratory of Structural Sciences, Center for Structural Biology and Drug Discovery, Van Andel Research Institute, Grand Rapids, Michigan 49503
| | - Dehua Yang
- The National Center for Drug Screening and the CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Bo Liu
- VARI-SIMM Center for Structure and Function of Drug Targets and the CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Li Hou
- VARI-SIMM Center for Structure and Function of Drug Targets and the CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Xiaoxi Wang
- VARI-SIMM Center for Structure and Function of Drug Targets and the CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Kuntal Pal
- Laboratory of Structural Sciences, Center for Structural Biology and Drug Discovery, Van Andel Research Institute, Grand Rapids, Michigan 49503
| | - Yi Jiang
- VARI-SIMM Center for Structure and Function of Drug Targets and the CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Yang Feng
- The National Center for Drug Screening and the CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Xiaoqing Cai
- The National Center for Drug Screening and the CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Antao Dai
- The National Center for Drug Screening and the CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Mingyao Liu
- From the Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai 200241, China, The Institute of Biosciences and Technology, Texas A&M University Health Science Center, Houston, Texas 77030
| | - Ming-Wei Wang
- The National Center for Drug Screening and the CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China, School of Pharmacy, Fudan University, 826 Zhangheng Road, Shanghai 201203, China
| | - Karsten Melcher
- Laboratory of Structural Sciences, Center for Structural Biology and Drug Discovery, Van Andel Research Institute, Grand Rapids, Michigan 49503,
| | - H Eric Xu
- VARI-SIMM Center for Structure and Function of Drug Targets and the CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China, Laboratory of Structural Sciences, Center for Structural Biology and Drug Discovery, Van Andel Research Institute, Grand Rapids, Michigan 49503,
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15
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Wootten D, Miller LJ, Koole C, Christopoulos A, Sexton PM. Allostery and Biased Agonism at Class B G Protein-Coupled Receptors. Chem Rev 2016; 117:111-138. [PMID: 27040440 DOI: 10.1021/acs.chemrev.6b00049] [Citation(s) in RCA: 77] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Class B G protein-coupled receptors (GPCRs) respond to paracrine or endocrine peptide hormones involved in control of bone homeostasis, glucose regulation, satiety, and gastro-intestinal function, as well as pain transmission. These receptors are targets for existing drugs that treat osteoporosis, hypercalcaemia, Paget's disease, type II diabetes, and obesity and are being actively pursued as targets for numerous other diseases. Exploitation of class B receptors has been limited by difficulties with small molecule drug discovery and development and an under appreciation of factors governing optimal therapeutic efficacy. Recently, there has been increasing awareness of novel attributes of GPCR function that offer new opportunity for drug development. These include the presence of allosteric binding sites on the receptor that can be exploited as drug binding pockets and the ability of individual drugs to enrich subpopulations of receptor conformations to selectively control signaling, a phenomenon termed biased agonism. In this review, current knowledge of biased signaling and small molecule allostery within class B GPCRs is discussed, highlighting areas that have progressed significantly over the past decade, in addition to those that remain largely unexplored with respect to these phenomena.
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Affiliation(s)
- Denise Wootten
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University , Parkville 3052, Victoria, Australia
| | - Laurence J Miller
- Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic , Scottsdale, Arizona 85259, United States
| | - Cassandra Koole
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University , Parkville 3052, Victoria, Australia.,Laboratory of Chemical Biology and Signal Transduction, The Rockefeller University , New York, New York 10065, United States
| | - Arthur Christopoulos
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University , Parkville 3052, Victoria, Australia
| | - Patrick M Sexton
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University , Parkville 3052, Victoria, Australia
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16
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Groß A, Hashimoto C, Sticht H, Eichler J. Synthetic Peptides as Protein Mimics. Front Bioeng Biotechnol 2016; 3:211. [PMID: 26835447 PMCID: PMC4717299 DOI: 10.3389/fbioe.2015.00211] [Citation(s) in RCA: 82] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2015] [Accepted: 12/22/2015] [Indexed: 12/21/2022] Open
Abstract
The design and generation of molecules capable of mimicking the binding and/or functional sites of proteins represents a promising strategy for the exploration and modulation of protein function through controlled interference with the underlying molecular interactions. Synthetic peptides have proven an excellent type of molecule for the mimicry of protein sites because such peptides can be generated as exact copies of protein fragments, as well as in diverse chemical modifications, which includes the incorporation of a large range of non-proteinogenic amino acids as well as the modification of the peptide backbone. Apart from extending the chemical and structural diversity presented by peptides, such modifications also increase the proteolytic stability of the molecules, enhancing their utility for biological applications. This article reviews recent advances by this and other laboratories in the use of synthetic protein mimics to modulate protein function, as well as to provide building blocks for synthetic biology.
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Affiliation(s)
- Andrea Groß
- Department of Chemistry and Pharmacy, University of Erlangen-Nuremberg, Erlangen, Germany
| | - Chie Hashimoto
- Department of Chemistry and Pharmacy, University of Erlangen-Nuremberg, Erlangen, Germany
| | - Heinrich Sticht
- Institute of Biochemistry, University of Erlangen-Nuremberg, Erlangen, Germany
| | - Jutta Eichler
- Department of Chemistry and Pharmacy, University of Erlangen-Nuremberg, Erlangen, Germany
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17
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Abstract
It is now recognized that G protein-coupled receptors (GPCRs), once considered largely independent functional units, have a far more diverse molecular architecture. Receptor activity-modifying proteins (RAMPs) provide an important example of proteins that interact with GPCRs to modify their function. RAMPs are able to act as pharmacological switches and chaperones, and they can regulate signaling and/or trafficking in a receptor-dependent manner. This review covers recent discoveries in the RAMP field and summarizes the known GPCR partners and functions of RAMPs. We also discuss the first peptide-bound structures of RAMP-GPCR complexes, which give insight into the molecular mechanisms that enable RAMPs to alter the pharmacology and signaling of GPCRs.
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Affiliation(s)
- Debbie L Hay
- School of Biological Sciences and Maurice Wilkins Center, University of Auckland, Auckland 1142, New Zealand;
| | - Augen A Pioszak
- Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104;
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18
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Conformational thermostabilisation of corticotropin releasing factor receptor 1. Sci Rep 2015; 5:11954. [PMID: 26159865 PMCID: PMC4498186 DOI: 10.1038/srep11954] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2015] [Accepted: 06/11/2015] [Indexed: 01/16/2023] Open
Abstract
Recent technical advances have greatly facilitated G-protein coupled receptors crystallography as evidenced by the number of successful x-ray structures that have been reported recently. These technical advances include novel detergents, specialised crystallography techniques as well as protein engineering solutions such as fusions and conformational thermostabilisation. Using conformational thermostabilisation, it is possible to generate variants of GPCRs that exhibit significantly increased stability in detergent micelles whilst preferentially occupying a single conformation. In this paper we describe for the first time the application of this technique to a member of a class B GPCR, the corticotropin releasing factor receptor 1 (CRF1R). Mutational screening in the presence of the inverse agonist, CP-376395, resulted in the identification of a construct with twelve point mutations that exhibited significantly increased thermal stability in a range of detergents. We further describe the subsequent construct engineering steps that eventually yielded a crystallisation-ready construct which recently led to the solution of the first x-ray structure of a class B receptor. Finally, we have used molecular dynamic simulation to provide structural insight into CRF1R instability as well as the stabilising effects of the mutants, which may be extended to other class B receptors considering the high degree of structural conservation.
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19
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Lee SM, Booe JM, Pioszak AA. Structural insights into ligand recognition and selectivity for classes A, B, and C GPCRs. Eur J Pharmacol 2015; 763:196-205. [PMID: 25981303 DOI: 10.1016/j.ejphar.2015.05.013] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Revised: 05/05/2015] [Accepted: 05/12/2015] [Indexed: 01/14/2023]
Abstract
The G protein-coupled receptor (GPCR) superfamily constitutes the largest collection of cell surface signaling proteins with approximately 800 members in the human genome. GPCRs regulate virtually all aspects of physiology and they are an important class of drug targets with ~30% of drugs on the market targeting a GPCR. Breakthroughs in GPCR structural biology in recent years have significantly expanded our understanding of GPCR structure and function and ushered in a new era of structure-based drug design for GPCRs. Crystal structures for nearly thirty distinct GPCRs are now available including receptors from each of the major classes, A, B, C, and F. These structures provide a foundation for understanding the molecular basis of GPCR pharmacology. Here, we review structural mechanisms of ligand recognition and selectivity of GPCRs with a focus on selected examples from classes A, B, and C, and we highlight major unresolved questions for future structural studies.
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Affiliation(s)
- Sang-Min Lee
- Department of Biochemistry and Molecular Biology, The University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA
| | - Jason M Booe
- Department of Biochemistry and Molecular Biology, The University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA
| | - Augen A Pioszak
- Department of Biochemistry and Molecular Biology, The University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
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20
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Perrin MH, Tan LA, Vaughan JM, Lewis KA, Donaldson CJ, Miller C, Erchegyi J, Rivier JE, Sawchenko PE. Characterization of a Pachymedusa dacnicolor-Sauvagine analog as a new high-affinity radioligand for corticotropin-releasing factor receptor studies. J Pharmacol Exp Ther 2015; 353:307-17. [PMID: 25736419 DOI: 10.1124/jpet.114.222307] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
The corticotropin-releasing factor (CRF) peptide family comprises the mammalian peptides CRF and the urocortins as well as frog skin sauvagine and fish urophyseal urotensin. Advances in understanding the roles of the CRF ligand family and associated receptors have often relied on radioreceptor assays using labeled CRF ligands. These assays depend on stable, high-affinity CRF analogs that can be labeled, purified, and chemically characterized. Analogs of several of the native peptides have been used in this context, most prominently including sauvagine from the frog Phyllomedusa sauvageii (PS-Svg). Because each of these affords both advantages and disadvantages, new analogs with superior properties would be welcome. We find that a sauvagine-like peptide recently isolated from a different frog species, Pachymedusa dacnicolor (PD-Svg), is a high-affinity agonist whose radioiodinated analog, [(125)ITyr(0)-Glu(1), Nle(17)]-PD-Svg, exhibits improved biochemical properties over those of earlier iodinated agonists. Specifically, the PD-Svg radioligand binds both CRF receptors with comparably high affinity as its PS-Svg counterpart, but detects a greater number of sites on both type 1 and type 2 receptors. PD-Svg is also ∼10 times more potent at stimulating cAMP accumulation in cells expressing the native receptors. Autoradiographic localization using the PD-Svg radioligand shows robust specific binding to rodent brain and peripheral tissues that identifies consensus CRF receptor-expressing sites in a greater number and/or with greater sensitivity than its PS-Svg counterpart. We suggest that labeled analogs of PD-Svg may be useful tools for biochemical, structural, pharmacological, and anatomic studies of CRF receptors.
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Affiliation(s)
- Marilyn H Perrin
- Clayton Foundation Laboratories for Peptide Biology (M.H.P., J.M.V., K.A.L., C.J.D., C.M., J.E., J.E.R., P.E.S.) and Laboratory of Neuronal Structure and Function (L.A.T., P.E.S.), The Salk Institute for Biological Studies, La Jolla, California
| | - Laura A Tan
- Clayton Foundation Laboratories for Peptide Biology (M.H.P., J.M.V., K.A.L., C.J.D., C.M., J.E., J.E.R., P.E.S.) and Laboratory of Neuronal Structure and Function (L.A.T., P.E.S.), The Salk Institute for Biological Studies, La Jolla, California
| | - Joan M Vaughan
- Clayton Foundation Laboratories for Peptide Biology (M.H.P., J.M.V., K.A.L., C.J.D., C.M., J.E., J.E.R., P.E.S.) and Laboratory of Neuronal Structure and Function (L.A.T., P.E.S.), The Salk Institute for Biological Studies, La Jolla, California
| | - Kathy A Lewis
- Clayton Foundation Laboratories for Peptide Biology (M.H.P., J.M.V., K.A.L., C.J.D., C.M., J.E., J.E.R., P.E.S.) and Laboratory of Neuronal Structure and Function (L.A.T., P.E.S.), The Salk Institute for Biological Studies, La Jolla, California
| | - Cynthia J Donaldson
- Clayton Foundation Laboratories for Peptide Biology (M.H.P., J.M.V., K.A.L., C.J.D., C.M., J.E., J.E.R., P.E.S.) and Laboratory of Neuronal Structure and Function (L.A.T., P.E.S.), The Salk Institute for Biological Studies, La Jolla, California
| | - Charleen Miller
- Clayton Foundation Laboratories for Peptide Biology (M.H.P., J.M.V., K.A.L., C.J.D., C.M., J.E., J.E.R., P.E.S.) and Laboratory of Neuronal Structure and Function (L.A.T., P.E.S.), The Salk Institute for Biological Studies, La Jolla, California
| | - Judit Erchegyi
- Clayton Foundation Laboratories for Peptide Biology (M.H.P., J.M.V., K.A.L., C.J.D., C.M., J.E., J.E.R., P.E.S.) and Laboratory of Neuronal Structure and Function (L.A.T., P.E.S.), The Salk Institute for Biological Studies, La Jolla, California
| | - Jean E Rivier
- Clayton Foundation Laboratories for Peptide Biology (M.H.P., J.M.V., K.A.L., C.J.D., C.M., J.E., J.E.R., P.E.S.) and Laboratory of Neuronal Structure and Function (L.A.T., P.E.S.), The Salk Institute for Biological Studies, La Jolla, California
| | - Paul E Sawchenko
- Clayton Foundation Laboratories for Peptide Biology (M.H.P., J.M.V., K.A.L., C.J.D., C.M., J.E., J.E.R., P.E.S.) and Laboratory of Neuronal Structure and Function (L.A.T., P.E.S.), The Salk Institute for Biological Studies, La Jolla, California
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21
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Rivier JE, Rivier CL. Corticotropin-releasing factor peptide antagonists: design, characterization and potential clinical relevance. Front Neuroendocrinol 2014; 35:161-70. [PMID: 24269930 PMCID: PMC3965584 DOI: 10.1016/j.yfrne.2013.10.006] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/08/2013] [Revised: 10/18/2013] [Accepted: 10/20/2013] [Indexed: 12/19/2022]
Abstract
Elusive for more than half a century, corticotropin-releasing factor (CRF) was finally isolated and characterized in 1981 from ovine hypothalami and shortly thereafter, from rat brains. Thirty years later, much has been learned about the function and localization of CRF and related family members (Urocortins 1, 2 and 3) and their 2 receptors, CRF receptor type 1 (CRFR1) and CRF receptor type 2 (CRFR2). Here, we report the stepwise development of peptide CRF agonists and antagonists, which led to the CRFR1 agonist Stressin1; the long-acting antagonists Astressin2-B which is specific for CRFR2; and Astressin B, which binds to both CRFR1 and CRFR2.This analog has potential for the treatment of CRF-dependent diseases in the periphery, such as irritable bowel syndrome.
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Affiliation(s)
- Jean E Rivier
- The Salk Institute, The Clayton Foundation Laboratories for Peptide Biology, La Jolla, CA 92037, USA.
| | - Catherine L Rivier
- The Salk Institute, The Clayton Foundation Laboratories for Peptide Biology, La Jolla, CA 92037, USA
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22
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Expression and functional characterization of membrane-integrated mammalian corticotropin releasing factor receptors 1 and 2 in Escherichia coli. PLoS One 2014; 9:e84013. [PMID: 24465390 PMCID: PMC3894963 DOI: 10.1371/journal.pone.0084013] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2012] [Accepted: 11/19/2013] [Indexed: 11/19/2022] Open
Abstract
Corticotropin-Releasing Factor Receptors (CRFRs) are class B1 G-protein-coupled receptors, which bind peptides of the corticotropin releasing factor family and are key mediators in the stress response. In order to dissect the receptors' binding specificity and enable structural studies, full-length human CRFR1α and mouse CRFR2β as well as fragments lacking the N-terminal extracellular domain, were overproduced in E. coli. The characteristics of different CRFR2β-PhoA gene fusion products expressed in bacteria were found to be in agreement with the predicted ones in the hepta-helical membrane topology model. Recombinant histidine-tagged CRFR1α and CRFR2β expression levels and bacterial subcellular localization were evaluated by cell fractionation and Western blot analysis. Protein expression parameters were assessed, including the influence of E. coli bacterial hosts, culture media and the impact of either PelB or DsbA signal peptide. In general, the large majority of receptor proteins became inserted in the bacterial membrane. Across all experimental conditions significantly more CRFR2β product was obtained in comparison to CRFR1α. Following a detergent screen analysis, bacterial membranes containing CRFR1α and CRFR2β were best solubilized with the zwitterionic detergent FC-14. Binding of different peptide ligands to CRFR1α and CRFR2β membrane fractions were similar, in part, to the complex pharmacology observed in eukaryotic cells. We suggest that our E. coli expression system producing functional CRFRs will be useful for large-scale expression of these receptors for structural studies.
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23
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Hollenstein K, de Graaf C, Bortolato A, Wang MW, Marshall FH, Stevens RC. Insights into the structure of class B GPCRs. Trends Pharmacol Sci 2013; 35:12-22. [PMID: 24359917 DOI: 10.1016/j.tips.2013.11.001] [Citation(s) in RCA: 172] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2013] [Revised: 10/30/2013] [Accepted: 11/01/2013] [Indexed: 02/08/2023]
Abstract
The secretin-like (class B) family of G protein-coupled receptors (GPCRs) are key players in hormonal homeostasis and are interesting drug targets for the treatment of several metabolic disorders (such as type 2 diabetes, osteoporosis, and obesity) and nervous system diseases (such as migraine, anxiety, and depression). The recently solved crystal structures of the transmembrane domains of the human glucagon receptor and human corticotropin-releasing factor receptor 1 have opened up new opportunities to study the structure and function of class B GPCRs. The current review shows how these structures offer more detailed explanations to previous biochemical and pharmacological studies of class B GPCRs, and provides new insights into their interactions with ligands.
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Affiliation(s)
- Kaspar Hollenstein
- Heptares Therapeutics Ltd, BioPark, Broadwater Road, Welwyn Garden City, AL7 3AX, UK
| | - Chris de Graaf
- Division of Medicinal Chemistry, Faculty of Sciences, Amsterdam Institute for Molecules, Medicines and Systems (AIMMS), VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
| | - Andrea Bortolato
- Heptares Therapeutics Ltd, BioPark, Broadwater Road, Welwyn Garden City, AL7 3AX, UK
| | - Ming-Wei Wang
- The National Center for Drug Screening and the CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences (CAS), 189 Guo Shou Jing Road, Shanghai, 201203, China
| | - Fiona H Marshall
- Heptares Therapeutics Ltd, BioPark, Broadwater Road, Welwyn Garden City, AL7 3AX, UK.
| | - Raymond C Stevens
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
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24
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Slominski AT, Zmijewski MA, Zbytek B, Tobin DJ, Theoharides TC, Rivier J. Key role of CRF in the skin stress response system. Endocr Rev 2013; 34:827-84. [PMID: 23939821 PMCID: PMC3857130 DOI: 10.1210/er.2012-1092] [Citation(s) in RCA: 277] [Impact Index Per Article: 25.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/30/2012] [Accepted: 08/02/2013] [Indexed: 02/08/2023]
Abstract
The discovery of corticotropin-releasing factor (CRF) or CRH defining the upper regulatory arm of the hypothalamic-pituitary-adrenal (HPA) axis, along with the identification of the corresponding receptors (CRFRs 1 and 2), represents a milestone in our understanding of central mechanisms regulating body and local homeostasis. We focused on the CRF-led signaling systems in the skin and offer a model for regulation of peripheral homeostasis based on the interaction of CRF and the structurally related urocortins with corresponding receptors and the resulting direct or indirect phenotypic effects that include regulation of epidermal barrier function, skin immune, pigmentary, adnexal, and dermal functions necessary to maintain local and systemic homeostasis. The regulatory modes of action include the classical CRF-led cutaneous equivalent of the central HPA axis, the expression and function of CRF and related peptides, and the stimulation of pro-opiomelanocortin peptides or cytokines. The key regulatory role is assigned to the CRFR-1α receptor, with other isoforms having modulatory effects. CRF can be released from sensory nerves and immune cells in response to emotional and environmental stressors. The expression sequence of peptides includes urocortin/CRF→pro-opiomelanocortin→ACTH, MSH, and β-endorphin. Expression of these peptides and of CRFR-1α is environmentally regulated, and their dysfunction can lead to skin and systemic diseases. Environmentally stressed skin can activate both the central and local HPA axis through either sensory nerves or humoral factors to turn on homeostatic responses counteracting cutaneous and systemic environmental damage. CRF and CRFR-1 may constitute novel targets through the use of specific agonists or antagonists, especially for therapy of skin diseases that worsen with stress, such as atopic dermatitis and psoriasis.
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Affiliation(s)
- Andrzej T Slominski
- MD, PhD, Department of Pathology and Laboratory Medicine, University of Tennessee Health Science Center; 930 Madison Avenue, Suite 500, Memphis, Tennessee 38163.
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25
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Coin I, Katritch V, Sun T, Xiang Z, Siu FY, Beyermann M, Stevens RC, Wang L. Genetically encoded chemical probes in cells reveal the binding path of urocortin-I to CRF class B GPCR. Cell 2013; 155:1258-69. [PMID: 24290358 DOI: 10.1016/j.cell.2013.11.008] [Citation(s) in RCA: 139] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2013] [Revised: 08/26/2013] [Accepted: 11/07/2013] [Indexed: 01/19/2023]
Abstract
Molecular determinants regulating the activation of class B G-protein-coupled receptors (GPCRs) by native peptide agonists are largely unknown. We have investigated here the interaction between the corticotropin releasing factor receptor type 1 (CRF1R) and its native 40-mer peptide ligand Urocortin-I directly in mammalian cells. By incorporating unnatural amino acid photochemical and new click-chemical probes into the intact receptor expressed in the native membrane of live cells, 44 intermolecular spatial constraints have been derived for the ligand-receptor interaction. The data were analyzed in the context of the recently resolved crystal structure of CRF1R transmembrane domain and existing extracellular domain structures, yielding a complete conformational model for the peptide-receptor complex. Structural features of the receptor-ligand complex yield molecular insights on the mechanism of receptor activation and the basis for discrimination between agonist and antagonist function.
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Affiliation(s)
- Irene Coin
- Jack H. Skirball Center for Chemical Biology and Proteomics, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA
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Rösner HI, Kragelund BB. Structure and dynamic properties of membrane proteins using NMR. Compr Physiol 2013; 2:1491-539. [PMID: 23798308 DOI: 10.1002/cphy.c110036] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Integral membrane proteins are one of the most challenging groups of macromolecules despite their apparent conformational simplicity. They manage and drive transport, circulate information, and participate in cellular movements via interactions with other proteins and through intricate conformational changes. Their structural and functional decoding is challenging and has imposed demanding experimental development. Solution nuclear magnetic resonance (NMR) spectroscopy is one of the techniques providing the capacity to make a significant difference in the deciphering of the membrane protein structure-function paradigm. The method has evolved dramatically during the last decade resulting in a plethora of new experiments leading to a significant increase in the scientific repertoire for studying membrane proteins. Besides solving the three-dimensional structures using state-of-the-art approaches, a large variety of developments of well-established techniques are available providing insight into membrane protein flexibility, dynamics, and interactions. Inspired by the speed of development in the application of new strategies, by invention of methods to measure solvent accessibility and describe low-populated states, this review seeks to introduce the vast possibilities solution NMR can offer to the study of membrane protein structure-function analyses with special focus on applicability.
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Affiliation(s)
- Heike I Rösner
- Structural Biology and NMR Laboratory, Department of Biology, University of Copenhagen, Copenhagen, Denmark
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Grammatopoulos DK. Insights into mechanisms of corticotropin-releasing hormone receptor signal transduction. Br J Pharmacol 2012; 166:85-97. [PMID: 21883143 DOI: 10.1111/j.1476-5381.2011.01631.x] [Citation(s) in RCA: 90] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
During evolution, mammals have developed remarkably similar molecular mechanisms to respond to external challenges and maintain survival. Critical regulators of these mechanisms are the family of 'stress'-peptides that consists of the corticotropin-releasing hormone (CRH) and urocortins (Ucns). These neuropeptides 'fine-tune' integration of an intricate series of physiological responses involving the autonomic, endocrine, immune, cardiovascular and reproductive systems, which induce a spectrum of behavioural and homeostatic changes. CRH and Ucns exert their actions by activating two types of CRH receptors (CRH-R), CRH-R1 and CRH-R2, which belong to the class-B1 family of GPCRs. The CRH-Rs exhibit signalling promiscuity facilitated by their ability to couple to multiple G-proteins and regulate diverse intracellular networks that involve intracellular effectors such as cAMP and an array of PKs in an agonist and tissue-specific manner, a property that allows them to exert unique roles in the integration of homeostatic mechanisms. We only now begin to unravel the plethora of CRH-R biological actions and the transcriptional and post-translational mechanisms such as alternative mRNA splicing or phosphorylation-mediated desensitization developed to tightly control CRH-Rs biological activity and regulate their physiological actions. This review summarizes the current understanding of CRH-R signalling complexity and regulatory mechanisms that underpin cellular responses to CRH and Ucns.
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Poyner DR, Hay DL. Secretin family (Class B) G protein-coupled receptors - from molecular to clinical perspectives. Br J Pharmacol 2012; 166:1-3. [PMID: 22489621 DOI: 10.1111/j.1476-5381.2011.01810.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Family B G protein-coupled receptors represent an important but under-researched group of receptors. This edition of the British Journal of Pharmacology considers the roles and pharmacology of a number of these receptors. Whilst common themes emerge, it is clear that more work is needed to understand the details of each receptor in order to properly exploit them therapeutically.
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Pal K, Melcher K, Xu HE. Structure and mechanism for recognition of peptide hormones by Class B G-protein-coupled receptors. Acta Pharmacol Sin 2012; 33:300-11. [PMID: 22266723 DOI: 10.1038/aps.2011.170] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Class B G-protein-coupled receptors (GPCRs) are receptors for peptide hormones that include glucagon, parathyroid hormone, and calcitonin. These receptors are involved in a wide spectrum of physiological activities, from metabolic regulation and stress control to development and maintenance of the skeletal system. As such, they are important drug targets for the treatment of diabetes, osteoporosis, and stress related disorders. Class B GPCRs are organized into two modular domains: an extracellular domain (ECD) and a helical bundle that contains seven transmembrane helices (TM domain). The ECD is responsible for the high affinity and specificity of hormone binding, and the TM domain is required for receptor activation and signal coupling to downstream G-proteins. Although the structure of the full-length receptor remains unknown, the ECD structures have been well characterized for a number of Class B GPCRs, revealing a common fold for ligand recognition. This review summarizes the general structural principles that guide hormone binding by Class B ECDs and their implications in the design of peptide hormone analogs for therapeutic purposes.
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Structural insights into RAMP modification of secretin family G protein-coupled receptors: implications for drug development. Trends Pharmacol Sci 2011; 32:591-600. [DOI: 10.1016/j.tips.2011.05.007] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2010] [Revised: 05/25/2011] [Accepted: 05/26/2011] [Indexed: 11/18/2022]
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31
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Coin I, Perrin MH, Vale WW, Wang L. Photo-cross-linkers incorporated into G-protein-coupled receptors in mammalian cells: a ligand comparison. Angew Chem Int Ed Engl 2011; 50:8077-81. [PMID: 21751313 DOI: 10.1002/anie.201102646] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2011] [Indexed: 01/07/2023]
Abstract
Capturing the right ligand at the right spot: a well-balanced system for non-natural amino acid mutagenesis allows the ligand binding sites of a class II G-protein coupled receptor to be mapped and distinct binding domains to be identified for different ligands in the native environment of mammalian cells.
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Affiliation(s)
- Irene Coin
- Jack H. Skirball Center for Chemical Biology and Proteomics, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA
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32
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Coin I, Perrin MH, Vale WW, Wang L. Photo-Cross-Linkers Incorporated into G-Protein-Coupled Receptors in Mammalian Cells: A Ligand Comparison. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201102646] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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33
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Walser R, Kleinschmidt JH, Zerbe O. A chimeric GPCR model mimicking the ligand binding site of the human Y1 receptor studied by NMR spectroscopy. Chembiochem 2011; 12:1690-3. [PMID: 21695755 DOI: 10.1002/cbic.201100244] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2011] [Indexed: 01/23/2023]
Affiliation(s)
- Reto Walser
- Institute of Organic Chemistry, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland
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Chen CR, McLachlan SM, Rapoport B. Evidence that the thyroid-stimulating hormone (TSH) receptor transmembrane domain influences kinetics of TSH binding to the receptor ectodomain. J Biol Chem 2010; 286:6219-24. [PMID: 21190937 DOI: 10.1074/jbc.m110.211003] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Thyroid-stimulating hormone (TSH)-induced reduction in ligand binding affinity (negative cooperativity) requires TSH receptor (TSHR) homodimerization, the latter involving primarily the transmembrane domain (TMD) but with the extracellular domain (ECD) also contributing to this association. To test the role of the TMD in negative cooperativity, we studied the TSHR ECD tethered to the cell surface by a glycosylphosphatidylinositol (GPI) anchor that multimerizes despite the absence of the TMD. Using the infinite ligand dilution approach, we confirmed that TSH increased the rate of dissociation (k(off)) of prebound (125)I-TSH from CHO cells expressing the TSH holoreceptor. Such negative cooperativity did not occur with TSHR ECD-GPI-expressing cells. However, even in the absence of added TSH, (125)I-TSH dissociated much more rapidly from the TSHR ECD-GPI than from the TSH holoreceptor. This phenomenon, suggesting a lower TSH affinity for the former, was surprising because both the TSHR ECD and TSH holoreceptor contain the entire TSH-binding site, and the TSH binding affinities for both receptor forms should, theoretically, be identical. In ligand competition studies, we observed that the TSH binding affinity for the TSHR ECD-GPI was significantly lower than that for the TSH holoreceptor. Further evidence for a difference in ligand binding kinetics for the TSH holoreceptor and TSHR ECD-GPI was obtained upon comparison of the TSH K(d) values for these two receptor forms at 4 °C versus room temperature. Our data provide the first evidence that the wild-type TSHR TMD influences ligand binding affinity for the ECD, possibly by altering the conformation of the closely associated hinge region that contributes to the TSH-binding site.
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Affiliation(s)
- Chun-Rong Chen
- Thyroid Autoimmune Disease Unit, Cedars-Sinai Research Institute and the David Geffen School of Medicine, UCLA, Los Angeles, California 90048, USA
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36
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Pal K, Swaminathan K, Xu HE, Pioszak AA. Structural basis for hormone recognition by the Human CRFR2{alpha} G protein-coupled receptor. J Biol Chem 2010; 285:40351-61. [PMID: 20966082 PMCID: PMC3001015 DOI: 10.1074/jbc.m110.186072] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2010] [Revised: 10/10/2010] [Indexed: 02/02/2023] Open
Abstract
The mammalian corticotropin releasing factor (CRF)/urocortin (Ucn) peptide hormones include four structurally similar peptides, CRF, Ucn1, Ucn2, and Ucn3, that regulate stress responses, metabolism, and cardiovascular function by activating either of two related class B G protein-coupled receptors, CRFR1 and CRFR2. CRF and Ucn1 activate both receptors, whereas Ucn2 and Ucn3 are CRFR2-selective. The molecular basis for selectivity is unclear. Here, we show that the purified N-terminal extracellular domains (ECDs) of human CRFR1 and the CRFR2α isoform are sufficient to discriminate the peptides, and we present three crystal structures of the CRFR2α ECD bound to each of the Ucn peptides. The CRFR2α ECD forms the same fold observed for the CRFR1 and mouse CRFR2β ECDs but contains a unique N-terminal α-helix formed by its pseudo signal peptide. The CRFR2α ECD peptide-binding site architecture is similar to that of CRFR1, and binding of the α-helical Ucn peptides closely resembles CRF binding to CRFR1. Comparing the electrostatic surface potentials of the ECDs suggests a charge compatibility mechanism for ligand discrimination involving a single amino acid difference in the receptors (CRFR1 Glu104/CRFR2α Pro-100) at a site proximate to peptide residue 35 (Arg in CRF/Ucn1, Ala in Ucn2/3). CRFR1 Glu-104 acts as a selectivity filter preventing Ucn2/3 binding because the nonpolar Ala-35 is incompatible with the negatively charged Glu-104. The structures explain the mechanisms of ligand recognition and discrimination and provide a molecular template for the rational design of therapeutic agents selectively targeting these receptors.
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Affiliation(s)
- Kuntal Pal
- From the Laboratory of Structural Sciences, Van Andel Research Institute, Grand Rapids, Michigan 49503 and
- the Department of Biological Sciences, National University of Singapore, Singapore 117543
| | | | - H. Eric Xu
- From the Laboratory of Structural Sciences, Van Andel Research Institute, Grand Rapids, Michigan 49503 and
| | - Augen A. Pioszak
- From the Laboratory of Structural Sciences, Van Andel Research Institute, Grand Rapids, Michigan 49503 and
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