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Gutiérrez-Mondragón MA, Vellido A, König C. A Study on the Robustness and Stability of Explainable Deep Learning in an Imbalanced Setting: The Exploration of the Conformational Space of G Protein-Coupled Receptors. Int J Mol Sci 2024; 25:6572. [PMID: 38928278 PMCID: PMC11203844 DOI: 10.3390/ijms25126572] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2024] [Revised: 06/03/2024] [Accepted: 06/12/2024] [Indexed: 06/28/2024] Open
Abstract
G-protein coupled receptors (GPCRs) are transmembrane proteins that transmit signals from the extracellular environment to the inside of the cells. Their ability to adopt various conformational states, which influence their function, makes them crucial in pharmacoproteomic studies. While many drugs target specific GPCR states to exert their effects-thereby regulating the protein's activity-unraveling the activation pathway remains challenging due to the multitude of intermediate transformations occurring throughout this process, and intrinsically influencing the dynamics of the receptors. In this context, computational modeling, particularly molecular dynamics (MD) simulations, may offer valuable insights into the dynamics and energetics of GPCR transformations, especially when combined with machine learning (ML) methods and techniques for achieving model interpretability for knowledge generation. The current study builds upon previous work in which the layer relevance propagation (LRP) technique was employed to interpret the predictions in a multi-class classification problem concerning the conformational states of the β2-adrenergic (β2AR) receptor from MD simulations. Here, we address the challenges posed by class imbalance and extend previous analyses by evaluating the robustness and stability of deep learning (DL)-based predictions under different imbalance mitigation techniques. By meticulously evaluating explainability and imbalance strategies, we aim to produce reliable and robust insights.
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Affiliation(s)
- Mario A. Gutiérrez-Mondragón
- Computer Science Department, Intelligent Data Science and Artificial Intelligence (IDEAI-UPC) Research Center, Universitat Politècnica de Catalunya, 08034 Barcelona, Spain; (M.A.G.-M.); (A.V.)
| | - Alfredo Vellido
- Computer Science Department, Intelligent Data Science and Artificial Intelligence (IDEAI-UPC) Research Center, Universitat Politècnica de Catalunya, 08034 Barcelona, Spain; (M.A.G.-M.); (A.V.)
- Centro de Investigacion Biomédica en Red (CIBER), 28029 Madrid, Spain
| | - Caroline König
- Computer Science Department, Intelligent Data Science and Artificial Intelligence (IDEAI-UPC) Research Center, Universitat Politècnica de Catalunya, 08034 Barcelona, Spain; (M.A.G.-M.); (A.V.)
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2
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Szukiewicz D. CX3CL1 (Fractalkine)-CX3CR1 Axis in Inflammation-Induced Angiogenesis and Tumorigenesis. Int J Mol Sci 2024; 25:4679. [PMID: 38731899 PMCID: PMC11083509 DOI: 10.3390/ijms25094679] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2024] [Revised: 04/19/2024] [Accepted: 04/24/2024] [Indexed: 05/13/2024] Open
Abstract
The chemotactic cytokine fractalkine (FKN, chemokine CX3CL1) has unique properties resulting from the combination of chemoattractants and adhesion molecules. The soluble form (sFKN) has chemotactic properties and strongly attracts T cells and monocytes. The membrane-bound form (mFKN) facilitates diapedesis and is responsible for cell-to-cell adhesion, especially by promoting the strong adhesion of leukocytes (monocytes) to activated endothelial cells with the subsequent formation of an extracellular matrix and angiogenesis. FKN signaling occurs via CX3CR1, which is the only known member of the CX3C chemokine receptor subfamily. Signaling within the FKN-CX3CR1 axis plays an important role in many processes related to inflammation and the immune response, which often occur simultaneously and overlap. FKN is strongly upregulated by hypoxia and/or inflammation-induced inflammatory cytokine release, and it may act locally as a key angiogenic factor in the highly hypoxic tumor microenvironment. The importance of the FKN/CX3CR1 signaling pathway in tumorigenesis and cancer metastasis results from its influence on cell adhesion, apoptosis, and cell migration. This review presents the role of the FKN signaling pathway in the context of angiogenesis in inflammation and cancer. The mechanisms determining the pro- or anti-tumor effects are presented, which are the cause of the seemingly contradictory results that create confusion regarding the therapeutic goals.
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Affiliation(s)
- Dariusz Szukiewicz
- Department of Biophysics, Physiology & Pathophysiology, Faculty of Health Sciences, Medical University of Warsaw, 02-004 Warsaw, Poland
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3
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Hicks C, Gardner J, Eiger DS, Camarda ND, Pham U, Dhar S, Rodriguez H, Chundi A, Rajagopal S. ACKR3 Proximity Labeling Identifies Novel G protein- and β-arrestin-independent GPCR Interacting Proteins. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.27.577545. [PMID: 38410489 PMCID: PMC10896341 DOI: 10.1101/2024.01.27.577545] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/28/2024]
Abstract
The canonical paradigm of GPCR signaling recognizes G proteins and β-arrestins as the two primary transducers that promote GPCR signaling. Recent evidence suggests the atypical chemokine receptor 3 (ACKR3) does not couple to G proteins, and β-arrestins are dispensable for some of its functions. Here, we employed proximity labeling to identify proteins that interact with ACKR3 in cells devoid of β-arrestin. We identified proteins involved in the endocytic machinery and evaluated a subset of proteins conserved across several GPCR-based proximity labeling experiments. We discovered that the bone morphogenic protein 2-inducible kinase (BMP2K) interacts with many different GPCRs with varying dependency on β-arrestin. Together, our work highlights the existence of modulators that can act independently of G proteins and β-arrestins to regulate GPCR signaling and provides important evidence for other targets that may regulate GPCR signaling.
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Affiliation(s)
- Chloe Hicks
- National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Julia Gardner
- Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Dylan Scott Eiger
- Department of Medicine, Brigham and Women’s Hospital, Boston, MA, 02215, USA
- Harvard Medical School, Boston, MA, 02215, USA
| | - Nicholas D. Camarda
- Genetics, Molecular, and Cellular Biology Program, Tufts Graduate School of Biomedical Sciences, Boston, MA, 02111, USA
| | - Uyen Pham
- Department of Biochemistry, Duke University, Durham, NC, 27710, USA
| | - Saisha Dhar
- Trinity College, Duke University, Durham, NC, 27710, USA
| | | | - Anand Chundi
- Pratt School of Engineering, Duke University, Durham, NC, 27710, USA
| | - Sudarshan Rajagopal
- Department of Biochemistry, Duke University, Durham, NC, 27710, USA
- Department of Medicine, Duke University, Durham, NC, 27710, USA
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4
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Park B, Cha YK, Kwak J, Hwang KS, Kim HS, Park S, Pak Y, Park TH, Song HS, Kim JH. Photosensitive Nanodiscs Composed of Human Photoreceptors for Refractive Index Modulation at Selective Wavelengths. NANO LETTERS 2022; 22:6825-6832. [PMID: 35801941 DOI: 10.1021/acs.nanolett.2c01685] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
A photoreceptor on the retina acts as an optical waveguide to transfer an individual photonic signal to the cell inside, which is determined by the refractive index of internal materials. Under the photoactivation of photoreceptors making conformational and chemical variation in a visual cell, the optical signal modulation is demonstrated using an artificial photoreceptor-based waveguide with a controlling beam refraction. Two types of nanodiscs are made of human photoreceptor proteins, short-wavelength-sensitive opsin and rhodopsin, with spectral sensitivity. The refractive index and nonlinear features of those two photosensitive nanodiscs are investigated as fundamental properties. The photonanodiscs are photoactivated in such a way that allow refractive index tuning over 0.18 according to the biological function of the respective proteins with color-dependent response.
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Affiliation(s)
- Byeongho Park
- Korea Institute of Science and Technology (KIST), Seongbuk-gu, Seoul 02792, Republic of Korea
| | - Yeon Kyung Cha
- Interdisciplinary Program in Bioengineering, Seoul National University, Gwanak-gu, Seoul 08826, Republic of Korea
| | - Jisung Kwak
- Korea Institute of Science and Technology (KIST), Seongbuk-gu, Seoul 02792, Republic of Korea
| | - Kyeong Seob Hwang
- Korea Institute of Science and Technology (KIST), Seongbuk-gu, Seoul 02792, Republic of Korea
- School of Mechanical Engineering, Yonsei University, Seoul 03722, Republic of Korea
| | - Hyo-Suk Kim
- Korea Institute of Science and Technology (KIST), Seongbuk-gu, Seoul 02792, Republic of Korea
| | - Subeen Park
- Korea Institute of Science and Technology (KIST), Seongbuk-gu, Seoul 02792, Republic of Korea
| | - Yusin Pak
- Korea Institute of Science and Technology (KIST), Seongbuk-gu, Seoul 02792, Republic of Korea
| | - Tai Hyun Park
- Interdisciplinary Program in Bioengineering, Seoul National University, Gwanak-gu, Seoul 08826, Republic of Korea
- School of Chemical and Biological Engineering, and Institute of Chemical Processes, Seoul National University, Gwanak-gu, Seoul 08826, Republic of Korea
| | - Hyun Seok Song
- Korea Institute of Science and Technology (KIST), Seongbuk-gu, Seoul 02792, Republic of Korea
- Division of Bio-Medical Science and Technology, KIST School, Korea University of Science and Technology (UST), Seoul 02792, Republic of Korea
| | - Jae Hun Kim
- Korea Institute of Science and Technology (KIST), Seongbuk-gu, Seoul 02792, Republic of Korea
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5
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Moo EV, Harpsøe K, Hauser AS, Masuho I, Bräuner-Osborne H, Gloriam DE, Martemyanov KA. Ligand-directed bias of G protein signaling at the dopamine D 2 receptor. Cell Chem Biol 2022; 29:226-238.e4. [PMID: 34302750 PMCID: PMC8770702 DOI: 10.1016/j.chembiol.2021.07.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Revised: 05/21/2021] [Accepted: 07/02/2021] [Indexed: 01/11/2023]
Abstract
G-protein-coupled receptors (GPCRs) represent the largest family of drug targets. Upon activation, GPCRs signal primarily via a diverse set of heterotrimeric G proteins. Most GPCRs can couple to several different G protein subtypes. However, how drugs act at GPCRs contributing to the selectivity of G protein recognition is poorly understood. Here, we examined the G protein selectivity profile of the dopamine D2 receptor (D2), a GPCR targeted by antipsychotic drugs. We show that D2 discriminates between six individual members of the Gi/o family, and its profile of functional selectivity is remarkably different across its ligands, which all engaged D2 with a distinct G protein coupling pattern. Using structural modeling, receptor mutagenesis, and pharmacological evaluation, we identified residues in the D2 binding pocket that shape these ligand-directed biases. We further provide pharmacogenomic evidence that natural variants in D2 differentially affect its G protein biases in response to different ligands.
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Affiliation(s)
- Ee Von Moo
- Department of Neuroscience, The Scripps Research Institute, 130 Scripps Way, Jupiter, FL 33458, USA,Department of Drug Design and Pharmacology, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark
| | - Kasper Harpsøe
- Department of Drug Design and Pharmacology, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark
| | - Alexander S Hauser
- Department of Drug Design and Pharmacology, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark
| | - Ikuo Masuho
- Department of Neuroscience, The Scripps Research Institute, 130 Scripps Way, Jupiter, FL 33458, USA
| | - Hans Bräuner-Osborne
- Department of Drug Design and Pharmacology, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark
| | - David E. Gloriam
- Department of Drug Design and Pharmacology, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark
| | - Kirill A. Martemyanov
- Department of Neuroscience, The Scripps Research Institute, 130 Scripps Way, Jupiter, FL 33458, USA
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6
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Vunnam N, Szymonski S, Hirsova P, Gores GJ, Sachs JN, Hackel BJ. Noncompetitive Allosteric Antagonism of Death Receptor 5 by a Synthetic Affibody Ligand. Biochemistry 2020; 59:3856-3868. [PMID: 32941010 PMCID: PMC7658720 DOI: 10.1021/acs.biochem.0c00529] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Fatty acid-induced upregulation of death receptor 5 (DR5) and its cognate ligand, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), promotes hepatocyte lipoapoptosis, which is a key mechanism in the progression of fatty liver disease. Accordingly, inhibition of DR5 signaling represents an attractive strategy for treating fatty liver disease. Ligand competition strategies are prevalent in tumor necrosis factor receptor antagonism, but recent studies have suggested that noncompetitive inhibition through perturbation of the receptor conformation may be a compelling alternative. To this end, we used yeast display and a designed combinatorial library to identify a synthetic 58-amino acid affibody ligand that specifically binds DR5. Biophysical and biochemical studies show that the affibody neither blocks TRAIL binding nor prevents the receptor-receptor interaction. Live-cell fluorescence lifetime measurements indicate that the affibody induces a conformational change in transmembrane dimers of DR5 and favors an inactive state of the receptor. The affibody inhibits apoptosis in TRAIL-treated Huh-7 cells, an in vitro model of fatty liver disease. Thus, this lead affibody serves as a potential drug candidate, with a unique mechanism of action, for fatty liver disease.
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Affiliation(s)
- Nagamani Vunnam
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN
| | - Sophia Szymonski
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN
| | - Petra Hirsova
- Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, MN
| | - Gregory J. Gores
- Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, MN
| | - Jonathan N. Sachs
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN
| | - Benjamin J. Hackel
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN
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7
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Zhang R, Liu Y, Liu Q, Zhang Y, Ma X, Song Q, Feng H. Facile microfluidic fabrication of monodispersed self-coupling microcavity with fine tunability. Electrophoresis 2019; 41:1418-1424. [PMID: 31797398 DOI: 10.1002/elps.201900281] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2019] [Revised: 11/12/2019] [Accepted: 11/25/2019] [Indexed: 11/12/2022]
Abstract
Whispering gallery mode (WGM) resonators have received extensive attention because of their nonlinear optical application in lasers and sensors. Optical microcavities are excellent candidates for constructing powerful microlasers and label-free biosensors, owing to their low optical losses and small size. However, most of these microcavity syntheses rely on sophisticated fabrication methods and cannot be manipulated easily. To achieve facile and versatile microcavity fabrication, we present a robust microfluidics method for monodispersed self-coupling optical microcavity fabrication with a fine tunability. The microcavity polydispersity was less than 3%. The optical microcavity size could be varied from 10 to 30 µm with a steady quality factor (Q) of approximately 1000. The lowest laser threshold that we obtained was 0.82 µJ with a microcavity size of 20 µm. The doped fluorescent dye concentration can be tuned precisely from 0.001 to 0.05 wt% to explore an optimized fluorescent background. The experimental results and theoretical simulation match well in terms of Q and the electrometric resonance field intensity. Compared with previous precise and practical fabrication methods, we have demonstrated a facile approach for versatile optical microcavity fabrication. This method can vary the microcavity materials, size, doped fluorescent dye concentration, WGM resonance spectrum, Q factor, and laser threshold easily to adapt to various circumstances and specific applications.
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Affiliation(s)
- Ran Zhang
- State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, P. R. China.,Flexible Printed Electronic Technology Center, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, P. R. China.,School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, P. R. China
| | - Yilin Liu
- Integrated Nanoscience Lab, School of Electric and Information Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, P. R. China
| | - Qing Liu
- State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, P. R. China.,Flexible Printed Electronic Technology Center, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, P. R. China.,School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, P. R. China
| | - Yueyue Zhang
- State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, P. R. China.,Flexible Printed Electronic Technology Center, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, P. R. China.,School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, P. R. China
| | - Xing Ma
- State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, P. R. China.,Flexible Printed Electronic Technology Center, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, P. R. China.,School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, P. R. China
| | - Qinghai Song
- Integrated Nanoscience Lab, School of Electric and Information Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, P. R. China
| | - Huanhuan Feng
- State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, P. R. China.,Flexible Printed Electronic Technology Center, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, P. R. China.,School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, P. R. China
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8
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Vassilakos G, Barton ER. Insulin-Like Growth Factor I Regulation and Its Actions in Skeletal Muscle. Compr Physiol 2018; 9:413-438. [PMID: 30549022 DOI: 10.1002/cphy.c180010] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The insulin-like growth factor (IGF) pathway is essential for promoting growth and survival of virtually all tissues. It bears high homology to its related protein insulin, and as such, there is an interplay between these molecules with regard to their anabolic and metabolic functions. Skeletal muscle produces a significant proportion of IGF-1, and is highly responsive to its actions, including increased muscle mass and improved regenerative capacity. In this overview, the regulation of IGF-1 production, stability, and activity in skeletal muscle will be described. Second, the physiological significance of the forms of IGF-1 produced will be discussed. Last, the interaction of IGF-1 with other pathways will be addressed. © 2019 American Physiological Society. Compr Physiol 9:413-438, 2019.
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Affiliation(s)
- Georgios Vassilakos
- Department of Applied Physiology and Kinesiology, College of Health and Human Performance, University of Florida, Gainesville, Florida, USA
| | - Elisabeth R Barton
- Department of Applied Physiology and Kinesiology, College of Health and Human Performance, University of Florida, Gainesville, Florida, USA
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9
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Is a dangerous blood clot formation a reversible process? Introduction of new characteristic parameter for thermodynamic clot blood characterization: Possible molecular mechanisms and pathophysiologic applications. J Mol Liq 2018. [DOI: 10.1016/j.molliq.2018.04.071] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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10
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Kuscu M, Akan OB. Maximum Likelihood Detection With Ligand Receptors for Diffusion-Based Molecular Communications in Internet of Bio-Nano Things. IEEE Trans Nanobioscience 2018; 17:44-54. [PMID: 29570074 DOI: 10.1109/tnb.2018.2792434] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Molecular Communication (MC) is a bio-inspired communication technique that uses molecules as a method of information transfer among nanoscale devices. MC receiver is an essential component having profound impact on the communication system performance. However, the interaction of the receiver with information bearing molecules has been usually oversimplified in modeling the reception process and developing signal detection techniques. In this paper, we focus on the signal detection problem of MC receivers employing receptor molecules to infer the transmitted messages encoded into the concentration of molecules, i.e., ligands. Exploiting the observable characteristics of ligand-receptor binding reaction, we first introduce a Maximum Likelihood (ML) detection method based on instantaneous receptor occupation ratio, as aligned with the current MC literature. Then, we propose a novel ML detection technique, which exploits the amount of time the receptors stay unbound in an observation time window. A comprehensive analysis is carried out to compare the performance of the detectors in terms of bit error probability. In evaluating the detection performance, emphasis is given to the receptor saturation problem resulting from the accumulation of messenger molecules at the receiver as a consequence of intersymbol interference. The results reveal that detection based on receptor unbound time is quite reliable even in saturation, whereas the reliability of detection based on receptor occupation ratio substantially decreases as the receiver gets saturated. Finally, we also discuss the potential methods of implementing the detectors.
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11
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Kauk M, Hoffmann C. Intramolecular and Intermolecular FRET Sensors for GPCRs - Monitoring Conformational Changes and Beyond. Trends Pharmacol Sci 2017; 39:123-135. [PMID: 29180026 DOI: 10.1016/j.tips.2017.10.011] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2017] [Revised: 10/27/2017] [Accepted: 10/31/2017] [Indexed: 11/18/2022]
Abstract
Within the past decade, a large increase in structural knowledge from crystallographic studies has significantly fostered our understanding of the structural biology of G protein-coupled receptors (GPCRs). However, information on dynamic events upon receptor activation or deactivation is not yet readily accessed by these structural approaches. GPCR-based fluorescence resonance energy transfer or bioluminescence resonance energy transfer sensors or sensors for interacting proteins (e.g., G proteins or arrestins) can in part cover this gap. The principal design of such sensors was reported 15 years ago. Since then, sensors for almost 20 different GPCRs have been designed. If used with necessary controls and cautious interpretation, such sensors can contribute significantly to our understanding of the basic mechanisms of GPCR function and beyond. In this review, we will discuss the recent developments in this area of GPCR dynamics.
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Affiliation(s)
- Michael Kauk
- Department of Pharmacology and Toxicology, University of Würzburg, Versbacher Straße 9, 97078 Würzburg, Germany
| | - Carsten Hoffmann
- Department of Pharmacology and Toxicology, University of Würzburg, Versbacher Straße 9, 97078 Würzburg, Germany; Institut für Molekulare Zellbiologie, CMB - Center for Molecular Biomedicine, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Hans-Knöll Straße 2, D-07745 Jena, Germany.
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12
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Bastiaan-Net S, van den Berg-Somhorst DB, Ariëns RM, Paques M, Mes JJ. A novel functional screening assay to monitor sweet taste receptor activation in vitro. FLAVOUR FRAG J 2017. [DOI: 10.1002/ffj.3431] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Shanna Bastiaan-Net
- Research Institute Wageningen Food & Biobased Research; Wageningen University and Research; Wageningen The Netherlands
| | | | - Renata M.C. Ariëns
- Research Institute Wageningen Food & Biobased Research; Wageningen University and Research; Wageningen The Netherlands
| | | | - Jurriaan J. Mes
- Research Institute Wageningen Food & Biobased Research; Wageningen University and Research; Wageningen The Netherlands
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13
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Scheggi S, Ferrari A, Pelliccia T, Devoto P, De Montis MG, Gambarana C. Fasting biases μ-opioid receptors toward β-arrestin2-dependent signaling in the accumbens shell. Neuroscience 2017; 352:19-29. [PMID: 28391016 DOI: 10.1016/j.neuroscience.2017.03.056] [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] [Received: 10/31/2016] [Revised: 03/03/2017] [Accepted: 03/28/2017] [Indexed: 10/19/2022]
Abstract
The μ-opioid receptor (MOR) and dopamine D1 receptor are co-expressed in the medium spiny neurons of striatal areas and the signaling pathways activated by these two receptors are in functional competition. However, in certain conditions an integrated response mediated by the dopamine D1 receptor transduction system is observed. In mice, morphine administration induces hypermotility and this response has been described in terms of a β-arrestin2-dependent mechanism that favors prevalent dopamine D1 receptor activation. In rats, acute morphine administration induces hypermotility only when the animals are food-deprived (FD). We aimed to further investigate the functional interaction between the MOR and dopamine D1 receptors in striatal areas and we studied the effects of acute pharmacological MOR stimulation on motility and nucleus accumbens shell (NAcS) dopamine D1 receptor signaling in control rats and rats with reduced β-arrestin2 expression in the NAcS, either non food-deprived (NFD) or FD. Motility and dopamine D1 receptor signaling increased only in FD rats in a β-arrestin2-dependent way. Moreover, FD rats showed a β-arrestin2-dependent increase in the levels of MOR-dopamine D1 receptor heteromeric complexes in the NAcS. Sucrose consumption is accompanied by release of endogenous opioids and dopamine in the NAcS. We then examined MOR-dopamine D1 receptor interactions after sucrose consumption. Sucrose increased NAcS dopamine D1 receptor signaling in NFD and FD rats, and a reduction in β-arrestin2 expression prevented this effect selectively in FD rats. These results show the β-arrestin2-dependent prevalence of dopamine D1 receptor signaling in response to acute morphine or sucrose consumption elicited by food deprivation in rats.
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Affiliation(s)
- Simona Scheggi
- Department of Molecular and Developmental Medicine, University of Siena, Siena, Italy
| | - Alberto Ferrari
- Department of Molecular and Developmental Medicine, University of Siena, Siena, Italy
| | - Teresa Pelliccia
- Department of Molecular and Developmental Medicine, University of Siena, Siena, Italy
| | - Paola Devoto
- Department of Biomedical Sciences, University of Cagliari, Italy
| | | | - Carla Gambarana
- Department of Molecular and Developmental Medicine, University of Siena, Siena, Italy.
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14
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Liebick M, Schläger C, Oppermann M. Analysis of Chemokine Receptor Trafficking by Site-Specific Biotinylation. PLoS One 2016; 11:e0157502. [PMID: 27310579 PMCID: PMC4911081 DOI: 10.1371/journal.pone.0157502] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2016] [Accepted: 05/31/2016] [Indexed: 12/17/2022] Open
Abstract
Chemokine receptors undergo internalization and desensitization in response to ligand activation. Internalized receptors are either preferentially directed towards recycling pathways (e.g. CCR5) or sorted for proteasomal degradation (e.g. CXCR4). Here we describe a method for the analysis of receptor internalization and recycling based on specific Bir A-mediated biotinylation of an acceptor peptide coupled to the receptor, which allows a more detailed analysis of receptor trafficking compared to classical antibody-based detection methods. Studies on constitutive internalization of the chemokine receptors CXCR4 (12.1% ± 0.99% receptor internalization/h) and CCR5 (13.7% ± 0.68%/h) reveals modulation of these processes by inverse (TAK779; 10.9% ± 0.95%/h) or partial agonists (Met-CCL5; 15.6% ± 0.5%/h). These results suggest an actively driven internalization process. We also demonstrate the advantages of specific biotinylation compared to classical antibody detection during agonist-induced receptor internalization, which may be used for immunofluorescence analysis as well. Site-specific biotinylation may be applicable to studies on trafficking of transmembrane proteins, in general.
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MESH Headings
- Amides/pharmacology
- Animals
- Antibodies, Monoclonal/biosynthesis
- Antibodies, Monoclonal/chemistry
- Antibodies, Monoclonal/isolation & purification
- Basophils/cytology
- Basophils/drug effects
- Basophils/metabolism
- Biotin/chemistry
- Biotin/metabolism
- Biotinylation
- CCR5 Receptor Antagonists/pharmacology
- Carbon-Nitrogen Ligases/genetics
- Carbon-Nitrogen Ligases/metabolism
- Cell Line, Tumor
- Chemokine CCL5/pharmacology
- Escherichia coli Proteins/genetics
- Escherichia coli Proteins/metabolism
- Gene Expression
- Genetic Vectors/chemistry
- Genetic Vectors/metabolism
- Mice
- Protein Transport/drug effects
- Quaternary Ammonium Compounds/pharmacology
- Rats
- Receptors, CXCR4/antagonists & inhibitors
- Receptors, CXCR4/genetics
- Receptors, CXCR4/metabolism
- Receptors, CXCR5/antagonists & inhibitors
- Receptors, CXCR5/genetics
- Receptors, CXCR5/metabolism
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/metabolism
- Repressor Proteins/genetics
- Repressor Proteins/metabolism
- Transfection
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Affiliation(s)
- Marcel Liebick
- Department of Cellular and Molecular Immunology, University of Göttingen, Göttingen, Niedersachsen, Germany
| | - Christian Schläger
- Department of Cellular and Molecular Immunology, University of Göttingen, Göttingen, Niedersachsen, Germany
| | - Martin Oppermann
- Department of Cellular and Molecular Immunology, University of Göttingen, Göttingen, Niedersachsen, Germany
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15
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Stumpf AD, Hoffmann C. Optical probes based on G protein-coupled receptors - added work or added value? Br J Pharmacol 2015; 173:255-66. [PMID: 26562218 DOI: 10.1111/bph.13382] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2015] [Revised: 09/22/2015] [Accepted: 10/26/2015] [Indexed: 12/22/2022] Open
Abstract
In 2003, the first report was published that presented proof of principle for a novel class of FRET biosensors for use in living cells. This novel sensor class was built on the base of GPCRs, which represent an integral transmembrane receptor family passing the membrane seven times and are thus also called the 7TM receptor family. As an estimated number of 30% of all marketed drugs exert their effects by modulating GPCR function, these initial reports promised the gain of novel insights into receptor function. Such FRET sensors have slowly, but progressively, made their way into the standard toolbox for GPCR research as several groups are now reporting on the generation and use of these sensors. By now, FRET sensors have been reported for 18 different GPCRs, and more are expected to be added. These particular receptor sensors have been used to investigate receptor dynamics in living cells to evaluate ligand binding and ligand efficacy in real time, to study voltage and mechanosensitivity of GPCRs or to study the influence of receptor polymorphisms on receptor function in real-time. In this review we will describe the different design principles of these GPCR-based sensors and will summarize their current biological applications in living cells.
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Affiliation(s)
- A D Stumpf
- Bio-Imaging Center, Rudolf-Virchow-Zentrum für Experimentelle Medizin, University of Würzburg, Würzburg, Germany.,Department of Pharmacology and Toxicology, University of Würzburg, Würzburg, Germany
| | - C Hoffmann
- Bio-Imaging Center, Rudolf-Virchow-Zentrum für Experimentelle Medizin, University of Würzburg, Würzburg, Germany.,Department of Pharmacology and Toxicology, University of Würzburg, Würzburg, Germany
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16
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Conformational kinetics reveals affinities of protein conformational states. Proc Natl Acad Sci U S A 2015; 112:9352-7. [PMID: 26162682 DOI: 10.1073/pnas.1502084112] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Most biological reactions rely on interplay between binding and changes in both macromolecular structure and dynamics. Practical understanding of this interplay requires detection of critical intermediates and determination of their binding and conformational characteristics. However, many of these species are only transiently present and they have often been overlooked in mechanistic studies of reactions that couple binding to conformational change. We monitored the kinetics of ligand-induced conformational changes in a small protein using six different ligands. We analyzed the kinetic data to simultaneously determine both binding affinities for the conformational states and the rate constants of conformational change. The approach we used is sufficiently robust to determine the affinities of three conformational states and detect even modest differences in the protein's affinities for relatively similar ligands. Ligand binding favors higher-affinity conformational states by increasing forward conformational rate constants and/or decreasing reverse conformational rate constants. The amounts by which forward rate constants increase and reverse rate constants decrease are proportional to the ratio of affinities of the conformational states. We also show that both the affinity ratio and another parameter, which quantifies the changes in conformational rate constants upon ligand binding, are strong determinants of the mechanism (conformational selection and/or induced fit) of molecular recognition. Our results highlight the utility of analyzing the kinetics of conformational changes to determine affinities that cannot be determined from equilibrium experiments. Most importantly, they demonstrate an inextricable link between conformational dynamics and the binding affinities of conformational states.
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17
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Woo AYH, Song Y, Zhu W, Xiao RP. Advances in receptor conformation research: the quest for functionally selective conformations focusing on the β2-adrenoceptor. Br J Pharmacol 2015; 172:5477-88. [PMID: 25537131 DOI: 10.1111/bph.13049] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2014] [Accepted: 12/14/2014] [Indexed: 01/14/2023] Open
Abstract
Seven-transmembrane receptors, also called GPCRs, represent the largest class of drug targets. Upon ligand binding, a GPCR undergoes conformational rearrangement and thereby changes its interaction with effector proteins including the cognate G-proteins and the multifunctional adaptor proteins, β-arrestins. These proteins, by initiating distinct signal transduction mechanisms, mediate one or several functional responses. Recently, the concept of ligand-directed GPCR signalling, also called functional selectivity or biased agonism, has been proposed to explain the phenomenon that chemically diverse ligands exhibit different efficacies towards the different signalling pathways of a single GPCR, and thereby act as functionally selective or 'biased' ligands. Current concepts support the notion that ligand-specific GPCR conformations are the basis of ligand-directed signalling. Multiple studies using fluorescence spectroscopy, X-ray crystallography, mass spectroscopy, nuclear magnetic resonance spectroscopy, single-molecule force spectroscopy and other techniques have provided the evidence to support this notion. It is anticipated that these techniques will ultimately help elucidate the structural basis of ligand-directed GPCR signalling at a precision meaningful for structure-based drug design and how a specific ligand molecular structure induces a unique receptor conformation leading to biased signalling. In this review, we will summarize recent advances in experimental techniques applied in the study of functionally selective GPCR conformations and breakthrough data obtained in these studies particularly those of the β2-adrenoceptor.
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Affiliation(s)
- Anthony Yiu-Ho Woo
- Institute of Molecular Medicine, Centre for Life Sciences, Peking University, Beijing, China.,Key Laboratory of Chemical Genomics, School of Chemical Biology and Biotechnology, Peking University Shenzhen Graduate School, Shenzhen, China
| | - Ying Song
- Institute of Molecular Medicine, Centre for Life Sciences, Peking University, Beijing, China
| | - Weizhong Zhu
- Department of Pharmacology, Nantong University School of Pharmacy, Nantong, China
| | - Rui-Ping Xiao
- Institute of Molecular Medicine, Centre for Life Sciences, Peking University, Beijing, China.,Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Peking University, Beijing, China
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18
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Communication over the network of binary switches regulates the activation of A2A adenosine receptor. PLoS Comput Biol 2015; 11:e1004044. [PMID: 25664580 PMCID: PMC4322061 DOI: 10.1371/journal.pcbi.1004044] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2014] [Accepted: 11/18/2014] [Indexed: 11/19/2022] Open
Abstract
Dynamics and functions of G-protein coupled receptors (GPCRs) are accurately regulated by the type of ligands that bind to the orthosteric or allosteric binding sites. To glean the structural and dynamical origin of ligand-dependent modulation of GPCR activity, we performed total ~ 5 μsec molecular dynamics simulations of A2A adenosine receptor (A2AAR) in its apo, antagonist-bound, and agonist-bound forms in an explicit water and membrane environment, and examined the corresponding dynamics and correlation between the 10 key structural motifs that serve as the allosteric hotspots in intramolecular signaling network. We dubbed these 10 structural motifs “binary switches” as they display molecular interactions that switch between two distinct states. By projecting the receptor dynamics on these binary switches that yield 210 microstates, we show that (i) the receptors in apo, antagonist-bound, and agonist-bound states explore vastly different conformational space; (ii) among the three receptor states the apo state explores the broadest range of microstates; (iii) in the presence of the agonist, the active conformation is maintained through coherent couplings among the binary switches; and (iv) to be most specific, our analysis shows that W246, located deep inside the binding cleft, can serve as both an agonist sensor and actuator of ensuing intramolecular signaling for the receptor activation. Finally, our analysis of multiple trajectories generated by inserting an agonist to the apo state underscores that the transition of the receptor from inactive to active form requires the disruption of ionic-lock in the DRY motif. As the key signal transmitters of a number of physiological processes, G-protein coupled receptors (GPCRs) are arguably one of the most important therapeutic targets. Orchestration of the intra-molecular signaling across transmembrane domain is key for the function of GPCRs. To investigate the microscopic underpinnings of intramolecular signaling that regulates the activation of GPCRs, we performed molecular dynamics simulations of the receptor in three distinct ligand-bound states using A2A adenosine receptor as a model system of GPCRs. Statistical analyses on the dynamics of and correlation among the 10 “binary switches” reveal that the three receptor states retain distinct dynamic properties. The antagonist- and agonist-bound forms of the receptors explore vastly different conformational space, and the apo form lies between them, yet located closer to the antagonist-bound form. In regard to the agonist-binding triggered activation mechanism, the correlation map among the 10 binary switches unequivocally shows that direct sensing of agonist ligand by the indole ring of W246 actuates the rest of intramolecular signaling.
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19
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Copik AJ, Baldys A, Nguyen K, Sahdeo S, Ho H, Kosaka A, Dietrich PJ, Fitch B, Raymond JR, Ford APDW, Button D, Milla ME. Isoproterenol acts as a biased agonist of the alpha-1A-adrenoceptor that selectively activates the MAPK/ERK pathway. PLoS One 2015; 10:e0115701. [PMID: 25606852 PMCID: PMC4301629 DOI: 10.1371/journal.pone.0115701] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2014] [Accepted: 11/26/2014] [Indexed: 11/24/2022] Open
Abstract
The α1A-AR is thought to couple predominantly to the Gαq/PLC pathway and lead to phosphoinositide hydrolysis and calcium mobilization, although certain agonists acting at this receptor have been reported to trigger activation of arachidonic acid formation and MAPK pathways. For several G protein-coupled receptors (GPCRs) agonists can manifest a bias for activation of particular effector signaling output, i.e. not all agonists of a given GPCR generate responses through utilization of the same signaling cascade(s). Previous work with Gαq coupling-defective variants of α1A-AR, as well as a combination of Ca2+ channel blockers, uncovered cross-talk between α1A-AR and β2-AR that leads to potentiation of a Gαq-independent signaling cascade in response to α1A-AR activation. We hypothesized that molecules exist that act as biased agonists to selectively activate this pathway. In this report, isoproterenol (Iso), typically viewed as β-AR-selective agonist, was examined with respect to activation of α1A-AR. α1A-AR selective antagonists were used to specifically block Iso evoked signaling in different cellular backgrounds and confirm its action at α1A-AR. Iso induced signaling at α1A-AR was further interrogated by probing steps along the Gαq /PLC, Gαs and MAPK/ERK pathways. In HEK-293/EBNA cells transiently transduced with α1A-AR, and CHO_α1A-AR stable cells, Iso evoked low potency ERK activity as well as Ca2+ mobilization that could be blocked by α1A-AR selective antagonists. The kinetics of Iso induced Ca2+ transients differed from typical Gαq- mediated Ca2+ mobilization, lacking both the fast IP3R mediated response and the sustained phase of Ca2+ re-entry. Moreover, no inositol phosphate (IP) accumulation could be detected in either cell line after stimulation with Iso, but activation was accompanied by receptor internalization. Data are presented that indicate that Iso represents a novel type of α1A-AR partial agonist with signaling bias toward MAPK/ERK signaling cascade that is likely independent of coupling to Gαq.
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Affiliation(s)
- Alicja. J. Copik
- Biochemical Pharmacology, Inflammation Discovery, Roche Palo Alto LLC, 3401 Hillview Drive, Palo Alto, CA 94304, United States of America
| | - Aleksander Baldys
- Nephrology Division, Department of Medicine, Medical University of South Carolina, and Medical and Research Services, Ralph H Johnson Veterans Affairs Medical Center, Charleston, South Carolina 29425, United States of America
| | - Khanh Nguyen
- Discovery Technologies, Roche Palo Alto LLC, 3401 Hillview Drive, Palo Alto, CA 94304, United States of America
| | - Sunil Sahdeo
- Biochemical Pharmacology, Inflammation Discovery, Roche Palo Alto LLC, 3401 Hillview Drive, Palo Alto, CA 94304, United States of America
| | - Hoangdung Ho
- Discovery Technologies, Roche Palo Alto LLC, 3401 Hillview Drive, Palo Alto, CA 94304, United States of America
| | - Alan Kosaka
- Discovery Technologies, Roche Palo Alto LLC, 3401 Hillview Drive, Palo Alto, CA 94304, United States of America
| | - Paul J. Dietrich
- Discovery Technologies, Roche Palo Alto LLC, 3401 Hillview Drive, Palo Alto, CA 94304, United States of America
| | - Bill Fitch
- Discovery Technologies, Roche Palo Alto LLC, 3401 Hillview Drive, Palo Alto, CA 94304, United States of America
| | - John R. Raymond
- Nephrology Division, Department of Medicine, Medical University of South Carolina, and Medical and Research Services, Ralph H Johnson Veterans Affairs Medical Center, Charleston, South Carolina 29425, United States of America
| | - Anthony P. D. W. Ford
- Biochemical Pharmacology, Inflammation Discovery, Roche Palo Alto LLC, 3401 Hillview Drive, Palo Alto, CA 94304, United States of America
| | - Donald Button
- Biochemical Pharmacology, Inflammation Discovery, Roche Palo Alto LLC, 3401 Hillview Drive, Palo Alto, CA 94304, United States of America
| | - Marcos E. Milla
- Biochemical Pharmacology, Inflammation Discovery, Roche Palo Alto LLC, 3401 Hillview Drive, Palo Alto, CA 94304, United States of America
- * E-mail:
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20
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Gadhe CG, Kim MH. Insights into the binding modes of CC chemokine receptor 4 (CCR4) inhibitors: a combined approach involving homology modelling, docking, and molecular dynamics simulation studies. MOLECULAR BIOSYSTEMS 2014; 11:618-34. [PMID: 25474265 DOI: 10.1039/c4mb00568f] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
CC chemokine receptor 4 (CCR4), a G protein-coupled receptor (GPCR), plays a vital role in the progression of asthma, T-cell lymphoma, inflammation, and Alzheimer's disease. To date, the structure of CCR4 has not been determined. Therefore, the nature of the interactions between inhibitors and CCR4 is not well known. In this study, we used CCR5 as a template to model the structure of CCR4. Docking studies were performed for four naphthalene-sulphonamide derivatives and crucial ligand-protein interactions were analysed. Molecular dynamics (MD) simulations of these complexes (100 ns each) were carried out to gain insights into the interactions between ligands and CCR4. MD simulations revealed that the residues identified by the docking were displaced and new residues were inserted near the ligands. Results of a principal component analysis (PCA) suggested that CCR4 unfolds at the extracellular site surrounding the ligands. Our simulations identified crucial residues involved in CCR4 antagonism, which were supported by previous mutational studies. Additionally, we identified Ser3.29, Leu3.33, Ser5.39, Phe6.47, Ile7.35, Thr7.38, Thr7.40, and Ala7.42 as residues that play crucial roles in CCR4 antagonism. Mutational studies will help elucidate the significance of these residues in CCR4 antagonism. An understanding of ligand-CCR4 interactions might aid in the design of novel CCR4 inhibitors.
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Affiliation(s)
- Changdev G Gadhe
- Department of Pharmacy, College of Pharmacy, Gachon University, 155 Gaetbeol-ro, Yeonsu-gu, Incheon, Republic of Korea.
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21
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Chilmonczyk Z, Bojarski AJ, Sylte I. Ligand-directed trafficking of receptor stimulus. Pharmacol Rep 2014; 66:1011-21. [DOI: 10.1016/j.pharep.2014.06.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Revised: 04/28/2014] [Accepted: 06/05/2014] [Indexed: 01/14/2023]
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22
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Le Naour M, Lunzer MM, Powers MD, Kalyuzhny AE, Benneyworth MA, Thomas MJ, Portoghese PS. Putative kappa opioid heteromers as targets for developing analgesics free of adverse effects. J Med Chem 2014; 57:6383-92. [PMID: 24978316 PMCID: PMC4136663 DOI: 10.1021/jm500159d] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2014] [Indexed: 11/29/2022]
Abstract
It is now generally recognized that upon activation by an agonist, β-arrestin associates with G protein-coupled receptors and acts as a scaffold in creating a diverse signaling network that could lead to adverse effects. As an approach to reducing side effects associated with κ opioid agonists, a series of β-naltrexamides 3-10 was synthesized in an effort to selectively target putative κ opioid heteromers without recruiting β-arrestin upon activation. The most potent derivative 3 (INTA) strongly activated KOR-DOR and KOR-MOR heteromers in HEK293 cells. In vivo studies revealed 3 to produce potent antinociception, which, when taken together with antagonism data, was consistent with the activation of both heteromers. 3 was devoid of tolerance, dependence, and showed no aversive effect in the conditioned place preference assay. As immunofluorescence studies indicated no recruitment of β-arrestin2 to membranes in coexpressed KOR-DOR cells, this study suggests that targeting of specific putative heteromers has the potential to identify leads for analgesics devoid of adverse effects.
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MESH Headings
- Analgesics/adverse effects
- Analgesics/chemistry
- Analgesics/pharmacology
- Animals
- Arrestins/metabolism
- Avoidance Learning/drug effects
- Calcium/metabolism
- Drug Tolerance
- HEK293 Cells
- Humans
- Indoles/adverse effects
- Indoles/chemistry
- Indoles/pharmacology
- Mice
- Naltrexone/adverse effects
- Naltrexone/analogs & derivatives
- Naltrexone/chemistry
- Naltrexone/pharmacology
- Protein Multimerization
- Receptors, Opioid, delta/agonists
- Receptors, Opioid, delta/metabolism
- Receptors, Opioid, kappa/agonists
- Receptors, Opioid, kappa/metabolism
- Receptors, Opioid, mu/agonists
- Receptors, Opioid, mu/metabolism
- Stereoisomerism
- Structure-Activity Relationship
- Substance-Related Disorders/etiology
- beta-Arrestins
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Affiliation(s)
- Morgan Le Naour
- Department of Medicinal Chemistry, College of Pharmacy, University of Minnesota , WDH 8-114, 308 Harvard Street SE, Minneapolis, Minnesota 55455, United States
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23
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Abstract
G-protein-coupled receptors (GPCRs) are the primary interaction partners for arrestins. The visual arrestins, arrestin1 and arrestin4, physiologically bind to only very few receptors, i.e., rhodopsin and the color opsins, respectively. In contrast, the ubiquitously expressed nonvisual variants β-arrestin1 and 2 bind to a large number of receptors in a fairly nonspecific manner. This binding requires two triggers, agonist activation and receptor phosphorylation by a G-protein-coupled receptor kinase (GRK). These two triggers are mediated by two different regions of the arrestins, the "phosphorylation sensor" in the core of the protein and a less well-defined "activation sensor." Binding appears to occur mostly in a 1:1 stoichiometry, involving the N-terminal domain of GPCRs, but in addition a second GPCR may loosely bind to the C-terminal domain when active receptors are abundant.Arrestin binding initially uncouples GPCRs from their G-proteins. It stabilizes receptors in an active conformation and also induces a conformational change in the arrestins that involves a rotation of the two domains relative to each other plus changes in the polar core. This conformational change appears to permit the interaction with further downstream proteins. The latter interaction, demonstrated mostly for β-arrestins, triggers receptor internalization as well as a number of nonclassical signaling pathways.Open questions concern the exact stoichiometry of the interaction, possible specificity with regard to the type of agonist and of GRK involved, selective regulation of downstream signaling (=biased signaling), and the options to use these mechanisms as therapeutic targets.
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Affiliation(s)
- Martin J Lohse
- Institute of Pharmacology and Toxicology, University of Würzburg, Versbacher Straße 9, 97078, Würzburg, Germany,
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24
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Contreras-Romo MC, Martínez-Archundia M, Deeb O, Ślusarz MJ, Ramírez-Salinas G, Garduño-Juárez R, Quintanar-Stephano A, Ramírez-Galicia G, Correa-Basurto J. Exploring the Ligand Recognition Properties of the Human Vasopressin V1a Receptor Using QSAR and Molecular Modeling Studies. Chem Biol Drug Des 2013; 83:207-23. [DOI: 10.1111/cbdd.12229] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Revised: 07/08/2013] [Accepted: 08/12/2013] [Indexed: 11/28/2022]
Affiliation(s)
- Martha C. Contreras-Romo
- Departamento de Fisiología y Farmacología; Centro de Ciencias Básicas; Universidad Autónoma de Aguascalientes; Av. Universidad 940 20131 Aguascalientes México
| | - Marlet Martínez-Archundia
- Laboratorio de Modelado Molecular y Bioinformática; Sección de Estudios de Posgrado e Investigación de la Escuela Superior de Medicina; Instituto Politécnico Nacional; Plan de San Luis y Díaz Mirón, Del. Miguel Hidalgo 11340 México City México
| | - Omar Deeb
- Faculty of Pharmacy; Al-Quds University; Jerusalem Palestine
| | | | - Gema Ramírez-Salinas
- Laboratorio de Modelado Molecular y Bioinformática; Sección de Estudios de Posgrado e Investigación de la Escuela Superior de Medicina; Instituto Politécnico Nacional; Plan de San Luis y Díaz Mirón, Del. Miguel Hidalgo 11340 México City México
| | - Ramón Garduño-Juárez
- Instituto de Ciencias Físicas; Universidad Nacional Autónoma de México; Cuernavaca Morelos 62210 México
| | - Andrés Quintanar-Stephano
- Departamento de Fisiología y Farmacología; Centro de Ciencias Básicas; Universidad Autónoma de Aguascalientes; Av. Universidad 940 20131 Aguascalientes México
| | - Guillermo Ramírez-Galicia
- División de Estudios de Posgrado; Universidad del Papaloapan; Circuito Central 200 Parque Industrial 68301 Tuxtepec Oaxaca México
| | - José Correa-Basurto
- Laboratorio de Modelado Molecular y Bioinformática; Sección de Estudios de Posgrado e Investigación de la Escuela Superior de Medicina; Instituto Politécnico Nacional; Plan de San Luis y Díaz Mirón, Del. Miguel Hidalgo 11340 México City México
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25
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Lohse MJ, Maiellaro I, Calebiro D. Kinetics and mechanism of G protein-coupled receptor activation. Curr Opin Cell Biol 2013; 27:87-93. [PMID: 24530699 DOI: 10.1016/j.ceb.2013.11.009] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2013] [Accepted: 11/24/2013] [Indexed: 10/25/2022]
Abstract
The activation of a G protein-coupled receptor is generally triggered by binding of an agonist to the receptor's binding pocket, or, in the case of rhodopsin, by light-induced changes of the pre-bound retinal. This is followed by a series of a conformational changes towards an active receptor conformation, which is capable of signalling to G proteins and other downstream proteins. In the past few years, a number of new techniques have been employed to analyze the kinetics of this activation process, including X-ray crystallographic three-dimensional structures of receptors in the inactive and the active states, NMR studies of labelled receptors, molecular simulations, and optical analyses with fluorescence resonance energy transfer (FRET). Here we review our current understanding of the activation process of GPCRs as well as open questions in the sequence of events ranging from (sub-)microsecond activation by light or agonist binding to millisecond activation of receptors by soluble ligands and the subsequent generation of an intracellular signal.
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Affiliation(s)
- Martin J Lohse
- Institute of Pharmacology and Toxicology, University of Würzburg, 97078 Würzburg, Germany; Rudolf Virchow Center, DFG-Research Center for Experimental Biomedicine, University of Würzburg, 97078 Würzburg, Germany.
| | - Isabella Maiellaro
- Institute of Pharmacology and Toxicology, University of Würzburg, 97078 Würzburg, Germany; Rudolf Virchow Center, DFG-Research Center for Experimental Biomedicine, University of Würzburg, 97078 Würzburg, Germany
| | - Davide Calebiro
- Institute of Pharmacology and Toxicology, University of Würzburg, 97078 Würzburg, Germany; Rudolf Virchow Center, DFG-Research Center for Experimental Biomedicine, University of Würzburg, 97078 Würzburg, Germany
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26
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The complexity of G-protein coupled receptor-ligand interactions. Sci China Chem 2013. [DOI: 10.1007/s11426-013-4911-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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27
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Li J, Jonsson AL, Beuming T, Shelley JC, Voth GA. Ligand-dependent activation and deactivation of the human adenosine A(2A) receptor. J Am Chem Soc 2013; 135:8749-59. [PMID: 23678995 PMCID: PMC4120839 DOI: 10.1021/ja404391q] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
G-protein-coupled receptors (GPCRs) are membrane proteins with critical functions in cellular signal transduction, representing a primary class of drug targets. Acting by direct binding, many drugs modulate GPCR activity and influence the signaling pathways associated with numerous diseases. However, complete details of ligand-dependent GPCR activation/deactivation are difficult to obtain from experiments. Therefore, it remains unclear how ligands modulate a GPCR's activity. To elucidate the ligand-dependent activation/deactivation mechanism of the human adenosine A2A receptor (AA2AR), a member of the class A GPCRs, we performed large-scale unbiased molecular dynamics and metadynamics simulations of the receptor embedded in a membrane. At the atomic level, we have observed distinct structural states that resemble the active and inactive states. In particular, we noted key structural elements changing in a highly concerted fashion during the conformational transitions, including six conformational states of a tryptophan (Trp246(6.48)). Our findings agree with a previously proposed view that, during activation, this tryptophan residue undergoes a rotameric transition that may be coupled to a series of coherent conformational changes, resulting in the opening of the G-protein binding site. Further, metadynamics simulations provide quantitative evidence for this mechanism, suggesting how ligand binding shifts the equilibrium between the active and inactive states. Our analysis also proposes that a few specific residues are associated with agonism/antagonism, affinity, and selectivity, and suggests that the ligand-binding pocket can be thought of as having three distinct regions, providing dynamic features for structure-based design. Additional simulations with AA2AR bound to a novel ligand are consistent with our proposed mechanism. Generally, our study provides insights into the ligand-dependent AA2AR activation/deactivation in addition to what has been found in crystal structures. These results should aid in the discovery of more effective and selective GPCR ligands.
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Affiliation(s)
- Jianing Li
- Department of Chemistry, Institute for Biophysical Dynamics, James Franck Institute and Computation Institute, The University of Chicago, 5735 South Ellis Avenue, Chicago, IL 60637
| | - Amanda L. Jonsson
- Department of Chemistry, Institute for Biophysical Dynamics, James Franck Institute and Computation Institute, The University of Chicago, 5735 South Ellis Avenue, Chicago, IL 60637
| | - Thijs Beuming
- Schrödinger, Inc., 120 West 45 Street, 17th Floor, New York, NY 10036
| | - John C. Shelley
- Schrödinger, Inc., 101 Southwest Main Street, Suite 1300, Portland, OR 97204
| | - Gregory A. Voth
- Department of Chemistry, Institute for Biophysical Dynamics, James Franck Institute and Computation Institute, The University of Chicago, 5735 South Ellis Avenue, Chicago, IL 60637
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G-protein-coupled receptor structure, ligand binding and activation as studied by solid-state NMR spectroscopy. Biochem J 2013; 450:443-57. [DOI: 10.1042/bj20121644] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
GPCRs (G-protein-coupled receptors) are versatile signalling molecules at the cell surface and make up the largest and most diverse family of membrane receptors in the human genome. They convert a large variety of extracellular stimuli into intracellular responses through the activation of heterotrimeric G-proteins, which make them key regulatory elements in a broad range of normal and pathological processes, and are therefore one of the most important targets for pharmaceutical drug discovery. Knowledge of a GPCR structure enables us to gain a mechanistic insight into its function and dynamics, and further aid rational drug design. Despite intensive research carried out over the last three decades, resolving the structural basis of GPCR function is still a major activity. The crystal structures obtained in the last 5 years provide the first opportunity to understand how protein structure dictates the unique functional properties of these complex signalling molecules. However, owing to the intrinsic hydrophobicity, flexibility and instability of membrane proteins, it is still a challenge to crystallize GPCRs, and, when this is possible, it is no longer in its native membrane environment and no longer without modification. Furthermore, the conformational change of the transmembrane α-helices associated with the structure activation increases the difficulty of capturing the activation state of a GPCR to a higher resolution by X-ray crystallography. On the other hand, solid-state NMR may offer a unique opportunity to study membrane protein structure, ligand binding and activation at atomic resolution in the native membrane environment, as well as described functionally significant dynamics. In the present review, we discuss some recent achievements of solid-state NMR for understanding GPCRs, the largest mammalian proteome at ~1% of the total expressed proteins. Structural information, details of determination, details of ligand conformations and the consequences of ligand binding to initiate activation can all be explored with solid-state NMR.
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Hoffmann C, Nuber S, Zabel U, Ziegler N, Winkler C, Hein P, Berlot CH, Bünemann M, Lohse MJ. Comparison of the activation kinetics of the M3 acetylcholine receptor and a constitutively active mutant receptor in living cells. Mol Pharmacol 2012; 82:236-45. [PMID: 22564786 PMCID: PMC11037427 DOI: 10.1124/mol.112.077578] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2012] [Accepted: 05/07/2012] [Indexed: 12/26/2022] Open
Abstract
Activation of G-protein-coupled receptors is the first step of the signaling cascade triggered by binding of an agonist. Here we compare the activation kinetics of the G(q)-coupled M(3) acetylcholine receptor (M(3)-AChR) with that of a constitutively active mutant receptor (M(3)-AChR-N514Y) using M(3)-AChR constructs that report receptor activation by changes in the fluorescence resonance energy transfer (FRET) signal. We observed a leftward shift in the concentration-dependent FRET response for acetylcholine and carbachol with M(3)-AChR-N514Y. Consistent with this result, at submaximal agonist concentrations, the activation kinetics of M(3)-AChR-N514Y were significantly faster, whereas at maximal agonist concentrations the kinetics of receptor activation were identical. Receptor deactivation was significantly faster with carbachol than with acetylcholine and was significantly delayed by the N514Y mutation. Receptor-G-protein interaction was measured by FRET between M(3)-AChR-yellow fluorescent protein (YFP) and cyan fluorescent protein (CFP)-Gγ(2). Agonist-induced receptor-G-protein coupling was of a time scale similar to that of receptor activation. As observed for receptor deactivation, receptor-G-protein dissociation was slower for acetylcholine than that for carbachol. Acetylcholine-stimulated increases in receptor-G-protein coupling of M(3)-AChR-N514Y reached only 12% of that of M(3)-AChR and thus cannot be kinetically analyzed. G-protein activation was measured using YFP-tagged Gα(q) and CFP-tagged Gγ(2). Activation of G(q) was significantly slower than receptor activation and indistinguishable for the two agonists. However, G(q) deactivation was significantly prolonged for acetylcholine compared with that for carbachol. Consistent with decreased agonist-stimulated coupling to G(q), agonist-stimulated G(q) activation by M(3)-AChR-N514Y was not detected. Taken together, these results indicate that the N514Y mutation produces constitutive activation of M(3)-AChR by decreasing the rate of receptor deactivation, while having minimal effect on receptor activation.
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Affiliation(s)
- Carsten Hoffmann
- Department of Pharmacology and Toxicology, University of Wuerzburg, Versbacher Strasse 9, Wuerzburg, Germany.
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Salon JA, Lodowski DT, Palczewski K. The significance of G protein-coupled receptor crystallography for drug discovery. Pharmacol Rev 2012; 63:901-37. [PMID: 21969326 DOI: 10.1124/pr.110.003350] [Citation(s) in RCA: 160] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Crucial as molecular sensors for many vital physiological processes, seven-transmembrane domain G protein-coupled receptors (GPCRs) comprise the largest family of proteins targeted by drug discovery. Together with structures of the prototypical GPCR rhodopsin, solved structures of other liganded GPCRs promise to provide insights into the structural basis of the superfamily's biochemical functions and assist in the development of new therapeutic modalities and drugs. One of the greatest technical and theoretical challenges to elucidating and exploiting structure-function relationships in these systems is the emerging concept of GPCR conformational flexibility and its cause-effect relationship for receptor-receptor and receptor-effector interactions. Such conformational changes can be subtle and triggered by relatively small binding energy effects, leading to full or partial efficacy in the activation or inactivation of the receptor system at large. Pharmacological dogma generally dictates that these changes manifest themselves through kinetic modulation of the receptor's G protein partners. Atomic resolution information derived from increasingly available receptor structures provides an entrée to the understanding of these events and practically applying it to drug design. Supported by structure-activity relationship information arising from empirical screening, a unified structural model of GPCR activation/inactivation promises to both accelerate drug discovery in this field and improve our fundamental understanding of structure-based drug design in general. This review discusses fundamental problems that persist in drug design and GPCR structural determination.
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Affiliation(s)
- John A Salon
- Department of Molecular Structure, Amgen Incorporated, Thousand Oaks, California, USA
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Saulière A, Bellot M, Paris H, Denis C, Finana F, Hansen JT, Altié MF, Seguelas MH, Pathak A, Hansen JL, Sénard JM, Galés C. Deciphering biased-agonism complexity reveals a new active AT1 receptor entity. Nat Chem Biol 2012; 8:622-30. [PMID: 22634635 DOI: 10.1038/nchembio.961] [Citation(s) in RCA: 163] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2011] [Accepted: 02/28/2012] [Indexed: 02/06/2023]
Abstract
Functional selectivity of G protein-coupled receptor (GPCR) ligands toward different downstream signals has recently emerged as a general hallmark of this receptor class. However, pleiotropic and crosstalk signaling of GPCRs makes functional selectivity difficult to decode. To look from the initial active receptor point of view, we developed new, highly sensitive and direct bioluminescence resonance energy transfer-based G protein activation probes specific for all G protein isoforms, and we used them to evaluate the G protein-coupling activity of [(1)Sar(4)Ile(8)Ile]-angiotensin II (SII), previously described as an angiotensin II type 1 (AT(1)) receptor-biased agonist that is G protein independent but β-arrestin selective. By multiplexing assays sensing sequential signaling events, from receptor conformations to downstream signaling, we decoded SII as an agonist stabilizing a G protein-dependent AT(1A) receptor signaling module different from that of the physiological agonist angiotensin II, both in recombinant and primary cells. Thus, a biased agonist does not necessarily select effects from the physiological agonist but may instead stabilize and create a new distinct active pharmacological receptor entity.
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Affiliation(s)
- Aude Saulière
- Institut des Maladies Métaboliques et Cardiovasculaires, Institut National de la Santé et de la Recherche Médicale, Université Toulouse III Paul Sabatier, Toulouse, France
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Structural insights into biased G protein-coupled receptor signaling revealed by fluorescence spectroscopy. Proc Natl Acad Sci U S A 2012; 109:6733-8. [PMID: 22493271 DOI: 10.1073/pnas.1201093109] [Citation(s) in RCA: 144] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
G protein-coupled receptors (GPCRs) are seven-transmembrane proteins that mediate most cellular responses to hormones and neurotransmitters, representing the largest group of therapeutic targets. Recent studies show that some GPCRs signal through both G protein and arrestin pathways in a ligand-specific manner. Ligands that direct signaling through a specific pathway are known as biased ligands. The arginine-vasopressin type 2 receptor (V2R), a prototypical peptide-activated GPCR, is an ideal model system to investigate the structural basis of biased signaling. Although the native hormone arginine-vasopressin leads to activation of both the stimulatory G protein (Gs) for the adenylyl cyclase and arrestin pathways, synthetic ligands exhibit highly biased signaling through either Gs alone or arrestin alone. We used purified V2R stabilized in neutral amphipols and developed fluorescence-based assays to investigate the structural basis of biased signaling for the V2R. Our studies demonstrate that the Gs-biased agonist stabilizes a conformation that is distinct from that stabilized by the arrestin-biased agonists. This study provides unique insights into the structural mechanisms of GPCR activation by biased ligands that may be relevant to the design of pathway-biased drugs.
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Lohse MJ, Nuber S, Hoffmann C. Fluorescence/bioluminescence resonance energy transfer techniques to study G-protein-coupled receptor activation and signaling. Pharmacol Rev 2012; 64:299-336. [PMID: 22407612 DOI: 10.1124/pr.110.004309] [Citation(s) in RCA: 251] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Fluorescence and bioluminescence resonance energy transfer (FRET and BRET) techniques allow the sensitive monitoring of distances between two labels at the nanometer scale. Depending on the placement of the labels, this permits the analysis of conformational changes within a single protein (for example of a receptor) or the monitoring of protein-protein interactions (for example, between receptors and G-protein subunits). Over the past decade, numerous such techniques have been developed to monitor the activation and signaling of G-protein-coupled receptors (GPCRs) in both the purified, reconstituted state and in intact cells. These techniques span the entire spectrum from ligand binding to the receptors down to intracellular second messengers. They allow the determination and the visualization of signaling processes with high temporal and spatial resolution. With these techniques, it has been demonstrated that GPCR signals may show spatial and temporal patterning. In particular, evidence has been provided for spatial compartmentalization of GPCRs and their signals in intact cells and for distinct physiological consequences of such spatial patterning. We review here the FRET and BRET technologies that have been developed for G-protein-coupled receptors and their signaling proteins (G-proteins, effectors) and the concepts that result from such experiments.
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Affiliation(s)
- Martin J Lohse
- Institute of Pharmacology and Toxicology, Versbacher Str. 9, 97078 Würzburg, Germany.
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Abrol R, Bray JK, Goddard WA. Bihelix: Towards de novo structure prediction of an ensemble of G-protein coupled receptor conformations. Proteins 2011; 80:505-18. [PMID: 22173949 DOI: 10.1002/prot.23216] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2011] [Revised: 09/10/2011] [Accepted: 09/27/2011] [Indexed: 11/12/2022]
Abstract
G-Protein Coupled Receptors (GPCRs) play a critical role in cellular signal transduction pathways and are prominent therapeutic targets. Recently there has been major progress in obtaining experimental structures for a few GPCRs. Each GPCR, however, exhibits multiple conformations that play a role in their function and we have been developing methods aimed at predicting structures for all these conformations. Analysis of available structures shows that these conformations differ in relative helix tilts and rotations. The essential issue is, determining how to orient each of the seven helices about its axis since this determines how it interacts with the other six helices. Considering all possible helix rotations to ensure that no important packings are overlooked, and using rotation angle increments of 30° about the helical axis would still lead to 12(7) or 35 million possible conformations each with optimal residue positions. We show in this paper how to accomplish this. The fundamental idea is to optimize the interactions between each pair of contacting helices while ignoring the other 5 and then to estimate the energies of all 35 million combinations using these pair-wise interactions. This BiHelix approach dramatically reduces the effort to examine the complete set of conformations and correctly identifies the crystal packing for the experimental structures plus other near-native packings we believe may play an important role in activation. This approach also enables a detailed structural analysis of functionally distinct conformations using helix-helix interaction energy landscapes and should be useful for other helical transmembrane proteins as well.
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Affiliation(s)
- Ravinder Abrol
- Materials and Process Simulation Center (MC 139-74), Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125.
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35
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Fanelli F, De Benedetti PG. Update 1 of: computational modeling approaches to structure-function analysis of G protein-coupled receptors. Chem Rev 2011; 111:PR438-535. [PMID: 22165845 DOI: 10.1021/cr100437t] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Francesca Fanelli
- Dulbecco Telethon Institute, University of Modena and Reggio Emilia, via Campi 183, 41125 Modena, Italy.
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36
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Abrol R, Kim SK, Bray JK, Griffith AR, Goddard WA. Characterizing and predicting the functional and conformational diversity of seven-transmembrane proteins. Methods 2011; 55:405-14. [PMID: 22197575 PMCID: PMC3286597 DOI: 10.1016/j.ymeth.2011.12.005] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2011] [Revised: 12/13/2011] [Accepted: 12/14/2011] [Indexed: 11/18/2022] Open
Abstract
The activation of seven-transmembrane receptors (7TMRs) allows cells to sense their environment and convert extracellular signals (like hormone binding) into intracellular signals (through G protein-coupled and/or β arrestin-coupled pathways). A single 7TMR is capable of transducing a wide spectrum of physiological responses inside a cell by coupling to these pathways. This intracellular pleiotropic action is enabled by multiple conformations exhibited by these receptors. Developments in membrane protein structure determination technologies have led to a rapid increase in crystal structures for many 7TMRs. Majority of these receptors have been crystallized in their inactive conformation and, for some, one of the many active conformations has also been crystallized. Given the topological constraints of a lipid bilayer that results in a single fold of seven almost parallel TM helices connected by mostly unstructured loops, these structures exhibit a diversity of conformations not only across the receptors but also across the different functional forms for receptors with structures for one of the functionally active conformations. Here we present a method to characterize this conformational diversity in terms of transmembrane helix topology (TMHTOP) parameters and how to use these helix orientation parameters to predict functionally-distinct multiple conformations for these receptors. The TMHTOP parameters enable a quantification of the structural changes that underlie 7TMR activation and also sheds a unique mechanistic light on the pleiotropic nature of these receptors. It provides a common language to describe the 7TMR activation mechanisms as well as differences across many receptors in terms of visually intuitive structural parameters. Protein structure prediction methods can use these parameters to describe 7TMR conformational ensembles, which coupled to experimental data can be used to develop testable hypotheses for the structural basis of 7TMR functions.
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Affiliation(s)
- Ravinder Abrol
- Materials and Process Simulation Center (MC 139-74), California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, United States.
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Reiter E, Ahn S, Shukla AK, Lefkowitz RJ. Molecular mechanism of β-arrestin-biased agonism at seven-transmembrane receptors. Annu Rev Pharmacol Toxicol 2011; 52:179-97. [PMID: 21942629 DOI: 10.1146/annurev.pharmtox.010909.105800] [Citation(s) in RCA: 461] [Impact Index Per Article: 35.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
The concept of biased agonism has recently come to the fore with the realization that seven-transmembrane receptors (7TMRs, also known as G protein-coupled receptors, or GPCRs) activate complex signaling networks and can adopt multiple active conformations upon agonist binding. As a consequence, the "efficacy" of receptors, which was classically considered linear, is now recognized as pluridimensional. Biased agonists selectively stabilize only a subset of receptor conformations induced by the natural "unbiased" ligand, thus preferentially activating certain signaling mechanisms. Such agonists thus reveal the intriguing possibility that one can direct cellular signaling with unprecedented precision and specificity and support the notion that biased agonists may identify new classes of therapeutic agents that have fewer side effects. This review focuses on one particular class of biased ligands that has the ability to alter the balance between G protein-dependent and β-arrestin-dependent signal transduction.
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Affiliation(s)
- Eric Reiter
- BIOS Group, INRA, UMR85, Unité Physiologie de la Reproduction et des Comportements, F-37380 Nouzilly, France
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Valant C, Robert Lane J, Sexton PM, Christopoulos A. The best of both worlds? Bitopic orthosteric/allosteric ligands of g protein-coupled receptors. Annu Rev Pharmacol Toxicol 2011; 52:153-78. [PMID: 21910627 DOI: 10.1146/annurev-pharmtox-010611-134514] [Citation(s) in RCA: 136] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
It is now acknowledged that G protein-coupled receptors, the largest class of drug targets, adopt multiple active states that can be preferentially stabilized by orthosteric ligands or allosteric modulators, thus giving rise to the phenomenon of pathway-biased signaling. In the past few years, researchers have begun to explore the potential of linking orthosteric and allosteric pharmacophores to yield bitopic hybrid ligands. This approach is an extension of the more traditional bivalent ligand concept and shares some of the same challenges, including the choice and role of the linker between the two pharmacophores and the validation of mechanism of action. Nonetheless, the promise of bitopic ligands is the generation of novel chemical tools that have improved affinity and/or selectivity profiles. Previously identified functionally selective compounds (and medicines) also may act via a bitopic mechanism, suggesting that the phenomenon is more widespread than currently appreciated.
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Affiliation(s)
- Celine Valant
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, and Department of Pharmacology, Monash University, Parkville, Victoria 3052, Australia.
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Billington CK, Hall IP. Real time analysis of β(2)-adrenoceptor-mediated signaling kinetics in human primary airway smooth muscle cells reveals both ligand and dose dependent differences. Respir Res 2011; 12:89. [PMID: 21722392 PMCID: PMC3143098 DOI: 10.1186/1465-9921-12-89] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2011] [Accepted: 07/02/2011] [Indexed: 11/23/2022] Open
Abstract
Background β2-adrenoceptor agonists elicit bronchodilator responses by binding to β2-adrenoceptors on airway smooth muscle (ASM). In vivo, the time between drug administration and clinically relevant bronchodilation varies significantly depending on the agonist used. Our aim was to utilise a fluorescent cyclic AMP reporter probe to study the temporal profile of β2-adrenoceptor-mediated signaling induced by isoproterenol and a range of clinically relevant agonists in human primary ASM (hASM) cells by using a modified Epac protein fused to CFP and a variant of YFP. Methods Cells were imaged in real time using a spinning disk confocal system which allowed rapid and direct quantification of emission ratio imaging following direct addition of β2-adrenoceptor agonists (isoproterenol, salbutamol, salmeterol, indacaterol and formoterol) into the extracellular buffer. For pharmacological comparison a radiolabeling assay for whole cell cyclic AMP formation was used. Results Temporal analysis revealed that in hASM cells the β2-adrenoceptor agonists studied did not vary significantly in the onset of initiation. However, once a response was initiated, significant differences were observed in the rate of this response with indacaterol and isoproterenol inducing a significantly faster response than salmeterol. Contrary to expectation, reducing the concentration of isoproterenol resulted in a significantly faster initiation of response. Conclusions We conclude that confocal imaging of the Epac-based probe is a powerful tool to explore β2-adrenoceptor signaling in primary cells. The ability to analyse the kinetics of clinically used β2-adrenoceptor agonists in real time and at a single cell level gives an insight into their possible kinetics once they have reached ASM cells in vivo.
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Affiliation(s)
- Charlotte K Billington
- Division of Therapeutics and Molecular Medicine, Nottingham Respiratory Biomedical Research Unit, Floor D, South Block, University Hospital of Nottingham, The University of Nottingham, Nottingham, NG7 2UH, UK.
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Rotational diffusion of the α(2a) adrenergic receptor revealed by FlAsH labeling in living cells. Biophys J 2011; 100:1139-48. [PMID: 21320460 DOI: 10.1016/j.bpj.2010.08.080] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2010] [Revised: 08/03/2010] [Accepted: 08/13/2010] [Indexed: 11/24/2022] Open
Abstract
The fluorescein arsenical hairpin binder (FlAsH) shows much promise to determine the relative orientations of protein regions and structures even in living cells and in the plasma membrane. In this study, we characterized FlAsH's photophysical properties by steady-state anisotropy and time-resolved single photon counting for further applications with G-protein coupled receptors. We find that FlAsH has a relatively high initial anisotropy of 0.31 ± 0.01 and a three-component fluorescence lifetime with an average of 4.1 ± 0.1 ns. We characterized the FlAsH fluorophore orientation in the α(2A) adrenergic receptor revealing rigid orientations of FlAsH in the membrane plane for rotational correlation times of ∼50 ns in living cells. To elucidate the fluorophore-membrane orientation and rotational correlation time, an anisotropy treatment similar to that of another researcher (Axelrod, D. 1979. Biophys. J. 26:557-573) was developed. The rotational correlation times were observed to increase by up to 16 ns after agonist addition. The rotational correlation time also allowed for a comparison to the theoretical relationship between translational and rotational diffusion (originally proposed by Saffman, P. G., and M. Delbrück. 1975. Proc. Natl. Acad. Sci. USA. 72:3111-3113) and revealed a discrepancy of a factor between 10 and 100.
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Abstract
The critical involvement of GPCRs (G-protein-coupled receptors) in nearly all physiological processes, and the presence of these receptors at the interface between the extracellular and the intracellular milieu, has positioned these receptors as pivotal therapeutic targets. Although a large number of drugs targeting GPCRs are currently available, significant efforts have been directed towards understanding receptor properties, with the goal of identifying and designing improved receptor ligands. Recent advances in GPCR pharmacology have demonstrated that different ligands binding to the same receptor can activate discrete sets of downstream effectors, a phenomenon known as 'ligand-directed signal specificity', which is currently being explored for drug development due to its potential therapeutic advantage. Emerging studies suggest that GPCR responses can also be modulated by contextual factors, such as interactions with other GPCRs. Association between different GPCR types leads to the formation of complexes, or GPCR heteromers, with distinct and unique signalling properties. Some of these heteromers activate discrete sets of signalling effectors upon activation by the same ligand, a phenomenon termed 'heteromer-directed signalling specificity'. This has been shown to be involved in the physiological role of receptors and, in some cases, in disease-specific dysregulation of a receptor effect. Hence targeting GPCR heteromers constitutes an emerging strategy to select receptor-specific responses and is likely to be useful in achieving specific beneficial therapeutic effects.
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FRET-based sensors for the human M1-, M3-, and M5-acetylcholine receptors. Bioorg Med Chem 2011; 19:1048-54. [DOI: 10.1016/j.bmc.2010.07.060] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2010] [Revised: 07/15/2010] [Accepted: 07/26/2010] [Indexed: 12/30/2022]
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Hoffmann C. G protein-coupled receptor activation: amino acid movements caught infra-red-handed. Chembiochem 2010; 11:2247-9. [PMID: 20922739 DOI: 10.1002/cbic.201000502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Carsten Hoffmann
- Department of Pharmacology and Toxicology, University of Würzburg, Würzburg, Germany.
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Reiner S, Ambrosio M, Hoffmann C, Lohse MJ. Differential signaling of the endogenous agonists at the beta2-adrenergic receptor. J Biol Chem 2010; 285:36188-98. [PMID: 20837485 DOI: 10.1074/jbc.m110.175604] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The concept of "functional selectivity" or "biased signaling" suggests that a ligand can have distinct efficacies with regard to different signaling pathways. We have investigated the question of whether biased signaling may be related to distinct agonist-induced conformational changes in receptors using the β(2)-adrenergic receptor (β(2)AR) and its two endogenous ligands epinephrine and norepinephrine as a model system. Agonist-induced conformational changes were determined in a fluorescently tagged β(2)AR FRET sensor. In this β(2)AR sensor, norepinephrine caused signals that amounted to only ≈50% of those induced by epinephrine and the standard "full" agonist isoproterenol. Furthermore, norepinephrine-induced changes in the β(2)AR FRET sensor were slower than those induced by epinephrine (rate constants, 47 versus 128 ms). A similar partial β(2)AR activation signal was revealed for the synthetic agonists fenoterol and terbutaline. However, norepinephrine was almost as efficient as epinephrine (and isoproterenol) in causing activation of G(s) and adenylyl cyclase. In contrast, fenoterol was quite efficient in triggering β-arrestin2 recruitment to the cell surface and its interaction with β(2)AR, as well as internalization of the receptors, whereas norepinephrine caused partial and slow changes in these assays. We conclude that partial agonism of norepinephrine at the β(2)AR is related to the induction of a different active conformation and that this conformation is efficient in signaling to G(s) and less efficient in signaling to β-arrestin2. These observations extend the concept of biased signaling to the endogenous agonists of the β(2)AR and link it to distinct conformational changes in the receptor.
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Affiliation(s)
- Susanne Reiner
- Institute of Pharmacology and Toxicology, Versbacher Strasse 9, D-97078 Würzburg, Germany
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45
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Ambrosio M, Zürn A, Lohse MJ. Sensing G protein-coupled receptor activation. Neuropharmacology 2010; 60:45-51. [PMID: 20727363 DOI: 10.1016/j.neuropharm.2010.08.006] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2010] [Accepted: 08/07/2010] [Indexed: 11/25/2022]
Abstract
G protein-coupled receptors (GPCRs) are the key elements of a highly regulated transduction machinery that generates different signaling outcomes to hormones and neurotransmitters. Until recently, it was assumed that diverse ligands of a given GPCR differ only in their ability to alter the balance between the OFF and the ON state of the receptor. However, it has now become evident that their activation mechanisms are more complex and that receptors presumably display distinguishable active conformational states, which are induced by different agonists and correlate to specific signaling outputs. The use of different labeling strategies to insert fluorescent labels into purified, reconstituted receptors, or into receptors in intact cells, has made it possible to sense receptor activation via changes in their fluorescence. Here, we summarize recent progress in the analysis of agonist-dependent activation mechanisms of GPCRs acquired using modern spectroscopic and crystallographic techniques.
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Affiliation(s)
- Manuela Ambrosio
- Institute of Pharmacology and Toxicology, University of Würzburg, Versbacher Strasse 9, 97078 Würzburg, Germany
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Selent J, Sanz F, Pastor M, De Fabritiis G. Induced effects of sodium ions on dopaminergic G-protein coupled receptors. PLoS Comput Biol 2010; 6. [PMID: 20711351 PMCID: PMC2920834 DOI: 10.1371/journal.pcbi.1000884] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2010] [Accepted: 07/14/2010] [Indexed: 12/05/2022] Open
Abstract
G-protein coupled receptors, the largest family of proteins in the human genome, are involved in many complex signal transduction pathways, typically activated by orthosteric ligand binding and subject to allosteric modulation. Dopaminergic receptors, belonging to the class A family of G-protein coupled receptors, are known to be modulated by sodium ions from an allosteric binding site, although the details of sodium effects on the receptor have not yet been described. In an effort to understand these effects, we performed microsecond scale all-atom molecular dynamics simulations on the dopaminergic D2 receptor, finding that sodium ions enter the receptor from the extracellular side and bind at a deep allosteric site (Asp2.50). Remarkably, the presence of a sodium ion at this allosteric site induces a conformational change of the rotamer toggle switch Trp6.48 which locks in a conformation identical to the one found in the partially inactive state of the crystallized human β2 adrenergic receptor. This study provides detailed quantitative information about binding of sodium ions in the D2 receptor and reports a possibly important sodium-induced conformational change for modulation of D2 receptor function. G-protein coupled receptors represent more than 50% of the current drug targets, hence playing a crucial role in drug discovery today. A deeper understanding of G-protein coupled receptor functioning and modulation will help in the development of new drugs that are able to interact with such systems in a more subtle way than simple agonists or antagonists. In the present work, we studied the energetics of sodium ions, which have been described to act as an allosteric regulator within the D2 receptor using long-time molecular dynamics simulations, in order to gain insight into the molecular mechanism by which they exert this effect. In our simulations, we observed how sodium ions are able to induce a conformational change of the Trp6.48, a molecular rotamer switch which is implicated in the activation mechanism of G-protein coupled receptors. This observation, never reported before, has interesting implications for the design of drugs able to interact in a proper way with D2 receptor in particular and GPCR in general.
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Affiliation(s)
- Jana Selent
- Computer-Assisted Drug Design Laboratory, Research Unit on Biomedical Informatics, IMIM, Universitat Pompeu Fabra, Barcelona, Spain
- * E-mail: (GDF); (JS)
| | - Ferran Sanz
- Integrative Biomedical Informatics Laboratory, Research Unit on Biomedical Informatics, IMIM, Universitat Pompeu Fabra, Barcelona, Spain
| | - Manuel Pastor
- Computer-Assisted Drug Design Laboratory, Research Unit on Biomedical Informatics, IMIM, Universitat Pompeu Fabra, Barcelona, Spain
| | - Gianni De Fabritiis
- Computational Biochemistry and Biophysics Laboratory, Research Unit on Biomedical Informatics, IMIM, Universitat Pompeu Fabra, Barcelona, Spain
- * E-mail: (GDF); (JS)
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Abstract
This themed section of BJP includes 11 reviews on the biology of G-protein coupled receptors (GPCRs) and the drug targets that these present, 21 research papers on the pharmacology of a range of GPCRs and Commentaries on four of the papers. Areas reviewed include molecular interactions, particular in respect of hetero-dimerisation between receptors and other membrane-located proteins and other key signalling molecules including cAMP and G12/13 proteins and recently de-orphanised receptors including the Neuromedins U & S and the Free Fatty Acid receptors FFA2 & FFA3. The research papers cover the pharmacology of a range of agents acting at GPCRs, including adrenoceptors, purinoceptors, 5HT, opioid, cannabinoid & PAR-2 receptors. A group of papers is concerned with the interesting and rapidly developing pharmacology of drugs acting at beta(2)-adrenoceptors. The reach of GPCRs is illustrated by the range of physiological systems and therapeutic applications involved, including pain, cancer, cardiovascular, gastrointestinal, visual and respiratory and central nervous systems.
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Mohr K, Tränkle C, Kostenis E, Barocelli E, De Amici M, Holzgrabe U. Rational design of dualsteric GPCR ligands: quests and promise. Br J Pharmacol 2010; 159:997-1008. [PMID: 20136835 DOI: 10.1111/j.1476-5381.2009.00601.x] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Dualsteric ligands represent a novel mode of targeting G protein-coupled receptors (GPCRs). These compounds attach simultaneously to both, the orthosteric transmitter binding site and an additional allosteric binding area of a receptor protein. This approach allows the exploitation of favourable characteristics of the orthosteric and the allosteric site by a single ligand molecule. The orthosteric interaction provides high affinity binding and activation of receptors. The allosteric interaction yields receptor subtype-selectivity and, in addition, may modulate both, efficacy and intracellular signalling pathway activation. Insight into the spatial arrangement of the orthosteric and the allosteric site is far advanced in the muscarinic acetylcholine receptor, and the design of dualsteric muscarinic agonists has now been accomplished. Using the muscarinic receptor as a paradigm, this review summarizes the way from suggestive evidence for an orthosteric/allosteric overlap binding to the rational design and experimental validation of dualsteric ligands. As allosteric interactions are increasingly described for GPCRs and as insight into the spatial geometry of ligand/GPCR-complexes is growing impressively, the rational design of dualsteric drugs is a promising new approach to achieve fine-tuned GPCR-modulation.
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Affiliation(s)
- Klaus Mohr
- Institute of Pharmacy, Rheinische Friedrich-Wilhelms-University, Bonn, Germany.
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Matsushita S, Nakata H, Kubo Y, Tateyama M. Ligand-induced rearrangements of the GABA(B) receptor revealed by fluorescence resonance energy transfer. J Biol Chem 2010; 285:10291-9. [PMID: 20129919 DOI: 10.1074/jbc.m109.077990] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The gamma-aminobutyric acid type B receptor (GABA(B)R), one of the family C G-protein-coupled receptor members, exists as a heterodimer comprised of subunits GB1 and GB2. To clarify the ligand-induced activation mechanism of the GABA(B)R, each subunit was fused with either Cerulean or enhanced yellow fluorescent protein at its intracellular loop, and fluorescence resonance energy transfer (FRET) changes upon agonist application were monitored. As a result, FRET decreases were observed between GB1a loop 2 and GB2 loop 2 and between GB1a loop 2 and GB2 loop 1, suggesting the dissociation of intracellular domains during the receptor activation. Both intersubunit FRET pairs were expected to faithfully capture the activation of the original receptor as their pharmacological properties were highly similar to that of the wild-type receptor. However, the intrasubunit data suggest that the receptor activation does not involve major structural changes within the transmembrane domain of each subunit. By combining the results obtained from two different levels, it was concluded that the GABA(B)R activation by agonist is associated with an asymmetrical intersubunit rearrangement of GB1a and GB2 on the membrane. This type of activation mode, an intersubunit rearrangement without apparent intrahelical structural changes, appears commonly shared by the GABA(B)R and the metabotropic glutamate receptor 1alpha, another family C G-protein-coupled receptor previously studied by our group. Nevertheless, the directions of intracellular domain movements and its asymmetry observed here highlight the qualitative difference between the two receptors.
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Affiliation(s)
- Shinichi Matsushita
- Division of Biophysics and Neurobiology, Department of Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Aichi 444-8585, Japan
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Evans BA, Sato M, Sarwar M, Hutchinson DS, Summers RJ. Ligand-directed signalling at beta-adrenoceptors. Br J Pharmacol 2010; 159:1022-38. [PMID: 20132209 DOI: 10.1111/j.1476-5381.2009.00602.x] [Citation(s) in RCA: 127] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
beta-Adrenoceptors (ARs) classically mediate responses to the endogenous ligands adrenaline and noradrenaline by coupling to Gsalpha and stimulating cAMP production; however, drugs designed as beta-AR agonists or antagonists can activate alternative cell signalling pathways, with the potential to influence clinical efficacy. Furthermore, drugs acting at beta-ARs have differential capacity for pathway activation, described as stimulus trafficking, biased agonism, functional selectivity or ligand-directed signalling. These terms refer to responses where drug A has higher efficacy than drug B for one signalling pathway, but a lower efficacy than drug B for a second pathway. The accepted explanation for such responses is that drugs A and B have the capacity to induce or stabilize distinct active conformations of the receptor that in turn display altered coupling efficiency to different effectors. This is consistent with biophysical studies showing that drugs can indeed promote distinct conformational states. Agonists acting at beta-ARs display ligand-directed signalling, but many drugs acting as cAMP antagonists are also able to activate signalling pathways central to cell survival and proliferation or cell death. The observed complexity of drug activity at beta-ARs, prototypical G protein-coupled receptors, necessitates rethinking of the approaches used for screening and characterization of novel therapeutic agents. Most studies of ligand-directed signalling employ recombinant cell systems with high receptor abundance. While such systems are valid for examining upstream signalling events, such as receptor conformational changes and G protein activation, they are less robust when comparing downstream signalling outputs as these are likely to be affected by complex pathway interactions.
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Affiliation(s)
- Bronwyn A Evans
- Monash Institute of Pharmaceutical Sciences & Department of Pharmacology, Parkville, Vic, Australia
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