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Cornejo MP, Mustafá ER, Barrile F, Cassano D, De Francesco PN, Raingo J, Perello M. THE INTRIGUING LIGAND-DEPENDENT AND LIGAND-INDEPENDENT ACTIONS OF THE GROWTH HORMONE SECRETAGOGUE RECEPTOR ON REWARD-RELATED BEHAVIORS. Neurosci Biobehav Rev 2020; 120:401-416. [PMID: 33157147 DOI: 10.1016/j.neubiorev.2020.10.017] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2020] [Revised: 10/18/2020] [Accepted: 10/20/2020] [Indexed: 02/07/2023]
Abstract
The growth hormone secretagogue receptor (GHSR) is a G-protein-coupled receptor (GPCR) highly expressed in the brain, and also in some peripheral tissues. GHSR activity is evoked by the stomach-derived peptide hormone ghrelin and abrogated by the intestine-derived liver-expressed antimicrobial peptide 2 (LEAP2). In vitro, GHSR displays ligand-independent actions, including a high constitutive activity and an allosteric modulation of other GPCRs. Beyond its neuroendocrine and metabolic effects, cumulative evidence shows that GHSR regulates the activity of the mesocorticolimbic pathway and modulates complex reward-related behaviors towards different stimuli. Here, we review current evidence indicating that ligand-dependent and ligand-independent actions of GHSR enhance reward-related behaviors towards appetitive stimuli and drugs of abuse. We discuss putative neuronal networks and molecular mechanisms that GHSR would engage to modulate such reward-related behaviors. Finally, we briefly discuss imaging studies showing that ghrelin would also regulate reward processing in humans. Overall, we conclude that GHSR is a key regulator of the mesocorticolimbic pathway that influences its activity and, consequently, modulates reward-related behaviors via ligand-dependent and ligand-independent actions.
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Affiliation(s)
- María P Cornejo
- Laboratory of Neurophysiology of the Multidisciplinary Institute of Cell Biology [IMBICE, Argentine Research Council (CONICET) and Scientific Research Commission, Province of Buenos Aires (CIC-PBA). National University of La Plata], 1900 La Plata, Buenos Aires, Argentina
| | - Emilio R Mustafá
- Laboratory of Electrophysiology of the IMBICE, 1900 La Plata, Buenos Aires, Argentina
| | - Franco Barrile
- Laboratory of Neurophysiology of the Multidisciplinary Institute of Cell Biology [IMBICE, Argentine Research Council (CONICET) and Scientific Research Commission, Province of Buenos Aires (CIC-PBA). National University of La Plata], 1900 La Plata, Buenos Aires, Argentina
| | - Daniela Cassano
- Laboratory of Neurophysiology of the Multidisciplinary Institute of Cell Biology [IMBICE, Argentine Research Council (CONICET) and Scientific Research Commission, Province of Buenos Aires (CIC-PBA). National University of La Plata], 1900 La Plata, Buenos Aires, Argentina
| | - Pablo N De Francesco
- Laboratory of Neurophysiology of the Multidisciplinary Institute of Cell Biology [IMBICE, Argentine Research Council (CONICET) and Scientific Research Commission, Province of Buenos Aires (CIC-PBA). National University of La Plata], 1900 La Plata, Buenos Aires, Argentina
| | - Jesica Raingo
- Laboratory of Electrophysiology of the IMBICE, 1900 La Plata, Buenos Aires, Argentina
| | - Mario Perello
- Laboratory of Neurophysiology of the Multidisciplinary Institute of Cell Biology [IMBICE, Argentine Research Council (CONICET) and Scientific Research Commission, Province of Buenos Aires (CIC-PBA). National University of La Plata], 1900 La Plata, Buenos Aires, Argentina.
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Nicke L, Müller R, Geyer A, Els-Heindl S. Side Chain Orientation of Tryptophan Analogues Determines Agonism and Inverse Agonism in Short Ghrelin Peptides. ChemMedChem 2019; 14:1849-1855. [PMID: 31442005 PMCID: PMC6899459 DOI: 10.1002/cmdc.201900409] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2019] [Revised: 08/23/2019] [Indexed: 02/06/2023]
Abstract
We describe two synthetic amino acids with inverted side chain stereochemistry, which induce opposite biological activity. Phe4 is an important part of the activation motif of ghrelin, and in short peptide inverse agonists such as KwFwLL-NH2 , the aromatic core is necessary for inactivation of the receptor. To restrict indole/phenyl mobility and simultaneously strengthen the interaction between peptide and receptor, we exchanged the natural monoaryl amino acids for diaryl amino acids derived from tryptophan. By standard solid-phase peptide synthesis, each of them was inserted into ghrelin or in the aromatic core of the inverse agonist. Both ghrelin analogues showed nanomolar activity, indicating sufficient space to accommodate the additional side chain. In contrast, diaryl amino acids in the inverse agonist had considerable influence on receptor signaling. Whereas the introduction of Wsf maintains inverse agonism of the peptide, Wrf shifts the receptor more to active states and can induce agonism depending on its introduction site.
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Affiliation(s)
- Lennart Nicke
- Faculty of Chemistry, Philipps-University Marburg, Hans-Meerwein-Strasse 4, 35032, Marburg, Germany
| | - Ronny Müller
- Faculty of Life Sciences, Institute of Biochemistry, Leipzig University, Brüderstrasse 34, 04103, Leipzig, Germany
| | - Armin Geyer
- Faculty of Chemistry, Philipps-University Marburg, Hans-Meerwein-Strasse 4, 35032, Marburg, Germany
| | - Sylvia Els-Heindl
- Faculty of Life Sciences, Institute of Biochemistry, Leipzig University, Brüderstrasse 34, 04103, Leipzig, Germany
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3
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Fowkes MM, Lalonde T, Yu L, Dhanvantari S, Kovacs MS, Luyt LG. Peptidomimetic growth hormone secretagogue derivatives for positron emission tomography imaging of the ghrelin receptor. Eur J Med Chem 2018; 157:1500-1511. [PMID: 30282322 DOI: 10.1016/j.ejmech.2018.08.062] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2018] [Revised: 08/16/2018] [Accepted: 08/22/2018] [Indexed: 02/06/2023]
Abstract
The ghrelin receptor is a seven-transmembrane (7-TM) receptor known to have an increased level of expression in human carcinoma and heart failure. Recent work has focused on the synthesis of positron emission tomography (PET) probes designed to target and image this receptor for disease diagnosis and staging. However, these probes have been restricted to small-molecule quinalizonones and peptide derivatives of the endogenous ligand ghrelin. We describe the design, synthesis and biological evaluation of a series of 4-fluorobenzoylated growth hormone secretagogues (GHSs) derived from peptidic (GHRP-1, GHPR-2 and GHRP-6) and peptidomimetic (G-7039, [1-Nal4]G-7039 and ipamorelin) families in order to test locations for the insertion of fluorine-18 for PET imaging. The peptidomimetic G-7039 was found to be the most suitable for 18F-radiolabelling as its non-radioactive 4-fluorobenzoylated analogue ([1-Nal4,Lys5(4-FB)]G-7039), had both a high binding affinity (IC50 = 69 nM) and promising in vitro efficacy (EC50 = 1.1 nM). Prosthetic group radiolabelling of the precursor compound [1-Nal4]G-7039 using N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB) delivered the PET probe [1-Nal4,Lys5(4-[18F]-FB)]G-7039 in an average decay-corrected radiochemical yield of 48%, a radio-purity ≥ 99% and an average molar activity of >34 GBq/μmol. This compound could be investigated as a PET probe for the detection of diseases that are characterised by overexpression of the ghrelin receptor.
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Affiliation(s)
- Milan M Fowkes
- Department of Chemistry, Western University, 1151 Richmond Street, London, Ontario, N6A 5B7, Canada; London Regional Cancer Program, Lawson Health Research Institute, 790 Commissioners Road East, London, Ontario, N6A 4L6, Canada
| | - Tyler Lalonde
- Department of Chemistry, Western University, 1151 Richmond Street, London, Ontario, N6A 5B7, Canada; London Regional Cancer Program, Lawson Health Research Institute, 790 Commissioners Road East, London, Ontario, N6A 4L6, Canada
| | - Lihai Yu
- Department of Chemistry, Western University, 1151 Richmond Street, London, Ontario, N6A 5B7, Canada; London Regional Cancer Program, Lawson Health Research Institute, 790 Commissioners Road East, London, Ontario, N6A 4L6, Canada
| | - Savita Dhanvantari
- Imaging Program, Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario, N6A 4V2, Canada
| | - Michael S Kovacs
- Imaging Program, Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario, N6A 4V2, Canada
| | - Leonard G Luyt
- Department of Chemistry, Western University, 1151 Richmond Street, London, Ontario, N6A 5B7, Canada; London Regional Cancer Program, Lawson Health Research Institute, 790 Commissioners Road East, London, Ontario, N6A 4L6, Canada; Imaging Program, Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario, N6A 4V2, Canada.
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4
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Els-Heindl S, Bellmann-Sickert K, Beck-Sickinger AG. C-terminus of a hexapeptidic ghrelin receptor inverse agonist can switch peptide behavior from inverse agonism to agonism. Biopolymers 2017; 106:101-8. [PMID: 26566778 DOI: 10.1002/bip.22768] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Revised: 11/05/2015] [Accepted: 11/09/2015] [Indexed: 11/10/2022]
Abstract
Subtle changes in the sequence at the N-terminus and in the aromatic core of hexapeptidic ghrelin receptor inverse agonists can switch behavior from inverse agonism to agonism, but the C-terminal role of the sequence is unclear. Thus, analogs of the ghrelin receptor inverse agonist KbFwLL-NH2 (b = β-(3-benzothienyl)-d-alanine) were synthesized by solid phase peptide synthesis in order to identify the influence of aromaticity, charge, and hydrophobicity. Potency and efficacy of the hexapeptides were evaluated in inositol triphosphate turnover assays. Notably, modifications directly at the C-terminal Leu(6) could influence peptide efficacy leading to decreased constitutive activity. High hydrophobicity at the C-terminal position was of importance for elevated inverse agonist activity, the introduction of charged amino acids led to decreased potency. In contrast, structure-activity relationship studies of Leu(5) located closer to the aromatic core revealed an agonism-inducing position. These findings imply that amino acids with possible cation-π or π-π interactions and a suitable orientation at the C-terminus of the aromatic core induce agonism. Receptor binding studies showed that most peptides bind to the receptor at a concentration of 1 µM and modification directly at the C-terminus is generally more accepted than Leu(5) substitution. Interestingly, this observation is not dependent on the type of modification. These studies reveal another switch region of the short ghrelin receptor ligand pointing out the sensitivity of the ghrelin receptor binding pocket.
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Affiliation(s)
- Sylvia Els-Heindl
- Faculty of Biosciences, Pharmacy and Psychology, Institute of Biochemistry, Universität Leipzig, Brüderstraße 34, Leipzig, 04103, Germany
| | - Kathrin Bellmann-Sickert
- Faculty of Biosciences, Pharmacy and Psychology, Institute of Biochemistry, Universität Leipzig, Brüderstraße 34, Leipzig, 04103, Germany
| | - Annette G Beck-Sickinger
- Faculty of Biosciences, Pharmacy and Psychology, Institute of Biochemistry, Universität Leipzig, Brüderstraße 34, Leipzig, 04103, Germany
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Hou J, Charron CL, Fowkes MM, Luyt LG. Bridging computational modeling with amino acid replacements to investigate GHS-R1a-peptidomimetic recognition. Eur J Med Chem 2016; 123:822-833. [DOI: 10.1016/j.ejmech.2016.07.078] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Revised: 07/13/2016] [Accepted: 07/31/2016] [Indexed: 12/26/2022]
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Affiliation(s)
- Naomi R. Latorraca
- Department of Computer Science, ‡Biophysics Program, §Department of Molecular
and Cellular
Physiology, and ∥Institute for Computational and Mathematical Engineering, Stanford University, Stanford, California 94305, United States
| | - A. J. Venkatakrishnan
- Department of Computer Science, ‡Biophysics Program, §Department of Molecular
and Cellular
Physiology, and ∥Institute for Computational and Mathematical Engineering, Stanford University, Stanford, California 94305, United States
| | - Ron O. Dror
- Department of Computer Science, ‡Biophysics Program, §Department of Molecular
and Cellular
Physiology, and ∥Institute for Computational and Mathematical Engineering, Stanford University, Stanford, California 94305, United States
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7
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Floquet N, Costa MGS, Batista PR, Renault P, Bisch PM, Raussin F, Martinez J, Morris MC, Perahia D. Conformational Equilibrium of CDK/Cyclin Complexes by Molecular Dynamics with Excited Normal Modes. Biophys J 2015; 109:1179-89. [PMID: 26255588 PMCID: PMC4576171 DOI: 10.1016/j.bpj.2015.07.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2015] [Revised: 06/16/2015] [Accepted: 07/01/2015] [Indexed: 01/21/2023] Open
Abstract
Cyclin-dependent kinases (CDKs) and their associated regulatory cyclins are central for timely regulation of cell-cycle progression. They constitute attractive pharmacological targets for development of anticancer therapeutics, since they are frequently deregulated in human cancers and contribute to sustained, uncontrolled tumor proliferation. Characterization of their structural/dynamic features is essential to gain in-depth insight into structure-activity relationships. In addition, the identification of druggable pockets or key intermediate conformations yields potential targets for the development of novel classes of inhibitors. Structural studies of CDK2/cyclin A have provided a wealth of information concerning monomeric/heterodimeric forms of this kinase. There is, however, much less structural information for other CDK/cyclin complexes, including CDK4/cyclin D1, which displays an alternative (open) position of the cyclin partner relative to CDK, contrasting with the closed CDK2/cyclin A conformation. In this study, we carried out normal-mode analysis and enhanced sampling simulations with our recently developed method, molecular dynamics with excited normal modes, to understand the conformational equilibrium on these complexes. Interestingly, the lowest-frequency normal mode computed for each complex described the transition between the open and closed conformations. Exploration of these motions with an explicit-solvent representation using molecular dynamics with excited normal modes confirmed that the closed conformation is the most stable for the CDK2/cyclin A complex, in agreement with their experimentally available structures. On the other hand, we clearly show that an open↔closed equilibrium may exist in CDK4/cyclin D1, with closed conformations resembling that captured for CDK2/cyclin A. Such conformational preferences may result from the distinct distributions of frustrated contacts in each complex. Using the same approach, the putative roles of the Thr(160) phosphoryl group and the T-loop conformation were investigated. These results provide a dynamic view of CDKs revealing intermediate conformations not yet characterized for CDK members other than CDK2, which will be useful for the design of inhibitors targeting critical conformational transitions.
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Affiliation(s)
- Nicolas Floquet
- Institut des Biomolécules Max Mousseron (IBMM), Centre National de la Recherche Scientifique UMR 5247, Université de Montpellier, Ecole Normale Supérieure de Chimie de Montpellier, Faculté de Pharmacie, Montpellier, France.
| | - Mauricio G S Costa
- Programa de Computação Científica, Fundação Oswaldo Cruz, Rio de Janeiro, Brazil
| | - Paulo R Batista
- Programa de Computação Científica, Fundação Oswaldo Cruz, Rio de Janeiro, Brazil
| | - Pedro Renault
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Paulo M Bisch
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Florent Raussin
- Institut des Biomolécules Max Mousseron (IBMM), Centre National de la Recherche Scientifique UMR 5247, Université de Montpellier, Ecole Normale Supérieure de Chimie de Montpellier, Faculté de Pharmacie, Montpellier, France
| | - Jean Martinez
- Institut des Biomolécules Max Mousseron (IBMM), Centre National de la Recherche Scientifique UMR 5247, Université de Montpellier, Ecole Normale Supérieure de Chimie de Montpellier, Faculté de Pharmacie, Montpellier, France
| | - May C Morris
- Institut des Biomolécules Max Mousseron (IBMM), Centre National de la Recherche Scientifique UMR 5247, Université de Montpellier, Ecole Normale Supérieure de Chimie de Montpellier, Faculté de Pharmacie, Montpellier, France
| | - David Perahia
- Laboratoire de Biologie et de Pharmacologie Appliquée, Ecole Normale Supérieure de Cachan, Centre National de la Recherche Scientifique, Cachan, France.
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Cofactor-dependent conformational heterogeneity of GAD65 and its role in autoimmunity and neurotransmitter homeostasis. Proc Natl Acad Sci U S A 2014; 111:E2524-9. [PMID: 24927554 DOI: 10.1073/pnas.1403182111] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The human neuroendocrine enzyme glutamate decarboxylase (GAD) catalyses the synthesis of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) using pyridoxal 5'-phosphate as a cofactor. GAD exists as two isoforms named according to their respective molecular weights: GAD65 and GAD67. Although cytosolic GAD67 is typically saturated with the cofactor (holoGAD67) and constitutively active to produce basal levels of GABA, the membrane-associated GAD65 exists mainly as the inactive apo form. GAD65, but not GAD67, is a prevalent autoantigen, with autoantibodies to GAD65 being detected at high frequency in patients with autoimmune (type 1) diabetes and certain other autoimmune disorders. The significance of GAD65 autoinactivation into the apo form for regulation of neurotransmitter levels and autoantibody reactivity is not understood. We have used computational and experimental approaches to decipher the nature of the holo → apo conversion in GAD65 and thus, its mechanism of autoinactivation. Molecular dynamics simulations of GAD65 reveal coupling between the C-terminal domain, catalytic loop, and pyridoxal 5'-phosphate-binding domain that drives structural rearrangement, dimer opening, and autoinactivation, consistent with limited proteolysis fragmentation patterns. Together with small-angle X-ray scattering and fluorescence spectroscopy data, our findings are consistent with apoGAD65 existing as an ensemble of conformations. Antibody-binding kinetics suggest a mechanism of mutually induced conformational changes, implicating the flexibility of apoGAD65 in its autoantigenicity. Although conformational diversity may provide a mechanism for cofactor-controlled regulation of neurotransmitter biosynthesis, it may also come at a cost of insufficient development of immune self-tolerance that favors the production of GAD65 autoantibodies.
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The growth hormone secretagogue receptor: its intracellular signaling and regulation. Int J Mol Sci 2014; 15:4837-55. [PMID: 24651458 PMCID: PMC3975427 DOI: 10.3390/ijms15034837] [Citation(s) in RCA: 90] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2014] [Revised: 03/06/2014] [Accepted: 03/11/2014] [Indexed: 01/29/2023] Open
Abstract
The growth hormone secretagogue receptor (GHSR), also known as the ghrelin receptor, is involved in mediating a wide variety of biological effects of ghrelin, including: stimulation of growth hormone release, increase of food intake and body weight, modulation of glucose and lipid metabolism, regulation of gastrointestinal motility and secretion, protection of neuronal and cardiovascular cells, and regulation of immune function. Dependent on the tissues and cells, activation of GHSR may trigger a diversity of signaling mechanisms and subsequent distinct physiological responses. Distinct regulation of GHSR occurs at levels of transcription, receptor interaction and internalization. Here we review the current understanding on the intracellular signaling pathways of GHSR and its modulation. An overview of the molecular structure of GHSR is presented first, followed by the discussion on its signaling mechanisms. Finally, potential mechanisms regulating GHSR are reviewed.
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10
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Louet M, Karakas E, Perret A, Perahia D, Martinez J, Floquet N. Conformational restriction of G-proteins Coupled Receptors (GPCRs) upon complexation to G-proteins: a putative activation mode of GPCRs? FEBS Lett 2013; 587:2656-61. [PMID: 23851072 DOI: 10.1016/j.febslet.2013.06.052] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2013] [Revised: 06/13/2013] [Accepted: 06/29/2013] [Indexed: 10/26/2022]
Abstract
GPCRs undergo large conformational changes during their activation. Starting from existing X-ray structures, we used Normal Modes Analyses to study the collective motions of the agonist-bound β2-adrenergic receptor both in its isolated "uncoupled" and G-protein "coupled" conformations. We interestingly observed that the receptor was able to adopt only one major motion in the protein:protein complex. This motion corresponded to an anti-symmetric rotation of both its extra- and intra-cellular parts, with a key role of previously identified highly conserved proline residues. Because this motion was also retrieved when performing NMA on 7 other GPCRs which structures were available, it is strongly suspected to possess a significant biological role, possibly being the "activation mode" of a GPCR when coupled to G-proteins.
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Affiliation(s)
- Maxime Louet
- Institut des Biomolécules Max Mousseron (IBMM, CNRS UMR5247), Faculté de Pharmacie, 15 avenue Charles Flahault, BP 14491, 34093 Montpellier Cedex 05, France
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11
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Mear Y, Enjalbert A, Thirion S. GHS-R1a constitutive activity and its physiological relevance. Front Neurosci 2013; 7:87. [PMID: 23754971 PMCID: PMC3665924 DOI: 10.3389/fnins.2013.00087] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2012] [Accepted: 05/09/2013] [Indexed: 12/14/2022] Open
Abstract
Abundant evidences have shown that ghrelin, by its binding to GHS-R1a, plays an important role for fundamental physiological functions. Increasing attention is given to the GHS-R1a unusually high constitutive activity and its contribution to downstream signaling and physiological processes. Here, we review recent lines of evidences showing that the interaction between ligand-binding pocket TM domains and the ECL2 could be partially responsible for this high constitutive activity. Interestingly, GHSR-1a constitutive activity activates in turn the downstream PLC, PKC, and CRE signaling pathways and this activation is reversed by the inverse agonist [D-Arg1, D-Phe5, D-Trp7,9, Leu11]-substance P (MSP). Noteworthy, GHSR-1a exhibits a C-terminal-dependent constitutive internalization. Non-sense GHS-R1a mutation (Ala204Glu), first discovered in Moroccan patients, supports the role of GHSR-1a constitutive activity in physiological impairments. Ala204Glu-point mutation, altering exclusively the GHSR-1a constitutive activity, was associated with familial short stature syndrome. Altogether, these findings suggest that GHS-R1a constitutive activity could contribute to GH secretion or body weight regulation. Consequently, future research on basic and clinical applications of GHS-R1a inverse agonists will be challenging and potentially rewarding.
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Affiliation(s)
- Yves Mear
- CNRS, CRN2M UMR7286, Aix Marseille University Marseille, France
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12
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Kaczor AA, Selent J, Poso A. Structure-based molecular modeling approaches to GPCR oligomerization. Methods Cell Biol 2013; 117:91-104. [PMID: 24143973 DOI: 10.1016/b978-0-12-408143-7.00005-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Classical structure-based drug design techniques using G-protein-coupled receptors (GPCRs) as targets focus nearly exclusively on binding at the orthosteric site of a single receptor. Dimerization and oligomerization of GPCRs, proposed almost 30 years ago, have, however, crucial relevance for drug design. Targeting these complexes selectively or designing small molecules that affect receptor-receptor interactions might provide new opportunities for novel drug discovery. In order to study the mechanisms and dynamics that rule GPCRs oligomerization, it is essential to understand the dynamic process of receptor-receptor association and to identify regions that are suitable for selective drug binding, which may be determined with experimental methods such as Förster resonance energy transfer (FRET) or Bioluminescence resonance energy transfer (BRET) and computational sequence- and structure-based approaches. The aim of this chapter is to provide a comprehensive description of the structure-based molecular modeling methods for studying GPCR dimerization, that is, protein-protein docking, molecular dynamics, normal mode analysis, and electrostatics studies.
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Affiliation(s)
- Agnieszka A Kaczor
- Department of Pharmaceutical Chemistry, School of Pharmacy, University of Eastern Finland, Kuopio, Finland; Department of Chemical Technology of Pharmaceutical Substances with Computer Modeling Lab, Faculty of Pharmacy with Division of Medical Analytics, Medical University of Lublin, Lublin, Poland
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13
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Louet M, Martinez J, Floquet N. GDP release preferentially occurs on the phosphate side in heterotrimeric G-proteins. PLoS Comput Biol 2012; 8:e1002595. [PMID: 22829757 PMCID: PMC3400569 DOI: 10.1371/journal.pcbi.1002595] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2012] [Accepted: 05/21/2012] [Indexed: 11/18/2022] Open
Abstract
After extra-cellular stimulation of G-Protein Coupled Receptors (GPCRs), GDP/GTP exchange appears as the key, rate limiting step of the intracellular activation cycle of heterotrimeric G-proteins. Despite the availability of a large number of X-ray structures, the mechanism of GDP release out of heterotrimeric G-proteins still remains unknown at the molecular level. Starting from the available X-ray structure, extensive unconstrained/constrained molecular dynamics simulations were performed on the complete membrane-anchored Gi heterotrimer complexed to GDP, for a total simulation time overcoming 500 ns. By combining Targeted Molecular Dynamics (TMD) and free energy profiles reconstruction by umbrella sampling, our data suggest that the release of GDP was much more favored on its phosphate side. Interestingly, upon the forced extraction of GDP on this side, the whole protein encountered large, collective motions in perfect agreement with those we described previously including a domain to domain motion between the two ras-like and helical sub-domains of Gα. Despite the availability of many structural and biochemical data, the activation of G-proteins remains to be understood at the molecular level. We used a computation tool to decipher the first limiting step of this activation: GDP release. Combining different methods of analysis, we propose that the GDP exit occurs on its phosphate side. This study helped to rationalize some experimental observations from the literature and opens many perspectives concerning the study of G-proteins activation and their putative inhibition.
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Affiliation(s)
| | | | - Nicolas Floquet
- Institut des Biomolécules Max Mousseron (IBMM), CNRS UMR5247, Université Montpellier 1, Université Montpellier 2, Faculté de Pharmacie, Montpellier, France
- * E-mail:
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14
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Ho BK, Perahia D, Buckle AM. Hybrid approaches to molecular simulation. Curr Opin Struct Biol 2012; 22:386-93. [PMID: 22633678 DOI: 10.1016/j.sbi.2012.05.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2012] [Revised: 05/07/2012] [Accepted: 05/08/2012] [Indexed: 10/28/2022]
Abstract
Molecular dynamics (MD) simulation is an established method for studying the conformational changes that are important for protein function. Recent advances in hardware and software have allowed MD simulations over the same timescales as experiment, improving the agreement between theory and experiment to a large extent. However, running such simulations are costly, in terms of resources, storage, and trajectory analysis. There is still a place for techniques that involve short MD simulations. In order to overcome the sampling paucity of short time-scales, hybrid methods that include some form of MD simulation can exploit certain features of the system of interest, often combining experimental information in surprising ways. Here, we review some recent hybrid approaches to the simulation of proteins.
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Affiliation(s)
- Bosco K Ho
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia
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15
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Zhou H, Skolnick J. FINDSITE(X): a structure-based, small molecule virtual screening approach with application to all identified human GPCRs. Mol Pharm 2012; 9:1775-84. [PMID: 22574683 DOI: 10.1021/mp3000716] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
We have developed FINDSITE(X), an extension of FINDSITE, a protein threading based algorithm for the inference of protein binding sites, biochemical function and virtual ligand screening, that removes the limitation that holo protein structures (those containing bound ligands) of a sufficiently large set of distant evolutionarily related proteins to the target be solved; rather, predicted protein structures and experimental ligand binding information are employed. To provide the predicted protein structures, a fast and accurate version of our recently developed TASSER(VMT), TASSER(VMT)-lite, for template-based protein structural modeling applicable up to 1000 residues is developed and tested, with comparable performance to the top CASP9 servers. Then, a hybrid approach that combines structure alignments with an evolutionary similarity score for identifying functional relationships between target and proteins with binding data has been developed. By way of illustration, FINDSITE(X) is applied to 998 identified human G-protein coupled receptors (GPCRs). First, TASSER(VMT)-lite provides updates of all human GPCR structures previously modeled in our lab. We then use these structures and the new function similarity detection algorithm to screen all human GPCRs against the ZINC8 nonredundant (TC < 0.7) ligand set combined with ligands from the GLIDA database (a total of 88,949 compounds). Testing (excluding GPCRs whose sequence identity > 30% to the target from the binding data library) on a 168 human GPCR set with known binding data, the average enrichment factor in the top 1% of the compound library (EF(0.01)) is 22.7, whereas EF(0.01) by FINDSITE is 7.1. For virtual screening when just the target and its native ligands are excluded, the average EF(0.01) reaches 41.4. We also analyze off-target interactions for the 168 protein test set. All predicted structures, virtual screening data and off-target interactions for the 998 human GPCRs are available at http://cssb.biology.gatech.edu/skolnick/webservice/gpcr/index.html .
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Affiliation(s)
- Hongyi Zhou
- Center for the Study of Systems Biology, School of Biology, Georgia Institute of Technology, 250 14th Street, N.W., Atlanta, Georgia 30318, United States
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16
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Abstract
Explicitly accounting for target flexibility in docking still constitutes a difficult challenge due to the high dimensionality of the conformational space to be sampled. This especially applies to the high-throughput scenario, where the screening of hundreds of thousands compounds takes place. The use of multiple receptor conformations (MRCs) to perform ensemble docking in a sequential fashion is a simple but powerful approach that allows to incorporate binding site structural diversity in the docking process. Whenever enough experimental structures to build a diverse ensemble are not available, normal mode analysis provides an appealing and efficient approach to in silico generate MRCs by distortion along few low-frequency modes that represent collective mid- and large-scale displacements. In this way, the dimension of the conformational space to be sampled is heavily reduced. This methodology is especially suited to incorporate target flexibility at the backbone level. In this chapter, the main components of normal mode-based approaches in the context of ensemble docking are presented and explained, including the theoretical and practical considerations needed for the successful development and implementation of this methodology.
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Affiliation(s)
- Claudio N Cavasotto
- School of Biomedical Informatics, The University of Texas Health Center, Houston, TX, USA.
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17
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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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18
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McGirr R, McFarland MS, McTavish J, Luyt LG, Dhanvantari S. Design and characterization of a fluorescent ghrelin analog for imaging the growth hormone secretagogue receptor 1a. ACTA ACUST UNITED AC 2011; 172:69-76. [DOI: 10.1016/j.regpep.2011.08.011] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2011] [Revised: 08/17/2011] [Accepted: 08/23/2011] [Indexed: 01/11/2023]
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19
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Damian M, Marie J, Leyris JP, Fehrentz JA, Verdié P, Martinez J, Banères JL, Mary S. High constitutive activity is an intrinsic feature of ghrelin receptor protein: a study with a functional monomeric GHS-R1a receptor reconstituted in lipid discs. J Biol Chem 2011; 287:3630-41. [PMID: 22117076 DOI: 10.1074/jbc.m111.288324] [Citation(s) in RCA: 114] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Despite its central role in signaling and the potential therapeutic applications of inverse agonists, the molecular mechanisms underlying G protein-coupled receptor (GPCR) constitutive activity remain largely to be explored. In this context, ghrelin receptor GHS-R1a is a peculiar receptor in the sense that it displays a strikingly high, physiologically relevant, constitutive activity. To identify the molecular mechanisms responsible for this high constitutive activity, we have reconstituted a purified GHS-R1a monomer in a lipid disc. Using this reconstituted system, we show that the isolated ghrelin receptor per se activates G(q) in the absence of agonist, as assessed through guanosine 5'-O-(thiotriphosphate) binding experiments. The measured constitutive activity is similar in its extent to that observed in heterologous systems and in vivo. This is the first direct evidence for the high constitutive activity of the ghrelin receptor being an intrinsic property of the protein rather than the result of influence of its cellular environment. Moreover, we show that the isolated receptor in lipid discs recruits arrestin-2 in an agonist-dependent manner, whereas it interacts with μ-AP2 in the absence of ligand or in the presence of ghrelin. Of importance, these differences are linked to ligand-specific GHS-R1a conformations, as assessed by intrinsic fluorescence measurements. The distinct ligand requirements for the interaction of purified GHS-R1a with arrestin and AP2 provide a new rationale to the differences in basal and agonist-induced internalization observed in cells.
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Affiliation(s)
- Marjorie Damian
- Institut des Biomolécules Max Mousseron, CNRS UMR 5247, Université de Montpellier 1, Faculté de Pharmacie, 15 avenue Charles Flahaut, BP 14491, 34093 Montpellier cedex 5, France
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20
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Batista PR, Pandey G, Pascutti PG, Bisch PM, Perahia D, Robert CH. Free Energy Profiles along Consensus Normal Modes Provide Insight into HIV-1 Protease Flap Opening. J Chem Theory Comput 2011; 7:2348-52. [PMID: 26606609 DOI: 10.1021/ct200237u] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Describing biological macromolecular energetics from computer simulations can pose major challenges, and often necessitates enhanced conformational sampling. We describe the calculation of conformational free-energy profiles along carefully chosen collective coordinates: "consensus" normal modes, developed recently as robust alternatives to conventional normal modes. In an application to the HIV-1 protease, we obtain efficient sampling of significant flap opening movements governing inhibitor binding from relatively short simulations, in close correspondence with experimental results.
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Affiliation(s)
- Paulo R Batista
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro , 21941-902, Brasil.,CNRS Institut de Biochimie et Biophysique Moléculaire et Cellulaire, Université Paris Sud 11 , 91405 Orsay, France.,CNRS BIMoDyM -Laboratoire de Biologie et Pharmacologie Appliquées - École Normale Supérieure de Cachan , 94235 Cachan, France
| | - Gaurav Pandey
- Indian Institute of Technology , Roorkee, 247667, India.,CNRS Institut de Biochimie et Biophysique Moléculaire et Cellulaire, Université Paris Sud 11 , 91405 Orsay, France
| | - Pedro G Pascutti
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro , 21941-902, Brasil
| | - Paulo M Bisch
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro , 21941-902, Brasil
| | - David Perahia
- CNRS Institut de Biochimie et Biophysique Moléculaire et Cellulaire, Université Paris Sud 11 , 91405 Orsay, France.,CNRS BIMoDyM -Laboratoire de Biologie et Pharmacologie Appliquées - École Normale Supérieure de Cachan , 94235 Cachan, France
| | - Charles H Robert
- CNRS Institut de Biochimie et Biophysique Moléculaire et Cellulaire, Université Paris Sud 11 , 91405 Orsay, France.,CNRS Laboratoire de Biochimie Théorique, Institut de Biologie Physico Chimique, Université Paris Diderot, Sorbonne Paris Cité , 75005 Paris, France
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21
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Jurenka R, Nusawardani T. The pyrokinin/ pheromone biosynthesis-activating neuropeptide (PBAN) family of peptides and their receptors in Insecta: evolutionary trace indicates potential receptor ligand-binding domains. INSECT MOLECULAR BIOLOGY 2011; 20:323-334. [PMID: 21199021 DOI: 10.1111/j.1365-2583.2010.01065.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The pyrokinin/pheromone biosynthesis-activating neuropeptide (PBAN) family of G-protein-coupled receptors and their ligands have been identified in various insects. Physiological functions of pyrokinin peptides include muscle contraction, whereas PBAN regulates, among other functions, pheromone production in moths which indicates the pleiotropic nature of these peptides. Based on the alignment of annotated genomic sequences, the pyrokinin/PBAN family of receptors have similarity with the corresponding structures of the capa or periviscerokinin receptors of insects and the neuromedin U receptors of vertebrates. In our study, evolutionary trace (ET) analysis on the insect receptor sequences was conducted to predict the putative ligand recognition and binding sites. The ET analysis of four class-specific receptors indicated several amino acid residues that are conserved in the transmembrane domains. The receptor extracellular domains exhibit several class-specific amino acid residues, which could indicate putative domains for activation of these receptors by ligand recognition and binding.
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Affiliation(s)
- R Jurenka
- Department of Entomology, Iowa State University, Ames, IA, USA.
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22
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Louet M, Perahia D, Martinez J, Floquet N. A concerted mechanism for opening the GDP binding pocket and release of the nucleotide in hetero-trimeric G-proteins. J Mol Biol 2011; 411:298-312. [PMID: 21663745 DOI: 10.1016/j.jmb.2011.05.034] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2010] [Revised: 05/14/2011] [Accepted: 05/20/2011] [Indexed: 11/26/2022]
Abstract
G-protein hetero-trimers play a fundamental role in cell function. Their dynamic behavior at the atomic level remains to be understood. We have studied the Gi hetero-trimer through a combination of molecular dynamics simulations and normal mode analyses. We showed that these big proteins could undergo large-amplitude conformational changes, without any energy penalty and with an intrinsic dynamics centered on their GDP binding pocket. Among the computed collective motions, one of the modes (mode 17) was particularly able to significantly open both the base and the phosphate sides of the GDP binding pocket. This mode describing mainly a motion between the Ras-like and the helical domains of G(α) was in close agreement with some available X-ray data and with many other biochemical/biophysical observations including the kink of helix α5. The use of a new protocol, which allows extraction of the GDP ligand along the computed normal modes, supported that the exit of GDP was largely coupled to an opening motion along mode 17. We propose for the first time a "concerted mechanism" model in which the opening of the GDP pocket and the kink of the α5 helix occur concomitantly and favor GDP release from G(αβγ) complexes. This model is discussed in the context of the G-protein-coupled receptor/G-protein interaction close to the cell membrane.
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Affiliation(s)
- Maxime Louet
- Institut des Biomolécules Max Mousseron (IBMM), CNRS UMR5247, Université Montpellier 1-Université Montpellier 2, Faculté de Pharmacie, 15 Avenue Charles Flahault, BP 14491, 34093 Montpellier Cedex 05, France
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23
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Rodríguez D, Piñeiro Á, Gutiérrez-de-Terán H. Molecular Dynamics Simulations Reveal Insights into Key Structural Elements of Adenosine Receptors. Biochemistry 2011; 50:4194-208. [DOI: 10.1021/bi200100t] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- David Rodríguez
- Fundación Pública Galega de Medicina Xenómica, Hospital Clínico Universitario de Santiago (CHUS), planta-2, A Choupana, s/n E-15706 Santiago de Compostela, Spain
| | - Ángel Piñeiro
- Soft Matter and Molecular Biophysics Group, Department of Applied Physics, University of Santiago de Compostela, Campus Vida s/n, E-15782 Santiago de Compostela, Spain
| | - Hugo Gutiérrez-de-Terán
- Fundación Pública Galega de Medicina Xenómica, Hospital Clínico Universitario de Santiago (CHUS), planta-2, A Choupana, s/n E-15706 Santiago de Compostela, Spain
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24
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Simpson LM, Wall ID, Blaney FE, Reynolds CA. Modeling GPCR active state conformations: the β(2)-adrenergic receptor. Proteins 2011; 79:1441-57. [PMID: 21337626 DOI: 10.1002/prot.22974] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2010] [Revised: 11/13/2010] [Accepted: 12/02/2010] [Indexed: 01/28/2023]
Abstract
The recent publication of several G protein-coupled receptor (GPCR) structures has increased the information available for homology modeling inactive class A GPCRs. Moreover, the opsin crystal structure shows some active features. We have therefore combined information from these two sources to generate an extensively validated model of the active conformation of the β(2)-adrenergic receptor. Experimental information on fully active GPCRs from zinc binding studies, site-directed spin labeling, and other spectroscopic techniques has been used in molecular dynamics simulations. The observed conformational changes reside mainly in transmembrane helix 6 (TM6), with additional small but significant changes in TM5 and TM7. The active model has been validated by manual docking and is in agreement with a large amount of experimental work, including site-directed mutagenesis information. Virtual screening experiments show that the models are selective for β-adrenergic agonists over other GPCR ligands, for (R)- over (S)-β-hydroxy agonists and for β(2)-selective agonists over β(1)-selective agonists. The virtual screens reproduce interactions similar to those generated by manual docking. The C-terminal peptide from a model of the stimulatory G protein, readily docks into the active model in a similar manner to which the C-terminal peptide from transducin, docks into opsin, as shown in a recent opsin crystal structure. This GPCR-G protein model has been used to explain site-directed mutagenesis data on activation. The agreement with experiment suggests a robust model of an active state of the β(2)-adrenergic receptor has been produced. The methodology used here should be transferable to modeling the active state of other GPCRs.
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Affiliation(s)
- Lisa M Simpson
- Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, United Kingdom
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25
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Nurisso A, Daina A, Walker RC. A practical introduction to molecular dynamics simulations: applications to homology modeling. Methods Mol Biol 2011; 857:137-73. [PMID: 22323220 DOI: 10.1007/978-1-61779-588-6_6] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
In this chapter, practical concepts and guidelines are provided for the use of molecular dynamics (MD) simulation for the refinement of homology models. First, an overview of the history and a theoretical background of MD are given. Literature examples of successful MD refinement of homology models are reviewed before selecting the Cytochrome P450 2J2 structure as a case study. We describe the setup of a system for classical MD simulation in a detailed stepwise fashion and how to perform the refinement described in the publication of Li et al. (Proteins 71:938-949, 2008). This tutorial is based on version 11 of the AMBER Molecular Dynamics software package (http://ambermd.org/). However, the approach discussed is equally applicable to any condensed phase MD simulation environment.
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Affiliation(s)
- Alessandra Nurisso
- School of Pharmaceutical Sciences, University of Geneva, University of Lausanne, Geneva, Switzerland
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26
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Sakhteman A, Lahtela-Kakkonen M, Poso A. Studying the catechol binding cavity in comparative models of human dopamine D2 receptor. J Mol Graph Model 2010; 29:685-92. [PMID: 21168353 DOI: 10.1016/j.jmgm.2010.11.012] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2010] [Revised: 11/16/2010] [Accepted: 11/22/2010] [Indexed: 10/18/2022]
Abstract
Obtaining more structural information of human dopamine D(2) receptor may help in the design of better therapeutic agents against diseases such as Parkinson. In this study attempts have been made to develop a functional model for the catechol binding site of the human dopamine D(2) receptor, with two primary models being postulated based on the presence of a disulfide bridge in the second extracellular loop. The models have been subjected to subsequent molecular dynamics simulation and receptor based virtual screening of catechol structures. During steady state of the simulations, representative models with the reduced disulfide bridge were more capable of discriminating between active and inactive catechol structures. It is postulated that similar conformational changes of the second extracellular loop observed in 5-HT4 and β-adrenergic receptors, might also take place in the human D(2) receptor during its interaction with agonist ligands.
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Affiliation(s)
- Amirhossein Sakhteman
- School of Pharmacy, Faculty of Health Sciences, University of Eastern Finland, Kuopio, Finland.
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27
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Bahar I. On the functional significance of soft modes predicted by coarse-grained models for membrane proteins. ACTA ACUST UNITED AC 2010; 135:563-73. [PMID: 20513758 PMCID: PMC2888054 DOI: 10.1085/jgp.200910368] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Ivet Bahar
- Department of Computational Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15213, USA.
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28
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Mutational analysis of predicted extracellular domains of human growth hormone secretagogue receptor 1a. ACTA ACUST UNITED AC 2010; 166:28-35. [PMID: 20727371 DOI: 10.1016/j.regpep.2010.08.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2010] [Revised: 07/19/2010] [Accepted: 08/11/2010] [Indexed: 11/20/2022]
Abstract
The Class A family of guanine nucleotide-binding protein (G protein)-coupled receptors that includes receptors for motilin, ghrelin, and growth hormone secretagogue (GHS) has substantial potential importance as drug targets. Understanding of the molecular basis of hormone binding and receptor activation should provide insights helpful in the development of such drugs. We previously reported that Cys residues and the perimembranous residues in the extracellular loops and amino-terminal tail of the motilin receptor are critical for peptide ligand, motilin, binding and biological activity. In the current work, we focused on the predicted extracellular domains of the human GHS receptor 1a, and identified functionally important residues by using sequential deletions ranging from one to twelve amino acid residues and site-directed replacement mutagenesis approach. Each construct was transiently expressed in COS cells, and characterized for ghrelin- and growth hormone releasing peptide (GHRP)-6-stimulated intracellular calcium responses and ghrelin radioligand binding. Cys residues in positions 116 and 198 in the first and second extracellular loops and the perimembranous Glu¹⁸⁷ residue in the second extracellular loop were critical for ghrelin and GHRP-6 biological activity. These results suggest that Cys residues in the extracellular domains in this family of Class A G protein-coupled receptor is likely involved in the highly conserved and functionally important disulfide bond, and that the perimembranous residues contribute peptide ligand binding and signaling.
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