1
|
Yang C, Meng Y, Wang X, Li X, Yu T, Liao W, Xie W, Jiang Q, Wang H, Shi C, Jiao W, Bian X, Hu F, Wang X, Liu Y, Zhang L, Wang K, Sun Q. Allosteric Activation of α7 Nicotinic Acetylcholine Receptors by Novel 2-Arylamino-thiazole-5-carboxylic Acid Amide Derivatives for the Improvement of Cognitive Deficits in Mice. J Med Chem 2024; 67:6344-6364. [PMID: 38393821 DOI: 10.1021/acs.jmedchem.3c02323] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/25/2024]
Abstract
Enhancing α7 nAChR function serves as a therapeutic strategy for cognitive disorders. Here, we report the synthesis and evaluation of 2-arylamino-thiazole-5-carboxylic acid amide derivatives 6-9 that as positive allosteric modulators (PAMs) activate human α7 nAChR current expressed in Xenopus ooctyes. Among the 4-amino derivatives, a representative atypical type I PAM 6p exhibits potent activation of α7 current with an EC50 of 1.3 μM and the maximum activation effect on the current over 48-fold in the presence of acetylcholine (100 μM). The structure-activity relationship (SAR) analysis reveals that the 4-amino group is crucial for the allosteric activation of α7 currents by compound 6p as the substitution of 4-methyl group results in its conversion to compound 7b (EC50 = 2.1 μM; max effect: 58-fold) characterized as a typical type I PAM. Furthermore, both 6p and 7b are able to rescue auditory gating deficits in mouse schizophrenia-like model of acoustic startle prepulse inhibition.
Collapse
Affiliation(s)
- Chenxia Yang
- Department of Pharmacology, School of Pharmacy, Qingdao University Medical College, #1 Ningde Road, Qingdao 266073, China
| | - Ying Meng
- State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - Xintong Wang
- State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - Xin Li
- State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - Tong Yu
- State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - Weiming Liao
- State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - Wenjun Xie
- State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - Qianchen Jiang
- State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - Han Wang
- State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - Cheng Shi
- State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - Wenxuan Jiao
- State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - Xiling Bian
- State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - Fang Hu
- Department of Pharmacology, School of Pharmacy, Qingdao University Medical College, #1 Ningde Road, Qingdao 266073, China
| | - Xiaowei Wang
- State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - Yani Liu
- Department of Pharmacology, School of Pharmacy, Qingdao University Medical College, #1 Ningde Road, Qingdao 266073, China
- Institute of Innovative Drugs, 38 Dengzhou Road, Qingdao University, Qingdao 266021, China
| | - Liangren Zhang
- State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - KeWei Wang
- Department of Pharmacology, School of Pharmacy, Qingdao University Medical College, #1 Ningde Road, Qingdao 266073, China
- Institute of Innovative Drugs, 38 Dengzhou Road, Qingdao University, Qingdao 266021, China
| | - Qi Sun
- State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| |
Collapse
|
2
|
Burke SM, Avstrikova M, Noviello CM, Mukhtasimova N, Changeux JP, Thakur GA, Sine SM, Cecchini M, Hibbs RE. Structural mechanisms of α7 nicotinic receptor allosteric modulation and activation. Cell 2024; 187:1160-1176.e21. [PMID: 38382524 PMCID: PMC10950261 DOI: 10.1016/j.cell.2024.01.032] [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: 08/31/2023] [Revised: 12/05/2023] [Accepted: 01/22/2024] [Indexed: 02/23/2024]
Abstract
The α7 nicotinic acetylcholine receptor is a pentameric ligand-gated ion channel that plays an important role in cholinergic signaling throughout the nervous system. Its unique physiological characteristics and implications in neurological disorders and inflammation make it a promising but challenging therapeutic target. Positive allosteric modulators overcome limitations of traditional α7 agonists, but their potentiation mechanisms remain unclear. Here, we present high-resolution structures of α7-modulator complexes, revealing partially overlapping binding sites but varying conformational states. Structure-guided functional and computational tests suggest that differences in modulator activity arise from the stable rotation of a channel gating residue out of the pore. We extend the study using a time-resolved cryoelectron microscopy (cryo-EM) approach to reveal asymmetric state transitions for this homomeric channel and also find that a modulator with allosteric agonist activity exploits a distinct channel-gating mechanism. These results define mechanisms of α7 allosteric modulation and activation with implications across the pentameric receptor superfamily.
Collapse
Affiliation(s)
- Sean M Burke
- Molecular Biophysics Graduate Program, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Department of Neurobiology, University of California, San Diego, La Jolla, CA 92093, USA
| | - Mariia Avstrikova
- Institut de Chimie de Strasbourg, UMR7177, CNRS, Université de Strasbourg, 67081 Strasbourg Cedex, France
| | - Colleen M Noviello
- Department of Neurobiology, University of California, San Diego, La Jolla, CA 92093, USA
| | - Nuriya Mukhtasimova
- Receptor Biology Laboratory, Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55902, USA; Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic College of Medicine, Rochester, MN 55902, USA
| | - Jean-Pierre Changeux
- Neuroscience Department, Institut Pasteur, Collège de France, 75015 Paris, France
| | - Ganesh A Thakur
- Department of Pharmaceutical Sciences, Northeastern University, Boston, MA 02115, USA
| | - Steven M Sine
- Receptor Biology Laboratory, Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55902, USA; Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic College of Medicine, Rochester, MN 55902, USA; Department of Neurology, Mayo Clinic College of Medicine, Rochester, MN 55902, USA.
| | - Marco Cecchini
- Institut de Chimie de Strasbourg, UMR7177, CNRS, Université de Strasbourg, 67081 Strasbourg Cedex, France.
| | - Ryan E Hibbs
- Department of Neurobiology, University of California, San Diego, La Jolla, CA 92093, USA; Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
| |
Collapse
|
3
|
Viscarra F, Chrestia JF, Sanchez Y, Pérez EG, Biggin PC, Bouzat C, Bermudez I, López JJ. Side Groups Convert the α7 Nicotinic Receptor Agonist Ether Quinuclidine into a Type I Positive Allosteric Modulator. ACS Chem Neurosci 2023; 14:2876-2887. [PMID: 37535446 DOI: 10.1021/acschemneuro.3c00225] [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] [Indexed: 08/05/2023] Open
Abstract
The quinuclidine scaffold has been extensively used for the development of nicotinic acetylcholine receptor (nAChR) agonists, with hydrophobic substituents at position 3 of the quinuclidine framework providing selectivity for α7 nAChRs. In this study, six new ligands (4-9) containing a 3-(pyridin-3-yloxy)quinuclidine moiety (ether quinuclidine) were synthesized to gain a better understanding of the structural-functional properties of ether quinuclidines. To evaluate the pharmacological activity of these ligands, two-electrode voltage-clamp and single-channel recordings were performed. Only ligand 4 activated α7 nAChR. Ligands 5 and 7 had no effects on α7 nAChR, but ligands 6, 8, and 9 potentiated the currents evoked by ACh. Ligand 6 was the most potent and efficacious of the potentiating ligands, with an estimated EC50 for potentiation of 12.6 ± 3.32 μM and a maximal potentiation of EC20 ACh responses of 850 ± 120%. Ligand 6 increased the maximal ACh responses without changing the kinetics of the current responses. At the single-channel level, the potentiation exerted by ligand 6 was evidenced in the low micromolar concentration range by the appearance of prolonged bursts of channel openings. Furthermore, computational studies revealed the preference of ligand 6 for an intersubunit site in the transmembrane domain and highlighted some putative key interactions that explain the different profiles of the synthesized ligands. Notably, Met276 in the 15' position of the transmembrane domain 2 almost abolished the effects of ligand 6 when mutated to Leu. We conclude that ligand 6 is a novel type I positive allosteric modulator (PAM-I) of α7 nAChR.
Collapse
Affiliation(s)
- Franco Viscarra
- Department of Biological and Medical Sciences, Oxford Brookes University, Gipsy Lane, Oxford OX3 0BP, U.K
- Structural Bioinformatics and Computational Biochemistry, Department of Biochemistry, Oxford University, South Parks Road, Oxford OX1 3QU, U.K
| | - Juan Facundo Chrestia
- Departamento de Biología, Bioquímica y Farmacia, Instituto de Investigaciones Bioquímicas de Bahía Blanca, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Camino La Carrindanga Km 7, Bahía Blanca 8000, Argentina
| | - Yaima Sanchez
- Department of Organic Chemistry, Faculty of Chemistry, Universidad de Concepción, Edmundo Larenas 129, Concepción 4070371, Chile
| | - Edwin G Pérez
- Department of Organic Chemistry, Faculty of Chemistry and Pharmacy, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago 7820436, Chile
| | - Philip C Biggin
- Structural Bioinformatics and Computational Biochemistry, Department of Biochemistry, Oxford University, South Parks Road, Oxford OX1 3QU, U.K
| | - Cecilia Bouzat
- Departamento de Biología, Bioquímica y Farmacia, Instituto de Investigaciones Bioquímicas de Bahía Blanca, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Camino La Carrindanga Km 7, Bahía Blanca 8000, Argentina
| | - Isabel Bermudez
- Department of Biological and Medical Sciences, Oxford Brookes University, Gipsy Lane, Oxford OX3 0BP, U.K
| | - Jhon J López
- Department of Organic Chemistry, Faculty of Chemistry, Universidad de Concepción, Edmundo Larenas 129, Concepción 4070371, Chile
| |
Collapse
|
4
|
Giovenale AMG, Ruotolo G, Soriano AA, Turco EM, Rotundo G, Casamassa A, D’Anzi A, Vescovi AL, Rosati J. Deepening the understanding of CNVs on chromosome 15q11-13 by using hiPSCs: An overview. Front Cell Dev Biol 2023; 10:1107881. [PMID: 36684422 PMCID: PMC9852989 DOI: 10.3389/fcell.2022.1107881] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2022] [Accepted: 12/16/2022] [Indexed: 01/09/2023] Open
Abstract
The human α7 neuronal nicotinic acetylcholine receptor gene (CHRNA7) is widely expressed in the central and peripheral nervous systems. This receptor is implicated in both brain development and adult neurogenesis thanks to its ability to mediate acetylcholine stimulus (Ach). Copy number variations (CNVs) of CHRNA7 gene have been identified in humans and are genetically linked to cognitive impairments associated with multiple disorders, including schizophrenia, bipolar disorder, epilepsy, Alzheimer's disease, and others. Currently, α7 receptor analysis has been commonly performed in animal models due to the impossibility of direct investigation of the living human brain. But the use of model systems has shown that there are very large differences between humans and mice when researchers must study the CNVs and, in particular, the CNV of chromosome 15q13.3 where the CHRNA7 gene is present. In fact, human beings present genomic alterations as well as the presence of genes of recent origin that are not present in other model systems as well as they show a very heterogeneous symptomatology that is associated with both their genetic background and the environment where they live. To date, the induced pluripotent stem cells, obtained from patients carrying CNV in CHRNA7 gene, are a good in vitro model for studying the association of the α7 receptor to human diseases. In this review, we will outline the current state of hiPSCs technology applications in neurological diseases caused by CNVs in CHRNA7 gene. Furthermore, we will discuss some weaknesses that emerge from the overall analysis of the published articles.
Collapse
Affiliation(s)
- Angela Maria Giada Giovenale
- Cellular Reprogramming Unit, Fondazione IRCCS Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy,Department of Biotechnology and Biosciences, University of Milano-Bicocca, Milan, Italy
| | - Giorgia Ruotolo
- Cellular Reprogramming Unit, Fondazione IRCCS Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy,Department of Biotechnology and Biosciences, University of Milano-Bicocca, Milan, Italy
| | - Amata Amy Soriano
- Cellular Reprogramming Unit, Fondazione IRCCS Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy
| | - Elisa Maria Turco
- Cellular Reprogramming Unit, Fondazione IRCCS Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy
| | - Giovannina Rotundo
- Cellular Reprogramming Unit, Fondazione IRCCS Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy
| | - Alessia Casamassa
- Cellular Reprogramming Unit, Fondazione IRCCS Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy
| | - Angela D’Anzi
- Cellular Reprogramming Unit, Fondazione IRCCS Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy
| | - Angelo Luigi Vescovi
- Cellular Reprogramming Unit, Fondazione IRCCS Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy,Department of Biotechnology and Biosciences, University of Milano-Bicocca, Milan, Italy,*Correspondence: Jessica Rosati, ; Angelo Luigi Vescovi,
| | - Jessica Rosati
- Cellular Reprogramming Unit, Fondazione IRCCS Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy,*Correspondence: Jessica Rosati, ; Angelo Luigi Vescovi,
| |
Collapse
|
5
|
Cannabidiol as a modulator of α7 nicotinic receptors. Cell Mol Life Sci 2022; 79:564. [DOI: 10.1007/s00018-022-04600-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2022] [Revised: 09/29/2022] [Accepted: 10/14/2022] [Indexed: 11/03/2022]
|
6
|
Zhuang Y, Noviello CM, Hibbs RE, Howard RJ, Lindahl E. Differential interactions of resting, activated, and desensitized states of the α7 nicotinic acetylcholine receptor with lipidic modulators. Proc Natl Acad Sci U S A 2022; 119:e2208081119. [PMID: 36251999 PMCID: PMC9618078 DOI: 10.1073/pnas.2208081119] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Accepted: 09/08/2022] [Indexed: 11/18/2022] Open
Abstract
The α7 nicotinic acetylcholine receptor is a pentameric ligand-gated ion channel that modulates neuronal excitability, largely by allowing Ca2+ permeation. Agonist binding promotes transition from a resting state to an activated state, and then rapidly to a desensitized state. Recently, cryogenic electron microscopy (cryo-EM) structures of the human α7 receptor in nanodiscs were reported in multiple conformations. These were selectively stabilized by inhibitory, activating, or potentiating compounds. However, the functional annotation of these structures and their differential interactions with unresolved lipids and ligands remain incomplete. Here, we characterized their ion permeation, membrane interactions, and ligand binding using computational electrophysiology, free-energy calculations, and coarse-grained molecular dynamics. In contrast to nonconductive structures in apparent resting and desensitized states, the structure determined in the presence of the potentiator PNU-120596 was consistent with an activated state permeable to Ca2+. Transition to this state was associated with compression and rearrangement of the membrane, particularly in the vicinity of the peripheral MX helix. An intersubunit transmembrane site was implicated in selective binding of either PNU-120596 in the activated state or cholesterol in the desensitized state. This substantiates functional assignment of all three lipid-embedded α7-receptor structures with ion-permeation simulations. It also proposes testable models of their state-dependent interactions with lipophilic ligands, including a mechanism for allosteric modulation at the transmembrane subunit interface.
Collapse
Affiliation(s)
- Yuxuan Zhuang
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, PO Box 1031, Solna, 171 21 Sweden
| | - Colleen M. Noviello
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Ryan E. Hibbs
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Rebecca J. Howard
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, PO Box 1031, Solna, 171 21 Sweden
| | - Erik Lindahl
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, PO Box 1031, Solna, 171 21 Sweden
- Department of Applied Physics, Swedish e-Science Research Center, KTH Royal Institute of Technology, PO Box 1031, Solna, 171 21 Sweden
| |
Collapse
|
7
|
Chrestia JF, Oliveira AS, Mulholland AJ, Gallagher T, Bermúdez I, Bouzat C. A Functional Interaction Between Y674-R685 Region of the SARS-CoV-2 Spike Protein and the Human α7 Nicotinic Receptor. Mol Neurobiol 2022; 59:6076-6090. [PMID: 35859025 PMCID: PMC9299415 DOI: 10.1007/s12035-022-02947-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2022] [Accepted: 06/28/2022] [Indexed: 11/15/2022]
Abstract
The α7 nicotinic acetylcholine receptor (nAChR) is present in neuronal and non-neuronal cells and has anti-inflammatory actions. Molecular dynamics simulations suggested that α7 nAChR interacts with a region of the SARS-CoV-2 spike protein (S), and a potential contribution of nAChRs to COVID-19 pathophysiology has been proposed. We applied whole-cell and single-channel recordings to determine whether a peptide corresponding to the Y674-R685 region of the S protein can directly affect α7 nAChR function. The S fragment exerts a dual effect on α7. It activates α7 nAChRs in the presence of positive allosteric modulators, in line with our previous molecular dynamics simulations showing favourable binding of this accessible region of the S protein to the nAChR agonist binding site. The S fragment also exerts a negative modulation of α7, which is evidenced by a profound concentration-dependent decrease in the durations of openings and activation episodes of potentiated channels and in the amplitude of macroscopic responses elicited by ACh. Our study identifies a potential functional interaction between α7 nAChR and a region of the S protein, thus providing molecular foundations for further exploring the involvement of nAChRs in COVID-19 pathophysiology.
Collapse
Affiliation(s)
- Juan Facundo Chrestia
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas Y Técnicas (CONICET), Camino La Carrindanga Km 7-8000, Bahía Blanca, Argentina
| | - Ana Sofia Oliveira
- Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK
| | - Adrian J Mulholland
- Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK
| | | | - Isabel Bermúdez
- Department of Biological and Medical Sciences, Oxford Brookes University, Oxford, OX3 0BP, UK.
| | - Cecilia Bouzat
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas Y Técnicas (CONICET), Camino La Carrindanga Km 7-8000, Bahía Blanca, Argentina.
| |
Collapse
|
8
|
Hone AJ, McIntosh JM. Alkaloid ligands enable function of homomeric human α10 nicotinic acetylcholine receptors. Front Pharmacol 2022; 13:981760. [PMID: 36188578 PMCID: PMC9523446 DOI: 10.3389/fphar.2022.981760] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Accepted: 08/23/2022] [Indexed: 01/29/2023] Open
Abstract
In the nervous system, nicotinic acetylcholine receptors (nAChRs) rapidly transduce a chemical signal into one that is electrical via ligand-gated ion flux through the central channel of the receptor. However, some nAChR subunits are expressed by non-excitable cells where signal transduction apparently occurs through non-ionic mechanisms. One such nAChR subunit, α10, is present in a discreet subset of immune cells and has been implicated in pathologies including cancer, neuropathic pain, and chronic inflammation. Longstanding convention holds that human α10 subunits require co-assembly with α9 subunits for function. Here we assessed whether cholinergic ligands can enable or uncover ionic functions from homomeric α10 nAChRs. Xenopus laevis oocytes expressing human α10 subunits were exposed to a panel of ligands and examined for receptor activation using voltage-clamp electrophysiology. Functional expression of human α10 nAChRs was achieved by exposing the oocytes to the alkaloids strychnine, brucine, or methyllycaconitine. Furthermore, acute exposure to the alkaloid ligands significantly enhanced ionic responses. Acetylcholine-gated currents mediated by α10 nAChRs were potently inhibited by the snake toxins α-bungarotoxin and α-cobratoxin but not by α-conotoxins that target α9 and α9α10 nAChRs. Our findings indicate that human α10 homomers are expressed in oocytes and exposure to certain ligands can enable ionic functions. To our knowledge, this is the first demonstration that human α10 subunits can assemble as functional homomeric nAChRs. These findings have potential implications for receptor regulatory-mechanisms and will enable structural, functional, and further pharmacological characterization of human α10 nAChRs.
Collapse
Affiliation(s)
- Arik J. Hone
- School of Biological Sciences, University of Utah, Salt Lake City, UT, United States
- MIRECC, George E. Whalen Veterans Affairs Medical Center, Salt Lake City, UT, United States
| | - J. Michael McIntosh
- School of Biological Sciences, University of Utah, Salt Lake City, UT, United States
- Department of Psychiatry, University of Utah, Salt Lake City, UT, United States
- George E. Whalen Veterans Affairs Medical Center, Salt Lake City, UT, United States
| |
Collapse
|
9
|
Membrane lipid organization and nicotinic acetylcholine receptor function: A two-way physiological relationship. Arch Biochem Biophys 2022; 730:109413. [DOI: 10.1016/j.abb.2022.109413] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Revised: 09/07/2022] [Accepted: 09/20/2022] [Indexed: 11/21/2022]
|
10
|
Borroni V, Barrantes FJ. Homomeric and Heteromeric α7 Nicotinic Acetylcholine Receptors in Health and Some Central Nervous System Diseases. MEMBRANES 2021; 11:membranes11090664. [PMID: 34564481 PMCID: PMC8465519 DOI: 10.3390/membranes11090664] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/23/2021] [Revised: 08/24/2021] [Accepted: 08/24/2021] [Indexed: 11/22/2022]
Abstract
Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated ion channels involved in the modulation of essential brain functions such as memory, learning, and attention. Homomeric α7 nAChR, formed exclusively by five identical α7 subunits, is involved in rapid synaptic transmission, whereas the heteromeric oligomers composed of α7 in combination with β subunits display metabotropic properties and operate in slower time frames. At the cellular level, the activation of nAChRs allows the entry of Na+ and Ca2+; the two cations depolarize the membrane and trigger diverse cellular signals, depending on the type of nAChR pentamer and neurons involved, the location of the intervening cells, and the networks of which these neuronal cells form part. These features make the α7 nAChR a central player in neurotransmission, metabolically associated Ca2+-mediated signaling, and modulation of diverse fundamental processes operated by other neurotransmitters in the brain. Due to its ubiquitous distribution and the multiple functions it displays in the brain, the α7 nAChR is associated with a variety of neurological and neuropsychiatric disorders whose exact etiopathogenic mechanisms are still elusive.
Collapse
Affiliation(s)
- Virginia Borroni
- Instituto de Tecnología en Polímeros y Nanotecnología (ITPN-UBA-CONICET), Universidad de Buenos Aires, Ciudad Universitaria, Buenos Aires C1127AAR, Argentina;
| | - Francisco J. Barrantes
- Laboratory of Molecular Neurobiology, Institute for Biomedical Research, UCA–CONICET, Faculty of Medical Sciences, Catholic University of Argentina, Av. Alicia Moreau de Justo 1600, Buenos Aires C1107AAZ, Argentina
- Correspondence:
| |
Collapse
|
11
|
Structure and gating mechanism of the α7 nicotinic acetylcholine receptor. Cell 2021; 184:2121-2134.e13. [PMID: 33735609 DOI: 10.1016/j.cell.2021.02.049] [Citation(s) in RCA: 119] [Impact Index Per Article: 39.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2020] [Revised: 01/13/2021] [Accepted: 02/22/2021] [Indexed: 12/13/2022]
Abstract
The α7 nicotinic acetylcholine receptor plays critical roles in the central nervous system and in the cholinergic inflammatory pathway. This ligand-gated ion channel assembles as a homopentamer, is exceptionally permeable to Ca2+, and desensitizes faster than any other Cys-loop receptor. The α7 receptor has served as a prototype for the Cys-loop superfamily yet has proven refractory to structural analysis. We present cryo-EM structures of the human α7 nicotinic receptor in a lipidic environment in resting, activated, and desensitized states, illuminating the principal steps in the gating cycle. The structures also reveal elements that contribute to its function, including a C-terminal latch that is permissive for channel opening, and an anionic ring in the extracellular vestibule that contributes to its high conductance and calcium permeability. Comparisons among the α7 structures provide a foundation for mapping the gating cycle and reveal divergence in gating mechanisms in the Cys-loop receptor superfamily.
Collapse
|
12
|
Kalashnyk O, Lykhmus O, Uspenska K, Izmailov M, Komisarenko S, Skok M. Mitochondrial α7 nicotinic acetylcholine receptors are displaced from complexes with VDAC1 to form complexes with Bax upon apoptosis induction. Int J Biochem Cell Biol 2020; 129:105879. [PMID: 33147521 DOI: 10.1016/j.biocel.2020.105879] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Revised: 09/16/2020] [Accepted: 10/12/2020] [Indexed: 02/06/2023]
Abstract
Nicotinic acetylcholine receptors (nAChRs) mediate fast synaptic transmission in muscles and autonomic ganglia and regulate cytokine and neurotransmitter release in the brain and non-excitable cells. The α7 nAChRs localized in the outer membrane of mitochondria regulate cytochrome c release stimulated by apoptosis-inducing agents. However, the mechanisms through which nAChRs influence mitochondrial permeability remain obscure. Here we put an aim to explore the interaction of nAChRs with voltage-dependent anion channels (VDAC1) and pro-apoptotic protein Bax in the course of apoptosis induction. By using molecular modeling in silico, it was shown that both Bax and VDAC1 can bind within the 4th transmembrane portion (M4) of nAChR subunits. Experimentally, α7 nAChR-Bax and α7 nAChR-VDAC1 complexes were identified by sandwich ELISA in mitochondria isolated from astrocytoma U373 cells. Stimulating apoptosis of U373 cells by H2O2 disrupted α7-VDAC complexes and favored formation of α7-Bax complexes accompanied by cytochrome c release from mitochondria. α7-selective agonist PNU282987 or type 2 positive allosteric modulator PNU120596 disrupted α7-Bax and returned α7 nAChR to complex with VDAC1 resulting in attenuation of cytochrome c release. It is concluded that mitochondrial nAChRs regulate apoptosis-induced mitochondrial channel formation by modulating the interplay of apoptosis-related proteins in mitochondria outer membrane.
Collapse
Affiliation(s)
- Olena Kalashnyk
- Department of Molecular Immunology, Palladin Institute of Biochemistry NAS of Ukraine, 9, Leontovycha str., 01054 Kyiv, Ukraine
| | - Olena Lykhmus
- Department of Molecular Immunology, Palladin Institute of Biochemistry NAS of Ukraine, 9, Leontovycha str., 01054 Kyiv, Ukraine
| | - Kateryna Uspenska
- Department of Molecular Immunology, Palladin Institute of Biochemistry NAS of Ukraine, 9, Leontovycha str., 01054 Kyiv, Ukraine
| | - Mykhailo Izmailov
- Department of Molecular Immunology, Palladin Institute of Biochemistry NAS of Ukraine, 9, Leontovycha str., 01054 Kyiv, Ukraine
| | - Sergiy Komisarenko
- Department of Molecular Immunology, Palladin Institute of Biochemistry NAS of Ukraine, 9, Leontovycha str., 01054 Kyiv, Ukraine
| | - Maryna Skok
- Department of Molecular Immunology, Palladin Institute of Biochemistry NAS of Ukraine, 9, Leontovycha str., 01054 Kyiv, Ukraine.
| |
Collapse
|
13
|
Nielsen BE, Stabile S, Vitale C, Bouzat C. Design, Synthesis, and Functional Evaluation of a Novel Series of Phosphonate-Functionalized 1,2,3-Triazoles as Positive Allosteric Modulators of α7 Nicotinic Acetylcholine Receptors. ACS Chem Neurosci 2020; 11:2688-2704. [PMID: 32786318 DOI: 10.1021/acschemneuro.0c00348] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The α7 nicotinic acetylcholine receptor is a pentameric ligand-gated ion channel widely distributed in the central nervous system, mainly in the hippocampus and cortex. The enhancement of its activity by positive allosteric modulators (PAMs) is a promising therapeutic strategy for cognitive deficits and neurodegenerative disorders. With the aim of developing novel scaffolds with PAM activity, we designed and synthesized a series of phosphonate-functionalized 1,4-disubstituted 1,2,3-triazoles using supported copper nanoparticles as the cycloaddition reaction catalyst and evaluated their activity on α7 receptors by single-channel and whole-cell recordings. We identified several triazole derivatives that displayed PAM activity, with the compound functionalized with the methyl phosphonate group being the most efficacious one. At the macroscopic level, α7 potentiation was evidenced as an increase of the maximal currents elicited by acetylcholine with minimal effects on desensitization, recapitulating the actions of type I PAMs. At the single-channel level, the active compounds did not affect channel amplitude but significantly increased the duration of channel openings and activation episodes. By using chimeric and mutant α7 receptors, we demonstrated that the new α7 PAMs share transmembrane structural determinants of potentiation with other chemically nonrelated PAMs. To gain further insight into the chemical basis of potentiation, we applied structure-activity relationship strategies involving modification of the chain length, inversion of substituent positions in the triazole ring, and changes in the aromatic nucleus. Our findings revealed that the phosphonate-functionalized 1,4-disubstituted 1,2,3-triazole is a novel pharmacophore for the development of therapeutic agents for neurological and neurodegenerative disorders associated with cholinergic dysfunction.
Collapse
Affiliation(s)
- Beatriz Elizabeth Nielsen
- Departamento de Biologı́a, Bioquı́mica y Farmacia, Instituto de Investigaciones Bioquı́micas de Bahı́a Blanca (INIBIBB), Departamento de Biologı́a, Bioquı́mica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Cientı́ficas y Técnicas (CONICET), Bahía Blanca 8000, Buenos Aires, Argentina
| | - Santiago Stabile
- Instituto de Quı́mica del Sur (INQUISUR), Departamento de Quı́mica, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca 8000, Buenos Aires, Argentina
| | - Cristian Vitale
- Instituto de Quı́mica del Sur (INQUISUR), Departamento de Quı́mica, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca 8000, Buenos Aires, Argentina
| | - Cecilia Bouzat
- Departamento de Biologı́a, Bioquı́mica y Farmacia, Instituto de Investigaciones Bioquı́micas de Bahı́a Blanca (INIBIBB), Departamento de Biologı́a, Bioquı́mica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Cientı́ficas y Técnicas (CONICET), Bahía Blanca 8000, Buenos Aires, Argentina
| |
Collapse
|
14
|
Caton M, Ochoa ELM, Barrantes FJ. The role of nicotinic cholinergic neurotransmission in delusional thinking. NPJ SCHIZOPHRENIA 2020; 6:16. [PMID: 32532978 PMCID: PMC7293341 DOI: 10.1038/s41537-020-0105-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/23/2019] [Accepted: 05/15/2020] [Indexed: 02/07/2023]
Abstract
Delusions are a difficult-to-treat and intellectually fascinating aspect of many psychiatric illnesses. Although scientific progress on this complex topic has been challenging, some recent advances focus on dysfunction in neural circuits, specifically in those involving dopaminergic and glutamatergic neurotransmission. Here we review the role of cholinergic neurotransmission in delusions, with a focus on nicotinic receptors, which are known to play a part in some illnesses where these symptoms appear, including delirium, schizophrenia spectrum disorders, bipolar disorder, Parkinson, Huntington, and Alzheimer diseases. Beginning with what we know about the emergence of delusions in these illnesses, we advance a hypothesis of cholinergic disturbance in the dorsal striatum where nicotinic receptors are operative. Striosomes are proposed to play a central role in the formation of delusions. This hypothesis is consistent with our current knowledge about the mechanism of action of cholinergic drugs and with our abstract models of basic cognitive mechanisms at the molecular and circuit levels. We conclude by pointing out the need for further research both at the clinical and translational levels.
Collapse
Affiliation(s)
- Michael Caton
- The Permanente Medical Group, Kaiser Santa Rosa Department of Psychiatry, 2235 Mercury Way, Santa Rosa, CA, 95047, USA
- Heritage Oaks Hospital, 4250 Auburn Boulevard, Sacramento, CA, 95841, USA
| | - Enrique L M Ochoa
- Heritage Oaks Hospital, 4250 Auburn Boulevard, Sacramento, CA, 95841, USA
- Volunteer Clinical Faculty, Department of Psychiatry and Behavioral Sciences, University of California at Davis, 2230 Stockton Boulevard, Sacramento, CA, 95817, USA
| | - Francisco J Barrantes
- Laboratory of Molecular Neurobiology, Institute for Biomedical Research (BIOMED), Faculty of Medical Sciences, UCA-CONICET, Av. Alicia Moreau de Justo 1600, C1107AFF, Buenos Aires, Argentina.
| |
Collapse
|
15
|
Tillman TS, Choi Z, Xu Y, Tang P. Functional Tolerance to Cysteine Mutations in Human α7 Nicotinic Acetylcholine Receptors. ACS Chem Neurosci 2020; 11:242-247. [PMID: 31951367 DOI: 10.1021/acschemneuro.9b00647] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
The α7 nicotinic acetylcholine receptor (α7 nAChR) is involved in various intracellular signaling pathways that mediate addiction, chronic pain, and other diseases, but its intracellular domain structures remain undetermined. The presence of 17 native cysteines in α7 nAChR provides opportunities for extracting structural information through site-directed labeling of chemical probes in strategic locations, but it also creates uncertainties in channel function when those native cysteines must be mutated. Using site-directed mutagenesis and two-electrode voltage clamp electrophysiology measurements, we found that α7 nAChR's function was well tolerated for mutations of all 13 cysteines as long as two pairs of disulfide-bond cysteines remained in the extracellular domain. Furthermore, surface plasmon resonance measurements showed that the cysteine mutations did not affect α7 nAChR binding to the intracellular protein PICK1. The study suggests that a high native cysteine content does not necessarily preclude the use of single cysteine labeling for acquiring structural information on functional proteins.
Collapse
Affiliation(s)
- Tommy S. Tillman
- Department of Anesthesiology and Perioperative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
| | - Zachary Choi
- Department of Anesthesiology and Perioperative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
| | - Yan Xu
- Department of Anesthesiology and Perioperative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
- Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
- Department of Structural Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
| | - Pei Tang
- Department of Anesthesiology and Perioperative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
- Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
- Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
| |
Collapse
|
16
|
Nielsen BE, Bermudez I, Bouzat C. Flavonoids as positive allosteric modulators of α7 nicotinic receptors. Neuropharmacology 2019; 160:107794. [PMID: 31560909 DOI: 10.1016/j.neuropharm.2019.107794] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2019] [Revised: 08/09/2019] [Accepted: 09/23/2019] [Indexed: 12/11/2022]
Abstract
The use of positive allosteric modulators (PAM) of α7 nicotinic receptors is a promising therapy for neurodegenerative, inflammatory and cognitive disorders. Flavonoids are polyphenolic compounds showing neuroprotective, anti-inflammatory and pro-cognitive actions. Besides their well-known antioxidant activity, flavonoids trigger intracellular pathways and interact with receptors, including α7. To reveal how the beneficial actions of flavonoids are linked to α7 function, we evaluated the effects of three representative flavonoids -genistein, quercetin and the neoflavonoid 5,7-dihydroxy-4-phenylcoumarin- on whole-cell and single-channel currents. All flavonoids increase the maximal currents elicited by acetylcholine with minimal effects on desensitization and do not reactivate desensitized receptors, a behaviour consistent with type I PAMs. At the single-channel level, they increase the duration of the open state and produce activation in long-duration episodes with a rank order of efficacy of genistein > quercetin ≥ neoflavonoid. By using mutant and chimeric α7 receptors, we demonstrated that flavonoids share transmembrane structural determinants with other PAMs. The α7-PAM activity of flavonoids results in decreased cell levels of reactive oxygen species. Thus, allosteric potentiation of α7 may be an additional mechanism underlying neuroprotective actions of flavonoids, which may be used as scaffolds for designing new therapeutic agents.
Collapse
Affiliation(s)
- Beatriz Elizabeth Nielsen
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca 8000, Argentina
| | - Isabel Bermudez
- Department of Medical and Biological Sciences, Oxford Brookes University, Oxford, OX3 0BP, United Kingdom
| | - Cecilia Bouzat
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca 8000, Argentina.
| |
Collapse
|
17
|
Pesti K, Lukacs P, Mike A. Type I-like behavior of the type II α7 nicotinic acetylcholine receptor positive allosteric modulator A-867744. PeerJ 2019; 7:e7542. [PMID: 31534841 PMCID: PMC6727837 DOI: 10.7717/peerj.7542] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2019] [Accepted: 07/24/2019] [Indexed: 11/24/2022] Open
Abstract
Cognitive impairment often involves the decreased expression or hypofunction of alpha 7-type nicotinic acetylcholine receptors (α7 nAChRs). Agonists or positive allosteric modulators (PAMs) of α7 nAChRs are known to be potential treatments for dementias, different neurodegenerative disorders, pain syndromes and conditions involving inflammation. In some of these conditions, it is desirable to maintain the temporal precision of fast cholinergic events, while in others, this temporal precision is unnecessary. For this reason, the optimal therapeutic effect for distinct indications may require PAMs with different mechanisms of action. The two major mechanisms are called “type I”, which are compounds that augment α7 nAChR-mediated currents but maintain their characteristic fast kinetics; and “type II”, which are compounds that produce augmented and prolonged currents. In this study, we performed a kinetic analysis of two type II PAMs of the α7 nAChR: PNU-120596 and A-867744, using a fast perfusion method that allowed high temporal resolution. We characterized the type of modulation produced by the two compounds, the state-dependence of the modulatory action, and the interaction between the two compounds. We found fundamental differences between the modulation mechanisms by PNU-120596 and A-867744. Most importantly, during brief agonist pulses, A-867744 caused a strikingly type I-like modulation, while PNU-120596 caused a type II-like prolonged activation. Our results demonstrate that specific compounds, even though all labeled as type II PAMs, can behave in completely different ways, including their onset and offset kinetics, state preference, and single channel open time. Our results emphasize that subtle details of the mechanism of action may be significant in assessing the therapeutic applicability of α7 nAChR PAM compounds.
Collapse
Affiliation(s)
- Krisztina Pesti
- MTA-ELTE NAP B Opto-Neuropharmacology Group, Eötvös Loránd University, Budapest, Hungary.,Department of Biochemistry, Eötvös Loránd University, Budapest, Hungary.,School of PhD Studies, Semmelweis University, Budapest, Hungary
| | - Peter Lukacs
- Plant Protection Institute, Centre for Agricultural Research, Hungarian Academy of Sciences, Martonvásár, Hungary
| | - Arpad Mike
- MTA-ELTE NAP B Opto-Neuropharmacology Group, Eötvös Loránd University, Budapest, Hungary.,Plant Protection Institute, Centre for Agricultural Research, Hungarian Academy of Sciences, Martonvásár, Hungary
| |
Collapse
|
18
|
Lasala M, Fabiani C, Corradi J, Antollini S, Bouzat C. Molecular Modulation of Human α7 Nicotinic Receptor by Amyloid-β Peptides. Front Cell Neurosci 2019; 13:37. [PMID: 30800059 PMCID: PMC6376857 DOI: 10.3389/fncel.2019.00037] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2018] [Accepted: 01/23/2019] [Indexed: 12/21/2022] Open
Abstract
Amyloid β peptide (Aβ) is a key player in the development of Alzheimer's disease (AD). It is the primary component of senile plaques in AD patients and is also found in soluble forms. Cholinergic activity mediated by α7 nicotinic receptors has been shown to be affected by Aβ soluble forms. To shed light into the molecular mechanism of this effect, we explored the direct actions of oligomeric Aβ1-40 and Aβ1-42 on human α7 by fluorescence spectroscopy and single-channel recordings. Fluorescence measurements using the conformational sensitive probe crystal violet (CrV) revealed that in the presence of Aβ α7 undergoes concentration-dependent conformational changes. Exposure of α7 to 100 pM Aβ changes CrV KD towards that of the desensitized state. However, α7 is still reactive to high carbamylcholine (Carb) concentrations. These observations are compatible with the induction of active/desensitized states as well as of a novel conformational state in the presence of both Aβ and Carb. At 100 nM Aβ, α7 adopts a resting-state-like structure which does not respond to Carb, suggesting stabilization of α7 in a blocked state. In real time, we found that Aβ is capable of eliciting α7 channel activity either in the absence or presence of the positive allosteric modulator (PAM) PNU-120596. Activation by Aβ is favored at picomolar or low nanomolar concentrations and is not detected at micromolar concentrations. At high Aβ concentrations, the mean duration of activation episodes elicited by ACh in the presence of PNU-120596 is significantly reduced, an effect compatible with slow open-channel block. We conclude that Aβ directly affects α7 function by acting as an agonist and a negative modulator. Whereas the capability of low concentrations of Aβ to activate α7 could be beneficial, the reduced α7 activity in the presence of higher Aβ concentrations or its long exposure may contribute to the cholinergic signaling deficit and may be involved in the initiation and development of AD.
Collapse
Affiliation(s)
- Matías Lasala
- Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB), Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca, Argentina
| | - Camila Fabiani
- Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB), Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca, Argentina
| | - Jeremías Corradi
- Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB), Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca, Argentina
| | - Silvia Antollini
- Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB), Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca, Argentina
| | - Cecilia Bouzat
- Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB), Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca, Argentina
| |
Collapse
|
19
|
Nielsen BE, Minguez T, Bermudez I, Bouzat C. Molecular function of the novel α7β2 nicotinic receptor. Cell Mol Life Sci 2018; 75:2457-2471. [PMID: 29313059 PMCID: PMC11105712 DOI: 10.1007/s00018-017-2741-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2017] [Revised: 11/30/2017] [Accepted: 12/27/2017] [Indexed: 01/03/2023]
Abstract
The α7 nicotinic receptor is a promising drug target for neurological and inflammatory disorders. Although it is the homomeric member of the family, a novel α7β2 heteromeric receptor has been discovered. To decipher the functional contribution of the β2 subunit, we generated heteromeric receptors with fixed stoichiometry by two different approaches comprising concatenated and unlinked subunits. Receptors containing up to three β2 subunits are functional. As the number of β2 subunits increases in the pentameric arrangement, the durations of channel openings and activation episodes increase progressively probably due to decreased desensitization. The prolonged activation episodes conform the kinetic signature of α7β2 and may have an impact on neuronal excitability. For activation of α7β2 receptors, an α7/α7 binding-site interface is required, thus indicating that the three β2 subunits are located consecutively in the pentameric arrangement. α7-positive allosteric modulators (PAMs) are emerging as novel therapeutic drugs. The presence of β2 in the pentamer affects neither type II PAM potentiation nor activation by an allosteric agonist whereas it impairs type I PAM potentiation. This first single-channel study provides fundamental basis required to decipher the role and function of the novel α7β2 receptor and opens doors to develop selective therapeutic drugs.
Collapse
Affiliation(s)
- Beatriz E Nielsen
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (UNS-CONICET), 8000, Bahía Blanca, Argentina
| | - Teresa Minguez
- Department of Medical and Biological Sciences, Oxford Brookes University, Oxford, OX3 0BP, UK
| | - Isabel Bermudez
- Department of Medical and Biological Sciences, Oxford Brookes University, Oxford, OX3 0BP, UK
| | - Cecilia Bouzat
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (UNS-CONICET), 8000, Bahía Blanca, Argentina.
| |
Collapse
|
20
|
Bouzat C, Sine SM. Nicotinic acetylcholine receptors at the single-channel level. Br J Pharmacol 2018; 175:1789-1804. [PMID: 28261794 PMCID: PMC5979820 DOI: 10.1111/bph.13770] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Revised: 02/21/2017] [Accepted: 02/24/2017] [Indexed: 01/28/2023] Open
Abstract
Over the past four decades, the patch clamp technique and nicotinic ACh (nACh) receptors have established an enduring partnership. Like all good partnerships, each partner has proven significant in its own right, while their union has spurred innumerable advances in life science research. A member and prototype of the superfamily of pentameric ligand-gated ion channels, the nACh receptor is a chemo-electric transducer, binding ACh released from nerves and rapidly opening its channel to cation flow to elicit cellular excitation. A subject of a Nobel Prize in Physiology or Medicine, the patch clamp technique provides unprecedented resolution of currents through single ion channels in their native cellular environments. Here, focusing on muscle and α7 nACh receptors, we describe the extraordinary contribution of the patch clamp technique towards understanding how they activate in response to neurotransmitter, how subtle structural and mechanistic differences among nACh receptor subtypes translate into significant physiological differences, and how nACh receptors are being exploited as therapeutic drug targets. LINKED ARTICLES This article is part of a themed section on Nicotinic Acetylcholine Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.11/issuetoc/.
Collapse
Affiliation(s)
- Cecilia Bouzat
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, INIBIBB (CONICET‐UNS), Departamento de Biología, Bioquímica y FarmaciaUniversidad Nacional del SurBahía BlancaArgentina
| | - Steven M Sine
- Receptor Biology Laboratory, Department of Physiology and Biomedical EngineeringMayo Clinic College of MedicineRochesterMN55905USA
- Department of NeurologyMayo Clinic College of MedicineRochesterMN55905USA
- Department of Pharmacology and Experimental TherapeuticsMayo Clinic College of MedicineRochesterMN55905USA
| |
Collapse
|
21
|
Lasala M, Corradi J, Bruzzone A, Esandi MDC, Bouzat C. A human-specific, truncated α7 nicotinic receptor subunit assembles with full-length α7 and forms functional receptors with different stoichiometries. J Biol Chem 2018; 293:10707-10717. [PMID: 29784875 DOI: 10.1074/jbc.ra117.001698] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2017] [Revised: 05/15/2018] [Indexed: 11/06/2022] Open
Abstract
The cholinergic α7 nicotinic receptor gene, CHRNA7, encodes a subunit that forms the homopentameric α7 receptor, involved in learning and memory. In humans, exons 5-10 in CHRNA7 are duplicated and fused to the FAM7A genetic element, giving rise to the hybrid gene CHRFAM7A Its product, dupα7, is a truncated subunit lacking part of the N-terminal extracellular ligand-binding domain and is associated with neurological disorders, including schizophrenia, and immunomodulation. We combined dupα7 expression on mammalian cells with patch clamp recordings to understand its functional role. Transfected cells expressed dupα7 protein, but they exhibited neither surface binding of the α7 antagonist α-bungarotoxin nor responses to acetylcholine (ACh) or to an allosteric agonist that binds to the conserved transmembrane region. To determine whether dupα7 assembles with α7, we generated receptors comprising α7 and dupα7 subunits, one of which was tagged with conductance substitutions that report subunit stoichiometry and monitored ACh-elicited channel openings in the presence of a positive allosteric α7 modulator. We found that α7 and dupα7 subunits co-assemble into functional heteromeric receptors, which require at least two α7 subunits for channel opening, and that dupα7's presence in the pentameric arrangement does not affect the duration of the potentiated events compared with that of α7. Using an α7 subunit mutant, we found that activation of (α7)2(dupα7)3 receptors occurs through ACh binding at the α7/α7 interfacial binding site. Our study contributes to the understanding of the modulation of α7 function by the human specific, duplicated subunit, associated with human disorders.
Collapse
Affiliation(s)
- Matías Lasala
- From the Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 8000 Bahía Blanca, Argentina
| | - Jeremías Corradi
- From the Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 8000 Bahía Blanca, Argentina
| | - Ariana Bruzzone
- From the Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 8000 Bahía Blanca, Argentina
| | - María Del Carmen Esandi
- From the Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 8000 Bahía Blanca, Argentina
| | - Cecilia Bouzat
- From the Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 8000 Bahía Blanca, Argentina
| |
Collapse
|
22
|
Gielen M, Corringer P. The dual-gate model for pentameric ligand-gated ion channels activation and desensitization. J Physiol 2018; 596:1873-1902. [PMID: 29484660 PMCID: PMC5978336 DOI: 10.1113/jp275100] [Citation(s) in RCA: 73] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2018] [Revised: 01/17/2018] [Accepted: 01/17/2018] [Indexed: 12/15/2022] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs) mediate fast neurotransmission in the nervous system. Their dysfunction is associated with psychiatric, neurological and neurodegenerative disorders such as schizophrenia, epilepsy and Alzheimer's disease. Understanding their biophysical and pharmacological properties, at both the functional and the structural level, thus holds many therapeutic promises. In addition to their agonist-elicited activation, most pLGICs display another key allosteric property, namely desensitization, in which they enter a shut state refractory to activation upon sustained agonist binding. While the activation mechanisms of several pLGICs have been revealed at near-atomic resolution, the structural foundation of desensitization has long remained elusive. Recent structural and functional data now suggest that the activation and desensitization gates are distinct, and are located at both sides of the ion channel. Such a 'dual gate mechanism' accounts for the marked allosteric effects of channel blockers, a feature illustrated herein by theoretical kinetics simulations. Comparison with other classes of ligand- and voltage-gated ion channels shows that this dual gate mechanism emerges as a common theme for the desensitization and inactivation properties of structurally unrelated ion channels.
Collapse
Affiliation(s)
- Marc Gielen
- Channel Receptors UnitInstitut PasteurCNRS UMR 3571ParisFrance
| | | |
Collapse
|
23
|
Affiliation(s)
- Derek Bowie
- Department of Pharmacology and TherapeuticsMcGill UniversityMontréalQuébec H3G 1Y6Canada
| |
Collapse
|
24
|
Uspenska K, Lykhmus O, Arias HR, Pons S, Maskos U, Komisarenko S, Skok M. Positive allosteric modulators of α7* or β2* nicotinic acetylcholine receptors trigger different kinase pathways in mitochondria. Int J Biochem Cell Biol 2018; 99:226-235. [PMID: 29704624 DOI: 10.1016/j.biocel.2018.04.018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Revised: 04/12/2018] [Accepted: 04/24/2018] [Indexed: 12/29/2022]
Abstract
Mitochondrial nicotinic acetylcholine receptors (nAChRs) regulate the early stage of mitochondria-driven apoptosis, including cytochrome c release. Mitochondrial nAChR signaling is mainly mediated by intra-mitochondrial kinases, in an ion-independent manner. To determine the relationship between specific nAChR subtypes and mitochondrial kinases, the effects of a set of nAChR subtype-selective positive allosteric modulators (PAMs) on cytochrome c release from mouse liver mitochondria stimulated by 0.9 μM Ca2+, 0.5 mM H2O2 or 1.0 μM wortmanin is studied. The results indicate that Ca2+-stimulated cytochrome c release from wild-type, but not α7-/-, mice mitochondria is attenuated by the potent agonist PNU-282987 or type II PAMs (PNU-120596, 4BP-TQS, and PAM-2-4), but not by NS-1738, a type I PAM. In contrast, wortmannin-stimulated cytochrome c release from wild-type and, to a lesser extent, α7-/- mice mitochondria is efficiently attenuated by the β2-selective PAM desformylfrustrabromine. In conclusion, the ligand-evoked α7* nAChR conformational changes required to induce intra-mitochondrial signaling can be triggered through orthosteric (agonists) and transmembrane (type II PAMs) sites, but not by the interaction with type I PAMs. The α7 and β2 nAChR subunits are responsible for the engagement of distinct kinase pathways, supporting the concept that multiple heteromeric nAChR subtypes ensure mitochondria resistance to various exogenous and endogenous apoptogenic agents.
Collapse
Affiliation(s)
- Kateryna Uspenska
- Palladin Institute of Biochemistry, 9, Leontovycha str., 01030, Kyiv, Ukraine
| | - Olena Lykhmus
- Palladin Institute of Biochemistry, 9, Leontovycha str., 01030, Kyiv, Ukraine
| | - Hugo R Arias
- CONICET, Godoy Cruz, 2290, Buenos Aires, Argentina
| | - Stephanie Pons
- Institut Pasteur, 25, rue du Dr Roux, 75015, Paris, France
| | - Uwe Maskos
- Institut Pasteur, 25, rue du Dr Roux, 75015, Paris, France
| | - Serghiy Komisarenko
- Palladin Institute of Biochemistry, 9, Leontovycha str., 01030, Kyiv, Ukraine
| | - Maryna Skok
- Palladin Institute of Biochemistry, 9, Leontovycha str., 01030, Kyiv, Ukraine.
| |
Collapse
|
25
|
An allosteric link connecting the lipid-protein interface to the gating of the nicotinic acetylcholine receptor. Sci Rep 2018; 8:3898. [PMID: 29497086 PMCID: PMC5832824 DOI: 10.1038/s41598-018-22150-x] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2017] [Accepted: 02/16/2018] [Indexed: 11/08/2022] Open
Abstract
The mechanisms underlying lipid-sensing by membrane proteins is of considerable biological importance. A unifying mechanistic question is how a change in structure at the lipid-protein interface is translated through the transmembrane domain to influence structures critical to protein function. Gating of the nicotinic acetylcholine receptor (nAChR) is sensitive to its lipid environment. To understand how changes at the lipid-protein interface influence gating, we examined how a mutation at position 418 on the lipid-facing surface of the outer most M4 transmembrane α-helix alters the energetic couplings between M4 and the remainder of the transmembrane domain. Human muscle nAChR is sensitive to mutations at position 418, with the Cys-to-Trp mutation resulting in a 16-fold potentiation in function that leads to a congenital myasthenic syndrome. Energetic coupling between M4 and the Cys-loop, a key structure implicated in gating, do not change with C418W. Instead, Trp418 and an adjacent residue couple energetically with residues on the M1 transmembrane α-helix, leading to a reorientation of M1 that stabilizes the open state. We thus identify an allosteric link connecting the lipid-protein interface of the nAChR to altered channel function.
Collapse
|
26
|
Targowska-Duda KM, Kaczor AA, Jozwiak K, Arias HR. Molecular interactions of type I and type II positive allosteric modulators with the human α7 nicotinic acetylcholine receptor: an in silico study. J Biomol Struct Dyn 2018; 37:411-439. [PMID: 29363414 DOI: 10.1080/07391102.2018.1427634] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The binding site locations and structural components for type I and type II positive allosteric modulators (PAMs) of the α7 nicotinic acetylcholine receptor (nAChR) have not been fully characterized yet. In this regard, homology models of the human α7 nAChR and hα7/m5-HT3A chimera, built using the crystal structure of the serotonin type 3A receptor (5-ΗΤ3ΑR), were used for molecular docking and molecular dynamics simulations to study the molecular interactions of selected type I (5-hydroxyindol, NS-1738, and LY-2087101) and type II (PNU-120596, PAM-2, and TBS-516) PAMs. The docking results indicate: (1) a site located in the extracellular domain (ECD) for type I PAMs such as NS-1738 and LY-2087101, but not for 5-HI; (2) an overlapping site in the ECD-transmembrane domain (TMD) junction for all studied PAMs. Additional docking results on the hα7/m5-HT3A chimera supported experimental results indicating that the ECD site might be relevant for type I PAM activity; and (3) two TMD sites, an intrasubunit site that recognizes type II PAMs, and an intersubunit pocket with high specificity for 5-HI (type I PAM). The in silico α7TSLMF mutant results support the view that M1-Ser223 and M3-Ile281 are key residues for the interaction of PAM-2 and PNU-120596 with the intrasubunit cavity. Our in silico results are in agreement with experimental data showing that the intrasubunit cavity is relevant for the activity of type II PAMs, and suggest that the ECD-TMD junction and intersubunit sites could be significant for the activity of type I PAMs.
Collapse
Affiliation(s)
| | - Agnieszka A Kaczor
- b Department of Synthesis and Chemical Technology of Pharmaceutical Substances with Computer Modeling Lab , Medical University of Lublin , Lublin , Poland.,c School of Pharmacy , University of Eastern Finland , Kuopio , Finland
| | - Krzysztof Jozwiak
- a Department of Biopharmacy , Medical University of Lublin , Lublin , Poland
| | - Hugo R Arias
- d Department of Basic Sciences , California Northstate University College of Medicine , Elk Grove , CA , USA
| |
Collapse
|
27
|
Bouzat C, Lasala M, Nielsen BE, Corradi J, Esandi MDC. Molecular function of α7 nicotinic receptors as drug targets. J Physiol 2017; 596:1847-1861. [PMID: 29131336 DOI: 10.1113/jp275101] [Citation(s) in RCA: 64] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Accepted: 11/02/2017] [Indexed: 12/20/2022] Open
Abstract
Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated ion channels involved in many physiological and pathological processes. In vertebrates, there are seventeen different nAChR subunits that combine to yield a variety of receptors with different pharmacology, function, and localization. The homomeric α7 receptor is one of the most abundant nAChRs in the nervous system and it is also present in non-neuronal cells. It plays important roles in cognition, memory, pain, neuroprotection, and inflammation. Its diverse physiological actions and associated disorders have made of α7 an attractive novel target for drug modulation. Potentiation of the α7 receptor has emerged as a novel therapeutic strategy for several neurological diseases, such as Alzheimer's and Parkinson's diseases, and inflammatory disorders. In contrast, increased α7 activity has been associated with cancer cell proliferation. The presence of different drug target sites offers a great potential for α7 modulation in different pathological contexts. In particular, compounds that target allosteric sites offer significant advantages over orthosteric agonists due to higher selectivity and a broader spectrum of degrees and mechanisms of modulation. Heterologous expression of α7, together with chaperone proteins, combined with patch clamp recordings have provided important advances in our knowledge of the molecular basis of α7 responses and their potential modulation for pathological processes. This review gives a synthetic view of α7 and its molecular function, focusing on how its unique activation and desensitization features can be modified by pharmacological agents. This fundamental information offers insights into therapeutic strategies.
Collapse
Affiliation(s)
- Cecilia Bouzat
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, CONICET/UNS, 8000, Bahía Blanca, Argentina
| | - Matías Lasala
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, CONICET/UNS, 8000, Bahía Blanca, Argentina
| | - Beatriz Elizabeth Nielsen
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, CONICET/UNS, 8000, Bahía Blanca, Argentina
| | - Jeremías Corradi
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, CONICET/UNS, 8000, Bahía Blanca, Argentina
| | - María Del Carmen Esandi
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, CONICET/UNS, 8000, Bahía Blanca, Argentina
| |
Collapse
|
28
|
Structural mechanisms of activation and desensitization in neurotransmitter-gated ion channels. Nat Struct Mol Biol 2017; 23:494-502. [PMID: 27273633 DOI: 10.1038/nsmb.3214] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2016] [Accepted: 03/29/2016] [Indexed: 12/31/2022]
Abstract
Ion channels gated by neurotransmitters are present across metazoans, in which they are essential for brain function, sensation and locomotion; closely related homologs are also found in bacteria. Structures of eukaryotic pentameric cysteine-loop (Cys-loop) receptors and tetrameric ionotropic glutamate receptors in multiple functional states have recently become available. Here, I describe how these studies relate to established ideas regarding receptor activation and how they have enabled decades' worth of functional work to be pieced together, thus allowing previously puzzling aspects of receptor activity to be understood.
Collapse
|
29
|
Therien JPD, Baenziger JE. Pentameric ligand-gated ion channels exhibit distinct transmembrane domain archetypes for folding/expression and function. Sci Rep 2017; 7:450. [PMID: 28348412 PMCID: PMC5428567 DOI: 10.1038/s41598-017-00573-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Accepted: 03/03/2017] [Indexed: 11/17/2022] Open
Abstract
Although transmembrane helix-helix interactions must be strong enough to drive folding, they must still permit the inter-helix movements associated with conformational change. Interactions between the outermost M4 and adjacent M1 and M3 α-helices of pentameric ligand-gated ion channels have been implicated in folding and function. Here, we evaluate the role of different physical interactions at this interface in the function of two prokaryotic homologs, GLIC and ELIC. Strikingly, disruption of most interactions in GLIC lead to either a reduction or a complete loss of expression and/or function, while analogous disruptions in ELIC often lead to gains in function. Structural comparisons suggest that GLIC and ELIC represent distinct transmembrane domain archetypes. One archetype, exemplified by GLIC, the glycine and GABA receptors and the glutamate activated chloride channel, has extensive aromatic contacts that govern M4-M1/M3 interactions and that are essential for expression and function. The other archetype, exemplified by ELIC and both the nicotinic acetylcholine and serotonin receptors, has relatively few aromatic contacts that are detrimental to function. These archetypes likely have evolved different mechanisms to balance the need for strong M4 "binding" to M1/M3 to promote folding/expression, and the need for weaker interactions that allow for greater conformational flexibility.
Collapse
Affiliation(s)
- J P Daniel Therien
- Department of Biochemistry, Microbiology, and Immunology University of Ottawa, Ottawa, ON, K1H 8M5, Canada
| | - John E Baenziger
- Department of Biochemistry, Microbiology, and Immunology University of Ottawa, Ottawa, ON, K1H 8M5, Canada.
| |
Collapse
|
30
|
Zanetti SR, Ziblat A, Torres NI, Zwirner NW, Bouzat C. Expression and Functional Role of α7 Nicotinic Receptor in Human Cytokine-stimulated Natural Killer (NK) Cells. J Biol Chem 2016; 291:16541-52. [PMID: 27284006 DOI: 10.1074/jbc.m115.710574] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Indexed: 12/18/2022] Open
Abstract
The homomeric α7 nicotinic receptor (nAChR) is one of the most abundant nAChRs in the central nervous system where it contributes to cognition, attention, and working memory. α7 nAChR is also present in lymphocytes, dendritic cells (DCs), and macrophages and it is emerging as an important drug target for intervention in inflammation and sepsis. Natural killer (NK) cells display cytotoxic activity against susceptible target cells and modulate innate and adaptive immune responses through their interaction with DCs. We here show that human NK cells also express α7 nAChR. α7 nAChR mRNA is detected by RT-PCR and cell surface expression of α7 nAChR is detected by confocal microscopy and flow cytometry using α-bungarotoxin, a specific antagonist. Both mRNA and protein levels increase during NK stimulation with cytokines (IL-12, IL-18, and IL-15). Exposure of cytokine-stimulated NK cells to PNU-282987, a specific α7 nAChR agonist, increases intracellular calcium concentration ([Ca(2+)]i) mainly released from intracellular stores, indicating that α7 nAChR is functional. Moreover, its activation by PNU-282987 plus a specific positive allosteric modulator greatly enhances the Ca(2+) responses in NK cells. Stimulation of NK cells with cytokines and PNU-282987 decreases NF-κB levels and nuclear mobilization, down-regulates NKG2D receptors, and decreases NKG2D-dependent cell-mediated cytotoxicity and IFN-γ production. Also, such NK cells are less efficient to trigger DC maturation. Thus, our results demonstrate the anti-inflammatory role of α7 nAChR in NK cells and suggest that modulation of its activity in these cells may constitute a novel target for regulation of the immune response.
Collapse
Affiliation(s)
- Samanta R Zanetti
- From the Instituto de Investigaciones Bioquímicas (INIBIBB), Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 8000 Bahía Blanca
| | - Andrea Ziblat
- the Instituto de Biología y Medicina Experimental, CONICET, C1428ADN-Ciudad de Buenos Aires, and
| | - Nicolás I Torres
- the Instituto de Biología y Medicina Experimental, CONICET, C1428ADN-Ciudad de Buenos Aires, and
| | - Norberto W Zwirner
- the Instituto de Biología y Medicina Experimental, CONICET, C1428ADN-Ciudad de Buenos Aires, and the Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, C1428ADN-Ciudad de Buenos Aires, Argentina
| | - Cecilia Bouzat
- From the Instituto de Investigaciones Bioquímicas (INIBIBB), Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 8000 Bahía Blanca,
| |
Collapse
|
31
|
Corradi J, Bouzat C. Understanding the Bases of Function and Modulation of α7 Nicotinic Receptors: Implications for Drug Discovery. Mol Pharmacol 2016; 90:288-99. [PMID: 27190210 DOI: 10.1124/mol.116.104240] [Citation(s) in RCA: 118] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Accepted: 05/05/2016] [Indexed: 01/01/2023] Open
Abstract
The nicotinic acetylcholine receptor (nAChR) belongs to a superfamily of pentameric ligand-gated ion channels involved in many physiologic and pathologic processes. Among nAChRs, receptors comprising the α7 subunit are unique because of their high Ca(2+) permeability and fast desensitization. nAChR agonists elicit a transient ion flux response that is further sustained by the release of calcium from intracellular sources. Owing to the dual ionotropic/metabotropic nature of α7 receptors, signaling pathways are activated. The α7 subunit is highly expressed in the nervous system, mostly in regions implicated in cognition and memory and has therefore attracted attention as a novel drug target. Additionally, its dysfunction is associated with several neuropsychiatric and neurologic disorders, such as schizophrenia and Alzheimer's disease. α7 is also expressed in non-neuronal cells, particularly immune cells, where it plays a role in immunity, inflammation, and neuroprotection. Thus, α7 potentiation has emerged as a therapeutic strategy for several neurologic and inflammatory disorders. With unique activation properties, the receptor is a sensitive drug target carrying different potential binding sites for chemical modulators, particularly agonists and positive allosteric modulators. Although macroscopic and single-channel recordings have provided significant information about the underlying molecular mechanisms and binding sites of modulatory compounds, we know just the tip of the iceberg. Further concerted efforts are necessary to effectively exploit α7 as a drug target for each pathologic situation. In this article, we focus mainly on the molecular basis of activation and drug modulation of α7, key pillars for rational drug design.
Collapse
Affiliation(s)
- Jeremías Corradi
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Universidad Nacional del Sur, CONICET/UNS, Bahía Blanca, Argentina
| | - Cecilia Bouzat
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Universidad Nacional del Sur, CONICET/UNS, Bahía Blanca, Argentina
| |
Collapse
|
32
|
Positive allosteric modulators of α7 nicotinic acetylcholine receptors affect neither the function of other ligand- and voltage-gated ion channels and acetylcholinesterase, nor β-amyloid content. Int J Biochem Cell Biol 2016; 76:19-30. [PMID: 27129924 DOI: 10.1016/j.biocel.2016.04.015] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Revised: 04/22/2016] [Accepted: 04/25/2016] [Indexed: 11/22/2022]
Abstract
The activity of positive allosteric modulators (PAMs) of α7 nicotinic acetylcholine receptors (AChRs), including 3-furan-2-yl-N-p-tolyl-acrylamide (PAM-2), 3-furan-2-yl-N-o-tolylacrylamide (PAM-3), and 3-furan-2-yl-N-phenylacrylamide (PAM-4), was tested on a variety of ligand- [i.e., human (h) α7, rat (r) α9α10, hα3-containing AChRs, mouse (m) 5-HT3AR, and several glutamate receptors (GluRs)] and voltage-gated (i.e., sodium and potassium) ion channels, as well as on acetylcholinesterase (AChE) and β-amyloid (Aβ) content. The functional results indicate that PAM-2 inhibits hα3-containing AChRs (IC50=26±6μM) with higher potency than that for NR1aNR2B and NR1aNR2A, two NMDA-sensitive GluRs. PAM-2 affects neither the activity of m5-HT3ARs, GluR5/KA2 (a kainate-sensitive GluR), nor AChE, and PAM-4 does not affect agonist-activated rα9α10 AChRs. Relevant clinical concentrations of PAM-2-4 do not inhibit Nav1.2 and Kv3.1 ion channels. These PAMs slightly enhance the activity of GluR1 and GluR2, two AMPA-sensitive GluRs. PAM-2 does not change the levels of Aβ42 in an Alzheimer's disease mouse model (i.e., 5XFAD). The molecular docking and dynamics results using the hα7 model suggest that the active sites for PAM-2 include the intrasubunit (i.e., PNU-120596 locus) and intersubunit sites. These results support our previous study showing that these PAMs are selective for the α7 AChR, and clarify that the procognitive/promnesic/antidepressant activity of PAM-2 is not mediated by other targets.
Collapse
|
33
|
Hamouda AK, Deba F, Wang ZJ, Cohen JB. Photolabeling a Nicotinic Acetylcholine Receptor (nAChR) with an (α4)3(β2)2 nAChR-Selective Positive Allosteric Modulator. Mol Pharmacol 2016; 89:575-84. [PMID: 26976945 DOI: 10.1124/mol.116.103341] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2016] [Accepted: 03/09/2016] [Indexed: 01/25/2023] Open
Abstract
Positive allosteric modulators (PAMs) of nicotinic acetylcholine (ACh) receptors (nAChRs) have potential clinical applications in the treatment of nicotine dependence and many neuropsychiatric conditions associated with decreased brain cholinergic activity, and 3-(2-chlorophenyl)-5-(5-methyl-1-(piperidin-4-yl)-1H-pyrrazol-4-yl)isoxazole (CMPI) has been identified as a PAM selective for neuronal nAChRs containing theα4 subunit. In this report, we compare CMPI interactions with low-sensitivity (α4)3(β2)2 and high-sensitivity (α4)2(β2)3 nAChRs, and with muscle-type nAChRs. In addition, we use the intrinsic reactivity of [(3)H]CMPI upon photolysis at 312 nm to identify its binding sites inTorpedonAChRs. Recording fromXenopusoocytes, we found that CMPI potentiated maximally the responses of (α4)3(β2)2nAChR to 10μM ACh (EC10) by 400% and with anEC50of ∼1µM. CMPI produced a left shift of the ACh concentration-response curve without altering ACh efficacy. In contrast, CMPI inhibited (∼35% at 10µM) ACh responses of (α4)2(β2)3nAChRs and fully inhibited human muscle andTorpedonAChRs with IC50values of ∼0.5µM. Upon irradiation at 312 nm, [(3)H]CMPI photoincorporated into eachTorpedo[(α1)2β1γδ] nAChR subunit. Sequencing of peptide fragments isolated from [(3)H]CMPI-photolabeled nAChR subunits established photolabeling of amino acids contributing to the ACh binding sites (αTyr(190),αTyr(198),γTrp(55),γTyr(111),γTyr(117),δTrp(57)) that was fully inhibitable by agonist and lower-efficiency, state-dependent [(3)H]CMPI photolabeling within the ion channel. Our results establish that CMPI is a potent potentiator of nAChRs containing anα4:α4 subunit interface, and that its intrinsic photoreactivy makes it of potential use to identify its binding sites in the (α4)3(β2)2nAChR.
Collapse
Affiliation(s)
- Ayman K Hamouda
- Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville, Texas (A.K.H., F.D., Z.-J.W.); and Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., J.B.C.)
| | - Farah Deba
- Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville, Texas (A.K.H., F.D., Z.-J.W.); and Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., J.B.C.)
| | - Ze-Jun Wang
- Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville, Texas (A.K.H., F.D., Z.-J.W.); and Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., J.B.C.)
| | - Jonathan B Cohen
- Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville, Texas (A.K.H., F.D., Z.-J.W.); and Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., J.B.C.)
| |
Collapse
|
34
|
Andersen ND, Nielsen BE, Corradi J, Tolosa MF, Feuerbach D, Arias HR, Bouzat C. Exploring the positive allosteric modulation of human α7 nicotinic receptors from a single-channel perspective. Neuropharmacology 2016; 107:189-200. [PMID: 26926428 DOI: 10.1016/j.neuropharm.2016.02.032] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2015] [Revised: 01/20/2016] [Accepted: 02/24/2016] [Indexed: 12/30/2022]
Abstract
Enhancement of α7 nicotinic receptor (nAChR) function by positive allosteric modulators (PAMs) is a promising therapeutic strategy to improve cognitive deficits. PAMs have been classified only on the basis of their macroscopic effects as type I, which only enhance agonist-induced currents, and type II, which also decrease desensitization and reactivate desensitized nAChRs. To decipher the molecular basis underlying these distinct activities, we explored the effects on single-α7 channel currents of representative members of each type and of less characterized compounds. Our results reveal that all PAMs enhance open-channel lifetime and produce episodes of successive openings, thus indicating that both types affect α7 kinetics. Different PAM types show different sensitivity to temperature, suggesting different mechanisms of potentiation. By using a mutant α7 receptor that is insensitive to the prototype type II PAM (PNU-120596), we show that some though not all type I PAMs share the structural determinants of potentiation. Overall, our study provides novel information on α7 potentiation, which is key to the ongoing development of therapeutic compounds.
Collapse
Affiliation(s)
- Natalia D Andersen
- Universidad Nacional del Sur/CONICET, Instituto de Investigaciones Bioquímicas de Bahía Blanca, Bahía Blanca 8000, Argentina
| | - Beatriz E Nielsen
- Universidad Nacional del Sur/CONICET, Instituto de Investigaciones Bioquímicas de Bahía Blanca, Bahía Blanca 8000, Argentina
| | - Jeremías Corradi
- Universidad Nacional del Sur/CONICET, Instituto de Investigaciones Bioquímicas de Bahía Blanca, Bahía Blanca 8000, Argentina
| | - María F Tolosa
- Universidad Nacional del Sur/CONICET, Instituto de Investigaciones Bioquímicas de Bahía Blanca, Bahía Blanca 8000, Argentina
| | - Dominik Feuerbach
- Neuroscience Research, Novartis Institutes for Biomedical Research, Basel, Switzerland
| | - Hugo R Arias
- Department of Medical Education, California Northstate University College of Medicine, Elk Grove, CA 95757, USA
| | - Cecilia Bouzat
- Universidad Nacional del Sur/CONICET, Instituto de Investigaciones Bioquímicas de Bahía Blanca, Bahía Blanca 8000, Argentina.
| |
Collapse
|
35
|
Multiple binding sites in the nicotinic acetylcholine receptors: An opportunity for polypharmacolgy. Pharmacol Res 2015; 101:9-17. [PMID: 26318763 DOI: 10.1016/j.phrs.2015.08.018] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/03/2015] [Revised: 08/20/2015] [Accepted: 08/20/2015] [Indexed: 12/21/2022]
Abstract
For decades, the development of selective compounds has been the main goal for chemists and biologists involved in drug discovery. However, diverse lines of evidence indicate that polypharmacological agents, i.e. those that act simultaneously at various protein targets, might show better profiles than selective ligands, regarding both efficacy and side effects. On the other hand, the availability of the crystal structure of different receptors allows a detailed analysis of the main interactions between drugs and receptors in a specific binding site. Neuronal nicotinic acetylcholine receptors (nAChRs) constitute a large and diverse family of ligand-gated ion channels (LGICs) that, as a product of its modulation, regulate neurotransmitter release, which in turns produce a global neuromodulation of the central nervous system. nAChRs are pentameric protein complexes in such a way that expression of compatible subunits can lead to various receptor assemblies or subtypes. The agonist binding site, located at the extracellular region, exhibits different properties depending on the subunits that conform the receptor. In the last years, it has been recognized that nAChRs could also contain one or more allosteric sites which could bind non-classical nicotinic ligands including several therapeutically useful drugs. The presence of multiple binding sites in nAChRs offers an interesting possibility for the development of novel polypharmacological agents with a wide spectrum of actions.
Collapse
|
36
|
Stoichiometry for α-bungarotoxin block of α7 acetylcholine receptors. Nat Commun 2015; 6:8057. [PMID: 26282895 PMCID: PMC4544739 DOI: 10.1038/ncomms9057] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2015] [Accepted: 07/12/2015] [Indexed: 12/21/2022] Open
Abstract
α-Bungarotoxin (α-Btx) binds to the five agonist binding sites on the homopentameric α7-acetylcholine receptor, yet the number of bound α-Btx molecules required to prevent agonist-induced channel opening remains unknown. To determine the stoichiometry for α-Btx blockade, we generate receptors comprised of wild-type and α-Btx-resistant subunits, tag one of the subunit types with conductance mutations to report subunit stoichiometry, and following incubation with α-Btx, monitor opening of individual receptor channels with defined subunit stoichiometry. We find that a single α-Btx-sensitive subunit confers nearly maximal suppression of channel opening, despite four binding sites remaining unoccupied by α-Btx and accessible to the agonist. Given structural evidence that α-Btx locks the agonist binding site in an inactive conformation, we conclude that the dominant mechanism of antagonism is non-competitive, originating from conformational arrest of the binding sites, and that the five α7 subunits are interdependent and maintain conformational symmetry in the open channel state. Since their discovery more than fifty years ago, α-neurotoxins have been used to study acetylcholine receptor-coupled ion channels. Here, daCosta et al. find that toxin binding to a single site of the pentameric α7 receptor blocks function, suggesting the five binding sites are interdependent and the toxin arrests the sites in the inactive conformation.
Collapse
|
37
|
Grupe M, Jensen AA, Ahring PK, Christensen JK, Grunnet M. Unravelling the mechanism of action of NS9283, a positive allosteric modulator of (α4)3(β2)2 nicotinic ACh receptors. Br J Pharmacol 2015; 168:2000-10. [PMID: 23278456 DOI: 10.1111/bph.12095] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2012] [Revised: 11/22/2012] [Accepted: 12/14/2012] [Indexed: 02/05/2023] Open
Abstract
BACKGROUND AND PURPOSE Strong implications in major neurological diseases make the neuronal α4β2 nicotinic ACh receptor (nAChR) a highly interesting drug target. In this study, we present a detailed electrophysiological characterization of NS9283, a potent positive allosteric modulator acting selectively at 3α:2β stoichiometry of α2* and α4* nAChRs. EXPERIMENTAL APPROACH The whole-cell patch-clamp technique equipped with an ultra-fast drug application system was used to perform electrophysiological characterization of NS9283 modulatory actions on human α4β2 nAChRs stably expressed in HEK293 cells (HEK293-hα4β2). KEY RESULTS NS9283 was demonstrated to increase the potency of ACh-evoked currents in HEK293-hα4β2 cells by left-shifting the concentration-response curve ~60-fold. Interestingly, this modulation did not significantly alter maximal efficacy levels of ACh. Further, NS9283 did not affect the rate of desensitization of ACh-evoked currents, was incapable of reactivating desensitized receptors and only moderately slowed recovery from desensitization. However, NS9283 strongly decreased the rate of deactivation kinetics and also modestly decreased the rate of activation. This resulted in a left-shift of the ACh window current of (α4)3(β2)2 nAChRs in the presence of NS9283. CONCLUSIONS AND IMPLICATIONS This study demonstrates that NS9283 increases responsiveness of human (α4)3(β2)2 nAChR to ACh with no change in maximum efficacy. We propose that this potentiation is due to a significant slowing of deactivation kinetics. In summary, the mechanism of action of NS9283 bears high resemblance to that of benzodiazepines at the GABAA receptor and to our knowledge, NS9283 constitutes the first nAChR compound of this class.
Collapse
Affiliation(s)
- M Grupe
- NeuroSearch A/S, Ballerup, Denmark.
| | | | | | | | | |
Collapse
|
38
|
Hamouda AK, Wang ZJ, Stewart DS, Jain AD, Glennon RA, Cohen JB. Desformylflustrabromine (dFBr) and [3H]dFBr-Labeled Binding Sites in a Nicotinic Acetylcholine Receptor. Mol Pharmacol 2015; 88:1-11. [PMID: 25870334 PMCID: PMC4468644 DOI: 10.1124/mol.115.098913] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Accepted: 04/13/2015] [Indexed: 12/11/2022] Open
Abstract
Desformylflustrabromine (dFBr) is a positive allosteric modulator (PAM) of α4β2 and α2β2 nAChRs that, at concentrations >1 µM, also inhibits these receptors and α7 nAChRs. However, its interactions with muscle-type nAChRs have not been characterized, and the locations of its binding site(s) in any nAChR are not known. We report here that dFBr inhibits human muscle (αβεδ) and Torpedo (αβγδ) nAChR expressed in Xenopus oocytes with IC50 values of ∼ 1 μM. dFBr also inhibited the equilibrium binding of ion channel blockers to Torpedo nAChRs with higher affinity in the nAChR desensitized state ([(3)H]phencyclidine; IC50 = 4 μM) than in the resting state ([(3)H]tetracaine; IC50 = 60 μM), whereas it bound with only very low affinity to the ACh binding sites ([(3)H]ACh, IC50 = 1 mM). Upon irradiation at 312 nm, [(3)H]dFBr photoincorporated into amino acids within the Torpedo nAChR ion channel with the efficiency of photoincorporation enhanced in the presence of agonist and the agonist-enhanced photolabeling inhibitable by phencyclidine. In the presence of agonist, [(3)H]dFBr also photolabeled amino acids in the nAChR extracellular domain within binding pockets identified previously for the nonselective nAChR PAMs galantamine and physostigmine at the canonical α-γ interface containing the transmitter binding sites and at the noncanonical δ-β subunit interface. These results establish that dFBr inhibits muscle-type nAChR by binding in the ion channel and that [(3)H]dFBr is a photoaffinity probe with broad amino acid side chain reactivity.
Collapse
Affiliation(s)
- Ayman K Hamouda
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., D.S.S., J.B.C.); Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, Virginia (A.D.J., R.A.G.); and Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville,Texas (A.K.H., Z.-J.W.)
| | - Ze-Jun Wang
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., D.S.S., J.B.C.); Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, Virginia (A.D.J., R.A.G.); and Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville,Texas (A.K.H., Z.-J.W.)
| | - Deirdre S Stewart
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., D.S.S., J.B.C.); Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, Virginia (A.D.J., R.A.G.); and Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville,Texas (A.K.H., Z.-J.W.)
| | - Atul D Jain
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., D.S.S., J.B.C.); Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, Virginia (A.D.J., R.A.G.); and Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville,Texas (A.K.H., Z.-J.W.)
| | - Richard A Glennon
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., D.S.S., J.B.C.); Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, Virginia (A.D.J., R.A.G.); and Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville,Texas (A.K.H., Z.-J.W.)
| | - Jonathan B Cohen
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., D.S.S., J.B.C.); Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, Virginia (A.D.J., R.A.G.); and Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville,Texas (A.K.H., Z.-J.W.)
| |
Collapse
|
39
|
Chatzidaki A, Fouillet A, Li J, Dage J, Millar NS, Sher E, Ursu D. Pharmacological Characterisation of Nicotinic Acetylcholine Receptors Expressed in Human iPSC-Derived Neurons. PLoS One 2015; 10:e0125116. [PMID: 25906356 PMCID: PMC4408108 DOI: 10.1371/journal.pone.0125116] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2014] [Accepted: 03/20/2015] [Indexed: 01/21/2023] Open
Abstract
Neurons derived from human induced pluripotent stem cells (iPSCs) represent a potentially valuable tool for the characterisation of neuronal receptors and ion channels. Previous studies on iPSC-derived neuronal cells have reported the functional characterisation of a variety of receptors and ion channels, including glutamate receptors, γ-aminobutyric acid (GABA) receptors and several voltage-gated ion channels. In the present study we have examined the expression and functional properties of nicotinic acetylcholine receptors (nAChRs) in human iPSC-derived neurons. Gene expression analysis indicated the presence of transcripts encoding several nAChR subunits, with highest levels detected for α3-α7, β1, β2 and β4 subunits (encoded by CHRNA3-CHRNA7, CHRNB1, CHRNB2 and CHRNB4 genes). In addition, similarly high transcript levels were detected for the truncated dupα7 subunit transcript, encoded by the partially duplicated gene CHRFAM7A, which has been associated with psychiatric disorders such as schizophrenia. The functional properties of these nAChRs have been examined by calcium fluorescence and by patch-clamp recordings. The data obtained suggest that the majority of functional nAChRs expressed in these cells have pharmacological properties typical of α7 receptors. Large responses were induced by a selective α7 agonist (compound B), in the presence of the α7-selective positive allosteric modulator (PAM) PNU-120596, which were blocked by the α7-selective antagonist methyllycaconitine (MLA). In addition, a small proportion of the neurons express nAChRs with properties typical of heteromeric (non-α7 containing) nAChR subtypes. These cells therefore represent a great tool to advance our understanding of the properties of native human nAChRs, α7 in particular.
Collapse
Affiliation(s)
- Anna Chatzidaki
- Department of Neuroscience, Physiology & Pharmacology, University College London, London, United Kingdom
| | - Antoine Fouillet
- Lilly Research Centre, Eli Lilly and Company, Windlesham, Surrey, United Kingdom
| | - Jingling Li
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285, United States of America
| | - Jeffrey Dage
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285, United States of America
| | - Neil S. Millar
- Department of Neuroscience, Physiology & Pharmacology, University College London, London, United Kingdom
| | - Emanuele Sher
- Lilly Research Centre, Eli Lilly and Company, Windlesham, Surrey, United Kingdom
| | - Daniel Ursu
- Lilly Research Centre, Eli Lilly and Company, Windlesham, Surrey, United Kingdom
- * E-mail:
| |
Collapse
|
40
|
The desensitization gate of inhibitory Cys-loop receptors. Nat Commun 2015; 6:6829. [PMID: 25891813 PMCID: PMC4410641 DOI: 10.1038/ncomms7829] [Citation(s) in RCA: 98] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2014] [Accepted: 03/03/2015] [Indexed: 11/09/2022] Open
Abstract
Cys-loop neurotransmitter-gated ion channels are vital for communication throughout the nervous system. Following activation, these receptors enter into a desensitized state in which the ion channel shuts even though the neurotransmitter molecules remain bound. To date, the molecular determinants underlying this most fundamental property of Cys-loop receptors have remained elusive. Here we present a generic mechanism for the desensitization of Cys-loop GABAA (GABAARs) and glycine receptors (GlyRs), which both mediate fast inhibitory synaptic transmission. Desensitization is regulated by interactions between the second and third transmembrane segments, which affect the ion channel lumen near its intracellular end. The GABAAR and GlyR pore blocker picrotoxin prevented desensitization, consistent with its deep channel-binding site overlapping a physical desensitization gate.
Collapse
|
41
|
Báez-Pagán CA, Delgado-Vélez M, Lasalde-Dominicci JA. Activation of the Macrophage α7 Nicotinic Acetylcholine Receptor and Control of Inflammation. J Neuroimmune Pharmacol 2015; 10:468-76. [PMID: 25870122 DOI: 10.1007/s11481-015-9601-5] [Citation(s) in RCA: 141] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2013] [Accepted: 03/12/2015] [Indexed: 01/03/2023]
Abstract
Inflammatory responses to stimuli are essential body defenses against foreign threats. However, uncontrolled inflammation may result in serious health problems, which can be life-threatening. The α7 nicotinic acetylcholine receptor, a ligand-gated ion channel expressed in the nervous and immune systems, has an essential role in the control of inflammation. Activation of the macrophage α7 receptor by acetylcholine, nicotine, or other agonists, selectively inhibits production of pro-inflammatory cytokines while leaving anti-inflammatory cytokines undisturbed. The neural control of this regulation pathway was discovered recently and it was named the cholinergic anti-inflammatory pathway (CAP). When afferent vagus nerve terminals are activated by cytokines or other pro-inflammatory stimuli, the message travels through the afferent vagus nerve, resulting in action potentials traveling down efferent vagus nerve fibers in a process that eventually leads to macrophage α7 activation by acetylcholine and inhibition of pro-inflammatory cytokines production. The mechanism by which activation of α7 in macrophages regulates pro-inflammatory responses is subject of intense research, and important insights have thus been made. The results suggest that activation of the macrophage α7 controls inflammation by inhibiting NF-κB nuclear translocation, and activating the JAK2/STAT3 pathway among other suggested pathways. While the α7 is well characterized as a ligand-gated ion channel in neurons, whole-cell patch clamp experiments suggest that α7's ion channel activity, defined as the translocation of ions across the membrane in response to ligands, is absent in leukocytes, and therefore, ion channel activity is generally assumed not to be required for the operation of the CAP. In this perspective, we briefly review macrophage α7 activation as it relates to the control of inflammation, and broaden the current view by providing single-channel currents as evidence that the α7 expressed in macrophages retains its ion translocation activity despite the absence of whole-cell currents. Whether this ion-translocating activity is relevant for the proper operation of the CAP or other important physiological processes remains obscure.
Collapse
Affiliation(s)
- Carlos A Báez-Pagán
- Department of Biology, University of Puerto Rico, Río Piedras Campus, PO Box 23360, San Juan, Puerto Rico, 00931,
| | | | | |
Collapse
|
42
|
Hernández-Vázquez F, Chavarría K, Garduño J, Hernández-López S, Mihailescu SP. Nicotine increases GABAergic input on rat dorsal raphe serotonergic neurons through alpha7 nicotinic acetylcholine receptor. J Neurophysiol 2014; 112:3154-63. [DOI: 10.1152/jn.00223.2014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The dorsal raphe nucleus (DRN) contains large populations of serotonergic (5-HT) neurons. This nucleus receives GABAergic inhibitory afferents from many brain areas and from DRN interneurons. Both GABAergic and 5-HT DRN neurons express functional nicotinic acetylcholine receptors (nAChRs). Previous studies have demonstrated that nicotine increases 5-HT release and 5-HT DRN neuron discharge rate by stimulating postsynaptic nAChRs and by increasing glutamate and norepinephrine release inside DRN. However, the influence of nicotine on the GABAergic input to 5-HT DRN neurons was poorly investigated. Therefore, the aim of this work was to determine the effect of nicotine on GABAergic spontaneous inhibitory postsynaptic currents (sIPSCs) of 5-HT DRN neurons and the subtype of nAChR(s) involved in this response. Experiments were performed in coronal slices obtained from young Wistar rats. GABAergic sIPSCs were recorded from post hoc-identified 5-HT DRN neurons with the whole cell voltage patch-clamp technique. Administration of nicotine (1 μM) increased sIPSC frequency in 72% of identified 5-HT DRN neurons. This effect was not reproduced by the α4β2 nAChR agonist RJR-2403 and was not influenced by TTX (1 μM). It was mimicked by the selective agonist for α7 nAChR, PNU-282987, and exacerbated by the positive allosteric modulator of the same receptor, PNU-120596. The nicotine-induced increase in sIPSC frequency was independent on voltage-gated calcium channels and dependent on Ca2+-induced Ca2+ release (CICR). These results demonstrate that nicotine increases the GABAergic input to most 5-HT DRN neurons, by activating α7 nAChRs and producing CICR in DRN GABAergic terminals.
Collapse
Affiliation(s)
- F. Hernández-Vázquez
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - K. Chavarría
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - J. Garduño
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - S. Hernández-López
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - S. P. Mihailescu
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, Mexico City, Mexico
| |
Collapse
|
43
|
Forman SA, Chiara DC, Miller KW. Anesthetics target interfacial transmembrane sites in nicotinic acetylcholine receptors. Neuropharmacology 2014; 96:169-77. [PMID: 25316107 DOI: 10.1016/j.neuropharm.2014.10.002] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2014] [Revised: 09/22/2014] [Accepted: 10/02/2014] [Indexed: 11/25/2022]
Abstract
General anesthetics are a heterogeneous group of small amphiphilic ligands that interact weakly at multiple allosteric sites on many pentameric ligand gated ion channels (pLGICs), resulting in either inhibition, potentiation of channel activity, or both. Allosteric principles imply that modulator sites must change configuration and ligand affinity during receptor state transitions. Thus, general anesthetics and related compounds are useful both as state-dependent probes of receptor structure and as potentially selective modulators of pLGIC functions. This review focuses on general anesthetic sites in nicotinic acetylcholine receptors, which were among the first anesthetic-sensitive pLGIC experimental models studied, with particular focus on sites formed by transmembrane domain elements. Structural models place many of these sites at interfaces between two or more pLGIC transmembrane helices both within subunits and between adjacent subunits, and between transmembrane helices and either lipids (the lipid-protein interface) or water (i.e. the ion channel). A single general anesthetic may bind at multiple allosteric sites in pLGICs, producing a net effect of either inhibition (e.g. blocking the ion channel) or enhanced channel gating (e.g. inter-subunit sites). Other general anesthetic sites identified by photolabeling or crystallography are tentatively linked to functional effects, including intra-subunit helix bundle sites and the lipid-protein interface. This article is part of the Special Issue entitled 'The Nicotinic Acetylcholine Receptor: From Molecular Biology to Cognition'.
Collapse
Affiliation(s)
- Stuart A Forman
- Dept. of Anesthesia Critical Care & Pain Medicine, Massachusetts General Hospital, Boston, 55 Fruit Street, MA 02114, USA; Dept. of Anaesthesia, Harvard Medical School, 25 Shattuck Street, Boston, MA 02115, USA.
| | - David C Chiara
- Dept. of Neurobiology, Harvard Medical School, 25 Shattuck Street, Boston, MA 02115, USA.
| | - Keith W Miller
- Dept. of Anesthesia Critical Care & Pain Medicine, Massachusetts General Hospital, Boston, 55 Fruit Street, MA 02114, USA; Dept. of Anaesthesia, Harvard Medical School, 25 Shattuck Street, Boston, MA 02115, USA.
| |
Collapse
|
44
|
Miller PS, Aricescu AR. Crystal structure of a human GABAA receptor. Nature 2014; 512:270-5. [PMID: 24909990 PMCID: PMC4167603 DOI: 10.1038/nature13293] [Citation(s) in RCA: 526] [Impact Index Per Article: 52.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2013] [Accepted: 03/28/2014] [Indexed: 01/01/2023]
Abstract
Type-A γ-aminobutyric acid receptors (GABAARs) are the principal mediators of rapid inhibitory synaptic transmission in the human brain. A decline in GABAAR signalling triggers hyperactive neurological disorders such as insomnia, anxiety and epilepsy. Here we present the first three-dimensional structure of a GABAAR, the human β3 homopentamer, at 3 Å resolution. This structure reveals architectural elements unique to eukaryotic Cys-loop receptors, explains the mechanistic consequences of multiple human disease mutations and shows an unexpected structural role for a conserved N-linked glycan. The receptor was crystallized bound to a previously unknown agonist, benzamidine, opening a new avenue for the rational design of GABAAR modulators. The channel region forms a closed gate at the base of the pore, representative of a desensitized state. These results offer new insights into the signalling mechanisms of pentameric ligand-gated ion channels and enhance current understanding of GABAergic neurotransmission.
Collapse
Affiliation(s)
- Paul S Miller
- Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, UK
| | - A Radu Aricescu
- Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, UK
| |
Collapse
|
45
|
Szabo AK, Pesti K, Mike A, Vizi ES. Mode of action of the positive modulator PNU-120596 on α7 nicotinic acetylcholine receptors. Neuropharmacology 2014; 81:42-54. [DOI: 10.1016/j.neuropharm.2014.01.033] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2013] [Revised: 01/13/2014] [Accepted: 01/21/2014] [Indexed: 01/13/2023]
|
46
|
Tillman TS, Seyoum E, Mowrey DD, Xu Y, Tang P. ELIC-α7 Nicotinic acetylcholine receptor (α7nAChR) chimeras reveal a prominent role of the extracellular-transmembrane domain interface in allosteric modulation. J Biol Chem 2014; 289:13851-7. [PMID: 24695730 PMCID: PMC4022858 DOI: 10.1074/jbc.m113.524611] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2013] [Revised: 03/10/2014] [Indexed: 01/08/2023] Open
Abstract
The native α7 nicotinic acetylcholine receptor (α7nAChR) is a homopentameric ligand-gated ion channel mediating fast synaptic transmission and is of pharmaceutical interest for treatment of numerous disorders. The transmembrane domain (TMD) of α7nAChR has been identified as a target for positive allosteric modulators (PAMs), but it is unclear whether modulation occurs through changes entirely within the TMD or changes involving both the TMD and the extracellular domain (ECD)-TMD interface. In this study, we constructed multiple chimeras using the TMD of human α7nAChR and the ECD of a prokaryotic homolog, ELIC, which is not sensitive to these modulators, and for which a high resolution structure has been solved. Functional ELIC-α7nAChR (EA) chimeras were obtained when their ECD-TMD interfaces were modified to resemble either the ELIC interface (EAELIC) or α7nAChR interface (EAα7). Both EAα7 and EAELIC show similar activation response and desensitization characteristics, but only EAα7 retained the unique pharmacology of α7nAChR evoked by PAMs, including potentiation by ivermectin, PNU-120596, and TQS, as well as activation by 4BP-TQS. This study suggests that PAM modulation through the TMD has a more stringent requirement at the ECD-TMD interface than agonist activation.
Collapse
Affiliation(s)
| | | | - David D Mowrey
- From the Departments of Anesthesiology, Computational and Systems Biology, and
| | - Yan Xu
- From the Departments of Anesthesiology, Pharmacology and Chemical Biology, Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15260
| | - Pei Tang
- From the Departments of Anesthesiology, Computational and Systems Biology, and Pharmacology and Chemical Biology,
| |
Collapse
|
47
|
Changeux JP. The concept of allosteric modulation: an overview. DRUG DISCOVERY TODAY. TECHNOLOGIES 2014; 10:e223-8. [PMID: 24050272 DOI: 10.1016/j.ddtec.2012.07.007] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
A brief historical overview of the concept of allosteric interaction is presented together with the different kinds of allosteric control recognized, in the past decades, with the model system of pentameric ligandgated ion channels. Multiple levels of allosteric modulation are identified that include sites distributed in the extracellular ligand binding domain (e.g. Ca2+ or benzodiazepines), the transmembrane domain (e.g. general anesthetic and various allosteric modulators) and the cytoplasmic domain, as potential targets for drug design. The new opportunities offered by the recent technological developments are discussed.
Collapse
|
48
|
Pesti K, Szabo AK, Mike A, Vizi ES. Kinetic properties and open probability of α7 nicotinic acetylcholine receptors. Neuropharmacology 2014; 81:101-15. [PMID: 24486379 DOI: 10.1016/j.neuropharm.2014.01.034] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2013] [Revised: 01/13/2014] [Accepted: 01/21/2014] [Indexed: 12/23/2022]
Abstract
The alpha7 nicotinic acetylcholine receptor (nAChR) has some peculiar kinetic properties. From the literature of α7 nAChR-mediated currents we concluded that experimentally measured kinetic properties reflected properties of the solution exchange system, rather than genuine kinetic properties of the receptors. We also concluded that all experimentally measured EC50 values for agonists must inherently be inaccurate. The aim of this study was to assess the undistorted kinetic properties of α7 nAChRs, and to construct an improved kinetic model, which can also serve as a basis of modeling the effect of the positive allosteric modulator PNU-120596, as it is described in the accompanying paper. Agonist-evoked currents were recorded from GH4C1 cells stably transfected with pCEP4/rat α7 nAChR using patch-clamp and fast solution exchange. We used two approaches to circumvent the problem of insufficient solution exchange rate: extrapolation and kinetic modeling. First, using different solution exchange rates we recorded evoked currents, and extrapolated their amplitude and kinetics to instantaneous solution exchange. Second, we constructed a kinetic model that reproduced concentration-dependence and solution exchange rate-dependence of receptors, and then we simulated receptor behavior at experimentally unattainably fast solution exchange. We also determined open probabilities during choline-evoked unmodulated and modulated currents using nonstationary fluctuation analysis. The peak open probability of 10 mM choline-evoked currents was 0.033 ± 0.006, while in the presence of choline (10 mM) and PNU-120596 (10 μM), it was increased to 0.599 ± 0.058. Our kinetic model could adequately reproduce low open probability, fast kinetics, fast recovery and solution exchange rate-dependent kinetics.
Collapse
Affiliation(s)
- Krisztina Pesti
- Semmelweis University, School of Ph.D. Studies, Üllői út 26, H-1085 Budapest, Hungary; Laboratory of Molecular Pharmacology, Institute of Experimental Medicine, Hungarian Academy of Sciences, P.O.B. 67, H-1450 Budapest, Hungary
| | - Anett K Szabo
- Semmelweis University, School of Ph.D. Studies, Üllői út 26, H-1085 Budapest, Hungary; Laboratory of Molecular Pharmacology, Institute of Experimental Medicine, Hungarian Academy of Sciences, P.O.B. 67, H-1450 Budapest, Hungary
| | - Arpad Mike
- Laboratory of Molecular Pharmacology, Institute of Experimental Medicine, Hungarian Academy of Sciences, P.O.B. 67, H-1450 Budapest, Hungary.
| | - E Sylvester Vizi
- Laboratory of Drug Research, Institute of Experimental Medicine, Hungarian Academy of Sciences, P.O.B. 67, H-1450 Budapest, Hungary
| |
Collapse
|
49
|
Abstract
Neuronal α7 nicotinic receptors elicit rapid cation influx in response to acetylcholine (ACh) or its hydrolysis product choline. They contribute to cognition, synaptic plasticity, and neuroprotection and have been implicated in neurodegenerative and neuropsychiatric disorders. α7, however, often localizes distal to sites of nerve-released ACh and binds ACh with low affinity, and thus elicits its biological response with low agonist occupancy. To assess the function of α7 when ACh occupies fewer than five of its identical binding sites, we measured the open-channel lifetime of individual receptors in which four of the five ACh binding sites were disabled. To improve the time resolution of the inherently brief α7 channel openings, background mutations or a potentiator was used to increase open duration. We find that, in receptors with only one intact binding site, the open-channel lifetime is indistinguishable from receptors with five intact binding sites, counter to expectations from prototypical neurotransmitter-gated ion channels where the open-channel lifetime increases with the number of binding sites occupied by agonist. Replacing the membrane-embedded domain of α7 by that of the related 5-HT3A receptor increases the number of sites that need to be occupied to achieve the maximal open-channel lifetime, thus revealing a unique interdependence between the detector and actuator domains of these receptors. The distinctive ability of a single occupancy to elicit a full biological response adapts α7 to volume transmission, a prevalent mechanism of ACh-mediated signaling in the nervous system and nonneuronal cells.
Collapse
|
50
|
Hamouda AK, Jayakar SS, Chiara DC, Cohen JB. Photoaffinity Labeling of Nicotinic Receptors: Diversity of Drug Binding Sites! J Mol Neurosci 2013; 53:480-6. [DOI: 10.1007/s12031-013-0150-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2013] [Accepted: 10/10/2013] [Indexed: 12/11/2022]
|