1
|
Sanders KM, Mutafova-Yambolieva VN. Neurotransmitters responsible for purinergic motor neurotransmission and regulation of GI motility. Auton Neurosci 2021; 234:102829. [PMID: 34146957 DOI: 10.1016/j.autneu.2021.102829] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 05/25/2021] [Accepted: 05/28/2021] [Indexed: 12/17/2022]
Abstract
Classical concepts of peripheral neurotransmission were insufficient to explain enteric inhibitory neurotransmission. Geoffrey Burnstock and colleagues developed the idea that ATP or a related purine satisfies the criteria for a neurotransmitter and serves as an enteric inhibitory neurotransmitter in GI muscles. Cloning of purinergic receptors and development of specific drugs and transgenic mice have shown that enteric inhibitory responses depend upon P2Y1 receptors in post-junctional cells. The post-junctional cells that transduce purinergic neurotransmitters in the GI tract are PDGFRα+ cells and not smooth muscle cells (SMCs). PDGFRα+ cells express P2Y1 receptors, are activated by enteric inhibitory nerve stimulation and generate Ca2+ oscillations, express small-conductance Ca2+-activated K+ channels (SK3), and generate outward currents when exposed to P2Y1 agonists. These properties are consistent with post-junctional purinergic responses, and similar responses and effectors are not functional in SMCs. Refinements in methodologies to measure purines in tissue superfusates, such as high-performance liquid chromatography (HPLC) coupled with etheno-derivatization of purines and fluorescence detection, revealed that multiple purines are released during stimulation of intrinsic nerves. β-NAD+ and other purines, better satisfy criteria for the purinergic neurotransmitter than ATP. HPLC has also allowed better detection of purine metabolites, and coupled with isolation of specific types of post-junctional cells, has provided new concepts about deactivation of purine neurotransmitters. In spite of steady progress, many unknowns about purinergic neurotransmission remain and require additional investigation to understand this important regulatory mechanism in GI motility.
Collapse
Affiliation(s)
- Kenton M Sanders
- Department of Physiology and Cell Biology, University of Nevada, School of Medicine, 1664 North Virginia Street, Reno, NV 89557, USA.
| | - Violeta N Mutafova-Yambolieva
- Department of Physiology and Cell Biology, University of Nevada, School of Medicine, 1664 North Virginia Street, Reno, NV 89557, USA
| |
Collapse
|
2
|
Qudah T, Quek GX, Indurthi D, Karim N, Halliday JI, Absalom N, McLeod MD, Chebib M. AE Succinimide, an Analogue of Methyllycaconitine, When Bound Generates a Nonconducting Conformation of the α4β2 Nicotinic Acetylcholine Receptor. ACS Chem Neurosci 2020; 11:344-355. [PMID: 31898891 DOI: 10.1021/acschemneuro.9b00525] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Nicotinic acetylcholine (nACh) receptors are pentameric ligand-gated ion channels that mediate fast synaptic transmission. The α4β2 nACh receptor is highly expressed in the brain and exists in two functional stoichiometries: the (α4)2(β2)3 and (α4)3(β2)2 that differ by an ACh-binding site at the α4-α4 interface of (α4)3(β2)2 receptors. Methyllycaconitine (MLA) is an nACh receptor antagonist, and while potent at both α7 and α4β2 nACh receptors, it has a higher selectivity for the α7 nACh receptor. The anthranilate-succinimide ester side-chain is important for its activity and selectivity. Here we identify a simplified MLA analogue that contains only the A and E ring skeleton of MLA, AE succinimide, that binds close to the channel lumen to display insurmountable inhibition at α4β2 nACh receptors. Although inhibition by AE succinimide was found to be voltage-dependent indicating a possible pore channel blocker, substituted-cysteine accessibility experiments indicated it did not bind between 2'-16' region of the channel pore. Instead, we found that upon binding and in the presence of ACh, there is a conformational change to the channel membrane that was identified when the compound was assessed against (α4 V13'C)β2 nACh receptors. It was found that in the 3:2 stoichiometry the two adjacent α4 subunits containing 13' cysteine mutations formed a disulfide bond and occluded ion conductance. This was reversed by treatment with the reducing agent, dithiothreitol. Thus, AE succinimide has a different mechanism of inhibition to both MLA and other AE analogues, such as AE bicyclic alcohol, in that upon binding to an as yet unidentified site, AE succinimide in the presence of ACh induces a conformational change to the channel that generates a ligand-bound closed state.
Collapse
Affiliation(s)
- Taima Qudah
- Brain and Mind Centre, School of Pharmacy, Faculty of Medicine and Health, Sydney, NSW 2050, The University of Sydney
| | - Gracia X. Quek
- Brain and Mind Centre, School of Pharmacy, Faculty of Medicine and Health, Sydney, NSW 2050, The University of Sydney
| | - Dinesh Indurthi
- Brain and Mind Centre, School of Pharmacy, Faculty of Medicine and Health, Sydney, NSW 2050, The University of Sydney
| | - Nasiara Karim
- Brain and Mind Centre, School of Pharmacy, Faculty of Medicine and Health, Sydney, NSW 2050, The University of Sydney
| | - Jill I. Halliday
- Research School of Chemistry, College of Science, The Australian National University, Canberra, ACT 2601, Australia
| | - Nathan Absalom
- Brain and Mind Centre, School of Pharmacy, Faculty of Medicine and Health, Sydney, NSW 2050, The University of Sydney
| | - Malcolm D. McLeod
- Research School of Chemistry, College of Science, The Australian National University, Canberra, ACT 2601, Australia
| | - Mary Chebib
- Brain and Mind Centre, School of Pharmacy, Faculty of Medicine and Health, Sydney, NSW 2050, The University of Sydney
| |
Collapse
|
3
|
A novel pharmacological activity of caffeine in the cholinergic system. Neuropharmacology 2018; 135:464-473. [DOI: 10.1016/j.neuropharm.2018.03.041] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2018] [Revised: 03/23/2018] [Accepted: 03/30/2018] [Indexed: 12/11/2022]
|
4
|
Degani-Katzav N, Gortler R, Weissman M, Paas Y. Mutational Analysis at Intersubunit Interfaces of an Anionic Glutamate Receptor Reveals a Key Interaction Important for Channel Gating by Ivermectin. Front Mol Neurosci 2017; 10:92. [PMID: 28428744 PMCID: PMC5382172 DOI: 10.3389/fnmol.2017.00092] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2016] [Accepted: 03/17/2017] [Indexed: 11/13/2022] Open
Abstract
The broad-spectrum anthelmintic drug ivermectin (IVM) activates and stabilizes an open-channel conformation of invertebrate chloride-selective glutamate receptors (GluClRs), thereby causing a continuous inflow of chloride ions and sustained membrane hyperpolarization. These effects suppress nervous impulses and vital physiological processes in parasitic nematodes. The GluClRs are pentamers. Homopentameric receptors assembled from the Caenorhabditis elegans (C. elegans) GluClα (GLC-1) subunit can inherently respond to IVM but not to glutamate (the neurotransmitter). In contrast, heteromeric GluClα/β (GLC-1/GLC-2) assemblies respond to both ligands, independently of each other. Glutamate and IVM bind at the interface between adjacent subunits, far away from each other; glutamate in the extracellular ligand-binding domain, and IVM in the ion-channel pore periphery. To understand the importance of putative intersubunit contacts located outside the glutamate and IVM binding sites, we introduced mutations at intersubunit interfaces, between these two binding-site types. Then, we determined the effect of these mutations on the activation of the heteromeric mutant receptors by glutamate and IVM. Amongst these mutations, we characterized an α-subunit point mutation located close to the putative IVM-binding pocket, in the extracellular end of the first transmembrane helix (M1). This mutation (αF276A) moderately reduced the sensitivity of the heteromeric GluClαF276A/βWT receptor to glutamate, and slightly decreased the receptor subunits’ cooperativity in response to glutamate. In contrast, the αF276A mutation drastically reduced the sensitivity of the receptor to IVM and significantly increased the receptor subunits’ cooperativity in response to IVM. We suggest that this mutation reduces the efficacy of channel gating, and impairs the integrity of the IVM-binding pocket, likely by disrupting important interactions between the tip of M1 and the M2-M3 loop of an adjacent subunit. We hypothesize that this physical contact between M1 and the M2-M3 loop tunes the relative orientation of the ion-channel transmembrane helices M1, M2 and M3 to optimize pore opening. Interestingly, pre-exposure of the GluClαF276A/βWT mutant receptor to subthreshold IVM concentration recovered the receptor sensitivity to glutamate. We infer that IVM likely retained its positive modulation activity by constraining the transmembrane helices in a preopen orientation sensitive to glutamate, with no need for the aforementioned disrupted interactions between M1 and the M2-M3 loop.
Collapse
Affiliation(s)
- Nurit Degani-Katzav
- Laboratory of Ion Channels, The Mina and Everard Goodman Faculty of Life Sciences, Institute of Nanotechnology and Advanced Materials, Bar-Ilan UniversityRamat Gan, Israel
| | - Revital Gortler
- Laboratory of Ion Channels, The Mina and Everard Goodman Faculty of Life Sciences, Institute of Nanotechnology and Advanced Materials, Bar-Ilan UniversityRamat Gan, Israel
| | - Marina Weissman
- Laboratory of Ion Channels, The Mina and Everard Goodman Faculty of Life Sciences, Institute of Nanotechnology and Advanced Materials, Bar-Ilan UniversityRamat Gan, Israel
| | - Yoav Paas
- Laboratory of Ion Channels, The Mina and Everard Goodman Faculty of Life Sciences, Institute of Nanotechnology and Advanced Materials, Bar-Ilan UniversityRamat Gan, Israel
| |
Collapse
|
5
|
Nkohkwo A, Agbor G, Asongalem E, Tagny C, Asonganyi T. Whole blood pathogen reduction technology and blood safety in sub-Saharan Africa: A systematic review with regional discussion. Afr J Lab Med 2016; 5:363. [PMID: 28879109 PMCID: PMC5436399 DOI: 10.4102/ajlm.v5i1.363] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2015] [Accepted: 03/01/2016] [Indexed: 11/17/2022] Open
Abstract
Background Despite vast improvements in transfusion services in sub-Saharan Africa over the last decade, there remain serious concerns on the safety and adequacy of the blood supply across the region. Objective This review paper ascertains the role of pathogen reduction technology (PRT) in improving blood safety and supply adequacy in the region. Method The state of blood safety in sub-Saharan Africa was reviewed. Meetings, seminars and correspondence were undertaken with key clinicians, scientists and professional bodies in the region, including the World Health Organization’s Regional Office for Africa, to examine the suitability of PRT for improving the safety of whole blood transfusion, a prevalent transfusion format in the region. Results Existing literature suggests that combining PRT with current blood safety measures (such as serology) would improve the safety and adequacy of the blood supply for transfusions in sub-Saharan Africa. This was echoed by the findings of the stakeholder meetings. Conclusion Following a detailed appraisal of two leading PRT systems, the Mirasol® PRT System and the Cerus S-303 System, we suggest that companies conduct comprehensive toxicological evaluation of the agents used for PRT and publish this in the scientific literature. We also recommend that the safety and efficacy of these technologies should be established in a randomised clinical trial conducted in sub-Saharan Africa.
Collapse
Affiliation(s)
| | - Gabriel Agbor
- Department of Biochemistry, Institute of Medical Research and Medicinal Plants Studies, Yaoundé, Cameroon
| | - Emmanuel Asongalem
- Department of Biomedical Sciences, Faculty of Health Sciences, University of Buea and Toxicology Society, Buea, Cameroon
| | - Claude Tagny
- Haematology and Blood Transfusion Service, University Teaching Hospital, Yaoundé, Cameroon
| | - Tazoacha Asonganyi
- Department of Biochemistry and Immunology, Faculty of Medicine and Biomedical Sciences, University of Yaoundé 1, Yaoundé, Cameroon
| |
Collapse
|
6
|
Dym O, Song W, Felder C, Roth E, Shnyrov V, Ashani Y, Xu Y, Joosten RP, Weiner L, Sussman JL, Silman I. The impact of crystallization conditions on structure-based drug design: A case study on the methylene blue/acetylcholinesterase complex. Protein Sci 2016; 25:1096-114. [PMID: 26990888 DOI: 10.1002/pro.2923] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Accepted: 03/07/2016] [Indexed: 11/05/2022]
Abstract
Structure-based drug design utilizes apoprotein or complex structures retrieved from the PDB. >57% of crystallographic PDB entries were obtained with polyethylene glycols (PEGs) as precipitant and/or as cryoprotectant, but <6% of these report presence of individual ethyleneglycol oligomers. We report a case in which ethyleneglycol oligomers' presence in a crystal structure markedly affected the bound ligand's position. Specifically, we compared the positions of methylene blue and decamethonium in acetylcholinesterase complexes obtained using isomorphous crystals precipitated with PEG200 or ammonium sulfate. The ligands' positions within the active-site gorge in complexes obtained using PEG200 are influenced by presence of ethyleneglycol oligomers in both cases bound to W84 at the gorge's bottom, preventing interaction of the ligand's proximal quaternary group with its indole. Consequently, both ligands are ∼3.0Å further up the gorge than in complexes obtained using crystals precipitated with ammonium sulfate, in which the quaternary groups make direct π-cation interactions with the indole. These findings have implications for structure-based drug design, since data for ligand-protein complexes with polyethylene glycol as precipitant may not reflect the ligand's position in its absence, and could result in selecting incorrect drug discovery leads. Docking methylene blue into the structure obtained with PEG200, but omitting the ethyleneglycols, yields results agreeing poorly with the crystal structure; excellent agreement is obtained if they are included. Many proteins display features in which precipitants might lodge. It will be important to investigate presence of precipitants in published crystal structures, and whether it has resulted in misinterpreting electron density maps, adversely affecting drug design.
Collapse
Affiliation(s)
- Orly Dym
- Israel Structural Proteomics Center, Weizmann Institute of Science, Rehovot, 76100, Israel.,Department of Biological Chemistry, Weizmann Institute of Science, Rehovot, 76100, Israel
| | - Wanling Song
- CAS Key Laboratory of Receptor Research, Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences (CAS), Shanghai (22), China
| | - Clifford Felder
- Department of Structural Biology, Weizmann Institute of Science, Rehovot, 76100, Israel
| | - Esther Roth
- Department of Neurobiology, Weizmann Institute of Science, Rehovot, 76100, Israel
| | - Valery Shnyrov
- Department of Biochemistry and Molecular Biology, Universidad de Salamanca, Salamanca, 37007, Spain
| | - Yacov Ashani
- Department of Structural Biology, Weizmann Institute of Science, Rehovot, 76100, Israel
| | - Yechun Xu
- CAS Key Laboratory of Receptor Research, Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences (CAS), Shanghai (22), China
| | - Robbie P Joosten
- Department of Biochemistry, Netherlands Cancer Institute, Amsterdam, CX, 1066, the Netherlands
| | - Lev Weiner
- Department of Chemical Research Support, Weizmann Institute of Science, Rehovot, 76100, Israel
| | - Joel L Sussman
- Israel Structural Proteomics Center, Weizmann Institute of Science, Rehovot, 76100, Israel.,Department of Structural Biology, Weizmann Institute of Science, Rehovot, 76100, Israel
| | - Israel Silman
- Department of Neurobiology, Weizmann Institute of Science, Rehovot, 76100, Israel
| |
Collapse
|
7
|
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
|
8
|
Mutafova-Yambolieva VN, Durnin L. The purinergic neurotransmitter revisited: a single substance or multiple players? Pharmacol Ther 2014; 144:162-91. [PMID: 24887688 PMCID: PMC4185222 DOI: 10.1016/j.pharmthera.2014.05.012] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2014] [Accepted: 05/23/2014] [Indexed: 12/20/2022]
Abstract
The past half century has witnessed tremendous advances in our understanding of extracellular purinergic signaling pathways. Purinergic neurotransmission, in particular, has emerged as a key contributor in the efficient control mechanisms in the nervous system. The identity of the purine neurotransmitter, however, remains controversial. Identifying it is difficult because purines are present in all cell types, have a large variety of cell sources, and are released via numerous pathways. Moreover, studies on purinergic neurotransmission have relied heavily on indirect measurements of integrated postjunctional responses that do not provide direct information for neurotransmitter identity. This paper discusses experimental support for adenosine 5'-triphosphate (ATP) as a neurotransmitter and recent evidence for possible contribution of other purines, in addition to or instead of ATP, in chemical neurotransmission in the peripheral, enteric and central nervous systems. Sites of release and action of purines in model systems such as vas deferens, blood vessels, urinary bladder and chromaffin cells are discussed. This is preceded by a brief discussion of studies demonstrating storage of purines in synaptic vesicles. We examine recent evidence for cell type targets (e.g., smooth muscle cells, interstitial cells, neurons and glia) for purine neurotransmitters in different systems. This is followed by brief discussion of mechanisms of terminating the action of purine neurotransmitters, including extracellular nucleotide hydrolysis and possible salvage and reuptake in the cell. The significance of direct neurotransmitter release measurements is highlighted. Possibilities for involvement of multiple purines (e.g., ATP, ADP, NAD(+), ADP-ribose, adenosine, and diadenosine polyphosphates) in neurotransmission are considered throughout.
Collapse
Affiliation(s)
| | - Leonie Durnin
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV 89557, United States
| |
Collapse
|
9
|
Growe RG, Luster MI, Fail PA, Lippes J. Quinacrine-induced occlusive fibrosis in the human fallopian tube is due to a unique inflammatory response and modification of repair mechanisms. J Reprod Immunol 2013; 97:159-66. [PMID: 23453701 DOI: 10.1016/j.jri.2012.12.003] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2012] [Revised: 12/11/2012] [Accepted: 12/13/2012] [Indexed: 12/17/2022]
Abstract
Quinacrine has been widely used in treatment of parasitic diseases such as malaria and giardiasis, and in the treatment of autoimmune diseases. Quinacrine has also been used as an effective substitute for surgical contraception by causing occlusion of the fallopian tube. This minimally invasive treatment protocol involves intrauterine insertion of the drug in the form of pellets and has been studied in humans in a number of countries, including the United States. Despite its development in the 1970s, the cellular and molecular events induced by quinacrine in the human fallopian tube have not been described. Here we describe a plausible mechanism for quinacrine action in the fallopian tube. This is manifested as an acute pro-inflammatory response in the uterus and fallopian tube, characterized by loss of epithelial cell adhesion. This response relies on properties of gated channels found on the surface of epithelial cells in the reproductive tract. While the uterus returns to normal, the inflammatory response affects the uterotubal junction and transmural segment of the human fallopian tube, and initiates formation of mature collagen in the lumen of the fallopian tube, resulting in its permanent occlusion. The response within the fallopian tube appears similar to the protective mechanisms that have evolved in women to minimize the likelihood of systemic infection from Neisseria gonorrhoeae, and to some extent from Chlamydia trachomatis. This review could assist in development of experimental models used in investigating the mechanisms of fibrotic responses in humans as well as development of techniques for permanent non-surgical female contraception.
Collapse
Affiliation(s)
- Roger G Growe
- International Federation for Family Health, Chapel Hill, NC, USA
| | | | | | | |
Collapse
|
10
|
Spurny R, Billen B, Howard RJ, Brams M, Debaveye S, Price KL, Weston DA, Strelkov SV, Tytgat J, Bertrand S, Bertrand D, Lummis SCR, Ulens C. Multisite binding of a general anesthetic to the prokaryotic pentameric Erwinia chrysanthemi ligand-gated ion channel (ELIC). J Biol Chem 2013; 288:8355-8364. [PMID: 23364792 PMCID: PMC3605653 DOI: 10.1074/jbc.m112.424507] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs), such as nicotinic acetylcholine, glycine, γ-aminobutyric acid GABAA/C receptors, and the Gloeobacter violaceus ligand-gated ion channel (GLIC), are receptors that contain multiple allosteric binding sites for a variety of therapeutics, including general anesthetics. Here, we report the x-ray crystal structure of the Erwinia chrysanthemi ligand-gated ion channel (ELIC) in complex with a derivative of chloroform, which reveals important features of anesthetic recognition, involving multiple binding at three different sites. One site is located in the channel pore and equates with a noncompetitive inhibitor site found in many pLGICs. A second transmembrane site is novel and is located in the lower part of the transmembrane domain, at an interface formed between adjacent subunits. A third site is also novel and is located in the extracellular domain in a hydrophobic pocket between the β7–β10 strands. Together, these results extend our understanding of pLGIC modulation and reveal several specific binding interactions that may contribute to modulator recognition, further substantiating a multisite model of allosteric modulation in this family of ion channels.
Collapse
Affiliation(s)
- Radovan Spurny
- Laboratory of Structural Neurobiology, Department of Cellular and Molecular Medicine, KU Leuven, Herestraat 49, PB 601, B-3000 Leuven, Belgium
| | - Bert Billen
- Laboratory of Structural Neurobiology, Department of Cellular and Molecular Medicine, KU Leuven, Herestraat 49, PB 601, B-3000 Leuven, Belgium
| | - Rebecca J Howard
- Waggoner Center for Alcohol and Addiction Research, The University of Texas, Austin, Texas 78712
| | - Marijke Brams
- Laboratory of Structural Neurobiology, Department of Cellular and Molecular Medicine, KU Leuven, Herestraat 49, PB 601, B-3000 Leuven, Belgium
| | - Sarah Debaveye
- Laboratory of Structural Neurobiology, Department of Cellular and Molecular Medicine, KU Leuven, Herestraat 49, PB 601, B-3000 Leuven, Belgium
| | - Kerry L Price
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB 1QW, United Kingdom
| | - David A Weston
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB 1QW, United Kingdom
| | - Sergei V Strelkov
- Laboratory of Biocrystallography, KU Leuven, Herestraat 49, PB 822, B-3000 Leuven, Belgium
| | - Jan Tytgat
- Laboratory of Toxicology, KU Leuven, Herestraat 49, PB 922, B-3000 Leuven, Belgium
| | - Sonia Bertrand
- HiQScreen Sàrl, 15 rue de l'Athénée, Case Postale 209, CH-1211 Geneva 12, Switzerland
| | - Daniel Bertrand
- HiQScreen Sàrl, 15 rue de l'Athénée, Case Postale 209, CH-1211 Geneva 12, Switzerland
| | - Sarah C R Lummis
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB 1QW, United Kingdom
| | - Chris Ulens
- Laboratory of Structural Neurobiology, Department of Cellular and Molecular Medicine, KU Leuven, Herestraat 49, PB 601, B-3000 Leuven, Belgium.
| |
Collapse
|
11
|
Pandhare A, Hamouda AK, Staggs B, Aggarwal S, Duddempudi PK, Lever JR, Lapinsky DJ, Jansen M, Cohen JB, Blanton MP. Bupropion binds to two sites in the Torpedo nicotinic acetylcholine receptor transmembrane domain: a photoaffinity labeling study with the bupropion analogue [(125)I]-SADU-3-72. Biochemistry 2012; 51:2425-35. [PMID: 22394379 DOI: 10.1021/bi300101r] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Bupropion, a clinically used antidepressant and smoking-cessation drug, acts as a noncompetitive antagonist of nicotinic acetylcholine receptors (nAChRs). To identify its binding site(s) in nAChRs, we developed a photoreactive bupropion analogue, (±)-2-(N-tert-butylamino)-3'-[(125)I]-iodo-4'-azidopropiophenone (SADU-3-72). Based on inhibition of [(125)I]SADU-3-72 binding, SADU-3-72 binds with high affinity (IC(50) = 0.8 μM) to the Torpedo nAChR in the resting (closed channel) state and in the agonist-induced desensitized state, and bupropion binds to that site with 3-fold higher affinity in the desensitized (IC(50) = 1.2 μM) than in the resting state. Photolabeling of Torpedo nAChRs with [(125)I]SADU-3-72 followed by limited in-gel digestion of nAChR subunits with endoproteinase Glu-C established the presence of [(125)I]SADU-3-72 photoincorporation within nAChR subunit fragments containing M1-M2-M3 helices (αV8-20K, βV8-22/23K, and γV8-24K) or M1-M2 helices (δV8-14). Photolabeling within βV8-22/23K, γV8-24K, and δV8-14 was reduced in the desensitized state and inhibited by ion channel blockers selective for the resting (tetracaine) or desensitized (thienycyclohexylpiperidine (TCP)) state, and this pharmacologically specific photolabeling was localized to the M2-9 leucine ring (δLeu(265), βLeu(257)) within the ion channel. In contrast, photolabeling within the αV8-20K was enhanced in the desensitized state and not inhibited by TCP but was inhibited by bupropion. This agonist-enhanced photolabeling was localized to αTyr(213) in αM1. These results establish the presence of two distinct bupropion binding sites within the Torpedo nAChR transmembrane domain: a high affinity site at the middle (M2-9) of the ion channel and a second site near the extracellular end of αM1 within a previously described halothane (general anesthetic) binding pocket.
Collapse
Affiliation(s)
- Akash Pandhare
- Department of Pharmacology and Neuroscience and the Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, United States
| | | | | | | | | | | | | | | | | | | |
Collapse
|
12
|
Ambrus JI, Halliday JI, Kanizaj N, Absalom N, Harpsøe K, Balle T, Chebib M, McLeod MD. Covalent attachment of antagonists to the α7 nicotinic acetylcholine receptor: synthesis and reactivity of substituted maleimides. Chem Commun (Camb) 2012; 48:6699-701. [DOI: 10.1039/c2cc32442c] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
|
13
|
Quek GXJ, Lin D, Halliday JI, Absalom N, Ambrus JI, Thompson AJ, Lochner M, Lummis SCR, McLeod MD, Chebib M. Identifying the binding site of novel methyllycaconitine (MLA) analogs at α4β2 nicotinic acetylcholine receptors. ACS Chem Neurosci 2010; 1:796-809. [PMID: 22778816 DOI: 10.1021/cn100073x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2010] [Accepted: 09/14/2010] [Indexed: 12/24/2022] Open
Abstract
Neuronal nicotinic acetylcholine receptors (nAChR) are ligand gated ion channels that mediate fast synaptic transmission. Methyllycaconitine (MLA) is a selective and potent antagonist of the α7 nAChR, and its anthranilate ester side-chain is important for its activity. Here we report the influence of structure on nAChR inhibition for a series of novel MLA analogs, incorporating either an alcohol or anthranilate ester side-chain to an azabicyclic or azatricyclic core against rat α7, α4β2, and α3β4 nAChRs expressed in Xenopus oocytes. The analogs inhibited ACh (EC(50)) within an IC(50) range of 2.3-26.6 μM. Most displayed noncompetitive antagonism, but the anthranilate ester analogs exerted competitive behavior at the α7 nAChR. At α4β2 nAChRs, inhibition by the azabicyclic alcohol was voltage-dependent suggesting channel block. The channel-lining residues of α4 subunits were mutated to cysteine and the effect of azabicyclic alcohol was evaluated by competition with methanethiosulfonate ethylammonium (MTSEA) and a thiol-reactive probe in the open, closed, and desensitized states of α4β2 nAChRs. The azabicyclic alcohol was found to compete with MTSEA between residues 6' and 13' in a state-dependent manner, but the reactive probe only bonded with 13' in the open state. The data suggest that the 13' position is the dominant binding site. Ligand docking of the azabicyclic alcohol into a (α4)(3)(β2)(2) homology model of the closed channel showed that the ligand can be accommodated at this location. Thus our data reveal distinct pharmacological differences between different nAChR subtypes and also identify a specific binding site for a noncompetitive channel blocker.
Collapse
Affiliation(s)
| | - Diana Lin
- Faculty of Pharmacy, The University of Sydney, Australia
| | - Jill I. Halliday
- Research School of Chemistry, The Australian National University, Australia
| | - Nathan Absalom
- Faculty of Pharmacy, The University of Sydney, Australia
| | - Joseph I. Ambrus
- Research School of Chemistry, The Australian National University, Australia
| | | | - Martin Lochner
- Department of Chemistry and Biochemistry, University of Bern, Switzerland
| | | | - Malcolm D. McLeod
- Research School of Chemistry, The Australian National University, Australia
| | - Mary Chebib
- Faculty of Pharmacy, The University of Sydney, Australia
| |
Collapse
|
14
|
Hilf RJC, Bertozzi C, Zimmermann I, Reiter A, Trauner D, Dutzler R. Structural basis of open channel block in a prokaryotic pentameric ligand-gated ion channel. Nat Struct Mol Biol 2010; 17:1330-6. [PMID: 21037567 DOI: 10.1038/nsmb.1933] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2010] [Accepted: 09/07/2010] [Indexed: 11/09/2022]
Abstract
The flow of ions through cation-selective members of the pentameric ligand-gated ion channel family is inhibited by a structurally diverse class of molecules that bind to the transmembrane pore in the open state of the protein. To obtain insight into the mechanism of channel block, we have investigated the binding of positively charged inhibitors to the open channel of the bacterial homolog GLIC by using X-ray crystallography and electrophysiology. Our studies reveal the location of two regions for interactions, with larger blockers binding in the center of the membrane and divalent transition metal ions binding to the narrow intracellular pore entry. The results provide a structural foundation for understanding the interactions of the channel with inhibitors that is relevant for the entire family.
Collapse
Affiliation(s)
- Ricarda J C Hilf
- Department of Biochemistry, University of Zürich, Zürich, Switzerland
| | | | | | | | | | | |
Collapse
|
15
|
Xu Y, Barrantes FJ, Shen J, Luo X, Zhu W, Chen K, Jiang H. Blocking of the Nicotinic Acetylcholine Receptor Ion Channel by Chlorpromazine, a Noncompetitive Inhibitor: A Molecular Dynamics Simulation Study. J Phys Chem B 2006; 110:20640-8. [PMID: 17034254 DOI: 10.1021/jp0604591] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A large series of pharmacological agents, distinct from the typical competitive antagonists, block in a noncompetitive manner the permeability response of the nicotinic acetylcholine receptor (nAChR) to the neurotransmitter acetylcholine. Taking the neuroleptic chlorpromazine (CPZ) as an example of such agents, the blocking mechanism of noncompetitive inhibitors to the ion channel pore of the nAChR has been explored at the atomic level using both conventional and steered molecular dynamics (MD) simulations. Repeated steered MD simulations have permitted calculation of the free energy (approximately 36 kJ/mol) of CPZ binding and identification of the optimal site in the region of the serine and leucine rings, at approximately 4 A from the pore entrance. Coulomb and the Lennard-Jones interactions between CPZ and the ion channel as well as the conformational fluctuations of CPZ were examined to assess the contribution of each to the binding of CPZ to the nAChR. The MD simulations disclose a dynamic interaction of CPZ binding to the nAChR ionic channel. The cationic ammonium head of CPZ forms strong hydrogen bonds with Glu262 (alpha), Asp268 (beta), Glu272 (beta), Ser276 (beta), Glu280 (delta), Gln271 (gamma), Glu275 (gamma), and Asn279 (gamma) nAChR residues. Finally, the conventional MD simulation of CPZ at its identified binding site demonstrates that the binding of CPZ not only blocks ion transport through the channel but also markedly inhibits the conformational transitions of the channel, necessary for nAChR to carry out its biological function.
Collapse
Affiliation(s)
- Yechun Xu
- Drug Discovery and Design Centre, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Shanghai Institutes for Biological Sciences, and Graduate School, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai 201203, China
| | | | | | | | | | | | | |
Collapse
|
16
|
Abstract
Ligand-gated ion channels (LGICs) are fast-responding channels in which the receptor, which binds the activating molecule (the ligand), and the ion channel are part of the same nanomolecular protein complex. This paper will describe the properties and functions of the nicotinic acetylcholine LGIC superfamily, which plays a critical role in the fast chemical transmission of electrical signals between nerve cells and between nerve and muscle cells. The superfamily will mainly be exemplified by the excitatory nicotinic acetylcholine receptor (nAChR) and the inhibitory glycine receptor (GlyR) channels.
Collapse
Affiliation(s)
- Peter H Barry
- School of Medical Sciences at the University of New South Wales, Sydney, NSW 2052, Australia.
| | | |
Collapse
|
17
|
Tikhonov DB, Mellor IR, Usherwood PNR. Modeling noncompetitive antagonism of a nicotinic acetylcholine receptor. Biophys J 2005; 87:159-70. [PMID: 15240454 PMCID: PMC1304339 DOI: 10.1529/biophysj.103.037457] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Models of closed and open channel pores of a muscle-type nicotinic acetylcholine receptor (nAChR) channel comprising M1 and M2 segments are presented. A model of the closed channel is proposed in which hydrophobic residues of the Equatorial Leucine ring screen the oxygen domain formed by the Serine ring, thereby preventing ion flux without completely occluding the pore. This model demonstrates a high similarity with the structure derived from a recent electron microscopy study. We propose that hydrophobic residues of the Equatorial Leucine ring are retracted when the pore is open. Our models provide a possible resolution of the nAChR gate controversy. We have also obtained explanations for the complex mechanisms underlying inhibition of nAChR by philanthotoxins (PhTXs). PhTX-343, containing a spermine moiety with a charge of +3, binds deep in the pore near the Serine ring where classical open channel blockers of nAChR bind. In contrast, PhTX-(12), which has a single charged amino group is unable to reach deeply located rings because of steric restrictions. Both philanthotoxins may bind to a hydrophobic site located close to the external entrance of the pore in a region that includes residues associated with the regulation of desensitization.
Collapse
Affiliation(s)
- Denis B Tikhonov
- Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg 194223, Russia
| | | | | |
Collapse
|