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Wang J, Zhang Z, Yu N, Wu X, Guo Z, Yan Y, Liu Z. Cys-loop ligand-gated ion channel superfamily of Pardosa pseudoannulata: Implication for natural enemy safety. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. PART D, GENOMICS & PROTEOMICS 2024; 49:101190. [PMID: 38278045 DOI: 10.1016/j.cbd.2024.101190] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Revised: 12/21/2023] [Accepted: 01/06/2024] [Indexed: 01/28/2024]
Abstract
Cys-loop ligand-gated channels mediate neurotransmission in insects and are receptors for many insecticides. Some insecticides acting on cysLGIC also have lethal effects on non-targeting organisms, but the mechanism of this negative effect is unclear due to information absence. The identification and analysis of cysLGIC family in Pardosa pseudoannulata, a pond wolf spider, can deepen the understanding of insecticides for natural enemy safety. Thirty-four cysLGIC genes were identified in P. pseudoannulata genome, including nicotinic acetylcholine receptors, γ-aminobutyric acid gated chloride channels, glutamate-gated chloride channels, histamine-gated chloride channels, and pH-sensitive chloride channels. The expansion of GABACls and HisCls accounts for the large number of cysLGICs in P. pseudoannulata, and the alternative splicing events in nAChR and RDL subunits enriched the diversity of the superfamily. Most cysLGIC genes show the highest expression in brain and lowest expression in the early-egg sac stage. Variable residues (R81, V83, R135, N137, F190, and W197) in P. pseudoannulata nAChR β subunits and critical differences in α6 subunit TM4 region compared with insects would apply for the insensitivity to neonicotinoids and spinosyn. In contrast, avermectin and dieldrin may be lethal to P. pseudoannulata due to the similar drugs binding sites in GluCls compared with insects. These findings will provide a valuable clue for natural enemy protection and environmentally friendly insecticide development.
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Affiliation(s)
- Jingting Wang
- Key laboratory of Integrated Management of Crop Diseases and Pests (Ministry of Education), College of Plant Protection, Nanjing Agricultural University, Weigang 1, Nanjing 210095, China
| | - Zhen Zhang
- Key laboratory of Integrated Management of Crop Diseases and Pests (Ministry of Education), College of Plant Protection, Nanjing Agricultural University, Weigang 1, Nanjing 210095, China
| | - Na Yu
- Key laboratory of Integrated Management of Crop Diseases and Pests (Ministry of Education), College of Plant Protection, Nanjing Agricultural University, Weigang 1, Nanjing 210095, China
| | - Xun Wu
- Key laboratory of Integrated Management of Crop Diseases and Pests (Ministry of Education), College of Plant Protection, Nanjing Agricultural University, Weigang 1, Nanjing 210095, China
| | - Zonglei Guo
- Key laboratory of Integrated Management of Crop Diseases and Pests (Ministry of Education), College of Plant Protection, Nanjing Agricultural University, Weigang 1, Nanjing 210095, China
| | - Yangyang Yan
- Key laboratory of Integrated Management of Crop Diseases and Pests (Ministry of Education), College of Plant Protection, Nanjing Agricultural University, Weigang 1, Nanjing 210095, China
| | - Zewen Liu
- Key laboratory of Integrated Management of Crop Diseases and Pests (Ministry of Education), College of Plant Protection, Nanjing Agricultural University, Weigang 1, Nanjing 210095, China.
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Habibi S, Nazareth K, Nichols J, Varley S, Forrester SG. The Haemonchus contortus LGC-39 subunit is a novel subtype of an acetylcholine-gated chloride channel. Int J Parasitol Drugs Drug Resist 2023; 22:20-26. [PMID: 37054482 PMCID: PMC10122009 DOI: 10.1016/j.ijpddr.2023.04.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2022] [Revised: 03/27/2023] [Accepted: 04/02/2023] [Indexed: 04/15/2023]
Abstract
The nematode genome exhibits a vast array of Cys-loop receptors that are activated by a diverse set of neurotransmitters and anthelmintic drugs such as ivermectin and levamisole. While many Cys-loop receptors have been functionally and pharmacologically characterized, there remains a large subset of orphan receptors where the agonist remains unknown. We have identified an orphan Cys-loop receptor, LGC-39, from the parasitic nematode Haemonchus contortus that is a novel type of cholinergic-sensitive ligand-gated chloride channel. This receptor groups outside of the acetylcholine-gated chloride channel family, in the previously named GGR-1 (GABA/Glycine Receptor-1) group of Cys-loop receptors. We found that LGC-39 forms a functional homomeric receptor when expressed in Xenopus laevis oocytes and is activated by several cholinergic ligands including acetylcholine, methacholine and surprisingly, atropine with an EC50 for atropine on the low μM range. A homology model was generated which revealed some key features of the LGC-39 ligand-binding pocket that may explain some of the elements important for atropine recognition of the LGC-39 receptor. Overall these results suggest that the GGR-1 family (now called LGC-57) of Cys-loop receptors includes novel acetylcholine-gated chloride channel subtypes and may represent important future drug targets.
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Affiliation(s)
- Sarah Habibi
- Faculty of Science, Ontario Tech University, 2000 Simcoe Street North, Oshawa, ON, L1H 7K4, Canada
| | - Kristen Nazareth
- Faculty of Science, Ontario Tech University, 2000 Simcoe Street North, Oshawa, ON, L1H 7K4, Canada
| | - Jennifer Nichols
- Faculty of Science, Ontario Tech University, 2000 Simcoe Street North, Oshawa, ON, L1H 7K4, Canada
| | - Sierra Varley
- Faculty of Science, Ontario Tech University, 2000 Simcoe Street North, Oshawa, ON, L1H 7K4, Canada
| | - Sean G Forrester
- Faculty of Science, Ontario Tech University, 2000 Simcoe Street North, Oshawa, ON, L1H 7K4, Canada.
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Barrantes FJ. Structure and function meet at the nicotinic acetylcholine receptor-lipid interface. Pharmacol Res 2023; 190:106729. [PMID: 36931540 DOI: 10.1016/j.phrs.2023.106729] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/04/2023] [Revised: 03/08/2023] [Accepted: 03/13/2023] [Indexed: 03/17/2023]
Abstract
The nicotinic acetylcholine receptor (nAChR) is a transmembrane protein that mediates fast intercellular communication in response to the endogenous neurotransmitter acetylcholine. It is the best characterized and archetypal molecule in the superfamily of pentameric ligand-gated ion channels (pLGICs). As a typical transmembrane macromolecule, it interacts extensively with its vicinal lipid microenvironment. Experimental evidence provides a wealth of information on receptor-lipid crosstalk: the nAChR exerts influence on its immediate membrane environment and conversely, the lipid moiety modulates ligand binding, affinity state transitions and gating of ion translocation functions of the receptor protein. Recent cryogenic electron microscopy (cryo-EM) studies have unveiled the occurrence of sites for phospholipids and cholesterol on the lipid-exposed regions of neuronal and electroplax nAChRs, confirming early spectroscopic and affinity labeling studies demonstrating the close contact of lipid molecules with the receptor transmembrane segments. This new data provides structural support to the postulated "lipid sensor" ability displayed by the outer ring of M4 transmembrane domains and their modulatory role on nAChR function, as we postulated a decade ago. Borrowing from the best characterized nAChR, the electroplax (muscle-type) receptor, and exploiting new structural information on the neuronal nAChR, it is now possible to achieve an improved depiction of these sites. In combination with site-directed mutagenesis, single-channel electrophysiology, and molecular dynamics studies, the new structural information delivers a more comprehensive portrayal of these lipid-sensitive loci, providing mechanistic explanations for their ability to modulate nAChR properties and raising the possibility of targetting them in disease.
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Affiliation(s)
- Francisco J Barrantes
- Laboratory of Molecular Neurobiology, Biomedical Research Institute, Faculty of Medical Sciences, Pontifical Catholic University of Argentina (UCA) - Argentine Scientific & Technol. Research Council (CONICET), Av. Alicia Moreau de Justo 1600, C1107AAZ Buenos Aires, Argentina.
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Morud J, Hardege I, Liu H, Wu T, Choi MK, Basu S, Zhang Y, Schafer WR. Deorphanization of novel biogenic amine-gated ion channels identifies a new serotonin receptor for learning. Curr Biol 2021; 31:4282-4292.e6. [PMID: 34388373 PMCID: PMC8536830 DOI: 10.1016/j.cub.2021.07.036] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2021] [Revised: 06/09/2021] [Accepted: 07/15/2021] [Indexed: 11/16/2022]
Abstract
Pentameric ligand-gated ion channels (LGICs) play conserved, critical roles in both excitatory and inhibitory synaptic transmission and can be activated by diverse neurochemical ligands. We have performed a characterization of orphan channels from the nematode C. elegans, identifying five new monoamine-gated LGICs with diverse functional properties and expression postsynaptic to aminergic neurons. These include polymodal anion channels activated by both dopamine and tyramine, which may mediate inhibitory transmission by both molecules in vivo. Intriguingly, we also find that a novel serotonin-gated cation channel, LGC-50, is essential for aversive olfactory learning of pathogenic bacteria, a process known to depend on serotonergic neurotransmission. Remarkably, the redistribution of LGC-50 to neuronal processes is modulated by olfactory conditioning, and lgc-50 point mutations that cause misregulation of receptor membrane expression interfere with olfactory learning. Thus, the intracellular trafficking and localization of these receptors at synapses may represent a molecular cornerstone of the learning mechanism.
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Affiliation(s)
- Julia Morud
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Iris Hardege
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - He Liu
- Department of Organismic and Evolutionary Biology, Harvard University, 52 Oxford Street, Cambridge, MA 02138, USA; Centre for Brain Science, Harvard University, Cambridge, MA 02138, USA
| | - Taihong Wu
- Department of Organismic and Evolutionary Biology, Harvard University, 52 Oxford Street, Cambridge, MA 02138, USA; Centre for Brain Science, Harvard University, Cambridge, MA 02138, USA
| | - Myung-Kyu Choi
- Department of Organismic and Evolutionary Biology, Harvard University, 52 Oxford Street, Cambridge, MA 02138, USA; Centre for Brain Science, Harvard University, Cambridge, MA 02138, USA
| | - Swaraj Basu
- Department of Medical Biochemistry and Cell Biology, Institute of Biomedicine, Medicinaregatan 9A, University of Gothenburg, 405 30 Gothenburg, Sweden
| | - Yun Zhang
- Department of Organismic and Evolutionary Biology, Harvard University, 52 Oxford Street, Cambridge, MA 02138, USA; Centre for Brain Science, Harvard University, Cambridge, MA 02138, USA
| | - William R Schafer
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK; Department of Biology, KU Leuven, Naamsestraat 59, 3000 Leuven, Belgium.
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Jones AK, Goven D, Froger JA, Bantz A, Raymond V. The cys-loop ligand-gated ion channel gene superfamilies of the cockroaches Blattella germanica and Periplaneta americana. PEST MANAGEMENT SCIENCE 2021; 77:3787-3799. [PMID: 33347700 DOI: 10.1002/ps.6245] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2020] [Revised: 11/27/2020] [Accepted: 12/21/2020] [Indexed: 06/12/2023]
Abstract
BACKGROUND Cockroaches are serious urban pests that can transfer disease-causing microorganisms as well as trigger allergic reactions and asthma. They are commonly managed by pesticides that act on cys-loop ligand-gated ion channels (cysLGIC). To provide further information that will enhance our understanding of how insecticides act on their molecular targets in cockroaches, we used genome and reverse transcriptase polymerase chain reaction (RT-PCR) data to characterize the cysLGIC gene superfamilies from Blattella germanica and Periplaneta americana. RESULTS The B. germanica and P. americana cysLGIC superfamilies consist of 30 and 32 subunit-encoding genes, respectively, which are the largest insect cysLGIC superfamilies characterized to date. As with other insects, the cockroaches possess ion channels predicted to be gated by acetylcholine, γ-aminobutyric acid, glutamate and histamine, as well as orthologues of the drosophila pH-sensitive chloride channel (pHCl), CG8916 and CG12344. The large cysLGIC superfamilies of cockroaches are a result of an expanded number of divergent nicotinic acetylcholine receptor subunits, with B. germanica and P. americana, respectively, possessing eight and ten subunit genes. Diversity of the cockroach cysLGICs is also broadened by alternative splicing and RNA A-to-I editing. Unusually, both cockroach species possess a second glutamate-gated chloride channel as well as another CG8916 subunit. CONCLUSION These findings on B. germanica and P. americana enhance our understanding of the evolution of the insect cysLGIC superfamily and provide a useful basis for the study of their function, the detection and management of insecticide resistance, and for the development of improved pesticides with greater specificity towards these major pests. © 2020 Society of Chemical Industry.
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Affiliation(s)
- Andrew K Jones
- Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Oxford, UK
| | - Delphine Goven
- Laboratoire « Signalisation Fonctionnelle des Canaux Ioniques et Récepteurs » (SiFCIR), UPRES-EA2647 USC INRAE 1330, SFR 4207 QUASAV, UFR Sciences, Université d'Angers, Angers, France
| | - Josy-Anne Froger
- Laboratoire « Signalisation Fonctionnelle des Canaux Ioniques et Récepteurs » (SiFCIR), UPRES-EA2647 USC INRAE 1330, SFR 4207 QUASAV, UFR Sciences, Université d'Angers, Angers, France
| | - Alexandre Bantz
- Laboratoire « Signalisation Fonctionnelle des Canaux Ioniques et Récepteurs » (SiFCIR), UPRES-EA2647 USC INRAE 1330, SFR 4207 QUASAV, UFR Sciences, Université d'Angers, Angers, France
| | - Valerie Raymond
- Laboratoire « Signalisation Fonctionnelle des Canaux Ioniques et Récepteurs » (SiFCIR), UPRES-EA2647 USC INRAE 1330, SFR 4207 QUASAV, UFR Sciences, Université d'Angers, Angers, France
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Perez Sirkin YA, Szleifer I, Tagliazucchi M. Voltage-Triggered Structural Switching of Polyelectrolyte-Modified Nanochannels. Macromolecules 2020. [DOI: 10.1021/acs.macromol.0c00082] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- Yamila A. Perez Sirkin
- INQUIMAE-CONICET and DQIAQF, University of Buenos Aires, School of Sciences, Ciudad Universitaria, Pabellón 2, Ciudad Autónoma de Buenos Aires C1428EHA, Argentina
| | - Igal Szleifer
- Department of Biomedical Engineering, Department of Chemistry and Chemistry of Life Processes Institute, Northwestern University, Evanston, Illinois 60208, United States
| | - Mario Tagliazucchi
- INQUIMAE-CONICET and DQIAQF, University of Buenos Aires, School of Sciences, Ciudad Universitaria, Pabellón 2, Ciudad Autónoma de Buenos Aires C1428EHA, Argentina
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Rinkevich FD, Bourgeois L. In silico identification and assessment of insecticide target sites in the genome of the small hive beetle, Aethina tumida. BMC Genomics 2020; 21:154. [PMID: 32050907 PMCID: PMC7017565 DOI: 10.1186/s12864-020-6551-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2019] [Accepted: 01/31/2020] [Indexed: 12/25/2022] Open
Abstract
BACKGROUND The small hive beetle, Aethina tumida, is a rapidly emerging global pest of honey bee colonies. Small hive beetle infestation can be extremely destructive, which may cause honey bees to abscond and render colony infrastructure unusable. Due to the impacts small hive beetles have on honey bees, a wide variety of physical, cultural, and chemical control measures have been implemented to manage small hive beetle infestations. The use of insecticides to control small hive beetle populations is an emerging management tactic. Currently, very little genomic information exists on insecticide target sites in the small hive beetle. Therefore, the objective of this study is to utilize focused in silico comparative genomics approaches to identify and assess the potential insecticide sensitivity of the major insecticide target sites in the small hive beetle genome. RESULTS No previously described resistance mutations were identified in any orthologs of insecticide target sites. Alternative exon use and A-to-I RNA editing were absent in AtumSC1. The ryanodine receptor in small hive beetle (Atum_Ryr) was highly conserved and no previously described resistance mutations were identified. A total of 12 nAChR subunits were identified with similar alternative exon use in other insects. Alternative exon use and critical structural features of the GABA-gated chloride channel subunits (Atum_RDL, Atum_GRD, and Atum_LCCH3) were conserved. Five splice variants were found for the glutamate-gated chloride channel subunit. Exon 3c of Atum_GluCl may be a beetle-specific alternative exon. The co-occurrence of exons 9a and 9b in the pH-sensitive chloride channel (Atum_pHCl) is a unique combination that introduces sites of post-translational modification. The repertoire and alternative exon use for histamine-gated chloride channels (Atum-HisCl), octopamine (Atum_OctR) and tyramine receptors (Atum_TAR) were conserved. CONCLUSIONS The recently published small hive beetle genome likely serves as a reference for insecticide-susceptible versions of insecticide target sites. These comparative in silico studies are the first step in discovering targets that can be exploited for small hive beetle-specific control as well as tracking changes in the frequency of resistance alleles as part of a resistance monitoring program. Comparative toxicity alongside honey bees is required to verify these in silico predictions.
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Affiliation(s)
- Frank D Rinkevich
- USDA-ARS Honey Bee Breeding, Genetics, and Physiology Laboratory, Baton Rouge, LA, USA.
| | - Lelania Bourgeois
- USDA-ARS Honey Bee Breeding, Genetics, and Physiology Laboratory, Baton Rouge, LA, USA
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Zhu S, Noviello CM, Teng J, Walsh RM, Kim JJ, Hibbs RE. Structure of a human synaptic GABA A receptor. Nature 2018; 559:67-72. [PMID: 29950725 PMCID: PMC6220708 DOI: 10.1038/s41586-018-0255-3] [Citation(s) in RCA: 325] [Impact Index Per Article: 54.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Accepted: 05/17/2018] [Indexed: 11/08/2022]
Abstract
Fast inhibitory neurotransmission in the brain is principally mediated by the neurotransmitter GABA (γ-aminobutyric acid) and its synaptic target, the type A GABA receptor (GABAA receptor). Dysfunction of this receptor results in neurological disorders and mental illnesses including epilepsy, anxiety and insomnia. The GABAA receptor is also a prolific target for therapeutic, illicit and recreational drugs, including benzodiazepines, barbiturates, anaesthetics and ethanol. Here we present high-resolution cryo-electron microscopy structures of the human α1β2γ2 GABAA receptor, the predominant isoform in the adult brain, in complex with GABA and the benzodiazepine site antagonist flumazenil, the first-line clinical treatment for benzodiazepine overdose. The receptor architecture reveals unique heteromeric interactions for this important class of inhibitory neurotransmitter receptor. This work provides a template for understanding receptor modulation by GABA and benzodiazepines, and will assist rational approaches to therapeutic targeting of this receptor for neurological disorders and mental illness.
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Affiliation(s)
- Shaotong Zhu
- Departments of Neuroscience and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Colleen M Noviello
- Departments of Neuroscience and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Jinfeng Teng
- Departments of Neuroscience and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Richard M Walsh
- Departments of Neuroscience and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Jeong Joo Kim
- Departments of Neuroscience and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Ryan E Hibbs
- Departments of Neuroscience and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA.
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Xu G, Wu SF, Teng ZW, Yao HW, Fang Q, Huang J, Ye GY. Molecular characterization and expression profiles of nicotinic acetylcholine receptors in the rice striped stem borer, Chilo suppressalis (Lepidoptera: Crambidae). INSECT SCIENCE 2017; 24:371-384. [PMID: 26847606 DOI: 10.1111/1744-7917.12324] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 01/13/2016] [Indexed: 06/05/2023]
Abstract
Nicotinic acetylcholine receptors (nAChRs) are members of the cys-loop ligand-gated ion channel (cysLGIC) superfamily, mediating fast synaptic cholinergic transmission in the central nervous system in insects. Insect nAChRs are the molecular targets of economically important insecticides, such as neonicotinoids and spinosad. Identification and characterization of the nAChR gene family in the rice striped stem borer, Chilo suppressalis, could provide beneficial information about this important receptor gene family and contribute to the investigation of the molecular modes of insecticide action and resistance for current and future chemical control strategies. We searched our C. suppressalis transcriptome database using Bombyx mori nAChR sequences in local BLAST searches and obtained the putative nAChR subunit complementary DNAs (cDNAs) via reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends methods. Similar to B. mori, C. suppressalis possesses 12 nAChR subunits, including nine α-type and three β-type subunits. Quantitative RT-PCR analysis revealed the expression profiles of the nAChR subunits in various tissues, including the brain, subesophageal ganglion, thoracic ganglion, abdominal ganglion, hemocytes, fat body, foregut, midgut, hindgut and Malpighian tubules. Developmental expression analyses showed clear differential expression of nAChR subunits throughout the C. suppressalis life cycle. The identification of nAChR subunits in this study will provide a foundation for investigating the diverse roles played by nAChRs in C. suppressalis and for exploring specific target sites for chemicals that control agricultural pests while sparing beneficial species.
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Affiliation(s)
- Gang Xu
- State Key Laboratory of Rice Biology & Key Laboratory of Agricultural Entomology of Ministry of Agriculture, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
| | - Shun-Fan Wu
- State Key Laboratory of Rice Biology & Key Laboratory of Agricultural Entomology of Ministry of Agriculture, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
- State & Local Joint Engineering Research Center of Green Pesticide Invention and Application, College of Plant Protection, Nanjing Agricultural University, Nanjing, China
| | - Zi-Wen Teng
- State Key Laboratory of Rice Biology & Key Laboratory of Agricultural Entomology of Ministry of Agriculture, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
| | - Hong-Wei Yao
- State Key Laboratory of Rice Biology & Key Laboratory of Agricultural Entomology of Ministry of Agriculture, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
| | - Qi Fang
- State Key Laboratory of Rice Biology & Key Laboratory of Agricultural Entomology of Ministry of Agriculture, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
| | - Jia Huang
- State Key Laboratory of Rice Biology & Key Laboratory of Agricultural Entomology of Ministry of Agriculture, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
| | - Gong-Yin Ye
- State Key Laboratory of Rice Biology & Key Laboratory of Agricultural Entomology of Ministry of Agriculture, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
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Effects of bilobalide, ginkgolide B and picrotoxinin on GABA A receptor modulation by structurally diverse positive modulators. Eur J Pharmacol 2017; 806:83-90. [PMID: 28416372 DOI: 10.1016/j.ejphar.2017.04.019] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Revised: 04/11/2017] [Accepted: 04/13/2017] [Indexed: 12/20/2022]
Abstract
Anxiolytics and anticonvulsants generally positively modulate the action of GABA, whereas many convulsants (including the chloride channel blocker picrotoxinin) negatively modulate the action of GABA on GABAA receptors. Like picrotoxinin, bilobalide and ginkgolide B, active constituents of Ginkgo biloba, have been shown to negatively modulate the action of GABA at α1β2γ2L GABAA receptors. However, unlike picrotoxinin, bilobalide and ginkgolide B are not known to cause convulsions. We have assessed the action of bilobalide, ginkgolide B and picrotoxinin on a range of GABAA modulators (etomidate, loreclezole, propofol, thiopentone sodium, diazepam, and allopregnanolone), using two-electrode voltage clamp electrophysiology at recombinant α1β2γ2L GABAA receptors expressed in Xenopus oocytes. The results indicate that bilobalide and ginkgolide B differ from picrotoxinin in their ability to inhibit the actions of a range of these structurally diverse GABAA positive modulators consistent with these modulators acting on a multiplicity of active sites associated with GABAA receptors. In the presence GABA, ginkgolide B was more potent than bilobalide in inhibiting the GABA-potentiating effect of propofol, equipotent against loreclezole and allopregnanolone, and less potent against etomidate, diazepam, and thiopentone sodium. This indicates that in comparison to picrotoxinin, bilobalide and ginkgolide B differ in their effects on the different modulators.
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Knoflach F, Hernandez MC, Bertrand D. GABAA receptor-mediated neurotransmission: Not so simple after all. Biochem Pharmacol 2016; 115:10-7. [DOI: 10.1016/j.bcp.2016.03.014] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Accepted: 03/17/2016] [Indexed: 12/28/2022]
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12
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Lee BH, Choi SH, Kim HJ, Jung SW, Hwang SH, Pyo MK, Rhim H, Kim HC, Kim HK, Lee SM, Nah SY. Differential Effects of Quercetin and Quercetin Glycosides on Human α7 Nicotinic Acetylcholine Receptor-Mediated Ion Currents. Biomol Ther (Seoul) 2016; 24:410-7. [PMID: 27098860 PMCID: PMC4930285 DOI: 10.4062/biomolther.2015.153] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2015] [Revised: 12/28/2015] [Accepted: 01/22/2016] [Indexed: 01/16/2023] Open
Abstract
Quercetin is a flavonoid usually found in fruits and vegetables. Aside from its antioxidative effects, quercetin, like other flavonoids, has a various neuropharmacological actions. Quercetin-3-O-rhamnoside (Rham1), quercetin-3-O-rutinoside (Rutin), and quercetin-3-(2(G)-rhamnosylrutinoside (Rham2) are mono-, di-, and tri-glycosylated forms of quercetin, respectively. In a previous study, we showed that quercetin can enhance α7 nicotinic acetylcholine receptor (α7 nAChR)-mediated ion currents. However, the role of the carbohydrates attached to quercetin in the regulation of α7 nAChR channel activity has not been determined. In the present study, we investigated the effects of quercetin glycosides on the acetylcholine induced peak inward current (IACh) in Xenopus oocytes expressing the α7 nAChR. IACh was measured with a two-electrode voltage clamp technique. In oocytes injected with α7 nAChR copy RNA, quercetin enhanced IACh, whereas quercetin glycosides inhibited IACh. Quercetin glycosides mediated an inhibition of IACh, which increased when they were pre-applied and the inhibitory effects were concentration dependent. The order of IACh inhibition by quercetin glycosides was Rutin≥Rham1>Rham2. Quercetin glycosides-mediated IACh enhancement was not affected by ACh concentration and appeared voltage-independent. Furthermore, quercetin-mediated IACh inhibition can be attenuated when quercetin is co-applied with Rham1 and Rutin, indicating that quercetin glycosides could interfere with quercetin-mediated α7 nAChR regulation and that the number of carbohydrates in the quercetin glycoside plays a key role in the interruption of quercetin action. These results show that quercetin and quercetin glycosides regulate the α7 nAChR in a differential manner.
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Affiliation(s)
- Byung-Hwan Lee
- Department of Physiology, College of Veterinary Medicine and BioMolecular Informatics Center, Konkuk University, Seoul 05029, Republic of Korea
| | - Sun-Hye Choi
- Department of Physiology, College of Veterinary Medicine and BioMolecular Informatics Center, Konkuk University, Seoul 05029, Republic of Korea
| | - Hyeon-Joong Kim
- Department of Physiology, College of Veterinary Medicine and BioMolecular Informatics Center, Konkuk University, Seoul 05029, Republic of Korea
| | - Seok-Won Jung
- Department of Physiology, College of Veterinary Medicine and BioMolecular Informatics Center, Konkuk University, Seoul 05029, Republic of Korea
| | - Sung-Hee Hwang
- Department of Pharmaceutical Engineering, Sangji University, Wonju 26339, Republic of Korea
| | - Mi-Kyung Pyo
- International Ginseng and Herb Research Institute, Geumsan 32724, Republic of Korea
| | - Hyewhon Rhim
- Life Science Division, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea
| | - Hyoung-Chun Kim
- Neuropsychopharmacology and Toxicology Program, College of Pharmacy, Kangwon National University, Chunchon 24341, Republic of Korea
| | - Ho-Kyoung Kim
- Mibyeong Research Center, Korea Institute of Oriental Medicine, Daejeon 34054, Republic of Korea
| | - Sang-Mok Lee
- Department of Physiology, College of Veterinary Medicine and BioMolecular Informatics Center, Konkuk University, Seoul 05029, Republic of Korea
| | - Seung-Yeol Nah
- Department of Physiology, College of Veterinary Medicine and BioMolecular Informatics Center, Konkuk University, Seoul 05029, Republic of Korea
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13
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Ng CC, Duke RK, Hinton T, Johnston GA. GABAA receptor cysteinyl mutants and the ginkgo terpenoid lactones bilobalide and ginkgolides. Eur J Pharmacol 2016; 777:136-46. [DOI: 10.1016/j.ejphar.2016.03.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2015] [Revised: 03/02/2016] [Accepted: 03/02/2016] [Indexed: 10/22/2022]
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14
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Kim GR, Yoon TH, Park WG, Park JY, Kang JH, Kim HW. Five nicotinic acetylcholine receptor subunits from the Morotoge shrimp,Pandalopsis japonica: cloning, tissue distribution, and functional expression inXenopusoocytes. Anim Cells Syst (Seoul) 2015. [DOI: 10.1080/19768354.2015.1109547] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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15
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Mukherjee A. Computational analysis of a cys-loop ligand gated ion channel from the green alga Chlamydomonas reinhardtii. Mol Biol 2015. [DOI: 10.1134/s002689331505012x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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16
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Cys-loop ligand-gated ion channel gene discovery in the Locusta migratoria manilensis through the neuron transcriptome. Gene 2015; 561:276-82. [DOI: 10.1016/j.gene.2015.02.048] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2014] [Revised: 01/26/2015] [Accepted: 02/14/2015] [Indexed: 11/23/2022]
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17
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Abstract
Under most circumstances, GABA activates chloride-selective channels and thereby inhibits neuronal activity. Here, we identify a GABA receptor in the nematode Caenorhabditis elegans that conducts cations and is therefore excitatory. Expression in Xenopus oocytes demonstrates that LGC-35 is a homopentameric cation-selective receptor of the cys-loop family exclusively activated by GABA. Phylogenetic analysis suggests that LGC-35 evolved from GABA-A receptors, but the pore-forming domain contains novel molecular determinants that confer cation selectivity. LGC-35 is expressed in muscles and directly mediates sphincter muscle contraction in the defecation cycle in hermaphrodites, and spicule eversion during mating in the male. In the locomotory circuit, GABA release directly activates chloride channels on the muscle to cause muscle relaxation. However, GABA spillover at these synapses activates LGC-35 on acetylcholine motor neurons, which in turn cause muscles to contract, presumably to drive wave propagation along the body. These studies demonstrate that both direct and indirect excitatory GABA signaling plays important roles in regulating neuronal circuit function and behavior in C. elegans.
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Lipovsek M, Fierro A, Pérez EG, Boffi JC, Millar NS, Fuchs PA, Katz E, Elgoyhen AB. Tracking the molecular evolution of calcium permeability in a nicotinic acetylcholine receptor. Mol Biol Evol 2014; 31:3250-65. [PMID: 25193338 PMCID: PMC4245820 DOI: 10.1093/molbev/msu258] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Nicotinic acetylcholine receptors are a family of ligand-gated nonselective cationic channels that participate in fundamental physiological processes at both the central and the peripheral nervous system. The extent of calcium entry through ligand-gated ion channels defines their distinct functions. The α9α10 nicotinic cholinergic receptor, expressed in cochlear hair cells, is a peculiar member of the family as it shows differences in the extent of calcium permeability across species. In particular, mammalian α9α10 receptors are among the ligand-gated ion channels which exhibit the highest calcium selectivity. This acquired differential property provides the unique opportunity of studying how protein function was shaped along evolutionary history, by tracking its evolutionary record and experimentally defining the amino acid changes involved. We have applied a molecular evolution approach of ancestral sequence reconstruction, together with molecular dynamics simulations and an evolutionary-based mutagenesis strategy, in order to trace the molecular events that yielded a high calcium permeable nicotinic α9α10 mammalian receptor. Only three specific amino acid substitutions in the α9 subunit were directly involved. These are located at the extracellular vestibule and at the exit of the channel pore and not at the transmembrane region 2 of the protein as previously thought. Moreover, we show that these three critical substitutions only increase calcium permeability in the context of the mammalian but not the avian receptor, stressing the relevance of overall protein structure on defining functional properties. These results highlight the importance of tracking evolutionarily acquired changes in protein sequence underlying fundamental functional properties of ligand-gated ion channels.
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Affiliation(s)
- Marcela Lipovsek
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Dr. Héctor N Torres, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
| | - Angélica Fierro
- Department of Organic Chemistry, Faculty of Chemistry, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Edwin G Pérez
- Department of Organic Chemistry, Faculty of Chemistry, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Juan C Boffi
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Dr. Héctor N Torres, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
| | - Neil S Millar
- Department of Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom
| | - Paul A Fuchs
- Department of Otolaryngology, Head and Neck Surgery, and Center for Hearing and Balance, The Johns Hopkins University School of Medicine, Baltimore, MD
| | - Eleonora Katz
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Dr. Héctor N Torres, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Ana Belén Elgoyhen
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Dr. Héctor N Torres, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina Departamento de Farmacología, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires, Argentina
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19
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White SH, Carter CJ, Magoski NS. A potentially novel nicotinic receptor in Aplysia neuroendocrine cells. J Neurophysiol 2014; 112:446-62. [DOI: 10.1152/jn.00796.2013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Nicotinic receptors form a diverse group of ligand-gated ionotropic receptors with roles in both synaptic transmission and the control of excitability. In the bag cell neurons of Aplysia, acetylcholine activates an ionotropic receptor, which passes inward current to produce a long-lasting afterdischarge and hormone release, leading to reproduction. While testing the agonist profile of the cholinergic response, we observed a second current that appeared to be gated only by nicotine and not acetylcholine. The peak nicotine-evoked current was markedly smaller in magnitude than the acetylcholine-induced current, cooperative (Hill value of 2.7), had an EC50 near 500 μM, readily recovered from desensitization, showed Ca2+ permeability, and was blocked by mecamylamine, dihydro-β-erythroidine, or strychnine, but not by α-conotoxin ImI, methyllycaconitine, or hexamethonium. Aplysia transcriptome analysis followed by PCR yielded 20 full-length potential nicotinic receptor subunits. Sixteen of these were predicted to be cation selective, and real-time PCR suggested that 15 of the 16 subunits were expressed to varying degrees in the bag cell neurons. The acetylcholine-induced current, but not the nicotine current, was reduced by double-strand RNA treatment targeted to both subunits ApAChR-C and -E. Conversely, the nicotine-evoked current, but not the acetylcholine current, was lessened by targeting both subunits ApAChR-H and -P. To the best of our knowledge, this is the first report suggesting that a nicotinic receptor is not gated by acetylcholine. Separate receptors may serve as a means to differentially trigger plasticity or safeguard propagation by assuring that only acetylcholine, the endogenous agonist, initiates large enough responses to trigger reproduction.
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Affiliation(s)
- Sean H. White
- Department of Biomedical and Molecular Sciences, Physiology Graduate Program, Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada
| | - Christopher J. Carter
- Department of Biomedical and Molecular Sciences, Physiology Graduate Program, Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada
| | - Neil S. Magoski
- Department of Biomedical and Molecular Sciences, Physiology Graduate Program, Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada
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20
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Lopes AMM, de Carvalho RA, de Azeredo-Espin AML. Glutamate-gated chloride channel subunit cDNA sequencing of Cochliomyia hominivorax (Diptera: Calliphoridae): cDNA variants and polymorphisms. INVERTEBRATE NEUROSCIENCE 2014; 14:137-46. [DOI: 10.1007/s10158-014-0172-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2014] [Accepted: 05/29/2014] [Indexed: 10/25/2022]
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21
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Juneja P, Horlacher R, Bertrand D, Krause R, Marger F, Welte W. An internally modulated, thermostable, pH-sensitive Cys loop receptor from the hydrothermal vent worm Alvinella pompejana. J Biol Chem 2014; 289:15130-40. [PMID: 24719323 DOI: 10.1074/jbc.m113.525576] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Cys loop receptors (CLRs) are commonly known as ligand-gated channels that transiently open upon binding of neurotransmitters to modify the membrane potential. However, a class of cation-selective bacterial homologues of CLRs have been found to open upon a sudden pH drop, suggesting further ligands and more functions of the homologues in prokaryotes. Here we report an anion-selective CLR from the hydrothermal vent annelid worm Alvinella pompejana that opens at low pH. A. pompejana expressed sequence tag databases were explored by us, and two full-length CLR sequences were identified, synthesized, cloned, expressed in Xenopus oocytes, and studied by two-electrode voltage clamp. One channel, named Alv-a1-pHCl, yielded functional receptors and opened upon a sudden pH drop but not by other known agonists. Sequence comparison showed that both CLR proteins share conserved characteristics with eukaryotic CLRs, such as an N-terminal helix, a cysteine loop motif, and an intracellular loop intermediate in length between the long loops of other eukaryotic CLRs and those of prokaryotic CLRs. Both full-length Alv-a1-pHCl and a truncated form, termed tAlv-a1-pHCl, lacking 37 amino-terminal residues that precede the N-terminal helix, formed functional channels in oocytes. After pH activation, tAlv-a1-pHCl showed desensitization and was not modulated by ivermectin. In contrast, pH-activated, full-length Alv-a1-pHCl showed a marked rebound current and was modulated significantly by ivermectin. A thermostability assay indicated that purified tAlv-a1-pHCl expressed in Sf9 cells denatured at a higher temperature than the nicotinic acetylcholine receptor from Torpedo californica.
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Affiliation(s)
- Puneet Juneja
- From the Fachbereich Biologie, Universität Konstanz, Universitätsstraβe 10, 78457 Konstanz, Germany
| | | | - Daniel Bertrand
- HiQScreen Sàrl, 6, rte. de Compois, 1222 Vésenaz, Geneva, Switzerland
| | - Ryoko Krause
- HiQScreen Sàrl, 6, rte. de Compois, 1222 Vésenaz, Geneva, Switzerland
| | - Fabrice Marger
- HiQScreen Sàrl, 6, rte. de Compois, 1222 Vésenaz, Geneva, Switzerland
| | - Wolfram Welte
- From the Fachbereich Biologie, Universität Konstanz, Universitätsstraβe 10, 78457 Konstanz, Germany,
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22
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Chen J, Tomich JM. Free energy analysis of conductivity and charge selectivity of M2GlyR-derived synthetic channels. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:2319-25. [PMID: 24582709 DOI: 10.1016/j.bbamem.2014.02.016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2014] [Accepted: 02/21/2014] [Indexed: 12/16/2022]
Abstract
Significant progresses have been made in the design, synthesis, modeling and in vitro testing of channel-forming peptides derived from the second transmembrane domain of the α-subunit of the glycine receptor (GlyR). The latest designs, including p22 (KKKKP ARVGL GITTV LTMTT QS), are highly soluble in water with minimal aggregation propensity and insert efficiently into cell membranes to form highly conductive ion channels. The last obstacle to a potential lead sequence for channel replacement treatment of CF patients is achieving adequate chloride selectivity. We have performed free energy simulation to analyze the conductance and charge selectivity of M2GlyR-derived synthetic channels. The results reveal that the pentameric p22 pore is non-selective. Moderate barriers for permeation of both K(+) and Cl(-) are dominated by the desolvation cost. Despite previous evidence suggesting a potential role of threonine side chains in anion selectivity, the hydroxyl group is not a good surrogate of water for coordinating these ions. We have also tested initial ideas of introducing additional rings of positive changes to various positions along the pore to increase anion selectivity. The results support the feasibility of achieving anion selectivity by modifying the electrostatic properties of the pore, but at the same time suggest that the peptide assembly and pore topology may also be dramatically modified, which could abolish the effects of modified electrostatics on anion selectivity. This was confirmed by subsequent two-electrode voltage clamp measurements showing that none of the tested mono-, di- and tri-Dap substituted sequences was selective. The current study thus highlights the importance of controlling channel topology besides modifying pore electrostatics for achieving anion selectivity. Several strategies are now being explored in our continued efforts to design an anion selective peptide channel with suitable biophysical, physiological and pharmacological properties as a potential treatment modality for channel replacement therapy. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.
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Affiliation(s)
- Jianhan Chen
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, KS 66506, USA.
| | - John M Tomich
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, KS 66506, USA.
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23
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Xie HB, Wang J, Sha Y, Cheng MS. Molecular dynamics investigation of Cl(-) transport through the closed and open states of the 2α12β2γ2 GABA(A) receptor. Biophys Chem 2013; 180-181:1-9. [PMID: 23771165 DOI: 10.1016/j.bpc.2013.05.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Revised: 05/18/2013] [Accepted: 05/20/2013] [Indexed: 01/16/2023]
Abstract
The α1β2γ2 gamma-aminobutyric type A receptor (GABA(A)R) is one of the most widely expressed GABA(A)R subtypes in the mammalian brain. GABA(A)Rsbelonging to the Cys-loop superfamily of ligand-gated ion channels have been identified as key targets for many clinical drugs, and the motions that govern the gating mechanism are still not well understood. In this study, an open-state GABA(A)R was constructed using the structure of the glutamate-gated chloride channel (GluCl), which has a high sequence identity to GABA(A)R. A closed-state model was constructed using the structure of the nicotinic acetylcholine receptor (nAChR). Molecular dynamics simulations of the open-state and closed-state GABA(A)R were performed. We calculated the electrostatic potential of the two conformations, the pore radius of the two ion channels and the root-mean-square fluctuation. We observed the presence of two positively charged girdles around the ion channel and found flexible regions in the GABA(A)R. Then, the free-energy of chloride ion permeations through the closed-state and open-state G GABA(A)R has been estimated using adaptive biasing force (ABF) simulation. For the closed-state G GABA(A)R, we observed two major energy barriers for chloride ion translocation in the transmembrane domain (TMD). For the open-state GABA(A)R, there was only one energy barrier formed by two Thr261 (α1), two Thr255 (β2) and one Thr271 (γ2). By using ABF simulation, the overall free-energy profile is obtained for Cl(-) transporting through GABA(A)R, which gives a complete map of the ion channel of Cl(-) permeation.
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Affiliation(s)
- Hong-Bo Xie
- Key Laboratory of Structure-Based Drugs Design & Discovery of Ministry of Education, School of Pharmaceutical Engineering, Shenyang Pharmaceutical University, Shenyang 110016, PR China
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24
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Lee BH, Choi SH, Hwang SH, Kim HJ, Lee JH, Nah SY. Resveratrol Inhibits GABAC ρ Receptor-Mediated Ion Currents Expressed in Xenopus Oocytes. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2013; 17:175-80. [PMID: 23626481 PMCID: PMC3634096 DOI: 10.4196/kjpp.2013.17.2.175] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/16/2013] [Revised: 03/19/2013] [Accepted: 04/01/2013] [Indexed: 12/21/2022]
Abstract
Resveratrol is a phytoalexin found in grapes, red wine, and berries. Resveratrol has been known to have many beneficial health effects, such as anti-cancer, neuroprotective, anti-inflammatory, and life-prolonging effects. However, relatively little is known about the effects of resveratrol on the regulation of ligand-gated ion channels. We have previously reported that resveratrol regulates subsets of homomeric ligand-gated ion channels such as those of 5-HT3A receptors. The γ-aminobutyric acidC (GABAC) receptor is mainly expressed in retinal bipolar cells and plays an important role in visual processing. In the present study, we examined the effects of resveratrol on the channel activity of homomeric GABAC receptor expressed in Xenopus oocytes injected with cRNA encoding human GABAC ρ subunits. Our data show that the application of GABA elicits an inward peak current (IGABA) in oocytes that express the GABAC receptor. Resveratrol treatment had no effect on oocytes injected with H2O or with GABAC receptor cRNA. Co-treatment with resveratrol and GABA inhibited IGABA in oocytes with GABAC receptors. The inhibition of IGABA by resveratrol was in a reversible and concentration-dependent manner. The IC50 of resveratrol was 28.9±2.8 µM in oocytes expressing GABAC receptor. The inhibition of IGABA by resveratrol was in voltage-independent and non-competitive manner. These results indicate that resveratrol might regulate GABAC receptor expression and that this regulation might be one of the pharmacological actions of resveratrol on the nervous system.
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Affiliation(s)
- Byung-Hwan Lee
- Department of Physiology, College of Veterinary Medicine and Bio-Molecular Informatics Center, Konkuk University, Seoul 143-701, Korea
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25
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Siddiqui SZ, Brown DDR, Accardi MV, Forrester SG. Hco-LGC-38 is novel nematode cys-loop GABA receptor subunit. Mol Biochem Parasitol 2012; 185:137-44. [PMID: 22940478 DOI: 10.1016/j.molbiopara.2012.08.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Revised: 08/11/2012] [Accepted: 08/15/2012] [Indexed: 11/28/2022]
Abstract
We have identified and characterized a novel cys-loop GABA receptor subunit (Hco-LGC-38) from the parasitic nematode Haemonchus contortus. This subunit is present in parasitic and free-living nematodes and shares similarity to both the UNC-49 group of GABA receptor subunits from nematodes and the resistant to dieldrin (RDL) receptors of insects. Expression of the Hco-lgc-38 gene in Xenopus oocytes and subsequent electrophysiological analysis has revealed that the gene encodes a homomeric channel sensitive to GABA (EC(50) 19 μM) and the GABA analogue muscimol. The sensitivity of the Hco-LGC-38 channel to GABA is similar to reported values for the Drosophila RDL receptor whereas its lower sensitivity to muscimol is similar to nematode GABA receptors. Hco-LGC-38 is also highly sensitive to the channel blocker picrotoxin and moderately sensitive to fipronil and dieldrin. Homology modeling of Hco-LGC-38 and subsequent docking of GABA and muscimol into the binding site has uncovered several types of potential interactions with binding-site residues and overall appears to share similarity with models of other invertebrate GABA receptors.
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Affiliation(s)
- Salma Z Siddiqui
- Applied Bioscience Graduate Program, University of Ontario Institute of Technology, Oshawa, Ontario, Canada
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26
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Shapiro MG, Frazier SJ, Lester HA. Unparalleled control of neural activity using orthogonal pharmacogenetics. ACS Chem Neurosci 2012; 3:619-29. [PMID: 22896806 DOI: 10.1021/cn300053q] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2012] [Accepted: 06/01/2012] [Indexed: 11/28/2022] Open
Abstract
Studying the functional architecture of the brain requires technologies to precisely measure and perturb the activity of specific neural cells and circuits in live animals. Substantial progress has been made in recent years to develop and apply such tools. In particular, technologies that provide precise control of activity in genetically defined populations of neurons have enabled the study of causal relationships between and among neural circuit elements and behavioral outputs. Here, we review an important subset of such technologies, in which neurons are genetically engineered to respond to specific chemical ligands that have no interfering pharmacological effect in the central nervous system. A rapidly expanding set of these "orthogonal pharmacogenetic" tools provides a unique combination of genetic specificity, functional diversity, spatiotemporal precision, and potential for multiplexing. We review the main classes of orthogonal pharmacogenetic technologies, including neuroreceptors to control neuronal excitability, systems to control gene transcription and translation, and general constructs to control protein-protein interactions, enzymatic function, and protein stability. We describe the key performance characteristics informing the use of these technologies in the brain, and potential directions for improvement and expansion of the orthogonal pharmacogenetics toolkit to enable more sophisticated systems neuroscience.
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Affiliation(s)
- Mikhail G. Shapiro
- Miller Research Institute, Department
of Bioengineering, and Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California
94720, United States
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27
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Lee BH, Hwang SH, Choi SH, Shin TJ, Kang J, Kim HJ, Kim HC, Lee JH, Nah SY. Inhibitory effects of dextrorotatory morphinans on the human 5-HT(3A) receptor expressed in Xenopus oocytes: Involvement of the N-terminal domain of the 5-HT(3A) receptor. Eur J Pharmacol 2012; 686:41-9. [PMID: 22575521 DOI: 10.1016/j.ejphar.2012.04.047] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2011] [Revised: 04/17/2012] [Accepted: 04/20/2012] [Indexed: 11/19/2022]
Abstract
We previously developed a series of dextromethorphan (DM, 3-methoxy-17-methylmorphinan) analogs modified at positions 3 and 17 of the morphinan ring system. Recent reports have shown that DM attenuates abdominal pain caused by irritable bowel syndrome, and multidrug regimens that include DM prevent nausea/vomiting following cancer surgery. However, little is known regarding the molecular mechanisms underlying the beneficial effects of DM. Here, we investigated the effects of DM, 3 of its analogs (AM, 3-allyloxy-17-methoxymorphian; CM, 3-cyclopropyl-17-methoxymorphinan; and DF, 3-methyl-17-methylmorphinan), and 1 of its metabolites (HM, 3-methoxymorphinan) on the activity of the human 5-HT(3A) receptor channel expressed in Xenopus laevis oocytes, using the 2-microelectrode voltage clamp technique. We found that intra-oocyte injection of human 5-HT(3A) receptor cRNAs elicited an inward current (I(5-HT)) in the presence of 5-HT. Cotreatment with AM, CM, DF, DM, or HM inhibited I(5-HT) in a dose-dependent, voltage-independent, and reversible manner. The IC(50) values for AM, CM, DF, DM, and HM were 24.5±1.4, 21.5±4.2, 132.6±35.8, 181.3±23.5, and 191.3±31.5μM, respectively. The IC(50) values of AM and CM were 7-fold lower than that of DM, and mechanistic analysis revealed that DM, DF, HM, AM, and CM were competitive inhibitors of I(5-HT). Point mutations of Arg241 in the N-terminal, but not amino acids in the pore region, to other amino acid residues attenuated or abolished DM- and DM-analog-induced inhibition of I(5-HT). Together, these results demonstrated that dextrorotatory morphinans might regulate 5-HT(3A) receptor channel activity via interaction with its N-terminal domain.
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Affiliation(s)
- Byung-Hwan Lee
- Department of Physiology, College of Veterinary Medicine, Bio/Molecular Informatics Center, Konkuk University, Seoul, Republic of Korea
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28
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Dermauw W, Ilias A, Riga M, Tsagkarakou A, Grbić M, Tirry L, Van Leeuwen T, Vontas J. The cys-loop ligand-gated ion channel gene family of Tetranychus urticae: implications for acaricide toxicology and a novel mutation associated with abamectin resistance. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2012; 42:455-465. [PMID: 22465149 DOI: 10.1016/j.ibmb.2012.03.002] [Citation(s) in RCA: 117] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2012] [Revised: 03/07/2012] [Accepted: 03/09/2012] [Indexed: 05/27/2023]
Abstract
The cys-loop ligand-gated ion channel (cysLGIC) super family of Tetranychus urticae, the two-spotted spider mite, represents the largest arthropod cysLGIC super family described to date and the first characterised one within the group of chelicerates. Genome annotation, phylogenetic analysis and comparison of the cysLGIC subunits with their counterparts in insects reveals that the T. urticae genome encodes for a high number of glutamate- and histamine-gated chloride channel genes (GluCl and HisCl) compared to insects. Three orthologues of the insect γ-aminobutyric acid (GABA)-gated chloride channel gene Rdl were detected. Other cysLGIC groups, such as the nAChR subunits, are more conserved and have clear insect orthologues. Members of cysLGIC family mediate endogenous chemical neurotransmission and they are prime targets of insecticides. Implications for toxicology associated with the identity and specific features of T. urticae family members are discussed. We further reveal the accumulation of known and novel mutations in different GluCl channel subunits (Tu_GluCl1 and Tu_GluCl3) associated with abamectin resistance in T. urticae, and provide genetic evidence for their causality. Our study provides useful toxicological insights for the exploration of the T. urticae cysLGIC subunits as putative molecular targets for current and future chemical control strategies.
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Affiliation(s)
- W Dermauw
- Laboratory of Agrozoology, Department of Crop Protection, Faculty of Agricultural and Applied, Biological Sciences, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium.
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Lee BH, Hwang SH, Choi SH, Shin TJ, Kang J, Lee SM, Nah SY. Resveratrol enhances 5-hydroxytryptamine type 3A receptor-mediated ion currents: the role of arginine 222 residue in pre-transmembrane domain I. Biol Pharm Bull 2011; 34:523-7. [PMID: 21467640 DOI: 10.1248/bpb.34.523] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Resveratrol, which is found in grapes, red wine, and berries, has many beneficial health effects, such as anti-cancer, neuro-protective, anti-inflammatory, and life-prolonging effects. However, the cellular mechanisms by which resveratrol acts are relatively unknown, especially in terms of possible regulation of receptors involved in synaptic transmission. 5-Hydroxytryptamine type 3A (5-HT(3A)) receptor is one of several ligand-gated ion channels involved in fast synaptic transmission. In the present study, we investigated the effect of resveratrol on mouse 5-HT(3A) receptor channel activity. 5-HT(3A) receptor was expressed in Xenopus oocytes, and the current was measured using a two-electrode voltage clamp technique. Treatment of resveratrol itself had no effect on the oocytes injected with H(2)O as well as on the oocytes injected with 5-HT(3A) receptor cRNA. In the oocytes injected with 5-HT(3A) receptor cRNA, co- or pre-treatment of resveratrol with 5-HT potentiated 5-HT-induced inward peak current (I(5-HT)) with concentration-, reversible, and voltage-independent manners. The EC(50) of resveratrol was 28.0±2.4 µM. The presence of resveratrol caused a leftward shift of 5-HT concentration-response curve. Protein kinase C (PKC) activator or inhibitor had no effect on resveratrol action on I(5-HT). Site-directed mutations of pre-transmembrane domain 1 (pre-TM1) such as R222A, R222D, R222E, R222K, and R222T abolished or attenuated resveratrol-induced enhancement of I(5-HT), indicating that resveratrol might interact with pre-TM1 of 5-HT(3A) receptor. These results indicate that resveratrol might regulate 5-HT(3A) receptor channel activity via interaction with the N-terminal domain and these results further show that resveratrol-mediated regulation of 5-HT(3A) receptor channel activity might be one of cellular mechanisms of resveratrol action.
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Affiliation(s)
- Byung-Hwan Lee
- Department of Physiology, College of Veterinary Medicine and Bio/Molecular Informatics Center, Konkuk University, Seoul, Korea
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Alhadeff R, Ganoth A, Krugliak M, Arkin IT. Promiscuous binding in a selective protein: the bacterial Na+/H+ antiporter. PLoS One 2011; 6:e25182. [PMID: 22022382 PMCID: PMC3192041 DOI: 10.1371/journal.pone.0025182] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2011] [Accepted: 08/26/2011] [Indexed: 11/19/2022] Open
Abstract
The ability to discriminate between highly similar substrates is one of the remarkable properties of enzymes. For example, transporters and channels that selectively distinguish between various solutes enable living organisms to maintain and control their internal environment in the face of a constantly changing surrounding. Herein, we examine in detail the selectivity properties of one of the most important salt transporters: the bacterial Na/H antiporter. Selectivity can be achieved at either the substrate binding step or in subsequent antiporting. Surprisingly, using both computational and experimental analyses synergistically, we show that binding per se is not a sufficient determinant of selectively. All alkali ions from Li to Cs were able to competitively bind the antiporter's binding site, whether the protein was capable of pumping them or not. Hence, we propose that NhaA's binding site is relatively promiscuous and that the selectivity is determined at a later stage of the transport cycle.
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Affiliation(s)
- Raphael Alhadeff
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Assaf Ganoth
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Miriam Krugliak
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Isaiah T. Arkin
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
- * E-mail:
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Bar-Lev DD, Degani-Katzav N, Perelman A, Paas Y. Molecular dissection of Cl--selective Cys-loop receptor points to components that are dispensable or essential for channel activity. J Biol Chem 2011; 286:43830-43841. [PMID: 21987577 DOI: 10.1074/jbc.m111.282715] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Cys-loop receptors are pentameric ligand-gated ion channels (pLGICs) that bind neurotransmitters to open an intrinsic transmembrane ion channel pore. The recent crystal structure of a prokaryotic pLGIC from the cyanobacterium Gloeobacter violaceus (GLIC) revealed that it naturally lacks an N-terminal extracellular α helix and an intracellular domain that are typical of eukaryotic pLGICs. GLIC does not respond to neurotransmitters acting at eukaryotic pLGICs but is activated by protons. To determine whether the structural differences account for functional differences, we used a eukaryotic chimeric acetylcholine-glutamate pLGIC that was modified to carry deletions corresponding to the sequences missing in the prokaryotic homolog GLIC. Deletions made in the N-terminal extracellular α helix did not prevent the expression of receptor subunits and the appearance of receptor assemblies on the cell surface but abolished the capability of the receptor to bind α-bungarotoxin (a competitive antagonist) and to respond to the neurotransmitter. Other truncated chimeric receptors that lacked the intracellular domain did bind ligands; displayed robust acetylcholine-elicited responses; and shared with the full-length chimeric receptor similar anionic selectivity, effective open pore diameter, and unitary conductance. We suggest that the integrity of the N-terminal α helix is crucial for ligand accommodation because it stabilizes the intersubunit interfaces adjacent to the neurotransmitter-binding pocket(s). We also conclude that the intracellular domain of the chimeric acetylcholine-glutamate receptor does not modulate the ion channel conductance and is not involved in positioning of the pore-lining helices in the conformation necessary for coordinating a Cl- ion within the intracellular vestibule of the ion channel pore.
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Affiliation(s)
- Dekel D Bar-Lev
- Laboratory of Ion Channels, Bar-Ilan University, Ramat Gan 52900, Israel; Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat Gan 52900, Israel
| | - Nurit Degani-Katzav
- Laboratory of Ion Channels, Bar-Ilan University, Ramat Gan 52900, Israel; Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat Gan 52900, Israel
| | - Alexander Perelman
- Scientific Equipment Unit, The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat Gan 52900, Israel
| | - Yoav Paas
- Laboratory of Ion Channels, Bar-Ilan University, Ramat Gan 52900, Israel; Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat Gan 52900, Israel.
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O'Toole KK, Jenkins A. Discrete M3-M4 intracellular loop subdomains control specific aspects of γ-aminobutyric acid type A receptor function. J Biol Chem 2011; 286:37990-37999. [PMID: 21903587 DOI: 10.1074/jbc.m111.258012] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The GABA type A receptor (GABA(A)R) is a member of the pentameric ligand gated ion channel (pLGIC) family that mediates ionotropic neurotransmission. Residues in the intracellular loop domain (ILD) have recently been shown to define part of the ion permeation pathway in several closely related members of the pentameric ligand gated ion channel family. In this study, we investigated the role the ILD of the GABA(A)R α1 subunit plays in channel function. Deletion of the α1 ILD resulted in a significant increase in GABA EC(50) and maximal current amplitude, suggesting that the ILD must be intact for proper receptor function. To test this hypothesis, we conducted a mutagenic screen of all amino acids harboring ionizable side chains within this domain to investigate the contribution of individual charged residues to ion permeation. Using macroscopic and single channel voltage-clamp recording techniques, we found that mutations within a subdomain of the α1 ILD near M3 altered GABA apparent affinity; interestingly, α1(K312E) exhibited reduced partial agonist efficacy. We introduced point mutations near M4, including α1(K383E) and α1(K384E), that enhanced receptor desensitization. Mutation of 5 charged residues within a 39-residue span contiguous with M4 reduced relative anion permeability of the channel and may represent a weak intracellular selectivity filter. Within this subdomain, the α1(K378E) mutation induced a significant reduction in single channel conductance, consistent with our hypothesis that the GABA(A)R α1 ILD contributes directly to the permeation pathway.
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Affiliation(s)
- Kate K O'Toole
- Departments of Anesthesiology and Pharmacology, Emory University, Atlanta, Georgia 30322
| | - Andrew Jenkins
- Departments of Anesthesiology and Pharmacology, Emory University, Atlanta, Georgia 30322.
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Lee BH, Shin TJ, Hwang SH, Choi SH, Kang J, Kim HJ, Park CW, Lee SH, Nah SY. Inhibitory Effects of Quercetin on Muscle-type of Nicotinic Acetylcholine Receptor-Mediated Ion Currents Expressed in Xenopus Oocytes. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2011; 15:195-201. [PMID: 21994477 DOI: 10.4196/kjpp.2011.15.4.195] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2011] [Revised: 07/20/2011] [Accepted: 08/02/2011] [Indexed: 11/15/2022]
Abstract
The flavonoid quercetin is a low molecular weight compound generally found in apple, gingko, tomato, onion and other red-colored fruits and vegetables. Like other flavonoids, quercetin has diverse pharmacological actions. However, relatively little is known about the influence of quercetin effects in the regulation of ligand-gated ion channels. Previously, we reported that quercetin regulates subsets of nicotinic acetylcholine receptors such as α3β4, α7 and α9α10. Presently, we investigated the effects of quercetin on muscle-type of nicotinic acetylcholine receptor channel activity expressed in Xenopus oocytes after injection of cRNA encoding human fetal or adult muscle-type of nicotinic acetylcholine receptor subunits. Acetylcholine treatment elicited an inward peak current (I(ACh)) in oocytes expressing both muscle-type of nicotinic acetylcholine receptors and co-treatment of quercetin with acetylcholine inhibited I(ACh). Pre-treatment of quercetin further inhibited I(ACh) in oocytes expressing adult and fetal muscle-type nicotinic acetylcholine receptors. The inhibition of I(ACh) by quercetin was reversible and concentration-dependent. The IC(50) of quercetin was 18.9±1.2 µM in oocytes expressing adult muscle-type nicotinic acetylcholine receptor. The inhibition of I(ACh) by quercetin was voltage-independent and non-competitive. These results indicate that quercetin might regulate human muscle-type nicotinic acetylcholine receptor channel activity and that quercetin-mediated regulation of muscle-type nicotinic acetylcholine receptor might be coupled to regulation of neuromuscular junction activity.
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Affiliation(s)
- Byung-Hwan Lee
- Department of Physiology, College of Veterinary Medicine and Bio/Molecular Informatics Center, Konkuk University, Seoul 143-701, Korea
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Livesey MR, Cooper MA, Lambert JJ, Peters JA. Rings of charge within the extracellular vestibule influence ion permeation of the 5-HT3A receptor. J Biol Chem 2011; 286:16008-17. [PMID: 21454663 PMCID: PMC3091210 DOI: 10.1074/jbc.m111.219618] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
The determinants of single channel conductance (γ) and ion selectivity within eukaryotic pentameric ligand-gated ion channels have traditionally been ascribed to amino acid residues within the second transmembrane domain and flanking sequences of their component subunits. However, recent evidence suggests that γ is additionally controlled by residues within the intracellular and extracellular domains. We examined the influence of two anionic residues (Asp113 and Asp127) within the extracellular vestibule of a high conductance human mutant 5-hydroxytryptamine type-3A (5-HT3A) receptor (5-HT3A(QDA)) upon γ, modulation of the latter by extracellular Ca2+, and the permeability of Ca2+ with respect to Cs+ (PCa/PCs). Mutations neutralizing (Asp → Asn), or reversing (Asp → Lys), charge at the 113 locus decreased inward γ by 46 and 58%, respectively, but outward currents were unaffected. The D127N mutation decreased inward γ by 82% and also suppressed outward currents, whereas the D127K mutation caused loss of observable single channel currents. The forgoing mutations, except for D127K, which could not be evaluated, ameliorated suppression of inwardly directed single channel currents by extracellular Ca2+. The PCa/PCs of 3.8 previously reported for the 5-HT3A(QDA) construct was reduced to 0.13 and 0.06 by the D127N and D127K mutations, respectively, with lesser, but clearly significant, effects caused by the D113N (1.04) and D113K (0.60) substitutions. Charge selectivity between monovalent cations and anions (PNa/PCl) was unaffected by any of the mutations examined. The data identify two key residues in the extracellular vestibule of the 5-HT3A receptor that markedly influence γ, PCa/PCs, and additionally the suppression of γ by Ca2+.
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Affiliation(s)
- Matthew R Livesey
- Centre for Neuroscience, Division of Medical Sciences, Ninewells Hospital and Medical School, University of Dundee, Dundee, United Kingdom
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Lee BH, Hwang SH, Choi SH, Shin TJ, Kang J, Lee SM, Nah SY. Quercetin Inhibits α3β4 Nicotinic Acetylcholine Receptor-Mediated Ion Currents Expressed in Xenopus Oocytes. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2011; 15:17-22. [PMID: 21461236 DOI: 10.4196/kjpp.2011.15.1.17] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/27/2010] [Revised: 01/17/2011] [Accepted: 01/18/2011] [Indexed: 11/15/2022]
Abstract
Quercetin mainly exists in the skin of colored fruits and vegetables as one of flavonoids. Recent studies show that quercetin, like other flavonoids, has diverse pharmacological actions. However, relatively little is known about quercetin effects in the regulations of ligand-gated ion channels. In the previous reports, we have shown that quercetin regulates subsets of homomeric ligand-gated ion channels such as glycine, 5-HT(3A) and α7 nicotinic acetylcholine receptors. In the present study, we examined quercetin effects on heteromeric neuronal α3β4 nicotinic acetylcholine receptor channel activity expressed in Xenopus oocytes after injection of cRNA encoding bovine neuronal α3 and β4 subunits. Treatment with acetylcholine elicited an inward peak current (I(ACh)) in oocytes expressing α3β4 nicotinic acetylcholine receptor. Co-treatment with quercetin and acetylcholine inhibited I(ACh) in oocytes expressing α3β4 nicotinic acetylcholine receptors. The inhibition of I(ACh) by quercetin was reversible and concentration-dependent. The half-inhibitory concentration (IC(50)) of quercetin was 14.9±0.8 µM in oocytes expressing α3β4 nicotinic acetylcholine receptor. The inhibition of I(ACh) by quercetin was voltage-independent and non-competitive. These results indicate that quercetin might regulate α3β4 nicotinic acetylcholine receptor and this regulation might be one of the pharmacological actions of quercetin in nervous systems.
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Affiliation(s)
- Byung-Hwan Lee
- Department of Physiology, College of Veterinary Medicine and Bio/Molecular Informatics Center, Konkuk University, Seoul 143-701, Korea
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Poudel KR, Keller DJ, Brozik JA. Single particle tracking reveals corralling of a transmembrane protein in a double-cushioned lipid bilayer assembly. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2011; 27:320-327. [PMID: 21141848 DOI: 10.1021/la104133m] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
A predominate question associated with supported bilayer assemblies containing proteins is whether or not the proteins remain active after incorporation. The major cause for concern is that strong interactions with solid supports can render the protein inactive. To address this question, a large transmembrane protein, the serotonin receptor, 5HT(3A), has been incorporated into several supported membrane bilayer assemblies of increasing complexity. The 5HT(3A) receptor has large extracellular domains on both sides of the membrane, which could cause strong interactions. The bilayer assemblies include a simple POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) supported planar bilayer, a “single-cushion” POPC bilayer with a PEG (poly(ethylene glycol)) layer between membrane and support, and a “double-cushion” POPC bilayer with both a PEG layer and a layer of BSA (bovine serum albumin). Single-cushion systems are designed to lift the bilayer from the surface, and double-cushion systems are designed to both lift the membrane and passivate the solid support. As in previously reported work, protein mobilities measured by ensemble fluorescence recovery after photobleaching (FRAP) are quite low, especially in the double-cushion system. But single-particle tracking of fluorescent 5HT(3A) molecules shows that individual proteins in the double-cushion system have quite high local mobilities but are spatially confined within small corralling domains (<r(C)2> 450 nm). Comparisons with the simple POPC membrane and the single-cushion POPC−PEG membrane reveal that BSA both serves to minimize interactions with the solid support and creates the corrals that reduce the long-range (ensemble averaged) mobility of large transmembrane proteins. These results suggest that in double-cushion assemblies proteins with large extra-membrane domains may remain active and unperturbed despite low bulk diffusion constants.
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Affiliation(s)
- Kumud R Poudel
- Department of Chemistry, Washington State University, PO Box 644630, Pullman, Washington 99164-4630, United States
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Lee BH, Choi SH, Shin TJ, Pyo MK, Hwang SH, Lee SM, Paik HD, Kim HC, Nah SY. Effects of quercetin on α9α10 nicotinic acetylcholine receptor-mediated ion currents. Eur J Pharmacol 2011; 650:79-85. [DOI: 10.1016/j.ejphar.2010.09.079] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2010] [Revised: 09/23/2010] [Accepted: 09/29/2010] [Indexed: 11/29/2022]
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Abstract
Cys-loop receptors are membrane-spanning neurotransmitter-gated ion channels that are responsible for fast excitatory and inhibitory transmission in the peripheral and central nervous systems. The best studied members of the Cys-loop family are nACh, 5-HT3, GABAA and glycine receptors. All these receptors share a common structure of five subunits, pseudo-symmetrically arranged to form a rosette with a central ion-conducting pore. Some are cation selective (e.g. nACh and 5-HT3) and some are anion selective (e.g. GABAA and glycine). Each receptor has an extracellular domain (ECD) that contains the ligand-binding sites, a transmembrane domain (TMD) that allows ions to pass across the membrane, and an intracellular domain (ICD) that plays a role in channel conductance and receptor modulation. Cys-loop receptors are the targets for many currently used clinically relevant drugs (e.g. benzodiazepines and anaesthetics). Understanding the molecular mechanisms of these receptors could therefore provide the catalyst for further development in this field, as well as promoting the development of experimental techniques for other areas of neuroscience.In this review, we present our current understanding of Cys-loop receptor structure and function. The ECD has been extensively studied. Research in this area has been stimulated in recent years by the publication of high-resolution structures of nACh receptors and related proteins, which have permitted the creation of many Cys loop receptor homology models of this region. Here, using the 5-HT3 receptor as a typical member of the family, we describe how homology modelling and ligand docking can provide useful but not definitive information about ligand interactions. We briefly consider some of the many Cys-loop receptors modulators. We discuss the current understanding of the structure of the TMD, and how this links to the ECD to allow channel gating, and consider the roles of the ICD, whose structure is poorly understood. We also describe some of the current methods that are beginning to reveal the differences between different receptor states, and may ultimately show structural details of transitions between them.
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Lee BH, Choi SH, Shin TJ, Pyo MK, Hwang SH, Kim BR, Lee SM, Lee JH, Kim HC, Park HY, Rhim H, Nah SY. Quercetin enhances human α7 nicotinic acetylcholine receptor-mediated ion current through interactions with Ca(2+) binding sites. Mol Cells 2010; 30:245-53. [PMID: 20803082 DOI: 10.1007/s10059-010-0117-9] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2010] [Revised: 06/10/2010] [Accepted: 06/14/2010] [Indexed: 10/19/2022] Open
Abstract
The flavonoid quercetin is a low molecular weight substance found in fruits and vegetables. Aside from its anti-oxidative effect, quercetin, like other flavonoids, has a wide range of neuropharmacological actions. The α7 nicotinic acetylcholine receptor (α7 nAChR) has a Ca(2+)-binding site, is highly permeable to the Ca(2+) ion, and plays important roles in Ca(2+)-related normal brain functions. Dysfunctions of α7 nAChR are associated with a variety of neurological disorders. In the present study, we investigated the effects of quercetin on the ACh-induced inward peak current (I(ACh)) in Xenopus oocytes that heterologously express human α7 nAChR. I(ACh) was measured with the two-electrode voltage clamp technique. In oocytes injected with α7 nAChR cRNA, the effects of the co-application of quercetin on I(ACh) were concentration-dependent and reversible. The ED(50) was 36.1 + 6.1 μM. Quercetin-mediated enhancement of I(ACh) caused more potentiation when quercetin was pre-applied. The degree of I(ACh) potentiation by quercetin pre-application was time-dependent and saturated after 1 min. Quercetin-mediated I(ACh) enhancement was not affected by ACh concentration and was voltage-independent. However, quercetin-mediated I(ACh) enhancement was dependent on extracellular Ca(2+) concentrations and was specific to the Ca(2+) ion, since the removal of extracellular Ca(2+) or the addition of Ba(2+) instead of Ca(2+) greatly diminished quercetin enhancement of I(ACh). The mutation of Glu195 to Gln195, in the Ca(2+)-binding site, almost completely diminished quercetin-mediated I(ACh) enhancement. These results indicate that quercetin-mediated I(ACh) enhancement human α7 nAChR heterologously expressed in Xenopus oocytes could be achieved through interactions with the Ca(2+)-binding site of the receptor.
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Affiliation(s)
- Byung-Hwan Lee
- Department of Physiology, College of Veterinary Medicine and Bio/Molecular Informatics Center, Konkuk University, Seoul, 143-701, Korea
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Bertaccini EJ. The Molecular Mechanisms of Anesthetic Action: Updates and Cutting Edge Developments from the Field of Molecular Modeling. Pharmaceuticals (Basel) 2010; 3:2178-2196. [PMID: 27713348 PMCID: PMC4036663 DOI: 10.3390/ph3072178] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2010] [Revised: 06/10/2010] [Accepted: 07/06/2010] [Indexed: 12/01/2022] Open
Abstract
For over 160 years, general anesthetics have been given for the relief of pain and suffering. While many theories of anesthetic action have been purported, it has become increasingly apparent that a significant molecular focus of anesthetic action lies within the family of ligand-gated ion channels (LGIC’s). These protein channels have a transmembrane region that is composed of a pentamer of four helix bundles, symmetrically arranged around a central pore for ion passage. While initial and some current models suggest a possible cavity for binding within this four helix bundle, newer calculations postulate that the actual cavity for anesthetic binding may exist between four helix bundles. In either scenario, these cavities have a transmembrane mode of access and may be partially bordered by lipid moieties. Their physicochemical nature is amphiphilic. Anesthetic binding may alter the overall motion of a ligand-gated ion channel by a “foot-in-door” motif, resulting in the higher likelihood of and greater time spent in a specific channel state. The overall gating motion of these channels is consistent with that shown in normal mode analyses carried out both in vacuo as well as in explicitly hydrated lipid bilayer models. Molecular docking and large scale molecular dynamics calculations may now begin to show a more exact mode by which anesthetic molecules actually localize themselves and bind to specific protein sites within LGIC’s, making the design of future improvements to anesthetic ligands a more realizable possibility.
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Affiliation(s)
- Edward J Bertaccini
- Department of Anesthesia, Stanford University School of Medicine, Co-Director of Operating Room and Intensive Care Services, Palo Alto VA Health Care System, 112A, PAVAHCS, 3801 Miranda Avenue, Palo Alto, CA 94304, USA.
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Yuan G, Gao W, Yang Y, Wu Y. Molecular cloning, genomic structure, and genetic mapping of two Rdl-orthologous genes of GABA receptors in the diamondback moth, Plutella xylostella. ARCHIVES OF INSECT BIOCHEMISTRY AND PHYSIOLOGY 2010; 74:81-90. [PMID: 20513056 DOI: 10.1002/arch.20361] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
The Resistance to dieldrin (Rdl) gene encodes a subunit of the insect gamma-aminobutyric acid (GABA) receptor. Cyclodiene resistance in many insects is associated with replacement of a single amino acid (alanine at position 302) with either a serine or a glycine in the Rdl gene. Two Rdl-orthologous genes of GABA receptors (PxGABARalpha1 and PxGABARalpha2) were cloned and sequenced from a susceptible strain (Roth) of Plutella xylostella. PxGABARalpha1 and PxGABARalpha2 showed 84% and 77% identity with the Rdl gene of Drosophila melanogaster at an amino acid level, respectively. The coding regions of PxGABARalpha1 and PxGABARalpha2 both comprise ten exons, with two alternative RNA-splicing forms in exon 3 of both genes. At the orthologous position of alanine-302 in D. melanogaster Rdl, PxGABARalpha1 has a conserved alanine at position 282. PxGABARalpha2 has a serine instead of an alanine at the equivalent position. With two informative DNA markers, both PxGABARalpha1 and PxGABARalpha2 were mapped onto the Z chromosome of P. xylostella.
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Affiliation(s)
- Guorui Yuan
- College of Plant Protection, Nanjing Agricultural University, Key Laboratory of Monitoring and Management of Crop Diseases and Pest Insects (Ministry of Agriculture of China), Nanjing, China
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Sugiharto S, Carland JE, Lewis TM, Moorhouse AJ, Barry PH. External divalent cations increase anion-cation permeability ratio in glycine receptor channels. Pflugers Arch 2010; 460:131-52. [PMID: 20198385 DOI: 10.1007/s00424-010-0792-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2009] [Revised: 01/15/2010] [Accepted: 01/22/2010] [Indexed: 11/24/2022]
Abstract
The functional role of ligand-gated ion channels in the central nervous system depends on their relative anion-cation permeability. Using standard whole-cell patch clamp measurements and NaCl dilution potential measurements, we explored the effect of external divalent ions on anion-cation selectivity in alpha1-homomeric wild-type glycine receptor channels. We show that increasing external Ca(2+) from 0 to 4 mM resulted in a sigmoidal increase in anion-cation permeability by 37%, reaching a maximum above about 2 mM. Our accurate quantification of this effect required rigorous correction for liquid junction potentials (LJPs) using ion activities, and allowing for an initial offset potential. Failure to do this results in a considerable overestimation of the Ca(2+)-induced increase in anion-cation permeability by almost three-fold at 4 mM external Ca(2+). Calculations of LJPs (using activities)_ were validated by precise agreement with direct experimental measurements. External SO (4) (2-) was found to decrease anion-cation permeability. Single-channel conductance measurements indicated that external Ca(2+) both decreased Na(+) permeability and increased Cl(-) permeability. There was no evidence of Ca(2+) changing channel pore diameter. Theoretical modeling indicates that the effect is not surface charge related. Rather, we propose that, under dilution conditions, the presence of an impermeant Ca(2+) ion in the channel pore region just external to the selectivity filter tends to electrostatically retard outward movement of Na(+) ions and to enhance movement of Cl(-) ions down their energy gradients.
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Affiliation(s)
- Silas Sugiharto
- Department of Physiology, School of Medical Sciences, University of New South Wales, Sydney, NSW, 2052, Australia
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Peters JA, Cooper MA, Carland JE, Livesey MR, Hales TG, Lambert JJ. Novel structural determinants of single channel conductance and ion selectivity in 5-hydroxytryptamine type 3 and nicotinic acetylcholine receptors. J Physiol 2010; 588:587-96. [PMID: 19933751 PMCID: PMC2828133 DOI: 10.1113/jphysiol.2009.183137] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Nicotinic acetylcholine (nACh) and 5-hydroxytryptamine type 3 (5-HT(3)) receptors are cation-selective ion channels of the pentameric ligand-gated ion channel (pLGIC) superfamily. Multiple lines of evidence adduced over the last 30 years indicate that the lining of the channel of such receptors is formed by the alpha-helical second transmembrane (TM2) domain and flanking sequences contributed by each of the five subunits present within the receptor complex. Specific amino acid residues within, and adjacent to, the TM2 domain influence single channel conductance, ion selectivity, and other aspects of receptor function that include gating and desensitization. However, more recent work has revealed important structural determinants of single channel conductance and ion selectivity that are not associated with the TM2 domain. Direct experimental evidence indicates that the intracellular domain of eukaryotic pLGICs, in particular a region of the loop linking TM3 and TM4 termed the membrane-associated (MA) stretch, exerts a strong influence upon ion channel biophysics. Moreover, recent computational approaches, complemented by experimentation, implicate the extracellular domain as an additional important determinant of ion conduction. This brief review describes how our knowledge of ion conduction and selectivity in cation-selective pLGICs has evolved beyond TM2.
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Affiliation(s)
- John A Peters
- Centre for Neuroscience, Division of Medical Sciences, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, UK.
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The cys-loop ligand-gated ion channel gene superfamily of the parasitoid wasp, Nasonia vitripennis. Heredity (Edinb) 2010; 104:247-59. [DOI: 10.1038/hdy.2009.97] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
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Jones AK, Sattelle DB. Diversity of Insect Nicotinic Acetylcholine Receptor Subunits. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 683:25-43. [DOI: 10.1007/978-1-4419-6445-8_3] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
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Alternative splicing of the Anopheles gambiae nicotinic acetylcholine receptor, Agamαβ9, generates both alpha and beta subunits. INVERTEBRATE NEUROSCIENCE 2009; 9:77-84. [DOI: 10.1007/s10158-009-0089-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2009] [Accepted: 07/23/2009] [Indexed: 01/01/2023]
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López-Hernández GY, Thinschmidt JS, Zheng G, Zhang Z, Crooks PA, Dwoskin LP, Papke RL. Selective inhibition of acetylcholine-evoked responses of alpha7 neuronal nicotinic acetylcholine receptors by novel tris- and tetrakis-azaaromatic quaternary ammonium antagonists. Mol Pharmacol 2009; 76:652-66. [PMID: 19556356 DOI: 10.1124/mol.109.056176] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A family of 20 tris-azaaromatic quaternary ammonium (AQA) compounds were tested for their inhibition of alpha7 nicotinic acetylcholine receptors (nAChRs) expressed in Xenopus laevis oocytes. The potency of inhibitory activity was related to the hydrophobic character of the tris head groups. Two tris-AQA compounds were studied in detail: the highly effective inhibitor 1,3,5-tri-[5-(1-quinolinum)-pent-1-yn-1-yl]-benzene tribromide (tPyQB) and the less potent antagonist 1,3,5,-tri-{5-[1-(2-picolinium)]-pent-1-yn-1-yl}benzene tribromide (tPy2PiB). In addition, we evaluated 1,2,4,5-tetra-{5-[1-(3-benzyl)pyridinium]pent-1-yl}benzene tetrabromide (tkP3BzPB), a tetrakis-AQA with very hydrophobic headgroups. We compared the activity of the AQA compounds to the frequently used alpha7-antagonist methyllycaconitine (MLA). Both tPyQB and tkP3BzPB were selective antagonists of alpha7. However, although inhibition by tPyQB was reversible within 5 min, the recovery time constant for tkP3BzPB inhibition was 26.6 +/- 0.8 min, so that the equilibrium inhibition in the prolonged presence of nanomolar concentrations of tkP3BzPB was nearly 100%. The potency, selectivity, and slow reversibility of tkP3BzPB were comparable with or greater than that of MLA. The inhibitory actions of tPyQB, tPy2PiB, and tkP3BzPB were evaluated on the acetylcholine (ACh)-evoked responses of native nAChRs in rat brain slices. The alpha7-mediated responses of hippocampal interneurons were effectively reduced by 1 microM tPyQB and tkP3BzPB but not tPy2PiB. In rat medial septum, tkP3BzPB produced a greater inhibition of ACh-evoked responses of cells with fast inward currents (type I) than of cells with predominantly slow kinetics (type II), suggesting that tkP3BzPB can block alpha7 yet preserve the responsiveness of non-alpha7 receptors. These agents might be helpful in elucidating complex receptor responses in brain regions with mixed populations of nAChRs.
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Affiliation(s)
- Gretchen Y López-Hernández
- Department of Pharmacology and Therapeutics, University of Florida, P.O. Box 100267, Gainesville, FL 32610-0267, USA
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Lee BH, Choi SH, Pyo MK, Shin TJ, Hwang SH, Kim BR, Lee SM, Lee JH, Lee JH, Lee HS, Choe H, Han KH, Kim HC, Rhim H, Yong JH, Nah SY. A role for Leu247 residue within transmembrane domain 2 in ginsenoside-mediated alpha7 nicotinic acetylcholine receptor regulation. Mol Cells 2009; 27:591-9. [PMID: 19466608 DOI: 10.1007/s10059-009-0073-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2009] [Revised: 03/18/2009] [Accepted: 03/19/2009] [Indexed: 10/20/2022] Open
Abstract
Nicotinic acetylcholine receptors (nAChRs) play important roles in nervous system functions and are involved in a variety of diseases. We previously demonstrated that ginsenosides, the active ingredients of Panax ginseng, inhibit subsets of nAChR channel currents, but not alpha7, expressed in Xenopus laevis oocytes. Mutation of the highly conserved Leu247 to Thr247 in the transmembrane domain 2 (TM2) channel pore region of alpha7 nAChR induces alterations in channel gating properties and converts alpha7 nAChR antagonists into agonists. In the present study, we assessed how point mutations in the Leu247 residue leading to various amino acids affect 20(S)-ginsenoside Rg(3) (Rg(3)) activity against the alpha7 nAChR. Mutation of L247 to L247A, L247D, L247E, L247I, L247S, and L247T, but not L247K, rendered mutant receptors sensitive to Rg(3). We further characterized Rg(3) regulation of L247T receptors. We found that Rg(3) inhibition of mutant alpha7 nAChR channel currents was reversible and concentration-dependent. Rg(3) inhibition was strongly voltage-dependent and noncompetitive manner. These results indicate that the interaction between Rg(3) and mutant receptors might differ from its interaction with the wild-type receptor. To identify differences in Rg(3) interactions between wild-type and L247T receptors, we utilized docked modeling. This modeling revealed that Rg(3) forms hydrogen bonds with amino acids, such as Ser240 of subunit I and Thr244 of subunit II and V at the channel pore, whereas Rg(3) localizes at the interface of the two wild-type receptor subunits. These results indicate that mutation of Leu247 to Thr247 induces conformational changes in the wild-type receptor and provides a binding pocket for Rg(3) at the channel pore.
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Affiliation(s)
- Byung-Hwan Lee
- Ginsentology Research Laboratory and Department of Physiology, College of Veterinary Medicine, Konkuk University, Seoul 143-701, Korea
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Rinkevich FD, Scott JG. Transcriptional diversity and allelic variation in nicotinic acetylcholine receptor subunits of the red flour beetle, Tribolium castaneum. INSECT MOLECULAR BIOLOGY 2009; 18:233-242. [PMID: 19320762 DOI: 10.1111/j.1365-2583.2009.00873.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Sequence analysis of 168 cDNA clones encoding 12 nicotinic acetylcholine receptor subunits, Tcasalpha1-Tcasalpha11 and Tcasbeta1, from the red flour beetle, Tribolium castaneum, revealed extensive post-transcriptional modification and multiple alleles. The greatest diversity was found for Tcasa6, where 18 unique transcripts, as a result of alternative and optional exon usage, were seen. A novel alternative exon 8d was found in one Tcasalpha6 transcript. Tcasalpha5 transcripts did not contain previously reported exons 8-10. Six subunits had transcripts that contained unspliced introns, which introduced premature stop codons. Intron 3' splice site variants were seen at six intron boundaries across five subunits. A-to-I RNA editing was seen only in Tcasalpha6. Alleles were found for all subunit genes, except Tcasalpha1 and Tcasalpha10. Transcriptional and allelic diversity are discussed with respect to receptor function and potential interactions with insecticides.
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Affiliation(s)
- F D Rinkevich
- Department of Entomology, Cornell University, Ithaca, NY 14853-0901, USA
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Anion-cation permeability correlates with hydrated counterion size in glycine receptor channels. Biophys J 2008; 95:4698-715. [PMID: 18708455 DOI: 10.1529/biophysj.107.125690] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The functional role of ligand-gated ion channels depends critically on whether they are predominantly permeable to cations or anions. However, these, and other ion channels, are not perfectly selective, allowing some counterions to also permeate. To address the mechanisms by which such counterion permeation occurs, we measured the anion-cation permeabilities of different alkali cations, Li(+) Na(+), and Cs(+), relative to either Cl(-) or NO(3)(-) anions in both a wild-type glycine receptor channel (GlyR) and a mutant GlyR with a wider pore diameter. We hypothesized and showed that counterion permeation in anionic channels correlated inversely with an equivalent or effective hydrated size of the cation relative to the channel pore radius, with larger counterion permeabilities being observed in the wider pore channel. We also showed that the anion component of conductance was independent of the nature of the cation. We suggest that anions and counterion cations can permeate through the pore as neutral ion pairs, to allow the cations to overcome the large energy barriers resulting from the positively charged selectivity filter in small GlyR channels, with the permeability of such ion pairs being dependent on the effective hydrated diameter of the ion pair relative to the pore diameter.
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