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Qiao X, Zhou T, Zhang J, Zhang L, Lu Y, Huang J. Functional validation of A2'N mutation of the RDL GABA receptor against fipronil via molecular modeling and genome engineering in drosophila. PEST MANAGEMENT SCIENCE 2024; 80:1924-1929. [PMID: 38086568 DOI: 10.1002/ps.7929] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2023] [Revised: 11/16/2023] [Accepted: 12/04/2023] [Indexed: 12/29/2023]
Abstract
BACKGROUND Insect RDL (resistant to dieldrin) receptors are essential pentameric ligand-gated chloride channels that mediate the neuroinhibitory effect of GABA, the chief inhibitory neurotransmitter in the central nervous system. These receptors serve as primary targets for various insecticides, including noncompetitive antagonists (NCAs) such as cyclodiene organochlorines and phenylpyrazoles, as well as allosteric modulators like meta-diamides and isoxazolines. This study focuses on a newly discovered A2'N mutation within the RDL receptors, identified in fipronil-resistant planthoppers. Despite in vitro electrophysiological studies have proposed its role in conferring target-site resistance, in vivo genetic functional validation of this mutation remains unexplored. RESULTS Our research employed toxicity bioassays, assessing various Rdl genotypes against a spectrum of insecticides, including fipronil, α-endosulfan, broflanilide, and isocycloseram. Results revealed distinct resistance profiles for A2'N and A2'S mutants, indicating different binding interactions of RDL receptors with NCAs. Significantly, the A2'N heterozygote showed substantial resistance to fipronil, despite its homozygous lethality. Molecular modeling and docking simulations further supported these findings, highlighting unique binding poses for fipronil and α-endosulfan. CONCLUSION This study confirmed that A2'N mutation of the RDL GABA receptor confer high resistance to fipronil in vivo. The observed resistance in A2'N mutants is likely attributable to a steric hindrance mechanism, wherein the introduction of larger side chains hampers fipronil binding, even in a heterozygous state. © 2023 Society of Chemical Industry.
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Affiliation(s)
| | - Tianhao Zhou
- Ministry of Agriculture Key Laboratory of Molecular Biology of Crop Pathogens and Insects, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
| | - Jing Zhang
- Institute of Functional Molecules, Shenyang University of Chemical Technology, Shenyang, China
| | - Lixin Zhang
- Institute of Functional Molecules, Shenyang University of Chemical Technology, Shenyang, China
| | | | - Jia Huang
- Ministry of Agriculture Key Laboratory of Molecular Biology of Crop Pathogens and Insects, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
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Guo L, Qiao X, Haji D, Zhou T, Liu Z, Whiteman NK, Huang J. Convergent resistance to GABA receptor neurotoxins through plant-insect coevolution. Nat Ecol Evol 2023; 7:1444-1456. [PMID: 37460839 PMCID: PMC10482695 DOI: 10.1038/s41559-023-02127-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Accepted: 06/22/2023] [Indexed: 09/08/2023]
Abstract
The molecular mechanisms of coevolution between plants and insects remain elusive. GABA receptors are targets of many neurotoxic terpenoids, which represent the most diverse array of natural products known. Over deep evolutionary time, as plant terpene synthases diversified in plants, so did plant terpenoid defence repertoires. Here we show that herbivorous insects and their predators evolved convergent amino acid changing substitutions in duplicated copies of the Resistance to dieldrin (Rdl) gene that encodes the GABA receptor, and that the evolution of duplicated Rdl and terpenoid-resistant GABA receptors is associated with the diversification of moths and butterflies. These same substitutions also evolved in pests exposed to synthetic insecticides that target the GABA receptor. We used in vivo genome editing in Drosophila melanogaster to evaluate the fitness effects of each putative resistance mutation and found that pleiotropy both facilitates and constrains the evolution of GABA receptor resistance. The same genetic changes that confer resistance to terpenoids across 300 Myr of insect evolution have re-evolved in response to synthetic analogues over one human lifespan.
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Affiliation(s)
- Lei Guo
- Ministry of Agriculture Key Laboratory of Molecular Biology of Crop Pathogens and Insects, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
| | | | - Diler Haji
- Department of Integrative Biology, University of California, Berkeley, CA, USA
| | - Tianhao Zhou
- Ministry of Agriculture Key Laboratory of Molecular Biology of Crop Pathogens and Insects, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
| | - Zhihan Liu
- Ministry of Agriculture Key Laboratory of Molecular Biology of Crop Pathogens and Insects, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
| | - Noah K Whiteman
- Department of Integrative Biology, University of California, Berkeley, CA, USA.
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, USA.
| | - Jia Huang
- Ministry of Agriculture Key Laboratory of Molecular Biology of Crop Pathogens and Insects, Institute of Insect Sciences, Zhejiang University, Hangzhou, China.
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De Rouck S, İnak E, Dermauw W, Van Leeuwen T. A review of the molecular mechanisms of acaricide resistance in mites and ticks. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2023; 159:103981. [PMID: 37391089 DOI: 10.1016/j.ibmb.2023.103981] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2023] [Revised: 05/12/2023] [Accepted: 06/11/2023] [Indexed: 07/02/2023]
Abstract
The Arachnida subclass of Acari comprises many harmful pests that threaten agriculture as well as animal health, including herbivorous spider mites, the bee parasite Varroa, the poultry mite Dermanyssus and several species of ticks. Especially in agriculture, acaricides are often used intensively to minimize the damage they inflict, promoting the development of resistance. Beneficial predatory mites used in biological control are also subjected to acaricide selection in the field. The development and use of new genetic and genomic tools such as genome and transcriptome sequencing, bulked segregant analysis (QTL mapping), and reverse genetics via RNAi or CRISPR/Cas9, have greatly increased our understanding of the molecular genetic mechanisms of resistance in Acari, especially in the spider mite Tetranychus urticae which emerged as a model species. These new techniques allowed to uncover and validate new resistance mutations in a larger range of species. In addition, they provided an impetus to start elucidating more challenging questions on mechanisms of gene regulation of detoxification associated with resistance.
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Affiliation(s)
- Sander De Rouck
- Laboratory of Agrozoology, Department of Plants and Crops, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000, Ghent, Belgium
| | - Emre İnak
- Laboratory of Agrozoology, Department of Plants and Crops, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000, Ghent, Belgium; Department of Plant Protection, Faculty of Agriculture, Ankara University, Dıskapı, 06110, Ankara, Turkiye
| | - Wannes Dermauw
- Laboratory of Agrozoology, Department of Plants and Crops, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000, Ghent, Belgium; Flanders Research Institute for Agriculture, Fisheries and Food (ILVO), Plant Sciences Unit, 9820 Merelbeke, Belgium
| | - Thomas Van Leeuwen
- Laboratory of Agrozoology, Department of Plants and Crops, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000, Ghent, Belgium.
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4
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ffrench-Constant RH. Transposable elements and xenobiotic resistance. FRONTIERS IN INSECT SCIENCE 2023; 3:1178212. [PMID: 38469483 PMCID: PMC10926513 DOI: 10.3389/finsc.2023.1178212] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/02/2023] [Accepted: 05/24/2023] [Indexed: 03/13/2024]
Abstract
Transposable elements or TEs are well known drivers of adaptive change in plants and animals but their role in insecticide resistance remains poorly documented. This review examines the potential role of transposons in resistance and identifies key areas where our understanding remains unclear. Despite well-known model systems such as upregulation of Drosophila Cyp6g1, many putative examples lack functional validation. The potential types of transposon-associated changes that could lead to resistance are reviewed, including changes in up-regulation, message stability, loss of function and alternative splicing. Where potential mechanisms appear absent from the resistance literature examples are drawn from other areas of biology. Finally, ways are suggested in which transgenic expression could be used to validate the biological significance of TE insertion. In the absence of such functional expression studies many examples of the association of TEs and resistance genes therefore remain as correlations.
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Mermans C, Dermauw W, Geibel S, Van Leeuwen T. Activity, selection response and molecular mode of action of the isoxazoline afoxolaner in Tetranychus urticae. PEST MANAGEMENT SCIENCE 2023; 79:183-193. [PMID: 36116012 DOI: 10.1002/ps.7187] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2022] [Revised: 09/13/2022] [Accepted: 09/18/2022] [Indexed: 06/15/2023]
Abstract
BACKGROUND Afoxolaner is a novel representative of the isoxazolines, a class of ectoparasiticides which has been commercialized for the control of tick and flea infestations in dogs. In this study, the biological efficacy of afoxolaner against the two-spotted spider mite Tetranychus urticae was evaluated. Furthermore, as isoxazolines are known inhibitors of γ-aminobutyric acid-gated chloride channels (GABACls), the molecular mode of action of afoxolaner on T. urticae GABACls (TuRdls) was studied using functional expression in Xenopus oocytes followed by two-electrode voltage-clamp (TEVC) electrophysiology, and results were compared with inhibition by fluralaner, fipronil and endosulfan. To examine the influence of known GABACl resistance mutations, H301A, I305T and A350T substitutions in TuRdl1 and a S301A substitution in TuRdl2 were introduced. RESULTS Bioasassays revealed excellent efficacy of afoxolaner against all developmental stages and no cross-resistance was found in a panel of strains resistant to most currently used acaricides. Laboratory selection over a period of 3 years did not result in resistance. TEVC revealed clear antagonistic activity of afoxolaner and fluralaner for all homomeric TuRdl1/2/3 channels. The introduction of single, double or triple mutations to TuRdl1 and TuRdl2 did not lower channel sensitivity. By contrast, both endosulfan and fipronil had minimal antagonistic activities against TuRdl1/2/3, and channels carrying single mutations, whereas the sensitivity of double and triple TuRdl1 mutants was significantly increased. CONCLUSIONS Our results demonstrate that afoxolaner is a potent antagonist of GABACls of T. urticae and has a powerful mode of action to control spider mites. © 2022 Society of Chemical Industry.
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Affiliation(s)
- Catherine Mermans
- Department of Plants and Crops | Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium
| | - Wannes Dermauw
- Department of Plants and Crops | Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium
- Plant Sciences Unit, Flanders Research Institute for Agriculture, Fisheries and Food (ILVO), Merelbeke, Belgium
| | - Sven Geibel
- CropScience Division, Bayer AG, Monheim, Germany
| | - Thomas Van Leeuwen
- Department of Plants and Crops | Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium
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Price KL, Lummis SCR. Characterisation of thymol effects on RDL receptors from the bee parasite Varroa destructor. PESTICIDE BIOCHEMISTRY AND PHYSIOLOGY 2022; 183:105064. [PMID: 35430066 DOI: 10.1016/j.pestbp.2022.105064] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2021] [Revised: 02/22/2022] [Accepted: 02/22/2022] [Indexed: 06/14/2023]
Abstract
A major contributor to bee colony decline is infestation with its most devastating pest, the mite Varroa destructor. To control these mites, thymol is often used, although how it achieves this is not understood. One well-documented action of thymol is to modulate GABA-activated ion channels, which includes insect RDL receptors, a known insecticidal target. Here we have cloned two Varroa RDL subunits, one of which is similar to the canonical RDL subunit, while the other has some differences in M4, and, to a lesser extent, M2 and its binding site loops. Expression of this unusual RDL receptor in Xenopus oocytes reveals GABA-activated receptors, with an EC50 of 56 μM. In contrast to canonical RDL receptors, thymol does not enhance GABA-elicited responses in this receptor, and concentration response curves reveal a decrease in GABA Imax in its presence; this decrease is not seen when similar data are obtained from Apis RDL receptors. We conclude that an M2 T6'M substitution is primarily responsible for the different thymol effects, and suggest that understanding how and where thymol acts could assist in the design of novel bee-friendly miticides.
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Affiliation(s)
- K L Price
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK
| | - S C R Lummis
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK.
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7
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Norris EJ, Chen R, Li Z, Geldenhuys W, Bloomquist JR, Swale DR. Mode of action and toxicological effects of the sesquiterpenoid, nootkatone, in insects. PESTICIDE BIOCHEMISTRY AND PHYSIOLOGY 2022; 183:105085. [PMID: 35430075 DOI: 10.1016/j.pestbp.2022.105085] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2022] [Revised: 03/16/2022] [Accepted: 03/18/2022] [Indexed: 06/14/2023]
Abstract
Nootkatone, a sesquiterpenoid isolated from Alaskan yellow cedar (Cupressus nootkatensis), is known to possess insect repellent and acaricidal properties and has recently been registered for commercial use by the Environmental Protection Agency. Previous studies failed to elucidate the mechanism of action of nootkatone, but we found a molecular overlay of picrotoxinin and nootkatone indicated a high degree of structural and electrostatic similarity. We therefore tested the hypothesis that nootkatone was a GABA-gated chloride channel antagonist, similar to picrotoxinin. The KD50 and LD50 of nootkatone on the insecticide-susceptible strain of Drosophila melanogaster (CSOR) showed resistance ratios of 8 and 11, respectively, compared to the cyclodiene-resistant strain of RDL1675, indicating significant cross-resistance. Nootkatone reversed GABA-mediated block of the larval CSOR central nervous system; nerve firing of 78 ± 17% of baseline in the CSOR strain was significantly different from 24 ± 11% of baseline firing in the RDL1675 strain (p = 0.035). This finding indicated that the resistance was expressed within the nervous system. Patch clamp recordings on D. melanogaster central neurons mirrored extracellular recordings where nootkatone inhibited GABA-stimulated currents by 44 ± 9% at 100 μM, whereas chloride current was inhibited 4.5-fold less at 100 μM in RDL1675. Taken together, these data suggest nootkatone toxicity in D. melanogaster is mediated through GABA receptor antagonism.
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Affiliation(s)
- Edmund J Norris
- Emerging Pathogens Institute, Entomology and Nematology Department, 2055 Mowry Road, University of Florida, Gainesville, FL 32610-0009, USA; USDA/ARS Center for Medical, Agricultural, and Veterinary Entomology, Gainesville, FL 32610-0009, USA
| | - Rui Chen
- Louisiana State University Agricultural Center, Department of Entomology, Baton Rouge, LA 70803, USA
| | - Zhilin Li
- Louisiana State University Agricultural Center, Department of Entomology, Baton Rouge, LA 70803, USA
| | - Werner Geldenhuys
- Department of Pharmaceutical Sciences, School of Pharmacy, West Virginia University, Morgantown, WV 26506, USA
| | - Jeffrey R Bloomquist
- Emerging Pathogens Institute, Entomology and Nematology Department, 2055 Mowry Road, University of Florida, Gainesville, FL 32610-0009, USA
| | - Daniel R Swale
- Louisiana State University Agricultural Center, Department of Entomology, Baton Rouge, LA 70803, USA.
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8
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Pressly B, Lee RD, Barnych B, Hammock BD, Wulff H. Identification of the Functional Binding Site for the Convulsant Tetramethylenedisulfotetramine in the Pore of the α 2 β 3 γ 2 GABA A Receptor. Mol Pharmacol 2020; 99:78-91. [PMID: 33109687 PMCID: PMC7746976 DOI: 10.1124/molpharm.120.000090] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Accepted: 10/06/2020] [Indexed: 11/22/2022] Open
Abstract
Tetramethylenedisulfotetramine (TETS) is a so-called "caged" convulsant that is responsible for thousands of accidental and malicious poisonings. Similar to the widely used GABA receptor type A (GABAA) antagonist picrotoxinin, TETS has been proposed to bind to the noncompetitive antagonist (NCA) site in the pore of the receptor channel. However, the TETS binding site has never been experimentally mapped, and we here set out to gain atomistic level insights into how TETS inhibits the human α 2 β 3 γ 2 GABAA receptor. Using the Rosetta molecular modeling suite, we generated three homology models of the α 2 β 3 γ 2 receptor in the open, desensitized, and closed/resting state. Three different ligand-docking algorithms (RosettaLigand, Glide, and Swissdock) identified two possible TETS binding sites in the channel pore. Using a combination of site-directed mutagenesis, electrophysiology, and modeling to probe both sites, we demonstrate that TETS binds at the T6' ring in the closed/resting-state model, in which it shows perfect space complementarity and forms hydrogen bonds or makes hydrophobic interactions with all five pore-lining threonine residues of the pentameric receptor. Mutating T6' in either the α 2 or β 3 subunit reduces the IC50 of TETS by ∼700-fold in whole-cell patch-clamp experiments. TETS is thus interacting at the NCA site in the pore of the GABAA receptor at a location that is overlapping but not identical to the picrotoxinin binding site. SIGNIFICANCE STATEMENT: Our study identifies the binding site of the highly toxic convulsant tetramethylenedisulfotetramine (TETS), which is classified as a threat agent by the World Health Organization. Using a combination of homology protein modeling, ligand docking, site-directed mutagenesis, and electrophysiology, we show that TETS is binding in the pore of the α2β3γ2 GABA receptor type A receptor at the so-called T6' ring, wherein five threonine residues line the permeation pathway of the pentameric receptor channel.
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Affiliation(s)
- Brandon Pressly
- Departments of Pharmacology (B.P., R.D.L, H.W.) and Entomology and Nematology, and Comprehensive Cancer Center (B.B., B.D.H.), University of California, Davis, California
| | - Ruth D Lee
- Departments of Pharmacology (B.P., R.D.L, H.W.) and Entomology and Nematology, and Comprehensive Cancer Center (B.B., B.D.H.), University of California, Davis, California
| | - Bogdan Barnych
- Departments of Pharmacology (B.P., R.D.L, H.W.) and Entomology and Nematology, and Comprehensive Cancer Center (B.B., B.D.H.), University of California, Davis, California
| | - Bruce D Hammock
- Departments of Pharmacology (B.P., R.D.L, H.W.) and Entomology and Nematology, and Comprehensive Cancer Center (B.B., B.D.H.), University of California, Davis, California
| | - Heike Wulff
- Departments of Pharmacology (B.P., R.D.L, H.W.) and Entomology and Nematology, and Comprehensive Cancer Center (B.B., B.D.H.), University of California, Davis, California
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Tian Y, Gao Y, Chen Y, Liu G, Ju X. Identification of The Fipronil Resistance Associated Mutations in Nilaparvata lugens GABA Receptors by Molecular Modeling. Molecules 2019; 24:E4116. [PMID: 31739499 PMCID: PMC6891292 DOI: 10.3390/molecules24224116] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2019] [Revised: 11/09/2019] [Accepted: 11/12/2019] [Indexed: 12/31/2022] Open
Abstract
Fipronil, as the first commercialized member of phenylpyrazole insecticides, has been widely used to control planthoppers in China due to its high insecticidal activity and low toxicity to mammals. However, insects have developed resistance to phenylpyrazoles after their long-term use. The resistance mechanism of insects to fipronil has not been well identified, which limited the development of phenylpyrazole insecticides. In the present study, we aimed to elucidate the related fipronil-resistance mechanism in N. lugens GABA receptors by homology modeling, molecular docking, and molecular dynamics. The results indicated that fipronil showed the weakest interaction with the mutant (R0'Q + A2'S) GABA receptors, which is consistent with the experimental study. The binding poses of fipronil were found to be changed when mutations were conducted. These findings verified the novel fipronil-resistance mechanism in silico and provide important information for the design of novel GABAR-targeting insecticides.
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Affiliation(s)
| | | | | | - Genyan Liu
- Key Laboratory for Green Chemical Process of Ministry of Education, School of Chemical Engineering and Pharmacy, Wuhan Institute of Technology, Wuhan 430205, China; (Y.T.); (Y.G.); (Y.C.)
| | - Xiulian Ju
- Key Laboratory for Green Chemical Process of Ministry of Education, School of Chemical Engineering and Pharmacy, Wuhan Institute of Technology, Wuhan 430205, China; (Y.T.); (Y.G.); (Y.C.)
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10
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Lee J, Iyengar A, Wu CF. Distinctions among electroconvulsion- and proconvulsant-induced seizure discharges and native motor patterns during flight and grooming: quantitative spike pattern analysis in Drosophila flight muscles. J Neurogenet 2019; 33:125-142. [PMID: 30982417 DOI: 10.1080/01677063.2019.1581188] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
In Drosophila, high-frequency electrical stimulation across the brain triggers a highly stereotypic repertoire of spasms. These electroconvulsive seizures (ECS) manifest as distinctive spiking discharges across the nervous system and can be stably assessed throughout the seizure repertoire in the large indirect flight muscles dorsal longitudinal muscles (DLMs) to characterize modifications in seizure-prone mutants. However, the relationships between ECS-spike patterns and native motor programs, including flight and grooming, are not known and their similarities and distinctions remain to be characterized. We employed quantitative spike pattern analyses for the three motor patterns including: (1) overall firing frequency, (2) spike timing between contralateral fibers, and (3) short-term variability in spike interval regularity (CV2) and instantaneous firing frequency (ISI-1). This base-line information from wild-type (WT) flies facilitated quantitative characterization of mutational effects of major neurotransmitter systems: excitatory cholinergic (Cha), inhibitory GABAergic (Rdl) and electrical (ShakB) synaptic transmission. The results provide an initial glimpse on the vulnerability of individual motor patterns to different perturbations. We found marked alterations of ECS discharge spike patterns in terms of either seizure threshold, spike frequency or spiking regularity. In contrast, no gross alterations during grooming and a small but noticeable reduction of firing frequency during Rdl mutant flight were found, suggesting a role for GABAergic modulation of flight motor programs. Picrotoxin (PTX), a known pro-convulsant that inhibits GABAA receptors, induced DLM spike patterns that displayed some features, e.g. left-right coordination and ISI-1 range, that could be found in flight or grooming, but distinct from ECS discharges. These quantitative techniques may be employed to reveal overlooked relationships among aberrant motor patterns as well as their links to native motor programs.
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Affiliation(s)
- Jisue Lee
- a Department of Biology , University of Iowa , Iowa City , IA , USA
| | - Atulya Iyengar
- a Department of Biology , University of Iowa , Iowa City , IA , USA.,b Interdisiplinary Graduate Program in Neuroscience , University of Iowa , Iowa City , IA , USA
| | - Chun-Fang Wu
- a Department of Biology , University of Iowa , Iowa City , IA , USA.,b Interdisiplinary Graduate Program in Neuroscience , University of Iowa , Iowa City , IA , USA
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11
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Seljeset S, Bright DP, Thomas P, Smart TG. Probing GABA A receptors with inhibitory neurosteroids. Neuropharmacology 2018; 136:23-36. [PMID: 29447845 PMCID: PMC6018617 DOI: 10.1016/j.neuropharm.2018.02.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Revised: 02/06/2018] [Accepted: 02/09/2018] [Indexed: 12/22/2022]
Abstract
γ-aminobutyric acid type A receptors (GABAARs) are important components of the central nervous system and they are functionally tasked with controlling neuronal excitability. These receptors are subject to post-translational modification and also to modulation by endogenous regulators, such as the neurosteroids. These modulators can either potentiate or inhibit GABAAR function. Whilst the former class of neurosteroids are considered to bind to and act from the transmembrane domain of the receptor, the domains that are important for the inhibitory neurosteroids remain less clear. In this study, we systematically compare a panel of recombinant synaptic-type and extrasynaptic-type GABAARs expressed in heterologous cell systems for their sensitivity to inhibition by the classic inhibitory neurosteroid, pregnenolone sulphate. Generally, peak GABA current responses were inhibited less compared to steady-state currents, implicating the desensitised state in inhibition. Moreover, pregnenolone sulphate inhibition increased with GABA concentration, but showed minimal voltage dependence. There was no strong dependence of inhibition on receptor subunit composition, the exception being the ρ1 receptor, which is markedly less sensitive. By using competition experiments with pregnenolone sulphate and the GABA channel blocker picrotoxinin, discrete binding sites are proposed. Furthermore, by assessing inhibition using site-directed mutagenesis and receptor chimeras comprising α, β or γ subunits with ρ1 subunits, the receptor transmembrane domains are strongly implicated in mediating inhibition and most likely the binding location for pregnenolone sulphate in GABAARs. This article is part of the “Special Issue Dedicated to Norman G. Bowery”. A range of GABAA receptor subtypes are inhibited by pregenolone sulphate. Peak GABA curents are less sensitive to inhibition than steady-state currents. Desensitised state of GABAA receptors most sensitive to neurosteroid inhibition. Inhibition increases with GABA concentration, but not strongly voltage-dependent. Pregnenolone sulphate binding site located within subunit transmembrane domains.
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Affiliation(s)
- Sandra Seljeset
- Department of Neuroscience, Physiology & Pharmacology, UCL, Gower Street, London, WC1E 6BT, United Kingdom
| | - Damian P Bright
- Department of Neuroscience, Physiology & Pharmacology, UCL, Gower Street, London, WC1E 6BT, United Kingdom
| | - Philip Thomas
- Department of Neuroscience, Physiology & Pharmacology, UCL, Gower Street, London, WC1E 6BT, United Kingdom
| | - Trevor G Smart
- Department of Neuroscience, Physiology & Pharmacology, UCL, Gower Street, London, WC1E 6BT, United Kingdom.
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12
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Garrood WT, Zimmer CT, Gutbrod O, Lüke B, Williamson MS, Bass C, Nauen R, Emyr Davies TG. Influence of the RDL A301S mutation in the brown planthopper Nilaparvata lugens on the activity of phenylpyrazole insecticides. PESTICIDE BIOCHEMISTRY AND PHYSIOLOGY 2017; 142:1-8. [PMID: 29107231 PMCID: PMC5672059 DOI: 10.1016/j.pestbp.2017.01.007] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/14/2016] [Revised: 12/18/2016] [Accepted: 01/04/2017] [Indexed: 06/07/2023]
Abstract
We discovered the A301S mutation in the RDL GABA-gated chloride channel of fiprole resistant rice brown planthopper, Nilaparvata lugens populations by DNA sequencing and SNP calling via RNASeq. Ethiprole selection of two field N. lugens populations resulted in strong resistance to both ethiprole and fipronil and resulted in fixation of the A301S mutation, as well as the emergence of another mutation, Q359E in one of the selected strains. To analyse the roles of these mutations in resistance to phenylpyrazoles, three Rdl constructs: wild type, A301S and A301S+Q359E were expressed in Xenopus laevis oocytes and assessed for their sensitivity to ethiprole and fipronil using two-electrode voltage-clamp electrophysiology. Neither of the mutant Rdl subtypes significantly reduced the antagonistic action of fipronil, however there was a significant reduction in response to ethiprole in the two mutated subtypes compared with the wild type. Bioassays with a Drosophila melanogaster strain carrying the A301S mutation showed strong resistance to ethiprole but not fipronil compared to a strain without this mutation, thus further supporting a causal role for the A301S mutation in resistance to ethiprole. Homology modelling of the N. lugens RDL channel did not suggest implications of Q359E for fiprole binding in contrast to A301S located in transmembrane domain M2 forming the channel pore. Synergist bioassays provided no evidence of a role for cytochrome P450s in N. lugens resistance to fipronil and the molecular basis of resistance to this compound remains unknown. In summary this study provides strong evidence that target-site resistance underlies widespread ethiprole resistance in N. lugens populations.
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Affiliation(s)
- William T Garrood
- Biological Chemistry and Crop Protection Department, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK
| | - Christoph T Zimmer
- College of Life and Environmental Sciences, Biosciences, University of Exeter, Penryn Campus, Penryn, Cornwall TR10 9FE, UK
| | - Oliver Gutbrod
- Bayer CropScience AG, R&D, Research Technologies, Monheim, Germany
| | - Bettina Lüke
- Bayer CropScience AG, R&D, Pest Control Biology, Monheim, Germany
| | - Martin S Williamson
- Biological Chemistry and Crop Protection Department, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK
| | - Chris Bass
- College of Life and Environmental Sciences, Biosciences, University of Exeter, Penryn Campus, Penryn, Cornwall TR10 9FE, UK
| | - Ralf Nauen
- Bayer CropScience AG, R&D, Pest Control Biology, Monheim, Germany
| | - T G Emyr Davies
- Biological Chemistry and Crop Protection Department, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK.
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13
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Jiang S, Tsikolia M, Bernier UR, Bloomquist JR. Mosquitocidal Activity and Mode of Action of the Isoxazoline Fluralaner. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2017; 14:ijerph14020154. [PMID: 28178191 PMCID: PMC5334708 DOI: 10.3390/ijerph14020154] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Revised: 01/24/2017] [Accepted: 01/31/2017] [Indexed: 01/14/2023]
Abstract
Mosquitoes, such as Aedes aegypti and Anopheles gambiae, are important vectors of human diseases. Fluralaner, a recently introduced parasiticide, was evaluated as a mosquitocide in this study. On Ae. aegypti and An. gambiae fourth-instar larvae, fluralaner had 24-h LC50 (lethal concentration for 50% mortality) values of 1.8 ppb and 0.4 ppb, respectively. Following topical application to adult Ae. aegypti, fluralaner toxicity reached a plateau in about 3 days, with 1- and 3-day LD50 (lethal dose for 50% mortality) values of 1.3 ng/mg and 0.26 ng/mg, suggesting a slowly developing toxicity. Fipronil outperformed fluralaner by up to 100-fold in adult topical, glass contact, and feeding assays on Ae. aegypti. These data show that fluralaner does not have exceptional toxicity to mosquitoes in typical exposure paradigms. In electrophysiological recordings on Drosophila melanogaster larval central nervous system, the effectiveness of fluralaner for restoring nerve firing after gamma-aminobutyric acid (GABA) treatment, a measure of GABA antagonism, was similar in susceptible Oregon-R and cyclodiene-resistant rdl-1675 strains, with EC50 (half maximal effective concentration) values of 0.34 µM and 0.29 µM. Although this finding suggests low cross resistance in the presence of rdl, the moderate potency, low contact activity, and slow action of fluralaner argue against its use as an adult mosquitocide for vector control.
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Affiliation(s)
- Shiyao Jiang
- Emerging Pathogens Institute, Department of Entomology and Nematology, University of Florida, Gainesville, FL 32610, USA.
| | - Maia Tsikolia
- Emerging Pathogens Institute, Department of Entomology and Nematology, University of Florida, Gainesville, FL 32610, USA.
| | - Ulrich R Bernier
- USDA-ARS, Center for Medical, Agricultural, and Veterinary Entomology, Gainesville, FL 32608, USA.
| | - Jeffrey R Bloomquist
- Emerging Pathogens Institute, Department of Entomology and Nematology, University of Florida, Gainesville, FL 32610, USA.
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14
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Taylor-Wells J, Jones AK. Variations in the Insect GABA Receptor, RDL, and Their Impact on Receptor Pharmacology. ACS SYMPOSIUM SERIES 2017. [DOI: 10.1021/bk-2017-1265.ch001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Jennina Taylor-Wells
- Faculty of Health and Life Sciences, Department of Biological and Medical Sciences, Oxford Brookes University, Headington, Oxford OX3 8NZ, United Kingdom
| | - Andrew K. Jones
- Faculty of Health and Life Sciences, Department of Biological and Medical Sciences, Oxford Brookes University, Headington, Oxford OX3 8NZ, United Kingdom
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15
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Abstract
Ion channels remain the primary target of most of the small molecule insecticides. This review examines how the subunit composition of heterologously expressed receptors determines their insecticide-specific pharmacology and how the pharmacology of expressed receptors differs from those found in the insect nervous system. We find that the insecticide-specific pharmacology of some receptors, like that containing subunits of the Rdl encoded GABA receptor, can be reconstituted with very few of the naturally occurring subunits expressed. In contrast, workers have struggled even to express functional insect nicotinic acetylcholine receptors (nAChRs), and work has therefore often relied upon the expression of vertebrate receptor subunits in their place. We also examine the extent to which insecticide-resistance-associated mutations, such as those in the para encoded voltage-gated sodium channel, can reveal details of insecticide-binding sites and mode of action. In particular, we examine whether mutations are present in the insecticide-binding site and/or at sites that allosterically affect the drug preferred conformation of the receptor. We also discuss the ryanodine receptor as a target for the recently developed diamides. Finally, we examine the lethality of the genes encoding these receptor subunits and discuss how this might determine the degree of conservation of the resistance-associated mutations found.
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Affiliation(s)
| | - Martin S Williamson
- b Biological Chemistry and Crop Protection, Rothamsted Research , Harpenden , Hertfordshire , UK
| | - T G Emyr Davies
- b Biological Chemistry and Crop Protection, Rothamsted Research , Harpenden , Hertfordshire , UK
| | - Chris Bass
- a Biosciences , University of Exeter in Cornwall , Falmouth , UK
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16
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Synergistic and compensatory effects of two point mutations conferring target-site resistance to fipronil in the insect GABA receptor RDL. Sci Rep 2016; 6:32335. [PMID: 27557781 PMCID: PMC4997714 DOI: 10.1038/srep32335] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Accepted: 08/04/2016] [Indexed: 11/29/2022] Open
Abstract
Insecticide resistance can arise from a variety of mechanisms, including changes to the target site, but is often associated with substantial fitness costs to insects. Here we describe two resistance-associated target-site mutations that have synergistic and compensatory effects that combine to produce high and persistent levels of resistance to fipronil, an insecticide targeting on γ-aminobytyric acid (GABA) receptors. In Nilaparvata lugens, a major pest of rice crops in many parts of Asia, we have identified a single point mutation (A302S) in the GABA receptor RDL that has been identified previously in other species and which confers low levels of resistance to fipronil (23-fold) in N. lugans. In addition, we have identified a second resistance-associated RDL mutation (R300Q) that, in combination with A302S, is associated with much higher levels of resistance (237-fold). The R300Q mutation has not been detected in the absence of A302S in either laboratory-selected or field populations, presumably due to the high fitness cost associated with this mutation. Significantly, it appears that the A302S mutation is able to compensate for deleterious effects of R300Q mutation on fitness cost. These findings identify a novel resistance mechanism and may have important implications for the spread of insecticide resistance.
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17
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Van Leeuwen T, Dermauw W. The Molecular Evolution of Xenobiotic Metabolism and Resistance in Chelicerate Mites. ANNUAL REVIEW OF ENTOMOLOGY 2016; 61:475-98. [PMID: 26982444 DOI: 10.1146/annurev-ento-010715-023907] [Citation(s) in RCA: 153] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Chelicerate mites diverged from other arthropod lineages more than 400 million years ago and subsequently developed specific and remarkable xenobiotic adaptations. The study of the two-spotted spider mite, Tetranychus urticae, for which a high-quality Sanger-sequenced genome was first available, revealed expansions and radiations in all major detoxification gene families, including P450 monooxygenases, carboxyl/cholinesterases, glutathione-S-transferases, and ATP-binding cassette transporters. Novel gene families that are not well studied in other arthropods, such as major facilitator family transporters and lipocalins, also reflect the evolution of xenobiotic adaptation. The acquisition of genes by horizontal gene transfer provided new routes to handle toxins, for example, the β-cyanoalanine synthase enzyme that metabolizes cyanide. The availability of genomic resources for other mite species has allowed researchers to study the lineage specificity of these gene family expansions and the distinct evolution of genes involved in xenobiotic metabolism in mites. Genome-based tools have been crucial in supporting the idiosyncrasies of mite detoxification and will further support the expanding field of mite-plant interactions.
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Affiliation(s)
- Thomas Van Leeuwen
- Department of Crop Protection, Faculty of Bioscience Engineering, Ghent University, B-9000 Ghent, Belgium; ,
- Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, 1090 GE Amsterdam, The Netherlands
| | - Wannes Dermauw
- Department of Crop Protection, Faculty of Bioscience Engineering, Ghent University, B-9000 Ghent, Belgium; ,
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18
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Seljeset S, Laverty D, Smart TG. Inhibitory Neurosteroids and the GABAA Receptor. DIVERSITY AND FUNCTIONS OF GABA RECEPTORS: A TRIBUTE TO HANNS MÖHLER, PART A 2015; 72:165-87. [DOI: 10.1016/bs.apha.2014.10.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
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19
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Price KL, Lummis SCR. An atypical residue in the pore of Varroa destructor GABA-activated RDL receptors affects picrotoxin block and thymol modulation. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2014; 55:19-25. [PMID: 25460510 PMCID: PMC4261083 DOI: 10.1016/j.ibmb.2014.10.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2014] [Revised: 10/08/2014] [Accepted: 10/10/2014] [Indexed: 05/16/2023]
Abstract
GABA-activated RDL receptors are the insect equivalent of mammalian GABAA receptors, and play a vital role in neurotransmission and insecticide action. Here we clone the pore lining M2 region of the Varroa mite RDL receptor and show that it has 4 atypical residues when compared to M2 regions of most other insects, including bees, which are the major host of Varroa mites. We create mutant Drosophila RDL receptors containing these substitutions and characterise their effects on function. Using two electrode voltage clamp electrophysiology we show that one substitution (T6'M) ablates picrotoxin inhibition and increases the potency of GABA. This mutation also alters the effect of thymol, which enhances both insect and mammalian GABA responses, and is widely used as a miticide. Thymol decreases the GABA EC50 of WT receptors, enhancing responses, but in T6'M-containing receptors it is inhibitory. The other 3 atypical residues have no major effects on either the GABA EC50, the picrotoxin potency or the effect of thymol. In conclusion we show that the RDL 6' residue is important for channel block, activation and modulation, and understanding its function also has the potential to prove useful in the design of Varroa-specific insecticidal agents.
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Affiliation(s)
- Kerry L Price
- Department of Biochemistry, University of Cambridge, Cambridge, CB2 1QW, UK
| | - Sarah C R Lummis
- Department of Biochemistry, University of Cambridge, Cambridge, CB2 1QW, UK.
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20
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Rossokhin AV, Sharonova IN, Bukanova JV, Kolbaev SN, Skrebitsky VG. Block of GABA(A) receptor ion channel by penicillin: electrophysiological and modeling insights toward the mechanism. Mol Cell Neurosci 2014; 63:72-82. [PMID: 25305478 DOI: 10.1016/j.mcn.2014.10.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Revised: 09/29/2014] [Accepted: 10/07/2014] [Indexed: 11/26/2022] Open
Abstract
GABA(A) receptors (GABA(A)R) mainly mediate fast inhibitory neurotransmission in the central nervous system. Different classes of modulators target GABA(A)R properties. Penicillin G (PNG) belongs to the class of noncompetitive antagonists blocking the open GABA(A)R and is a prototype of β-lactam antibiotics. In this study, we combined electrophysiological and modeling approaches to investigate the peculiarities of PNG blockade of GABA-activated currents recorded from isolated rat Purkinje cells and to predict the PNG binding site. Whole-cell patch-сlamp recording and fast application system was used in the electrophysiological experiments. PNG block developed after channel activation and increased with membrane depolarization suggesting that the ligand binds within the open channel pore. PNG blocked stationary component of GABA-activated currents in a concentration-dependent manner with IC50 value of 1.12mM at -70mV. The termination of GABA and PNG co-application was followed by a transient tail current. Protection of the tail current from bicuculline block and dependence of its kinetic parameters on agonist affinity suggest that PNG acts as a sequential open channel blocker that prevents agonist dissociation while the channel remains blocked. We built the GABA(A)R models based on nAChR and GLIC structures and performed an unbiased systematic search of the PNG binding site. Monte-Carlo energy minimization was used to find the lowest energy binding modes. We have shown that PNG binds close to the intracellular vestibule. In both models the maximum contribution to the energy of ligand-receptor interactions revealed residues located on the level of 2', 6' and 9' rings formed by a bundle of M2 transmembrane segments, indicating that these residues most likely participate in PNG binding. The predicted structural models support the described mechanism of PNG block.
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Affiliation(s)
- Alexey V Rossokhin
- Research Center of Neurology, Russian Academy of Medical Sciences, 105064 Moscow, Russia.
| | - Irina N Sharonova
- Research Center of Neurology, Russian Academy of Medical Sciences, 105064 Moscow, Russia
| | - Julia V Bukanova
- Research Center of Neurology, Russian Academy of Medical Sciences, 105064 Moscow, Russia
| | - Sergey N Kolbaev
- Research Center of Neurology, Russian Academy of Medical Sciences, 105064 Moscow, Russia
| | - Vladimir G Skrebitsky
- Research Center of Neurology, Russian Academy of Medical Sciences, 105064 Moscow, Russia
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21
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Palmer MJ, Harvey J. Honeybee Kenyon cells are regulated by a tonic GABA receptor conductance. J Neurophysiol 2014; 112:2026-35. [PMID: 25031259 DOI: 10.1152/jn.00180.2014] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The higher cognitive functions of insects are dependent on their mushroom bodies (MBs), which are particularly large in social insects such as honeybees. MB Kenyon cells (KCs) receive multisensory input and are involved in associative learning and memory. In addition to receiving sensory input via excitatory nicotinic synapses, KCs receive inhibitory GABAergic input from MB feedback neurons. Cultured honeybee KCs exhibit ionotropic GABA receptor currents, but the properties of GABA-mediated inhibition in intact MBs are currently unknown. Here, using whole cell recordings from KCs in acutely isolated honeybee brain, we show that KCs exhibit a tonic current that is inhibited by picrotoxin but not by bicuculline. Bath application of GABA (5 μM) and taurine (1 mM) activate a tonic current in KCs, but l-glutamate (0.1-0.5 mM) has no effect. The tonic current is strongly potentiated by the allosteric GABAA receptor modulator pentobarbital and is reduced by inhibition of Ca(2+) channels with Cd(2+) or nifedipine. Noise analysis of the GABA-evoked current gives a single-channel conductance value for the underlying receptors of 27 ± 3 pS, similar to that of resistant to dieldrin (RDL) receptors. The amount of injected current required to evoke action potential firing in KCs is significantly lower in the presence of picrotoxin. KCs recorded in an intact honeybee head preparation similarly exhibit a tonic GABA receptor conductance that reduces neuronal excitability, a property that is likely to contribute to the sparse coding of sensory information in insect MBs.
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Affiliation(s)
- Mary J Palmer
- Division of Neuroscience, Medical Research Institute, University of Dundee, Dundee, United Kingdom
| | - Jenni Harvey
- Division of Neuroscience, Medical Research Institute, University of Dundee, Dundee, United Kingdom
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22
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Abstract
A new study integrates biochemistry, genetics and structural biology to reveal the mechanism of metabolic resistance in a vector mosquito in unprecedented detail. See related research http://genomebiology.com/2014/15/2/R27
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23
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Abstract
The past 60 years have seen a revolution in our understanding of the molecular genetics of insecticide resistance. While at first the field was split by arguments about the relative importance of mono- vs. polygenic resistance and field- vs. laboratory-based selection, the application of molecular cloning to insecticide targets and to the metabolic enzymes that degrade insecticides before they reach those targets has brought out an exponential growth in our understanding of the mutations involved. Molecular analysis has confirmed the relative importance of single major genes in target-site resistance and has also revealed some interesting surprises about the multi-gene families, such as cytochrome P450s, involved in metabolic resistance. Identification of the mutations involved in resistance has also led to parallel advances in our understanding of the enzymes and receptors involved, often with implications for the role of these receptors in humans. This Review seeks to provide an historical perspective on the impact of molecular biology on our understanding of resistance and to begin to look forward to the likely impact of rapid advances in both sequencing and genome-wide association analysis.
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24
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Abstract
Sleep is an essential and evolutionarily conserved behavior that is closely related to synaptic function. However, whether neuroligins (Nlgs), which are cell adhesion molecules involved in synapse formation and synaptic transmission, are involved in sleep is not clear. Here, we show that Drosophila Nlg4 (DNlg4) is highly expressed in large ventral lateral clock neurons (l-LNvs) and that l-LNv-derived DNlg4 is essential for sleep regulation. GABA transmission is impaired in mutant l-LNv, and sleep defects in dnlg4 mutant flies can be rescued by genetic manipulation of GABA transmission. Furthermore, dnlg4 mutant flies exhibit a severe reduction in GABAA receptor RDL clustering, and DNlg4 associates with RDLs in vivo. These results demonstrate that DNlg4 regulates sleep through modulating GABA transmission in l-LNvs, which provides the first known link between a synaptic adhesion molecule and sleep in Drosophila.
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25
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Ozoe Y, Kita T, Ozoe F, Nakao T, Sato K, Hirase K. Insecticidal 3-benzamido-N-phenylbenzamides specifically bind with high affinity to a novel allosteric site in housefly GABA receptors. PESTICIDE BIOCHEMISTRY AND PHYSIOLOGY 2013; 107:285-292. [PMID: 24267689 DOI: 10.1016/j.pestbp.2013.09.005] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2013] [Revised: 09/10/2013] [Accepted: 09/17/2013] [Indexed: 06/02/2023]
Abstract
γ-Aminobutyric acid (GABA) receptors (GABARs) are an important target for existing insecticides such as fiproles. These insecticides act as noncompetitive antagonists (channel blockers) for insect GABARs by binding to a site within the intrinsic channel of the GABAR. Recently, a novel class of insecticides, 3-benzamido-N-phenylbenzamides (BPBs), was shown to inhibit GABARs by binding to a site distinct from the site for fiproles. We examined the binding site of BPBs in the adult housefly by means of radioligand-binding and electrophysiological experiments. 3-Benzamido-N-(2,6-dimethyl-4-perfluoroisopropylphenyl)-2-fluorobenzamide (BPB 1) (the N-demethyl BPB) was a partial, but potent, inhibitor of [(3)H]4'-ethynyl-4-n-propylbicycloorthobenzoate (GABA channel blocker) binding to housefly head membranes, whereas the 3-(N-methyl)benzamido congener (the N-methyl BPB) had low or little activity. A total of 15 BPB analogs were tested for their abilities to inhibit [(3)H]BPB 1 binding to the head membranes. The N-demethyl analogs, known to be highly effective insecticides, potently inhibited the [(3)H]BPB 1 binding, but the N-methyl analogs did not even though they, too, are considered highly effective. [(3)H]BPB 1 equally bound to the head membranes from wild-type and dieldrin-resistant (rdl mutant) houseflies. GABA allosterically inhibited [(3)H]BPB 1 binding. By contrast, channel blocker-type antagonists enhanced [(3)H]BPB 1 binding to housefly head membranes by increasing the affinity of BPB 1. Antiparasitic macrolides, such as ivermectin B1a, were potent inhibitors of [(3)H]BPB 1 binding. BPB 1 inhibited GABA-induced currents in housefly GABARs expressed in Xenopus oocytes, whereas it failed to inhibit l-glutamate-induced currents in inhibitory l-glutamate receptors. Overall, these findings indicate that BPBs act at a novel allosteric site that is different from the site for channel blocker-type antagonists and that is probably overlapped with the site for macrolides in insect GABARs.
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Affiliation(s)
- Yoshihisa Ozoe
- Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, Matsue, Shimane 690-8504, Japan.
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26
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Li X, Overton IM, Baines RA, Keegan LP, O'Connell MA. The ADAR RNA editing enzyme controls neuronal excitability in Drosophila melanogaster. Nucleic Acids Res 2013; 42:1139-51. [PMID: 24137011 PMCID: PMC3902911 DOI: 10.1093/nar/gkt909] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
RNA editing by deamination of specific adenosine bases to inosines during pre-mRNA processing generates edited isoforms of proteins. Recoding RNA editing is more widespread in Drosophila than in vertebrates. Editing levels rise strongly at metamorphosis, and Adar5G1 null mutant flies lack editing events in hundreds of CNS transcripts; mutant flies have reduced viability, severely defective locomotion and age-dependent neurodegeneration. On the other hand, overexpressing an adult dADAR isoform with high enzymatic activity ubiquitously during larval and pupal stages is lethal. Advantage was taken of this to screen for genetic modifiers; Adar overexpression lethality is rescued by reduced dosage of the Rdl (Resistant to dieldrin), gene encoding a subunit of inhibitory GABA receptors. Reduced dosage of the Gad1 gene encoding the GABA synthetase also rescues Adar overexpression lethality. Drosophila Adar5G1 mutant phenotypes are ameliorated by feeding GABA modulators. We demonstrate that neuronal excitability is linked to dADAR expression levels in individual neurons; Adar-overexpressing larval motor neurons show reduced excitability whereas Adar5G1 null mutant or targeted Adar knockdown motor neurons exhibit increased excitability. GABA inhibitory signalling is impaired in human epileptic and autistic conditions, and vertebrate ADARs may have a relevant evolutionarily conserved control over neuronal excitability.
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Affiliation(s)
- Xianghua Li
- MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine at the University of Edinburgh, Crewe Road, Edinburgh EH4 2XU, Scotland, UK, Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester M13 9PT, UK and Department of Molecular Biosciences, The Wenner Gren Institute, Stockholm University, Svante Arrhenius väg 20C, 106 91 Stockholm, Sweden
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27
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Carpenter TS, Lau EY, Lightstone FC. Identification of a possible secondary picrotoxin-binding site on the GABA(A) receptor. Chem Res Toxicol 2013; 26:1444-54. [PMID: 24028067 DOI: 10.1021/tx400167b] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The type A GABA receptors (GABARs) are ligand-gated ion channels (LGICs) found in the brain and are the major inhibitory neurotransmitter receptors. Upon binding of an agonist, the GABAR opens and increases the intraneuronal concentration of chloride ions, thus hyperpolarizing the cell and inhibiting the transmission of the nerve action potential. GABARs also contain many other modulatory binding pockets that differ from the agonist-binding site. The composition of the GABAR subunits can alter the properties of these modulatory sites. Picrotoxin is a noncompetitive antagonist for LGICs, and by inhibiting GABAR, picrotoxin can cause overstimulation and induce convulsions. We use addition of picrotoxin to probe the characteristics and possible mechanism of an additional modulatory pocket located at the interface between the ligand-binding domain and the transmembrane domain of the GABAR. Picrotoxin is widely regarded as a pore-blocking agent that acts at the cytoplasmic end of the channel. However, there are also data to suggest that there may be an additional, secondary binding site for picrotoxin. Through homology modeling, molecular docking, and molecular dynamics simulations, we show that binding of picrotoxin to this interface pocket correlates with these data, and negative modulation occurs at the pocket via a kinking of the pore-lining helices into a more closed orientation.
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Affiliation(s)
- Timothy S Carpenter
- Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory , 7000 East Avenue, Livermore, California 94550, United States
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28
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Wang H, Coates BS, Chen H, Sappington TW, Guillemaud T, Siegfried BD. Role of a γ-aminobutryic acid (GABA) receptor mutation in the evolution and spread of Diabrotica virgifera virgifera resistance to cyclodiene insecticides. INSECT MOLECULAR BIOLOGY 2013; 22:473-484. [PMID: 23841833 DOI: 10.1111/imb.12037] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The western corn rootworm, Diabrotica virgifera virgifera, is a damaging pest of cultivated corn that was controlled by applications of cyclodiene insecticides from the late 1940s until resistance evolved ∼10 years later. Range expansion from the western plains into eastern USA coincides with resistance development. An alanine to serine amino acid substitution within the Rdl subunit of the gamma-aminobutyric acid (GABA) receptor confers resistance to cyclodiene insecticides in many species. We found that the non-synonymous single nucleotide polymorphism (SNP) G/T at the GABA receptor cDNA position 838 (G/T(838)) of D. v. virgifera resulted in the alanine to serine change, and the codominant SNP allele T(838) was genetically linked to survival of beetles in aldrin bioassays. A phenotypic gradient of decreasing susceptibility from west to east was correlated with higher frequencies of the resistance-conferring T(838) allele in the eastern-most populations. This pattern exists in opposition to perceived selective pressures since the more eastern and most resistant populations probably experienced reduced exposure. The reasons for the observed distribution are uncertain, but historical records of the range expansion combined with the distribution of susceptible and resistant phenotypes and genotypes provide an opportunity to better understand factors affecting the species' range expansion.
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MESH Headings
- Aldrin/toxicity
- Animals
- Biological Assay/methods
- Chromosomes, Artificial, Bacterial/drug effects
- Chromosomes, Artificial, Bacterial/genetics
- Coleoptera/genetics
- Coleoptera/metabolism
- Evolution, Molecular
- Hydrocarbons, Chlorinated/toxicity
- Insecticide Resistance/genetics
- Insecticide Resistance/physiology
- Insecticides/toxicity
- Mutation
- North America
- Polymorphism, Single Nucleotide/drug effects
- Receptors, GABA/genetics
- Receptors, GABA/physiology
- Sequence Analysis, DNA
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Affiliation(s)
- H Wang
- University of Nebraska, Department of Entomology, Lincoln, NE, USA
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29
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Remnant EJ, Good RT, Schmidt JM, Lumb C, Robin C, Daborn PJ, Batterham P. Gene duplication in the major insecticide target site, Rdl, in Drosophila melanogaster. Proc Natl Acad Sci U S A 2013; 110:14705-10. [PMID: 23959864 PMCID: PMC3767507 DOI: 10.1073/pnas.1311341110] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The Resistance to Dieldrin gene, Rdl, encodes a GABA-gated chloride channel subunit that is targeted by cyclodiene and phenylpyrazole insecticides. The gene was first characterized in Drosophila melanogaster by genetic mapping of resistance to the cyclodiene dieldrin. The 4,000-fold resistance observed was due to a single amino acid replacement, Ala(301) to Ser. The equivalent change was subsequently identified in Rdl orthologs of a large range of resistant insect species. Here, we report identification of a duplication at the Rdl locus in D. melanogaster. The 113-kb duplication contains one WT copy of Rdl and a second copy with two point mutations: an Ala(301) to Ser resistance mutation and Met(360) to Ile replacement. Individuals with this duplication exhibit intermediate dieldrin resistance compared with single copy Ser(301) homozygotes, reduced temperature sensitivity, and altered RNA editing associated with the resistant allele. Ectopic recombination between Roo transposable elements is involved in generating this genomic rearrangement. The duplication phenotypes were confirmed by construction of a transgenic, artificial duplication integrating the 55.7-kb Rdl locus with a Ser(301) change into an Ala(301) background. Gene duplications can contribute significantly to the evolution of insecticide resistance, most commonly by increasing the amount of gene product produced. Here however, duplication of the Rdl target site creates permanent heterozygosity, providing unique potential for adaptive mutations to accrue in one copy, without abolishing the endogenous role of an essential gene.
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Affiliation(s)
- Emily J Remnant
- Department of Genetics and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Melbourne, VIC 3010, Australia.
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30
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Kita T, Ozoe F, Azuma M, Ozoe Y. Differential distribution of glutamate- and GABA-gated chloride channels in the housefly Musca domestica. JOURNAL OF INSECT PHYSIOLOGY 2013; 59:887-893. [PMID: 23806605 DOI: 10.1016/j.jinsphys.2013.06.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2013] [Revised: 06/11/2013] [Accepted: 06/14/2013] [Indexed: 06/02/2023]
Abstract
l-Glutamic acid (glutamate) mediates fast inhibitory neurotransmission by affecting glutamate-gated chloride channels (GluCls) in invertebrates. The molecular function and pharmacological properties of GluCls have been well studied, but not much is known about their physiological role and localization in the insect body. The distribution of GluCls in the housefly (Musca domestica L.) was thus compared with the distribution of γ-aminobutyric acid (GABA)-gated chloride channels (GABACls). Quantitative PCR and ligand-binding experiments indicate that the GluCl and GABACl transcripts and proteins are predominantly expressed in the adult head. Intense GluCl immunostaining was detected in the lamina, leg motor neurons, and legs of adult houseflies. The GABACl (Rdl) immunostaining was more widely distributed, and was found in the medulla, lobula, lobula plate, mushroom body, antennal lobe, and ellipsoid body. The present findings suggest that GluCls have physiological roles in different tissues than GABACls.
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Affiliation(s)
- Tomo Kita
- Division of Bioscience and Biotechnology, The United Graduate School of Agricultural Sciences, Tottori University, Tottori 680-8553, Japan
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31
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Silva MC, Amaral MD, Morimoto RI. Neuronal reprograming of protein homeostasis by calcium-dependent regulation of the heat shock response. PLoS Genet 2013; 9:e1003711. [PMID: 24009518 PMCID: PMC3757039 DOI: 10.1371/journal.pgen.1003711] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2013] [Accepted: 06/25/2013] [Indexed: 12/20/2022] Open
Abstract
Protein quality control requires constant surveillance to prevent misfolding, aggregation, and loss of cellular function. There is increasing evidence in metazoans that communication between cells has an important role to ensure organismal health and to prevent stressed cells and tissues from compromising lifespan. Here, we show in C. elegans that a moderate increase in physiological cholinergic signaling at the neuromuscular junction (NMJ) induces the calcium (Ca(2+))-dependent activation of HSF-1 in post-synaptic muscle cells, resulting in suppression of protein misfolding. This protective effect on muscle cell protein homeostasis was identified in an unbiased genome-wide screening for modifiers of protein aggregation, and is triggered by downregulation of gei-11, a Myb-family factor and proposed regulator of the L-type acetylcholine receptor (AChR). This, in-turn, activates the voltage-gated Ca(2+) channel, EGL-19, and the sarcoplasmic reticulum ryanodine receptor in response to acetylcholine signaling. The release of calcium into the cytoplasm of muscle cells activates Ca(2+)-dependent kinases and induces HSF-1-dependent expression of cytoplasmic chaperones, which suppress misfolding of metastable proteins and stabilize the folding environment of muscle cells. This demonstrates that the heat shock response (HSR) can be activated in muscle cells by neuronal signaling across the NMJ to protect proteome health.
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Affiliation(s)
- M. Catarina Silva
- Department of Molecular Biosciences, Rice Institute for Biomedical Research, Northwestern University, Evanston, Illinois, United States of America
- Faculty of Sciences, Centre for Biodiversity, Functional and Integrative Genomics (BioFIG), University of Lisboa, Lisboa, Portugal
| | - Margarida D. Amaral
- Faculty of Sciences, Centre for Biodiversity, Functional and Integrative Genomics (BioFIG), University of Lisboa, Lisboa, Portugal
- Centre of Human Genetics, National Institute of Health, Lisboa, Portugal
| | - Richard I. Morimoto
- Department of Molecular Biosciences, Rice Institute for Biomedical Research, Northwestern University, Evanston, Illinois, United States of America
- * E-mail:
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32
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Akiyoshi Y, Ju XL, Furutani S, Matsuda K, Ozoe Y. Electrophysiological evidence for 4-isobutyl-3-isopropylbicyclophosphorothionate as a selective blocker of insect GABA-gated chloride channels. Bioorg Med Chem Lett 2013; 23:3373-6. [DOI: 10.1016/j.bmcl.2013.03.085] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2013] [Revised: 03/19/2013] [Accepted: 03/22/2013] [Indexed: 02/07/2023]
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33
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Othman NA, Gallacher M, Deeb TZ, Baptista-Hon DT, Perry DC, Hales TG. Influences on blockade by t-butylbicyclo-phosphoro-thionate of GABA(A) receptor spontaneous gating, agonist activation and desensitization. J Physiol 2011; 590:163-78. [PMID: 22083597 DOI: 10.1113/jphysiol.2011.213249] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Picrotoxin and t-butylbicyclophosphorothionate (TBPS) are GABA(A) receptor (GABA(A)R) open channel blockers. However, picrotoxin displaceable [(35)S]TBPS binding to α1β2γ2 GABA(A)Rs occurs in the absence of GABA, suggesting that access to the binding site is independent of activation. Alternatively, spontaneous gating may provide access to the channel. In the absence of episodic GABA application, picrotoxin and TBPS blocked (by 91 ± 3% and 85 ± 5%, respectively) GABA-evoked currents mediated by α1β2γ2 receptors. We used two approaches to inhibit spontaneous GABA(A)R gating, bicuculline, which inhibits spontaneous current in the absence of exogenous agonist and the α1(K278M) mutant subunit. Whole-cell patch-clamp recordings demonstrated that α1(K278M)β2γ2 receptors have negligible spontaneous gating. Application of bicuculline to α1β2γ2 receptors in the absence of exogenous GABA caused a 35% reduction of current blockade by TBPS and reduced [(35)S]TBPS binding by 25%. Consistent with this, in the absence of exogenous GABA, α1(K278M)β2γ2 receptors exhibited reduced blockade by TBPS current compared to wild-type receptors. These data suggest that a decrease in spontaneous gating reduces accessibility of TBPS to its binding site. GABA application during picrotoxin or TBPS administration enhanced α1β2γ2 receptor blockade (to 98% in both cases). The GABA-dependent component of TBPS blockade accounts for the stimulation of [(35)S]TBPS binding to α1β2γ2 receptors seen with GABA (1 μm) application. Moreover, application of GABA at concentrations that cause significant steady-state desensitization reduced [(35)S]TBPS binding. The α1(K278M) subunit slowed desensitization kinetics and increased the rate of deactivation of GABA-evoked currents. Furthermore, there was a marked increase in the GABA EC(50) for desensitization of α1(K278M)β2γ2 receptors associated with a large increase in the GABA-dependent stimulation of [(35)S]TBPS binding. These data establish a relationship between GABA(A)R function and the three phases of [(35)S]TBPS binding seen in the absence and the presence of GABA.
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Affiliation(s)
- Nidaa A Othman
- The Institute of Academic Anaesthesia, Division of Neuroscience, University of Dundee, Dundee DD1 9SY, UK
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34
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Two amino acid residues contribute to a cation-π binding interaction in the binding site of an insect GABA receptor. J Neurosci 2011; 31:12371-6. [PMID: 21865479 DOI: 10.1523/jneurosci.1610-11.2011] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Cys-loop receptor binding sites characteristically possess an "aromatic box," where several aromatic amino acid residues surround the bound ligand. A cation-π interaction between one of these residues and the natural agonist is common, although the residue type and location are not conserved. Even in the closely related vertebrate GABA(A) and GABA(C) receptors, residues in distinct locations perform this role: in GABA(A) receptors, a Tyr residue in loop A forms a cation-π interaction with GABA, while in GABA(C) receptors it is a loop B residue. GABA-activated Cys-loop receptors also exist in invertebrates, where they have distinct pharmacologies and are the target of a range of pesticides. Here we examine the location of GABA in an insect binding site by incorporating a series of fluorinated Phe derivatives into the receptor binding pocket using unnatural amino acid mutagenesis, and evaluating the resulting receptors when expressed in Xenopus oocytes. A homology model suggests that two aromatic residues (in loops B and C) are positioned such that they could contribute to a cation-π interaction with the primary ammonium of GABA, and the data reveal a clear correlation between the GABA EC(50) and the cation-π binding ability both at Phe206 (loop B) and Tyr254 (loop C), demonstrating for the first time the contribution of two aromatic residues to a cation-π interaction in a Cys-loop receptor.
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35
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Perry T, Batterham P, Daborn PJ. The biology of insecticidal activity and resistance. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2011; 41:411-22. [PMID: 21426939 DOI: 10.1016/j.ibmb.2011.03.003] [Citation(s) in RCA: 114] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2010] [Revised: 03/01/2011] [Accepted: 03/11/2011] [Indexed: 05/12/2023]
Abstract
Identifying insecticide resistance mechanisms is paramount for pest insect control, as the understandings that underpin insect control strategies must provide ways of detecting and managing resistance. Insecticide resistance studies rely heavily on detailed biochemical and genetic analyses. Although there have been many successes, there are also many examples of resistance that still challenge us. As a precursor to rational pest insect control, the biology of the insect, within the contexts of insecticide modes of action and insecticide metabolism, must be well understood. It makes sense to initiate this research in the best model insect system, Drosophila melanogaster, and translate these findings and methodologies to other insects. Here we explore the usefulness of the D. melanogaster model in studying metabolic-based insecticide resistances, target-site mediated resistances and identifying novel insecticide targets, whilst highlighting the importance of having a more complete understanding of insect biology for insecticide studies.
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Affiliation(s)
- Trent Perry
- Department of Genetics, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Victoria 3010, Australia
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36
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McGonigle I, Lummis SCR. Molecular characterization of agonists that bind to an insect GABA receptor. Biochemistry 2010; 49:2897-902. [PMID: 20180551 PMCID: PMC2852148 DOI: 10.1021/bi901698c] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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Ionotropic GABA receptors are widely distributed throughout the vertebrate and invertebrate central nervous system (CNS) where they mediate inhibitory neurotransmission. One of the most widely studied insect GABA receptors is constructed from RDL (resistance to dieldrin) subunits from Drosophila melanogaster. The aim of this study was to determine critical features of agonists binding to RDL receptors using in silico and experimental data. Partial atomic charges and dipole separation distances of a range of GABA analogues were calculated, and the potency of the analogues was determined using RDL receptors expressed in Xenopus oocytes. These data revealed functional agonists require an ammonium group and an acidic group with an optimum separation distance of ∼5 Å. To determine how the agonists bind to the receptor, a homology model of the extracellular domain was generated and agonists were docked into the binding site. The docking studies support the requirements for functional agonists and also revealed a range of potential interactions with binding site residues, including hydrogen bonds and cation−π interactions. We conclude that the model and docking procedures yield a good model of the insect GABA receptor binding site and the location of agonists within it.
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Affiliation(s)
- Ian McGonigle
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
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37
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Abstract
RDL receptors are invertebrate members of the Cys-loop family of ligand-gated ion channels. They are GABA (gamma-aminobutyric acid)-activated chloride-selective receptors that are closely related to their vertebrate orthologues, the GABA(A) receptors, as well as other Cys-loop receptors such as the ionotropic glycine, nicotinic acetylcholine and 5-HT(3) receptors. RDL receptors are widely expressed throughout the insect CNS (central nervous system) and are important in inhibitory neurotransmission. They are therefore a major insecticidal target site.
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38
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Muroi Y, Theusch CM, Czajkowski C, Jackson MB. Distinct structural changes in the GABAA receptor elicited by pentobarbital and GABA. Biophys J 2009; 96:499-509. [PMID: 19167300 DOI: 10.1016/j.bpj.2008.09.037] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Accepted: 09/30/2008] [Indexed: 10/21/2022] Open
Abstract
The barbiturate pentobarbital binds to gamma-aminobutyric acid type A (GABA(A)) receptors, and this interaction plays an important role in the anesthetic action of this drug. Depending on its concentration, pentobarbital can potentiate (approximately 10-100 microM), activate (approximately 100-800 microM), or block (approximately 1-10 mM) the channel, but the mechanisms underlying these three distinct actions are poorly understood. To investigate the drug-induced structural rearrangements in the GABA(A) receptor, we labeled cysteine mutant receptors expressed in Xenopus oocytes with the sulfhydryl-reactive, environmentally sensitive fluorescent probe tetramethylrhodamine-6-maleimide (TMRM). We then used combined voltage clamp and fluorometry to monitor pentobarbital-induced channel activity and local protein movements simultaneously in real time. High concentrations of pentobarbital induced a decrease in TMRM fluorescence (F(TMRM)) of labels tethered to two residues in the extracellular domain (alpha(1)L127C and beta(2)L125C) that have been shown previously to produce an increase in F(TMRM) in response to GABA. Label at beta(2)K274C in the extracellular end of the M2 transmembrane helix reported a small but significant F(TMRM) increase during application of low modulating pentobarbital concentrations, and it showed a much greater F(TMRM) increase at higher concentrations. In contrast, GABA decreased F(TMRM) at this site. These results indicate that GABA and pentobarbital induce different structural rearrangements in the receptor, and thus activate the receptor by different mechanisms. Labels at alpha(1)L127C and beta(2)K274C change their fluorescence by substantial amounts during channel blockade by pentobarbital. In contrast, picrotoxin blockade produces no change in F(TMRM) at these sites, and the pattern of F(TMRM) signals elicited by the antagonist SR95531 differs from that produced by other antagonists. Thus, with either channel block by antagonists or activation by agonists, the structural changes in the GABA(A) receptor protein differ during transitions that are functionally equivalent.
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Affiliation(s)
- Yukiko Muroi
- Department of Physiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
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39
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RNA editing regulates insect gamma-aminobutyric acid receptor function and insecticide sensitivity. Neuroreport 2008; 19:939-43. [PMID: 18520997 DOI: 10.1097/wnr.0b013e32830216c7] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
A-to-I pre-mRNA editing by adenosine deaminase enzymes has been reported to enhance protein diversity in the nervous system. In Drosophila, the resistance to dieldrin (RDL) gamma-aminobutyric acid (GABA) receptor subunit displays an editing site (R122) that is close to the putative GABA-binding site. We assessed the functional effects of editing at this site by expressing homomeric RDL receptors in Xenopus oocytes. After replacement of arginine 122 with a glycine, both agonist and fipronil potencies were shifted to the right in either fipronil-sensitive receptors or mutated resistant receptors (A301G/T350M). These data provide the first insight on the influence of RNA editing on GABA receptor function.
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40
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Hirata K, Ishida C, Eguchi Y, Sakai K, Ozoe F, Ozoe Y, Matsuda K. Role of a serine residue (S278) in the pore-facing region of the housefly L-glutamate-gated chloride channel in determining sensitivity to noncompetitive antagonists. INSECT MOLECULAR BIOLOGY 2008; 17:341-350. [PMID: 18651916 DOI: 10.1111/j.1365-2583.2008.00806.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Gamma-hexachlorocyclohexane (gamma-HCH), fipronil and picrotoxinin are noncompetitive antagonists (NCAs) of L-glutamate-gated chloride channels (GluCls), yet their potencies are weaker than those on gamma-aminobutyric acid receptors (GABARs). The A302S mutation of Drosophila RDL (resistant to dieldrin) GABAR confers NCA resistance, and housefly GluCls (MdGluCls) possess S278 as the residue corresponding to the A302. Thus, the effects of S278A mutation on the NCA actions on MdGluCls were investigated. The S278A mutation resulted in enhanced blocking by NCAs of the MdGluCl response to 30 microM L-glutamate. However, such actions of gamma-HCH and picrotoxinin, but not of fipronil, on the S278A mutant were reduced with 200 microM L-glutamate. Further increases in the L-glutamate concentration led to potentiation by NCAs of the mutant response to L-glutamate.
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Affiliation(s)
- K Hirata
- Department of Applied Biological Chemistry, School of Agriculture, Kinki University, Nakamachi, Nara, Japan
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41
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Abstract
This unit describes the use of whole-cell voltage clamping to study voltage-gated channels. Stepwise changes in voltage produced by this technique cause channels to interconvert between different states, and these transitions are monitored as changes in membrane current. The time course of this redistribution of states contains a great deal of information about the mechanism of channel gating. Furthermore, the voltage clamp can be used to activate different populations of channels selectively. In this way, a specific channel targeted by biological or pharmacological manipulations can often be identified and studied in detail. This technique is also readily adapted to the study of ligand-gated channels, synaptic potentials, and exocytosis.
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Affiliation(s)
- M B Jackson
- University of Wisconsin Medical School, Madison, Wisconsin, USA
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42
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Morozova TV, Anholt RRH, Mackay TFC. Phenotypic and transcriptional response to selection for alcohol sensitivity in Drosophila melanogaster. Genome Biol 2008; 8:R231. [PMID: 17973985 PMCID: PMC2246305 DOI: 10.1186/gb-2007-8-10-r231] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2007] [Revised: 07/31/2007] [Accepted: 10/31/2007] [Indexed: 02/04/2023] Open
Abstract
Gene-expression profiling combined with selection for genetically divergent Drosophila lines either highly sensitive or resistant to ethanol exposure has been used to identify candidate genes that affect alcohol sensitivity, including 23 novel genes that have human orthologs. Background Alcoholism is a complex disorder determined by interactions between genetic and environmental risk factors. Drosophila represents a powerful model system to dissect the genetic architecture of alcohol sensitivity, as large numbers of flies can readily be reared in defined genetic backgrounds and under controlled environmental conditions. Furthermore, flies exposed to ethanol undergo physiological and behavioral changes that resemble human alcohol intoxication, including loss of postural control, sedation, and development of tolerance. Results We performed artificial selection for alcohol sensitivity for 35 generations and created duplicate selection lines that are either highly sensitive or resistant to ethanol exposure along with unselected control lines. We used whole genome expression analysis to identify 1,678 probe sets with different expression levels between the divergent lines, pooled across replicates, at a false discovery rate of q < 0.001. We assessed to what extent genes with altered transcriptional regulation might be causally associated with ethanol sensitivity by measuring alcohol sensitivity of 37 co-isogenic P-element insertional mutations in 35 candidate genes, and found that 32 of these mutants differed in sensitivity to ethanol exposure from their co-isogenic controls. Furthermore, 23 of these novel genes have human orthologues. Conclusion Combining whole genome expression profiling with selection for genetically divergent lines is an effective approach for identifying candidate genes that affect complex traits, such as alcohol sensitivity. Because of evolutionary conservation of function, it is likely that human orthologues of genes affecting alcohol sensitivity in Drosophila may contribute to alcohol-associated phenotypes in humans.
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Affiliation(s)
- Tatiana V Morozova
- Department of Zoology, North Carolina State University, Raleigh, NC 27695, USA.
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43
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Modulation of GABAA receptor desensitization uncouples sleep onset and maintenance in Drosophila. Nat Neurosci 2008; 11:354-9. [PMID: 18223647 DOI: 10.1038/nn2046] [Citation(s) in RCA: 138] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2007] [Accepted: 01/03/2008] [Indexed: 11/08/2022]
Abstract
Many lines of evidence indicate that GABA and GABA(A) receptors make important contributions to human sleep regulation. Pharmacological manipulation of these receptors has differential effects on sleep onset and sleep maintenance insomnia. Here we show that sleep is regulated by GABA in Drosophila and that a mutant GABA(A) receptor, Rdl(A302S), specifically decreases sleep latency. The drug carbamazepine (CBZ) has the opposite effect on sleep; it increases sleep latency as well as decreasing sleep. Behavioral and physiological experiments indicated that Rdl(A302S) mutant flies are resistant to the effects of CBZ on sleep latency and that mutant RDL(A302S) channels are resistant to the effects of CBZ on desensitization, respectively. These results suggest that this biophysical property of the channel, specifically channel desensitization, underlies the regulation of sleep latency in flies. These experiments uncouple the regulation of sleep latency from that of sleep duration and suggest that the kinetics of GABA(A) receptor signaling dictate sleep latency.
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44
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An ionotropic GABA receptor in cultured mushroom body Kenyon cells of the honeybee and its modulation by intracellular calcium. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2008; 194:329-40. [DOI: 10.1007/s00359-007-0308-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2007] [Revised: 11/30/2007] [Accepted: 12/04/2007] [Indexed: 11/25/2022]
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45
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Narusuye K, Nakao T, Abe R, Nagatomi Y, Hirase K, Ozoe Y. Molecular cloning of a GABA receptor subunit from Laodelphax striatella (Fallén) and patch clamp analysis of the homo-oligomeric receptors expressed in a Drosophila cell line. INSECT MOLECULAR BIOLOGY 2007; 16:723-733. [PMID: 18093001 DOI: 10.1111/j.1365-2583.2007.00766.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
A cDNA encoding a gamma-aminobutyric acid (GABA) receptor subunit was cloned from the small brown planthopper Laodelphax striatella. The L. striatella GABA receptor subunit was found to have high amino acid sequence similarity to the bd-type splice variant of the Drosophila GABA receptor Rdl subunit and several other GABA receptor subunits, with identities of over 70%. The cDNA was inserted into the expression vector pAc5.1-lac-Hygro. Clonal cell lines stably expressing homo-oligomeric L. striatella GABA receptors were generated by transfecting the vector into D.mel-2 cells. Expression of functional GABA receptors in the cell lines was demonstrated by whole-cell patch clamp recordings. GABA induced inward currents with an EC(50) value of 29 microM and a Hill coefficient of 1.7. The GABA-evoked responses reversed close to the Nernst equilibrium potential for chloride ions. The amplitudes of agonist-induced currents were found to be in the order muscimol (100 microM) >/= GABA (100 microM) > isoguvacine (100 microM) > cis-4-aminocrotonic acid (CACA) (100 microM) > 5-(4-piperidyl)-3-isoxazolol (4-PIOL) (1 mM). Antagonists such as fipronil (100 nM), 4'-ethynyl-4-n-propylbicycloorthobenzoate (EBOB) (100 nM), dieldrin (100 nM) and SR95531 (gabazine) (1 microM) suppressed GABA-induced currents. The functional expression of a GABA receptor from an agricultural pest presents a unique opportunity to discover new molecules active at this important target site.
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Affiliation(s)
- K Narusuye
- Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, Matsue, Shimane, Japan
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46
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Yang Z, Cromer BA, Harvey RJ, Parker MW, Lynch JW. A proposed structural basis for picrotoxinin and picrotin binding in the glycine receptor pore. J Neurochem 2007; 103:580-9. [PMID: 17714449 DOI: 10.1111/j.1471-4159.2007.04850.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Picrotoxin, an antagonist of structurally-rated GABA(A) receptors (GABA(A)Rs) and glycine receptors (GlyRs), is an equimolar mixture of picrotoxinin (PTXININ) and picrotin (PTN). These compounds share a common structure except that PTN contains a slightly larger dimethylmethanol in place of the PTXININ isopropenyl group. Although the homomeric alpha1 GlyR is equally sensitive to both compounds, we show here that homomeric alpha2 and alpha3 GlyRs, like most GABA(A)Rs, are selectively inhibited by PTXININ. As conservative mutations to pore-lining 6' threonines equally affect the sensitivity of the alpha1 GlyR to both compounds, we conclude that PTXININ and PTN bind to 6' threonines by hydrogen bonding with exocyclic oxygens common to both molecules. In contrast, substitution of the 2' pore-lining glycine by serine selectively reduces PTN sensitivity, whereas the introduction of 2' alanines selectively increases PTXININ sensitivity. These results define the orientation of PTXININ and PTN binding in the alpha1 GlyR pore and allow us to conclude that the relatively reduced sensitivity of PTN at GABA(A)Rs and alpha2 and alpha3 GlyRs is due predominantly to its larger size and reduced ability to form hydrophobic interactions with 2' alanines.
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MESH Headings
- DNA, Complementary/biosynthesis
- DNA, Complementary/genetics
- Data Interpretation, Statistical
- Electrophysiology
- Glycine/pharmacology
- Humans
- Hydrogen Bonding
- Models, Molecular
- Mutagenesis
- Neurons, Afferent/drug effects
- Pain/physiopathology
- Patch-Clamp Techniques
- Picrotoxin/analogs & derivatives
- Picrotoxin/chemistry
- Picrotoxin/metabolism
- Receptors, GABA-A/chemistry
- Receptors, GABA-A/drug effects
- Receptors, GABA-A/metabolism
- Receptors, Glycine/chemistry
- Receptors, Glycine/genetics
- Receptors, Glycine/metabolism
- Sesterterpenes
- Synapses/drug effects
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Affiliation(s)
- Zhe Yang
- School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia
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47
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Lebwohl M, Clark L, Levitt J. Therapy for head lice based on life cycle, resistance, and safety considerations. Pediatrics 2007; 119:965-74. [PMID: 17473098 DOI: 10.1542/peds.2006-3087] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
The timing of head lice maturation most favorable to their survival in the presence of anti-lice agents is the maximum time as an ovum (12 days) and the shortest possible time of maturing from newly hatched nymph to egg-laying adult (8.5 days). Pediculicides that are not reliably ovicidal (pyrethroids and lindane) require 2 to 3 treatment cycles to eradicate lice. Ovicidal therapies (malathion) require 1 to 2 treatments. Treatment with an agent to which there is genetic resistance is unproductive. In the United States, lice have become increasingly resistant to pyrethroids and lindane but not to malathion. Treatment with malathion has favorable efficacy and safety profiles and enables the immediate, safe return to school. Nit combing can be performed adjunctively. No-nit policies should be rendered obsolete.
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Affiliation(s)
- Mark Lebwohl
- Department of Dermatology, Mount Sinai School of Medicine, New York, NY 10029, USA
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48
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Abstract
Considerable controversy surrounds the location of the closed channel gate in members of the Cys-loop receptor family of neurotransmitter-gated ion channels that includes the GABAA, glycine, acetylcholine, and 5-HT3 receptors. Cysteine-accessibility studies concluded that the gate is near the cytoplasmic end of the channel in acetylcholine and GABAA receptors but in the middle of the 5-HT3A receptor channel. Zn2+ accessibility studies in a chimeric 5-HT3-ACh receptor suggested the gate is near the channel's cytoplasmic end. In the 4-Å resolution structure of the acetylcholine receptor closed state determined by cryoelectron microscopy, the narrowest region, inferred to be the gate, is in the channel's midsection from 9' to 14' but the M1–M2 loop residues at the channel's cytoplasmic end were not resolved in that structure. We used blocker trapping experiments with picrotoxin, a GABAA receptor open channel blocker, to determine whether a gate exists at a position more extracellular than the picrotoxin binding site, which is in the vicinity of α1Val257 (2') near the channel's cytoplasmic end. We show that picrotoxin can be trapped in the channel after removal of GABA. By using the state-dependent accessibility of engineered cysteines as reporters for the channel's structural state we infer that after GABA washout, with picrotoxin trapped in the channel, the channel appears to be in the closed state. We infer that a gate exists between the picrotoxin binding site and the channel's extracellular end, consistent with a closed channel gate in the middle of the channel. Given the homology with acetylcholine and 5-HT3 receptors there is probably a similar gate in those channels as well. This does not preclude the existence of an additional gate at a more cytoplasmic location.
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Affiliation(s)
- Moez Bali
- Department of Physiology, Albert Einstein College of Medicine of Yeshiva University, Bronx, NY 10461, USA
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49
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Ffrench-Constant RH. Which came first: insecticides or resistance? Trends Genet 2007; 23:1-4. [PMID: 17125882 DOI: 10.1016/j.tig.2006.11.006] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2006] [Revised: 10/10/2006] [Accepted: 11/09/2006] [Indexed: 11/16/2022]
Abstract
Mutations that confer resistance to insecticides are well documented. However, so far, we have been unable to determine whether these mutations arose before or after the introduction of insecticides. Recently, a landmark study showed that resistance to Malathion can be detected in pinned specimens of Australian sheep blowflies that were collected before the introduction of the insecticide. This finding has numerous implications for our understanding of the prevalence of resistance to new compounds. It also indicates that pre-existing resistance alleles might not carry the fitness cost that is associated with new mutations.
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Affiliation(s)
- Richard H Ffrench-Constant
- Centre for Ecology and Conservation, School of Biosciences, University of Exeter, Cornwall Campus, Tremough, Cornwall TR10 9EZ, UK.
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50
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Stilwell GE, Saraswati S, Littleton JT, Chouinard SW. Development of aDrosophilaseizure model forin vivohigh-throughput drug screening. Eur J Neurosci 2006; 24:2211-22. [PMID: 17074045 DOI: 10.1111/j.1460-9568.2006.05075.x] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
An important application of model organisms in neurological research has been to identify and characterise therapeutic approaches for epilepsy, a recurrent seizure disorder that affects > 1% of the human population. Proconvulsant-treated rodent models have been widely used for antiepileptic drug discovery and development, but are not suitable for high-throughput screening. To generate a genetically tractable model that would be suitable for large-scale, high-throughput screening for antiepileptic drug candidates, we characterized a Drosophila chemical treatment model using the GABA(A) receptor antagonist picrotoxin. This proconvulsant, delivered to Drosophila larvae via simple feeding methods suitable for automated screening, generated robust generalised seizures with lethality occurring at doses between 0.3 and 0.5 mg/mL. Electrophysiological analysis of CNS motor neuron output in picrotoxin-treated larvae revealed generalised seizures within minutes of drug exposure. At subthreshold doses for seizure induction, picrotoxin produced an increased frequency of motor neuron action potential bursting, indicating that CNS GABAergic transmission regulates patterned activity. Mutants in the Drosophila Rdl GABA(A) receptor are resistant to picrotoxin, confirming that seizure induction occurs via a conserved GABA(A) receptor pathway. To validate the usefulness of this model for in vivo drug screening, we identified several classes of neuroactive antiepileptic compounds in a pilot screen, including phenytoin and nifedipine, which can rescue the seizures and lethal neurotoxicity induced by picrotoxin. The well-defined actions of picrotoxin in Drosophila and the ease with which compounds can be assayed for antiseizure activity makes this genetically tractable model attractive for high-throughput in vivo screens to identify novel anticonvulsants and seizure susceptibility loci.
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