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Stuebler AG, Jansen M. Mobility of Lower MA-Helices for Ion Conduction through Lateral Portals in 5-HT 3A Receptors. Biophys J 2020; 119:2593-2603. [PMID: 33157122 PMCID: PMC7822733 DOI: 10.1016/j.bpj.2020.10.029] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Revised: 10/19/2020] [Accepted: 10/27/2020] [Indexed: 01/22/2023] Open
Abstract
The intracellular domain of the serotonin type 3A receptor, a pentameric ligand-gated ion channel, is crucial for regulating conductance. Ion permeation through the extracellular vestibule and the transmembrane channel is well understood, whereas the specific ion conduction pathway through the intracellular domain is less clear. The intracellular domain starts with a short loop after the third transmembrane segment, followed by a short α-helical segment, a large unstructured loop, and finally, the membrane-associated MA-helix that continues into the last transmembrane segment. The MA-helices from all five subunits form the extension of the transmembrane ion channel and shape what has been described as a “closed vestibule,” with their lateral portals obstructed by loops and their cytosolic ends forming a tight hydrophobic constriction. The question remains whether the lateral portals or cytosolic constriction conduct ions upon channel opening. In our study, we used disulfide bond formation between pairs of engineered cysteines to probe the proximity and mobility of segments of the MA-helices most distal to the membrane bilayer. Our results indicate that the proximity and orientation for cysteine pairs at I409C/R410C, in close proximity to the lateral windows, and L402C/L403C, at the cytosolic ends of the MA-helices, are conducive for disulfide bond formation. Although conformational changes associated with gating promote cross-linking for I409C/R410C, which in turn decreases channel currents, cross-linking of L402C/L403C is functionally silent in macroscopic currents. These results support the hypothesis that concerted conformational changes open the lateral portals for ion conduction, rendering ion conduction through the vertical portal unlikely.
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Affiliation(s)
- Antonia G Stuebler
- Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas
| | - Michaela Jansen
- Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas.
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Rodriguez Araujo N, Fabiani C, Mazzarini Dimarco A, Bouzat C, Corradi J. Orthosteric and Allosteric Activation of Human 5-HT 3A Receptors. Biophys J 2020; 119:1670-1682. [PMID: 32946769 DOI: 10.1016/j.bpj.2020.08.029] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Revised: 07/18/2020] [Accepted: 08/24/2020] [Indexed: 12/24/2022] Open
Abstract
The serotonin type 3 receptor (5-HT3) is a ligand-gated ion channel that converts the binding of the neurotransmitter serotonin (5-HT) into a transient cation current that mediates fast excitatory responses in peripheral and central nervous systems. Information regarding the activation and modulation of the human 5-HT3 type A receptor has been based only on macroscopic current measurements because of its low ion conductance. By constructing a high-conductance human 5-HT3A receptor, we here revealed mechanistic information regarding the orthosteric activation by 5-HT and by the partial agonist tryptamine, and the allosteric activation by the terpenoids, carvacrol, and thymol. Terpenoids potentiated macroscopic currents elicited by the orthosteric agonist and directly elicited currents with slow-rising phases and submaximal amplitudes. At the single-channel level, activation by orthosteric and allosteric agonists appeared as openings in quick succession (bursts) that showed no ligand concentration dependence. Bursts were grouped into long-duration clusters in the presence of 5-HT and even longer in the presence of terpenoids, whereas they remained isolated in the presence of tryptamine. Kinetic analysis revealed that allosteric and orthosteric activation mechanisms can be described by the same scheme that includes transitions of the agonist-bound receptor to closed intermediate states before opening (priming). Reduced priming explained the partial agonism of tryptamine; however, equilibrium constants for gating and priming were similar for 5-HT and terpenoid activation. Thus, our kinetic analysis revealed that terpenoids are efficacious agonists for 5-HT3A receptors. These findings not only extend our knowledge about the human 5-HT3A molecular function but also provide novel insights into the mechanisms of action of allosteric ligands, which are of increasing interest as therapeutic drugs in all the superfamily.
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Affiliation(s)
- Noelia Rodriguez Araujo
- Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB), Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur (UNS)-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca, Argentina
| | - Camila Fabiani
- Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB), Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur (UNS)-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca, Argentina
| | - Albano Mazzarini Dimarco
- Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB), Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur (UNS)-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca, Argentina
| | - Cecilia Bouzat
- Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB), Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur (UNS)-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca, Argentina.
| | - Jeremías Corradi
- Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB), Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur (UNS)-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca, Argentina.
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Hauser SR, Bracken AL, Deehan GA, Toalston JE, Ding ZM, Truitt WA, Bell RL, McBride WJ, Rodd ZA. Selective breeding for high alcohol preference increases the sensitivity of the posterior VTA to the reinforcing effects of nicotine. Addict Biol 2014; 19:800-11. [PMID: 23496648 PMCID: PMC3715585 DOI: 10.1111/adb.12048] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The rate of codependency for alcohol and nicotine is extremely high. Numerous studies have indicated that there is a common genetic association for alcoholism and nicotine dependency. The current experiments examined whether selective breeding for high alcohol preference in rats may be associated with increased sensitivity of the posterior ventral tegmental area (pVTA) to the reinforcing properties of nicotine. In addition, nicotine can directly bind to the serotonin-3 (5-HT3 ) receptor, which has been shown to mediate the reinforcing properties of other drugs of abuse within the pVTA Wistar rats were assigned to groups that were allowed to self-infuse 0, 10, 50, 100, 200, 400 or 800 μM nicotine in two-lever (active and inactive) operant chambers. P rats were allowed to self-infuse 0, 1, 10, 50 or 100 μM nicotine. Co-infusion of 5-HT3 receptor antagonists with nicotine into the pVTA was also determined. P rats self-infused nicotine at lower concentrations than required to support self-administration in Wistar rats. In addition, P rats received more self-infusions of 50 and 100 μM nicotine than Wistar rats; including a 5HT3 receptor antagonist (LY-278,584 or zacopride) with nicotine reduced responding on the active lever. Overall, the data support an association between selective breeding for high alcohol preference and increased sensitivity of the pVTA to the reinforcing properties of nicotine. In addition, the data suggest that activation of 5HT3 receptors may be required to maintain the local reinforcing actions of nicotine within the pVTA.
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Affiliation(s)
- Sheketha R Hauser
- Institute of Psychiatric Research, Departments of Psychiatry & Anatomy, Indiana School of Medicine, and Department of Psychology, Purdue School of Science, Indiana University-Purdue University at Indianapolis, Indianapolis, IN, USA
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Hauser SR, Deehan GA, Toalston JE, Bell RL, McBride WJ, Rodd ZA. Enhanced alcohol-seeking behavior by nicotine in the posterior ventral tegmental area of female alcohol-preferring (P) rats: modulation by serotonin-3 and nicotinic cholinergic receptors. Psychopharmacology (Berl) 2014; 231:3745-55. [PMID: 24599396 PMCID: PMC4516288 DOI: 10.1007/s00213-014-3508-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/14/2013] [Accepted: 02/12/2014] [Indexed: 12/13/2022]
Abstract
RATIONALE Alcohol and nicotine co-use can reciprocally promote self-administration and drug-craving/drug-seeking behaviors. To date, the neurocircuitry in which nicotine influences ethanol (EtOH) seeking has not been elucidated. Clinical and preclinical research has suggested that the activation of the mesolimbic dopamine system is involved in the promotion of drug seeking. Alcohol, nicotine, and serotonin-3 (5-HT3) receptors interact within the posterior ventral tegmental area (pVTA) to regulate drug reward. Recently, our laboratory has reported that systemic administration of nicotine can promote context-induced EtOH seeking. OBJECTIVES The goals of the current study were to (1) determine if microinjections of pharmacologically relevant levels of nicotine into the pVTA would enhance EtOH seeking, (2) determine if coadministration of nicotinic cholinergic receptor antagonist (nACh) or 5-HT3 receptor antagonists would block the ability of nicotine microinjected into the pVTA to promote EtOH seeking, and (3) determine if 5-HT3 receptors in the pVTA can modulate EtOH seeking. RESULTS Nicotine (100 and 200 μM) microinjected into the pVTA enhanced EtOH seeking. Coinfusion with 200 μM mecamylamine (nACh antagonist) or 100 and 200 μM zacopride (5-HT3 receptor antagonist) blocked the observed nicotine enhancement of EtOH seeking. The data also indicated that microinjection of 1 μM CPBG (5-HT3 receptor agonist) promotes context-induced EtOH seeking; conversely, microinjection of 100 and 200 μM zacopride alone reduced context-induced EtOH seeking. CONCLUSIONS Overall, the results show that nicotine-enhanced EtOH-seeking behavior is modulated by 5-HT3 and nACh receptors within the pVTA and that the 5-HT3 receptor system within pVTA may be a potential pharmacological target to inhibit EtOH-seeking behaviors.
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Affiliation(s)
- Sheketha R Hauser
- Institute of Psychiatric Research, Department of Psychiatry, Indiana University School of Medicine, 791 Union Drive, Indianapolis, IN, 46202-4887, USA,
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Side-chain conformation at the selectivity filter shapes the permeation free-energy landscape of an ion channel. Proc Natl Acad Sci U S A 2014; 111:E3196-205. [PMID: 25049389 DOI: 10.1073/pnas.1408950111] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
On the basis of single-channel currents recorded from the muscle nicotinic acetylcholine receptor (AChR), we have recently hypothesized that the conformation adopted by the glutamate side chains at the first turn of the pore-lining α-helices is a key determinant of the rate of ion permeation. In this paper, we set out to test these ideas within a framework of atomic detail and stereochemical rigor by conducting all-atom molecular dynamics and Brownian dynamics simulations on an extensively validated model of the open-channel muscle AChR. Our simulations provided ample support to the notion that the different rotamers of these glutamates partition into two classes that differ markedly in their ability to catalyze ion conduction, and that the conformations of the four wild-type glutamates are such that two of them "fall" in each rotamer class. Moreover, the simulations allowed us to identify the mm (χ(1) ≅ -60°; χ(2) ≅ -60°) and tp (χ(1) ≅ 180°; χ(2) ≅ +60°) rotamers as the likely conduction-catalyzing conformations of the AChR's selectivity-filter glutamates. More generally, our work shows an example of how experimental benchmarks can guide molecular simulations into providing a type of structural and mechanistic insight that seems otherwise unattainable.
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Tammimäki A, Herder P, Li P, Esch C, Laughlin JR, Akk G, Stitzel JA. Impact of human D398N single nucleotide polymorphism on intracellular calcium response mediated by α3β4α5 nicotinic acetylcholine receptors. Neuropharmacology 2012; 63:1002-11. [PMID: 22820273 DOI: 10.1016/j.neuropharm.2012.07.022] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2012] [Revised: 07/06/2012] [Accepted: 07/09/2012] [Indexed: 10/28/2022]
Abstract
The human CHRNA5 D398N polymorphism (rs16969968) causes an aspartic acid to asparagine change in the nicotinic acetylcholine receptor (nAChR) α5 subunit gene. The N398 variant of CHRNA5 is linked to increased risk for nicotine dependence. In this study, we explored the effect of the CHRNA5 D398N polymorphism on the properties of human α3β4* nicotinic acetylcholine receptors in human embryonic kidney (HEK) cells. Addition of either D398 or N398 variant of α5 subunit in the α3β4* receptor did not affect total [(125)I]-epibatidine binding or surface expression of the receptor. However, addition of α5(D398) into α3β4* receptor decreased the maximal response to agonist without significantly affecting EC(50) in aequorin intracellular calcium assay. α3β4α5(N398) nAChRs showed further decreased maximal response. The differences in agonist efficacy between the receptor subtypes were found to be dependent upon the concentration of external calcium but independent of external sodium. Moreover, activation of α3β4α5 nAChRs led to significantly greater intracellular calcium release from IP(3) stores relative to α3β4 nAChRs although no effect of the α5 polymorphism was observed. Finally, inclusion of the α5 variant caused a small shift to the left in IC(50) for some of the antagonists tested, depending upon α5 variant but did not affect sensitivity of α3β4* receptors to desensitization in response to incubation with nicotine. In conclusion, addition of either variant of α5 into an α3β4α5 receptor similarly effects receptor pharmacology and function. However, the N398 variant exhibits a reduced response to agonists when extracellular calcium is high and it may lead to distinct downstream cellular signaling.
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Affiliation(s)
- Anne Tammimäki
- Institute for Behavioral Genetics, University of Colorado at Boulder, Boulder, CO 80309, USA.
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Sabatelli M, Eusebi F, Al-Chalabi A, Conte A, Madia F, Luigetti M, Mancuso I, Limatola C, Trettel F, Sobrero F, Di Angelantonio S, Grassi F, Di Castro A, Moriconi C, Fucile S, Lattante S, Marangi G, Murdolo M, Orteschi D, Del Grande A, Tonali P, Neri G, Zollino M. Rare missense variants of neuronal nicotinic acetylcholine receptor altering receptor function are associated with sporadic amyotrophic lateral sclerosis. Hum Mol Genet 2009; 18:3997-4006. [PMID: 19628475 DOI: 10.1093/hmg/ddp339] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Sporadic amyotrophic lateral sclerosis (SALS) is a motor neuron degenerative disease of unknown etiology. Current thinking on SALS is that multiple genetic and environmental factors contribute to disease liability. Since neuronal acetylcholine receptors (nAChRs) are part of the glutamatergic pathway, we searched for sequence variants in CHRNA3, CHRNA4 and CHRNB4 genes, encoding neuronal nicotinic AChR subunits, in 245 SALS patients and in 450 controls. We characterized missense variants by in vitro mutagenesis, cell transfection and electrophysiology. Sequencing the regions encoding the intracellular loop of AChRs subunits disclosed 15 missense variants (6.1%) in 14 patients compared with only six variants (1.3%) in controls (P = 0.001; OR 4.48, 95% CI 1.7-11.8). The frequency of variants in exons encoding extracellular and transmembrane domains and in intronic regions did not differ. NAChRs formed by mutant alpha3 and alpha4 and wild-type (WT) beta4 subunits exhibited altered affinity for nicotine (Nic), reduced use-dependent rundown of Nic-activated currents (I(Nic)) and reduced desensitization leading to sustained intracellular Ca(2+) concentration, in comparison with WT-nAChR. The cellular loop has a crucial importance for receptor trafficking and regulating ion channel properties. Missense variants in this domain are significantly over-represented in SALS patients and alter functional properties of nAChR in vitro, resulting in increased Ca(2+) entry into the cells. We suggest that these gain-of-function variants might contribute to disease liability in a subset of SALS because Ca(2+) signals mediate nAChR's neuromodulatory effects, including regulation of glutamate release and control of cell survival.
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Affiliation(s)
- Mario Sabatelli
- Istituto di Neurologia, Università Cattolica del Sacro Cuore, Roma, Italy
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Abstract
Nicotine achieves its psychopharmacological effects by interacting with nicotinic acetylcholine receptors (nAChRs) in the brain. There are numerous subtypes of nAChR that differ in their properties, including their sensitivity to nicotine, permeability to calcium and propensity to desensitise. The nAChRs are differentially localised to different brain regions and are found on presynaptic terminals as well as in somatodendritic regions of neurones. Through their permeability to cations, these ion channel proteins can influence both neuronal excitability and cell signalling mechanisms, and these various responses can contribute to the development or maintenance of dependence. However, many questions and uncertainties remain in our understanding of these events and their relevance to tobacco addiction. In this chapter, we briefly overview the fundamental characteristics of nAChRs that are germane to nicotine's effects and then consider the cellular responses to acute and chronic nicotine, with particular emphasis on dopamine systems because they have been the most widely studied in the context of nicotine dependence. Where appropriate, methodological aspects are critically reviewed.
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Affiliation(s)
- Jacques Barik
- Department of Biology & Biochemistry, University of Bath, Bath, UK
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Krzywkowski K. Do polymorphisms in the human 5-HT3 genes contribute to pathological phenotypes? Biochem Soc Trans 2007; 34:872-6. [PMID: 17052218 DOI: 10.1042/bst0340872] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
5-HT3 receptors are members of the Cys-loop superfamily of ligand-gated ion channels. In both the central and the peripheral nervous systems, 5-HT3 receptors excite postsynaptic cells and modulate the release of neurotransmitters from presynaptic neurons. 5-HT3 receptors are known to be involved in mediation of nausea/emesis caused by chemo/radio-therapy and anaesthesia, and more recently have also been found to be involved in irritable bowel syndrome. 5-HT3 receptors have also been suggested to play a role in a range of other indications, including various psychiatric disorders. This review summarizes the current evidence for the contribution of 5-HT3 subunit genes to disease phenotypes arising from association studies. Furthermore, it suggests how in vitro characterization of naturally occurring genetic variants can be used to obtain a better understanding of the causal relationship between gene and disease.
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Affiliation(s)
- K Krzywkowski
- Department of Medicinal Chemistry, The Danish University of Pharmaceutical Sciences, Copenhagen, Denmark.
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