301
|
Poveda JA, Marcela Giudici A, Lourdes Renart M, Morales A, González-Ros JM. Towards understanding the molecular basis of ion channel modulation by lipids: Mechanistic models and current paradigms. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:1507-1516. [PMID: 28408206 DOI: 10.1016/j.bbamem.2017.04.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2016] [Revised: 03/27/2017] [Accepted: 04/09/2017] [Indexed: 10/19/2022]
Abstract
Research on ion channel modulation has become a hot topic because of the key roles these membrane proteins play in both prokaryotic and eukaryotic organisms. In this respect, lipid modulation adds to the overall modulatory mechanisms as a potential via to find new pharmacological targets for drug design based on interfering with lipid/channel interactions. However, our knowledge in this field is scarce and often circumscribed to the sites where lipids bind and/or its final functional consequences. To fully understand this process it is necessary to improve our knowledge on its molecular basis, from the binding sites to the signalling pathways that derive in structural and functional effects on the ion channel. In this review, we have compiled information about such mechanisms and established a classification into four different modes of action. Afterwards, we have revised in more detail the lipid modulation of Cys-loop receptors and of the potassium channel KcsA, which were chosen as model channels modulated by specific lipids. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.
Collapse
Affiliation(s)
- José A Poveda
- Instituto de Biología Molecular y Celular, Universidad Miguel Hernández, Elche, 03202 Alicante, Spain.
| | - A Marcela Giudici
- Instituto de Biología Molecular y Celular, Universidad Miguel Hernández, Elche, 03202 Alicante, Spain
| | - M Lourdes Renart
- Instituto de Biología Molecular y Celular, Universidad Miguel Hernández, Elche, 03202 Alicante, Spain
| | - Andrés Morales
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, 03080 Alicante, Spain
| | - José M González-Ros
- Instituto de Biología Molecular y Celular, Universidad Miguel Hernández, Elche, 03202 Alicante, Spain.
| |
Collapse
|
302
|
Therien JPD, Baenziger JE. Pentameric ligand-gated ion channels exhibit distinct transmembrane domain archetypes for folding/expression and function. Sci Rep 2017; 7:450. [PMID: 28348412 PMCID: PMC5428567 DOI: 10.1038/s41598-017-00573-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Accepted: 03/03/2017] [Indexed: 11/17/2022] Open
Abstract
Although transmembrane helix-helix interactions must be strong enough to drive folding, they must still permit the inter-helix movements associated with conformational change. Interactions between the outermost M4 and adjacent M1 and M3 α-helices of pentameric ligand-gated ion channels have been implicated in folding and function. Here, we evaluate the role of different physical interactions at this interface in the function of two prokaryotic homologs, GLIC and ELIC. Strikingly, disruption of most interactions in GLIC lead to either a reduction or a complete loss of expression and/or function, while analogous disruptions in ELIC often lead to gains in function. Structural comparisons suggest that GLIC and ELIC represent distinct transmembrane domain archetypes. One archetype, exemplified by GLIC, the glycine and GABA receptors and the glutamate activated chloride channel, has extensive aromatic contacts that govern M4-M1/M3 interactions and that are essential for expression and function. The other archetype, exemplified by ELIC and both the nicotinic acetylcholine and serotonin receptors, has relatively few aromatic contacts that are detrimental to function. These archetypes likely have evolved different mechanisms to balance the need for strong M4 "binding" to M1/M3 to promote folding/expression, and the need for weaker interactions that allow for greater conformational flexibility.
Collapse
Affiliation(s)
- J P Daniel Therien
- Department of Biochemistry, Microbiology, and Immunology University of Ottawa, Ottawa, ON, K1H 8M5, Canada
| | - John E Baenziger
- Department of Biochemistry, Microbiology, and Immunology University of Ottawa, Ottawa, ON, K1H 8M5, Canada.
| |
Collapse
|
303
|
Molgó J, Marchot P, Aráoz R, Benoit E, Iorga BI, Zakarian A, Taylor P, Bourne Y, Servent D. Cyclic imine toxins from dinoflagellates: a growing family of potent antagonists of the nicotinic acetylcholine receptors. J Neurochem 2017; 142 Suppl 2:41-51. [PMID: 28326551 DOI: 10.1111/jnc.13995] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Revised: 02/13/2017] [Accepted: 02/15/2017] [Indexed: 12/24/2022]
Abstract
We present an overview of the toxicological profile of the fast-acting, lipophilic macrocyclic imine toxins, an emerging family of organic compounds associated with algal blooms, shellfish contamination and neurotoxicity. Worldwide, shellfish contamination incidents are expanding; therefore, the significance of these toxins for the shellfish food industry deserves further study. Emphasis is directed to the dinoflagellate species involved in their production, their chemical structures, and their specific mode of interaction with their principal natural molecular targets, the nicotinic acetylcholine receptors, or with the soluble acetylcholine-binding protein, used as a surrogate receptor model. The dinoflagellates Karenia selliformis and Alexandrium ostenfeldii / A. peruvianum have been implicated in the biosynthesis of gymnodimines and spirolides, while Vulcanodinium rugosum is the producer of pinnatoxins and portimine. The cyclic imine toxins are characterized by a macrocyclic skeleton comprising 14-27 carbon atoms, flanked by two conserved moieties, the cyclic imine and the spiroketal ring system. These phycotoxins generally display high affinity and broad specificity for the muscle type and neuronal nicotinic acetylcholine receptors, a feature consistent with their binding site at the receptor subunit interfaces, composed of residues highly conserved among all nAChRs, and explaining the diverse toxicity among animal species. This is an article for the special issue XVth International Symposium on Cholinergic Mechanisms.
Collapse
Affiliation(s)
- Jordi Molgó
- Commissariat à l'Energie Atomique et aux énergies alternatives (CEA), Institut de Biologie et Technologies de Saclay (IBITECS), Université Paris-Saclay, Service d'Ingénierie Moléculaire des Protéines, Gif-sur-Yvette, France.,Institut des Neurosciences Paris-Saclay, UMR 9197, Centre National de la Recherche Scientifique (CNRS)/Université Paris-Sud, Gif-sur-Yvette Cedex, France
| | - Pascale Marchot
- Aix-Marseille Université / Centre National de la Recherche Scientifique, Architecture et Fonction des Macromolécules Biologiques laboratory, Marseille, France
| | - Rómulo Aráoz
- Commissariat à l'Energie Atomique et aux énergies alternatives (CEA), Institut de Biologie et Technologies de Saclay (IBITECS), Université Paris-Saclay, Service d'Ingénierie Moléculaire des Protéines, Gif-sur-Yvette, France.,Institut des Neurosciences Paris-Saclay, UMR 9197, Centre National de la Recherche Scientifique (CNRS)/Université Paris-Sud, Gif-sur-Yvette Cedex, France
| | - Evelyne Benoit
- Commissariat à l'Energie Atomique et aux énergies alternatives (CEA), Institut de Biologie et Technologies de Saclay (IBITECS), Université Paris-Saclay, Service d'Ingénierie Moléculaire des Protéines, Gif-sur-Yvette, France.,Institut des Neurosciences Paris-Saclay, UMR 9197, Centre National de la Recherche Scientifique (CNRS)/Université Paris-Sud, Gif-sur-Yvette Cedex, France
| | - Bogdan I Iorga
- Centre National de la Recherche Scientifique (CNRS), Institut de Chimie des Substances Naturelles, UPR 2301, Labex LERMIT, Gif-sur-Yvette, France
| | - Armen Zakarian
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, California, USA
| | - Palmer Taylor
- Department of Pharmacology, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, California, USA
| | - Yves Bourne
- Aix-Marseille Université / Centre National de la Recherche Scientifique, Architecture et Fonction des Macromolécules Biologiques laboratory, Marseille, France
| | - Denis Servent
- Commissariat à l'Energie Atomique et aux énergies alternatives (CEA), Institut de Biologie et Technologies de Saclay (IBITECS), Université Paris-Saclay, Service d'Ingénierie Moléculaire des Protéines, Gif-sur-Yvette, France
| |
Collapse
|
304
|
Post MR, Lester HA, Dougherty DA. Probing for and Quantifying Agonist Hydrogen Bonds in α6β2 Nicotinic Acetylcholine Receptors. Biochemistry 2017; 56:1836-1840. [PMID: 28287260 DOI: 10.1021/acs.biochem.7b00213] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Designing subtype-selective agonists for neuronal nicotinic acetylcholine receptors is a challenging and significant goal aided by intricate knowledge of each subtype's binding patterns. We previously reported that in α6β2 receptors, acetylcholine makes a functional cation-π interaction with Trp149, but nicotine and TC299423 do not, suggesting a distinctive binding site. This work explores hydrogen binding at the backbone carbonyl associated with α6β2 Trp149. Substituting residue i + 1, Thr150, with its α-hydroxy analogue (Tah) attenuates the carbonyl's hydrogen bond accepting ability. At α6(T150Tah)β2, nicotine shows a 24-fold loss of function, TC299423 shows a modest loss, and acetylcholine shows no effect. Nicotine was further analyzed via a double-mutant cycle analysis utilizing N'-methylnicotinium, which indicated a hydrogen bond in α6β2 with a ΔΔG of 2.6 kcal/mol. Thus, even though nicotine does not make the conserved cation-π interaction with Trp149, it still makes a functional hydrogen bond to its associated backbone carbonyl.
Collapse
Affiliation(s)
- Michael R Post
- Division of Chemistry and Chemical Engineering and ‡Division of Biology and Biological Engineering, California Institute of Technology , Pasadena, California 91125, United States
| | - Henry A Lester
- Division of Chemistry and Chemical Engineering and ‡Division of Biology and Biological Engineering, California Institute of Technology , Pasadena, California 91125, United States
| | - Dennis A Dougherty
- Division of Chemistry and Chemical Engineering and ‡Division of Biology and Biological Engineering, California Institute of Technology , Pasadena, California 91125, United States
| |
Collapse
|
305
|
Wang J, Lindstrom J. Orthosteric and allosteric potentiation of heteromeric neuronal nicotinic acetylcholine receptors. Br J Pharmacol 2017; 175:1805-1821. [PMID: 28199738 DOI: 10.1111/bph.13745] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Revised: 01/30/2017] [Accepted: 02/06/2017] [Indexed: 12/16/2022] Open
Abstract
Heteromeric nicotinic ACh receptors (nAChRs) were thought to have two orthodox agonist-binding sites at two α/β subunit interfaces. Highly selective ligands are hard to develop by targeting orthodox agonist sites because of high sequence similarity of this binding pocket among different subunits. Recently, unorthodox ACh-binding sites have been discovered at some α/α and β/α subunit interfaces, such as α4/α4, α5/α4 and β3/α4. Targeting unorthodox sites may yield subtype-selective ligands, such as those for (α4β2)2 α5, (α4β2)2 β3 and (α6β2)2 β3 nAChRs. The unorthodox sites have unique pharmacology. Agonist binding at one unorthodox site is not sufficient to activate nAChRs, but it increases activation from the orthodox sites. NS9283, a selective agonist for the unorthodox α4/α4 site, was initially thought to be a positive allosteric modulator (PAM). NS9283 activates nAChRs with three engineered α4/α4 sites. PAMs, on the other hand, act at allosteric sites where ACh cannot bind. Known PAM sites include the ACh-homologous non-canonical site (e.g. morantel at β/α), the C-terminus (e.g. Br-PBTC and 17β-estradiol), a transmembrane domain (e.g. LY2087101) or extracellular and transmembrane domain interfaces (e.g. NS206). Some of these PAMs, such as Br-PBTC and 17β-estradiol, require only one subunit to potentiate activation of nAChRs. In this review, we will discuss differences between activation from orthosteric and allosteric sites, their selective ligands and clinical implications. These studies have advanced understanding of the structure, assembly and pharmacology of heteromeric neuronal nAChRs. LINKED ARTICLES This article is part of a themed section on Nicotinic Acetylcholine Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.11/issuetoc.
Collapse
Affiliation(s)
- Jingyi Wang
- Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA
| | - Jon Lindstrom
- Department of Neuroscience, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| |
Collapse
|
306
|
Menny A, Lefebvre SN, Schmidpeter PA, Drège E, Fourati Z, Delarue M, Edelstein SJ, Nimigean CM, Joseph D, Corringer PJ. Identification of a pre-active conformation of a pentameric channel receptor. eLife 2017; 6. [PMID: 28294942 PMCID: PMC5398890 DOI: 10.7554/elife.23955] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Accepted: 03/14/2017] [Indexed: 11/26/2022] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs) mediate fast chemical signaling through global allosteric transitions. Despite the existence of several high-resolution structures of pLGICs, their dynamical properties remain elusive. Using the proton-gated channel GLIC, we engineered multiple fluorescent reporters, each incorporating a bimane and a tryptophan/tyrosine, whose close distance causes fluorescence quenching. We show that proton application causes a global compaction of the extracellular subunit interface, coupled to an outward motion of the M2-M3 loop near the channel gate. These movements are highly similar in lipid vesicles and detergent micelles. These reorganizations are essentially completed within 2 ms and occur without channel opening at low proton concentration, indicating that they report a pre-active intermediate state in the transition pathway toward activation. This provides a template to investigate the gating of eukaryotic neurotransmitter receptors, for which intermediate states also participate in activation. DOI:http://dx.doi.org/10.7554/eLife.23955.001 In the nervous system, proteins of the pLGIC family are found in the membrane that surrounds each neuron. These proteins have channels that can allow ions to pass through the membrane and are responsible for transmitting electrical signals from one neuron to the next. Small molecules called neurotransmitters interact with the pLGICs to open or close the ion channel. If the ability of the pLGIC channels to open is altered, it can lead to behavioral changes like addiction, or diseases such as schizophrenia or epilepsy. For a pLGIC channel to switch between the “open” and “closed” states, specific parts of the protein need to move in relation to each other. However, to study these transitions researchers have previously relied on comparing the three-dimensional structures of open and closed pLGICs extracted out of the cell membrane. Different techniques are needed to directly follow these movements within membranes. Bacteria also have proteins belonging to the pLGIC family, and Menny et al. have now investigated one such bacterial protein to understand how pLGICs open. First, a small fluorescent molecule that glows differently if the environment around it changes was attached to various parts of the bacterial channel. These fluorescent markers revealed how several parts of the protein move and they also made it possible to measure how quickly these movements take place. Some of these movements happen before the channel opens, suggesting that the activation of this pLGIC protein happens in stages and involves the protein adopting a temporary intermediate state. The next step will be to better understand the structure of the intermediate state, which could help us to understand how pLGICs work in the nervous systems of animals. In future this may aid the design of new drugs that can modify the activity of these channels in patients with neurological conditions or addictions. DOI:http://dx.doi.org/10.7554/eLife.23955.002
Collapse
Affiliation(s)
- Anaïs Menny
- Channel Receptors Unit, Institut Pasteur, Paris, France.,Unité Mixte de Recherche 3571, Centre National de la Recherche Scientifique, Paris, France.,Université Pierre et Marie Curie, Cellule Pasteur, Paris, France
| | - Solène N Lefebvre
- Channel Receptors Unit, Institut Pasteur, Paris, France.,Unité Mixte de Recherche 3571, Centre National de la Recherche Scientifique, Paris, France.,Université Pierre et Marie Curie, Cellule Pasteur, Paris, France
| | - Philipp Am Schmidpeter
- Departments of Anesthesiology, Physiology and Biophysics, Biochemistry, Weill Cornell Medicine, New York, United States
| | - Emmanuelle Drège
- BioCIS, Université Paris-Sud, CNRS, Université Paris-Saclay, Châtenay-Malabry, France
| | - Zaineb Fourati
- Unité de Dynamique Structurale des Macromolécules, Institut Pasteur, Paris, France.,Unité Mixte de Recherche 3528, Centre National de la Recherche Scientifique, Paris, France
| | - Marc Delarue
- Unité de Dynamique Structurale des Macromolécules, Institut Pasteur, Paris, France.,Unité Mixte de Recherche 3528, Centre National de la Recherche Scientifique, Paris, France
| | - Stuart J Edelstein
- Biologie Cellulaire de la Synapse, Institute of Biology, Ecole Normale Supérieure, Paris, France
| | - Crina M Nimigean
- Departments of Anesthesiology, Physiology and Biophysics, Biochemistry, Weill Cornell Medicine, New York, United States
| | - Delphine Joseph
- BioCIS, Université Paris-Sud, CNRS, Université Paris-Saclay, Châtenay-Malabry, France
| | - Pierre-Jean Corringer
- Channel Receptors Unit, Institut Pasteur, Paris, France.,Unité Mixte de Recherche 3571, Centre National de la Recherche Scientifique, Paris, France
| |
Collapse
|
307
|
Elberson BW, Whisenant TE, Cortes DM, Cuello LG. A cost-effective protocol for the over-expression and purification of fully-functional and more stable Erwinia chrysanthemi ligand-gated ion channel. Protein Expr Purif 2017; 133:177-186. [PMID: 28279818 DOI: 10.1016/j.pep.2017.03.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Revised: 02/21/2017] [Accepted: 03/04/2017] [Indexed: 10/20/2022]
Abstract
The Erwinia chrysanthemi ligand-gated ion channel, ELIC, is considered an excellent structural and functional surrogate for the whole pentameric ligand-gated ion channel family. Despite its simplicity, ELIC is structurally capable of undergoing ligand-dependent activation and a concomitant desensitization process. To determine at the molecular level the structural changes underlying ELIC's function, it is desirable to produce large quantities of protein. This protein should be properly folded, fully-functional and amenable to structural determinations. In the current paper, we report a completely new protocol for the expression and purification of milligram quantities of fully-functional, more stable and crystallizable ELIC. The use of an autoinduction media and inexpensive detergents during ELIC extraction, in addition to the high-quality and large quantity of the purified channel, are the highlights of this improved biochemical protocol.
Collapse
Affiliation(s)
- Benjamin W Elberson
- Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, Texas Tech University Health Sciences Center, 3601 4th Street STOP 6551, Lubbock, TX 79430, USA
| | - Ty E Whisenant
- Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, Texas Tech University Health Sciences Center, 3601 4th Street STOP 6551, Lubbock, TX 79430, USA
| | - D Marien Cortes
- Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, Texas Tech University Health Sciences Center, 3601 4th Street STOP 6551, Lubbock, TX 79430, USA
| | - Luis G Cuello
- Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, Texas Tech University Health Sciences Center, 3601 4th Street STOP 6551, Lubbock, TX 79430, USA.
| |
Collapse
|
308
|
Basak S, Schmandt N, Gicheru Y, Chakrapani S. Crystal structure and dynamics of a lipid-induced potential desensitized-state of a pentameric ligand-gated channel. eLife 2017; 6:23886. [PMID: 28262093 PMCID: PMC5378477 DOI: 10.7554/elife.23886] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2016] [Accepted: 03/04/2017] [Indexed: 12/14/2022] Open
Abstract
Desensitization in pentameric ligand-gated ion channels plays an important role in regulating neuronal excitability. Here, we show that docosahexaenoic acid (DHA), a key ω−3 polyunsaturated fatty acid in synaptic membranes, enhances the agonist-induced transition to the desensitized state in the prokaryotic channel GLIC. We determined a 3.25 Å crystal structure of the GLIC-DHA complex in a potentially desensitized conformation. The DHA molecule is bound at the channel-periphery near the M4 helix and exerts a long-range allosteric effect on the pore across domain-interfaces. In this previously unobserved conformation, the extracellular-half of the pore-lining M2 is splayed open, reminiscent of the open conformation, while the intracellular-half is constricted, leading to a loss of both water and permeant ions. These findings, in combination with spin-labeling/EPR spectroscopic measurements in reconstituted-membranes, provide novel mechanistic details of desensitization in pentameric channels. DOI:http://dx.doi.org/10.7554/eLife.23886.001 The nerve cells (or neurons) in the brain communicate with each other by releasing chemicals called neurotransmitters that bind to ion channels on neighboring neurons. This ultimately causes ions to flow in or out of the receiving neuron through these ion channels; this ion flow determines how the neuron responds. One family of ion channels that is found at the junction between neurons, and between neurons and muscle fibers, is known as the pentameric ligand-gated ion channels (or pLGICs). These channels act as ‘gates’ that open to allow ions through them when a neurotransmitter binds to the channel. In addition to the open ‘active’ state, the channels can take on two different ‘inactive’ states that do not allow ions to pass through the channel: a closed (resting) state and a desensitized state (that is still bound to the neurotransmitter). Understanding how channels switch between these states is important for designing drugs that correct problems that cause the channels to work incorrectly. Problems that affect the desensitized state have been linked to neurological disorders such as epilepsy. Medically important molecules such as anesthetics and alcohols are thought to affect desensitization, and drugs that target desensitized ion channels may present ways of treating neurological disorders with fewer side effects. Docosahexaenoic acid (DHA) is an abundant lipid molecule that is present in the membranes of neurons. It is one of the key ingredients in fish oil supplements and is thought to enhance learning and memory. DHA affects the desensitization of pLGICs but it is not clear exactly how it does so. Basak et al. now show that DHA affects a bacterial pLGIC in the same way as it affects human channels – by enhancing desensitization. Using a technique called X-ray crystallography to analyze the channel while bound to DHA revealed a previously unobserved channel structure. The DHA molecule binds to a site at the edge of the channel and causes a change in its structure that leaves the upper part of the channel open while the lower part is constricted. Basak et al. predict that molecules such as anesthetics target this desensitized state. The next step will be to obtain the structures of bacterial and human pLGIC channels in a natural membrane environment. This will allow us to better understand the changes in structure that the channels go through as they transmit signals between neurons, and so help in the development of new treatments for neurological disorders. DOI:http://dx.doi.org/10.7554/eLife.23886.002
Collapse
Affiliation(s)
- Sandip Basak
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, United States
| | - Nicolaus Schmandt
- Department of Neuroscience, School of Medicine, Case Western Reserve University, Cleveland, United States
| | - Yvonne Gicheru
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, United States
| | - Sudha Chakrapani
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, United States
| |
Collapse
|
309
|
Baptista-Hon DT, Gulbinaite S, Hales TG. Loop G in the GABA A receptor α1 subunit influences gating efficacy. J Physiol 2017; 595:1725-1741. [PMID: 27981574 DOI: 10.1113/jp273752] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2016] [Accepted: 12/01/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS The functional importance of residues in loop G of the GABAA receptor has not been investigated. D43 and T47 in the α1 subunit are of particular significance as their structural modification inhibits activation by GABA. While the T47C substitution had no significant effect, non-conservative substitution of either residue (D43C or T47R) reduced the apparent potency of GABA. Propofol potentiated maximal GABA-evoked currents mediated by α1(D43C)β2γ2 and α1(T47R)β2γ2 receptors. Non-stationary variance analysis revealed a reduction in maximal GABA-evoked Popen , suggesting impaired agonist efficacy. Further analysis of α1(T47R)β2γ2 receptors revealed that the efficacy of the partial agonist THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-3-ol) relative to GABA was impaired. GABA-, THIP- and propofol-evoked currents mediated by α1(T47R)β2γ2 receptors deactivated faster than those mediated by α1β2γ2 receptors, indicating that the mutation impairs agonist-evoked gating. Spontaneous gating caused by the β2(L285R) mutation was also reduced in α1(T47R)β2(L285R)γ2 compared to α1β2(L285R)γ2 receptors, confirming that α1(T47R) impairs gating independently of agonist activation. ABSTRACT The modification of cysteine residues (substituted for D43 and T47) by 2-aminoethyl methanethiosulfonate in the GABAA α1 subunit loop G is known to impair activation of α1β2γ2 receptors by GABA and propofol. While the T47C substitution had no significant effect, non-conservative substitution of either residue (D43C or T47R) reduced the apparent potency of GABA. Propofol (1 μm), which potentiates sub-maximal but not maximal GABA-evoked currents mediated by α1β2γ2 receptors, also potentiated maximal currents mediated by α1(D43C)β2γ2 and α1(T47R)β2γ2 receptors. Furthermore, the peak open probabilities of α1(D43C)β2γ2 and α1(T47R)β2γ2 receptors were reduced. The kinetics of macroscopic currents mediated by α1(D43C)β2γ2 and α1(T47R)β2γ2 receptors were characterised by slower desensitisation and faster deactivation. Similar changes in macroscopic current kinetics, together with a slower activation rate, were observed with the loop D α1(F64C) substitution, known to impair both efficacy and agonist binding, and when the partial agonist THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-3-ol) was used to activate WT or α1(T47R)β2γ2 receptors. Propofol-evoked currents mediated by α1(T47R)β2γ2 and α1(F64C)β2γ2 receptors also exhibited faster deactivation than their WT counterparts, revealing that these substitutions impair gating through a mechanism independent of orthosteric binding. Spontaneous gating caused by the introduction of the β2(L285R) mutation was also reduced in α1(T47R)β2(L285R)γ2 compared to α1β2(L285R)γ2 receptors, confirming that α1(T47R) impairs gating independently of activation by any agonist. These findings implicate movement of the GABAA receptor α1 subunit's β1 strand during agonist-dependent and spontaneous gating. Immobilisation of the β1 strand may provide a mechanism for the inhibition of gating by inverse agonists such as bicuculline.
Collapse
Affiliation(s)
- Daniel T Baptista-Hon
- The Institute of Academic Anaesthesia, Division of Neuroscience, School of Medicine, Ninewells Hospital, University of Dundee, Dundee, UK
| | - Simona Gulbinaite
- The Institute of Academic Anaesthesia, Division of Neuroscience, School of Medicine, Ninewells Hospital, University of Dundee, Dundee, UK
| | - Tim G Hales
- The Institute of Academic Anaesthesia, Division of Neuroscience, School of Medicine, Ninewells Hospital, University of Dundee, Dundee, UK
| |
Collapse
|
310
|
Boffi JC, Marcovich I, Gill-Thind JK, Corradi J, Collins T, Lipovsek MM, Moglie M, Plazas PV, Craig PO, Millar NS, Bouzat C, Elgoyhen AB. Differential Contribution of Subunit Interfaces to α9α10 Nicotinic Acetylcholine Receptor Function. Mol Pharmacol 2017; 91:250-262. [PMID: 28069778 PMCID: PMC5325082 DOI: 10.1124/mol.116.107482] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Accepted: 01/04/2017] [Indexed: 12/31/2022] Open
Abstract
Nicotinic acetylcholine receptors can be assembled from either homomeric or heteromeric pentameric subunit combinations. At the interface of the extracellular domains of adjacent subunits lies the acetylcholine binding site, composed of a principal component provided by one subunit and a complementary component of the adjacent subunit. Compared with neuronal nicotinic acetylcholine cholinergic receptors (nAChRs) assembled from α and β subunits, the α9α10 receptor is an atypical member of the family. It is a heteromeric receptor composed only of α subunits. Whereas mammalian α9 subunits can form functional homomeric α9 receptors, α10 subunits do not generate functional channels when expressed heterologously. Hence, it has been proposed that α10 might serve as a structural subunit, much like a β subunit of heteromeric nAChRs, providing only complementary components to the agonist binding site. Here, we have made use of site-directed mutagenesis to examine the contribution of subunit interface domains to α9α10 receptors by a combination of electrophysiological and radioligand binding studies. Characterization of receptors containing Y190T mutations revealed unexpectedly that both α9 and α10 subunits equally contribute to the principal components of the α9α10 nAChR. In addition, we have shown that the introduction of a W55T mutation impairs receptor binding and function in the rat α9 subunit but not in the α10 subunit, indicating that the contribution of α9 and α10 subunits to complementary components of the ligand-binding site is nonequivalent. We conclude that this asymmetry, which is supported by molecular docking studies, results from adaptive amino acid changes acquired only during the evolution of mammalian α10 subunits.
Collapse
Affiliation(s)
- Juan Carlos Boffi
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Irina Marcovich
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - JasKiran K Gill-Thind
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Jeremías Corradi
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Toby Collins
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - María Marcela Lipovsek
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Marcelo Moglie
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Paola V Plazas
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Patricio O Craig
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Neil S Millar
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Cecilia Bouzat
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Ana Belén Elgoyhen
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B).
| |
Collapse
|
311
|
Brannigan G. Direct Interactions of Cholesterol With Pentameric Ligand-Gated Ion Channels: Testable Hypotheses From Computational Predictions. CURRENT TOPICS IN MEMBRANES 2017; 80:163-186. [DOI: 10.1016/bs.ctm.2017.06.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
|
312
|
Baenziger JE, Domville JA, Therien JD. The Role of Cholesterol in the Activation of Nicotinic Acetylcholine Receptors. CURRENT TOPICS IN MEMBRANES 2017; 80:95-137. [DOI: 10.1016/bs.ctm.2017.05.002] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
|
313
|
Mazzaferro S, Bermudez I, Sine SM. α4β2 Nicotinic Acetylcholine Receptors: RELATIONSHIPS BETWEEN SUBUNIT STOICHIOMETRY AND FUNCTION AT THE SINGLE CHANNEL LEVEL. J Biol Chem 2016; 292:2729-2740. [PMID: 28031459 DOI: 10.1074/jbc.m116.764183] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Revised: 12/09/2016] [Indexed: 11/06/2022] Open
Abstract
Acetylcholine receptors comprising α4 and β2 subunits are the most abundant class of nicotinic acetylcholine receptor in the brain. They contribute to cognition, reward, mood, and nociception and are implicated in a range of neurological disorders. Previous measurements of whole-cell macroscopic currents showed that α4 and β2 subunits assemble in two predominant pentameric stoichiometries, which differ in their sensitivity to agonists, antagonists, and allosteric modulators. Here we compare agonist-elicited single channel currents from receptors assembled with an excess of either the α4 or β2 subunit, forming receptor populations biased toward one or the other stoichiometry, with currents from receptors composed of five concatemeric subunits in which the subunit stoichiometry is predetermined. Our results associate each subunit stoichiometry with a unique single channel conductance, mean open channel lifetime, and sensitivity to the allosteric potentiator 3-[3-(3-pyridinyl)-1,2,4-oxadiazol-5-yl]benzonitrile (NS-9283). Receptors with the composition (α4β2)2α4 exhibit high single channel conductance, brief mean open lifetime, and strong potentiation by NS-9283, whereas receptors with the composition (α4β2)2β2 exhibit low single channel conductance and long mean open lifetime and are not potentiated by NS-9283. Thus single channel current measurements reveal bases for the distinct functional and pharmacological properties endowed by different stoichiometries of α4 and β2 subunits and establish pentameric concatemers as a means to delineate interactions between subunits that confer these properties.
Collapse
Affiliation(s)
- Simone Mazzaferro
- From the Receptor Biology Laboratory, Department of Physiology and Biomedical Engineering and
| | - Isabel Bermudez
- the School of Life Sciences, Oxford Brookes University, Oxford OX3 OBP, United Kingdom
| | - Steven M Sine
- From the Receptor Biology Laboratory, Department of Physiology and Biomedical Engineering and .,Departments of Neurology and.,Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic College of Medicine, Rochester, Minnesota 55905 and
| |
Collapse
|
314
|
Gupta S, Chakraborty S, Vij R, Auerbach A. A mechanism for acetylcholine receptor gating based on structure, coupling, phi, and flip. J Gen Physiol 2016; 149:85-103. [PMID: 27932572 PMCID: PMC5217088 DOI: 10.1085/jgp.201611673] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Revised: 09/20/2016] [Accepted: 11/10/2016] [Indexed: 01/29/2023] Open
Abstract
Gupta et al. use single-channel electrophysiology to investigate the gating mechanism of acetylcholine receptor ion channels. They propose that channel opening starts at the M2–M3 linker and ligand-binding sites and proceeds through four brief intermediate conformations before ending with the collapse of a gate bubble. Nicotinic acetylcholine receptors are allosteric proteins that generate membrane currents by isomerizing (“gating”) between resting and active conformations under the influence of neurotransmitters. Here, to explore the mechanisms that link the transmitter-binding sites (TBSs) with the distant gate, we use mutant cycle analyses to measure coupling between residue pairs, phi value analyses to sequence domain rearrangements, and current simulations to reproduce a microsecond shut component (“flip”) apparent in single-channel recordings. Significant interactions between amino acids separated by >15 Å are rare; an exception is between the αM2–M3 linkers and the TBSs that are ∼30 Å apart. Linker residues also make significant, local interactions within and between subunits. Phi value analyses indicate that without agonists, the linker is the first region in the protein to reach the gating transition state. Together, the phi pattern and flip component suggest that a complete, resting↔active allosteric transition involves passage through four brief intermediate states, with brief shut events arising from sojourns in all or a subset. We derive energy landscapes for gating with and without agonists, and propose a structure-based model in which resting→active starts with spontaneous rearrangements of the M2–M3 linkers and TBSs. These conformational changes stabilize a twisted extracellular domain to promote transmembrane helix tilting, gate dilation, and the formation of a “bubble” that collapses to initiate ion conduction. The energy landscapes suggest that twisting is the most energetically unfavorable step in the resting→active conformational change and that the rate-limiting step in the reverse process is bubble formation.
Collapse
Affiliation(s)
- Shaweta Gupta
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214
| | - Srirupa Chakraborty
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214
| | - Ridhima Vij
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214
| | - Anthony Auerbach
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214
| |
Collapse
|
315
|
Sun J, Comeau JF, Baenziger JE. Probing the structure of the uncoupled nicotinic acetylcholine receptor. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1859:146-154. [PMID: 27871840 DOI: 10.1016/j.bbamem.2016.11.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2016] [Revised: 11/10/2016] [Accepted: 11/17/2016] [Indexed: 10/20/2022]
Abstract
In the absence of activating anionic lipids and cholesterol, the nicotinic acetylcholine receptor (nAChR) from Torpedo adopts an uncoupled conformation that does not usually gate open in response to agonist. The uncoupled conformation binds both agonists and non-competitive channel blockers with a lower affinity than the desensitized state, consistent with both the extracellular agonist-binding and transmembrane channel-gating domains individually adopting resting-state like conformations. To test this hypothesis, we characterized the binding of the agonist, acetylcholine, and two fluorescent channel blockers, ethidium and crystal violet, to resting, desensitized and uncoupled nAChRs in reconstituted membranes. The measured Kd for acetylcholine binding to the uncoupled nAChR is similar to that for the resting state, confirming that the agonist binding site adopts a resting-state like conformation. Although both ethidium and crystal violet bind to the resting and desensitized channel pores with distinct affinities, no binding of either probe was detected to the uncoupled nAChR. Our data suggest that the transmembrane domain of the uncoupled nAChR adopts a conformation distinct from that of the resting and desensitized states. The lack of binding is consistent with a more constricted channel pore, possibly along the lines of what is observed in crystal structures of the prokaryotic homolog, ELIC.
Collapse
Affiliation(s)
- Jiayin Sun
- Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, 451 Smyth Rd, K1H 8M5 Ottawa, ON, Canada
| | - J Frederique Comeau
- Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, 451 Smyth Rd, K1H 8M5 Ottawa, ON, Canada
| | - John E Baenziger
- Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, 451 Smyth Rd, K1H 8M5 Ottawa, ON, Canada.
| |
Collapse
|
316
|
Alcaino C, Musgaard M, Minguez T, Mazzaferro S, Faundez M, Iturriaga-Vasquez P, Biggin PC, Bermudez I. Role of the Cys Loop and Transmembrane Domain in the Allosteric Modulation of α4β2 Nicotinic Acetylcholine Receptors. J Biol Chem 2016; 292:551-562. [PMID: 27864368 DOI: 10.1074/jbc.m116.751206] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2016] [Revised: 11/04/2016] [Indexed: 11/06/2022] Open
Abstract
Allosteric modulators of pentameric ligand-gated ion channels are thought to act on elements of the pathways that couple agonist binding to channel gating. Using α4β2 nicotinic acetylcholine receptors and the α4β2-selective positive modulators 17β-estradiol (βEST) and desformylflustrabromine (dFBr), we have identified pathways that link the binding sites for these modulators to the Cys loop, a region that is critical for channel gating in all pentameric ligand-gated ion channels. Previous studies have shown that the binding site for potentiating βEST is in the C-terminal (post-M4) region of the α4 subunit. Here, using homology modeling in combination with mutagenesis and electrophysiology, we identified the binding site for potentiating dFBr on the top half of a cavity between the third (M3) and fourth transmembrane (M4) α-helices of the α4 subunit. We found that the binding sites for βEST and dFBr communicate with the Cys loop, through interactions between the last residue of post-M4 and Phe170 of the conserved FPF sequence of the Cys loop, and that these interactions affect potentiating efficacy. In addition, interactions between a residue in M3 (Tyr309) and Phe167, a residue adjacent to the Cys loop FPF motif, also affect dFBr potentiating efficacy. Thus, the Cys loop acts as a key control element in the allosteric transduction pathway for potentiating βEST and dFBr. Overall, we propose that positive allosteric modulators that bind the M3-M4 cavity or post-M4 region increase the efficacy of channel gating through interactions with the Cys loop.
Collapse
Affiliation(s)
- Constanza Alcaino
- From the Department of Biological and Medical Sciences, Oxford Brookes University, Oxford OX3 0BP, United Kingdom
| | - Maria Musgaard
- the Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Teresa Minguez
- From the Department of Biological and Medical Sciences, Oxford Brookes University, Oxford OX3 0BP, United Kingdom
| | - Simone Mazzaferro
- From the Department of Biological and Medical Sciences, Oxford Brookes University, Oxford OX3 0BP, United Kingdom
| | - Manuel Faundez
- the Faculty of Sciences, University of Chile, Santiago 7800003, Chile, and
| | - Patricio Iturriaga-Vasquez
- the Departamento de Ciencias Quimicas y Recursos Naturales, Facultad de Ingenieria y Ciencias, Universidad de la Frontera, Temuco 4811230, Chile
| | - Philip C Biggin
- the Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Isabel Bermudez
- From the Department of Biological and Medical Sciences, Oxford Brookes University, Oxford OX3 0BP, United Kingdom,
| |
Collapse
|