1
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Ananchenko A, Gao RY, Dehez F, Baenziger JE. State-dependent binding of cholesterol and an anionic lipid to the muscle-type Torpedo nicotinic acetylcholine receptor. Commun Biol 2024; 7:437. [PMID: 38600247 PMCID: PMC11006840 DOI: 10.1038/s42003-024-06106-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2023] [Accepted: 03/25/2024] [Indexed: 04/12/2024] Open
Abstract
The ability of the Torpedo nicotinic acetylcholine receptor (nAChR) to undergo agonist-induced conformational transitions requires the presence of cholesterol and/or anionic lipids. Here we use recently solved structures along with multiscale molecular dynamics simulations to examine lipid binding to the nAChR in bilayers that have defined effects on nAChR function. We examine how phosphatidic acid and cholesterol, lipids that support conformational transitions, individually compete for binding with phosphatidylcholine, a lipid that does not. We also examine how the two lipids work synergistically to stabilize an agonist-responsive nAChR. We identify rapidly exchanging lipid binding sites, including both phospholipid sites with a high affinity for phosphatidic acid and promiscuous cholesterol binding sites in the grooves between adjacent transmembrane α-helices. A high affinity cholesterol site is confirmed in the inner leaflet framed by a key tryptophan residue on the MX α-helix. Our data provide insight into the dynamic nature of lipid-nAChR interactions and set the stage for a detailed understanding of the mechanisms by which lipids facilitate nAChR function at the neuromuscular junction.
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Affiliation(s)
- Anna Ananchenko
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, ON, Canada
| | - Rui Yan Gao
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, ON, Canada
| | - François Dehez
- CNRS, LPCT, Université de Lorraine, F-54000 Nancy, France.
| | - John E Baenziger
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, ON, Canada.
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2
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Oishi K, Nagamori M, Kashino Y, Sekiguchi H, Sasaki YC, Miyazawa A, Nishino Y. Ligand-Dependent Intramolecular Motion of Native Nicotinic Acetylcholine Receptors Determined in Living Myotube Cells via Diffracted X-ray Tracking. Int J Mol Sci 2023; 24:12069. [PMID: 37569445 PMCID: PMC10418694 DOI: 10.3390/ijms241512069] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2023] [Revised: 07/20/2023] [Accepted: 07/26/2023] [Indexed: 08/13/2023] Open
Abstract
Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that play an important role in signal transduction at the neuromuscular junction (NMJ). Movement of the nAChR extracellular domain following agonist binding induces conformational changes in the extracellular domain, which in turn affects the transmembrane domain and opens the ion channel. It is known that the surrounding environment, such as the presence of specific lipids and proteins, affects nAChR function. Diffracted X-ray tracking (DXT) facilitates measurement of the intermolecular motions of receptors on the cell membranes of living cells, including all the components involved in receptor function. In this study, the intramolecular motion of the extracellular domain of native nAChR proteins in living myotube cells was analyzed using DXT for the first time. We revealed that the motion of the extracellular domain in the presence of an agonist (e.g., carbamylcholine, CCh) was restricted by an antagonist (i.e., alpha-bungarotoxin, BGT).
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Affiliation(s)
- Koichiro Oishi
- Graduate School of Sciences, University of Hyogo, 3-2-1 Kouto, Kamigori-cho, Ako-gun, Kobe 678-1297, Hyogo, Japan; (K.O.); (Y.K.)
| | - Mayu Nagamori
- Graduate School of Sciences, University of Hyogo, 3-2-1 Kouto, Kamigori-cho, Ako-gun, Kobe 678-1297, Hyogo, Japan; (K.O.); (Y.K.)
| | - Yasuhiro Kashino
- Graduate School of Sciences, University of Hyogo, 3-2-1 Kouto, Kamigori-cho, Ako-gun, Kobe 678-1297, Hyogo, Japan; (K.O.); (Y.K.)
| | - Hiroshi Sekiguchi
- Center for Synchrotron Radiation Research, Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Sayo 679-5198, Hyogo, Japan; (H.S.); (Y.C.S.)
| | - Yuji C. Sasaki
- Center for Synchrotron Radiation Research, Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Sayo 679-5198, Hyogo, Japan; (H.S.); (Y.C.S.)
- Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8561, Chiba, Japan
- AIST-UTokyo Advanced Operando-Measurement Technology Open Innovation Laboratory, National Institute of Advanced Industrial Science and Technology, 6-2-3 Kashiwanoha, Kashiwa 277-0882, Chiba, Japan
| | - Atsuo Miyazawa
- Graduate School of Sciences, University of Hyogo, 3-2-1 Kouto, Kamigori-cho, Ako-gun, Kobe 678-1297, Hyogo, Japan; (K.O.); (Y.K.)
| | - Yuri Nishino
- Graduate School of Sciences, University of Hyogo, 3-2-1 Kouto, Kamigori-cho, Ako-gun, Kobe 678-1297, Hyogo, Japan; (K.O.); (Y.K.)
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3
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Petroff JT, Dietzen NM, Santiago-McRae E, Deng B, Washington MS, Chen LJ, Trent Moreland K, Deng Z, Rau M, Fitzpatrick JAJ, Yuan P, Joseph TT, Hénin J, Brannigan G, Cheng WWL. Open-channel structure of a pentameric ligand-gated ion channel reveals a mechanism of leaflet-specific phospholipid modulation. Nat Commun 2022; 13:7017. [PMID: 36385237 PMCID: PMC9668969 DOI: 10.1038/s41467-022-34813-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2022] [Accepted: 11/08/2022] [Indexed: 11/18/2022] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs) mediate synaptic transmission and are sensitive to their lipid environment. The mechanism of phospholipid modulation of any pLGIC is not well understood. We demonstrate that the model pLGIC, ELIC (Erwinia ligand-gated ion channel), is positively modulated by the anionic phospholipid, phosphatidylglycerol, from the outer leaflet of the membrane. To explore the mechanism of phosphatidylglycerol modulation, we determine a structure of ELIC in an open-channel conformation. The structure shows a bound phospholipid in an outer leaflet site, and structural changes in the phospholipid binding site unique to the open-channel. In combination with streamlined alchemical free energy perturbation calculations and functional measurements in asymmetric liposomes, the data support a mechanism by which an anionic phospholipid stabilizes the activated, open-channel state of a pLGIC by specific, state-dependent binding to this site.
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Affiliation(s)
- John T Petroff
- Department of Anesthesiology, Washington University School of Medicine, Saint Louis, MO, USA
| | - Noah M Dietzen
- Department of Anesthesiology, Washington University School of Medicine, Saint Louis, MO, USA
| | - Ezry Santiago-McRae
- Center for Computational and Integrative Biology, Rutgers University, Camden, NJ, USA
| | - Brett Deng
- Department of Anesthesiology, Washington University School of Medicine, Saint Louis, MO, USA
| | - Maya S Washington
- Department of Anesthesiology, Washington University School of Medicine, Saint Louis, MO, USA
| | - Lawrence J Chen
- Department of Anesthesiology, Washington University School of Medicine, Saint Louis, MO, USA
| | - K Trent Moreland
- Department of Anesthesiology, Washington University School of Medicine, Saint Louis, MO, USA
| | - Zengqin Deng
- Department of Cell Biology and Physiology, Washington University School of Medicine, Saint Louis, MO, USA
- Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, Saint Louis, MO, USA
| | - Michael Rau
- Center for Cellular Imaging, Washington University School of Medicine, Saint Louis, MO, USA
| | - James A J Fitzpatrick
- Department of Cell Biology and Physiology, Washington University School of Medicine, Saint Louis, MO, USA
- Center for Cellular Imaging, Washington University School of Medicine, Saint Louis, MO, USA
- Department of Neuroscience, Washington University School of Medicine, Saint Louis, MO, USA
- Department of Biomedical Engineering, Washington University School of Medicine, Saint Louis, MO, USA
| | - Peng Yuan
- Department of Cell Biology and Physiology, Washington University School of Medicine, Saint Louis, MO, USA
- Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, Saint Louis, MO, USA
| | - Thomas T Joseph
- Department of Anesthesiology and Critical Care, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Jérôme Hénin
- Laboratoire de Biochimie Théorique, Institut de Biologie Physico-Chimique, Université Paris Cité, CNRS UPR 9080, Paris, France
| | - Grace Brannigan
- Center for Computational and Integrative Biology, Rutgers University, Camden, NJ, USA
- Department of Physics, Rutgers University, Camden, NJ, USA
| | - Wayland W L Cheng
- Department of Anesthesiology, Washington University School of Medicine, Saint Louis, MO, USA.
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Gallagher CI, Ha DA, Harvey RJ, Vandenberg RJ. Positive Allosteric Modulators of Glycine Receptors and Their Potential Use in Pain Therapies. Pharmacol Rev 2022; 74:933-961. [PMID: 36779343 PMCID: PMC9553105 DOI: 10.1124/pharmrev.122.000583] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2022] [Revised: 04/26/2022] [Accepted: 05/13/2022] [Indexed: 11/22/2022] Open
Abstract
Glycine receptors are ligand-gated ion channels that mediate synaptic inhibition throughout the mammalian spinal cord, brainstem, and higher brain regions. They have recently emerged as promising targets for novel pain therapies due to their ability to produce antinociception by inhibiting nociceptive signals within the dorsal horn of the spinal cord. This has greatly enhanced the interest in developing positive allosteric modulators of glycine receptors. Several pharmaceutical companies and research facilities have attempted to identify new therapeutic leads by conducting large-scale screens of compound libraries, screening new derivatives from natural sources, or synthesizing novel compounds that mimic endogenous compounds with antinociceptive activity. Advances in structural techniques have also led to the publication of multiple high-resolution structures of the receptor, highlighting novel allosteric binding sites and providing additional information for previously identified binding sites. This has greatly enhanced our understanding of the functional properties of glycine receptors and expanded the structure activity relationships of novel pharmacophores. Despite this, glycine receptors are yet to be used as drug targets due to the difficulties in obtaining potent, selective modulators with favorable pharmacokinetic profiles that are devoid of side effects. This review presents a summary of the structural basis for how current compounds cause positive allosteric modulation of glycine receptors and discusses their therapeutic potential as analgesics. SIGNIFICANCE STATEMENT: Chronic pain is a major cause of disability, and in Western societies, this will only increase as the population ages. Despite the high level of prevalence and enormous socioeconomic burden incurred, treatment of chronic pain remains limited as it is often refractory to current analgesics, such as opioids. The National Institute for Drug Abuse has set finding effective, safe, nonaddictive strategies to manage chronic pain as their top priority. Positive allosteric modulators of glycine receptors may provide a therapeutic option.
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Affiliation(s)
- Casey I Gallagher
- Molecular Biomedicine, School of Medical Sciences, University of Sydney, Sydney, Australia (C.I.G., D.A.H., R.J.V.) and Biomedical Science, School of Health and Behavioural Sciences and Sunshine Coast Health Institute, University of the Sunshine Coast, Maroochydore, Australia (R.J.H.)
| | - Damien A Ha
- Molecular Biomedicine, School of Medical Sciences, University of Sydney, Sydney, Australia (C.I.G., D.A.H., R.J.V.) and Biomedical Science, School of Health and Behavioural Sciences and Sunshine Coast Health Institute, University of the Sunshine Coast, Maroochydore, Australia (R.J.H.)
| | - Robert J Harvey
- Molecular Biomedicine, School of Medical Sciences, University of Sydney, Sydney, Australia (C.I.G., D.A.H., R.J.V.) and Biomedical Science, School of Health and Behavioural Sciences and Sunshine Coast Health Institute, University of the Sunshine Coast, Maroochydore, Australia (R.J.H.)
| | - Robert J Vandenberg
- Molecular Biomedicine, School of Medical Sciences, University of Sydney, Sydney, Australia (C.I.G., D.A.H., R.J.V.) and Biomedical Science, School of Health and Behavioural Sciences and Sunshine Coast Health Institute, University of the Sunshine Coast, Maroochydore, Australia (R.J.H.)
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5
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Recent Insight into Lipid Binding and Lipid Modulation of Pentameric Ligand-Gated Ion Channels. Biomolecules 2022; 12:biom12060814. [PMID: 35740939 PMCID: PMC9221113 DOI: 10.3390/biom12060814] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2022] [Revised: 06/03/2022] [Accepted: 06/08/2022] [Indexed: 02/04/2023] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs) play a leading role in synaptic communication, are implicated in a variety of neurological processes, and are important targets for the treatment of neurological and neuromuscular disorders. Endogenous lipids and lipophilic compounds are potent modulators of pLGIC function and may help shape synaptic communication. Increasing structural and biophysical data reveal sites for lipid binding to pLGICs. Here, we update our evolving understanding of pLGIC–lipid interactions highlighting newly identified modes of lipid binding along with the mechanistic understanding derived from the new structural data.
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6
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Thompson MJ, Domville JA, Edrington CH, Venes A, Giguère PM, Baenziger JE. Distinct functional roles for the M4 α-helix from each homologous subunit in the hetero-pentameric ligand-gated ion channel nAChR. J Biol Chem 2022; 298:102104. [PMID: 35679899 PMCID: PMC9260303 DOI: 10.1016/j.jbc.2022.102104] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2021] [Revised: 05/30/2022] [Accepted: 06/03/2022] [Indexed: 11/04/2022] Open
Abstract
The outermost lipid-exposed α-helix (M4) in each of the homologous α, β, δ, and γ/ε subunits of the muscle nicotinic acetylcholine receptor (nAChR) has previously been proposed to act as a lipid sensor. However, the mechanism by which this sensor would function is not clear. To explore how the M4 α-helix from each subunit in human adult muscle nAChR influences function, and thus explore its putative role in lipid sensing, we functionally characterized alanine mutations at every residue in αM4, βM4, δM4, and εM4, along with both alanine and deletion mutations in the post-M4 region of each subunit. Although no critical interactions involving residues on M4 or in post-M4 were identified, we found that numerous mutations at the M4–M1/M3 interface altered the agonist-induced response. In addition, homologous mutations in M4 in different subunits were found to have different effects on channel function. The functional effects of multiple mutations either along M4 in one subunit or at homologous positions of M4 in different subunits were also found to be additive. Finally, when characterized in both Xenopus oocytes and human embryonic kidney 293T cells, select αM4 mutations displayed cell-specific phenotypes, possibly because of the different membrane lipid environments. Collectively, our data suggest different functional roles for the M4 α-helix in each heteromeric nAChR subunit and predict that lipid sensing involving M4 occurs primarily through the cumulative interactions at the M4–M1/M3 interface, as opposed to the alteration of specific interactions that are critical to channel function.
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7
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Conformational transitions and ligand-binding to a muscle-type nicotinic acetylcholine receptor. Neuron 2022; 110:1358-1370.e5. [PMID: 35139364 DOI: 10.1016/j.neuron.2022.01.013] [Citation(s) in RCA: 41] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Revised: 11/02/2021] [Accepted: 01/10/2022] [Indexed: 12/15/2022]
Abstract
Fast synaptic communication requires receptors that respond to the presence of neurotransmitter by opening an ion channel across the post-synaptic membrane. The muscle-type nicotinic acetylcholine receptor from the electric fish, Torpedo, is the prototypic ligand-gated ion channel, yet the structural changes underlying channel activation remain undefined. Here we use cryo-EM to solve apo and agonist-bound structures of the Torpedo nicotinic receptor embedded in a lipid nanodisc. Using both a direct biochemical assay to define the conformational landscape and molecular dynamics simulations to assay flux through the pore, we correlate structures with functional states and elucidate the motions that lead to pore activation of a heteromeric nicotinic receptor. We highlight an underappreciated role for the complementary subunit in channel gating, establish the structural basis for the differential agonist affinities of α/δ versus α /γ sites, and explain why nicotine is less potent at muscle nicotinic receptors compared to neuronal ones.
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8
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Sharp L, Brannigan G. Spontaneous lipid binding to the nicotinic acetylcholine receptor in a native membrane. J Chem Phys 2021; 154:185102. [PMID: 34241006 DOI: 10.1063/5.0046333] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The nicotinic acetylcholine receptor (nAChR) and other pentameric ligand-gated ion channels are native to neuronal membranes with an unusual lipid composition. While it is well-established that these receptors can be significantly modulated by lipids, the underlying mechanisms have been primarily studied in model membranes with few lipid species. Here, we use coarse-grained molecular dynamics simulation to probe specific binding of lipids in a complex quasi-neuronal membrane. We ran a total of 50 μs of simulations of a single nAChR in a membrane composed of 36 species of lipids. Competition between multiple lipid species produces a complex distribution. We find that overall, cholesterol selects for concave inter-subunit sites and polyunsaturated fatty acids select for convex M4 sites, while monounsaturated and saturated lipids are unenriched in the nAChR boundary. We propose the "density-threshold affinity" as a metric calculated from continuous density distributions, which reduces to a standard affinity in two-state binding. We find that the density-threshold affinity for M4 weakens with chain rigidity, which suggests that flexible chains may help relax packing defects caused by the conical protein shape. For any site, PE headgroups have the strongest affinity of all phospholipid headgroups, but anionic lipids still yield moderately high affinities for the M4 sites as expected. We observe cooperative effects between anionic headgroups and saturated chains at the M4 site in the inner leaflet. We also analyze affinities for individual anionic headgroups. When combined, these insights may reconcile several apparently contradictory experiments on the role of anionic phospholipids in modulating nAChR.
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Affiliation(s)
- Liam Sharp
- Center for Computational and Integrative Biology, Rutgers University-Camden, Camden, New Jersey 08102, USA
| | - Grace Brannigan
- Center for Computational and Integrative Biology, Rutgers University-Camden, Camden, New Jersey 08102, USA
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9
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Thompson MJ, Baenziger JE. Ion channels as lipid sensors: from structures to mechanisms. Nat Chem Biol 2020; 16:1331-1342. [PMID: 33199909 DOI: 10.1038/s41589-020-00693-3] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2020] [Accepted: 10/08/2020] [Indexed: 12/18/2022]
Abstract
Ion channels play critical roles in cellular function by facilitating the flow of ions across the membrane in response to chemical or mechanical stimuli. Ion channels operate in a lipid bilayer, which can modulate or define their function. Recent technical advancements have led to the solution of numerous ion channel structures solubilized in detergent and/or reconstituted into lipid bilayers, thus providing unprecedented insight into the mechanisms underlying ion channel-lipid interactions. Here, we describe how ion channel structures have evolved to respond to both lipid modulators and lipid activators to control the electrical activities of cells, highlighting diverse mechanisms and common themes.
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Affiliation(s)
- Mackenzie J Thompson
- Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa, Ontario, Canada
| | - John E Baenziger
- Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa, Ontario, Canada.
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10
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Thompson MJ, Baenziger JE. Structural basis for the modulation of pentameric ligand-gated ion channel function by lipids. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1862:183304. [DOI: 10.1016/j.bbamem.2020.183304] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2019] [Revised: 03/20/2020] [Accepted: 04/05/2020] [Indexed: 10/24/2022]
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11
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Identification of N-acyl amino acids that are positive allosteric modulators of glycine receptors. Biochem Pharmacol 2020; 180:114117. [PMID: 32579961 DOI: 10.1016/j.bcp.2020.114117] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Revised: 06/16/2020] [Accepted: 06/18/2020] [Indexed: 01/31/2023]
Abstract
Glycine receptors (GlyRs) mediate inhibitory neurotransmission within the spinal cord and play a crucial role in nociceptive signalling. This makes them primary targets for the development of novel chronic pain therapies. Endogenous lipids have previously been shown to modulate glycine receptors and produce analgesia in pain models, however little is known about what chemical features mediate these effects. In this study, we characterised lipid modulation of GlyRs by screening a library of N-acyl amino acids across all receptor subtypes and determined chemical features crucial for their activity. Acyl-glycine's with a C18 carbon tail were found to produce the greatest potentiation, and require a cis double bond within the central region of the carbon tail (ω6 - ω9) to be active. At 1 µM, C18 ω6,9 glycine potentiated glycine induced currents in α3 and α3β receptors by over 50%, and α1, α2, α1β and α2β receptors by over 100%. C18 ω9 glycine (N-oleoyl glycine) significantly enhance glycine induced peak currents and cause a dose-dependent shift in the glycine concentration response. In the presence of 3 µM C18 ω9 glycine, the EC5o of glycine at the α1 receptor was reduced from 17 µM to 10 µM. This study has identified several acyl-amino acids which are positive allosteric modulators of GlyRs and make promising lead compounds for the development of novel chronic pain therapies.
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12
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Thompson MJ, Domville JA, Baenziger JE. The functional role of the αM4 transmembrane helix in the muscle nicotinic acetylcholine receptor probed through mutagenesis and coevolutionary analyses. J Biol Chem 2020; 295:11056-11067. [PMID: 32527728 DOI: 10.1074/jbc.ra120.013751] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Revised: 06/10/2020] [Indexed: 01/22/2023] Open
Abstract
The activity of the muscle-type Torpedo nicotinic acetylcholine receptor (nAChR) is highly sensitive to lipids, but the underlying mechanisms remain poorly understood. The nAChR transmembrane α-helix, M4, is positioned at the perimeter of each subunit in direct contact with lipids and likely plays a central role in lipid sensing. To gain insight into the mechanisms underlying nAChR lipid sensing, we used homology modeling, coevolutionary analyses, site-directed mutagenesis, and electrophysiology to examine the role of the α-subunit M4 (αM4) in the function of the adult muscle nAChR. Ala substitutions for most αM4 residues, including those in clusters of polar residues at both the N and C termini, and deletion of up to 11 C-terminal residues had little impact on the agonist-induced response. Even Ala substitutions for coevolved pairs of residues at the interface between αM4 and the adjacent helices, αM1 and αM3, had little effect, although some impaired nAChR expression. On the other hand, Ala substitutions for Thr422 and Arg429 caused relatively large losses of function, suggesting functional roles for these specific residues. Ala substitutions for aromatic residues at the αM4-αM1/αM3 interface generally led to gains of function, as previously reported for the prokaryotic homolog, the Erwinia chrysanthemi ligand-gated ion channel (ELIC). The functional effects of individual Ala substitutions in αM4 were found to be additive, although not in a completely independent manner. Our results provide insight into the structural features of αM4 that are important. They also suggest how lipid-dependent changes in αM4 structure ultimately modify nAChR function.
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Affiliation(s)
- Mackenzie J Thompson
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario, Canada
| | - Jaimee A Domville
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario, Canada
| | - John E Baenziger
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario, Canada
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13
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Trombik P, Cieślik-Boczula K. Influence of phenothiazine molecules on the interactions between positively charged poly-l-lysine and negatively charged DPPC/DPPG membranes. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2020; 227:117563. [PMID: 31689607 DOI: 10.1016/j.saa.2019.117563] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2019] [Revised: 09/20/2019] [Accepted: 09/21/2019] [Indexed: 06/10/2023]
Abstract
Phenothiazines are very effective antipsychotic drugs, which also have anticancer and antimicrobial activities. Despite being used in human treatment, the molecular mechanism of the biological actions of these molecules is not yet understood in detail. The role of the interactions between phenothiazines and proteins or lipid membranes has been much discussed. Herein, fourier-transform infrared (FTIR) spectroscopic studies were used to investigate the effect of three phenothiazines: fluphenazine (FPh); chlorpromazine (ChP); and propionylpromazine (PP) on the structures of a positively charged poly-l-lysine (PLL) peptide, a negatively charged dipalmitoylphosphatidylcholine/dipalmitoylphosphatidylglycerol (DPPC/DPPG) membrane, and on the mutual interactions between electrostatically associated PLL molecules and DPPC/DPPG membranes. Phenothiazine-induced alterations in the secondary structure of PLL, the conformational state (trans/gauche) of the hydrocarbon lipid chains, and the hydration of the DPPC/DPPG membrane interface were studied on the basis of amide I' vibrations, antisymmetric and symmetric stretching vibrations of the CH2 groups of the lipid hydrocarbon chains (νsCH2), and stretching vibrations of the lipid C=O groups (νC = O), respectively. It was shown that in the presence of negatively charged DPPC/DPPG membranes, the phenothiazines were able to modify the secondary structure of charged PLL molecules. Additionally, the effect of PLL on the structure of DPPC/DPPG membranes was also altered by the presence of the phenothiazine molecules.
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Affiliation(s)
- Paulina Trombik
- Faculty of Chemistry, University of Wroclaw, F. Joliot-Curie 14, 50-383, Wroclaw, Poland
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14
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Cryo-EM structures of a lipid-sensitive pentameric ligand-gated ion channel embedded in a phosphatidylcholine-only bilayer. Proc Natl Acad Sci U S A 2020; 117:1788-1798. [PMID: 31911476 PMCID: PMC6983364 DOI: 10.1073/pnas.1906823117] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The lipid dependence of the nicotinic acetylcholine receptor from the Torpedo electric organ has long been recognized, and one of the most consistent experimental observations is that, when reconstituted in membranes formed by zwitterionic phospholipids alone, exposure to agonist fails to elicit ion-flux activity. More recently, it has been suggested that the bacterial homolog ELIC (Erwinia chrysanthemi ligand-gated ion channel) has a similar lipid sensitivity. As a first step toward the elucidation of the structural basis of this phenomenon, we solved the structures of ELIC embedded in palmitoyl-oleoyl-phosphatidylcholine- (POPC-) only nanodiscs in both the unliganded (4.1-Å resolution) and agonist-bound (3.3 Å) states using single-particle cryoelectron microscopy. Comparison of the two structural models revealed that the largest differences occur at the level of loop C-at the agonist-binding sites-and the loops at the interface between the extracellular and transmembrane domains (ECD and TMD, respectively). On the other hand, the transmembrane pore is occluded in a remarkably similar manner in both structures. A straightforward interpretation of these findings is that POPC-only membranes frustrate the ECD-TMD coupling in such a way that the "conformational wave" of liganded-receptor gating takes place in the ECD and the interfacial M2-M3 linker but fails to penetrate the membrane and propagate into the TMD. Furthermore, analysis of the structural models and molecular simulations suggested that the higher affinity for agonists characteristic of the open- and desensitized-channel conformations results, at least in part, from the tighter confinement of the ligand to its binding site; this limits the ligand's fluctuations, and thus delays its escape into bulk solvent.
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15
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Tong A, Petroff JT, Hsu FF, Schmidpeter PA, Nimigean CM, Sharp L, Brannigan G, Cheng WW. Direct binding of phosphatidylglycerol at specific sites modulates desensitization of a ligand-gated ion channel. eLife 2019; 8:50766. [PMID: 31724949 PMCID: PMC6855808 DOI: 10.7554/elife.50766] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Accepted: 10/09/2019] [Indexed: 12/31/2022] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs) are essential determinants of synaptic transmission, and are modulated by specific lipids including anionic phospholipids. The exact modulatory effect of anionic phospholipids in pLGICs and the mechanism of this effect are not well understood. Using native mass spectrometry, coarse-grained molecular dynamics simulations and functional assays, we show that the anionic phospholipid, 1-palmitoyl-2-oleoyl phosphatidylglycerol (POPG), preferentially binds to and stabilizes the pLGIC, Erwinia ligand-gated ion channel (ELIC), and decreases ELIC desensitization. Mutations of five arginines located in the interfacial regions of the transmembrane domain (TMD) reduce POPG binding, and a subset of these mutations increase ELIC desensitization. In contrast, a mutation that decreases ELIC desensitization, increases POPG binding. The results support a mechanism by which POPG stabilizes the open state of ELIC relative to the desensitized state by direct binding at specific sites.
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Affiliation(s)
- Ailing Tong
- Department of Anesthesiology, Washington University, Saint Louis, United States
| | - John T Petroff
- Department of Anesthesiology, Washington University, Saint Louis, United States
| | - Fong-Fu Hsu
- Department of Internal Medicine, Mass Spectrometry Resource, Division of Endocrinology, Diabetes, Metabolism, and Lipid Research, Washington University, Saint Louis, United States
| | | | - Crina M Nimigean
- Department of Anesthesiology, Weill Cornell Medical College, New York, United States
| | - Liam Sharp
- Center for Computational and Integrative Biology, Rutgers University, Camden, United States
| | - Grace Brannigan
- Center for Computational and Integrative Biology, Rutgers University, Camden, United States.,Department of Physics, Rutgers University, Camden, United States
| | - Wayland Wl Cheng
- Department of Anesthesiology, Washington University, Saint Louis, United States
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16
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Hénault CM, Govaerts C, Spurny R, Brams M, Estrada-Mondragon A, Lynch J, Bertrand D, Pardon E, Evans GL, Woods K, Elberson BW, Cuello LG, Brannigan G, Nury H, Steyaert J, Baenziger JE, Ulens C. A lipid site shapes the agonist response of a pentameric ligand-gated ion channel. Nat Chem Biol 2019; 15:1156-1164. [PMID: 31591563 DOI: 10.1038/s41589-019-0369-4] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2018] [Accepted: 08/21/2019] [Indexed: 12/11/2022]
Abstract
Phospholipids are key components of cellular membranes and are emerging as important functional regulators of different membrane proteins, including pentameric ligand-gated ion channels (pLGICs). Here, we take advantage of the prokaryote channel ELIC (Erwinia ligand-gated ion channel) as a model to understand the determinants of phospholipid interactions in this family of receptors. A high-resolution structure of ELIC in a lipid-bound state reveals a phospholipid site at the lower half of pore-forming transmembrane helices M1 and M4 and at a nearby site for neurosteroids, cholesterol or general anesthetics. This site is shaped by an M4-helix kink and a Trp-Arg-Pro triad that is highly conserved in eukaryote GABAA/C and glycine receptors. A combined approach reveals that M4 is intrinsically flexible and that M4 deletions or disruptions of the lipid-binding site accelerate desensitization in ELIC, suggesting that lipid interactions shape the agonist response. Our data offer a structural context for understanding lipid modulation in pLGICs.
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Affiliation(s)
- Camille M Hénault
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario, Canada
| | - Cedric Govaerts
- Laboratory for the Structure and Function of Biological Membranes, Center for Structural Biology and Bioinformatics, Université libre de Bruxelles, Brussels, Belgium
| | - Radovan Spurny
- Laboratory of Structural Neurobiology, Department of Cellular and Molecular Medicine, KU Leuven, Leuven, Belgium
| | - Marijke Brams
- Laboratory of Structural Neurobiology, Department of Cellular and Molecular Medicine, KU Leuven, Leuven, Belgium
| | | | - Joseph Lynch
- Queensland Brain Institute, University of Queensland, Brisbane, Queensland, Australia
| | | | - Els Pardon
- Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium.,VIB-VUB Center for Structural Biology, VIB, Brussels, Belgium
| | - Genevieve L Evans
- Laboratory of Structural Neurobiology, Department of Cellular and Molecular Medicine, KU Leuven, Leuven, Belgium
| | - Kristen Woods
- Center for Computational and Integrative Biology, Rutgers University-Camden, Camden, NJ, USA.,Department of Physics, Rutgers University-Camden, Camden, NJ, USA
| | - Benjamin W Elberson
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, TTUHSC, Lubbock, TX, USA
| | - Luis G Cuello
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, TTUHSC, Lubbock, TX, USA
| | - Grace Brannigan
- Center for Computational and Integrative Biology, Rutgers University-Camden, Camden, NJ, USA.,Department of Physics, Rutgers University-Camden, Camden, NJ, USA
| | - Hugues Nury
- University Grenoble Alpes, CNRS, IBS, Grenoble, France
| | - Jan Steyaert
- Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium.,VIB-VUB Center for Structural Biology, VIB, Brussels, Belgium
| | - John E Baenziger
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario, Canada.
| | - Chris Ulens
- Laboratory of Structural Neurobiology, Department of Cellular and Molecular Medicine, KU Leuven, Leuven, Belgium.
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17
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Liu W, Su K. A Review on the Receptor-ligand Molecular Interactions in the Nicotinic Receptor Signaling Systems. Pak J Biol Sci 2019; 21:51-66. [PMID: 30221881 DOI: 10.3923/pjbs.2018.51.66] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Nicotine is regarded as the main active addictive ingredient in tobacco products driving continued tobacco abuse behavior (smoking) to the addiction behavior, whereas nicotinic acetylcholine receptors (nAChR) is the crucial effective apparatus or molecular effector of nicotine and acetylcholine and other similar ligands. Many nAChR subunits have been revealed to bind to either neurotransmitters or exogenous ligands, such as nicotine and acetylcholine, being involved in the nicotinic receptor signal transduction. Therefore, the nicotinic receptor signalling molecules and the receptor-ligand molecular interactions between nAChRs and their ligands are universally regarded as crucial mediators of cellular functions and drug targets in medical treatment and clinical diagnosis. Given numerous endeavours have been made in defining the roles of nAChRs in response to nicotine and other addictive drugs, this review focuses on studies and reports in recent years on the receptor-ligand interactions between nAChR receptors and ligands, including lipid-nAChR and protein-nAChR molecular interactions, relevant signal transduction pathways and their molecular mechanisms in the nicotinic receptor signalling systems. All the references were carefully retrieved from the PubMed database by searching key words "nicotine", "acetylcholine", "nicotinic acetylcholine receptor(s)", "nAChR*", "protein and nAChR", "lipid and nAChR", "smok*" and "tobacco". All the relevant referred papers and reports retrieved were fully reviewed for manual inspection. This effort intend to get a quick insight and understanding of the nicotinic receptor signalling and their molecular interactions mechanisms. Understanding the cellular receptor-ligand interactions and molecular mechanisms between nAChRs and ligands will lead to a better translational and therapeutic operations and outcomes for the prevention and treatment of nicotine addiction and other chronic drug addictions in the brain's reward circuitry.
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18
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Enkavi G, Javanainen M, Kulig W, Róg T, Vattulainen I. Multiscale Simulations of Biological Membranes: The Challenge To Understand Biological Phenomena in a Living Substance. Chem Rev 2019; 119:5607-5774. [PMID: 30859819 PMCID: PMC6727218 DOI: 10.1021/acs.chemrev.8b00538] [Citation(s) in RCA: 175] [Impact Index Per Article: 35.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Indexed: 12/23/2022]
Abstract
Biological membranes are tricky to investigate. They are complex in terms of molecular composition and structure, functional over a wide range of time scales, and characterized by nonequilibrium conditions. Because of all of these features, simulations are a great technique to study biomembrane behavior. A significant part of the functional processes in biological membranes takes place at the molecular level; thus computer simulations are the method of choice to explore how their properties emerge from specific molecular features and how the interplay among the numerous molecules gives rise to function over spatial and time scales larger than the molecular ones. In this review, we focus on this broad theme. We discuss the current state-of-the-art of biomembrane simulations that, until now, have largely focused on a rather narrow picture of the complexity of the membranes. Given this, we also discuss the challenges that we should unravel in the foreseeable future. Numerous features such as the actin-cytoskeleton network, the glycocalyx network, and nonequilibrium transport under ATP-driven conditions have so far received very little attention; however, the potential of simulations to solve them would be exceptionally high. A major milestone for this research would be that one day we could say that computer simulations genuinely research biological membranes, not just lipid bilayers.
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Affiliation(s)
- Giray Enkavi
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
| | - Matti Javanainen
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
- Institute
of Organic Chemistry and Biochemistry of the Czech Academy
of Sciences, Flemingovo naḿesti 542/2, 16610 Prague, Czech Republic
- Computational
Physics Laboratory, Tampere University, P.O. Box 692, FI-33014 Tampere, Finland
| | - Waldemar Kulig
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
| | - Tomasz Róg
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
- Computational
Physics Laboratory, Tampere University, P.O. Box 692, FI-33014 Tampere, Finland
| | - Ilpo Vattulainen
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
- Computational
Physics Laboratory, Tampere University, P.O. Box 692, FI-33014 Tampere, Finland
- MEMPHYS-Center
for Biomembrane Physics
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19
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Ghosh M, Wang LC, Huber RG, Gao Y, Morgan LK, Tulsian NK, Bond PJ, Kenney LJ, Anand GS. Engineering an Osmosensor by Pivotal Histidine Positioning within Disordered Helices. Structure 2019; 27:302-314.e4. [PMID: 30503779 DOI: 10.1016/j.str.2018.10.012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2018] [Revised: 08/18/2018] [Accepted: 10/18/2018] [Indexed: 10/27/2022]
Abstract
Histidine kinases (HKs) funnel diverse environmental stimuli into a single autophosphorylation event at a conserved histidine residue. The HK EnvZ is a global sensor of osmolality and cellular acid pH. In previous studies, we discovered that osmosensing in EnvZ was mediated through osmolyte-induced stabilization of the partially disordered helical backbone spanning the conserved histidine autophosphorylation site (His243). Here, we describe how backbone stabilization leads to changes in the microenvironment of His243, resulting in enhanced autophosphorylation through relief of inhibition and repositioning of critical side chains and imidazole rotamerization. The conserved His-Asp/Glu dyad within the partially structured helix is equally geared to respond to acid pH, an alternative environmental stimulus in bacteria. This high-resolution "double-clamp" switch model proposes that a His-Asp/Glu dyad functions as an integrative node for regulating autophosphorylation in HKs. Because the His-Asp/Glu dyad is highly conserved in HKs, this study provides a universal model for describing HK function.
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Affiliation(s)
- Madhubrata Ghosh
- Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, Nanos, Singapore 138669, Singapore
| | - Loo Chien Wang
- Institute of Molecular and Cell Biology, 61 Biopolis Drive, Proteos, Singapore 138673, Singapore
| | - Roland G Huber
- Bioinformatics Institute (A(∗)STAR), 30 Biopolis Street, Matrix, Singapore 138671, Singapore
| | - Yunfeng Gao
- Mechanobiology Institute, 5A Engineering Drive 1, Singapore 117411, Singapore
| | - Leslie K Morgan
- Jesse Brown Veteran Affairs Medical Center, 820 S. Damen Avenue, Chicago, IL 60612, USA; Department of Microbiology and Immunology, University of Illinois-Chicago, 835 S. Wolcott Avenue, Chicago, IL 60612, USA
| | - Nikhil Kumar Tulsian
- Department of Biochemistry, National University of Singapore, 28 Medical Drive, Singapore 117546, Singapore; Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Singapore
| | - Peter J Bond
- Bioinformatics Institute (A(∗)STAR), 30 Biopolis Street, Matrix, Singapore 138671, Singapore; Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Singapore
| | - Linda J Kenney
- Mechanobiology Institute, 5A Engineering Drive 1, Singapore 117411, Singapore; Jesse Brown Veteran Affairs Medical Center, 820 S. Damen Avenue, Chicago, IL 60612, USA; Department of Microbiology and Immunology, University of Illinois-Chicago, 835 S. Wolcott Avenue, Chicago, IL 60612, USA; Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Singapore.
| | - Ganesh S Anand
- Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Singapore.
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20
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An allosteric link connecting the lipid-protein interface to the gating of the nicotinic acetylcholine receptor. Sci Rep 2018; 8:3898. [PMID: 29497086 PMCID: PMC5832824 DOI: 10.1038/s41598-018-22150-x] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2017] [Accepted: 02/16/2018] [Indexed: 11/08/2022] Open
Abstract
The mechanisms underlying lipid-sensing by membrane proteins is of considerable biological importance. A unifying mechanistic question is how a change in structure at the lipid-protein interface is translated through the transmembrane domain to influence structures critical to protein function. Gating of the nicotinic acetylcholine receptor (nAChR) is sensitive to its lipid environment. To understand how changes at the lipid-protein interface influence gating, we examined how a mutation at position 418 on the lipid-facing surface of the outer most M4 transmembrane α-helix alters the energetic couplings between M4 and the remainder of the transmembrane domain. Human muscle nAChR is sensitive to mutations at position 418, with the Cys-to-Trp mutation resulting in a 16-fold potentiation in function that leads to a congenital myasthenic syndrome. Energetic coupling between M4 and the Cys-loop, a key structure implicated in gating, do not change with C418W. Instead, Trp418 and an adjacent residue couple energetically with residues on the M1 transmembrane α-helix, leading to a reorientation of M1 that stabilizes the open state. We thus identify an allosteric link connecting the lipid-protein interface of the nAChR to altered channel function.
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21
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Kuć M, Cieślik-Boczula K, Rospenk M. Anesthetic-dependent changes in the chain-melting phase transition of DPPG liposomes studied using near-infrared spectroscopy supported by PCA. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2017; 186:37-43. [PMID: 28605687 DOI: 10.1016/j.saa.2017.06.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2017] [Revised: 05/18/2017] [Accepted: 06/05/2017] [Indexed: 06/07/2023]
Abstract
The effect of inhalation anesthetics (enflurane, isoflurane, sevoflurane or halothane) on the lipid chain-melting phase transition of negatively charged phospholipid membranes was studied using near-infrared (NIR) spectroscopy supported by Principal Component Analysis (PCA). NIR spectra of anesthetics-mixed dipalmitoylphosphatidylglycerol (DPPG) membranes were recorded in a range of the first overtone of the symmetric and antisymmetric stretching vibrations of CH2 groups of lipid aliphatic chains as a function of increasing temperature. Anesthetic-dependent changes in the trans to gauche conformers ratio of CH2 groups in the hydrocarbon lipid chains were characterized in detail and compared with the zwitterionic lipid membranes, which were built of dipalmitoylphosphatidylcholine (DPPC) molecules.
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Affiliation(s)
- Marta Kuć
- Faculty of Chemistry, University of Wroclaw, Joliot- Curie 14, 50-383 Wroclaw, Poland
| | | | - Maria Rospenk
- Faculty of Chemistry, University of Wroclaw, Joliot- Curie 14, 50-383 Wroclaw, Poland
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22
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Gonzalez-Gutierrez G, Wang Y, Cymes GD, Tajkhorshid E, Grosman C. Chasing the open-state structure of pentameric ligand-gated ion channels. J Gen Physiol 2017; 149:1119-1138. [PMID: 29089419 PMCID: PMC5715906 DOI: 10.1085/jgp.201711803] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2017] [Revised: 09/14/2017] [Accepted: 10/05/2017] [Indexed: 11/25/2022] Open
Abstract
Members of the pentameric ligand-gated ion channel family have been crystallized in different conformations, including one in which the transmembrane pore is surprisingly wide. Gonzalez-Gutierrez et al. show that the open-channel conformation of animal members is more similar to the models with narrow pores. Remarkable advances have been made toward the structural characterization of ion channels in the last two decades. However, the unambiguous assignment of well-defined functional states to the obtained structural models has proved challenging. In the case of the superfamily of nicotinic-receptor channels (also referred to as pentameric ligand-gated ion channels [pLGICs]), for example, two different types of model of the open-channel conformation have been proposed on the basis of structures solved to resolutions better than 4.0 Å. At the level of the transmembrane pore, the open-state models of the proton-gated pLGIC from Gloeobacter violaceus (GLIC) and the invertebrate glutamate-gated Cl– channel (GluCl) are very similar to each other, but that of the glycine receptor (GlyR) is considerably wider. Indeed, the mean distances between the axis of ion permeation and the Cα atoms at the narrowest constriction of the pore (position −2′) differ by ∼2 Å in these two classes of model, a large difference when it comes to understanding the physicochemical bases of ion conduction and charge selectivity. Here, we take advantage of the extreme open-channel stabilizing effect of mutations at pore-facing position 9′. We find that the I9′A mutation slows down entry into desensitization of GLIC to the extent that macroscopic currents decay only slightly by the end of pH 4.5 solution applications to the extracellular side for several minutes. We crystallize (at pH 4.5) two variants of GLIC carrying this mutation and solve their structures to resolutions of 3.12 Å and 3.36 Å. Furthermore, we perform all-atom molecular dynamics simulations of ion permeation and picrotoxinin block, using the different open-channel structural models. On the basis of these results, we favor the notion that the open-channel structure of pLGICs from animals is much closer to that of the narrow models (of GLIC and GluCl) than it is to that of the GlyR.
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Affiliation(s)
| | - Yuhang Wang
- Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL.,Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL
| | - Gisela D Cymes
- Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, IL
| | - Emad Tajkhorshid
- Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL.,Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL.,Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL
| | - Claudio Grosman
- Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, IL .,Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL.,Neuroscience Program, University of Illinois at Urbana-Champaign, Urbana, IL
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23
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Lipid-Mediated Regulation of Embedded Receptor Kinases via Parallel Allosteric Relays. Biophys J 2017; 112:643-654. [PMID: 28256224 DOI: 10.1016/j.bpj.2016.12.027] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Revised: 11/15/2016] [Accepted: 12/12/2016] [Indexed: 01/29/2023] Open
Abstract
Membrane-anchored receptors are essential cellular signaling elements for stimulus sensing, propagation, and transmission inside cells. However, the contributions of lipid interactions to the function and dynamics of embedded receptor kinases have not been described in detail. In this study, we used amide hydrogen/deuterium exchange mass spectrometry, a sensitive biophysical approach, to probe the dynamics of a membrane-embedded receptor kinase, EnvZ, together with functional assays to describe the role of lipids in receptor kinase function. Our results reveal that lipids play an important role in regulating receptor function through interactions with transmembrane segments, as well as through peripheral interactions with nonembedded domains. Specifically, the lipid membrane allosterically modulates the activity of the embedded kinase by altering the dynamics of a glycine-rich motif that is critical for phosphotransfer from ATP. This allostery in EnvZ is independent of membrane composition and involves direct interactions with transmembrane and periplasmic segments, as well as peripheral interactions with nonembedded domains of the protein. In the absence of the membrane-spanning regions, lipid allostery is propagated entirely through peripheral interactions. Whereas lipid allostery impacts the phosphotransferase function of the kinase, extracellular stimulus recognition is mediated via a four-helix bundle subdomain located in the cytoplasm, which functions as the osmosensing core through osmolality-dependent helical stabilization. Our findings emphasize the functional modularity in a membrane-embedded kinase, separated into membrane association, phosphotransferase function, and stimulus recognition. These components are integrated through long-range communication relays, with lipids playing an essential role in regulation.
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24
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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.
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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.
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25
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A combined X-ray scattering and simulation study of halothane in membranes at raised pressures. Chem Phys Lett 2017. [DOI: 10.1016/j.cplett.2016.12.041] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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26
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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]
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27
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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.
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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.
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Hénault CM, Baenziger JE. Functional characterization of two prokaryotic pentameric ligand-gated ion channel chimeras - role of the GLIC transmembrane domain in proton sensing. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1859:218-227. [PMID: 27845033 DOI: 10.1016/j.bbamem.2016.11.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2016] [Revised: 10/21/2016] [Accepted: 11/10/2016] [Indexed: 10/20/2022]
Abstract
With the long-term goal of using a chimeric approach to dissect the distinct lipid sensitivities and thermal stabilities of the pentameric ligand-gated ion channels (pLGIC), GLIC and ELIC, we constructed chimeras by cross-combining their extracellular (ECD) and transmembrane (TMD) domains. As expected, the chimera formed between GLIC-ECD and ELIC-TMD (GE) responded to protons, the agonist for GLIC, but not cysteamine, the agonist for ELIC, although GE exhibited a 25-fold decrease in proton-sensitivity relative to wild type. The chimera formed between ELIC-ECD and the GLIC-TMD (EG) was usually toxic, unless it contained a pore-lining Ile9'Ala gain-of-function mutation. No significant improvements in expression/toxicity were observed with extensive loop substitutions at the ECD/TMD interface. Surprisingly, oocytes expressing EG-I9'A responded to both the ELIC agonist, cysteamine and the GLIC agonist, protons - the latter at pH values ≤4.0. The cysteamine- and proton-induced currents in EG-I9'A were inhibited by the GLIC TMD pore blocker, amantadine. The cysteamine-induced response of EG-I9'A was also inhibited by protons at pH values down to 4.5, but potentiated at lower pH values. Proton-induced gating at low pH was not abolished by mutation of an intramembrane histidine residue previously implicated in GLIC TMD function. We show that the TMD plays a major role governing the thermal stability of a pLGIC, and identify three distinct mechanisms by which agonists and protons influence the gating of the EG chimera. A structural basis for the impaired function of GE is suggested.
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Affiliation(s)
- Camille M Hénault
- Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, 451 Smyth Rd, Ottawa, ON K1H 8M5, Canada
| | - John E Baenziger
- Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, 451 Smyth Rd, Ottawa, ON K1H 8M5, Canada.
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Limon A, Estrada-Mondragón A, Ruiz JMR, Miledi R. Dipicrylamine Modulates GABAρ1 Receptors through Interactions with Residues in the TM4 and Cys-Loop Domains. Mol Pharmacol 2016; 89:446-56. [PMID: 26869399 DOI: 10.1124/mol.116.103432] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2016] [Accepted: 02/09/2016] [Indexed: 02/02/2023] Open
Abstract
Dipicrylamine (DPA) is a commonly used acceptor agent in Förster resonance energy transfer experiments that allows the study of high-frequency neuronal activity in the optical monitoring of voltage in living cells. However, DPA potently antagonizes GABAA receptors that contain α1 and β2 subunits by a mechanism which is not clearly understood. In this work, we aimed to determine whether DPA modulation is a general phenomenon of Cys-loop ligand-gated ion channels (LGICs), and whether this modulation depends on particular amino acid residues. For this, we studied the effects of DPA on human homomeric GABAρ1, α7 nicotinic, and 5-HT3A serotonin receptors expressed in Xenopus oocytes. Our results indicate that DPA is an allosteric modulator of GABAρ1 receptors with an IC50 of 1.6 µM, an enhancer of α7 nicotinic receptors at relatively high concentrations of DPA, and has little, if any, effect on 5-HT3A receptors. DPA antagonism of GABAρ1 was strongly enhanced by preincubation, was slightly voltage-dependent, and its washout was accelerated by bovine serum albumin. These results indicate that DPA modulation is not a general phenomenon of LGICs, and structural differences between receptors may account for disparities in DPA effects. In silico modeling of DPA docking to GABAρ1, α7 nicotinic, and 5-HT3A receptors suggests that a hydrophobic pocket within the Cys-loop and the M4 segment in GABAρ1, located at the extracellular/membrane interface, facilitates the interaction with DPA that leads to inhibition of the receptor. Functional examinations of mutant receptors support the involvement of the M4 segment in the allosteric modulation of GABAρ1 by DPA.
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Affiliation(s)
- Agenor Limon
- Neurobiology and Behavior, University of California, Irvine, California (A.L., J.M.R.R., R.M.); Psychiatry and Human Behavior, University of California, Irvine, California (A.L.); and The Queensland Brain Institute, St. Lucia, Queensland, Australia (A.E.-M.)
| | - Argel Estrada-Mondragón
- Neurobiology and Behavior, University of California, Irvine, California (A.L., J.M.R.R., R.M.); Psychiatry and Human Behavior, University of California, Irvine, California (A.L.); and The Queensland Brain Institute, St. Lucia, Queensland, Australia (A.E.-M.)
| | - Jorge M Reyes Ruiz
- Neurobiology and Behavior, University of California, Irvine, California (A.L., J.M.R.R., R.M.); Psychiatry and Human Behavior, University of California, Irvine, California (A.L.); and The Queensland Brain Institute, St. Lucia, Queensland, Australia (A.E.-M.)
| | - Ricardo Miledi
- Neurobiology and Behavior, University of California, Irvine, California (A.L., J.M.R.R., R.M.); Psychiatry and Human Behavior, University of California, Irvine, California (A.L.); and The Queensland Brain Institute, St. Lucia, Queensland, Australia (A.E.-M.)
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30
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Carswell CL, Hénault CM, Murlidaran S, Therien JPD, Juranka PF, Surujballi JA, Brannigan G, Baenziger JE. Role of the Fourth Transmembrane α Helix in the Allosteric Modulation of Pentameric Ligand-Gated Ion Channels. Structure 2015; 23:1655-1664. [PMID: 26235032 PMCID: PMC4824752 DOI: 10.1016/j.str.2015.06.020] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2014] [Revised: 06/01/2015] [Accepted: 06/27/2015] [Indexed: 01/22/2023]
Abstract
The gating of pentameric ligand-gated ion channels is sensitive to a variety of allosteric modulators that act on structures peripheral to those involved in the allosteric pathway leading from the agonist site to the channel gate. One such structure, the lipid-exposed transmembrane α helix, M4, is the target of lipids, neurosteroids, and disease-causing mutations. Here we show that M4 interactions with the adjacent transmembrane α helices, M1 and M3, modulate pLGIC function. Enhanced M4 interactions promote channel function while ineffective interactions reduce channel function. The interface chemistry governs the intrinsic strength of M4-M1/M3 inter-helical interactions, both influencing channel gating and imparting distinct susceptibilities to the potentiating effects of a lipid-facing M4 congenital myasthenic syndrome mutation. Through aromatic substitutions, functional studies, and molecular dynamics simulations, we elucidate a mechanism by which M4 modulates channel function.
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Affiliation(s)
- Casey L Carswell
- Department of Biochemistry, Microbiology, and Immunology, 451 Smyth Road, Ottawa, ON K1H 8M5, Canada
| | - Camille M Hénault
- Department of Biochemistry, Microbiology, and Immunology, 451 Smyth Road, Ottawa, ON K1H 8M5, Canada
| | - Sruthi Murlidaran
- Center for Computational and Integrative Biology, Rutgers University-Camden, Camden, NJ 08102, USA
| | - J P Daniel Therien
- Department of Biochemistry, Microbiology, and Immunology, 451 Smyth Road, Ottawa, ON K1H 8M5, Canada
| | - Peter F Juranka
- Department of Biochemistry, Microbiology, and Immunology, 451 Smyth Road, Ottawa, ON K1H 8M5, Canada
| | - Julian A Surujballi
- Department of Biochemistry, Microbiology, and Immunology, 451 Smyth Road, Ottawa, ON K1H 8M5, Canada
| | - Grace Brannigan
- Center for Computational and Integrative Biology, Rutgers University-Camden, Camden, NJ 08102, USA; Department of Physics, Rutgers University-Camden, Camden, NJ 08103, USA
| | - John E Baenziger
- Department of Biochemistry, Microbiology, and Immunology, 451 Smyth Road, Ottawa, ON K1H 8M5, Canada.
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31
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Hénault CM, Juranka PF, Baenziger JE. The M4 Transmembrane α-Helix Contributes Differently to Both the Maturation and Function of Two Prokaryotic Pentameric Ligand-gated Ion Channels. J Biol Chem 2015; 290:25118-28. [PMID: 26318456 DOI: 10.1074/jbc.m115.676833] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2015] [Indexed: 01/22/2023] Open
Abstract
The role of the outermost transmembrane α-helix in both the maturation and function of the prokaryotic pentameric ligand-gated ion channels, GLIC and ELIC, was examined by Ala scanning mutagenesis, deletion mutations, and mutant cycle analyses. Ala mutations at the M4-M1/M3 interface lead to loss-of-function phenotypes in GLIC, with the largest negative effects occurring near the M4 C terminus. In particular, two aromatic residues at the M4 C terminus form a network of π-π and/or cation-π interactions with residues on M3 and the β6-β7 loop that is essential for both maturation and function. M4-M1/M3 interactions appear to be optimized in GLIC with even subtle structural changes at this interface leading to detrimental effects. In contrast, mutations along the M4-M1/M3 interface of ELIC typically lead to gain-of-function phenotypes, suggesting that these interactions in ELIC are not optimized for channel function. In addition, no cluster of interacting residues involving the M4 C terminus, M3, and the β6-β7 loop was found, suggesting that the M4 C terminus plays little role in ELIC maturation or function. This study shows that M4 makes distinct contributions to the maturation and gating of these two closely related homologs, suggesting that GLIC and ELIC exhibit divergent features of channel function.
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Affiliation(s)
- Camille M Hénault
- From the Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
| | - Peter F Juranka
- From the Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
| | - John E Baenziger
- From the Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
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32
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Barrantes FJ. Phylogenetic conservation of protein-lipid motifs in pentameric ligand-gated ion channels. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1848:1796-805. [PMID: 25839355 DOI: 10.1016/j.bbamem.2015.03.028] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2015] [Revised: 03/20/2015] [Accepted: 03/25/2015] [Indexed: 12/13/2022]
Abstract
Using the crosstalk between the nicotinic acetylcholine receptor (nAChR) and its lipid microenvironment as a paradigm, this short overview analyzes the occurrence of structural motifs which appear not only to be conserved within the nAChR family and contemporary eukaryotic members of the pentameric ligand-gated ion channel (pLGIC) superfamily, but also extend to prokaryotic homologues found in bacteria. The evolutionarily conserved design is manifested in: 1) the concentric three-ring architecture of the transmembrane region, 2) the occurrence in this region of distinct lipid consensus motifs in prokaryotic and eukaryotic pLGIC and 3) the key participation of the outer TM4 ring in conveying the influence of the lipid membrane environment to the middle TM1-TM3 ring and this, in turn, to the inner TM2 channel-lining ring, which determines the ion selectivity of the channel. The preservation of these constant structural-functional features throughout such a long phylogenetic span likely points to the successful gain-of-function conferred by their early acquisition. This article is part of a Special Issue entitled: Lipid-protein interactions.
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Affiliation(s)
- Francisco J Barrantes
- Laboratory of Molecular Neurobiology, Institute for Biomedical Research (BIOMED), Faculty of Medical Sciences, UCA-CONICET, Av. Alicia Moreau de Justo 1600, C1107AFF Buenos Aires, Argentina.
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Nicotinic acetylcholine receptor-lipid interactions: Mechanistic insight and biological function. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1848:1806-17. [PMID: 25791350 DOI: 10.1016/j.bbamem.2015.03.010] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2015] [Revised: 02/15/2015] [Accepted: 03/09/2015] [Indexed: 01/14/2023]
Abstract
Membrane lipids are potent modulators of the nicotinic acetylcholine receptor (nAChR) from Torpedo. Lipids influence nAChR function by both conformational selection and kinetic mechanisms, stabilizing varying proportions of activatable versus non-activatable conformations, as well as influencing the transitions between these conformational states. Of note, some membranes stabilize an electrically silent uncoupled conformation that binds agonist but does not undergo agonist-induced conformational transitions. The uncoupled nAChR, however, does transition to activatable conformations in relatively thick lipid bilayers, such as those found in lipid rafts. In this review, we discuss current understanding of lipid-nAChR interactions in the context of increasingly available high resolution structural and functional data. These data highlight different sites of lipid action, including the lipid-exposed M4 transmembrane α-helix. Current evidence suggests that lipids alter nAChR function by modulating interactions between M4 and the adjacent transmembrane α-helices, M1 and M3. These interactions have also been implicated in both the folding and trafficking of nAChRs to the cell surface. We review current mechanistic understanding of lipid-nAChR interactions, and highlight potential biological roles for lipid-nAChR interactions in modulating the synaptic response. This article is part of a Special Issue entitled: Lipid-protein interactions.
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34
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Carswell CL, Sun J, Baenziger JE. Intramembrane aromatic interactions influence the lipid sensitivities of pentameric ligand-gated ion channels. J Biol Chem 2014; 290:2496-507. [PMID: 25519904 DOI: 10.1074/jbc.m114.624395] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Although the Torpedo nicotinic acetylcholine receptor (nAChR) reconstituted into phosphatidylcholine (PC) membranes lacking cholesterol and anionic lipids adopts a conformation where agonist binding is uncoupled from channel gating, the underlying mechanism remains to be defined. Here, we examine the mechanism behind lipid-dependent uncoupling by comparing the propensities of two prokaryotic homologs, Gloebacter and Erwinia ligand-gated ion channel (GLIC and ELIC, respectively), to adopt a similar uncoupled conformation. Membrane-reconstituted GLIC and ELIC both exhibit folded structures in the minimal PC membranes that stabilize an uncoupled nAChR. GLIC, with a large number of aromatic interactions at the interface between the outermost transmembrane α-helix, M4, and the adjacent transmembrane α-helices, M1 and M3, retains the ability to flux cations in this uncoupling PC membrane environment. In contrast, ELIC, with a level of aromatic interactions intermediate between that of the nAChR and GLIC, does not undergo agonist-induced channel gating, although it does not exhibit the expected biophysical characteristics of the uncoupled state. Engineering new aromatic interactions at the M4-M1/M3 interface to promote effective M4 interactions with M1/M3, however, increases the stability of the transmembrane domain to restore channel function. Our data provide direct evidence that M4 interactions with M1/M3 are modulated during lipid sensing. Aromatic residues strengthen M4 interactions with M1/M3 to reduce the sensitivities of pentameric ligand-gated ion channels to their surrounding membrane environment.
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Affiliation(s)
- Casey L Carswell
- From the Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa Ontario, K1H 8M5, Canada
| | - Jiayin Sun
- From the Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa Ontario, K1H 8M5, Canada
| | - John E Baenziger
- From the Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa Ontario, K1H 8M5, Canada
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35
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The role of the M4 lipid-sensor in the folding, trafficking, and allosteric modulation of nicotinic acetylcholine receptors. Neuropharmacology 2014; 96:157-68. [PMID: 25433148 DOI: 10.1016/j.neuropharm.2014.11.011] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2014] [Revised: 10/31/2014] [Accepted: 11/18/2014] [Indexed: 11/24/2022]
Abstract
With the availability of high resolution structural data, increasing attention has focused on the mechanisms by which drugs and endogenous compounds allosterically modulate nicotinic acetylcholine receptor (nAChR) function. Lipids are potent modulators of the nAChR from Torpedo. Membrane lipids influence nAChR function by both conformational selection and kinetic mechanisms, stabilizing varying proportions of pre-existing resting, open, desensitized, and uncoupled conformations, as well as influencing the transitions between these conformational states. Structural and functional data highlight a role for the lipid-exposed M4 transmembrane α-helix of each subunit in lipid sensing, and suggest that lipids influence gating by altering the binding of M4 to the adjacent transmembrane α-helices, M1 and M3. M4 has also been implicated in both the folding and trafficking of nAChRs to the cell surface, as well as in the potentiation of nAChR gating by neurosteroids. Here, we discuss the roles of M4 in the folding, trafficking, and allosteric modulation of nAChRs. We also consider the hypothesis that variable chemistry at the M4-M1/M3 transmembrane α-helical interface in different nAChR subunits governs the capacity for potentiation by activating lipids. This article is part of the Special Issue entitled 'The Nicotinic Acetylcholine Receptor: From Molecular Biology to Cognition'.
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36
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Christopoulos A, Changeux JP, Catterall WA, Fabbro D, Burris TP, Cidlowski JA, Olsen RW, Peters JA, Neubig RR, Pin JP, Sexton PM, Kenakin TP, Ehlert FJ, Spedding M, Langmead CJ. International Union of Basic and Clinical Pharmacology. XC. multisite pharmacology: recommendations for the nomenclature of receptor allosterism and allosteric ligands. Pharmacol Rev 2014; 66:918-47. [PMID: 25026896 PMCID: PMC11060431 DOI: 10.1124/pr.114.008862] [Citation(s) in RCA: 151] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Allosteric interactions play vital roles in metabolic processes and signal transduction and, more recently, have become the focus of numerous pharmacological studies because of the potential for discovering more target-selective chemical probes and therapeutic agents. In addition to classic early studies on enzymes, there are now examples of small molecule allosteric modulators for all superfamilies of receptors encoded by the genome, including ligand- and voltage-gated ion channels, G protein-coupled receptors, nuclear hormone receptors, and receptor tyrosine kinases. As a consequence, a vast array of pharmacologic behaviors has been ascribed to allosteric ligands that can vary in a target-, ligand-, and cell-/tissue-dependent manner. The current article presents an overview of allostery as applied to receptor families and approaches for detecting and validating allosteric interactions and gives recommendations for the nomenclature of allosteric ligands and their properties.
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Affiliation(s)
- Arthur Christopoulos
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (A.C., P.M.S., C.J.L.); Collège de France and CNRS URA 2182, Institut Pasteur, Paris, France (J.-P.C.); Department of Pharmacology, School of Medicine, University of Washington, Seattle, Washington (W.A.C.); PIQUR Therapeutics AG, Basel, Switzerland (D.F.); Department of Pharmacological & Physiological Science, Saint Louis University School of Medicine, St. Louis, Louisiana (T.P.B.); Signal Transduction Laboratory, Molecular Endocrinology Group, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina (J.A.C.); Department of Molecular and Medical Pharmacology, University of California, Los Angeles, California (R.W.O.); Division of Neuroscience, School of Medicine, University of Dundee, Scotland, United Kingdom (J.A.P.); Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (R.R.N.); Institut de Genomique Fonctionelle, CNRS, Montpellier, France (J.-P.P.); Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina (T.P.K.); Department of Pharmacology, University of California, Irvine, California (F.J.E.); and Research Solutions SARL, Paris, France (M.S.)
| | - Jean-Pierre Changeux
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (A.C., P.M.S., C.J.L.); Collège de France and CNRS URA 2182, Institut Pasteur, Paris, France (J.-P.C.); Department of Pharmacology, School of Medicine, University of Washington, Seattle, Washington (W.A.C.); PIQUR Therapeutics AG, Basel, Switzerland (D.F.); Department of Pharmacological & Physiological Science, Saint Louis University School of Medicine, St. Louis, Louisiana (T.P.B.); Signal Transduction Laboratory, Molecular Endocrinology Group, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina (J.A.C.); Department of Molecular and Medical Pharmacology, University of California, Los Angeles, California (R.W.O.); Division of Neuroscience, School of Medicine, University of Dundee, Scotland, United Kingdom (J.A.P.); Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (R.R.N.); Institut de Genomique Fonctionelle, CNRS, Montpellier, France (J.-P.P.); Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina (T.P.K.); Department of Pharmacology, University of California, Irvine, California (F.J.E.); and Research Solutions SARL, Paris, France (M.S.)
| | - William A Catterall
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (A.C., P.M.S., C.J.L.); Collège de France and CNRS URA 2182, Institut Pasteur, Paris, France (J.-P.C.); Department of Pharmacology, School of Medicine, University of Washington, Seattle, Washington (W.A.C.); PIQUR Therapeutics AG, Basel, Switzerland (D.F.); Department of Pharmacological & Physiological Science, Saint Louis University School of Medicine, St. Louis, Louisiana (T.P.B.); Signal Transduction Laboratory, Molecular Endocrinology Group, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina (J.A.C.); Department of Molecular and Medical Pharmacology, University of California, Los Angeles, California (R.W.O.); Division of Neuroscience, School of Medicine, University of Dundee, Scotland, United Kingdom (J.A.P.); Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (R.R.N.); Institut de Genomique Fonctionelle, CNRS, Montpellier, France (J.-P.P.); Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina (T.P.K.); Department of Pharmacology, University of California, Irvine, California (F.J.E.); and Research Solutions SARL, Paris, France (M.S.)
| | - Doriano Fabbro
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (A.C., P.M.S., C.J.L.); Collège de France and CNRS URA 2182, Institut Pasteur, Paris, France (J.-P.C.); Department of Pharmacology, School of Medicine, University of Washington, Seattle, Washington (W.A.C.); PIQUR Therapeutics AG, Basel, Switzerland (D.F.); Department of Pharmacological & Physiological Science, Saint Louis University School of Medicine, St. Louis, Louisiana (T.P.B.); Signal Transduction Laboratory, Molecular Endocrinology Group, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina (J.A.C.); Department of Molecular and Medical Pharmacology, University of California, Los Angeles, California (R.W.O.); Division of Neuroscience, School of Medicine, University of Dundee, Scotland, United Kingdom (J.A.P.); Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (R.R.N.); Institut de Genomique Fonctionelle, CNRS, Montpellier, France (J.-P.P.); Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina (T.P.K.); Department of Pharmacology, University of California, Irvine, California (F.J.E.); and Research Solutions SARL, Paris, France (M.S.)
| | - Thomas P Burris
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (A.C., P.M.S., C.J.L.); Collège de France and CNRS URA 2182, Institut Pasteur, Paris, France (J.-P.C.); Department of Pharmacology, School of Medicine, University of Washington, Seattle, Washington (W.A.C.); PIQUR Therapeutics AG, Basel, Switzerland (D.F.); Department of Pharmacological & Physiological Science, Saint Louis University School of Medicine, St. Louis, Louisiana (T.P.B.); Signal Transduction Laboratory, Molecular Endocrinology Group, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina (J.A.C.); Department of Molecular and Medical Pharmacology, University of California, Los Angeles, California (R.W.O.); Division of Neuroscience, School of Medicine, University of Dundee, Scotland, United Kingdom (J.A.P.); Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (R.R.N.); Institut de Genomique Fonctionelle, CNRS, Montpellier, France (J.-P.P.); Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina (T.P.K.); Department of Pharmacology, University of California, Irvine, California (F.J.E.); and Research Solutions SARL, Paris, France (M.S.)
| | - John A Cidlowski
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (A.C., P.M.S., C.J.L.); Collège de France and CNRS URA 2182, Institut Pasteur, Paris, France (J.-P.C.); Department of Pharmacology, School of Medicine, University of Washington, Seattle, Washington (W.A.C.); PIQUR Therapeutics AG, Basel, Switzerland (D.F.); Department of Pharmacological & Physiological Science, Saint Louis University School of Medicine, St. Louis, Louisiana (T.P.B.); Signal Transduction Laboratory, Molecular Endocrinology Group, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina (J.A.C.); Department of Molecular and Medical Pharmacology, University of California, Los Angeles, California (R.W.O.); Division of Neuroscience, School of Medicine, University of Dundee, Scotland, United Kingdom (J.A.P.); Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (R.R.N.); Institut de Genomique Fonctionelle, CNRS, Montpellier, France (J.-P.P.); Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina (T.P.K.); Department of Pharmacology, University of California, Irvine, California (F.J.E.); and Research Solutions SARL, Paris, France (M.S.)
| | - Richard W Olsen
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (A.C., P.M.S., C.J.L.); Collège de France and CNRS URA 2182, Institut Pasteur, Paris, France (J.-P.C.); Department of Pharmacology, School of Medicine, University of Washington, Seattle, Washington (W.A.C.); PIQUR Therapeutics AG, Basel, Switzerland (D.F.); Department of Pharmacological & Physiological Science, Saint Louis University School of Medicine, St. Louis, Louisiana (T.P.B.); Signal Transduction Laboratory, Molecular Endocrinology Group, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina (J.A.C.); Department of Molecular and Medical Pharmacology, University of California, Los Angeles, California (R.W.O.); Division of Neuroscience, School of Medicine, University of Dundee, Scotland, United Kingdom (J.A.P.); Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (R.R.N.); Institut de Genomique Fonctionelle, CNRS, Montpellier, France (J.-P.P.); Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina (T.P.K.); Department of Pharmacology, University of California, Irvine, California (F.J.E.); and Research Solutions SARL, Paris, France (M.S.)
| | - John A Peters
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (A.C., P.M.S., C.J.L.); Collège de France and CNRS URA 2182, Institut Pasteur, Paris, France (J.-P.C.); Department of Pharmacology, School of Medicine, University of Washington, Seattle, Washington (W.A.C.); PIQUR Therapeutics AG, Basel, Switzerland (D.F.); Department of Pharmacological & Physiological Science, Saint Louis University School of Medicine, St. Louis, Louisiana (T.P.B.); Signal Transduction Laboratory, Molecular Endocrinology Group, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina (J.A.C.); Department of Molecular and Medical Pharmacology, University of California, Los Angeles, California (R.W.O.); Division of Neuroscience, School of Medicine, University of Dundee, Scotland, United Kingdom (J.A.P.); Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (R.R.N.); Institut de Genomique Fonctionelle, CNRS, Montpellier, France (J.-P.P.); Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina (T.P.K.); Department of Pharmacology, University of California, Irvine, California (F.J.E.); and Research Solutions SARL, Paris, France (M.S.)
| | - Richard R Neubig
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (A.C., P.M.S., C.J.L.); Collège de France and CNRS URA 2182, Institut Pasteur, Paris, France (J.-P.C.); Department of Pharmacology, School of Medicine, University of Washington, Seattle, Washington (W.A.C.); PIQUR Therapeutics AG, Basel, Switzerland (D.F.); Department of Pharmacological & Physiological Science, Saint Louis University School of Medicine, St. Louis, Louisiana (T.P.B.); Signal Transduction Laboratory, Molecular Endocrinology Group, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina (J.A.C.); Department of Molecular and Medical Pharmacology, University of California, Los Angeles, California (R.W.O.); Division of Neuroscience, School of Medicine, University of Dundee, Scotland, United Kingdom (J.A.P.); Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (R.R.N.); Institut de Genomique Fonctionelle, CNRS, Montpellier, France (J.-P.P.); Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina (T.P.K.); Department of Pharmacology, University of California, Irvine, California (F.J.E.); and Research Solutions SARL, Paris, France (M.S.)
| | - Jean-Philippe Pin
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (A.C., P.M.S., C.J.L.); Collège de France and CNRS URA 2182, Institut Pasteur, Paris, France (J.-P.C.); Department of Pharmacology, School of Medicine, University of Washington, Seattle, Washington (W.A.C.); PIQUR Therapeutics AG, Basel, Switzerland (D.F.); Department of Pharmacological & Physiological Science, Saint Louis University School of Medicine, St. Louis, Louisiana (T.P.B.); Signal Transduction Laboratory, Molecular Endocrinology Group, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina (J.A.C.); Department of Molecular and Medical Pharmacology, University of California, Los Angeles, California (R.W.O.); Division of Neuroscience, School of Medicine, University of Dundee, Scotland, United Kingdom (J.A.P.); Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (R.R.N.); Institut de Genomique Fonctionelle, CNRS, Montpellier, France (J.-P.P.); Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina (T.P.K.); Department of Pharmacology, University of California, Irvine, California (F.J.E.); and Research Solutions SARL, Paris, France (M.S.)
| | - Patrick M Sexton
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (A.C., P.M.S., C.J.L.); Collège de France and CNRS URA 2182, Institut Pasteur, Paris, France (J.-P.C.); Department of Pharmacology, School of Medicine, University of Washington, Seattle, Washington (W.A.C.); PIQUR Therapeutics AG, Basel, Switzerland (D.F.); Department of Pharmacological & Physiological Science, Saint Louis University School of Medicine, St. Louis, Louisiana (T.P.B.); Signal Transduction Laboratory, Molecular Endocrinology Group, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina (J.A.C.); Department of Molecular and Medical Pharmacology, University of California, Los Angeles, California (R.W.O.); Division of Neuroscience, School of Medicine, University of Dundee, Scotland, United Kingdom (J.A.P.); Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (R.R.N.); Institut de Genomique Fonctionelle, CNRS, Montpellier, France (J.-P.P.); Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina (T.P.K.); Department of Pharmacology, University of California, Irvine, California (F.J.E.); and Research Solutions SARL, Paris, France (M.S.)
| | - Terry P Kenakin
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (A.C., P.M.S., C.J.L.); Collège de France and CNRS URA 2182, Institut Pasteur, Paris, France (J.-P.C.); Department of Pharmacology, School of Medicine, University of Washington, Seattle, Washington (W.A.C.); PIQUR Therapeutics AG, Basel, Switzerland (D.F.); Department of Pharmacological & Physiological Science, Saint Louis University School of Medicine, St. Louis, Louisiana (T.P.B.); Signal Transduction Laboratory, Molecular Endocrinology Group, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina (J.A.C.); Department of Molecular and Medical Pharmacology, University of California, Los Angeles, California (R.W.O.); Division of Neuroscience, School of Medicine, University of Dundee, Scotland, United Kingdom (J.A.P.); Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (R.R.N.); Institut de Genomique Fonctionelle, CNRS, Montpellier, France (J.-P.P.); Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina (T.P.K.); Department of Pharmacology, University of California, Irvine, California (F.J.E.); and Research Solutions SARL, Paris, France (M.S.)
| | - Frederick J Ehlert
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (A.C., P.M.S., C.J.L.); Collège de France and CNRS URA 2182, Institut Pasteur, Paris, France (J.-P.C.); Department of Pharmacology, School of Medicine, University of Washington, Seattle, Washington (W.A.C.); PIQUR Therapeutics AG, Basel, Switzerland (D.F.); Department of Pharmacological & Physiological Science, Saint Louis University School of Medicine, St. Louis, Louisiana (T.P.B.); Signal Transduction Laboratory, Molecular Endocrinology Group, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina (J.A.C.); Department of Molecular and Medical Pharmacology, University of California, Los Angeles, California (R.W.O.); Division of Neuroscience, School of Medicine, University of Dundee, Scotland, United Kingdom (J.A.P.); Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (R.R.N.); Institut de Genomique Fonctionelle, CNRS, Montpellier, France (J.-P.P.); Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina (T.P.K.); Department of Pharmacology, University of California, Irvine, California (F.J.E.); and Research Solutions SARL, Paris, France (M.S.)
| | - Michael Spedding
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (A.C., P.M.S., C.J.L.); Collège de France and CNRS URA 2182, Institut Pasteur, Paris, France (J.-P.C.); Department of Pharmacology, School of Medicine, University of Washington, Seattle, Washington (W.A.C.); PIQUR Therapeutics AG, Basel, Switzerland (D.F.); Department of Pharmacological & Physiological Science, Saint Louis University School of Medicine, St. Louis, Louisiana (T.P.B.); Signal Transduction Laboratory, Molecular Endocrinology Group, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina (J.A.C.); Department of Molecular and Medical Pharmacology, University of California, Los Angeles, California (R.W.O.); Division of Neuroscience, School of Medicine, University of Dundee, Scotland, United Kingdom (J.A.P.); Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (R.R.N.); Institut de Genomique Fonctionelle, CNRS, Montpellier, France (J.-P.P.); Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina (T.P.K.); Department of Pharmacology, University of California, Irvine, California (F.J.E.); and Research Solutions SARL, Paris, France (M.S.)
| | - Christopher J Langmead
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (A.C., P.M.S., C.J.L.); Collège de France and CNRS URA 2182, Institut Pasteur, Paris, France (J.-P.C.); Department of Pharmacology, School of Medicine, University of Washington, Seattle, Washington (W.A.C.); PIQUR Therapeutics AG, Basel, Switzerland (D.F.); Department of Pharmacological & Physiological Science, Saint Louis University School of Medicine, St. Louis, Louisiana (T.P.B.); Signal Transduction Laboratory, Molecular Endocrinology Group, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina (J.A.C.); Department of Molecular and Medical Pharmacology, University of California, Los Angeles, California (R.W.O.); Division of Neuroscience, School of Medicine, University of Dundee, Scotland, United Kingdom (J.A.P.); Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan (R.R.N.); Institut de Genomique Fonctionelle, CNRS, Montpellier, France (J.-P.P.); Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina (T.P.K.); Department of Pharmacology, University of California, Irvine, California (F.J.E.); and Research Solutions SARL, Paris, France (M.S.)
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Zaydman MA, Cui J. PIP2 regulation of KCNQ channels: biophysical and molecular mechanisms for lipid modulation of voltage-dependent gating. Front Physiol 2014; 5:195. [PMID: 24904429 PMCID: PMC4034418 DOI: 10.3389/fphys.2014.00195] [Citation(s) in RCA: 93] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2014] [Accepted: 05/08/2014] [Indexed: 12/28/2022] Open
Abstract
Voltage-gated potassium (Kv) channels contain voltage-sensing (VSD) and pore-gate (PGD) structural domains. During voltage-dependent gating, conformational changes in the two domains are coupled giving rise to voltage-dependent opening of the channel. In addition to membrane voltage, KCNQ (Kv7) channel opening requires the membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP2). Recent studies suggest that PIP2 serves as a cofactor to mediate VSD-PGD coupling in KCNQ1 channels. In this review, we put these findings in the context of the current understanding of voltage-dependent gating, lipid modulation of Kv channel activation, and PIP2-regulation of KCNQ channels. We suggest that lipid-mediated coupling of functional domains is a common mechanism among KCNQ channels that may be applicable to other Kv channels and membrane proteins.
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Affiliation(s)
- Mark A Zaydman
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis St. Louis, MO, USA
| | - Jianmin Cui
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis St. Louis, MO, USA
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daCosta CJB, Baenziger JE. Gating of pentameric ligand-gated ion channels: structural insights and ambiguities. Structure 2014; 21:1271-83. [PMID: 23931140 DOI: 10.1016/j.str.2013.06.019] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Revised: 05/31/2013] [Accepted: 06/26/2013] [Indexed: 01/09/2023]
Abstract
Pentameric ligand-gated ion channels (pLGICs) mediate fast synaptic communication by converting chemical signals into an electrical response. Recently solved agonist-bound and agonist-free structures greatly extend our understanding of these complex molecular machines. A key challenge to a full description of function, however, is the ability to unequivocally relate determined structures to the canonical resting, open, and desensitized states. Here, we review current understanding of pLGIC structure, with a focus on the conformational changes underlying channel gating. We compare available structural information and review the evidence supporting the assignment of each structure to a particular conformational state. We discuss multiple factors that may complicate the interpretation of crystal structures, highlighting the potential influence of lipids and detergents. We contend that further advances in the structural biology of pLGICs will require deeper insight into the nature of pLGIC-lipid interactions.
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Affiliation(s)
- Corrie J B daCosta
- Receptor Biology Laboratory, Departments of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55905, USA
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Dellisanti CD, Ghosh B, Hanson SM, Raspanti JM, Grant VA, Diarra GM, Schuh AM, Satyshur K, Klug CS, Czajkowski C. Site-directed spin labeling reveals pentameric ligand-gated ion channel gating motions. PLoS Biol 2013; 11:e1001714. [PMID: 24260024 PMCID: PMC3833874 DOI: 10.1371/journal.pbio.1001714] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Accepted: 10/08/2013] [Indexed: 11/21/2022] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs) are neurotransmitter-activated receptors that mediate fast synaptic transmission. In pLGICs, binding of agonist to the extracellular domain triggers a structural rearrangement that leads to the opening of an ion-conducting pore in the transmembrane domain and, in the continued presence of neurotransmitter, the channels desensitize (close). The flexible loops in each subunit that connect the extracellular binding domain (loops 2, 7, and 9) to the transmembrane channel domain (M2–M3 loop) are essential for coupling ligand binding to channel gating. Comparing the crystal structures of two bacterial pLGIC homologues, ELIC and the proton-activated GLIC, suggests channel gating is associated with rearrangements in these loops, but whether these motions accurately predict the motions in functional lipid-embedded pLGICs is unknown. Here, using site-directed spin labeling (SDSL) electron paramagnetic resonance (EPR) spectroscopy and functional GLIC channels reconstituted into liposomes, we examined if, and how far, the loops at the ECD/TMD gating interface move during proton-dependent gating transitions from the resting to desensitized state. Loop 9 moves ∼9 Å inward toward the channel lumen in response to proton-induced desensitization. Loop 9 motions were not observed when GLIC was in detergent micelles, suggesting detergent solubilization traps the protein in a nonactivatable state and lipids are required for functional gating transitions. Proton-induced desensitization immobilizes loop 2 with little change in position. Proton-induced motion of the M2–M3 loop was not observed, suggesting its conformation is nearly identical in closed and desensitized states. Our experimentally derived distance measurements of spin-labeled GLIC suggest ELIC is not a good model for the functional resting state of GLIC, and that the crystal structure of GLIC does not correspond to a desensitized state. These findings advance our understanding of the molecular mechanisms underlying pLGIC gating. Ligand-gated ion channels reside in the membranes of nerve and muscle cells. These proteins form channels that span the membrane, where they transduce chemical signals into changes in electrical excitability. Neurotransmitters bind to the extracellular surface of these proteins to trigger global structural rearrangements that open the channel, allowing ions to flow across the cell membrane. In the continued presence of neurotransmitters, the channels desensitize and close. Channel opening and closing regulate muscle contraction and signaling in the brain, and defects in these channels lead to a variety of diseases. While crystal structures have provided frozen snapshots of these proteins in presumed closed and open channel states, little is known about how the channels desensitize and move during actual signaling events. Here, we applied a technique to investigate the structure and local dynamics of proteins known as site-directed spin labeling to a prototypical ligand-gated channel, GLIC. We directly quantified ligand-induced motions in regions at the boundary between the binding domain (loops 2 and 9) and the channel domain (M2–M3 loop). We show that a large movement of loop 9 and an immobilization of loop 2, which rearranges the interface between the binding and channel domains, accompanies GLIC channel gating transitions into a desensitized state. These data provide new insights into the protein movements that underlie electrochemical transmission of signals between cells.
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Affiliation(s)
- Cosma D. Dellisanti
- Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Borna Ghosh
- Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Susan M. Hanson
- Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, United States of America
| | - James M. Raspanti
- Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Valerie A. Grant
- Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Gaoussou M. Diarra
- Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Abby M. Schuh
- Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Kenneth Satyshur
- Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Candice S. Klug
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
| | - Cynthia Czajkowski
- Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, United States of America
- * E-mail:
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Nicotinic acetylcholine receptor and the structural basis of neuromuscular transmission: insights from Torpedo postsynaptic membranes. Q Rev Biophys 2013; 46:283-322. [PMID: 24050525 PMCID: PMC3820380 DOI: 10.1017/s0033583513000061] [Citation(s) in RCA: 97] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The nicotinic acetylcholine (ACh) receptor, at the neuromuscular junction, is a neurotransmitter-gated ion channel that has been fine-tuned through evolution to transduce a chemical signal into an electrical signal with maximum efficiency and speed. It is composed from three similar and two identical polypeptide chains, arranged in a ring around a narrow membrane pore. Central to the design of this assembly is a hydrophobic gate in the pore, more than 50 Å away from sites in the extracellular domain where ACh binds. Although the molecular properties of the receptor have been explored intensively over the last few decades, only recently have structures emerged revealing its complex architecture and illuminating how ACh entering the binding sites opens the distant gate. Postsynaptic membranes isolated from the (muscle-derived) electric organ of the Torpedo ray have underpinned most of the structural studies: the membranes form tubular vesicles having receptors arranged on a regular surface lattice, which can be imaged directly in frozen physiological solutions. Advances in electron crystallographic techniques have also been important, enabling analysis of the closed- and open-channel forms of the receptor in unreacted tubes or tubes reacted briefly with ACh. The structural differences between these two forms show that all five subunits participate in a concerted conformational change communicating the effect of ACh binding to the gate, but that three of them (αγ, β and δ) play a dominant role. Flexing of oppositely facing pore-lining α-helices is the principal motion determining the closed/open state of the gate. These results together with the findings of biochemical, biophysical and other structural studies allow an integrated description of the receptor and of its mode of action at the synapse.
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A distinct mechanism for activating uncoupled nicotinic acetylcholine receptors. Nat Chem Biol 2013; 9:701-7. [DOI: 10.1038/nchembio.1338] [Citation(s) in RCA: 82] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2012] [Accepted: 08/06/2013] [Indexed: 01/08/2023]
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Labriola JM, Pandhare A, Jansen M, Blanton MP, Corringer PJ, Baenziger JE. Structural sensitivity of a prokaryotic pentameric ligand-gated ion channel to its membrane environment. J Biol Chem 2013; 288:11294-303. [PMID: 23463505 DOI: 10.1074/jbc.m113.458133] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Although the activity of the nicotinic acetylcholine receptor (nAChR) is exquisitely sensitive to its membrane environment, the underlying mechanisms remain poorly defined. The homologous prokaryotic pentameric ligand-gated ion channel, Gloebacter ligand-gated ion channel (GLIC), represents an excellent model for probing the molecular basis of nAChR sensitivity because of its high structural homology, relative ease of expression, and amenability to crystallographic analysis. We show here that membrane-reconstituted GLIC exhibits structural and biophysical properties similar to those of the membrane-reconstituted nAChR, although GLIC is substantially more thermally stable. GLIC, however, does not possess the same exquisite lipid sensitivity. In particular, GLIC does not exhibit the same propensity to adopt an uncoupled conformation where agonist binding is uncoupled from channel gating. Structural comparisons provide insight into the chemical features that may predispose the nAChR to the formation of an uncoupled state.
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Affiliation(s)
- Jonathan M Labriola
- Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
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Baenziger JE, daCosta CJB. Molecular mechanisms of acetylcholine receptor-lipid interactions: from model membranes to human biology. Biophys Rev 2012; 5:1-9. [PMID: 28510176 DOI: 10.1007/s12551-012-0078-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2012] [Accepted: 04/18/2012] [Indexed: 12/27/2022] Open
Abstract
Lipids are potent modulators of the Torpedo nicotinic acetylcholine receptor. Lipids influence nicotinic receptor function by allosteric mechanisms, stabilizing varying proportions of pre-existing resting, open, desensitized, and uncoupled conformations. Recent structures reveal that lipids could alter function by modulating transmembrane α-helix/α-helix packing, which in turn could alter the conformation of the allosteric interface that links the agonist-binding and transmembrane pore domains-this interface is essential in the coupling of agonist binding to channel gating. We discuss potential mechanisms by which lipids stabilize different conformational states in the context of the hypothesis that lipid-nicotinic receptor interactions modulate receptor function at biological synapses.
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Affiliation(s)
- John E Baenziger
- Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa, ON, K1H 8M5, Canada.
| | - Corrie J B daCosta
- Receptor Biology Laboratory, Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA
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Mutations that stabilize the open state of the Erwinia chrisanthemi ligand-gated ion channel fail to change the conformation of the pore domain in crystals. Proc Natl Acad Sci U S A 2012; 109:6331-6. [PMID: 22474383 DOI: 10.1073/pnas.1119268109] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The determination of structural models of the various stable states of an ion channel is a key step toward the characterization of its conformational dynamics. In the case of nicotinic-type receptors, different structures have been solved but, thus far, these different models have been obtained from different members of the superfamily. In the case of the bacterial member ELIC, a cysteamine-gated channel from Erwinia chrisanthemi, a structural model of the protein in the absence of activating ligand (and thus, conceivably corresponding to the closed state of this channel) has been previously generated. In this article, electrophysiological characterization of ELIC mutants allowed us to identify pore mutations that slow down the time course of desensitization to the extent that the channel seems not to desensitize at all for the duration of the agonist applications (>20 min). Thus, it seems reasonable to conclude that the probability of ELIC occupying the closed state is much lower for the ligand-bound mutants than for the unliganded wild-type channel. To gain insight into the conformation adopted by ELIC under these conditions, we solved the crystal structures of two of these mutants in the presence of a concentration of cysteamine that elicits an intracluster open probability of >0.9. Curiously, the obtained structural models turned out to be nearly indistinguishable from the model of the wild-type channel in the absence of bound agonist. Overall, our findings bring to light the limited power of functional studies in intact membranes when it comes to inferring the functional state of a channel in a crystal, at least in the case of the nicotinic-receptor superfamily.
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Gergalova G, Lykhmus O, Kalashnyk O, Koval L, Chernyshov V, Kryukova E, Tsetlin V, Komisarenko S, Skok M. Mitochondria express α7 nicotinic acetylcholine receptors to regulate Ca2+ accumulation and cytochrome c release: study on isolated mitochondria. PLoS One 2012; 7:e31361. [PMID: 22359587 PMCID: PMC3281078 DOI: 10.1371/journal.pone.0031361] [Citation(s) in RCA: 119] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2011] [Accepted: 01/06/2012] [Indexed: 11/30/2022] Open
Abstract
Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that mediate synaptic transmission in the muscle and autonomic ganglia and regulate transmitter release in the brain. The nAChRs composed of α7 subunits are also expressed in non-excitable cells to regulate cell survival and proliferation. Up to now, functional α7 nAChRs were found exclusively on the cell plasma membrane. Here we show that they are expressed in mitochondria and regulate early pro-apoptotic events like cytochrome c release. The binding of α7-specific antibody with mouse liver mitochondria was revealed by electron microscopy. Outer membranes of mitochondria from the wild-type and β2−/− but not α7−/− mice bound α7 nAChR-specific antibody and toxins: FITC-labeled α-cobratoxin or Alexa 555-labeled α-bungarotoxin. α7 nAChR agonists (1 µM acetylcholine, 10 µM choline or 30 nM PNU-282987) impaired intramitochondrial Ca2+ accumulation and significantly decreased cytochrome c release stimulated with either 90 µM CaCl2 or 0.5 mM H2O2. α7-specific antagonist methyllicaconitine (50 nM) did not affect Ca2+ accumulation in mitochondria but attenuated the effects of agonists on cytochrome c release. Inhibitor of voltage-dependent anion channel (VDAC) 4,4′-diisothio-cyano-2,2′-stilbene disulfonic acid (0.5 µM) decreased cytochrome c release stimulated with apoptogens similarly to α7 nAChR agonists, and VDAC was co-captured with the α7 nAChR from mitochondria outer membrane preparation in both direct and reverse sandwich ELISA. It is concluded that α7 nAChRs are expressed in mitochondria outer membrane to regulate the VDAC-mediated Ca2+ transport and mitochondrial permeability transition.
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Affiliation(s)
- Galyna Gergalova
- Department of Molecular Immunology, Palladin Institute of Biochemistry, Kyiv, Ukraine
| | - Olena Lykhmus
- Department of Molecular Immunology, Palladin Institute of Biochemistry, Kyiv, Ukraine
| | - Olena Kalashnyk
- Department of Molecular Immunology, Palladin Institute of Biochemistry, Kyiv, Ukraine
| | - Lyudmyla Koval
- Department of Molecular Immunology, Palladin Institute of Biochemistry, Kyiv, Ukraine
| | - Volodymyr Chernyshov
- Department of Molecular Immunology, Palladin Institute of Biochemistry, Kyiv, Ukraine
| | - Elena Kryukova
- Department of Molecular Bases of Neurosignaling, Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia
| | - Victor Tsetlin
- Department of Molecular Bases of Neurosignaling, Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia
| | - Sergiy Komisarenko
- Department of Molecular Immunology, Palladin Institute of Biochemistry, Kyiv, Ukraine
| | - Maryna Skok
- Department of Molecular Immunology, Palladin Institute of Biochemistry, Kyiv, Ukraine
- * E-mail:
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X-ray structures of general anaesthetics bound to a pentameric ligand-gated ion channel. Nature 2011; 469:428-31. [PMID: 21248852 DOI: 10.1038/nature09647] [Citation(s) in RCA: 342] [Impact Index Per Article: 26.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2010] [Accepted: 11/01/2010] [Indexed: 11/08/2022]
Abstract
General anaesthetics have enjoyed long and widespread use but their molecular mechanism of action remains poorly understood. There is good evidence that their principal targets are pentameric ligand-gated ion channels (pLGICs) such as inhibitory GABA(A) (γ-aminobutyric acid) receptors and excitatory nicotinic acetylcholine receptors, which are respectively potentiated and inhibited by general anaesthetics. The bacterial homologue from Gloeobacter violaceus (GLIC), whose X-ray structure was recently solved, is also sensitive to clinical concentrations of general anaesthetics. Here we describe the crystal structures of the complexes propofol/GLIC and desflurane/GLIC. These reveal a common general-anaesthetic binding site, which pre-exists in the apo-structure in the upper part of the transmembrane domain of each protomer. Both molecules establish van der Waals interactions with the protein; propofol binds at the entrance of the cavity whereas the smaller, more flexible, desflurane binds deeper inside. Mutations of some amino acids lining the binding site profoundly alter the ionic response of GLIC to protons, and affect its general-anaesthetic pharmacology. Molecular dynamics simulations, performed on the wild type (WT) and two GLIC mutants, highlight differences in mobility of propofol in its binding site and help to explain these effects. These data provide a novel structural framework for the design of general anaesthetics and of allosteric modulators of brain pLGICs.
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Schultz ZD, Levin IW. Vibrational spectroscopy of biomembranes. ANNUAL REVIEW OF ANALYTICAL CHEMISTRY (PALO ALTO, CALIF.) 2011; 4:343-66. [PMID: 21456972 DOI: 10.1146/annurev-anchem-061010-114048] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Vibrational spectroscopy, commonly associated with IR absorption and Raman scattering, has provided a powerful approach for investigating interactions between biomolecules that make up cellular membranes. Because the IR and Raman signals arise from the intrinsic properties of these molecules, vibrational spectroscopy probes the delicate interactions that regulate biomembranes with minimal perturbation. Numerous innovative measurements, including nonlinear optical processes and confined bilayer assemblies, have provided new insights into membrane behavior. In this review, we highlight the use of vibrational spectroscopy to study lipid-lipid interactions. We also examine recent work in which vibrational measurements have been used to investigate the incorporation of peptides and proteins into lipid bilayers, and we discuss the interactions of small molecules and drugs with membrane structures. Emerging techniques and measurements on intact cellular membranes provide a prospective on the future of vibrational spectroscopic studies of biomembranes.
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Affiliation(s)
- Zachary D Schultz
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA.
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Baenziger JE, Corringer PJ. 3D structure and allosteric modulation of the transmembrane domain of pentameric ligand-gated ion channels. Neuropharmacology 2011; 60:116-25. [DOI: 10.1016/j.neuropharm.2010.08.007] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2010] [Revised: 07/26/2010] [Accepted: 08/07/2010] [Indexed: 01/09/2023]
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On the role of anionic lipids in charged protein interactions with membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1808:1673-83. [PMID: 21073855 DOI: 10.1016/j.bbamem.2010.11.009] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2010] [Revised: 11/01/2010] [Accepted: 11/03/2010] [Indexed: 11/22/2022]
Abstract
We investigate the role of anionic lipids in the binding to, and subsequent movement of charged protein groups in lipid membranes, to help understand the role of membrane composition in all membrane-active protein sequences. We demonstrate a small effect of phosphatidylglycerol (PG) lipids on the ability of an arginine (Arg) side chain to bind to, and cross a lipid membrane, despite possessing a neutralizing charge. We observe similar membrane deformations in lipid bilayers composed of phosphatidylcholine (PC) and PC/PG mixtures, with comparable numbers of water and lipid head groups pulled into the bilayer hydrocarbon core, and prohibitively large ~20 kcal/mol barriers for Arg transfer across each bilayer, dropping by just 2-3 kcal/mol due to the binding of PG lipids. We explore the causes of this small effect of introducing PG lipids and offer an explanation in terms of the limited membrane interaction for the choline groups of PC lipids bound to the translocating ion. Our calculations reveal a surprising lack of preference for Arg binding to PG lipids themselves, but a small increase in interfacial binding affinity for lipid bilayers containing PG lipids. These results help to explain the nature of competitive lipid binding to charged protein sequences, with implications for a wide range of membrane binding domains and cell perturbing peptides.
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