1
|
Seljeset S, Sintsova O, Wang Y, Harb HY, Lynagh T. Constitutive activity of ionotropic glutamate receptors via hydrophobic substitutions in the ligand-binding domain. Structure 2024; 32:966-978.e6. [PMID: 38677289 DOI: 10.1016/j.str.2024.04.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2023] [Revised: 02/11/2024] [Accepted: 04/02/2024] [Indexed: 04/29/2024]
Abstract
Neurotransmitter ligands electrically excite neurons by activating ionotropic glutamate receptor (iGluR) ion channels. Knowledge of the iGluR amino acid residues that dominate ligand-induced activation would enable the prediction of function from sequence. We therefore explored the molecular determinants of activity in rat N-methyl-D-aspartate (NMDA)-type iGluRs (NMDA receptors), complex heteromeric iGluRs comprising two glycine-binding GluN1 and two glutamate-binding GluN2 subunits, using amino acid sequence analysis, mutagenesis, and electrophysiology. We find that a broadly conserved aspartate residue controls both ligand potency and channel activity, to the extent that certain substitutions at this position bypass the need for ligand binding in GluN1 subunits, generating NMDA receptors activated solely by glutamate. Furthermore, we identify a homomeric iGluR from the placozoan Trichoplax adhaerens that has utilized native mutations of this crucial residue to evolve into a leak channel that is inhibited by neurotransmitter binding, pointing to a dominant role of this residue throughout the iGluR superfamily.
Collapse
Affiliation(s)
- Sandra Seljeset
- Michael Sars Centre, University of Bergen, 5008 Bergen, Norway
| | - Oksana Sintsova
- Michael Sars Centre, University of Bergen, 5008 Bergen, Norway
| | - Yuhong Wang
- Michael Sars Centre, University of Bergen, 5008 Bergen, Norway
| | - Hassan Y Harb
- Concept Life Sciences Limited, Frith Knoll Road, Chapel-en-le-Frith, SK23 0PG High Peak, UK
| | - Timothy Lynagh
- Michael Sars Centre, University of Bergen, 5008 Bergen, Norway.
| |
Collapse
|
2
|
Germann AL, Pierce SR, Tateiwa H, Sugasawa Y, Reichert DE, Evers AS, Steinbach JH, Akk G. Intrasubunit and Intersubunit Steroid Binding Sites Independently and Additively Mediate α1 β2 γ2L GABA A Receptor Potentiation by the Endogenous Neurosteroid Allopregnanolone. Mol Pharmacol 2021; 100:19-31. [PMID: 33958479 DOI: 10.1124/molpharm.121.000268] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2021] [Accepted: 04/22/2021] [Indexed: 12/18/2022] Open
Abstract
Prior work employing functional analysis, photolabeling, and X-ray crystallography have identified three distinct binding sites for potentiating steroids in the heteromeric GABAA receptor. The sites are located in the membrane-spanning domains of the receptor at the β-α subunit interface (site I) and within the α (site II) and β subunits (site III). Here, we have investigated the effects of mutations to these sites on potentiation of the rat α1β2γ2L GABAA receptor by the endogenous neurosteroid allopregnanolone (3α5αP). The mutations were introduced alone or in combination to probe the additivity of effects. We show that the effects of amino acid substitutions in sites I and II are energetically additive, indicating independence of the actions of the two steroid binding sites. In site III, none of the mutations tested reduced potentiation by 3α5αP, nor did a mutation in site III modify the effects of mutations in sites I or II. We infer that the binding sites for 3α5αP act independently. The independence of steroid action at each site is supported by photolabeling data showing that mutations in either site I or site II selectively change steroid orientation in the mutated site without affecting labeling at the unmutated site. The findings are discussed in the context of linking energetic additivity to empirical changes in receptor function and ligand binding. SIGNIFICANCE STATEMENT: Prior work has identified three distinct binding sites for potentiating steroids in the heteromeric γ-aminobutyric acid type A receptor. This study shows that the sites act independently and additively in the presence of the steroid allopregnanolone and provide estimates of energetic contributions made by steroid binding to each site.
Collapse
Affiliation(s)
- Allison L Germann
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - Spencer R Pierce
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - Hiroki Tateiwa
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - Yusuke Sugasawa
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - David E Reichert
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - Alex S Evers
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - Joe Henry Steinbach
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - Gustav Akk
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| |
Collapse
|
3
|
Miwa JM, Anderson KR, Hoffman KM. Lynx Prototoxins: Roles of Endogenous Mammalian Neurotoxin-Like Proteins in Modulating Nicotinic Acetylcholine Receptor Function to Influence Complex Biological Processes. Front Pharmacol 2019; 10:343. [PMID: 31114495 PMCID: PMC6502960 DOI: 10.3389/fphar.2019.00343] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Accepted: 03/19/2019] [Indexed: 12/19/2022] Open
Abstract
The cholinergic system modulates many biological functions, due to the widespread distribution of cholinergic neuronal terminals, and the diffuse release of its neurotransmitter, acetylcholine. Several layers of regulation help to refine and control the scope of this excitatory neurotransmitter system. One such regulatory mechanism is imparted through endogenous toxin-like proteins, prototoxins, which largely control the function of nicotinic receptors of the cholinergic system. Prototoxins and neurotoxins share the distinct three finger toxin fold, highly effective as a receptor binding protein, and the former are expressed in the mammalian brain, immune system, epithelium, etc. Prototoxins and elapid snake neurotoxins appear to be related through gene duplication and divergence from a common ancestral gene. Protein modulators can provide a graded response of the cholinergic system, and within the brain, stabilize neural circuitry through direct interaction with nicotinic receptors. Understanding the roles of each prototoxin (e.g., lynx1, lynx2/lypd1, PSCA, SLURP1, SLURP2, Lypd6, lypd6b, lypdg6e, PATE-M, PATE-B, etc.), their binding specificity and unique expression profile, has the potential to uncover many fascinating cholinergic-dependent mechanisms in the brain. Each family member can provide a spatially restricted level of control over nAChR function based on its expression in the brain. Due to the difficulty in the pharmacological targeting of nicotinic receptors in the brain as a result of widespread expression patterns and similarities in receptor sequences, unique interfaces between prototoxin and nicotinic receptor could provide more specific targeting than nicotinic receptors alone. As such, this family is intriguing from a long-term therapeutic perspective.
Collapse
Affiliation(s)
- Julie M Miwa
- Department of Biological Sciences, Lehigh University, Bethlehem, PA, United States
| | - Kristin R Anderson
- Department of Biological Sciences, Lehigh University, Bethlehem, PA, United States
| | - Katie M Hoffman
- Department of Biological Sciences, Lehigh University, Bethlehem, PA, United States
| |
Collapse
|
4
|
Identifying coupled clusters of allostery participants through chemical shift perturbations. Proc Natl Acad Sci U S A 2019; 116:2078-2085. [PMID: 30679272 DOI: 10.1073/pnas.1811168116] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Allosteric couplings underlie many cellular signaling processes and provide an exciting avenue for development of new diagnostics and therapeutics. A general method for identifying important residues in allosteric mechanisms would be very useful, but remains elusive due to the complexity of long-range phenomena. Here, we introduce an NMR method to identify residues involved in allosteric coupling between two ligand-binding sites in a protein, which we call chemical shift detection of allostery participants (CAP). Networks of functional groups responding to each ligand are defined through correlated NMR perturbations. In this process, we also identify allostery participants, groups that respond to both binding events and likely play a role in the coupling between the binding sites. Such residues exhibit multiple functional states with distinct NMR chemical shifts, depending on binding status at both binding sites. Such a strategy was applied to the prototypical ion channel KcsA. We had previously shown that the potassium affinity at the extracellular selectivity filter is strongly dependent on proton binding at the intracellular pH sensor. Here, we analyzed proton and potassium binding networks and identified groups that depend on both proton and potassium binding (allostery participants). These groups are viewed as candidates for transmitting information between functional units. The vital role of one such identified amino acid was validated through site-specific mutagenesis, electrophysiology functional studies, and NMR-detected thermodynamic analysis of allosteric coupling. This strategy for identifying allostery participants is likely to have applications for many other systems.
Collapse
|
5
|
Callau-Vázquez D, Pless SA, Lynagh T. Investigation of Agonist Recognition and Channel Properties in a Flatworm Glutamate-Gated Chloride Channel. Biochemistry 2018; 57:1360-1368. [PMID: 29411605 DOI: 10.1021/acs.biochem.7b01245] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Glutamate-gated chloride channels (GluCls) are neurotransmitter receptors that mediate crucial inhibitory signaling in invertebrate neuromuscular systems. Their role in invertebrate physiology and their absence from vertebrates make GluCls a prime target for antiparasitic drugs. GluCls from flatworm parasites are substantially different from and are much less understood than those from roundworm and insect parasites, hindering the development of potential therapeutics targeting GluCls in flatworm-related diseases such as schistosomiasis. Here, we sought to dissect the molecular and chemical basis for ligand recognition in the extracellular glutamate binding site of SmGluCl-2 from Schistosoma mansoni, using site-directed mutagenesis, noncanonical amino acid incorporation, and electrophysiological recordings. Our results indicate that aromatic residues in ligand binding loops A, B, and C are important for SmGluCl-2 function. Loop C, which differs in length compared to other pentameric ligand-gated ion channels (pLGICs), contributes to ligand recognition through both an aromatic residue and two vicinal threonine residues. We also show that, in contrast to other pLGICs, the hydrophobic channel gate in SmGluCl-2 extends from the 9' position to the 6' position in the channel-forming M2 helix. The 6' and 9' positions also seem to control sensitivity to the pore blocker picrotoxin.
Collapse
Affiliation(s)
- Daniel Callau-Vázquez
- Center for Biopharmaceuticals, Department of Drug Design and Pharmacology, University of Copenhagen , Jagtvej 160, 2100 Copenhagen, Denmark
| | - Stephan A Pless
- Center for Biopharmaceuticals, Department of Drug Design and Pharmacology, University of Copenhagen , Jagtvej 160, 2100 Copenhagen, Denmark
| | - Timothy Lynagh
- Center for Biopharmaceuticals, Department of Drug Design and Pharmacology, University of Copenhagen , Jagtvej 160, 2100 Copenhagen, Denmark
| |
Collapse
|
6
|
Mosesso R, Dougherty DA. A triad of residues is functionally transferrable between 5-HT 3 serotonin receptors and nicotinic acetylcholine receptors. J Biol Chem 2018; 293:2903-2914. [PMID: 29298898 DOI: 10.1074/jbc.m117.810432] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Revised: 11/29/2017] [Indexed: 11/06/2022] Open
Abstract
Cys-loop receptors are pentameric ligand-gated ion channels that facilitate communication within the nervous system. Upon neurotransmitter binding, these receptors undergo an allosteric activation mechanism connecting the binding event to the membrane-spanning channel pore, which expands to conduct ions. Some of the earliest steps in this activation mechanism are carried out by residues proximal to the binding site, the relative positioning of which may reflect functional differences among members of the Cys-loop family of receptors. Herein, we investigated key side-chain interactions near the binding site via mutagenesis and two-electrode voltage-clamp electrophysiology in serotonin-gated 5-HT3A receptors (5-HT3ARs) and nicotinic acetylcholine receptors (nAChRs) expressed in Xenopus laevis oocytes. We found that a triad of residues aligning to Thr-152, Glu-209, and Lys-211 in the 5-HT3AR can be exchanged between the homomeric 5-HT3AR and the muscle-type nAChR α-subunit with small functional consequences. Via triple mutant cycle analysis, we demonstrated that this triad forms an interdependent network in the muscle-type nAChR. Furthermore, nAChR-type mutations of the 5-HT3AR affect the affinity of nicotine, a competitive antagonist of 5-HT3ARs, in a cooperative manner. Using mutant cycle analyses between the 5-HT3A triad, loop A residues Asn-101 and Glu-102, β9 residue Lys-197, and the channel gate at Thr-257, we observed that residues in this region are energetically linked to the channel gate and are particularly sensitive to mutations that introduce a net positive charge. This study expands our understanding of the differences and similarities in the activation mechanisms of Cys-loop receptors.
Collapse
Affiliation(s)
- Richard Mosesso
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125
| | - Dennis A Dougherty
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125.
| |
Collapse
|
7
|
Boffi JC, Marcovich I, Gill-Thind JK, Corradi J, Collins T, Lipovsek MM, Moglie M, Plazas PV, Craig PO, Millar NS, Bouzat C, Elgoyhen AB. Differential Contribution of Subunit Interfaces to α9α10 Nicotinic Acetylcholine Receptor Function. Mol Pharmacol 2017; 91:250-262. [PMID: 28069778 PMCID: PMC5325082 DOI: 10.1124/mol.116.107482] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Accepted: 01/04/2017] [Indexed: 12/31/2022] Open
Abstract
Nicotinic acetylcholine receptors can be assembled from either homomeric or heteromeric pentameric subunit combinations. At the interface of the extracellular domains of adjacent subunits lies the acetylcholine binding site, composed of a principal component provided by one subunit and a complementary component of the adjacent subunit. Compared with neuronal nicotinic acetylcholine cholinergic receptors (nAChRs) assembled from α and β subunits, the α9α10 receptor is an atypical member of the family. It is a heteromeric receptor composed only of α subunits. Whereas mammalian α9 subunits can form functional homomeric α9 receptors, α10 subunits do not generate functional channels when expressed heterologously. Hence, it has been proposed that α10 might serve as a structural subunit, much like a β subunit of heteromeric nAChRs, providing only complementary components to the agonist binding site. Here, we have made use of site-directed mutagenesis to examine the contribution of subunit interface domains to α9α10 receptors by a combination of electrophysiological and radioligand binding studies. Characterization of receptors containing Y190T mutations revealed unexpectedly that both α9 and α10 subunits equally contribute to the principal components of the α9α10 nAChR. In addition, we have shown that the introduction of a W55T mutation impairs receptor binding and function in the rat α9 subunit but not in the α10 subunit, indicating that the contribution of α9 and α10 subunits to complementary components of the ligand-binding site is nonequivalent. We conclude that this asymmetry, which is supported by molecular docking studies, results from adaptive amino acid changes acquired only during the evolution of mammalian α10 subunits.
Collapse
Affiliation(s)
- Juan Carlos Boffi
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Irina Marcovich
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - JasKiran K Gill-Thind
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Jeremías Corradi
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Toby Collins
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - María Marcela Lipovsek
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Marcelo Moglie
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Paola V Plazas
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Patricio O Craig
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Neil S Millar
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Cecilia Bouzat
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Ana Belén Elgoyhen
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B).
| |
Collapse
|
8
|
Michałowski MA, Kraszewski S, Mozrzymas JW. Binding site opening by loop C shift and chloride ion-pore interaction in the GABAAreceptor model. Phys Chem Chem Phys 2017; 19:13664-13678. [DOI: 10.1039/c7cp00582b] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Molecular dynamics simulations of the shut α1β2γ2GABAAheteropentamer receptor homology model reveal significant differences between intersubunit interfaces (ligand binding G1, G2 and non-binding) compared to homomeric receptor assemblies and possible ion interaction sites in the top part of the transmembrane domain (TMD).
Collapse
Affiliation(s)
- M. A. Michałowski
- Laboratory of Neuroscience
- Department of Biophysics
- Wrocław Medical University
- ul. Chałubińskiego 3a
- 50-358 Wrocław
| | - S. Kraszewski
- Department of Biomedical Engineering
- Faculty of Fundamental Problems of Technology
- Wroclaw University of Science and Technology
- Wyb. Wyspiańskiego 27
- 50-370 Wrocław
| | - J. W. Mozrzymas
- Laboratory of Neuroscience
- Department of Biophysics
- Wrocław Medical University
- ul. Chałubińskiego 3a
- 50-358 Wrocław
| |
Collapse
|
9
|
Marotta CB, Lester HA, Dougherty DA. An Unaltered Orthosteric Site and a Network of Long-Range Allosteric Interactions for PNU-120596 in α7 Nicotinic Acetylcholine Receptors. ACTA ACUST UNITED AC 2015. [PMID: 26211363 DOI: 10.1016/j.chembiol.2015.06.018] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Nicotinic acetylcholine receptors (nAChRs) are vital to neuronal signaling, are implicated in important processes such as learning and memory, and are therapeutic targets for neural diseases. The α7 nAChR has been implicated in Alzheimer's disease and schizophrenia, and allosteric modulators have become one focus of drug development efforts. We investigate the mode of action of the α7-selective positive allosteric modulator, PNU-120596, and show that the higher potency of acetylcholine in the presence of PNU-120596 is not due to an altered agonist binding site. In addition, we propose several residues in the gating interface and transmembrane region that are functionally important to transduction of allosteric properties, and link PNU-120596, the acetylcholine binding region, and the receptor gate. These results suggest global protein stabilization from a communication network through several key residues that alter the gating equilibrium of the receptor while leaving the agonist binding properties unperturbed.
Collapse
Affiliation(s)
- Christopher B Marotta
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA
| | - Henry A Lester
- Division of Biology and Biological Engineering, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA
| | - Dennis A Dougherty
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA.
| |
Collapse
|
10
|
Post MR, Limapichat W, Lester HA, Dougherty DA. Heterologous expression and nonsense suppression provide insights into agonist behavior at α6β2 nicotinic acetylcholine receptors. Neuropharmacology 2015; 97:376-82. [PMID: 25908401 DOI: 10.1016/j.neuropharm.2015.04.009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2015] [Revised: 03/27/2015] [Accepted: 04/10/2015] [Indexed: 10/23/2022]
Abstract
The α6-containing subtypes of the nicotinic acetylcholine receptor (nAChR) are localized to presynaptic terminals of the dopaminergic pathways of the central nervous system. Selective ligands for these nAChRs are potentially useful in both Parkinson's disease and addiction. For these and other goals, it is important to distinguish the binding behavior of agonists at the α6-β2 binding site versus other subtypes. To study this problem, we apply nonsense suppression-based non-canonical amino acid mutagenesis. We report a combination of four mutations in α6β2 that yield high-level heterologous expression in Xenopus oocytes. By varying mRNA injection ratios, two populations were observed with unique characteristics, likely due to differing stoichiometries. Responses to nine known nAChR agonists were analyzed at the receptor, and their corresponding EC50 values and efficacies are reported. The system is compatible with nonsense suppression, allowing structure-function studies between Trp149 - a conserved residue on loop B found to make a cation-π interaction at several nAChR subtypes - and several agonists. These studies reveal that acetylcholine forms a strong cation-π interaction with the conserved tryptophan, while nicotine and TC299423 do not, suggesting a unique pharmacology for the α6β2 nAChR.
Collapse
Affiliation(s)
- Michael R Post
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E California Blvd., Pasadena, CA 91125, USA
| | - Walrati Limapichat
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E California Blvd., Pasadena, CA 91125, USA
| | - Henry A Lester
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Dennis A Dougherty
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E California Blvd., Pasadena, CA 91125, USA.
| |
Collapse
|
11
|
Short CA, Cao AT, Wingfield MA, Doers ME, Jobe EM, Wang N, Levandoski MM. Subunit interfaces contribute differently to activation and allosteric modulation of neuronal nicotinic acetylcholine receptors. Neuropharmacology 2015; 91:157-68. [PMID: 25486620 PMCID: PMC4332533 DOI: 10.1016/j.neuropharm.2014.11.027] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2014] [Revised: 10/21/2014] [Accepted: 11/26/2014] [Indexed: 01/27/2023]
Abstract
Neuronal nicotinic acetylcholine receptors (nAChRs) are widely distributed in the nervous system and are implicated in many normal and pathological processes. The structural determinants of allostery in nAChRs are not well understood. One class of nAChR allosteric modulators, including the small molecule morantel (Mor), acts from a site that is structurally homologous to the canonical agonist site but exists in the β(+)/α(-) subunit interface. We hypothesized that all nAChR subunits move with respect to each other during channel activation and allosteric modulation. We therefore studied five pairs of residues predicted to span the interfaces of α3β2 receptors, one at the agonist interface and four at the modulator interface. Substituting cysteines in these positions, we used disulfide trapping to perturb receptor function. The pair α3Y168-β2D190, involving the C loop region of the β2 subunit, mediates modulation and agonist activation, because evoked currents were reduced up to 50% following oxidation (H2O2) treatment. The pair α3S125-β2Q39, below the canonical site, is also involved in channel activation, in accord with previous studies of the muscle-type receptor; however, the pair is differentially sensitive to ACh activation and Mor modulation (currents decreased 60% and 80%, respectively). The pairs α3Q37-β2A127 and α3E173-β2R46, both in the non-canonical interface, showed increased currents following oxidation, suggesting that subunit movements are not symmetrical. Together, our results from disulfide trapping and further mutation analysis indicate that subunit interface movement is important for allosteric modulation of nAChRs, but that the two types of interfaces contribute unequally to receptor activation.
Collapse
Affiliation(s)
- Caitlin A Short
- Department of Chemistry and Programs in Biological Chemistry and Neuroscience, Grinnell College, Grinnell, IA 50112, USA
| | - Angela T Cao
- Department of Chemistry and Programs in Biological Chemistry and Neuroscience, Grinnell College, Grinnell, IA 50112, USA
| | - Molly A Wingfield
- Department of Chemistry and Programs in Biological Chemistry and Neuroscience, Grinnell College, Grinnell, IA 50112, USA
| | - Matthew E Doers
- Department of Chemistry and Programs in Biological Chemistry and Neuroscience, Grinnell College, Grinnell, IA 50112, USA
| | - Emily M Jobe
- Department of Chemistry and Programs in Biological Chemistry and Neuroscience, Grinnell College, Grinnell, IA 50112, USA
| | - Nan Wang
- Department of Chemistry and Programs in Biological Chemistry and Neuroscience, Grinnell College, Grinnell, IA 50112, USA
| | - Mark M Levandoski
- Department of Chemistry and Programs in Biological Chemistry and Neuroscience, Grinnell College, Grinnell, IA 50112, USA.
| |
Collapse
|
12
|
Chowdhury S, Haehnel BM, Chanda B. A self-consistent approach for determining pairwise interactions that underlie channel activation. ACTA ACUST UNITED AC 2014; 144:441-55. [PMID: 25311637 PMCID: PMC4210424 DOI: 10.1085/jgp.201411184] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Net free-energy measurements can be combined with mutant cycle analysis to determine interaction energies between specific amino acid pairs during channel activation. Signaling proteins such as ion channels largely exist in two functional forms, corresponding to the active and resting states, connected by multiple intermediates. Multiparametric kinetic models based on sophisticated electrophysiological experiments have been devised to identify molecular interactions of these conformational transitions. However, this approach is arduous and is not suitable for large-scale perturbation analysis of interaction pathways. Recently, we described a model-free method to obtain the net free energy of activation in voltage- and ligand-activated ion channels. Here we extend this approach to estimate pairwise interaction energies of side chains that contribute to gating transitions. Our approach, which we call generalized interaction-energy analysis (GIA), combines median voltage estimates obtained from charge-voltage curves with mutant cycle analysis to ascertain the strengths of pairwise interactions. We show that, for a system with an arbitrary gating scheme, the nonadditive contributions of amino acid pairs to the net free energy of activation can be computed in a self-consistent manner. Numerical analyses of sequential and allosteric models of channel activation also show that this approach can measure energetic nonadditivities even when perturbations affect multiple transitions. To demonstrate the experimental application of this method, we reevaluated the interaction energies of six previously described long-range interactors in the Shaker potassium channel. Our approach offers the ability to generate detailed interaction energy maps in voltage- and ligand-activated ion channels and can be extended to any force-driven system as long as associated “displacement” can be measured.
Collapse
Affiliation(s)
- Sandipan Chowdhury
- Graduate Program in Biophysics and Department of Neuroscience, University of Wisconsin, Madison, WI 53705 Graduate Program in Biophysics and Department of Neuroscience, University of Wisconsin, Madison, WI 53705
| | - Benjamin M Haehnel
- Graduate Program in Biophysics and Department of Neuroscience, University of Wisconsin, Madison, WI 53705 Graduate Program in Biophysics and Department of Neuroscience, University of Wisconsin, Madison, WI 53705
| | - Baron Chanda
- Graduate Program in Biophysics and Department of Neuroscience, University of Wisconsin, Madison, WI 53705 Graduate Program in Biophysics and Department of Neuroscience, University of Wisconsin, Madison, WI 53705
| |
Collapse
|
13
|
LeVine MV, Weinstein H. NbIT--a new information theory-based analysis of allosteric mechanisms reveals residues that underlie function in the leucine transporter LeuT. PLoS Comput Biol 2014; 10:e1003603. [PMID: 24785005 PMCID: PMC4006702 DOI: 10.1371/journal.pcbi.1003603] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2013] [Accepted: 03/24/2014] [Indexed: 11/23/2022] Open
Abstract
Complex networks of interacting residues and microdomains in the structures of biomolecular systems underlie the reliable propagation of information from an input signal, such as the concentration of a ligand, to sites that generate the appropriate output signal, such as enzymatic activity. This information transduction often carries the signal across relatively large distances at the molecular scale in a form of allostery that is essential for the physiological functions performed by biomolecules. While allosteric behaviors have been documented from experiments and computation, the mechanism of this form of allostery proved difficult to identify at the molecular level. Here, we introduce a novel analysis framework, called N-body Information Theory (NbIT) analysis, which is based on information theory and uses measures of configurational entropy in a biomolecular system to identify microdomains and individual residues that act as (i)-channels for long-distance information sharing between functional sites, and (ii)-coordinators that organize dynamics within functional sites. Application of the new method to molecular dynamics (MD) trajectories of the occluded state of the bacterial leucine transporter LeuT identifies a channel of allosteric coupling between the functionally important intracellular gate and the substrate binding sites known to modulate it. NbIT analysis is shown also to differentiate residues involved primarily in stabilizing the functional sites, from those that contribute to allosteric couplings between sites. NbIT analysis of MD data thus reveals rigorous mechanistic elements of allostery underlying the dynamics of biomolecular systems. We developed the new information theory-based analysis framework presented here, NbIT analysis, for the study of allosteric mechanisms in biomolecular systems from Molecular Dynamics trajectories. The illustrative application of NbIT to the analysis of the occluded state in the bacterial transporter LeuT, produced a quantitative representation of the allosteric behavior, and identified intramolecular channels that enable the long-distance information transmission. Our findings, identifying the roles of specific residues in the communication of the allosteric information, were validated by the recognition of residues that have been previously shown to play functional roles in this very well studied system. In addition, we show that application of NbIT analysis leads to the discrimination of functional roles by differentiating between residues that are essential to the dynamics within functional sites (e.g., the substrate binding sites), and residues whose role is to communicate between such functional sites. These results demonstrate that the information theoretical analysis presented here is a powerful tool for quantifying complex allosteric behavior in biomolecular systems and for identifying the crucial components underlying those behaviors.
Collapse
Affiliation(s)
- Michael V. LeVine
- Department of Physiology and Biophysics, Weill Cornell Medical College of Cornell University (WCMC), New York, New York, United States of America
| | - Harel Weinstein
- Department of Physiology and Biophysics, Weill Cornell Medical College of Cornell University (WCMC), New York, New York, United States of America
- HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute of Computational Biomedicine, Weill Cornell Medical College of Cornell University, New York, New York, United States of America
- * E-mail:
| |
Collapse
|
14
|
Campbell AP, MacDougall IJA, Griffith R, Finch AM. An aspartate in the second extracellular loop of the α(1B) adrenoceptor regulates agonist binding. Eur J Pharmacol 2014; 733:90-6. [PMID: 24690260 DOI: 10.1016/j.ejphar.2014.03.034] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2013] [Revised: 03/20/2014] [Accepted: 03/24/2014] [Indexed: 11/30/2022]
Abstract
The extracellular loops of the adrenoceptors present a potential therapeutic target in the design of highly selective adrenergic drugs. These regions are less conserved than the orthosteric binding site but have to date not been implicated in activation of adrenoceptors. A previously generated homology model identified an extracellular residue, D191, as a potential regulator of agonist binding. We have generated mutants of the α1B adrenoceptor replacing the charged aspartate, D191, as well as a potential interaction partner, K331, with uncharged alanines to observe effects on ligand binding and receptor activation. Significant 4-6 fold reductions in affinity for the endogenous agonists, epinephrine and norepinephrine were observed for receptors with the D191A mutation in the second extracellular loop. While changes in EC50 were observed, operational analysis yielded no apparent change in receptor activation. Based on these findings, we suggest that D191, in the second extracellular loop of the α1B adrenoceptor, acts as a 'point of first contact' for the receptor's endogenous agonists. Implication of the non-conserved extracellular regions of the receptor in agonist binding makes it a potential target for the design of highly selective drugs.
Collapse
Affiliation(s)
- Adrian P Campbell
- Department of Pharmacology, School of Medical Sciences, University of New South Wales, Kensington, NSW 2052, Australia
| | - Iain J A MacDougall
- School of Environmental and Life Sciences, The University of Newcastle, Callaghan, NSW 2308, Australia
| | - Renate Griffith
- Department of Pharmacology, School of Medical Sciences, University of New South Wales, Kensington, NSW 2052, Australia
| | - Angela M Finch
- Department of Pharmacology, School of Medical Sciences, University of New South Wales, Kensington, NSW 2052, Australia.
| |
Collapse
|
15
|
Marotta CB, Dilworth CN, Lester HA, Dougherty DA. Probing the non-canonical interface for agonist interaction with an α5 containing nicotinic acetylcholine receptor. Neuropharmacology 2014; 77:342-9. [PMID: 24144909 PMCID: PMC3934363 DOI: 10.1016/j.neuropharm.2013.09.028] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2013] [Revised: 09/25/2013] [Accepted: 09/30/2013] [Indexed: 11/18/2022]
Abstract
Nicotinic acetylcholine receptors (nAChRs) containing the α5 subunit are of interest because genome-wide association studies and candidate gene studies have identified polymorphisms in the α5 gene that are linked to an increased risk for nicotine dependence, lung cancer, and/or alcohol addiction. To probe the functional impact of an α5 subunit on nAChRs, a method to prepare a homogeneous population of α5-containing receptors must be developed. Here we use a gain of function (9') mutation to isolate populations of α5-containing nAChRs for characterization by electrophysiology. We find that the α5 subunit modulates nAChR rectification when co-assembled with α4 and β2 subunits. We also probe the α5-α4 interface for possible ligand-binding interactions. We find that mutations expected to ablate an agonist-binding site involving the α5 subunit have no impact on receptor function. The most straightforward interpretation of this observation is that agonists do not bind at the α5-α4 interface, in contrast to what has recently been demonstrated for the α4-α4 interface in related receptors. In addition, our mutational results suggest that the α5 subunit does not replace the α4 or β2 subunits and is relegated to occupying only the auxiliary position of the pentameric receptor.
Collapse
Affiliation(s)
- Christopher B Marotta
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E California Blvd., Pasadena, CA 91125, USA
| | - Crystal N Dilworth
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E California Blvd., Pasadena, CA 91125, USA
| | - Henry A Lester
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Dennis A Dougherty
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E California Blvd., Pasadena, CA 91125, USA.
| |
Collapse
|
16
|
Lynagh T, Kunz A, Laube B. Propofol modulation of α1 glycine receptors does not require a structural transition at adjacent subunits that is crucial to agonist-induced activation. ACS Chem Neurosci 2013; 4:1469-78. [PMID: 23992940 DOI: 10.1021/cn400134p] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Pentameric glycine receptors (GlyRs) couple agonist binding to activation of an intrinsic ion channel. Substitution of the R271 residue impairs agonist-induced activation and is associated with the human disease hyperekplexia. On the basis of a homology model of the α1 GlyR, we substituted residues in the vicinity of R271 with cysteines, generating R271C, Q226C, and D284C single-mutant GlyRs and R271C/Q226C and R271C/D284C double-mutant GlyRs. We then examined the impact of interactions between these positions on receptor activation by glycine and modulation by the anesthetic propofol, as measured by electrophysiological experiments. Upon expression in Xenopus laevis oocytes, D284C-containing receptors were nonfunctional, despite biochemical evidence of successful cell surface expression. At R271C/Q226C GlyRs, glycine-activated whole-cell currents were increased 3-fold in the presence of the thiol reductant dithiothreitol, whereas the ability of propofol to enhance glycine-activated currents was not affected by dithiothreitol. Biochemical experiments showed that mutant R271C/Q226C subunits form covalently linked pentamers, showing that intersubunit disulfide cross-links are formed. These data indicate that intersubunit disulfide links in the transmembrane domain prevent a structural transition that is crucial to agonist-induced activation of GlyRs but not to modulation by the anesthetic propofol and implicate D284 in the functional integrity of GlyRs.
Collapse
Affiliation(s)
- Timothy Lynagh
- Neurophysiology and Neurosensory Systems, Technische Universität Darmstadt, Schnittspahnstrasse 3, 64287 Darmstadt, Germany
| | - Alexander Kunz
- Neurophysiology and Neurosensory Systems, Technische Universität Darmstadt, Schnittspahnstrasse 3, 64287 Darmstadt, Germany
| | - Bodo Laube
- Neurophysiology and Neurosensory Systems, Technische Universität Darmstadt, Schnittspahnstrasse 3, 64287 Darmstadt, Germany
| |
Collapse
|
17
|
Frazier SJ, Cohen BN, Lester HA. An engineered glutamate-gated chloride (GluCl) channel for sensitive, consistent neuronal silencing by ivermectin. J Biol Chem 2013; 288:21029-21042. [PMID: 23720773 DOI: 10.1074/jbc.m112.423921] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A modified invertebrate glutamate-gated Cl(-) channel (GluCl αβ) was previously employed to allow pharmacologically induced silencing of electrical activity in CNS neurons upon exposure to the anthelmintic drug ivermectin (IVM). Usefulness of the previous receptor was limited by 1) the high concentration of IVM necessary to elicit a consistent silencing phenotype, raising concern about potential side effects, and 2) the variable extent of neuronal spike suppression, due to variations in the co-expression levels of the fluorescent protein-tagged α and β subunits. To address these issues, mutant receptors generated via rational protein engineering strategies were examined for improvement. Introduction of a gain-of-function mutation (L9'F) in the second transmembrane domain of the α subunit appears to facilitate β subunit incorporation and substantially increase heteromeric GluCl αβ sensitivity to IVM. Removal of an arginine-based endoplasmic reticulum retention motif (RSR mutated to AAA) from the intracellular loop of the β subunit further promotes heteromeric expression at the plasma membrane possibly by preventing endoplasmic reticulum-associated degradation of the β subunit rather than simply reducing endoplasmic reticulum retention. A monomeric XFP (mXFP) mutation that prevents fluorescent protein dimerization complements the mutant channel effects. Expression of the newly engineered GluCl opt α-mXFP L9'F + opt β-mXFP Y182F RSR_AAA receptor in dissociated neuronal cultures markedly increases conductance and reduces variability in spike suppression at 1 nm IVM. This receptor, named "GluClv2.0," is an improved tool for IVM-induced silencing.
Collapse
Affiliation(s)
- Shawnalea J Frazier
- From the Biochemistry and Molecular Biophysics Option and; the Division of Biology, California Institute of Technology, Pasadena, California 91125
| | - Bruce N Cohen
- the Division of Biology, California Institute of Technology, Pasadena, California 91125
| | - Henry A Lester
- the Division of Biology, California Institute of Technology, Pasadena, California 91125.
| |
Collapse
|
18
|
Blum AP, Van Arnam EB, German LA, Lester HA, Dougherty DA. Binding interactions with the complementary subunit of nicotinic receptors. J Biol Chem 2013; 288:6991-7. [PMID: 23349463 DOI: 10.1074/jbc.m112.439968] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The agonist-binding site of nicotinic acetylcholine receptors (nAChRs) spans an interface between two subunits of the pentameric receptor. The principal component of this binding site is contributed by an α subunit, and it binds the cationic moiety of the nicotinic pharmacophore. The other part of the pharmacophore, a hydrogen bond acceptor, has recently been shown to bind to the complementary non-α subunit via the backbone NH of a conserved Leu. This interaction was predicted by studies of ACh-binding proteins and confirmed by functional studies of the neuronal (CNS) nAChR, α4β2. The ACh-binding protein structures further suggested that the hydrogen bond to the backbone NH is mediated by a water molecule and that a second hydrogen bonding interaction occurs between the water molecule and the backbone CO of a conserved Asn, also on the non-α subunit. Here, we provide new insights into the nature of the interactions between the hydrogen bond acceptor of nicotinic agonists and the complementary subunit backbone. We studied both the nAChR of the neuromuscular junction (muscle-type) and a neuronal subtype, (α4)2(β4)3. In the muscle-type receptor, both ACh and nicotine showed a strong interaction with the Leu NH, but the potent nicotine analog epibatidine did not. This interaction was much attenuated in the α4β4 receptor. Surprisingly, we found no evidence for a functionally significant interaction with the backbone carbonyl of the relevant Asn in either receptor with an array of agonists.
Collapse
Affiliation(s)
- Angela P Blum
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA
| | | | | | | | | |
Collapse
|
19
|
Chowdhury S, Chanda B. Free-energy relationships in ion channels activated by voltage and ligand. ACTA ACUST UNITED AC 2012; 141:11-28. [PMID: 23250866 PMCID: PMC3536522 DOI: 10.1085/jgp.201210860] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Many ion channels are modulated by multiple stimuli, which allow them to integrate a variety of cellular signals and precisely respond to physiological needs. Understanding how these different signaling pathways interact has been a challenge in part because of the complexity of underlying models. In this study, we analyzed the energetic relationships in polymodal ion channels using linkage principles. We first show that in proteins dually modulated by voltage and ligand, the net free-energy change can be obtained by measuring the charge-voltage (Q-V) relationship in zero ligand condition and the ligand binding curve at highly depolarizing membrane voltages. Next, we show that the voltage-dependent changes in ligand occupancy of the protein can be directly obtained by measuring the Q-V curves at multiple ligand concentrations. When a single reference ligand binding curve is available, this relationship allows us to reconstruct ligand binding curves at different voltages. More significantly, we establish that the shift of the Q-V curve between zero and saturating ligand concentration is a direct estimate of the interaction energy between the ligand- and voltage-dependent pathway. These free-energy relationships were tested by numerical simulations of a detailed gating model of the BK channel. Furthermore, as a proof of principle, we estimate the interaction energy between the ligand binding and voltage-dependent pathways for HCN2 channels whose ligand binding curves at various voltages are available. These emerging principles will be useful for high-throughput mutagenesis studies aimed at identifying interaction pathways between various regulatory domains in a polymodal ion channel.
Collapse
Affiliation(s)
- Sandipan Chowdhury
- Graduate Program in Biophysics, University of Wisconsin, Madison, WI 53706, USA
| | | |
Collapse
|
20
|
Miles TF, Bower KS, Lester HA, Dougherty DA. A coupled array of noncovalent interactions impacts the function of the 5-HT3A serotonin receptor in an agonist-specific way. ACS Chem Neurosci 2012; 3:753-60. [PMID: 23077719 DOI: 10.1021/cn3000586] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Accepted: 07/20/2012] [Indexed: 11/28/2022] Open
Abstract
The serotonin type 3A (5-HT(3)A) receptor is a Cys-loop (pentameric) neurotransmitter-gated ion channel found in the central and peripheral nervous systems and implicated in numerous diseases. In previous studies with the endogenous agonist serotonin, we identified two interactions critical for receptor function: a cation-π interaction with W183 in loop B (TrpB) and a hydrogen bond to E129 in loop A. Here we employ mutant cycle analyses utilizing conventional and unnatural amino acid mutagenesis to demonstrate that a third residue, D124 of loop A, forms two functionally important hydrogen bonds to the backbone of loop B. We also show that these three interactions, the cation-π interaction, the backbone hydrogen bonds, and the E129 hydrogen bond, are tightly coupled to each other, suggesting they function as a single unit. We also identify key functional differences between serotonin and the competitive partial agonist m-chlorophenyl biguanide (mCPBG) at these residues. mCPBG displays no cation-π at TrpB and extreme sensitivity to the positioning of E129, on which it is reliant for initiation of channel gating.
Collapse
Affiliation(s)
- Timothy F. Miles
- Division
of Biology and ‡Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California
91125, United States
| | - Kiowa S. Bower
- Division
of Biology and ‡Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California
91125, United States
| | - Henry A. Lester
- Division
of Biology and ‡Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California
91125, United States
| | - Dennis A. Dougherty
- Division
of Biology and ‡Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California
91125, United States
| |
Collapse
|
21
|
Unwin N, Fujiyoshi Y. Gating movement of acetylcholine receptor caught by plunge-freezing. J Mol Biol 2012; 422:617-634. [PMID: 22841691 PMCID: PMC3443390 DOI: 10.1016/j.jmb.2012.07.010] [Citation(s) in RCA: 144] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2012] [Revised: 06/06/2012] [Accepted: 07/10/2012] [Indexed: 11/19/2022]
Abstract
The nicotinic acetylcholine (ACh) receptor converts transiently to an open-channel form when activated by ACh released into the synaptic cleft. We describe here the conformational change underlying this event, determined by electron microscopy of ACh-sprayed and freeze-trapped postsynaptic membranes. ACh binding to the α subunits triggers a concerted rearrangement in the ligand-binding domain, involving an ~1-Å outward displacement of the extracellular portion of the β subunit where it interacts with the juxtaposed ends of α-helices shaping the narrow membrane-spanning pore. The β-subunit helices tilt outward to accommodate this displacement, destabilising the arrangement of pore-lining helices, which in the closed channel bend inward symmetrically to form a central hydrophobic gate. Straightening and tangential motion of the pore-lining helices effect channel opening by widening the pore asymmetrically and increasing its polarity in the region of the gate. The pore-lining helices of the α(γ) and δ subunits, by flexing between alternative bent and straight conformations, undergo the greatest movements. This coupled allosteric transition shifts the structure from a tense (closed) state toward a more relaxed (open) state.
Collapse
Affiliation(s)
- Nigel Unwin
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, UK.
| | - Yoshinori Fujiyoshi
- Department of Biophysics, Faculty of Science, Kyoto University, Oiwake, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan
| |
Collapse
|
22
|
Shanata JAP, Frazier SJ, Lester HA, Dougherty DA. Using mutant cycle analysis to elucidate long-range functional coupling in allosteric receptors. Methods Mol Biol 2012; 796:97-113. [PMID: 22052487 PMCID: PMC4006985 DOI: 10.1007/978-1-61779-334-9_6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
Functional coupling of residues that are far apart in space is the quintessential property of allosteric receptors. Data from functional studies of allosteric receptors, such as whole-cell dose-response relations, can be used to determine if mutation to a receptor significantly impacts agonist potency. However, the classification of perturbations as primarily impacting binding or allosteric function is more challenging, often requiring detailed kinetic studies. This protocol describes a simple strategy, derived from mutant cycle analysis, for elucidating long-range functional coupling in allosteric receptors (ELFCAR). Introduction of a gain-of-function reporter mutation, followed by a mutant cycle analysis of the readily measured macroscopic EC(50) values can provide insight into the role of many physically distant targets. This new method should find broad application in determining the functional roles of residues in allosteric receptors.
Collapse
Affiliation(s)
- Jai A. P. Shanata
- Divisions of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Blvd., Pasadena, CA 91125
| | - Shawnalea J. Frazier
- Division of Biology, California Institute of Technology, 1200 East California Blvd., Pasadena, CA 91125
| | - Henry A. Lester
- Division of Biology, California Institute of Technology, 1200 East California Blvd., Pasadena, CA 91125
| | - Dennis A. Dougherty
- Divisions of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Blvd., Pasadena, CA 91125
| |
Collapse
|
23
|
Maksay G. Allostery in pharmacology: Thermodynamics, evolution and design. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2011; 106:463-73. [DOI: 10.1016/j.pbiomolbio.2011.01.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/03/2011] [Accepted: 01/03/2011] [Indexed: 12/13/2022]
|
24
|
Martínez-Delgado G, Estrada-Mondragón A, Miledi R, Martínez-Torres A. An Update on GABAρ Receptors. Curr Neuropharmacol 2011; 8:422-33. [PMID: 21629448 PMCID: PMC3080597 DOI: 10.2174/157015910793358141] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2009] [Revised: 04/08/2010] [Accepted: 06/21/2010] [Indexed: 01/29/2023] Open
Abstract
The present review discusses the functional and molecular diversity of GABAρ receptors. These receptors were originally described in the mammalian retina, and their functional role in the visual pathway has been recently elucidated; however new studies on their distribution in the brain and spinal cord have revealed that they are more spread than originally thought, and thus it will be important to determine their physiological contribution to the GABAergic transmission in other areas of the central nervous system. In addition, molecular modeling has revealed peculiar traits of these receptors that have impacted on the interpretations of the latest pharmacolgical and biophysical findings. Finally, sequencing of several vertebrate genomes has permitted a comparative analysis of the organization of the GABAρ genes.
Collapse
Affiliation(s)
- Gustavo Martínez-Delgado
- Instituto de Neurbiología, Departamento de Neurobiología Celular y Molecular, Laboratorio D15, Campus UNAM Juriquilla. Querétaro 76230, México
| | | | | | | |
Collapse
|
25
|
Yu R, Craik DJ, Kaas Q. Blockade of neuronal α7-nAChR by α-conotoxin ImI explained by computational scanning and energy calculations. PLoS Comput Biol 2011; 7:e1002011. [PMID: 21390272 PMCID: PMC3048385 DOI: 10.1371/journal.pcbi.1002011] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2010] [Accepted: 01/05/2011] [Indexed: 01/01/2023] Open
Abstract
α-Conotoxins potently inhibit isoforms of nicotinic acetylcholine receptors (nAChRs), which are essential for neuronal and neuromuscular transmission. They are also used as neurochemical tools to study nAChR physiology and are being evaluated as drug leads to treat various neuronal disorders. A number of experimental studies have been performed to investigate the structure-activity relationships of conotoxin/nAChR complexes. However, the structural determinants of their binding interactions are still ambiguous in the absence of experimental structures of conotoxin-receptor complexes. In this study, the binding modes of α-conotoxin ImI to the α7-nAChR, currently the best-studied system experimentally, were investigated using comparative modeling and molecular dynamics simulations. The structures of more than 30 single point mutants of either the conotoxin or the receptor were modeled and analyzed. The models were used to explain qualitatively the change of affinities measured experimentally, including some nAChR positions located outside the binding site. Mutational energies were calculated using different methods that combine a conformational refinement procedure (minimization with a distance dependent dielectric constant or explicit water, or molecular dynamics using five restraint strategies) and a binding energy function (MM-GB/SA or MM-PB/SA). The protocol using explicit water energy minimization and MM-GB/SA gave the best correlations with experimental binding affinities, with an R2 value of 0.74. The van der Waals and non-polar desolvation components were found to be the main driving force for binding of the conotoxin to the nAChR. The electrostatic component was responsible for the selectivity of the various ImI mutants. Overall, this study provides novel insights into the binding mechanism of α-conotoxins to nAChRs and the methodological developments reported here open avenues for computational scanning studies of a rapidly expanding range of wild-type and chemically modified α-conotoxins. Conotoxins are peptide toxins extracted from the venom of carnivorous marine cone snails. Members of the α-conotoxin subfamily potently block nicotinic acetylcholine receptors (nAChRs), which are involved in signal transmission between two neurons or between neurons and muscle fibers. nAChRs are important pharmacological targets due to their involvement in the transmission of pain stimuli and also in numerous neurone diseases and disorders. Their potency and specificity have led to the development of α-conotoxins as drug leads, and also to their use in the investigation of the role of nAChRs in various physiological processes. The most studied conotoxin/nAChR system, ImI/α7, was modeled in this study, and several computational methods were tested for their ability to explain the perturbations observed experimentally after introducing single point mutations into either ImI or the α7 receptor. The aim of this study was to establish a theoretical basis to rapidly identify new α-conotoxin mutants that might have improved specificity and affinity for a given receptor subtype. Furthermore, hundreds of thousands of conotoxins are predicted to exist, and computational methods are needed to help streamline the discovery of their molecular targets.
Collapse
Affiliation(s)
- Rilei Yu
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia
| | - David J. Craik
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia
| | - Quentin Kaas
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia
- * E-mail:
| |
Collapse
|
26
|
Dellisanti CD, Hanson SM, Chen L, Czajkowski C. Packing of the extracellular domain hydrophobic core has evolved to facilitate pentameric ligand-gated ion channel function. J Biol Chem 2010; 286:3658-70. [PMID: 21098036 DOI: 10.1074/jbc.m110.156851] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Protein function depends on conformational flexibility and folding stability. Loose packing of hydrophobic cores is not infrequent in proteins, as the enhanced flexibility likely contributes to their biological function. Here, using experimental and computational approaches, we show that eukaryotic pentameric ligand-gated ion channels are characterized by loose packing of their extracellular domain β-sandwich cores, and that loose packing contributes to their ability to rapidly switch from closed to open channel states in the presence of ligand. Functional analyses of GABA(A) receptors show that increasing the β-core packing disrupted GABA-mediated currents, with impaired GABA efficacy and slowed GABA current activation and desensitization. We propose that loose packing of the hydrophobic β-core developed as an evolutionary strategy aimed to facilitate the allosteric mechanisms of eukaryotic pentameric ligand-gated ion channels.
Collapse
Affiliation(s)
- Cosma D Dellisanti
- Department of Physiology, University of Wisconsin, Madison, Wisconsin 53711, USA
| | | | | | | |
Collapse
|
27
|
Abstract
An allosteric model is used to describe changes in lifetimes of biological receptor-ligand bonds subjected to an external force. Force-induced transitions between the two states of the allosteric site lead to changes in the receptor conformation. The ligand bound to the receptor fluctuates between two different potentials formed by the two receptor conformations. The effect of the force on the receptor-ligand interaction potential is described by the Bell mechanism. The probability of detecting the ligand in the bound state is found to depend on the relaxation times of both ligand and allosteric sites. An analytic expression for the bond lifetime is derived as a function of force. The formal theoretical results are used to explain the anomalous force and time dependences of the integrin-fibronectin bond lifetimes measured by atomic force microscopy (Kong, F.; et al J. Cell Biol. 2009, 185, 1275-1284). The analytic expression and model parameters describe very well all anomalous dependences identified in the experiments.
Collapse
Affiliation(s)
| | - Oleg V. Prezhdo
- Department of Chemistry, University of Washington, Seattle, WA 98195
| | | |
Collapse
|
28
|
Boyer JA, Clay CJ, Luce KS, Edgell MH, Lee AL. Detection of native-state nonadditivity in double mutant cycles via hydrogen exchange. J Am Chem Soc 2010; 132:8010-9. [PMID: 20481530 DOI: 10.1021/ja1003922] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Proteins have evolved to exploit long-range structural and dynamic effects as a means of regulating function. Understanding communication between sites in proteins is therefore vital to our comprehension of such phenomena as allostery, catalysis, and ligand binding/ejection. Double mutant cycle analysis has long been used to determine the existence of communication between pairs of sites, proximal or distal, in proteins. Typically, nonadditivity (or "thermodynamic coupling") is measured from global transitions in concert with a single probe. Here, we have applied the atomic resolution of NMR in tandem with native-state hydrogen exchange (HX) to probe the structure/energy landscape for information transduction between a large number of distal sites in a protein. Considering the event of amide proton exchange as an energetically quantifiable structural perturbation, m n-dimensional cycles can be constructed from mutation of n-1 residues, where m is the number of residues for which HX data is available. Thus, efficient mapping of a large number of couplings is made possible. We have applied this technique to one additive and two nonadditive double mutant cycles in a model system, eglin c. We find heterogeneity of HX-monitored couplings for each cycle, yet averaging results in strong agreement with traditionally measured values. Furthermore, long-range couplings observed at locally exchanging residues indicate that the basis for communication can occur within the native state ensemble, a conclusion not apparent from traditional measurements. We propose that higher-order couplings can be obtained and show that such couplings provide a mechanistic basis for understanding lower-order couplings via "spheres of perturbation". The method is presented as an additional tool for identifying a large number of couplings with greater coverage of the protein of interest.
Collapse
Affiliation(s)
- Joshua A Boyer
- Department of Biochemistry and Biophysics, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599, USA
| | | | | | | | | |
Collapse
|
29
|
Lynagh T, Lynch JW. An improved ivermectin-activated chloride channel receptor for inhibiting electrical activity in defined neuronal populations. J Biol Chem 2010; 285:14890-14897. [PMID: 20308070 PMCID: PMC2865309 DOI: 10.1074/jbc.m110.107789] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2010] [Revised: 03/02/2010] [Indexed: 11/06/2022] Open
Abstract
The ability to silence the electrical activity of defined neuronal populations in vivo is dramatically advancing our understanding of brain function. This technology may eventually be useful clinically for treating a variety of neuropathological disorders caused by excessive neuronal activity. Several neuronal silencing methods have been developed, with the bacterial light-activated halorhodopsin and the invertebrate allatostatin-activated G protein-coupled receptor proving the most successful to date. However, both techniques may be difficult to implement clinically due to their requirement for surgically implanted stimulus delivery methods and their use of nonhuman receptors. A third silencing method, an invertebrate glutamate-gated chloride channel receptor (GluClR) activated by ivermectin, solves the stimulus delivery problem as ivermectin is a safe, well tolerated drug that reaches the brain following systemic administration. However, the limitations of this method include poor functional expression, possibly due to the requirement to coexpress two different subunits in individual neurons, and the nonhuman origin of GluClR. Here, we describe the development of a modified human alpha1 glycine receptor as an improved ivermectin-gated silencing receptor. The crucial development was the identification of a mutation, A288G, which increased ivermectin sensitivity almost 100-fold, rendering it similar to that of GluClR. Glycine sensitivity was eliminated via the F207A mutation. Its large unitary conductance, homomeric expression, and human origin may render the F207A/A288G alpha1 glycine receptor an improved silencing receptor for neuroscientific and clinical purposes. As all known highly ivermectin-sensitive GluClRs contain an endogenous glycine residue at the corresponding location, this residue appears essential for exquisite ivermectin sensitivity.
Collapse
Affiliation(s)
- Timothy Lynagh
- Queensland Brain Institute and School of Biomedical Sciences, The University of Queensland, Brisbane QLD 4072, Australia
| | - Joseph W Lynch
- Queensland Brain Institute and School of Biomedical Sciences, The University of Queensland, Brisbane QLD 4072, Australia.
| |
Collapse
|
30
|
Aldea M, Castillo M, Mulet J, Sala S, Criado M, Sala F. Role of the extracellular transmembrane domain interface in gating and pharmacology of a heteromeric neuronal nicotinic receptor. J Neurochem 2010; 113:1036-45. [DOI: 10.1111/j.1471-4159.2010.06665.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
|
31
|
Gleitsman KR, Lester HA, Dougherty DA. Probing the role of backbone hydrogen bonding in a critical beta sheet of the extracellular domain of a cys-loop receptor. Chembiochem 2009; 10:1385-91. [PMID: 19405066 DOI: 10.1002/cbic.200900092] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Probing the sheet: The network of hydrogen bonds formed in the outer beta sheet of the nicotinic acetylcholine receptor (nAChR; see figure) is fairly robust and tolerates single amide-to-ester mutations throughout. However, eliminating two proximal hydrogen bonds completely destroys receptor function; this adds further support to gating models that ascribe important roles to these beta strands of the nAChR extracellular domain.Long-range communication is essential for the function of members of the Cys-loop family of neurotransmitter-gated ion channels. The involvement of the peptide backbone in binding-induced conformational changes that lead to channel gating in these membrane proteins is an interesting, but unresolved issue. To probe the role of the peptide backbone, we incorporated a series of alpha-hydroxy acid analogues into the beta-sheet-rich extracellular domain of the muscle subtype of the nicotinic acetylcholine receptor, the prototypical Cys-loop receptor. Specifically, mutations were made in beta strands 7 and 10 of the alpha subunit. A number of single backbone mutations in this region were well tolerated. However, simultaneous introduction of two proximal backbone mutations led to surface-expressed, nonfunctional receptors. Together, these data suggest that while the receptor is remarkably robust in its ability to tolerate single amide-to-ester mutations throughout these beta strands, more substantial perturbations to this region have a profound effect on the protein. These results support a model in which backbone movements in the outer beta sheet are important for receptor function.
Collapse
Affiliation(s)
- Kristin R Gleitsman
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91106, USA
| | | | | |
Collapse
|