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Eddy MT, Su Y, Silvers R, Andreas L, Clark L, Wagner G, Pintacuda G, Emsley L, Griffin RG. Lipid bilayer-bound conformation of an integral membrane beta barrel protein by multidimensional MAS NMR. JOURNAL OF BIOMOLECULAR NMR 2015; 61:299-310. [PMID: 25634301 PMCID: PMC4398622 DOI: 10.1007/s10858-015-9903-1] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Accepted: 01/20/2015] [Indexed: 05/09/2023]
Abstract
The human voltage dependent anion channel 1 (VDAC) is a 32 kDa β-barrel integral membrane protein that controls the transport of ions across the outer mitochondrial membrane. Despite the determination of VDAC solution and diffraction structures, a structural basis for the mechanism of its function is not yet fully understood. Biophysical studies suggest VDAC requires a lipid bilayer to achieve full function, motivating the need for atomic resolution structural information of VDAC in a membrane environment. Here we report an essential step toward that goal: extensive assignments of backbone and side chain resonances for VDAC in DMPC lipid bilayers via magic angle spinning nuclear magnetic resonance (MAS NMR). VDAC reconstituted into DMPC lipid bilayers spontaneously forms two-dimensional lipid crystals, showing remarkable spectral resolution (0.5-0.3 ppm for (13)C line widths and <0.5 ppm (15)N line widths at 750 MHz). In addition to the benefits of working in a lipid bilayer, several distinct advantages are observed with the lipid crystalline preparation. First, the strong signals and sharp line widths facilitated extensive NMR resonance assignments for an integral membrane β-barrel protein in lipid bilayers by MAS NMR. Second, a large number of residues in loop regions were readily observed and assigned, which can be challenging in detergent-solubilized membrane proteins where loop regions are often not detected due to line broadening from conformational exchange. Third, complete backbone and side chain chemical shift assignments could be obtained for the first 25 residues, which comprise the functionally important N-terminus. The reported assignments allow us to compare predicted torsion angles for VDAC prepared in DMPC 2D lipid crystals, DMPC liposomes, and LDAO-solubilized samples to address the possible effects of the membrane mimetic environment on the conformation of the protein. Concluding, we discuss the strengths and weaknesses of the reported assignment approach and the great potential for even more complete assignment studies and de novo structure determination via (1)H detected MAS NMR.
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Affiliation(s)
- Matthew T. Eddy
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Yongchao Su
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Robert Silvers
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Loren Andreas
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Lindsay Clark
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Gerhard Wagner
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA
| | - Guido Pintacuda
- Centre de RMN à Tres̀ Hauts Champs, Institut des Sciences Analytiques (CNRS, ENS Lyon, UCB Lyon 1), Université de Lyon, 69100 Villeurbanne, France
| | - Lyndon Emsley
- Centre de RMN à Tres̀ Hauts Champs, Institut des Sciences Analytiques (CNRS, ENS Lyon, UCB Lyon 1), Université de Lyon, 69100 Villeurbanne, France
| | - Robert G. Griffin
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Corresponding Author:
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2
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Solution- and solid-state NMR studies of GPCRs and their ligands. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1808:1462-75. [DOI: 10.1016/j.bbamem.2010.10.003] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2010] [Revised: 10/02/2010] [Accepted: 10/05/2010] [Indexed: 12/29/2022]
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3
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Aisenbrey C, Cusan M, Lambotte S, Jasperse P, Georgescu J, Harzer U, Bechinger B. Specific Isotope Labeling of Colicin E1 and B Channel Domains For Membrane Topological Analysis by Oriented Solid-State NMR Spectroscopy. Chembiochem 2008; 9:944-51. [DOI: 10.1002/cbic.200700507] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
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4
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The conformation of acetylcholine at its target site in the membrane-embedded nicotinic acetylcholine receptor. Proc Natl Acad Sci U S A 2007; 104:18031-6. [PMID: 17989232 DOI: 10.1073/pnas.0704785104] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The conformation of the neurotransmitter acetylcholine bound to the fully functional nicotinic acetylcholine receptor embedded in its native membrane environment has been characterized by using frequency-selective recoupling solid-state NMR. Six dipolar couplings among five resolved (13)C-labeled atoms of acetylcholine were measured. Bound acetylcholine adopts a bent conformation characterized with a quaternary ammonium-to-carbonyl distance of 5.1 A. In this conformation, and with its orientation constrained to that previously determined by us, the acetylcholine could be docked satisfactorily in the agonist pocket of the agonist-bound, but not the agonist-free, crystal structure of a soluble acetylcholine-binding protein from Lymnaea stagnali. The quaternary ammonium group of the acetylcholine was determined to be within 3.9 A of five aromatic residues and its acetyl group close to residues C187/188 of the principle and residue L112 of the complementary subunit. The observed >C O chemical shift is consistent with H bonding to the nicotinic acetylcholine receptor residues gammaY116 and deltaT119 that are homologous to L112 in the soluble acetylcholine-binding protein.
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5
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Hulme EC, Soper AK, McLain SE, Finney JL. The hydration of the neurotransmitter acetylcholine in aqueous solution. Biophys J 2006; 91:2371-80. [PMID: 16798812 PMCID: PMC1557574 DOI: 10.1529/biophysj.106.089185] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Neutron diffraction augmented with hydrogen isotope substitution has been used to examine the water structure around the acetylcholine molecular ion in aqueous solution. It is shown that the nearest-neighbor water molecules in the region around the trimethylammonium headgroup are located either in a ring around the central nitrogen atom or between the carbon atoms, forming a sheath around the onium group. Moreover the water molecules in this cavity do not bond to the onium group but rather form hydrogen bonds with water molecules in the surrounding aqueous environment. Given that in the bound state the onium headgroup must be completely desolvated, the absence of bonding between the onium headgroup and the surrounding water solvent may be selectively favorable to acetylcholine-binding in the receptor site. Away from the headgroup, pronounced hydrogen-bonding of water to the carbonyl oxygen is observed, but not to the ether oxygen in the acetylcholine chain.
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Affiliation(s)
- E C Hulme
- Division of Physical Biochemistry, MRC National Institute for Medical Research, London, United Kingdom
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6
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7
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Watts A. Solid-state NMR in drug design and discovery for membrane-embedded targets. Nat Rev Drug Discov 2005; 4:555-68. [PMID: 16052240 DOI: 10.1038/nrd1773] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Observing drugs and ligands at their site of action in membrane proteins is now possible through the use of a development in biomolecular NMR spectroscopy known as solid-state NMR. Even large, functionally active complexes are being examined using this method, with structural details being resolved at super-high subnanometre resolution. This is supplemented by detailed dynamic and electronic information about the surrounding ligand environment, and gives surprising new insights into the way in which ligands bind, which can aid drug design.
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Affiliation(s)
- Anthony Watts
- Biomembrane Structure Unit, Biochemistry Department, University of Oxford, Oxford OX1 3QU, UK.
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8
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Gyermek L. Development of ultra short-acting muscle relaxant agents: History, research strategies, and challenges. Med Res Rev 2005; 25:610-54. [PMID: 16086361 DOI: 10.1002/med.20036] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Author has reviewed the literature and his own work related to the chemistry, pharmacology, and clinical aspects of new muscle relaxants. Emphasis has been placed on the basic science concepts and technologies (e.g. structure-activity relationships, nicotinic receptor pharmacology, and investigation of side effects) behind the development of rapidly and short acting nondepolarizing muscle relaxants.
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Affiliation(s)
- Laszlo Gyermek
- Department of Anesthesiology, Harbor-UCLA Medical Center, Box 10, 1000 W. Carson Street, Torrance, California 90509, USA.
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9
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Morcombe CR, Zilm KW. Chemical shift referencing in MAS solid state NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2003; 162:479-86. [PMID: 12810033 DOI: 10.1016/s1090-7807(03)00082-x] [Citation(s) in RCA: 628] [Impact Index Per Article: 29.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Solid state 13C magic angle spinning (MAS) NMR spectra are typically referenced externally using a probe which does not incorporate a field frequency lock. Solution NMR shifts on the other hand are more often determined with respect to an internal reference and using a deuterium based field frequency lock. Further differences arise in solution NMR of proteins and nucleic acids where both 13C and 1H shifts are referenced by recording the frequency of the 1H resonance of DSS (sodium salt of 2,2-dimethyl-2-silapentane-5-sulphonic acid) instead of TMS (tetramethylsilane). In this note we investigate the difficulties in relating shifts measured relative to TMS and DSS by these various approaches in solution and solids NMR, and calibrate adamantane as an external 13C standard for solids NMR. We find that external chemical shift referencing of magic angle spinning spectra is typically quite reproducible and accurate, with better than +/-0.03 ppm accuracy being straight forward to achieve. Solid state and liquid phase NMR shifts obtained by magic angle spinning with external referencing agree with those measured using typical solution NMR hardware with the sample tube aligned with the applied field as long as magnetic susceptibility corrections and solvent shifts are taken into account. The DSS and TMS reference scales for 13C and 1H are related accurately using MAS NMR. Large solvent shifts for the 13C resonance in TMS in either deuterochloroform or methanol are observed, being +0.71 ppm and -0.74 ppm from external TMS, respectively. The ratio of the 13C resonance frequencies for the two carbons in solid adamantane to the 1H resonance of TMS is reported.
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Affiliation(s)
- Corey R Morcombe
- Department of Chemistry, Yale University, P.O. Box 208107, New Haven, CT 06520-8107, USA
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10
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Williamson PTF, Bains S, Chung C, Cooke R, Watts A. Probing the environment of neurotensin whilst bound to the neurotensin receptor by solid state NMR. FEBS Lett 2002; 518:111-5. [PMID: 11997028 DOI: 10.1016/s0014-5793(02)02656-x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
A functionally active analogue of neurotensin, neurotensin(8-13), has been observed whilst bound to the agonist-binding site of the rat neurotensin receptor by nuclear magnetic resonance (NMR). Through the application of slow magic angle sample spinning and high-power proton decoupling, sufficient resolution and sensitivity were obtained in the carbon-13 spectrum to allow an assignment of many of the side chain resonances arising from uniformly carbon-13/nitrogen-15-labelled neurotensin(8-13) whilst bound to the neurotensin receptor. Significant perturbations in carbon-13 chemical shift were observed upon the binding of the neurotensin(8-13) to the receptor. Most importantly significant shifts were observed in both the carboxy terminus and tyrosine side chain of the neurotensin(8-13), suggesting that these sites are important in the interaction of the neurotensin with the agonist-binding site on the neurotensin receptor. Conversely, no perturbations were observed for the carbon-13 sites within the guanidinium groups of the arginine side chains, indicating little interaction with the receptor-binding site, or a shielding of the local environment by the surrounding nitrogen atoms. These NMR observations lend further support to previous structure-activity studies, site-directed mutagenesis and modelling studies of the agonist-binding site of the neurotensin receptor, from which the same specific residues for which NMR perturbations were observed are important for neurotensin receptor activation by neurotensin.
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Affiliation(s)
- P T F Williamson
- Laboratorium für Physikalische Chemie, ETH-Hönggerberg, CH-8093 Zurich, Switzerland
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11
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Watts JA, Watts A, Middleton DA. A model of reversible inhibitors in the gastric H+/K+-ATPase binding site determined by rotational echo double resonance NMR. J Biol Chem 2001; 276:43197-204. [PMID: 11479301 DOI: 10.1074/jbc.m104808200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Several close analogues of the noncovalent H(+)/K(+)-ATPase inhibitor SCH28080 (2-methyl-3-cyanomethyl-8-(phenylmethoxy)imidazo[1,2-a]pyridine) have been screened for activity and examined in the pharmacological site of action by solid-state NMR spectroscopy. TMPIP, the 1,2,3-trimethyl analogue of SCH28080, and variants of TMPIP containing fluorine in the phenylmethoxy ring exhibited IC(50) values for porcine H(+)/K(+)-ATPase inhibition falling in the sub-10 microm range. Deuterium NMR spectra of a (2)H-labeled inhibitor titrated into H(+)/K(+)-ATPase membranes revealed that 80-100% of inhibitor was bound to the protein, and K(+)-competition (2)H NMR experiments confirmed that the inhibitor lay within the active site. The active binding conformation of the pentafluorophenylmethoxy analogue of TMPIP was determined from (13)C-(19)F dipolar coupling measurements using the cross-polarization magic angle spinning NMR method, REDOR. It was found that the inhibitor adopts an energetically favorable extended conformation falling between fully planar and partially bowed extremes. These findings allowed a model to be proposed for the binding of this inhibitor to H(+)/K(+)-ATPase based on the results of independent site-directed mutagenesis studies. In the model, the partially bowed inhibitor interacts with Phe(126) close to the N-terminal membrane spanning helix M1 and residues in the extracellular loop bridging membrane helices M5 and M6 and is flanked by residues in M4.
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Affiliation(s)
- J A Watts
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom
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12
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Williamson PT, Watts JA, Addona GH, Miller KW, Watts A. Dynamics and orientation of N+(CD3)3-bromoacetylcholine bound to its binding site on the nicotinic acetylcholine receptor. Proc Natl Acad Sci U S A 2001; 98:2346-51. [PMID: 11226242 PMCID: PMC30141 DOI: 10.1073/pnas.031361698] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2000] [Indexed: 11/18/2022] Open
Abstract
Dynamic and structural information has been obtained for an analogue of acetylcholine while bound to the agonist binding site on the nicotinic acetylcholine receptor (nAcChoR), using wide-line deuterium solid-state NMR. Analysis of the deuterium lineshape obtained at various temperatures from unoriented nAcChoR membranes labeled with deuterated bromoacetylcholine (BAC) showed that the quaternary ammonium group of the ligand is well constrained within the agonist binding site when compared with the dynamics observed in the crystalline solids. This motional restriction would suggest that a high degree of complementarity exists between the quaternary ammonium group of the ligand and the protein within the agonist binding site. nAcChoR membranes were uniaxially oriented by isopotential centrifugation as determined by phosphorous NMR of the membrane phospholipids. Analysis of the deuterium NMR lineshape of these oriented membranes enriched with the nAcChoR labeled with N(+)(CD(3))(3)-BAC has enabled us to determine that the angle formed between the quaternary ammonium group of the BAC and the membrane normal is 42 degrees in the desensitized form of the receptor. This measurement allows us to orient in part the bound ligand within the proposed receptor binding site.
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Affiliation(s)
- P T Williamson
- Biomembrane Structure Unit, Biochemistry Department, University of Oxford, South Parks Road, Oxford, OX1 3QU United Kingdom
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13
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Glaubitz C, Gröger A, Gottschalk K, Spooner P, Watts A, Schuldiner S, Kessler H. 31P-CP-MAS NMR studies on TPP+ bound to the ion-coupled multidrug transport protein EmrE. FEBS Lett 2000; 480:127-31. [PMID: 11034313 DOI: 10.1016/s0014-5793(00)01916-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The binding of tetraphenylphosphonium (TPP+) to EmrE, a membrane-bound, 110 residue Escherichia coli multidrug transport protein, has been observed by 31P cross-polarisation-magic-angle spinning nuclear magnetic resonance spectroscopy (CP-MAS NMR). EmrE has been reconstituted into dimyristoyl phosphatidylcholine bilayers. CP-MAS could selectively distinguish binding of TPP+ to EmrE in the fluid membrane. A population of bound ligand appears shifted 4 ppm to lower frequency compared to free ligand in solution, which suggests a rather direct and specific type of interaction of the ligand with the protein. This is also supported by the observed restricted motion of the bound ligand. The observation of another weakly bound substrate population arises from ligand binding to negatively charged residues in the protein loop regions.
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Affiliation(s)
- C Glaubitz
- Department of Biochemistry, University of Oxford, UK.
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14
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Arias HR. Localization of agonist and competitive antagonist binding sites on nicotinic acetylcholine receptors. Neurochem Int 2000; 36:595-645. [PMID: 10771117 DOI: 10.1016/s0197-0186(99)00154-0] [Citation(s) in RCA: 156] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Identification of all residues involved in the recognition and binding of cholinergic ligands (e.g. agonists, competitive antagonists, and noncompetitive agonists) is a primary objective to understand which structural components are related to the physiological function of the nicotinic acetylcholine receptor (AChR). The picture for the localization of the agonist/competitive antagonist binding sites is now clearer in the light of newer and better experimental evidence. These sites are located mainly on both alpha subunits in a pocket approximately 30-35 A above the surface membrane. Since both alpha subunits are identical, the observed high and low affinity for different ligands on the receptor is conditioned by the interaction of the alpha subunit with other non-alpha subunits. This molecular interaction takes place at the interface formed by the different subunits. For example, the high-affinity acetylcholine (ACh) binding site of the muscle-type AChR is located on the alphadelta subunit interface, whereas the low-affinity ACh binding site is located on the alphagamma subunit interface. Regarding homomeric AChRs (e.g. alpha7, alpha8, and alpha9), up to five binding sites may be located on the alphaalpha subunit interfaces. From the point of view of subunit arrangement, the gamma subunit is in between both alpha subunits and the delta subunit follows the alpha aligned in a clockwise manner from the gamma. Although some competitive antagonists such as lophotoxin and alpha-bungarotoxin bind to the same high- and low-affinity sites as ACh, other cholinergic drugs may bind with opposite specificity. For instance, the location of the high- and the low-affinity binding site for curare-related drugs as well as for agonists such as the alkaloid nicotine and the potent analgesic epibatidine (only when the AChR is in the desensitized state) is determined by the alphagamma and the alphadelta subunit interface, respectively. The case of alpha-conotoxins (alpha-CoTxs) is unique since each alpha-CoTx from different species is recognized by a specific AChR type. In addition, the specificity of alpha-CoTxs for each subunit interface is species-dependent. In general terms we may state that both alpha subunits carry the principal component for the agonist/competitive antagonist binding sites, whereas the non-alpha subunits bear the complementary component. Concerning homomeric AChRs, both the principal and the complementary component exist on the alpha subunit. The principal component on the muscle-type AChR involves three loops-forming binding domains (loops A-C). Loop A (from mouse sequence) is mainly formed by residue Y(93), loop B is molded by amino acids W(149), Y(152), and probably G(153), while loop C is shaped by residues Y(190), C(192), C(193), and Y(198). The complementary component corresponding to each non-alpha subunit probably contributes with at least four loops. More specifically, the loops at the gamma subunit are: loop D which is formed by residue K(34), loop E that is designed by W(55) and E(57), loop F which is built by a stretch of amino acids comprising L(109), S(111), C(115), I(116), and Y(117), and finally loop G that is shaped by F(172) and by the negatively-charged amino acids D(174) and E(183). The complementary component on the delta subunit, which corresponds to the high-affinity ACh binding site, is formed by homologous loops. Regarding alpha-neurotoxins, several snake and alpha-CoTxs bear specific residues that are energetically coupled with their corresponding pairs on the AChR binding site. The principal component for snake alpha-neurotoxins is located on the residue sequence alpha1W(184)-D(200), which includes loop C. In addition, amino acid sequence 55-74 from the alpha1 subunit (which includes loop E), and residues gammaL(119) (close to loop F) and gammaE(176) (close to loop G) at the low-affinity binding site, or deltaL(121) (close to the homologous region of loop G) at the high-affinity binding site, are i
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Affiliation(s)
- H R Arias
- Instituto de Matemática de Bahía Blanca, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and Universidad Nacional del Sur, Av. Alem 1253, 8000 Bahía Blanca, Argentina.
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Baenziger JE, Morris ML, Darsaut TE, Ryan SE. Effect of membrane lipid composition on the conformational equilibria of the nicotinic acetylcholine receptor. J Biol Chem 2000; 275:777-84. [PMID: 10625607 DOI: 10.1074/jbc.275.2.777] [Citation(s) in RCA: 122] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The effects of cholesterol (Chol) and an anionic lipid, dioleoylphosphatidic acid (DOPA) on the conformational equilibria of the nicotinic acetylcholine receptor (nAChR) have been investigated using Fourier transform infrared difference spectroscopy. The difference between spectra recorded in the presence and absence of agonist from the nAChR reconstituted into 3:1:1 egg phosphatidylcholine (EPC)/DOPA/Chol membranes exhibits positive and negative bands that serve as markers of the structural changes associated with the resting to desensitized conformational change. These markers are absent in similar difference spectra recorded from the nAChR reconstituted into EPC membranes lacking both Chol and DOPA, indicating that the nAChR cannot undergo conformational change in response to agonist binding. When low levels of either Chol or DOPA up to 25 mol % of the total lipid are included in the EPC membranes, the markers suggest the predominant stabilization of a conformation that is a structural intermediate between the resting and desensitized states. At higher levels of either Chol or DOPA, the nAChR is stabilized in a conformation that is capable of undergoing agonist-induced desensitization, although DOPA appears to be required for the nAChR to adopt a conformation fully equivalent to that found in native and 3:1:1 EPC/DOPA/Chol membranes. The ability of these two structurally diverse lipids, as well as others (Ryan, S. E., Demers, C. N., Chew, J. P., Baenziger, J. E. (1996) J. Biol. Chem. 271, 24590-24597), to modulate the functional state of the nAChR suggests that lipids act on the nAChR via an indirect effect on some physical property of the lipid bilayer. The data also suggest that anionic lipids are essential to stabilize a fully functional nAChR. We propose that membrane fluidity modulates the relative populations of nAChRs in the resting and desensitized states but that subtle structural changes in the presence of anionic lipids are essential for full activity.
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Affiliation(s)
- J E Baenziger
- Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada.
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Abstract
NMR methods are now able to give detailed structural, dynamic and electronic information about drugs and ligands while constrained at their site of action in membrane-embedded receptors, information which is essential for mechanistic descriptions of their action and design of new ligands. Using solid state NMR methods, a peptic ulcer drug analogue has been described at atomic resolution (to +/- 0.3 A between two atoms) at its site of action in the gastric H+/K+-ATPase, and the aromaticity of the agonist binding site of the nicotinic acetylcholine receptor has been demonstrated, with both targets in functionally competent membranes under conditions similar to those used in screening assays. G-protein-coupled receptor ligands and prosthetic groups are also being resolved using NMR methods.
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Affiliation(s)
- A Watts
- Biomembrane Structure Unit Biochemistry Department University of Oxford Oxford OX1 3QU UK.
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