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Rucktooa P, Smit AB, Sixma TK. Insight in nAChR subtype selectivity from AChBP crystal structures. Biochem Pharmacol 2009; 78:777-87. [DOI: 10.1016/j.bcp.2009.06.098] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2009] [Revised: 06/19/2009] [Accepted: 06/22/2009] [Indexed: 10/20/2022]
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Paleari L, Cesario A, Fini M, Russo P. alpha7-Nicotinic receptor antagonists at the beginning of a clinical era for NSCLC and Mesothelioma? Drug Discov Today 2009; 14:822-36. [PMID: 19616116 DOI: 10.1016/j.drudis.2009.06.016] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2008] [Revised: 06/25/2009] [Accepted: 06/26/2009] [Indexed: 11/26/2022]
Abstract
Of the human solid cancers, Non-Small Cell Lung Cancer (NSCLC) and Malignant Pleural Mesothelioma (MPM) display a natural history supporting the concept that they develop from multiple preneoplastic pathways. Recently, new evidence suggested that nicotinic Acetylcholine Receptors (nAChRs) play a significant role in lung cancer predisposition and natural history. This review is based on some translational research aimed at evaluating the potential therapeutic effect of nAChR antagonists on NSCLC and MPM. The background and rationale of this approach are based on the experimental observations that: (a) NSCLC and MPM cells express nAChRs and (b) the activation of these receptors by agonists, namely nicotine, inhibits apoptosis, whereas receptor antagonists have a pro-apoptotic effect.
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Affiliation(s)
- Laura Paleari
- Lung Cancer Unit, National Cancer Research Institute, Genoa, Italy.
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Matsuda K, Kanaoka S, Akamatsu M, Sattelle DB. Diverse actions and target-site selectivity of neonicotinoids: structural insights. Mol Pharmacol 2009; 76:1-10. [PMID: 19321668 PMCID: PMC2701451 DOI: 10.1124/mol.109.055186] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2009] [Accepted: 03/25/2009] [Indexed: 11/22/2022] Open
Abstract
The nicotinic acetylcholine receptors (nAChRs) are targets for human and veterinary medicines as well as insecticides. Subtype-selectivity among the diverse nAChR family members is important for medicines targeting particular disorders, and pest-insect selectivity is essential for the development of safer, environmentally acceptable insecticides. Neonicotinoid insecticides selectively targeting insect nAChRs have important applications in crop protection and animal health. Members of this class exhibit strikingly diverse actions on their nAChR targets. Here we review the chemistry and diverse actions of neonicotinoids on insect and mammalian nAChRs. Electrophysiological studies on native nAChRs and on wild-type and mutagenized recombinant nAChRs have shown that basic residues particular to loop D of insect nAChRs are likely to interact electrostatically with the nitro group of neonicotinoids. In 2008, the crystal structures were published showing neonicotinoids docking into the acetylcholine binding site of molluscan acetylcholine binding proteins with homology to the ligand binding domain (LBD) of nAChRs. The crystal structures showed that 1) glutamine in loop D, corresponding to the basic residues of insect nAChRs, hydrogen bonds with the NO(2) group of imidacloprid and 2) neonicotinoid-unique stacking and CH-pi bonds at the LBD. A neonicotinoid-resistant strain obtained by laboratory-screening has been found to result from target site mutations, and possible reasons for this are also suggested by the crystal structures. The prospects of designing neonicotinoids that are safe not only for mammals but also for beneficial insects such as honey bees (Apis mellifera) are discussed in terms of interactions with non-alpha nAChR subunits.
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Affiliation(s)
- Kazuhiko Matsuda
- Department of Applied Biological Chemistry, School of Agriculture, Kinki University, Nara, Japan.
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Gleitsman KR, Shanata JAP, Frazier SJ, Lester HA, Dougherty DA. Long-range coupling in an allosteric receptor revealed by mutant cycle analysis. Biophys J 2009; 96:3168-78. [PMID: 19383461 DOI: 10.1016/j.bpj.2008.12.3949] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2008] [Revised: 12/12/2008] [Accepted: 12/15/2008] [Indexed: 11/26/2022] Open
Abstract
The functional coupling of residues that are far apart in space is the quintessential property of allosteric proteins. For example, in Cys-loop receptors, the gating of an intrinsic ion channel is allosterically regulated by the binding of small molecule neurotransmitters 50-60 A from the channel gate. Some residues near the binding site must have as their primary function the communication of the binding event to the gating region. These gating pathway residues are essential to function, but their identification and characterization can be challenging. This work introduces a simple strategy, derived from mutant cycle analysis, for identifying gating pathway residues using macroscopic measurements alone. In the exemplar Cys-loop receptor, the nicotinic acetylcholine receptor, a well-characterized reporter mutation (betaL9'S) known to impact gating, was combined with mutations of target residues in the ligand-binding domain hypothesized or previously found to be functionally significant. A mutant cycle analysis of the macroscopic EC(50) measurements can then provide insights into the role of the target residue. This new method, elucidating long-range functional coupling in allosteric receptors, can be applied to several reporter mutations in a wide variety of receptors to identify previously characterized and novel mutations that impact the gating pathway. We support our interpretation of macroscopic data with single-channel studies. Elucidating long-range functional coupling in allosteric receptors should be broadly applicable to determining functional roles of residues in allosteric receptors.
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Affiliation(s)
- Kristin R Gleitsman
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA
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Givelet C, Buffeteau T, Arnaud-Neu F, Hubscher-Bruder V, Bibal B. A Hydrosoluble Triphenylene That Preferentially Binds Acetylcholine, Epibatidine, and Nicotine. J Org Chem 2009; 74:5059-62. [DOI: 10.1021/jo900683x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Affiliation(s)
- Cécile Givelet
- Université de Bordeaux, Institut des Sciences Moléculaires, CNRS UMR 5255, 351 cours de la Libération, 33405 Talence, France, and Laboratoire de Chimie Physique, DSA, IPHC, UMR UDS-CNRS 7178, 25 rue Becquerel, 67087 Strasbourg, France
| | - Thierry Buffeteau
- Université de Bordeaux, Institut des Sciences Moléculaires, CNRS UMR 5255, 351 cours de la Libération, 33405 Talence, France, and Laboratoire de Chimie Physique, DSA, IPHC, UMR UDS-CNRS 7178, 25 rue Becquerel, 67087 Strasbourg, France
| | - Françoise Arnaud-Neu
- Université de Bordeaux, Institut des Sciences Moléculaires, CNRS UMR 5255, 351 cours de la Libération, 33405 Talence, France, and Laboratoire de Chimie Physique, DSA, IPHC, UMR UDS-CNRS 7178, 25 rue Becquerel, 67087 Strasbourg, France
| | - Véronique Hubscher-Bruder
- Université de Bordeaux, Institut des Sciences Moléculaires, CNRS UMR 5255, 351 cours de la Libération, 33405 Talence, France, and Laboratoire de Chimie Physique, DSA, IPHC, UMR UDS-CNRS 7178, 25 rue Becquerel, 67087 Strasbourg, France
| | - Brigitte Bibal
- Université de Bordeaux, Institut des Sciences Moléculaires, CNRS UMR 5255, 351 cours de la Libération, 33405 Talence, France, and Laboratoire de Chimie Physique, DSA, IPHC, UMR UDS-CNRS 7178, 25 rue Becquerel, 67087 Strasbourg, France
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Rogachev AY, Petrukhina MA. Insights Into Metal−π Arene Interactions of the Highly Lewis Acidic Rh24+ Core with a Broad Set of π-Ligands: From Ethylene to Corannulene and C60-Fullerene. J Phys Chem A 2009; 113:5743-53. [DOI: 10.1021/jp901271g] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Affiliation(s)
- Andrey Yu. Rogachev
- Department of Chemistry, University at Albany, State University of New York, 1400 Washington Avenue, Albany, New York 12222-0100
| | - Marina A. Petrukhina
- Department of Chemistry, University at Albany, State University of New York, 1400 Washington Avenue, Albany, New York 12222-0100
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Lester HA, Xiao C, Srinivasan R, Son CD, Miwa J, Pantoja R, Banghart MR, Dougherty DA, Goate AM, Wang JC. Nicotine is a selective pharmacological chaperone of acetylcholine receptor number and stoichiometry. Implications for drug discovery. AAPS JOURNAL 2009; 11:167-77. [PMID: 19280351 DOI: 10.1208/s12248-009-9090-7] [Citation(s) in RCA: 132] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2008] [Accepted: 02/07/2009] [Indexed: 01/11/2023]
Abstract
The acronym SePhaChARNS, for "selective pharmacological chaperoning of acetylcholine receptor number and stoichiometry," is introduced. We hypothesize that SePhaChARNS underlies classical observations that chronic exposure to nicotine causes "upregulation" of nicotinic receptors (nAChRs). If the hypothesis is proven, (1) SePhaChARNS is the molecular mechanism of the first step in neuroadaptation to chronic nicotine; and (2) nicotine addiction is partially a disease of excessive chaperoning. The chaperone is a pharmacological one, nicotine; and the chaperoned molecules are alpha4beta2* nAChRs. SePhaChARNS may also underlie two inadvertent therapeutic effects of tobacco use: (1) the inverse correlation between tobacco use and Parkinson's disease; and (2) the suppression of seizures by nicotine in autosomal dominant nocturnal frontal lobe epilepsy. SePhaChARNS arises from the thermodynamics of pharmacological chaperoning: ligand binding, especially at subunit interfaces, stabilizes AChRs during assembly and maturation, and this stabilization is most pronounced for the highest-affinity subunit compositions, stoichiometries, and functional states of receptors. Several chemical and pharmacokinetic characteristics render exogenous nicotine a more potent pharmacological chaperone than endogenous acetylcholine. SePhaChARNS is modified by desensitized states of nAChRs, by acid trapping of nicotine in organelles, and by other aspects of proteostasis. SePhaChARNS is selective at the cellular, and possibly subcellular, levels because of variations in the detailed nAChR subunit composition, as well as in expression of auxiliary proteins such as lynx. One important implication of the SePhaChARNS hypothesis is that therapeutically relevant nicotinic receptor drugs could be discovered by studying events in intracellular compartments rather than exclusively at the surface membrane.
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Affiliation(s)
- Henry A Lester
- Division of Biology 156-29, California Institute of Technology, Pasadena, CA 91125, USA.
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58
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Xiu X, Puskar NL, Shanata JAP, Lester HA, Dougherty DA. Nicotine binding to brain receptors requires a strong cation-pi interaction. Nature 2009; 458:534-7. [PMID: 19252481 PMCID: PMC2755585 DOI: 10.1038/nature07768] [Citation(s) in RCA: 282] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2008] [Accepted: 01/09/2009] [Indexed: 11/29/2022]
Abstract
Nicotine addiction begins with high-affinity binding of nicotine to acetylcholine (ACh) receptors in the brain. The end result is over 4,000,000 smoking-related deaths annually worldwide and the largest source of preventable mortality in developed countries. Stress reduction, pleasure, improved cognition, and other CNS effects are strongly associated with smoking. But, if nicotine activated ACh receptors found in muscle as potently as it does brain receptors, smoking would cause intolerable and perhaps fatal muscle contractions. Despite extensive pharmacological, functional, and structural studies of ACh receptors, the basis for the differential action of nicotine on brain vs. muscle ACh receptors has not been determined. Here we show that at the α4β2 brain receptors thought to underlie nicotine addiction, the high affinity of nicotine is the result of a strong cation-п interaction to a specific aromatic amino acid of the receptor, TrpB. In contrast, the low affinity of nicotine at the muscle-type receptor is largely due to the fact that this key interaction is absent, even though the immediate binding site residues, including the key TrpB, are identical in the brain and muscle receptors. At the same time a hydrogen bond from nicotine to the backbone carbonyl of TrpB is enhanced in the neuronal receptor relative to the muscle-type. A point mutation near TrpB that differentiates α4β2 and muscle-type receptors appears to influence the shape of the binding site, allowing nicotine to interact more strongly with TrpB in the neuronal receptor. ACh receptors are established therapeutic targets for Alzheimer’s disease, schizophrenia, Parkinson’s disease, smoking cessation, pain, attention deficit-hyperactivity disorder, epilepsy, autism, and depression1. Along with solving a chemical mystery in nicotine addiction, our results provide guidance for efforts to develop drugs that target specific types of nicotinic receptors.
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Affiliation(s)
- Xinan Xiu
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA
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59
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Martin DE, Robertson EG, MacLellan JG, Godfrey PD, Thompson CD, Morrison RJS. A Spectroscopic Study of Nicotine Analogue 2-Phenylpyrrolidine (PPD) Using Resonant Two-Photon Ionization (R2PI), Microwave, and 2D NMR Techniques. J Am Chem Soc 2009; 131:2638-46. [DOI: 10.1021/ja807995n] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Affiliation(s)
| | | | | | - Peter D. Godfrey
- School of Chemistry, Monash University, Victoria 3800, Australia
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60
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Molecular modeling of the α9α10 nicotinic acetylcholine receptor subtype. Bioorg Med Chem Lett 2009; 19:251-4. [DOI: 10.1016/j.bmcl.2008.10.094] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2008] [Accepted: 10/20/2008] [Indexed: 11/24/2022]
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61
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Tantama M, Licht S. Use of calculated cation-pi binding energies to predict relative strengths of nicotinic acetylcholine receptor agonists. ACS Chem Biol 2008; 3:693-702. [PMID: 19032090 DOI: 10.1021/cb800189y] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Agonists and antagonists of the nicotinic acetylcholine receptor (nAChR) are used to treat nicotine addiction, neuromuscular disorders, and neurological diseases. In designing small molecule therapeutics with the nAChR as a target, it is useful to identify chemical parameters that correlate with ability to activate the receptor. Previous studies have shown that cation-pi interactions at the transmitter binding sites of the nAChR are important for receptor activation by strong agonists such as acetylcholine. We hypothesized that a calculated estimate of cation-pi binding ability could be used to predict the efficiency for channel opening (i.e., the gating efficiency) associated with activation of the acetylcholine receptor by a series of structurally related organic cations. We demonstrate that the calculated cation-pi energy is strongly correlated with gating efficiency but only weakly correlated with closed-state binding affinity. Our results suggest that cation-pi interactions contribute significantly to the open-state affinity of these cations and that the calculated cation-pi energy will be a useful parameter for designing nAChR agonists and antagonists.
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Affiliation(s)
- Mathew Tantama
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Building 16, Room 573B, Cambridge, Massachusetts 02139
| | - Stuart Licht
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Building 16, Room 573B, Cambridge, Massachusetts 02139
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63
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Abstract
The 5-HT3 receptor belongs to a family of therapeutically important neurotransmitter-gated receptors whose ligand binding sites are formed by the convergence of six peptide loops (A-F). Here we have mutated 15 amino acid residues in and around loop B of the 5-HT3 receptor (Ser-177 to Asn-191) to Ala or a residue with similar chemical properties. Changes in [3H]granisetron binding affinity (Kd) and 5-HT EC50 were determined using receptors expressed in human embryonic kidney 293 cells. Substitutions at all but one residue (Thr-181) altered or eliminated binding for one or both mutants. Receptors were nonfunctional or EC50 values were altered for all but two mutants (S182T, I190L). Homology modeling indicates that loop B contributes two residues to a hydrophobic core that faces into the β-sandwich of the subunit, and the experimental data indicate that they are important for both the structure and the function of the receptor. The models also show that close to the apex of the loop (Ser-182 to Ile-190), loop B residues form an extensive network of hydrogen bonds, both with other loop B residues and with adjacent regions of the protein. Overall, the data suggest that loop B has a major role in maintaining the structure of the region by a series of noncovalent interactions that are easily disrupted by amino acid substitutions.
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64
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Atomic interactions of neonicotinoid agonists with AChBP: molecular recognition of the distinctive electronegative pharmacophore. Proc Natl Acad Sci U S A 2008; 105:7606-11. [PMID: 18477694 DOI: 10.1073/pnas.0802197105] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Acetylcholine-binding proteins (AChBPs) from mollusks are suitable structural and functional surrogates of the nicotinic acetylcholine receptors when combined with transmembrane spans of the nicotinic receptor. These proteins assemble as a pentamer with identical ACh binding sites at the subunit interfaces and show ligand specificities resembling those of the nicotinic receptor for agonists and antagonists. A subset of ligands, termed the neonicotinoids, exhibit specificity for insect nicotinic receptors and selective toxicity as insecticides. AChBPs are of neither mammalian nor insect origin and exhibit a distinctive pattern of selectivity for the neonicotinoid ligands. We define here the binding orientation and determinants of differential molecular recognition for the neonicotinoids and classical nicotinoids by estimates of kinetic and equilibrium binding parameters and crystallographic analysis. Neonicotinoid complex formation is rapid and accompanied by quenching of the AChBP tryptophan fluorescence. Comparisons of the neonicotinoids imidacloprid and thiacloprid in the binding site from Aplysia californica AChBP at 2.48 and 1.94 A in resolution reveal a single conformation of the bound ligands with four of the five sites occupied in the pentameric crystal structure. The neonicotinoid electronegative pharmacophore is nestled in an inverted direction compared with the nicotinoid cationic functionality at the subunit interfacial binding pocket. Characteristic of several agonists, loop C largely envelops the ligand, positioning aromatic side chains to interact optimally with conjugated and hydrophobic regions of the neonicotinoid. This template defines the association of interacting amino acids and their energetic contributions to the distinctive interactions of neonicotinoids.
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65
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Affiliation(s)
- Dennis A. Dougherty
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125
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66
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Abstract
The challenges to obtaining chemical-scale information on the molecules of neuroscience are considerable. Most targets are complex integral membrane proteins that are not amenable to direct structural characterization. However, by combining the tools of organic synthesis, molecular biology, and electrophysiology, rational and systematic structure-function studies can be performed in what we have termed physical organic chemistry on the brain. Using these tools, we have probed hydrophobic effects, hydrogen bonding, cation-pi interactions, and conformational changes associated with channel gating. The insights gained provide important guidance for drug discovery efforts targeting ion channels and neuroreceptors and mechanistic insights for the complex proteins of neuroscience.
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Affiliation(s)
- Dennis A Dougherty
- Division of Chemistry and Chemical Engineering California Institute of Technology, Pasadena, CA 91125, USA.
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Crystal structures of Lymnaea stagnalis AChBP in complex with neonicotinoid insecticides imidacloprid and clothianidin. INVERTEBRATE NEUROSCIENCE 2008; 8:71-81. [PMID: 18338186 PMCID: PMC2413115 DOI: 10.1007/s10158-008-0069-3] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/20/2008] [Accepted: 02/29/2008] [Indexed: 11/22/2022]
Abstract
Neonicotinoid insecticides, which act on nicotinic acetylcholine receptors (nAChRs) in a variety of ways, have extremely low mammalian toxicity, yet the molecular basis of such actions is poorly understood. To elucidate the molecular basis for nAChR–neonicotinoid interactions, a surrogate protein, acetylcholine binding protein from Lymnaea stagnalis (Ls-AChBP) was crystallized in complex with neonicotinoid insecticides imidacloprid (IMI) or clothianidin (CTD). The crystal structures suggested that the guanidine moiety of IMI and CTD stacks with Tyr185, while the nitro group of IMI but not of CTD makes a hydrogen bond with Gln55. IMI showed higher binding affinity for Ls-AChBP than that of CTD, consistent with weaker CH–π interactions in the Ls-AChBP–CTD complex than in the Ls-AChBP–IMI complex and the lack of the nitro group-Gln55 hydrogen bond in CTD. Yet, the NH at position 1 of CTD makes a hydrogen bond with the backbone carbonyl of Trp143, offering an explanation for the diverse actions of neonicotinoids on nAChRs.
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Seydou M, Grégoire G, Liquier J, Lemaire J, Schermann JP, Desfrançois C. Experimental Observation of the Transition between Gas-Phase and Aqueous Solution Structures for Acetylcholine, Nicotine, and Muscarine Ions. J Am Chem Soc 2008; 130:4187-95. [DOI: 10.1021/ja710040p] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- Mahamadou Seydou
- Laboratoire de Physique des lasers, UMR 7538 CNRS, Université Paris 13, 93430 Villetaneuse, France, Laboratoire de Biophysique Moléculaire, Cellulaire et Tissulaire UMR 7033 CNRS, Université Paris 13, 93017 Bobigny, France, and Laboratoire de Chimie Physique, UMR 8000 CNRS, Université Paris XI, Bat. 350, 91405 Orsay Cedex, France
| | - Gilles Grégoire
- Laboratoire de Physique des lasers, UMR 7538 CNRS, Université Paris 13, 93430 Villetaneuse, France, Laboratoire de Biophysique Moléculaire, Cellulaire et Tissulaire UMR 7033 CNRS, Université Paris 13, 93017 Bobigny, France, and Laboratoire de Chimie Physique, UMR 8000 CNRS, Université Paris XI, Bat. 350, 91405 Orsay Cedex, France
| | - Jean Liquier
- Laboratoire de Physique des lasers, UMR 7538 CNRS, Université Paris 13, 93430 Villetaneuse, France, Laboratoire de Biophysique Moléculaire, Cellulaire et Tissulaire UMR 7033 CNRS, Université Paris 13, 93017 Bobigny, France, and Laboratoire de Chimie Physique, UMR 8000 CNRS, Université Paris XI, Bat. 350, 91405 Orsay Cedex, France
| | - J. Lemaire
- Laboratoire de Physique des lasers, UMR 7538 CNRS, Université Paris 13, 93430 Villetaneuse, France, Laboratoire de Biophysique Moléculaire, Cellulaire et Tissulaire UMR 7033 CNRS, Université Paris 13, 93017 Bobigny, France, and Laboratoire de Chimie Physique, UMR 8000 CNRS, Université Paris XI, Bat. 350, 91405 Orsay Cedex, France
| | - Jean Pierre Schermann
- Laboratoire de Physique des lasers, UMR 7538 CNRS, Université Paris 13, 93430 Villetaneuse, France, Laboratoire de Biophysique Moléculaire, Cellulaire et Tissulaire UMR 7033 CNRS, Université Paris 13, 93017 Bobigny, France, and Laboratoire de Chimie Physique, UMR 8000 CNRS, Université Paris XI, Bat. 350, 91405 Orsay Cedex, France
| | - Charles Desfrançois
- Laboratoire de Physique des lasers, UMR 7538 CNRS, Université Paris 13, 93430 Villetaneuse, France, Laboratoire de Biophysique Moléculaire, Cellulaire et Tissulaire UMR 7033 CNRS, Université Paris 13, 93017 Bobigny, France, and Laboratoire de Chimie Physique, UMR 8000 CNRS, Université Paris XI, Bat. 350, 91405 Orsay Cedex, France
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69
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Pedretti A, Marconi C, Bolchi C, Fumagalli L, Ferrara R, Pallavicini M, Valoti E, Vistoli G. Modelling of full-length human alpha4beta2 nicotinic receptor by fragmental approach and analysis of its binding modes. Biochem Biophys Res Commun 2008; 369:648-53. [PMID: 18302933 DOI: 10.1016/j.bbrc.2008.02.080] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2008] [Accepted: 02/14/2008] [Indexed: 10/22/2022]
Abstract
The objective of the study was to generate a full-length model for the heteropentameric structure of human alpha4beta2 nicotinic receptor. The monomers structure was derived using a fragmental approach and the pentamer was assembled by protein-protein docking. The reliability of the model was assessed docking a representative set of known nicotinic ligands. Docking results unveiled that the ligand affinity depends on key interactions that the ligand's charged moiety realizes with conserved apolar residues of alpha4 monomer, whereas the H-bond acceptor group interacts with a less conserved and more heterogeneous subpocket, involving polar residues of beta2 subunit. The consistency of docking results and the agreement with the experimental data afford an encouraging validation for the proposed model and emphasize the soundness of such a fragmental approach to model any transmembrane protein.
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Affiliation(s)
- Alessandro Pedretti
- Istituto di Chimica Farmaceutica e Tossicologica "Pietro Pratesi", Università di Milano, Via Mangiagalli, 25 I-20133 Milano, Italy
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Atypical nicotinic agonist bound conformations conferring subtype selectivity. Proc Natl Acad Sci U S A 2008; 105:1728-32. [PMID: 18230720 DOI: 10.1073/pnas.0711724105] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The nicotinic acetylcholine (ACh) receptor (nAChR) plays a crucial role in excitatory neurotransmission and is an important target for drugs and insecticides. Diverse nAChR subtypes with various subunit combinations confer differential selectivity for nicotinic drugs. We investigated the subtype selectivity of nAChR agonists by comparing two ACh-binding proteins (AChBPs) as structural surrogates with distinct pharmacological profiles [i.e., Lymnaea stagnalis (Ls) AChBP of low neonicotinoid and high nicotinoid sensitivities and Aplysia californica (Ac) AChBP of high neonicotinoid sensitivity] mimicking vertebrate and insect nAChR subtypes, respectively. The structural basis of subtype selectivity was examined here by photoaffinity labeling. Two azidoneonicotinoid probes in the Ls-AChBP surprisingly modified two distinct and distant subunit interface sites: loop F Y164 of the complementary or (-)-face subunit and loop C Y192 of the principal or (+)-face subunit, whereas three azidonicotinoid probes derivatized only Y192. Both the neonicotinoid and nicotinoid probes labeled Ac-AChBP at only one position at the interface between loop C Y195 and loop E M116. These findings were used to establish structural models of the two AChBP subtypes. In the Ac-AChBP, the neonicotinoids and nicotinoids are nestled in similar bound conformations. Intriguingly, for the Ls-AChBP, the neonicotinoids have two bound conformations that are inverted relative to each other, whereas nicotinoids appear buried in only one conserved conformation as seen for the Ac-AChBP subtype. Accordingly, the subtype selectivity is based on two disparate bound conformations of nicotinic agonists, thereby establishing an atypical concept for neonicotinoid versus nicotinoid selectivity between insect and vertebrate nAChRs.
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71
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Wang J, Lester HA, Dougherty DA. Establishing an ion pair interaction in the homomeric rho1 gamma-aminobutyric acid type A receptor that contributes to the gating pathway. J Biol Chem 2007; 282:26210-6. [PMID: 17606618 DOI: 10.1074/jbc.m702314200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
gamma-Aminobutyric acid type A (GABA(A)) receptors are members of the Cys-loop superfamily of ligand-gated ion channels. Upon agonist binding, the receptor undergoes a structural transition from the closed to the open state, but the mechanism of gating is not well understood. Here we utilized a combination of conventional mutagenesis and the high precision methodology of unnatural amino acid incorporation to study the gating interface of the human homopentameric rho1 GABA(A) receptor. We have identified an ion pair interaction between two conserved charged residues, Glu(92) in loop 2 of the extracellular domain and Arg(258) in the pre-M1 region. We hypothesize that the salt bridge exists in the closed state by kinetic measurements and free energy analysis. Several other charged residues at the gating interface are not critical to receptor function, supporting previous conclusions that it is the global charge pattern of the gating interface that controls receptor function in the Cys-loop superfamily.
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Affiliation(s)
- Jinti Wang
- Division of Chemistry and Chemical Engineering and Division of Biology, California Institute of Technology, Pasadena, California 91125, USA
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72
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Tomizawa M, Maltby D, Medzihradszky KF, Zhang N, Durkin KA, Presley J, Talley TT, Taylor P, Burlingame AL, Casida JE. Defining nicotinic agonist binding surfaces through photoaffinity labeling. Biochemistry 2007; 46:8798-806. [PMID: 17614369 PMCID: PMC4778401 DOI: 10.1021/bi700667v] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Nicotinic acetylcholine (ACh) receptor (nAChR) agonists are potential therapeutic agents for neurological dysfunction. In the present study, the homopentameric mollusk ACh binding protein (AChBP), used as a surrogate for the extracellular ligand-binding domain of the nAChR, was specifically derivatized by the highly potent agonist azidoepibatidine (AzEPI) prepared as a photoaffinity probe and radioligand. One EPI-nitrene photoactivated molecule was incorporated in each subunit interface binding site based on analysis of the intact derivatized protein. Tryptic fragments of the modified AChBP were analyzed by collision-induced dissociation and Edman sequencing of radiolabeled peptides. Each specific EPI-nitrene-modified site involved either Tyr195 of loop C on the principal or (+)-face or Met116 of loop E on the complementary or (-)-face. The two derivatization sites were observed in similar frequency, providing evidence of the reactivity of the azido/nitrene probe substituent and close proximity to both residues. [3H]AzEPI binds to the alpha4beta2 nAChR at a single high-affinity site and photoaffinity-labels only the alpha4 subunit, presumably modifying Tyr225 spatially corresponding to Tyr195 of AChBP. Phe137 of the beta2 nAChR subunit, equivalent to Met116 of AChBP, conceivably lacks sufficient reactivity with the nitrene generated from the probe. The present photoaffinity labeling in a physiologically relevant condition combined with the crystal structure of AChBP allows development of precise structural models for the AzEPI interactions with AChBP and alpha4beta2 nAChR. These findings enabled us to use AChBP as a structural surrogate to define the nAChR agonist site.
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Affiliation(s)
- Motohiro Tomizawa
- Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720-3112
| | - David Maltby
- Mass Spectrometry Facility, University of California, San Francisco, California 94143-0446
| | | | - Nanjing Zhang
- Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720-3112
| | - Kathleen A. Durkin
- Molecular Graphics and Computation Facility, College of Chemistry, University of California, Berkeley, California 94720-1460
| | - Jack Presley
- Molecular Structure Facility, University of California, Davis, California 95616
| | - Todd T. Talley
- Department of Pharmacology, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, La Jolla, California 92093-0650
| | - Palmer Taylor
- Department of Pharmacology, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, La Jolla, California 92093-0650
| | - Alma L. Burlingame
- Mass Spectrometry Facility, University of California, San Francisco, California 94143-0446
| | - John E. Casida
- Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720-3112
- To whom correspondence should be addressed. Phone: 510-642-5424. Fax: 510-642-6497.
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73
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Zhang H, Li H, Ma Q. QSAR study of a large set of 3-pyridyl ethers as ligands of the α4β2 nicotinic acetylcholine receptor. J Mol Graph Model 2007; 26:226-35. [PMID: 17208024 DOI: 10.1016/j.jmgm.2006.11.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2006] [Revised: 11/27/2006] [Accepted: 11/28/2006] [Indexed: 11/22/2022]
Abstract
Extensive 3D-QSAR studies were performed on 158 diverse analogues of 3-pyridyl ethers, which are excellent ligands of alpha4beta2 neuronal nicotinic acetylcholine receptor (NnAChR). Comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) techniques were used to relate the binding affinities with the ligand structures. Two QSAR models were obtained using CoMFA and CoMSIA techniques. The two QSAR models were proved to be statistically significant and have high predictive power. The best CoMFA model yielded the cross-validated q(2)=0.605 and the non-cross-validated r(2)=0.862. The derived model indicated the importance of steric (85.9%) as well as electrostatic (14.1%) contributions. The CoMFA model demonstrated the steric field as the major descriptor of the ligand binding. The best CoMSIA model gave q(2)=0.723 and r(2)=0.685. This model showed that steric (30.3%) and H-bond interaction (61.8%) properties played major roles in ligand binding process. The squares of correlation coefficient for external test set of 28 molecules were 0.723 and 0.685 for the CoMFA model and the CoMSIA model, respectively. The two models were further graphically interpreted in terms of field contribution maps. SAR studies were also performed on different series of compounds in order to get a more reasonable understanding of the interactions between the ligands and the receptor. With the results, we have also presumed some assistant elements as supplements to the traditional pharmacophoric elements. A crude vision of ligand localization in the ligand-binding pocket of the receptor was also obtained, which would favor for the docking study of this kind of ligands.
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Affiliation(s)
- Huabei Zhang
- Department of Chemistry, Beijing Normal University, 19# Street Xinjiekou, Beijing 100875, China.
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74
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Dölker N, Deupi X, Pardo L, Campillo M. Charge-charge and cation-π interactions in ligand binding to G protein-coupled receptors. Theor Chem Acc 2007. [DOI: 10.1007/s00214-007-0341-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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75
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Pogocki D, Ruman T, Danilczuk M, Danilczuk M, Celuch M, Wałajtys-Rode E. Application of nicotine enantiomers, derivatives and analogues in therapy of neurodegenerative disorders. Eur J Pharmacol 2007; 563:18-39. [PMID: 17376429 DOI: 10.1016/j.ejphar.2007.02.038] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2007] [Revised: 02/04/2007] [Accepted: 02/15/2007] [Indexed: 12/21/2022]
Abstract
This review gives a brief overview over the major aspects of application of the nicotine alkaloid and its close derivatives in the therapy of some neurodegenerative disorders and diseases (e.g. Alzheimer's disease, Parkinson's disease, Tourette's syndrome, schizophrenia etc.). The issues concerning methods of nicotine analysis and isolation, and some molecular aspects of nicotine pharmacology are included. The natural and synthetic analogues of nicotine that are considered for medical practice are also mentioned. The molecular properties of two naturally occurring nicotine enantiomers are compared--the less-common but less-toxic (R)-nicotine is suggested as a natural compound that may find its place in pharmaceutical practice.
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Affiliation(s)
- Dariusz Pogocki
- Rzeszów University of Technology, Faculty of Chemistry, Department of Biochemistry and Biotechnology, 6 Powstańców Warszawy Ave. 35-959 Rzeszów, Poland
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76
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Tomizawa M, Talley TT, Maltby D, Durkin KA, Medzihradszky KF, Burlingame AL, Taylor P, Casida JE. Mapping the elusive neonicotinoid binding site. Proc Natl Acad Sci U S A 2007; 104:9075-80. [PMID: 17485662 PMCID: PMC1885630 DOI: 10.1073/pnas.0703309104] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Two types of structurally similar nicotinic agonists have very different biological and physicochemical properties. Neonicotinoids, important insecticides including imidacloprid and thiacloprid, are nonprotonated and selective for insects and their nicotinic receptors, whereas nicotinoids such as nicotine and epibatidine are cationic and selective for mammalian systems. We discovered that a mollusk acetylcholine binding protein (AChBP), as a structural surrogate for the extracellular ligand-binding domain of the nicotinic receptor, is similarly sensitive to neonicotinoids and nicotinoids. It therefore seemed possible that the proposed very different interactions of the neonicotinoids and nicotinoids might be examined with a single AChBP by using optimized azidochloropyridinyl photoaffinity probes. Two azidoneonicotinoids with a nitro or cyano group were compared with the corresponding desnitro or descyano azidonicotinoids. The four photoactivated nitrene probes modified AChBP with up to one agonist for each subunit based on analysis of the intact derivatized protein. Identical modification sites were observed by collision-induced dissociation analysis for the neonicotinoids and nicotinoids with similar labeling frequency of Tyr-195 of loop C and Met-116 of loop E at the subunit interface. The nitro- or cyano-substituted guanidine/amidine planes of the neonicotinoids provide a unique electronic conjugation system to interact with loop C Tyr-188. The neonicotinoid nitro oxygen and cyano nitrogen contact loop C Cys-190/Ser-189, whereas the cationic head of the corresponding nicotinoids is inverted for hydrogen-bonding and cation-pi contact with Trp-147 and Tyr-93. These structural models based on AChBP directly map the elusive neonicotinoid binding site and further describe the molecular determinants of agonists on nicotinic receptors.
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Affiliation(s)
- Motohiro Tomizawa
- *Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720-3112
| | - Todd T. Talley
- Department of Pharmacology, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, La Jolla, CA 92093-0650
| | - David Maltby
- Mass Spectrometry Facility, University of California, San Francisco, CA 94143-0446; and
| | - Kathleen A. Durkin
- Molecular Graphics and Computation Facility, College of Chemistry, University of California, Berkeley, CA 94720-1460
| | | | - Alma L. Burlingame
- Mass Spectrometry Facility, University of California, San Francisco, CA 94143-0446; and
| | - Palmer Taylor
- Department of Pharmacology, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, La Jolla, CA 92093-0650
| | - John E. Casida
- *Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720-3112
- To whom correspondence should be addressed. E-mail:
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77
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Cashin AL, Torrice MM, McMenimen KA, Lester HA, Dougherty DA. Chemical-scale studies on the role of a conserved aspartate in preorganizing the agonist binding site of the nicotinic acetylcholine receptor. Biochemistry 2007; 46:630-9. [PMID: 17223685 PMCID: PMC3164877 DOI: 10.1021/bi061638b] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The nicotinic acetylcholine receptor and related Cys-loop receptors are ligand-gated ion channels that mediate fast synaptic transmission throughout the central and peripheral nervous system. A highly conserved aspartate residue (D89) that is near the agonist binding site but does not directly contact the ligand plays a critical part in receptor function. Here we probe the role of D89 using unnatural amino acid mutagenesis coupled with electrophysiology. Homology modeling implicates several hydrogen bonds involving D89. We find that no single hydrogen bond is essential to proper receptor function. Apparently, the side chain of D89 establishes a redundant network of hydrogen bonds; these bonds preorganize the agonist binding site by positioning a critical tryptophan residue that directly contacts the ligand. Earlier studies of the D89N mutant led to the proposal that a negative charge at this position is essential for receptor function. However, we find that receptors with neutral side chains at position 89 can function well, if the side chain is less perturbing than the amide of asparagine (nitro or keto groups allow function) or if a compensating backbone mutation is introduced to relieve unfavorable electrostatics.
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Affiliation(s)
| | | | | | | | - Dennis A. Dougherty
- Author to whom correspondence should be addressed. Phone (626) 395-6089; Fax (626) 564-9297;
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78
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Padgett CL, Hanek AP, Lester HA, Dougherty DA, Lummis SCR. Unnatural amino acid mutagenesis of the GABA(A) receptor binding site residues reveals a novel cation-pi interaction between GABA and beta 2Tyr97. J Neurosci 2007; 27:886-92. [PMID: 17251430 PMCID: PMC2649369 DOI: 10.1523/jneurosci.4791-06.2007] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The binding pockets of Cys-loop receptors are dominated by aromatic amino acids. In the GABA(A) receptor alpha1Phe65, beta2Tyr97, beta2Tyr157, and beta2Tyr205 are present at the beta2/alpha1 interface and have been implicated in forming an important part of the GABA binding site. Here, we have probed interactions of these residues using subtle chemical changes: unnatural amino acid mutagenesis was used to introduce a range of Phe analogs, and mutant receptors expressed in oocytes were studied using voltage-clamp electrophysiology. Serial mutations at beta(2)97 revealed a approximately 20-fold increase in EC50 with the addition of each fluorine atom to a phenylalanine, indicating a cation-pi interaction between GABA and this residue. This is the first example of a cation-pi interaction in loop A of a Cys-loop receptor. Along with previous studies that identified cation-pi interactions in loop B and loop C, the result emphasizes that the location of this interaction is not conserved in the Cys-loop family. The data further show that alpha(1)65 (in loop D) is tolerant to subtle changes. Conversely, mutating either beta2Tyr157 (in loop B) or beta2Tyr205 (in loop C) to Phe substantially disrupts receptor function. Substitution of 4-F-Phe, however, at either position, or 4-MeO-Phe at beta2Tyr157, resulted in receptors with wild-type EC50 values, suggesting a possible hydrogen bond. The molecular scale insights provided by these data allow the construction of a model for GABA docking to the agonist binding site of the GABA(A) receptor.
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Affiliation(s)
- Claire L. Padgett
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1AG, United Kingdom, and
| | - Ariele P. Hanek
- California Institute of Technology, Pasadena, California 91125
| | - Henry A. Lester
- California Institute of Technology, Pasadena, California 91125
| | | | - Sarah C. R. Lummis
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1AG, United Kingdom, and
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79
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Arnaud V, Berthelot M, Evain M, Graton J, Le Questel JY. Hydrogen-Bond Interactions of Nicotine and Acetylcholine Salts: A Combined Crystallographic, Spectroscopic, Thermodynamic and Theoretical Study. Chemistry 2007; 13:1499-510. [PMID: 17103466 DOI: 10.1002/chem.200600808] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The hydrogen-bond (HB) interactions of the monocharged active forms of nicotine and acetylcholine (ACh) have been compared theoretically by using density functional theory (DFT) calculations and experimentally on the basis of crystallographic observations and the measurement of equilibrium constants in solution. The 2,4,6-trinitrophenolate (picrate) counterion was used to determine the experimental HB basicity of the cations despite its potential multisite HB acceptor properties. The preferred HB interaction site of the ammonium picrate salts was determined from a survey of crystallographic data found in the Cambridge Structural Database (CSD) and is supported by theoretical calculations. Two distinct classes of ammonium groups were characterised depending on the absence (quaternary ammonium) or presence (tertiary, secondary and primary ammoniums) of an N(+)HO hydrogen bond linking the two ions. The crystal structure of nicotinium picrate was determined and compared with that of ACh. This analysis revealed the peculiar behaviour of the ammonium moiety of nicotinic acetylcholine receptor (nAChR) ligands towards the picrate anion. Dedicated methods have been developed to separate the individual contributions of the anion and cation accepting sites to the overall HB basicity of the ion pairs measured in solution. The HB basicities of the picrate anions associated with the two different ammonium classes were determined in dichloromethane solution by using several model ion pairs with non-basic ammonium cations. The experimental and theoretical studies performed on the nicotine and ACh cations consistently show the significant HB ability of the acceptor site of nAChR agonists in their charged form. Both the greater HB basicity of the pyridinic nitrogen over the carbonyl oxygen and the greater HB acidity of the N(+)H unit relative to N(+)CH could contribute to the higher affinity for nAChRs of nicotine-like ligands relative to ACh-like ligands.
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Affiliation(s)
- Virginie Arnaud
- EA 1149, FR CNRS 2465, Université de Nantes, Nantes Atlantique Universités, Faculté des Sciences et des Techniques de Nantes, 2, rue de la Houssinière, BP 92208, 44322 Nantes Cedex 3, France
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80
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Ihara M, Shimomura M, Ishida C, Nishiwaki H, Akamatsu M, Sattelle DB, Matsuda K. A hypothesis to account for the selective and diverse actions of neonicotinoid insecticides at their molecular targets, nicotinic acetylcholine receptors: catch and release in hydrogen bond networks. INVERTEBRATE NEUROSCIENCE 2007; 7:47-51. [PMID: 17265057 DOI: 10.1007/s10158-006-0043-x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2006] [Accepted: 12/21/2006] [Indexed: 11/26/2022]
Abstract
The low mammalian toxicity of neonicotinoid insecticides has been shown to be attributable, at least in part, to their selective actions on insect nicotinic acetylcholine receptors (nAChRs). There are multiple nAChRs in insects and a wealth of neonicotinoid chemicals. Studies to date have discribed a wide range of effects on nAChRs, notably partial agonist, super agonist and antagonist actions. Both the diversity of the neonicotinoid actions and their selectivity for insect over vertebrate nAChRs are the result of physicochemical and steric interactions at their molecular targets (nAChRs). In such interactions, the formation and breakage of hydrogen bond (HB) networks plays a key role. Therefore the loss or gain of even a single HB resulting from either structural changes in neonicotinoids, or the amino acid sequence of a particular nAChR subunit, could result in a drastic modification of neonicotinoid actions. In addition to the amino acid residues, the backbone carbonyl of nAChRs may also be involved in the formation of HB networks with neonicotinoids.
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Affiliation(s)
- Makoto Ihara
- RIKEN Harima Institute, SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo, Hyogo, 679-5148, Japan
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81
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Leonik FM, Papke RL, Horenstein NA. Quinuclidines as selective agonists for alpha-7 nicotinic acetylcholine receptors. Bioorg Med Chem Lett 2007; 17:1520-2. [PMID: 17276680 DOI: 10.1016/j.bmcl.2007.01.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2006] [Revised: 12/16/2006] [Accepted: 01/03/2007] [Indexed: 11/20/2022]
Abstract
The alpha7 subtype of the neuronal nicotinic acetylcholine receptors (nAChRs) was targeted for the design of selective agonists deriving from the quinuclidine scaffold. Arylidene groups at the 3-position and N-methyl quinuclidine were found to be selective agonists with EC(50)s of 1.5 and 40 microM, respectively.
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Affiliation(s)
- Fedra M Leonik
- Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA
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82
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Huang X, Zheng F, Chen X, Crooks PA, Dwoskin LP, Zhan CG. Modeling Subtype-Selective Agonists Binding with α4β2 and α7 Nicotinic Acetylcholine Receptors: Effects of Local Binding and Long-Range Electrostatic Interactions. J Med Chem 2006; 49:7661-74. [PMID: 17181149 DOI: 10.1021/jm0606701] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The subtype-selective binding of 14 representative agonists with alpha4beta2 and alpha7 nicotinic acetylcholine receptors (nAChRs) has been studied by performing homology modeling, molecular docking, geometry optimizations, and microscopic and phenomenological binding free energy calculations. All of the computational results demonstrate that the subtype selectivity of the agonists binding with alpha4beta2 and alpha7 7 nAChRs is affected by both local binding and long-range electrostatic interactions between the receptors and the protonated structures of the agonists. The effects of the long-range electrostatic interactions are mainly due to the distinct difference in the net charge of the ligand-binding domain between the two nAChR subtypes. For the alpha4beta2-selective agonists examined, the microscopic binding modes with the alpha4beta2 nAChR are very similar to the corresponding modes with the alpha7 nAChR, and therefore, the subtype selectivity of these agonists binding with alpha4beta2 and alpha7 nAChRs is dominated by the long-range electrostatic interactions. For the alpha7-selective agonists, their microscopic binding modes with the alpha7 nAChR are remarkably different from those with the alpha4beta2 nAChR so that the local binding (including the hydrogen bonding and cation-pi interactions) with the alpha7 nAChR is much stronger than that with the alpha4beta2 nAChR. The calculated phenomenological binding free energies are in good agreement with available experimental data for the relative binding free energies concerning the subtype selectivity of agonists binding with the two different nAChR subtypes. The fundamental insights obtained in the present study should be valuable for future rational design of potential therapeutic agents targeted to specific nAChR subtypes.
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Affiliation(s)
- Xiaoqin Huang
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, 725 Rose Street, Lexington, KY 40536, USA
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83
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Masci B, Persiani D, Thuéry P. Complexation of Quaternary Ammonium Ions by Tetraester Derivatives of [3.1.3.1]Homooxacalixarene in Mobile and in Fixed Conformation. J Org Chem 2006; 71:9784-90. [PMID: 17168597 DOI: 10.1021/jo0617621] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In the tetraalkylation of p-tert-butyl[3.1.3.1]homooxacalixarene with BrCH2CO2R and K2CO3 in acetone, the initially formed cone conformer is converted into the more stable 1,4-alternate conformer when R = Me or Et, but not when R = i-Pr or t-Bu. In the case of R = i-Pr, derivatives in fixed 1,4-alternate conformation and in partial cone conformation were also isolated. Compounds in fixed cone conformation are good ligands for tetramethylammonium, acetylcholine, and N-methylpyridinium salts in CDCl3, but the partial cone isomer proved to be somewhat better and even the 1,4-alternate conformer turned out to be active. The possible involvement of the ester functions as additional binding sites is discussed; moreover, an insight into the energetics of the complexation and conformational isomerization processes is given.
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Affiliation(s)
- Bernardo Masci
- Dipartimento di Chimica and IMC-CNR, Università La Sapienza, P.le Aldo Moro 5, 00185 Roma, Italy.
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84
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White R, Malpass JR, Handa S, Richard Baker S, Broad LM, Folly L, Mogg A. Epibatidine isomers and analogues: Structure–activity relationships. Bioorg Med Chem Lett 2006; 16:5493-7. [PMID: 16934977 DOI: 10.1016/j.bmcl.2006.08.049] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2006] [Revised: 08/09/2006] [Accepted: 08/09/2006] [Indexed: 11/30/2022]
Abstract
Binding affinities for a range of epibatidine isomers and analogues at the alpha4beta2 and alpha3beta4 nAChR subtypes are reported; compounds having similar N-N distances to epibatidine show similar, high potencies.
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Affiliation(s)
- Richard White
- Department of Chemistry, University of Leicester, Leicester LE1 7RH, UK
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85
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Clements A, Lewis M. Arene−Cation Interactions of Positive Quadrupole Moment Aromatics and Arene−Anion Interactions of Negative Quadrupole Moment Aromatics. J Phys Chem A 2006; 110:12705-10. [PMID: 17107123 DOI: 10.1021/jp065175v] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Intermolecular interactions involving aromatic pi-electron density are widely believed to be governed by the aromatic molecular quadrupole moment, Theta(zz). Arene-cation binding is believed to occur primarily with negative Theta(zz) aromatics, and arene-anion binding is believed to occur largely with positive Theta(zz) aromatics. We have performed quantum mechanical computations that show the cation binding of positive Theta(zz) aromatics and the anion binding of negative Theta(zz) aromatics is quite common in the gas phase. The pi-electron density of hexafluorobenzene, the prototypical positive Theta(zz ) aromatic (experimental Theta(zz) = 9.5 +/- 0.5 DA), has a Li+ binding enthalpy of -4.37 kcal/mol at the MP2(full)/6-311G**level of theory. The RHF/6-311G** calculated Theta(zz) value of 1,4-dicyanobenzene is +11.81 DA, yet it has an MP2(full)/6-311G** Li+ binding enthalpy of -12.65 kcal/mol and a Na+ binding enthalpy of -3.72 kcal/mol. The pi-electron density of benzene, the prototypical negative Theta(zz) aromatic (experimental Theta(zz) = -8.7 +/- 0.5 DA), has a F- binding enthalpy of -5.51 kcal/mol. The RHF/6-311G** calculated Theta(zz) of C6H2I4 is -10.45 DA, yet it has an MP2(full)/6-311++G** calculated F- binding enthalpy of -20.13 kcal/mol. Our results show that as the aromatic Theta(zz) value increases the cation binding enthalpy decreases; a plot of cation binding enthalpies versus aromatic Theta(zz) gives a line of best of fit with R2 = 0.778. No such correlation exists between the aromatic Theta(zz) value and the anion binding enthalpy; the line of best fit has R2 = 0.297. These results are discussed in terms of electrostatic and polarizability contributions to the overall binding enthalpies.
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Affiliation(s)
- Aimee Clements
- Department of Chemistry, Saint Louis University, 3501 Laclede Avenue, Saint Louis, Missouri 63103, USA
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86
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Cavalli A, Carloni P, Recanatini M. Target-Related Applications of First Principles Quantum Chemical Methods in Drug Design. Chem Rev 2006; 106:3497-519. [PMID: 16967914 DOI: 10.1021/cr050579p] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Andrea Cavalli
- Department of Pharmaceutical Sciences, University of Bologna, Via Belmeloro 6, I-40126 Bologna, Italy
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87
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Tran D, Beg S, Clements A, Lewis M. Substituent constants for predicting aromatic molecular quadrupole moments. Chem Phys Lett 2006. [DOI: 10.1016/j.cplett.2006.05.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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88
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McMenimen KA, Dougherty DA, Lester HA, Petersson EJ. Probing the Mg2+ blockade site of an N-methyl-D-aspartate (NMDA) receptor with unnatural amino acid mutagenesis. ACS Chem Biol 2006; 1:227-34. [PMID: 17163677 DOI: 10.1021/cb6000944] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The N -methyl-D-aspartate (NMDA) receptor plays a central role in learning and memory in the mammalian CNS. At normal neuronal resting membrane potentials, the pore of this glutamate-gated ion channel is blocked by a Mg(2+) ion. Previous work suggests that the Mg(2+) binding site is quite novel, involving several asparagine residues and a cation-pi interaction between Mg(2+) and a conserved tryptophan in the pore. Using unnatural amino acid mutagenesis, we show that no such cation-pi interaction exists. The implicated tryptophan instead appears to play a structural role that can only be fulfilled by a rigid, flat, hydrophobic residue. This is the first demonstration of unnatural amino acid incorporation in the NMDA receptor, and it opens the way for future investigations of this pivotal neuroreceptor.
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Affiliation(s)
- Kathryn A McMenimen
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA
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89
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Shilling RA, Venter H, Velamakanni S, Bapna A, Woebking B, Shahi S, van Veen HW. New light on multidrug binding by an ATP-binding-cassette transporter. Trends Pharmacol Sci 2006; 27:195-203. [PMID: 16545467 DOI: 10.1016/j.tips.2006.02.008] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2005] [Revised: 11/23/2005] [Accepted: 02/22/2006] [Indexed: 11/26/2022]
Abstract
ATP-binding-cassette (ABC) multidrug transporters confer multidrug resistance to pathogenic microorganisms and human tumour cells by mediating the extrusion of structurally unrelated chemotherapeutic drugs from the cell. The molecular basis by which ABC multidrug transporters bind and transport drugs is far from clear. Genetic analyses during the past 14 years reveal that the replacement of many individual amino acids in mammalian multidrug resistance P-glycoproteins can affect cellular resistance to drugs, but these studies have failed to identify specific regions in the primary amino acid sequence that are part of a defined drug-binding pocket. The recent publication of an X-ray crystallographic structure of the bacterial P-glycoprotein homologue MsbA and an MsbA-based homology model of human P-glycoprotein creates an opportunity to compare the original mutagenesis data with the three-dimensional structures of transporters. Our comparisons reveal that mutations that alter specificity are present in three-dimensional 'hotspot' regions in the membrane domains of P-glycoprotein.
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MESH Headings
- ATP Binding Cassette Transporter, Subfamily B, Member 1/chemistry
- ATP Binding Cassette Transporter, Subfamily B, Member 1/genetics
- ATP Binding Cassette Transporter, Subfamily B, Member 1/metabolism
- ATP-Binding Cassette Transporters/chemistry
- ATP-Binding Cassette Transporters/genetics
- ATP-Binding Cassette Transporters/metabolism
- Amino Acid Sequence
- Animals
- Antineoplastic Agents/metabolism
- Binding Sites/genetics
- Biological Transport
- Drug Resistance, Multiple
- Drug Resistance, Neoplasm
- Humans
- Models, Molecular
- Molecular Sequence Data
- Mutation
- Protein Structure, Tertiary
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Affiliation(s)
- Richard A Shilling
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, UK, CB2 1PD
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90
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Abstract
The QPatch 16 significantly increases throughput for gigaseal patch clamp experiments, making direct measurements in ion channel drug discovery and safety testing feasible. Released to the market in the Autumn of 2004 by Sophion Bioscience, the QPatch originated from work done at NeuroSearch (Denmark) in the early days of automated patch clamp. Today, the QPatch provides many unique features. For example, only the QPatch includes an automated cell preparation station making several hours of unattended operation possible. The 16-channel electrode array, called the QPlate, includes glass-coated microfluidic channels for less compound absorption and, hence, more accurate IC(50) values. The microfluidic pathways also allow for very small amounts of compound used for each experiment ( approximately 5 microl per addition). Only the QPatch has four independent pipetting heads for more efficient liquid handling (especially for ligand-gated ion channel experiments). Patch clamp recordings with the QPatch match the high quality of conventional patch clamp and in some cases the results are even better. For example, only the QPatch includes 100% series resistance compensation for the elimination of false positives due to voltage errors. Finally, the modular QPatch 16 was designed with more channels in mind. The upgrade pathway to 48-channels (the QPatch HT) will be discussed.
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Affiliation(s)
- Chris Mathes
- Sophion Bioscience, Inc., 675 US Highway One, North Brunswick, NJ 08902, USA.
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91
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Roelfes G, Mootz HD. Probing the Molecular Basis of Protein Function through Chemistry. Chembiochem 2006; 7:545-9. [PMID: 16453350 DOI: 10.1002/cbic.200500547] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Gerard Roelfes
- Department of Organic Chemistry, Stratingh Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
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92
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Koné M, Illien B, Laurence C, Gal JF, Maria PC. Are nicotinoids protonated on the pyridine or the amino nitrogen in the gas phase? J PHYS ORG CHEM 2006. [DOI: 10.1002/poc.1006] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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93
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Masci B, Mortera SL, Persiani D, Thuéry P. Methyl Ether Derivatives of p-tert-Butyl[3.1.3.1]homooxacalixarene. Formation, Structure, and Complexes with Quaternary Ammonium Ions. J Org Chem 2005; 71:504-11. [PMID: 16408957 DOI: 10.1021/jo051922t] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
[structure: see text] The whole set (five compounds) of partially O-methylated products of p-tert-butyl[3.1.3.1]homooxacalixarene, currently named p-tert-butyltetrahomodioxacalix[4]arene, have been prepared. Their structure has been investigated in solution through NMR techniques and in the solid state by single-crystal X-ray diffraction. A systematic investigation, extended to the parent tetraphenol and to the tetramethyl ether derivative, has been carried out on the complexation of tetramethylammonium, acetylcholine, N-methylpyridinium, and tetraethylammonium picrate in CDCl3. The observed trends in the binding and in the selectivity of the strictly related hosts could be analyzed on the basis of the varying importance of intramolecular hydrogen bonding and its effects on the conformation of the free and of the complexed ligands. On increasing the number of methyl ether functions, the cone conformation appears to be relatively less stable but deeper, so small organic cations can be more effectively encircled.
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Affiliation(s)
- Bernardo Masci
- Dipartimento di Chimica and IMC-CNR, Università La Sapienza, Box 34-Roma 62, P.le Aldo Moro 5, 00185 Roma, Italy.
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94
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95
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Cassels BK, Bermúdez I, Dajas F, Abin-Carriquiry JA, Wonnacott S. From ligand design to therapeutic efficacy: the challenge for nicotinic receptor research. Drug Discov Today 2005; 10:1657-65. [PMID: 16376826 DOI: 10.1016/s1359-6446(05)03665-2] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
S-Nicotine, the principal psychoactive constituent of Nicotiana tabacum, underpins addiction to tobacco smoking. Although tobacco consumption is a leading cause of death worldwide, nicotine itself is also proposed to have potential therapeutic benefits for a diverse range of conditions. Nicotine interacts with its cognate receptors in the central nervous system to exert a predominantly modulatory influence, making neuronal nicotinic receptors attractive therapeutic targets. Here, we focus on three natural products as lead compounds for drug discovery programs, nicotine, epibatidine and cytisine, and consider the aims and limitations that shape these drug discovery endeavors.
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Affiliation(s)
- Bruce K Cassels
- Department of Chemistry, Faculty of Sciences, University of Chile, Casilla 653, Santiago, Chile.
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96
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Xiu X, Hanek AP, Wang J, Lester HA, Dougherty DA. A Unified View of the Role of Electrostatic Interactions in Modulating the Gating of Cys Loop Receptors. J Biol Chem 2005; 280:41655-66. [PMID: 16216879 DOI: 10.1074/jbc.m508635200] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In the Cys loop superfamily of ligand-gated ion channels, a global conformational change, initiated by agonist binding, results in channel opening and the passage of ions across the cell membrane. The detailed mechanism of channel gating is a subject that has lent itself to both structural and electrophysiological studies. Here we defined a gating interface that incorporates elements from the ligand binding domain and transmembrane domain previously reported as integral to proper channel gating. An overall analysis of charged residues within the gating interface across the entire superfamily showed a conserved charging pattern, although no specific interacting ion pairs were conserved. We utilized a combination of conventional mutagenesis and the high precision methodology of unnatural amino acid incorporation to study extensively the gating interface of the mouse muscle nicotinic acetylcholine receptor. We found that charge reversal, charge neutralization, and charge introduction at the gating interface are often well tolerated. Furthermore, based on our data and a reexamination of previously reported data on gamma-aminobutyric acid, type A, and glycine receptors, we concluded that the overall charging pattern of the gating interface, and not any specific pairwise electrostatic interactions, controls the gating process in the Cys loop superfamily.
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MESH Headings
- Acetylcholine/chemistry
- Amino Acid Sequence
- Amino Acids/chemistry
- Animals
- Biochemistry/methods
- Blotting, Western
- Bungarotoxins/chemistry
- Cations
- Cell Membrane/metabolism
- Cysteine/chemistry
- Cystine/chemistry
- Databases, Protein
- Dose-Response Relationship, Drug
- Electrodes
- Electrophysiology
- Glycine/chemistry
- Ions
- Kinetics
- Ligands
- Mice
- Models, Chemical
- Models, Molecular
- Molecular Sequence Data
- Mutagenesis
- Mutation
- Oocytes/metabolism
- Protein Binding
- Protein Conformation
- Protein Structure, Secondary
- Protein Structure, Tertiary
- RNA, Messenger/metabolism
- Receptors, Nicotinic/chemistry
- Sequence Homology, Amino Acid
- Static Electricity
- Torpedo
- Xenopus laevis
- gamma-Aminobutyric Acid/chemistry
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Affiliation(s)
- Xinan Xiu
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA
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97
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Huang X, Zheng F, Crooks PA, Dwoskin L, Zhan CG. Modeling multiple species of nicotine and deschloroepibatidine interacting with alpha4beta2 nicotinic acetylcholine receptor: from microscopic binding to phenomenological binding affinity. J Am Chem Soc 2005; 127:14401-14. [PMID: 16218635 PMCID: PMC3182463 DOI: 10.1021/ja052681+] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A variety of molecular modeling, molecular docking, and first-principles electronic structure calculations were performed to study how the alpha4beta2 nicotinic acetylcholine receptor (nAChR) binds with different species of two typical agonists, (S)-(-)-nicotine and (R)-(-)-deschloroepibatidine, each of which is distinguished by different free bases and protonation states. On the basis of these results, predictions were made regarding the corresponding microscopic binding free energies. Hydrogen-bonding and cation-pi interactions between the receptor and the respective ligands were found to be the dominant factors differentiating the binding strengths of different microscopic binding species. The calculated results and analyses demonstrate that, for each agonist, all the species are interchangeable and can quickly achieve a thermodynamic equilibrium in solution and at the nAChR binding site. This allows quantitation of the equilibrium concentration distributions of the free ligand species and the corresponding microscopic ligand-receptor binding species, their pH dependence, and their contributions to the phenomenological binding affinity. The predicted equilibrium concentration distributions, pK(a) values, absolute phenomenological binding affinities, and their pH dependence are all in good agreement with available experimental data, suggesting that the computational strategy from the microscopic binding species and affinities to the phenomenological binding affinity is reliable for studying alpha4beta2 nAChR-ligand binding. This should provide valuable information for future rational design of drugs targeting nAChRs. The general strategy of the "from-microscopic-to-phenomenological" approach for studying interactions of alpha4beta2 nAChRs with (S)-(-)-nicotine and (R)-(-)-deschloroepibatidine may also be useful in studying other types of ligand-protein interactions involving multiple molecular species of a ligand and in associated rational drug design.
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Affiliation(s)
- Xiaoqin Huang
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, 725 Rose Street, Lexington, Kentucky 40536
| | - Fang Zheng
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, 725 Rose Street, Lexington, Kentucky 40536
| | - Peter A. Crooks
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, 725 Rose Street, Lexington, Kentucky 40536
| | - Linda Dwoskin
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, 725 Rose Street, Lexington, Kentucky 40536
| | - Chang-Guo Zhan
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, 725 Rose Street, Lexington, Kentucky 40536
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