1
|
Oliveira ASF, Ibarra AA, Bermudez I, Casalino L, Gaieb Z, Shoemark DK, Gallagher T, Sessions RB, Amaro RE, Mulholland AJ. A potential interaction between the SARS-CoV-2 spike protein and nicotinic acetylcholine receptors. Biophys J 2021; 120:983-993. [PMID: 33609494 PMCID: PMC7889469 DOI: 10.1016/j.bpj.2021.01.037] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Revised: 01/11/2021] [Accepted: 01/13/2021] [Indexed: 01/08/2023] Open
Abstract
Changeux et al. (Changeux et al. C. R. Biol. 343:33-39.) recently suggested that the SARS-CoV-2 spike protein may interact with nicotinic acetylcholine receptors (nAChRs) and that such interactions may be involved in pathology and infectivity. This hypothesis is based on the fact that the SARS-CoV-2 spike protein contains a sequence motif similar to known nAChR antagonists. Here, we use molecular simulations of validated atomically detailed structures of nAChRs and of the spike to investigate the possible binding of the Y674-R685 region of the spike to nAChRs. We examine the binding of the Y674-R685 loop to three nAChRs, namely the human α4β2 and α7 subtypes and the muscle-like αβγδ receptor from Tetronarce californica. Our results predict that Y674-R685 has affinity for nAChRs. The region of the spike responsible for binding contains a PRRA motif, a four-residue insertion not found in other SARS-like coronaviruses. The conformational behavior of the bound Y674-R685 is highly dependent on the receptor subtype; it adopts extended conformations in the α4β2 and α7 complexes but is more compact when bound to the muscle-like receptor. In the α4β2 and αβγδ complexes, the interaction of Y674-R685 with the receptors forces the loop C region to adopt an open conformation, similar to other known nAChR antagonists. In contrast, in the α7 complex, Y674-R685 penetrates deeply into the binding pocket in which it forms interactions with the residues lining the aromatic box, namely with TrpB, TyrC1, and TyrC2. Estimates of binding energy suggest that Y674-R685 forms stable complexes with all three nAChR subtypes. Analyses of simulations of the glycosylated spike show that the Y674-R685 region is accessible for binding. We suggest a potential binding orientation of the spike protein with nAChRs, in which they are in a nonparallel arrangement to one another.
Collapse
Affiliation(s)
- A Sofia F Oliveira
- Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol, United Kingdom; Bristol Synthetic Biology Centre, BrisSynBio, Bristol, United Kingdom
| | - Amaurys Avila Ibarra
- Research Software Engineering, Advanced Computing Research Centre, University of Bristol, Bristol, United Kingdom
| | - Isabel Bermudez
- Department of Biological and Medical Sciences, Oxford Brookes University, Oxford, United Kingdom
| | - Lorenzo Casalino
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California
| | - Zied Gaieb
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California
| | - Deborah K Shoemark
- School of Biochemistry, University of Bristol, Bristol, United Kingdom; Bristol Synthetic Biology Centre, BrisSynBio, Bristol, United Kingdom
| | - Timothy Gallagher
- Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol, United Kingdom
| | | | - Rommie E Amaro
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California
| | - Adrian J Mulholland
- Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol, United Kingdom.
| |
Collapse
|
2
|
Oliveira ASF, Ibarra AA, Bermudez I, Casalino L, Gaieb Z, Shoemark DK, Gallagher T, Sessions RB, Amaro RE, Mulholland AJ. Simulations support the interaction of the SARS-CoV-2 spike protein with nicotinic acetylcholine receptors. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2020:2020.07.16.206680. [PMID: 32743575 PMCID: PMC7386492 DOI: 10.1101/2020.07.16.206680] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Changeux et al. recently suggested that the SARS-CoV-2 spike (S) protein may interact with nicotinic acetylcholine receptors (nAChRs). Such interactions may be involved in pathology and infectivity. Here, we use molecular simulations of validated atomically detailed structures of nAChRs, and of the S protein, to investigate this 'nicotinic hypothesis'. We examine the binding of the Y674-R685 loop of the S protein to three nAChRs, namely the human α4β2 and α7 subtypes and the muscle-like αβγδ receptor from Tetronarce californica. Our results indicate that Y674-R685 has affinity for nAChRs and the region responsible for binding contains the PRRA motif, a four-residue insertion not found in other SARS-like coronaviruses. In particular, R682 has a key role in the stabilisation of the complexes as it forms interactions with loops A, B and C in the receptor's binding pocket. The conformational behaviour of the bound Y674-R685 region is highly dependent on the receptor subtype, adopting extended conformations in the α4β2 and α7 complexes and more compact ones when bound to the muscle-like receptor. In the α4β2 and αβγδ complexes, the interaction of Y674-R685 with the receptors forces the loop C region to adopt an open conformation similar to other known nAChR antagonists. In contrast, in the α7 complex, Y674-R685 penetrates deeply into the binding pocket where it forms interactions with the residues lining the aromatic box, namely with TrpB, TyrC1 and TyrC2. Estimates of binding energy suggest that Y674-R685 forms stable complexes with all three nAChR subtypes. Analyses of the simulations of the full-length S protein show that the Y674-R685 region is accessible for binding, and suggest a potential binding orientation of the S protein with nAChRs.
Collapse
Affiliation(s)
- A. Sofia F. Oliveira
- Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
| | - Amaurys Avila Ibarra
- Research Software Engineering, Advanced Computing Research Centre, University of Bristol, Bristol BS1 5QD, UK
| | - Isabel Bermudez
- Department of Biological and Medical Sciences, Oxford Brookes University, Oxford OX30BP, UK
| | - Lorenzo Casalino
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA, 92093 USA
| | - Zied Gaieb
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA, 92093 USA
| | | | - Timothy Gallagher
- Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
| | | | - Rommie E. Amaro
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA, 92093 USA
| | - Adrian J. Mulholland
- Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
| |
Collapse
|
3
|
Mosesso R, Dougherty DA. A triad of residues is functionally transferrable between 5-HT 3 serotonin receptors and nicotinic acetylcholine receptors. J Biol Chem 2018; 293:2903-2914. [PMID: 29298898 DOI: 10.1074/jbc.m117.810432] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Revised: 11/29/2017] [Indexed: 11/06/2022] Open
Abstract
Cys-loop receptors are pentameric ligand-gated ion channels that facilitate communication within the nervous system. Upon neurotransmitter binding, these receptors undergo an allosteric activation mechanism connecting the binding event to the membrane-spanning channel pore, which expands to conduct ions. Some of the earliest steps in this activation mechanism are carried out by residues proximal to the binding site, the relative positioning of which may reflect functional differences among members of the Cys-loop family of receptors. Herein, we investigated key side-chain interactions near the binding site via mutagenesis and two-electrode voltage-clamp electrophysiology in serotonin-gated 5-HT3A receptors (5-HT3ARs) and nicotinic acetylcholine receptors (nAChRs) expressed in Xenopus laevis oocytes. We found that a triad of residues aligning to Thr-152, Glu-209, and Lys-211 in the 5-HT3AR can be exchanged between the homomeric 5-HT3AR and the muscle-type nAChR α-subunit with small functional consequences. Via triple mutant cycle analysis, we demonstrated that this triad forms an interdependent network in the muscle-type nAChR. Furthermore, nAChR-type mutations of the 5-HT3AR affect the affinity of nicotine, a competitive antagonist of 5-HT3ARs, in a cooperative manner. Using mutant cycle analyses between the 5-HT3A triad, loop A residues Asn-101 and Glu-102, β9 residue Lys-197, and the channel gate at Thr-257, we observed that residues in this region are energetically linked to the channel gate and are particularly sensitive to mutations that introduce a net positive charge. This study expands our understanding of the differences and similarities in the activation mechanisms of Cys-loop receptors.
Collapse
Affiliation(s)
- Richard Mosesso
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125
| | - Dennis A Dougherty
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125.
| |
Collapse
|
4
|
Synthesis and biological activities of indolizine derivatives as alpha-7 nAChR agonists. Eur J Med Chem 2016; 115:94-108. [PMID: 26994846 DOI: 10.1016/j.ejmech.2016.03.016] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Revised: 03/03/2016] [Accepted: 03/04/2016] [Indexed: 12/16/2022]
Abstract
Human α7 nicotinic acetylcholine receptor (nAChR) is a promising therapeutic target for the treatment of schizophrenia accompanied with cognitive impairment. Herein, we report the synthesis and agonistic activities of a series of indolizine derivatives targeting to α7 nAChR. The results show that all synthesized compounds have affinity to α7 nAChR and some give strong agonistic activity, particularly most active agonists show higher potency than control EVP-6124. The docking and structure-activity relationship studies provide insights to develop more potent novel α7 nAChR agonists.
Collapse
|
5
|
Zhang Q, Du Y, Zhang J, Xu X, Xue F, Guo C, Huang Y, Lukas RJ, Chang Y. Functional Impact of 14 Single Nucleotide Polymorphisms Causing Missense Mutations of Human α7 Nicotinic Receptor. PLoS One 2015; 10:e0137588. [PMID: 26340537 PMCID: PMC4560414 DOI: 10.1371/journal.pone.0137588] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2015] [Accepted: 08/18/2015] [Indexed: 01/17/2023] Open
Abstract
The α7nicotinic receptor (nAChR) is a major subtype of the nAChRs in the central nervous system, and the receptor plays an important role in brain function. In the dbSNP database, there are 55 single nucleotide polymorphisms (SNPs) that cause missense mutations of the human α7nAChR in the coding region. In this study, we tested the impact of 14 SNPs that cause missense mutations in the agonist binding site or the coupling region between binding site and channel gate on the receptor function. The wild type or mutant receptors were expressed or co-expressed in Xenopus oocytes, and the agonist-induced currents were tested using two-electrode voltage clamp. Our results demonstrated that 6 mutants were nonfunctional, 4 mutants had reduced current expression, and 1 mutants altered ACh and nicotine efficacy in the opposite direction, and one additional mutant had slightly reduced agonist sensitivity. Interestingly, the function of most of these nonfunctional mutants could be rescued by α7nAChR positive allosteric modulator PNU-120596 and agonist-PAM 4BP-TQS. Finally, when coexpressed with the wild type, the nonfunctional mutants could also influence the receptor function. These changes of the receptor properties by the mutations could potentially have an impact on the physiological function of the α7nAChR-mediated cholinergic synaptic transmission and anti-inflammatory effects in the human SNP carriers. Rescuing the nonfunctional mutants could provide a novel way to treat the related disorders.
Collapse
Affiliation(s)
- Qinhui Zhang
- Department of Zoology, College of Life Sciences, Sichuan University, Chengdu, Sichuan Province, 610064, China
- Chengdu institute of Biology, Chinese Academy of Sciences, Chengdu, Sichuan 610041, China
- Division of Neurobiology, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona 85013, United States of America
| | - Yingjie Du
- University of California Los Angeles, Henry Samueli School of Engineering and Applied Science, Los Angeles, California 90095, United States of America
| | - Jianliang Zhang
- Division of Neurobiology, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona 85013, United States of America
- Department of Neurobiology, Beijing Institute of Brain Disorders, Capital Medical University, Key Laboratory for Neurodegenerative Disease of the Ministry of Education, Beijing Center of Neural Regeneration and Repair, Beijing Key Laboratory of Brain Major Disorders; State Key Lab Incubation Base, Beijing Neuroscience Disciplines, Beijing 100069, China
| | - Xiaojun Xu
- Division of Neurobiology, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona 85013, United States of America
| | - Fenqin Xue
- Division of Neurobiology, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona 85013, United States of America
- Core Facilities for Electrophysiology, Core Facilities Center, Capital Medical University, Beijing 100069, China
| | - Cong Guo
- Department of Zoology, College of Life Sciences, Sichuan University, Chengdu, Sichuan Province, 610064, China
- Chengdu institute of Biology, Chinese Academy of Sciences, Chengdu, Sichuan 610041, China
| | - Yao Huang
- Department of Obstetrics and Gynecology, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona 85013, United States of America
| | - Ronald J. Lukas
- Division of Neurobiology, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona 85013, United States of America
| | - Yongchang Chang
- Division of Neurobiology, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona 85013, United States of America
- * E-mail:
| |
Collapse
|
6
|
Mazzaferro S, Gasparri F, New K, Alcaino C, Faundez M, Iturriaga Vasquez P, Vijayan R, Biggin PC, Bermudez I. Non-equivalent ligand selectivity of agonist sites in (α4β2)2α4 nicotinic acetylcholine receptors: a key determinant of agonist efficacy. J Biol Chem 2014; 289:21795-806. [PMID: 24936069 DOI: 10.1074/jbc.m114.555136] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The α4β2 nicotinic acetylcholine receptor (nAChR) is the most abundant nAChR type in the brain, and this receptor type exists in alternate (α4β2)2α4 and (α4β2)2β2 forms, which are activated by agonists with strikingly differing efficacies. Recent breakthroughs have identified an additional operational agonist binding site in the (α4β2)2α4 nAChR that is responsible for the signature sensitivity of this receptor to activation by agonists, yet the structural mechanisms determining agonist efficacy at this receptor type are not yet fully understood. In this study, we characterized the ligand selectivity of the individual agonist sites of the (α4β2)2α4 nAChR to determine whether differences in agonist selectivity influence agonist efficacy. Applying the substituted cysteine accessibility method to individual agonist sites in concatenated (α4β2)2α4 receptors, we determined the agonist selectivity of the agonist sites of the (α4β2)2α4 receptor. We show that (a) accessibility of substituted cysteines to covalent modification by methanesulfonate reagent depends on the agonist site at which the modification occurs and (b) that agonists such as sazetidine-A and TC-2559 are excluded from the site at the α4/α4 interface. Given that additional binding to the agonist site in the α4/α4 interface increases acetylcholine efficacy and that agonists excluded from the agonist site at the α4/α4 interface behave as partial agonists, we conclude that the ability to engage all agonist sites in (α4β2)2α4 nAChRs is a key determinant of agonist efficacy. The findings add another level of complexity to the structural mechanisms that govern agonist efficacy in heteromeric nAChRs and related ligand-gated ion channels.
Collapse
Affiliation(s)
- Simone Mazzaferro
- From the Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Gipsy Lane, Oxford OX3 0BP, United Kingdom
| | - Federica Gasparri
- From the Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Gipsy Lane, Oxford OX3 0BP, United Kingdom
| | - Karina New
- From the Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Gipsy Lane, Oxford OX3 0BP, United Kingdom
| | - Constanza Alcaino
- From the Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Gipsy Lane, Oxford OX3 0BP, United Kingdom
| | - Manuel Faundez
- the Department of Chemistry, Faculty of Sciences, University of Chile, Santiago, Chile
| | | | - Ranjit Vijayan
- Department of Biology, College of Science, United Arab Emirates University, Al Ain, United Arab Emirates, and
| | - Philip C Biggin
- Structural Bioinformatics and Computational Biochemistry, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Isabel Bermudez
- From the Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Gipsy Lane, Oxford OX3 0BP, United Kingdom,
| |
Collapse
|
7
|
Papke RL. Merging old and new perspectives on nicotinic acetylcholine receptors. Biochem Pharmacol 2014; 89:1-11. [PMID: 24486571 PMCID: PMC4755309 DOI: 10.1016/j.bcp.2014.01.029] [Citation(s) in RCA: 137] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Revised: 01/17/2014] [Accepted: 01/22/2014] [Indexed: 01/02/2023]
Abstract
This review covers history underlying the discovery of the molecular mediators of nicotine's effects in the brain and the diversity of the nicotinic acetylcholine receptor (nAChR) subtypes. Models are presented for both their structure and their function as mediators of signal transduction, with special consideration of the differences between the two main subtypes: heteromeric receptors, which are specialized for rapid electrochemical signal transduction, and homomeric α7 receptors, which have come to be implicated in both ionotropic and metabotropic signaling. This review presents perspectives on the pharmacology and therapeutic targeting of nAChRs for the treatment of nicotine dependence or disease.
Collapse
Affiliation(s)
- Roger L Papke
- Department of Pharmacology and Therapeutics, University of Florida, College of Medicine, PO Box 100267, 1200 Newell Drive, Gainesville, FL 32610-0267, USA.
| |
Collapse
|
8
|
Papke RL, Horenstein NA, Kulkarni AR, Stokes C, Corrie LW, Maeng CY, Thakur GA. The activity of GAT107, an allosteric activator and positive modulator of α7 nicotinic acetylcholine receptors (nAChR), is regulated by aromatic amino acids that span the subunit interface. J Biol Chem 2013; 289:4515-31. [PMID: 24362025 DOI: 10.1074/jbc.m113.524603] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
GAT107, the (+)-enantiomer of racemic 4-(4-bromophenyl)-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinoline-8-sulfonamide, is a strong positive allosteric modulator (PAM) of α7 nicotinic acetylcholine receptor (nAChR) activation by orthosteric agonists with intrinsic allosteric agonist activities. The direct activation produced by GAT107 in electrophysiological studies is observed only as long as GAT107 is freely diffusible in solution, although the potentiating activity primed by GAT107 can persist for over 30 min after drug washout. Direct activation is sensitive to α7 nAChR antagonist methyllycaconitine, although the primed potentiation is not. The data are consistent with GAT107 activity arising from two different sites. We show that the coupling between PAMs and the binding of orthosteric ligands requires tryptophan 55 (Trp-55), which is located at the subunit interface on the complementary surface of the orthosteric binding site. Mutations of Trp-55 increase the direct activation produced by GAT107 and reduce or prevent the synergy between allosteric and orthosteric binding sites, so that these mutants can also be directly activated by other PAMs such as PNU-120596 and TQS, which do not activate wild-type α7 in the absence of orthosteric agonists. We identify Tyr-93 as an essential element for orthosteric activation, because Y93C mutants are insensitive to orthosteric agonists but respond to GAT107. Our data show that both orthosteric and allosteric activation of α7 nAChR require cooperative activity at the interface between the subunits in the extracellular domain. These cooperative effects rely on key aromatic residues, and although mutations of Trp-55 reduce the restraints placed on the requirement for orthosteric agonists, Tyr-93 can conduct both orthosteric activation and desensitization among the subunits.
Collapse
Affiliation(s)
- Roger L Papke
- From the Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville, Florida 32610
| | | | | | | | | | | | | |
Collapse
|
9
|
Isaacson MD, Horenstein NA, Stokes C, Kem WR, Papke RL. Point-to-point ligand-receptor interactions across the subunit interface modulate the induction and stabilization of conformational states of alpha7 nAChR by benzylidene anabaseines. Biochem Pharmacol 2013; 85:817-28. [PMID: 23352650 DOI: 10.1016/j.bcp.2013.01.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2012] [Revised: 01/14/2013] [Accepted: 01/15/2013] [Indexed: 12/17/2022]
Abstract
The homomeric α7 nicotinic acetylcholine receptor is a well-studied therapeutic target, though its characteristically rapid desensitization complicates the development of drugs with specific agonist effects. Moreover, some experimental compounds such as GTS-21 (2,4diMeOBA), a derivative of the α7-selective partial agonist benzylidene anabaseine (BA), produce a prolonged residual desensitization (RD) in which the receptor remains non-activatable long after the drug has been removed from extracellular solution. In contrast, the desensitization caused by GTS-21's dihydroxy metabolite (2,4diOHBA) is relatively short-lived. RD is hypothetically due to stable binding of the ligand to the receptor in its desensitized state. We can attribute the reduction in RD to a single BA hydroxyl group on the 4' benzylidene position. Computational prediction derived from homology modeling showed the serine36 (S36) residue of α7 as a reasonable candidate for point-to-point interaction between BA compounds and the receptor. Through evaluating the activity of BA and simple derivatives on wild-type and mutant α7 receptors, it was observed that the drug-receptor pairs which were capable of hydrogen bonding at residue 36 exhibited significantly less stable desensitization. Further experiments involving the type II positive allosteric modulator (PAM) PNU-120596 showed that the various BA compounds' preference to induce either a PAM-sensitive (D(s)) or PAM-insensitive (D(i)) desensitized state is concentration dependent and suggested that both states are destabilized by S36 H-bonding. These results indicate that the fine-tuning of agonists for specific interaction with S36 can facilitate the development of therapeutics with targeted effects on ion channel desensitization properties and conformational state stability.
Collapse
Affiliation(s)
- Matthew D Isaacson
- Department of Pharmacology and Therapeutics, University of Florida College of Medicine, P.O. Box 100267, Gainesville, FL 32610, United States.
| | | | | | | | | |
Collapse
|
10
|
Williams DK, Wang J, Papke RL. Investigation of the molecular mechanism of the α7 nicotinic acetylcholine receptor positive allosteric modulator PNU-120596 provides evidence for two distinct desensitized states. Mol Pharmacol 2011; 80:1013-32. [PMID: 21885620 DOI: 10.1124/mol.111.074302] [Citation(s) in RCA: 96] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Although α7 nicotinic acetylcholine receptors are considered potentially important therapeutic targets, the development of selective agonists has been stymied by the α7 receptor's intrinsically low probability of opening (P(open)) and the concern that an agonist-based therapeutic approach would disrupt endogenous cholinergic function. Development of α7 positive allosteric modulators (PAMs) holds promise of avoiding both issues. N-(5-Chloro-2,4-dimethoxyphenyl)-N'-(5-methyl-3-isoxazolyl)-urea (PNU-120596) is one of the most effective α7 PAMs, with a mechanism associated, at least in part, with the destabilization of desensitized states. We studied the mechanism of PNU-120596 potentiation of α7 receptors expressed in Xenopus laevis oocytes and outside-out patches from BOSC 23 cells. We identify two forms of α7 desensitization: one is destabilized by PNU-120596 (D(s)), and the other is induced by strong episodes of activation and is stable in the presence of the PAM (D(i)). Our characterization of prolonged bursts of single-channel currents that occur with PNU-120596 provide a remarkable contrast to the behavior of the channels in the absence of the PAM. Individual channels that avoid the D(i) state show a 100,000-fold increase in P(open) compared with receptors in the nonpotentiated state. In the presence of PNU-120596, balance between D(s) and D(i) is dynamically regulated by both agonist and PAM binding, with maximal ion channel activity at intermediate levels of binding to both classes of sites. In the presence of high agonist concentrations, competitive antagonists may have the effect of shifting the balance in favor of D(s) and increasing ion channel currents.
Collapse
Affiliation(s)
- Dustin K Williams
- Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville, FL 32610-0267, USA
| | | | | |
Collapse
|
11
|
Williams DK, Stokes C, Horenstein NA, Papke RL. The effective opening of nicotinic acetylcholine receptors with single agonist binding sites. J Gen Physiol 2011; 137:369-84. [PMID: 21444659 PMCID: PMC3068282 DOI: 10.1085/jgp.201010587] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2010] [Accepted: 02/17/2011] [Indexed: 11/20/2022] Open
Abstract
We have identified a means by which agonist-evoked responses of nicotinic receptors can be conditionally eliminated. Modification of α7L119C mutants by the sulfhydryl reagent 2-aminoethyl methanethiosulfonate (MTSEA) reduces responses to acetylcholine (ACh) by more than 97%, whereas corresponding mutations in muscle-type receptors produce effects that depend on the specific subunits mutated and ACh concentration. We coexpressed α7L119C subunits with pseudo wild-type α7C116S subunits, as well as ACh-insensitive α7Y188F subunits with wild-type α7 subunits in Xenopus laevis oocytes using varying ratios of cRNA. When mutant α7 cRNA was coinjected at a 5:1 ratio with wild-type cRNA, net charge responses to 300 µM ACh were retained by α7L119C-containing mutants after MTSEA modification and by the ACh-insensitive Y188F-containing mutants, even though the expected number of ACh-sensitive wild-type binding sites would on average be fewer than two per receptor. Responses of muscle-type receptors with one MTSEA-sensitive subunit were reduced at low ACh concentrations, but much less of an effect was observed when ACh concentrations were high (1 mM), indicating that saturation of a single binding site with agonist can evoke strong activation of nicotinic ACh receptors. Single-channel patch clamp analysis revealed that the burst durations of fetal wild-type and α1β1γδL121C receptors were equivalent until the α1β1γδL121C mutants were exposed to MTSEA, after which the majority (81%) of bursts were brief (≤2 ms). The longest duration events of the receptors modified at only one binding site were similar to the long bursts of native receptors traditionally associated with the activation of receptors with two sites containing bound agonists.
Collapse
Affiliation(s)
- Dustin K. Williams
- Department of Pharmacology and Therapeutics, and Department of Chemistry, University of Florida, Gainesville, FL 32610
| | - Clare Stokes
- Department of Pharmacology and Therapeutics, and Department of Chemistry, University of Florida, Gainesville, FL 32610
| | - Nicole A. Horenstein
- Department of Pharmacology and Therapeutics, and Department of Chemistry, University of Florida, Gainesville, FL 32610
| | - Roger L. Papke
- Department of Pharmacology and Therapeutics, and Department of Chemistry, University of Florida, Gainesville, FL 32610
| |
Collapse
|
12
|
Brams M, Gay EA, Sáez JC, Guskov A, van Elk R, van der Schors RC, Peigneur S, Tytgat J, Strelkov SV, Smit AB, Yakel JL, Ulens C. Crystal structures of a cysteine-modified mutant in loop D of acetylcholine-binding protein. J Biol Chem 2010; 286:4420-8. [PMID: 21115477 DOI: 10.1074/jbc.m110.188730] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Covalent modification of α7 W55C nicotinic acetylcholine receptors (nAChR) with the cysteine-modifying reagent [2-(trimethylammonium)ethyl] methanethiosulfonate (MTSET(+)) produces receptors that are unresponsive to acetylcholine, whereas methyl methanethiolsulfonate (MMTS) produces enhanced acetylcholine-gated currents. Here, we investigate structural changes that underlie the opposite effects of MTSET(+) and MMTS using acetylcholine-binding protein (AChBP), a homolog of the extracellular domain of the nAChR. Crystal structures of Y53C AChBP show that MTSET(+)-modification stabilizes loop C in an extended conformation that resembles the antagonist-bound state, which parallels our observation that MTSET(+) produces unresponsive W55C nAChRs. The MMTS-modified mutant in complex with acetylcholine is characterized by a contracted C-loop, similar to other agonist-bound complexes. Surprisingly, we find two acetylcholine molecules bound in the ligand-binding site, which might explain the potentiating effect of MMTS modification in W55C nAChRs. Unexpectedly, we observed in the MMTS-Y53C structure that ten phosphate ions arranged in two rings at adjacent sites are bound in the vestibule of AChBP. We mutated homologous residues in the vestibule of α1 GlyR and observed a reduction in the single channel conductance, suggesting a role of this site in ion permeation. Taken together, our results demonstrate that targeted modification of a conserved aromatic residue in loop D is sufficient for a conformational switch of AChBP and that a defined region in the vestibule of the extracellular domain contributes to ion conduction in anion-selective Cys-loop receptors.
Collapse
Affiliation(s)
- Marijke Brams
- Laboratory of Structural Neurobiology, KULeuven, 3000 Leuven, Belgium
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
13
|
Cysteine accessibility analysis of the human alpha7 nicotinic acetylcholine receptor ligand-binding domain identifies L119 as a gatekeeper. Neuropharmacology 2010; 60:159-71. [PMID: 20650284 DOI: 10.1016/j.neuropharm.2010.07.014] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2010] [Revised: 07/06/2010] [Accepted: 07/13/2010] [Indexed: 01/09/2023]
Abstract
A large number of structurally diverse ligands have been produced to selectively target α7 nicotinic acetylcholine receptors (nAChRs). We applied the method of scanning cysteine accessibility mutations (SCAM) to the ligand-binding domain of the α7 nAChR to identify subdomains of particular importance to the binding and subsequent activation by select agonists. We evaluated the activity of four structurally distinct α7 agonists on wild-type human α7 and 44 targeted mutants expressed in Xenopus oocytes. Responses were measured prior and subsequent to the application of the sulfhydryl reagent methanethiosulfonate ethylammonium (MTSEA). One mutant (C116S) served as a Cys-null control, and the additional mutants were made in the C116S background. In many cases, the insertion of free cysteines into the agonist-binding site had a negative effect on function, with 12 of 44 mutants showing no detectable responses to ACh, and with only 19 of the 44 mutants showing sufficiently large responses to permit further study. Several of the cysteine mutations, including W55C, showed selectively reduced responses to the largest agonist tested, 2-methoxy,4-hydroxy-benzylidene anabaseine. Interestingly, although homology models suggest that most of the introduced cysteine mutations should have had good solvent accessibility, application of MTSEA had no effect or produced only modest changes in the agonist response profile of most mutants. Consistent with previous studies implicating W55 to play important roles in agonist activation, MTSEA treatment further decreased the functional responses of W55C to all the test agonists. While the cysteine mutation at L119 itself had relatively little effect on receptor function, treatment of L119C receptors with MTSEA or alternative cationic sulfhydryl reagents profoundly decreased activation by all agonists tested, suggesting a general block of gating. The homologous mutation in heteromeric nAChRs produced similar results, provided that the mutation was placed in the beta subunit complementary surface of the ligand-binding domain. Structural models locate the L119 residue directly across the subunit interface from the C-loop of the primary face of the binding domain. Our data suggest that a covalent modification of L119C by MTSEA or other cationic reagents might block the binding of even small agonists such as TMA through electrostatic interactions. Reaction of L119C with small non-polar reagents increases activation by small agonists but can block the access of large ligands such as benzylidene anabaseines to the ligand-binding domain.
Collapse
|
14
|
Iturriaga-Vásquez P, Carbone A, García-Beltrán O, Livingstone PD, Biggin PC, Cassels BK, Wonnacott S, Zapata-Torres G, Bermudez I. Molecular determinants for competitive inhibition of alpha4beta2 nicotinic acetylcholine receptors. Mol Pharmacol 2010; 78:366-75. [PMID: 20547737 DOI: 10.1124/mol.110.065490] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The Erythrina alkaloids erysodine and dihydro-beta-erythroidine (DHbetaE) are potent and selective competitive inhibitors of alpha4beta2 nicotinic acetylcholine receptors (nAChRs), but little is known about the molecular determinants of the sensitivity of this receptor subtype to inhibition by this class of antagonists. We addressed this issue by examining the effects of DHbetaE and a range of aromatic Erythrina alkaloids on [(3)H]cytisine binding and receptor function in conjunction with homology models of the alpha4beta2 nAChR, mutagenesis, and functional assays. The lactone group of DHbetaE and a hydroxyl group at position C-16 in aromatic Erythrina alkaloids were identified as major determinants of potency, which was decreased when the conserved residue Tyr126 in loop A of the alpha4 subunit was substituted by alanine. Sensitivity to inhibition was also decreased by substituting the conserved aromatic residues alpha4Trp182 (loop B), alpha4Tyr230 (loop C), and beta2Trp82 (loop D) and the nonconserved beta2Thr84; however, only alpha4Trp182 was predicted to contact bound antagonist, suggesting alpha4Tyr230, beta2Trp82, and beta2Thr84 contribute allosterically to the closed state elicited by bound antagonist. In addition, homology modeling predicted strong ionic interactions between the ammonium center of the Erythrina alkaloids and beta2Asp196, leading to the uncapping of loop C. Consistent with this, beta2D196A abolished sensitivity to inhibition by DHbetaE or erysodine but not by epierythratidine, which is not predicted to form ionic bonds with beta2Asp196. This residue is not conserved in subunits that comprise nAChRs with low sensitivity to inhibition by DHbetaE or erysodine, which highlights beta2Asp196 as a major determinant of the receptor selectivity of Erythrina alkaloids.
Collapse
|
15
|
Gao B, Hierl M, Clarkin K, Juan T, Nguyen H, van der Valk M, Deng H, Guo W, Lehto SG, Matson D, McDermott JS, Knop J, Gaida K, Cao L, Waldon D, Albrecht BK, Boezio AA, Copeland KW, Harmange JC, Springer SK, Malmberg AB, McDonough SI. Pharmacological effects of nonselective and subtype-selective nicotinic acetylcholine receptor agonists in animal models of persistent pain. Pain 2010; 149:33-49. [DOI: 10.1016/j.pain.2010.01.007] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2009] [Revised: 12/16/2009] [Accepted: 01/11/2010] [Indexed: 12/20/2022]
|
16
|
Sgrignani J, Bonaccini C, Grazioso G, Chioccioli M, Cavalli A, Gratteri P. Insights into docking and scoring neuronal alpha4beta2 nicotinic receptor agonists using molecular dynamics simulations and QM/MM calculations. J Comput Chem 2009; 30:2443-54. [PMID: 19360794 DOI: 10.1002/jcc.21251] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
A combined quantum mechanical (QM)-polarized docking and molecular dynamics approach to study the binding mode and to predict the binding affinity of ligands acting at the alpha4beta2-nAChR is presented. The results obtained in this study indicate that the quantum mechanical/molecular mechanics docking protocol well describes the charge-driven interactions occurring in the binding of nicotinic agonists, and it is able to represent the polarization effects on the ligand exerted by the surrounding atoms of the receptor at the binding site. This makes it possible to properly score agonists of alpha4beta2-nAChR and to reproduce the experimental binding affinity data with good accuracy, within a mean error of 2.2 kcal/mol. Moreover, applying the QM-polarized docking to an ensemble of nAChR conformations obtained from MD simulations enabled us to accurately capture nAChR-ligand induced-fit effects.
Collapse
Affiliation(s)
- Jacopo Sgrignani
- Laboratorio di Molecular Modeling, Cheminformatics and QSAR, Dipartimento di Scienze Farmaceutiche, Laboratorio di Progettazione, Sintesi e Studio di Eterocicli Biologicamente Attivi, Polo Scientifico, Università degli Studi di Firenze, Via Ugo Schiff, 6, 50019 Sesto Fiorentino (FI), Italy
| | | | | | | | | | | |
Collapse
|
17
|
López-Hernández GY, Thinschmidt JS, Morain P, Trocme-Thibierge C, Kem WR, Soti F, Papke RL. Positive modulation of alpha7 nAChR responses in rat hippocampal interneurons to full agonists and the alpha7-selective partial agonists, 4OH-GTS-21 and S 24795. Neuropharmacology 2009; 56:821-30. [PMID: 19705574 DOI: 10.1016/j.neuropharm.2009.01.011] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
One approach for the identification of therapeutic agents for Alzheimer's disease has focused on the research of alpha7 nAChR-selective agonists such as the partial agonists 3-(4-hydroxy,2-methoxybenzylidene)anabaseine (4OH-GTS-21) and, more recently, 2-[2-(4-bromophenyl)-2-oxoethyl]-1-methyl pyridinium (S 24795). An alternative approach for targeting alpha7 nAChR has been the development of positive modulators for this receptor. In this study we examined the interactions between full or partial agonists and positive modulators of alpha7 nAChRs in situ in brain tissue. Three positive modulators were used, 5-hydroxyindole (5-HI), 1-(5-chloro-2,4-dimethoxy-phenyl)-3-(5-methyl-isoxanol-3-yl)-urea (PNU-120596), and genistein. Whole-cell recordings were performed in stratum radiatum interneurons from rat brain slices. Hippocampal interneurons were stimulated by ACh, choline, S 24795, or 4OH-GTS-21, before and after bath perfusion with the positive modulators. 5-HI was not effective at potentiating 200 microM 4OH-GTS-21-evoked responses, however 5-HI induced a sustained potentiation of responses evoked by 30 microM 4OH-GTS-21. When 1 mM ACh and 200 microM 4OH-GTS-21 were applied alternately alpha7-mediated responses to both agonists were reduced, suggesting that high concentration of 4OH-GTS-21 produces residual inhibition or desensitization and that 5-HI is not effective at overcoming receptor desensitization. Similar results were obtained with alpha7 receptors expressed in Xenopus oocytes. Interestingly, responses evoked by S 24795 were potentiated by 5-HI but not by genistein. Additionally, PNU-120596 was able to potentiate alpha7-mediated responses, regardless of the nature of the agonist. We demonstrated that the potentiation of alpha7 nAChR response would depend on the nature and the effective concentration of the agonist involved and its particular interaction with the positive modulator.
Collapse
Affiliation(s)
- Gretchen Y López-Hernández
- Department of Pharmacology and Therapeutics, University of Florida, College of Medicine, Gainesville, FL 32610-0267, USA.
| | | | | | | | | | | | | |
Collapse
|
18
|
Nicotinic receptors: allosteric transitions and therapeutic targets in the nervous system. Nat Rev Drug Discov 2009; 8:733-50. [PMID: 19721446 DOI: 10.1038/nrd2927] [Citation(s) in RCA: 527] [Impact Index Per Article: 35.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Nicotinic receptors - a family of ligand-gated ion channels that mediate the effects of the neurotransmitter acetylcholine - are among the most well understood allosteric membrane proteins from a structural and functional perspective. There is also considerable interest in modulating nicotinic receptors to treat nervous-system disorders such as Alzheimer's disease, schizophrenia, depression, attention deficit hyperactivity disorder and tobacco addiction. This article describes both recent advances in our understanding of the assembly, activity and conformational transitions of nicotinic receptors, as well as developments in the therapeutic application of nicotinic receptor ligands, with the aim of aiding novel drug discovery by bridging the gap between these two rapidly developing fields.
Collapse
|
19
|
Williams DK, Stokes C, Horenstein NA, Papke RL. Differential regulation of receptor activation and agonist selectivity by highly conserved tryptophans in the nicotinic acetylcholine receptor binding site. J Pharmacol Exp Ther 2009; 330:40-53. [PMID: 19339660 DOI: 10.1124/jpet.109.151225] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have shown previously that a highly conserved Tyr in the nicotinic acetylcholine receptor (nAChR) ligand-binding domain (LBD) (alpha7 Tyr188 or alpha4 Tyr195) differentially regulates the activity of acetylcholine (ACh) and the alpha7-selective agonist 3-(4-hydroxy,2-methoxybenzylidene)anabaseine (4OH-GTS-21) in alpha4beta2 and alpha7 nAChR. In this study, we mutated two highly conserved LBD Trp residues in human alpha7 and alpha4beta2 and expressed the receptors in Xenopus laevis oocytes. Alpha7 receptors with Trp55 mutated to Gly or Tyr became less responsive to 4OH-GTS-21, whereas mutation of the homologous Trp57 in beta2 to Gly, Tyr, Phe, or Ala resulted in alpha4beta2 receptors that showed increased responses to 4OH-GTS-21. Mutation of alpha7 Trp55 to Val resulted in receptors for which the partial agonist 4OH-GTS-21 became equally efficacious as ACh, whereas alpha4beta2 receptors with the homologous mutation remained nonresponsive to 4OH-GTS-21. In contrast to the striking alterations in agonist activity profiles that were observed with mutations of alpha7 Trp55 and beta2 Trp57, mutations of alpha7 Trp149 or alpha4 Trp154 universally resulted in receptors with reduced function. Our data support the hypothesis that some conserved residues in the nAChR LBD differentially regulate receptor activation by subtype-selective agonists, whereas other equally well conserved residues play fundamental roles in receptor activation by any agonist. Residues like alpha7 Trp149 (alpha4 Trp154) may be considered pillars upon which basic receptor function depends, whereas alpha7 Trp55 (beta2 Trp57) and alpha7 Tyr188 (alpha4 Tyr195) may be fulcra upon which agonists may operate differentially in specific receptor subtypes, consistent with the hypothesis that ACh and 4OH-GTS-21 are able to activate nAChR in distinct ways.
Collapse
Affiliation(s)
- Dustin K Williams
- Department of Pharmacology and Therapeutics, University of Florida College of Medicine, P.O. Box 100267, Gainesville, FL 32610-0267, USA
| | | | | | | |
Collapse
|
20
|
Bernal JA, Mulet J, Castillo M, Criado M, Sala F, Sala S. Single-channel study of the binding-gating coupling in the slowly desensitizing chimeric α7-5HT3A receptor. FEBS Lett 2009; 583:1045-51. [DOI: 10.1016/j.febslet.2009.02.026] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2008] [Revised: 02/13/2009] [Accepted: 02/16/2009] [Indexed: 11/26/2022]
|
21
|
Papke RL, Kem WR, Soti F, López-Hernández GY, Horenstein NA. Activation and desensitization of nicotinic alpha7-type acetylcholine receptors by benzylidene anabaseines and nicotine. J Pharmacol Exp Ther 2009; 329:791-807. [PMID: 19223664 DOI: 10.1124/jpet.108.150151] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Nicotinic receptor activation is inextricably linked to desensitization. This duality affects our ability to develop useful therapeutics targeting nicotinic acetylcholine receptor (nAChR). Nicotine and some alpha7-selective experimental partial agonists produce a transient activation of alpha7 receptors followed by a period of prolonged residual inhibition or desensitization (RID). The object of the present study was to determine whether RID was primarily due to prolonged desensitization or due to channel block. To make this determination, we used agents that varied significantly in their production of RID and two alpha7-selective positive allosteric modulators (PAMs): 5-hydroxyindole (5HI), a type 1 PAM that does not prevent desensitization; and 1-(5-chloro-2,4-dimethoxy-phenyl)-3-(5-methyl-isoxanol-3-yl)-urea (PNU-120596), a type 2 PAM that reactivates desensitized receptors. The RID-producing compounds nicotine and 3-(2,4-dimethoxybenzylidene)anabaseine (diMeOBA) could obscure the potentiating effects of 5HI. However, through the use of nicotine, diMeOBA, and the RID-negative compound 3-(2,4-dihydroxybenzylidene)anabaseine (diOHBA) in combination with PNU-120596, we confirmed that diMeOBA produces short-lived channel block of alpha7 but that RID is because of the induction of a desensitized state that is stable in the absence of PNU-120596 and activated in the presence of PNU-120596. In contrast, diOHBA produced channel block but only readily reversible desensitization, whereas nicotine produced desensitization that could be converted into activation by PNU-120596 but no demonstrable channel block. Steady-state currents through receptors that would otherwise be desensitized could also be produced by the application of PNU-120596 in the presence of a physiologically relevant concentration of choline (60 microM), which may be significant for the therapeutic development of type 2 PAMs.
Collapse
Affiliation(s)
- Roger L Papke
- Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville, FL 32610-0267, USA.
| | | | | | | | | |
Collapse
|
22
|
Abstract
Voltage-clamp techniques are typically used to study the plasma membrane proteins, such as ion channels and transporters that control bioelectrical signals. Many of these proteins have been cloned and can now be studied as potential targets for drug development. The two approaches most commonly used for heterologous expression of cloned ion channels and transporters involve either transfection of the genes into small cells grown in tissue culture or the injection of the genetic material into larger cells. The standard large cells used for the expression of cloned cDNA or synthetic RNA are the egg progenitor cells (oocytes) of the African frog, Xenopus laevis. Until recently, cellular electrophysiology was performed manually by a single operator, one cell at a time. However, methods of high throughput electrophysiology have been developed which are automated and permit data acquisition and analysis from multiple cells in parallel. These methods are breaking a bottleneck in drug discovery, useful in some cases for primary screening as well as for thorough characterization of new drugs. Increasing throughput of high-quality functional data greatly augments the efficiency of academic research and pharmaceutical drug development. Some examples of studies that benefit most from high throughput electrophysiology include pharmaceutical screening of targeted compound libraries, secondary screening of identified compounds for subtype selectivity, screening mutants of ligand-gated channels for changes in receptor function, scanning mutagenesis of protein segments, and mutant-cycle analysis. We describe here the main features and potential applications of OpusXpress, an efficient commercially available system for automated recording from Xenopus oocytes. We show some types of data that have been gathered by this system and review realized and potential applications.
Collapse
Affiliation(s)
- Roger L Papke
- Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville, Florida, USA.
| | | |
Collapse
|
23
|
Bernal JA, Mulet J, Castillo M, Criado M, Sala S, Sala F. Binding-gating coupling in a nondesensitizing alpha7 nicotinic receptor A single channel pharmacological study. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1788:410-6. [PMID: 19063861 DOI: 10.1016/j.bbamem.2008.11.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2008] [Revised: 10/31/2008] [Accepted: 11/04/2008] [Indexed: 11/29/2022]
Abstract
The highly conserved alphaLys145 has been suggested to play an important role in the early steps of activation of the nicotinic acetylcholine receptor (nAChR) by acetylcholine. Both macroscopic and single channel currents were recorded in the slowly desensitizing mutants L248T- and K145A-L248T-alpha7 receptors expressed in Xenopus oocytes. On ACh-evoked currents, substitution of Lys145 by alanine showed the same effects that in wild type receptors: moderately decreased gating function and a more-than-expected loss of ACh potency, thus validating the experimental model. Single channel analysis quantitatively agreed with macroscopic data and revealed that impaired gating function in the double mutant alpha7K145A/L248T is the consequence of a slower opening rate, beta. Several nicotinic agonists were also studied, showing important features. Particularly, dimethylphenylpiperazinium (DMPP), acting as an antagonist in alpha7K145A, became a full agonist in alpha7K145A/L248T. Single channel analysis of DMPP-evoked currents showed effects of Lys145 removal similar to those observed with ACh. Data suggest that alpha7Lys145 facilitates the early steps of channel activation. Moreover, the slowly desensitizing mutant alpha7L248T could be an interesting tool for the study of channel activation in alpha7 receptors. Nevertheless, its extensively altered pharmacology precludes the simple extrapolation of pharmacological data obtained in singly mutated alpha7 receptors.
Collapse
Affiliation(s)
- José Antonio Bernal
- Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Sant Joan d'Alacant, 03550-Alicante, Spain
| | | | | | | | | | | |
Collapse
|
24
|
Huang X, Zheng F, Stokes C, Papke RL, Zhan CG. Modeling binding modes of alpha7 nicotinic acetylcholine receptor with ligands: the roles of Gln117 and other residues of the receptor in agonist binding. J Med Chem 2008; 51:6293-302. [PMID: 18826295 DOI: 10.1021/jm800607u] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Extensive molecular docking, molecular dynamics simulations, and binding free energy calculations have been performed to understand how alpha7-specific agonists of nicotinic acetylcholine receptor (nAChR), including AR-R17779 (1), GTS-21 (4), and 4-OH-GTS-21 (5), interact with the alpha7 receptor, leading to important new insights into the receptor-agonist binding. In particular, the cationic head of 4 and 5 has favorable hydrogen bonding and cation-pi interactions with residue Trp149. The computational results have also led us to better understand the roles of Gln117 and other residues in the receptor binding with agonists. The computational predictions are supported by data obtained from wet experimental tests. The new insights into the binding and structure-activity relationship obtained from this study should be valuable for future rational design of more potent and selective agonists of the alpha7 receptor.
Collapse
Affiliation(s)
- Xiaoqin Huang
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, 725 Rose Street, Lexington, Kentucky 40536, USA
| | | | | | | | | |
Collapse
|
25
|
Horenstein NA, Leonik FM, Papke RL. Multiple pharmacophores for the selective activation of nicotinic alpha7-type acetylcholine receptors. Mol Pharmacol 2008; 74:1496-511. [PMID: 18768388 DOI: 10.1124/mol.108.048892] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The activation of heteromeric and homomeric nicotinic acetylcholine receptors was studied in Xenopus laevis oocytes to identify key structures of putative agonist molecules associated with the selective activation of homomeric alpha7 receptors. We observed that selectivity between alpha7 and alpha4beta2 was more readily obtained than selectivity between alpha7 and alpha3beta4. Based on structural comparisons of previously characterized selective and nonselective agonists, we hypothesize at least three chemical motifs exist that, when present in molecules containing an appropriate cationic center, could be associated with the selective activation of alpha7 receptors. We identify the three distinct structural motifs based on prototypical drugs as the choline motif, the tropane motif, and the benzylidene motif. The choline motif involves the location of an oxygen-containing polar group such as a hydroxyl or carbonyl separated by two carbons from the charged nitrogen. The tropane motif provides alpha7-selectivity based on the addition of multiple small hydrophobic groups positioned away from the cationic center in specific orientations. We show that this motif can convert the nonselective agonists quinuclidine and ethyltrimethyl-ammonium to the alpha7-selective analogs methyl-quinuclidine and diethyldimethyl-ammonium, respectively. We have shown previously that the benzylidene group of 3-2,4, dimethoxy-benzylidene anabaseine (GTS-21) converts anabaseine into an alpha7-selective agonist. The benzylidene motif was also applied to quinuclidine to generate another distinct family of alpha7-selective agonists. Our results provide insight for the further development of nicotinic therapeutics and will be useful to direct future experiments with protein structure-based modeling and site-directed mutagenesis.
Collapse
Affiliation(s)
- Nicole A Horenstein
- Department of Pharmacology and Therapeutics, University of Florida, Gainesville, Florida 32610-0267, USA
| | | | | |
Collapse
|
26
|
Criado M, Mulet J, Castillo M, Aldea M, Sala S, Sala F. Interactions between loop 5 and beta-strand beta6' are involved in alpha7 nicotinic acetylcholine receptors channel gating. J Neurochem 2007; 104:719-30. [PMID: 17961148 DOI: 10.1111/j.1471-4159.2007.05010.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Binding of agonists to nicotinic acetylcholine receptors (nAChR) is coupled to channel opening through local rearrangements of different domains of the protein. Recent structural data suggest that two of these regions could be the loop 5 (L5) and the beta-strand beta6', both forming the inner part of the N-terminal domain. Amino acids in these domains were mutated in alpha7 nAChRs, and expression levels and functional responses of mutant receptors were measured. Mutations located at the putative apex of L5, Asp97 and Glu98, and also at Phe100, gave receptors with smaller currents, showing qualitative differences with respect to muscle nAChRs. In contrast, mutations in the beta-strand beta6' (at Phe124 and Lys125) showed increased functional responses. Mutations affected equally the responses to acetylcholine and dimethylphenylpiperazinium, except in Phe100 where the latter was sevenfold less effective than in wild-type. Currents in mutants decayed with almost the same kinetics, ruling out large effects on desensitization. Analysis of double mutants demonstrated a functional coupling among the three electrically charged amino acids Asp97, Glu98, and Lys125, and also between Phe100 and Phe124. The results are compatible with the involvement of functional interactions between L5 and beta-strand beta6' during nAChR activation.
Collapse
Affiliation(s)
- Manuel Criado
- Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Sant Joan d'Alacant, Alicante, Spain
| | | | | | | | | | | |
Collapse
|
27
|
Lerman C, LeSage MG, Perkins KA, O'Malley SS, Siegel SJ, Benowitz NL, Corrigall WA. Translational research in medication development for nicotine dependence. Nat Rev Drug Discov 2007; 6:746-62. [PMID: 17690709 DOI: 10.1038/nrd2361] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
A major obstacle to the development of medications for nicotine dependence is the lack of animal and human laboratory models with sufficient predictive clinical validity to support the translation of knowledge from laboratory studies to clinical research. This Review describes the animal and human laboratory paradigms commonly used to investigate the pathophysiology of nicotine dependence, and proposes how their predictive validity might be determined and improved, thereby enhancing the development of new medications.
Collapse
Affiliation(s)
- Caryn Lerman
- Department of Psychiatry and Abramson Cancer Center, University of Pennsylvania, 3535 Market Street, Suite 4100, Philadelphia, Pennsylvania 19104, USA.
| | | | | | | | | | | | | |
Collapse
|