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Fabiani C, Biscussi B, Munafo JP, Murray AP, Corradi J, Antollini SS. NEW SYNTHETIC CAFFEINE ANALOGS AS MODULATORS OF THE CHOLINERGIC SYSTEM. Mol Pharmacol 2021; 101:154-167. [PMID: 34969831 DOI: 10.1124/molpharm.121.000415] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2021] [Accepted: 12/26/2021] [Indexed: 11/22/2022] Open
Abstract
Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder. Since cholinergic deficit is a major factor in this disease, two molecular targets for its treatment are the acetylcholinesterase (AChE) and the nicotinic acetylcholine receptors (nAChRs). Given that caffeine is a natural compound that behaves as an AChE inhibitor and as a partial agonist of nAChRs, the aim of this work was to synthetize more potent bifunctional caffeine analogs that modulate these two molecular targets. To this end, a theophylline structure was connected to a pyrrolidine structure through a methylene chain of different lengths (3 to 7 carbon atoms) to give compounds 7-11 All caffeine derivatives inhibited the AChE, of which compound 11 showed the strongest effect. Electrophysiological studies showed that all compounds behave as agonists of the muscle and the neuronal α7 nAChR with greater potency than caffeine. To explore if the different analogs could affect the nAChR conformational state, the nAChR conformational-sensitive probe crystal violet (CrV) was used. Compounds 9 and 10 conduced the nAChR to a different conformational state comparable with a control nAChR desensitized state. Finally, molecular docking experiments showed that all derivatives interacted with both the catalytic and anionic sites of AChE and with the orthosteric binding site of the nAChR. Thus, the new synthetized compounds can inhibit the AChE and activate muscle and α7 nAChRs with greater potency than caffeine, which suggests that they could be useful leaders for the development of new therapies for the treatment of different neurological diseases. Significance Statement In this work we synthetized caffeine derivatives which can inhibit the AChE and activate both muscle and α7 nAChRs with higher potency than caffeine. These analogs can be divided into two groups: a non-desensitizing and a desensitizing nAChR group. From the nAChR-non desensitizing group, we propose compound 11 as the most interesting analog for further studies since it inhibits AChE with the highest potency and activates the nAChRs in the picomolar range without inducing receptor desensitization.
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Affiliation(s)
- Camila Fabiani
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur y Consejo Nacional de Investigaciones Científicas y Técnicas, Camino La Carrindanga km 7, Argentina
| | - Brunella Biscussi
- Instituto de Química del Sur, Departamento de Química, Universidad Nacional del Sur y Consejo Nacional de Investigaciones Científicas y Técnicas, Av. Alem 1253, Argentina
| | - Juan Pablo Munafo
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur y Consejo Nacional de Investigaciones Científicas y Técnicas, Camino La Carrindanga km 7, Argentina
| | - Ana Paula Murray
- Instituto de Química del Sur, Departamento de Química, Universidad Nacional del Sur y Consejo Nacional de Investigaciones Científicas y Técnicas, Av. Alem 1253, Argentina
| | - Jeremias Corradi
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur y Consejo Nacional de Investigaciones Científicas y Técnicas, Camino La Carrindanga km 7, Argentina
| | - Silvia Susana Antollini
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur y Consejo Nacional de Investigaciones Científicas y Técnicas, Camino La Carrindanga km 7, Argentina
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Hénault CM, Baenziger JE. Functional characterization of two prokaryotic pentameric ligand-gated ion channel chimeras - role of the GLIC transmembrane domain in proton sensing. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1859:218-227. [PMID: 27845033 DOI: 10.1016/j.bbamem.2016.11.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2016] [Revised: 10/21/2016] [Accepted: 11/10/2016] [Indexed: 10/20/2022]
Abstract
With the long-term goal of using a chimeric approach to dissect the distinct lipid sensitivities and thermal stabilities of the pentameric ligand-gated ion channels (pLGIC), GLIC and ELIC, we constructed chimeras by cross-combining their extracellular (ECD) and transmembrane (TMD) domains. As expected, the chimera formed between GLIC-ECD and ELIC-TMD (GE) responded to protons, the agonist for GLIC, but not cysteamine, the agonist for ELIC, although GE exhibited a 25-fold decrease in proton-sensitivity relative to wild type. The chimera formed between ELIC-ECD and the GLIC-TMD (EG) was usually toxic, unless it contained a pore-lining Ile9'Ala gain-of-function mutation. No significant improvements in expression/toxicity were observed with extensive loop substitutions at the ECD/TMD interface. Surprisingly, oocytes expressing EG-I9'A responded to both the ELIC agonist, cysteamine and the GLIC agonist, protons - the latter at pH values ≤4.0. The cysteamine- and proton-induced currents in EG-I9'A were inhibited by the GLIC TMD pore blocker, amantadine. The cysteamine-induced response of EG-I9'A was also inhibited by protons at pH values down to 4.5, but potentiated at lower pH values. Proton-induced gating at low pH was not abolished by mutation of an intramembrane histidine residue previously implicated in GLIC TMD function. We show that the TMD plays a major role governing the thermal stability of a pLGIC, and identify three distinct mechanisms by which agonists and protons influence the gating of the EG chimera. A structural basis for the impaired function of GE is suggested.
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Affiliation(s)
- Camille M Hénault
- Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, 451 Smyth Rd, Ottawa, ON K1H 8M5, Canada
| | - John E Baenziger
- Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, 451 Smyth Rd, Ottawa, ON K1H 8M5, Canada.
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Carswell CL, Sun J, Baenziger JE. Intramembrane aromatic interactions influence the lipid sensitivities of pentameric ligand-gated ion channels. J Biol Chem 2014; 290:2496-507. [PMID: 25519904 DOI: 10.1074/jbc.m114.624395] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Although the Torpedo nicotinic acetylcholine receptor (nAChR) reconstituted into phosphatidylcholine (PC) membranes lacking cholesterol and anionic lipids adopts a conformation where agonist binding is uncoupled from channel gating, the underlying mechanism remains to be defined. Here, we examine the mechanism behind lipid-dependent uncoupling by comparing the propensities of two prokaryotic homologs, Gloebacter and Erwinia ligand-gated ion channel (GLIC and ELIC, respectively), to adopt a similar uncoupled conformation. Membrane-reconstituted GLIC and ELIC both exhibit folded structures in the minimal PC membranes that stabilize an uncoupled nAChR. GLIC, with a large number of aromatic interactions at the interface between the outermost transmembrane α-helix, M4, and the adjacent transmembrane α-helices, M1 and M3, retains the ability to flux cations in this uncoupling PC membrane environment. In contrast, ELIC, with a level of aromatic interactions intermediate between that of the nAChR and GLIC, does not undergo agonist-induced channel gating, although it does not exhibit the expected biophysical characteristics of the uncoupled state. Engineering new aromatic interactions at the M4-M1/M3 interface to promote effective M4 interactions with M1/M3, however, increases the stability of the transmembrane domain to restore channel function. Our data provide direct evidence that M4 interactions with M1/M3 are modulated during lipid sensing. Aromatic residues strengthen M4 interactions with M1/M3 to reduce the sensitivities of pentameric ligand-gated ion channels to their surrounding membrane environment.
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Affiliation(s)
- Casey L Carswell
- From the Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa Ontario, K1H 8M5, Canada
| | - Jiayin Sun
- From the Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa Ontario, K1H 8M5, Canada
| | - John E Baenziger
- From the Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa Ontario, K1H 8M5, Canada
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A distinct mechanism for activating uncoupled nicotinic acetylcholine receptors. Nat Chem Biol 2013; 9:701-7. [DOI: 10.1038/nchembio.1338] [Citation(s) in RCA: 82] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2012] [Accepted: 08/06/2013] [Indexed: 01/08/2023]
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Labriola JM, Pandhare A, Jansen M, Blanton MP, Corringer PJ, Baenziger JE. Structural sensitivity of a prokaryotic pentameric ligand-gated ion channel to its membrane environment. J Biol Chem 2013; 288:11294-303. [PMID: 23463505 DOI: 10.1074/jbc.m113.458133] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Although the activity of the nicotinic acetylcholine receptor (nAChR) is exquisitely sensitive to its membrane environment, the underlying mechanisms remain poorly defined. The homologous prokaryotic pentameric ligand-gated ion channel, Gloebacter ligand-gated ion channel (GLIC), represents an excellent model for probing the molecular basis of nAChR sensitivity because of its high structural homology, relative ease of expression, and amenability to crystallographic analysis. We show here that membrane-reconstituted GLIC exhibits structural and biophysical properties similar to those of the membrane-reconstituted nAChR, although GLIC is substantially more thermally stable. GLIC, however, does not possess the same exquisite lipid sensitivity. In particular, GLIC does not exhibit the same propensity to adopt an uncoupled conformation where agonist binding is uncoupled from channel gating. Structural comparisons provide insight into the chemical features that may predispose the nAChR to the formation of an uncoupled state.
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Affiliation(s)
- Jonathan M Labriola
- Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
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NMR structures of the transmembrane domains of the α4β2 nAChR. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1818:1261-8. [PMID: 22361591 DOI: 10.1016/j.bbamem.2012.02.008] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2011] [Revised: 01/30/2012] [Accepted: 02/07/2012] [Indexed: 11/21/2022]
Abstract
The α4β2 nicotinic acetylcholine receptor (nAChR) is the predominant heteromeric subtype of nAChRs in the brain, which has been implicated in numerous neurological conditions. The structural information specifically for the α4β2 and other neuronal nAChRs is presently limited. In this study, we determined structures of the transmembrane (TM) domains of the α4 and β2 subunits in lauryldimethylamine-oxide (LDAO) micelles using solution NMR spectroscopy. NMR experiments and size exclusion chromatography-multi-angle light scattering (SEC-MALS) analysis demonstrated that the TM domains of α4 and β2 interacted with each other and spontaneously formed pentameric assemblies in the LDAO micelles. The Na(+) flux assay revealed that α4β2 formed Na(+) permeable channels in lipid vesicles. Efflux of Na(+) through the α4β2 channels reduced intra-vesicle Sodium Green™ fluorescence in a time-dependent manner that was not observed in vesicles without incorporating α4β2. The study provides structural insight into the TM domains of the α4β2 nAChR. It offers a valuable structural framework for rationalizing extensive biochemical data collected previously on the α4β2 nAChR and for designing new therapeutic modulators.
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Franks WT, Linden AH, Kunert B, van Rossum BJ, Oschkinat H. Solid-state magic-angle spinning NMR of membrane proteins and protein-ligand interactions. Eur J Cell Biol 2011; 91:340-8. [PMID: 22019511 DOI: 10.1016/j.ejcb.2011.09.002] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2011] [Revised: 09/09/2011] [Accepted: 09/09/2011] [Indexed: 10/15/2022] Open
Abstract
Structural biology is developing into a universal tool for visualizing biological processes in space and time at atomic resolution. The field has been built by established methodology like X-ray crystallography, electron microscopy and solution NMR and is now incorporating new techniques, such as small-angle X-ray scattering, electron tomography, magic-angle-spinning solid-state NMR and femtosecond X-ray protein nanocrystallography. These new techniques all seek to investigate non-crystalline, native-like biological material. Solid-state NMR is a relatively young technique that has just proven its capabilities for de novo structure determination of model proteins. Further developments promise great potential for investigations on functional biological systems such as membrane-integrated receptors and channels, and macromolecular complexes attached to cytoskeletal proteins. Here, we review the development and applications of solid-state NMR from the first proof-of-principle investigations to mature structure determination projects, including membrane proteins. We describe the development of the methodology by looking at examples in detail and provide an outlook towards future 'big' projects.
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Affiliation(s)
- W Trent Franks
- Leibniz-Institut für Molekulare Pharmakologie (FMP), Robert Rössle Str. 10, 13125 Berlin, Germany
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