scholarly journals X-Ray Crystallographic Studies for Revealing Binding Sites of General Anesthetics in Pentameric Ligand-Gated Ion Channels

2018 ◽  
pp. 21-47 ◽  
Author(s):  
Qiang Chen ◽  
Yan Xu ◽  
Pei Tang
Keyword(s):  
Ion Channels ◽  
Binding Sites ◽  
General Anesthetics ◽  
X Ray ◽  
Gated Ion Channels ◽  
Ligand Gated Ion Channels

Ligand-gated ion channels as targets of neuroactive insecticides

2021 ◽  
Author(s):  
Makoto Ihara
Keyword(s):  
Ion Channels ◽  
Molecular Mechanisms ◽  
Functional Expression ◽  
X Ray ◽  
Acetylcholine Binding Protein ◽  
Site Selectivity ◽  
Future Drug ◽  
Cl Channels ◽  
Gated Ion Channels ◽  
Ligand Gated Ion Channels

Abstract The Cys-loop superfamily of ligand-gated ion channels (Cys-loop receptors) is one of the most ubiquitous ion channel families in vertebrates and invertebrates. Despite their ubiquity, they are targeted by several classes of pesticides, including neonicotinoids, phenylpyrazols, and macrolides such as ivermectins. The current commercialized compounds have high target site selectivity, which contributes to the safety of insecticide use. Structural analyses have accelerated progress in this field; notably, the X-ray crystal structures of acetylcholine binding protein and glutamate-gated Cl channels revealed the details of the molecular interactions between insecticides and their targets. Recently, the functional expression of the insect nicotinic acetylcholine receptor (nAChR) has been described, and detailed evaluations using the insect nAChR have emerged. This review discusses the basic concepts and the current insights into the molecular mechanisms of neuroactive insecticides targeting the ligand-gated ion channels, particularly Cys-loop receptors, and presents insights into target-based selectivity, resistance, and future drug design.

Effects of Gaseous Anesthetics Nitrous Oxide and Xenon on Ligand-gated Ion Channels

2000 ◽  
Vol 93 (4) ◽  
pp. 1095-1101 ◽  
Author(s):  
Tomohiro Yamakura ◽  
R. Adron Harris
Keyword(s):  
Nitrous Oxide ◽  
Ion Channels ◽  
Nmda Receptors ◽  
Glutamate Receptors ◽  
Gabaa Receptors ◽  
Receptor Type ◽  
Gamma Aminobutyric Acid ◽  
General Anesthetics ◽  
Gated Ion Channels ◽  
Ligand Gated Ion Channels

Background Ligand-gated ion channels are considered to be potential general anesthetic targets. Although most general anesthetics potentiate the function of gamma-aminobutyric acid receptor type A (GABAA), the gaseous anesthetics nitrous oxide and xenon are reported to have little effect on GABAA receptors but inhibit N-methyl-d-aspartate (NMDA) receptors. To define the spectrum of effects of nitrous oxide and xenon on receptors thought to be important in anesthesia, the authors tested these anesthetics on a variety of recombinant brain receptors. Methods The glycine, GABAA, GABA receptor type C (GABAC), NMDA, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA), kainate, 5-hydroxytryptamine3 (5-HT3), and nicotinic acetylcholine (nACh) receptors were expressed in Xenopus oocytes and effects of nitrous oxide and xenon, and as equipotent concentrations of isoflurane and ethanol, were studied using the two-electrode voltage clamp. Results Nitrous oxide (0.58 atmosphere [atm]) and xenon (0.46 atm) exhibited similar effects on various receptors. Glycine and GABAA receptors were potentiated by gaseous anesthetics much less than by isoflurane, whereas nitrous oxide inhibited GABAC receptors. Glutamate receptors were inhibited by gaseous anesthetics more markedly than by isoflurane, but less than by ethanol. NMDA receptors were the most sensitive among glutamate receptors and were inhibited by nitrous oxide by 31%. 5-HT3 receptors were slightly inhibited by nitrous oxide. The nACh receptors were inhibited by gaseous and volatile anesthetics, but ethanol potentiated them. The sensitivity was different between alpha4beta2 and alpha4beta4 nACh receptors; alpha4beta2 receptors were inhibited by nitrous oxide by 39%, whereas alpha4beta4 receptors were inhibited by 7%. The inhibition of NMDA and nACh receptors by nitrous oxide was noncompetitive and was slightly different depending on membrane potentials for NMDA receptors, but not for nACh receptors. Conclusions Nitrous oxide and xenon displayed a similar spectrum of receptor actions, but this spectrum is distinct from that of isoflurane or ethanol. These results suggest that NMDA receptors and nACh receptors composed of beta2 subunits are likely targets for nitrous oxide and xenon.

scholarly journals Probing Pentameric Ligand-Gated Ion Channels with Bromoform Reveals Many Interconnected Anesthetic Binding Sites

2014 ◽  
Vol 106 (2) ◽  
pp. 342a
Author(s):  
Benoist Laurent ◽  
Samuel Murail ◽  
Ludovic Sauguet ◽  
Marc Delarue ◽  
Marc Baaden
Keyword(s):  
Ion Channels ◽  
Binding Sites ◽  
Gated Ion Channels ◽  
Ligand Gated Ion Channels

scholarly journals A Functionally Conserved Mechanism of Modulation via a Vestibule Site in Pentameric Ligand-Gated Ion Channels

2019 ◽  
Author(s):  
Marijke Brams ◽  
Cedric Govaerts ◽  
Kumiko Kambara ◽  
Kerry Price ◽  
Radovan Spurny ◽  
...  
Keyword(s):  
Ion Channels ◽  
Binding Site ◽  
Binding Sites ◽  
Allosteric Modulators ◽  
Channel Opening ◽  
Single Domain Antibodies ◽  
Allosteric Binding Sites ◽  
Target Binding ◽  
Gated Ion Channels ◽  
Ligand Gated Ion Channels

ABSTRACTPentameric ligand-gated ion channels (pLGICs) belong to a class of ion channels involved in fast synaptic signaling in the central and peripheral nervous systems. Molecules acting as allosteric modulators target binding sites that are remote from the neurotransmitter binding site, but functionally affect coupling of ligand binding to channel opening. Here, we investigated an allosteric binding site in the ion channel vestibule, which has converged from a series of studies on prokaryote and eukaryote channel homologs. We discovered single domain antibodies, called nanobodies, which are functionally active as allosteric modulators, and solved co-crystal structures of the prokaryote channel ELIC bound either to a positive (PAM) or a negative (NAM) allosteric modulator. We extrapolate the functional importance of the vestibule binding site to eukaryote ion channels, suggesting a conserved mechanism of allosteric modulation. This work identifies key elements of allosteric binding sites and extends drug design possibilities in pLGICs using nanobodies.

General Anesthetics Modify the Kinetics of Nicotinic Acetylcholine Receptor Desensitization at Clinically Relevant Concentrations 

1995 ◽  
Vol 82 (1) ◽  
pp. 276-287 ◽  
Author(s):  
Douglas E. Raines ◽  
Saffron E. Rankin ◽  
Keith W. Miller
Keyword(s):  
Ion Channels ◽  
Acetylcholine Receptor ◽  
Nicotinic Acetylcholine Receptor ◽  
Electric Organ ◽  
General Anesthetics ◽  
Nicotinic Acetylcholine ◽  
Rate Processes ◽  
Kinetics Of ◽  
Gated Ion Channels ◽  
Ligand Gated Ion Channels

Background General anesthetics are thought to induce anesthesia through their actions on ligand-gated ion channels. One such channel, the nicotinic acetylcholine receptor (nAcChoR), can be found in different subtypes in the central nervous system and at the periphery in the neuromuscular junction. The latter subtype of the nAcChoR is a useful model for examining interactions between general anesthetics and ligand-gated ion channels, because it can be isolated and purified in sufficient quantities to allow for biophysical and biochemical studies. This study examines the actions of general anesthetics on agonist-induced conversion of the nAcChoR to inactive desensitized conformational states. Methods Nicotinic acetylcholine receptor membranes were purified from the electric organ of Torpedo nobiliana. Agonist-induced desensitization was characterized from the time-dependent increase in fluorescence intensity that results from the binding of the fluorescent acetylcholine analog, Dns-C6-Cho, to the nAcChoR. Results Mixing Dns-C6-Cho with nAcChoR-rich membranes results in an increase in fluorescence that is characterized by four rate processes. Concentrations of isoflurane and butanol, which range from subclinical to toxic increase the rates of the third and fourth components of fluorescence, corresponding to fast and slow desensitization, respectively. At concentrations that are twice their EC50s for anesthesia, isoflurane, butanol, chloroform, methanol, and cyclopentanemethanol increase the apparent rates of fast and slow desensitization by an average of 92 +/- 22% and 108 +/- 22%, respectively. Conclusions The concentration range over which general anesthetics modify the kinetics of nAcChoR desensitization is similar to those reported for anesthetic actions on the GABAA receptor. Thus, the nAcChoR, like other members of this superfamily, is a sensitive target of general anesthetics.

scholarly journals Common Anesthetic-binding Site for Inhibition of Pentameric Ligand-gated Ion Channels

2016 ◽  
Vol 124 (3) ◽  
pp. 664-673 ◽  
Author(s):  
Monica N. Kinde ◽  
Weiming Bu ◽  
Qiang Chen ◽  
Yan Xu ◽  
Roderic G. Eckenhoff ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Ion Channels ◽  
Magnetic Resonance ◽  
Binding Sites ◽  
Molecular Mechanisms ◽  
Transmembrane Domain ◽  
Functional Responses ◽  
Nuclear Magnetic ◽  
Gated Ion Channels ◽  
Ligand Gated Ion Channels

Abstract Background Identifying functionally relevant anesthetic-binding sites in pentameric ligand-gated ion channels (pLGICs) is an important step toward understanding the molecular mechanisms underlying anesthetic action. The anesthetic propofol is known to inhibit cation-conducting pLGICs, including a prokaryotic pLGIC from Erwinia chrysanthemi (ELIC), but the sites responsible for functional inhibition remain undetermined. Methods We photolabeled ELIC with a light-activated derivative of propofol (AziPm) and performed fluorine-19 nuclear magnetic resonance experiments to support propofol binding to a transmembrane domain (TMD) intrasubunit pocket. To differentiate sites responsible for propofol inhibition from those that are functionally irrelevant, we made an ELIC-γ-aminobutyric acid receptor (GABAAR) chimera that replaced the ELIC-TMD with the α1β3GABAAR-TMD and compared functional responses of ELIC-GABAAR and ELIC with propofol modulations. Results Photolabeling showed multiple AziPm-binding sites in the extracellular domain (ECD) but only one site in the TMD with labeled residues M265 and F308 in the resting state of ELIC. Notably, this TMD site is an intrasubunit pocket that overlaps with binding sites for anesthetics, including propofol, found previously in other pLGICs. Fluorine-19 nuclear magnetic resonance experiments supported propofol binding to this TMD intrasubunit pocket only in the absence of agonist. Functional measurements of ELIC-GABAAR showed propofol potentiation of the agonist-elicited current instead of inhibition observed on ELIC. Conclusions The distinctly different responses of ELIC and ELIC-GABAAR to propofol support the functional relevance of propofol binding to the TMD. Combining the newly identified TMD intrasubunit pocket in ELIC with equivalent TMD anesthetic sites found previously in other cationic pLGICs, we propose this TMD pocket as a common site for anesthetic inhibition of pLGICs.

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