Allosteric Modulation of Ligand Gated Ion Channels by Ivermectin

Ivermectin acts as a positive allosteric regulator of several ligand-gated channels including the glutamate-gated chloride channel (GluCl),  aminobutyric acid type-A receptor, glycine receptor, neuronal α7-nicotinic receptor and purinergic P2X4 receptor. In most of the ivermectin-sensitive channels, the effects of ivermectin include the potentiation of agonist-induced currents at low concentrations and channel opening at higher concentrations. Based on mutagenesis, electrophysiological recordings and functional analysis of chimeras between ivermectin-sensitive and ivermectin-insensitive receptors, it has been concluded that ivermectin acts by insertion between transmembrane helices. The three-dimensional structure of C. elegans GluCl complexed with ivermectin has revealed the details of the ivermectin-binding site, however, no generic motif of amino acids could accurately predict ivermectin binding site for other ligand gated channels. Here, we will review what is currently known about ivermectin binding and modulation of Cys-loop receptor family of ligand-gated ion channels and what are the critical structural determinants underlying potentiation of the P2X4 receptor channel.

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Structural elements involved in activation of the γ-aminobutyric acid type A (GABAA) receptor

Biochemical Society Transactions ◽

10.1042/bst0320540 ◽

2004 ◽

Vol 32 (3) ◽

pp. 540-546 ◽

Cited By ~ 45

Author(s):

T.L. Kash ◽

J.R. Trudell ◽

N.L. Harrison

Keyword(s):

Ion Channels ◽

Ion Channel ◽

Binding Site ◽

Type A ◽

Aminobutyric Acid ◽

Structural Elements ◽

Agonist Binding ◽

Acid Type ◽

Gated Ion Channels ◽

Ligand Gated Ion Channels

Ligand-gated ion channels function as rapid signal transducers, converting chemical signals (in the form of neurotransmitters) into electrical signals in the postsynaptic neuron. This is achieved by the recognition of neurotransmitter at its specific-binding sites, which then triggers the opening of an ion channel (‘gating’). For this to occur rapidly (<1 ms), there must be an efficient coupling between the agonist-binding site and the gate, located more than 30 Å (1 Å=0.1 nm) away. Whereas a great deal of progress has been made in elucidating the structure and function of both the agonist-binding site and the ion permeation pathway in ligand-gated ion channels, our knowledge of the coupling mechanism between these domains has been limited. In this review, we summarize recent studies of the agonist-binding site and the ion channel in the γ-aminobutyric acid type A receptor, and discuss those structural elements that may mediate coupling between them. We will also consider some possible molecular mechanisms of receptor activation.

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Conserved quaternary structure of ligand-gated ion channels: the postsynaptic glycine receptor is a pentamer.

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.85.19.7394 ◽

1988 ◽

Vol 85 (19) ◽

pp. 7394-7398 ◽

Cited By ~ 256

Author(s):

D. Langosch ◽

L. Thomas ◽

H. Betz

Keyword(s):

Ion Channels ◽

Quaternary Structure ◽

Glycine Receptor ◽

Gated Ion Channels ◽

Ligand Gated Ion Channels

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

10.1101/770719 ◽

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.

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Identifying the elusive link between amino acid sequence and charge selectivity in pentameric ligand-gated ion channels

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1608519113 ◽

2016 ◽

Vol 113 (45) ◽

pp. E7106-E7115 ◽

Cited By ~ 15

Author(s):

Gisela D. Cymes ◽

Claudio Grosman

Keyword(s):

Ion Channels ◽

Careful Analysis ◽

Side Chains ◽

Electrophysiological Recordings ◽

Charge Selectivity ◽

The Many ◽

Backbone Atoms ◽

Charge Sign ◽

Gated Ion Channels ◽

Ligand Gated Ion Channels

Among neurotransmitter-gated ion channels, the superfamily of pentameric ligand-gated ion channels (pLGICs) is unique in that its members display opposite permeant-ion charge selectivities despite sharing the same structural fold. Although much effort has been devoted to the identification of the mechanism underlying the cation-versus-anion selectivity of these channels, a careful analysis of past work reveals that discrepancies exist, that different explanations for the same phenomenon have often been put forth, and that no consensus view has yet been reached. To elucidate the molecular basis of charge selectivity for the superfamily as a whole, we performed extensive mutagenesis and electrophysiological recordings on six different cation-selective and anion-selective homologs from vertebrate, invertebrate, and bacterial origin. We present compelling evidence for the critical involvement of ionized side chains—whether pore-facing or buried—rather than backbone atoms and propose a mechanism whereby not only their charge sign but also their conformation determines charge selectivity. Insertions, deletions, and residue-to-residue mutations involving nonionizable residues in the intracellular end of the pore seem to affect charge selectivity by changing the rotamer preferences of the ionized side chains in the first turn of the M2 α-helices. We also found that, upon neutralization of the charged residues in the first turn of M2, the control of charge selectivity is handed over to the many other ionized side chains that decorate the pore. This explains the long-standing puzzle as to why the neutralization of the intracellular-mouth glutamates affects charge selectivity to markedly different extents in different cation-selective pLGICs.

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Chasing the open-state structure of pentameric ligand-gated ion channels

The Journal of General Physiology ◽

10.1085/jgp.201711803 ◽

2017 ◽

Vol 149 (12) ◽

pp. 1119-1138 ◽

Cited By ~ 21

Author(s):

Giovanni Gonzalez-Gutierrez ◽

Yuhang Wang ◽

Gisela D. Cymes ◽

Emad Tajkhorshid ◽

Claudio Grosman

Keyword(s):

Ion Channels ◽

Open Channel ◽

Glycine Receptor ◽

Structural Models ◽

Channel Structure ◽

Ion Permeation ◽

Charge Selectivity ◽

State Models ◽

Gated Ion Channels ◽

Ligand Gated Ion Channels

Remarkable advances have been made toward the structural characterization of ion channels in the last two decades. However, the unambiguous assignment of well-defined functional states to the obtained structural models has proved challenging. In the case of the superfamily of nicotinic-receptor channels (also referred to as pentameric ligand-gated ion channels [pLGICs]), for example, two different types of model of the open-channel conformation have been proposed on the basis of structures solved to resolutions better than 4.0 Å. At the level of the transmembrane pore, the open-state models of the proton-gated pLGIC from Gloeobacter violaceus (GLIC) and the invertebrate glutamate-gated Cl– channel (GluCl) are very similar to each other, but that of the glycine receptor (GlyR) is considerably wider. Indeed, the mean distances between the axis of ion permeation and the Cα atoms at the narrowest constriction of the pore (position −2′) differ by ∼2 Å in these two classes of model, a large difference when it comes to understanding the physicochemical bases of ion conduction and charge selectivity. Here, we take advantage of the extreme open-channel stabilizing effect of mutations at pore-facing position 9′. We find that the I9′A mutation slows down entry into desensitization of GLIC to the extent that macroscopic currents decay only slightly by the end of pH 4.5 solution applications to the extracellular side for several minutes. We crystallize (at pH 4.5) two variants of GLIC carrying this mutation and solve their structures to resolutions of 3.12 Å and 3.36 Å. Furthermore, we perform all-atom molecular dynamics simulations of ion permeation and picrotoxinin block, using the different open-channel structural models. On the basis of these results, we favor the notion that the open-channel structure of pLGICs from animals is much closer to that of the narrow models (of GLIC and GluCl) than it is to that of the GlyR.

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