Full mutational mapping of titratable residues helps to identify proton-sensors involved in the control of channel gating in the Gloeobacter violaceus pentameric ligand-gated ion channel.

Catherine Van Renterghem,Marc Delarue,Ákos Nemecz,Pierre-Jean Corringer,Zaineb Fourati,Haidai Hu

doi:10.1371/journal.pbio.2004470

Catherine Van Renterghem, Marc Delarue + Show 4 more

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https://doi.org/10.1371/journal.pbio.2004470

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Journal: PLoS biology	Publication Date: Dec 27, 2017
Citations: 26	License type: CC BY 4.0

Affiliation: Institut Pasteur

Abstract

The Gloeobacter violaceus ligand-gated ion channel (GLIC) has been extensively studied by X-ray crystallography and other biophysical techniques. This provided key insights into the general gating mechanism of pentameric ligand-gated ion channel (pLGIC) signal transduction. However, the GLIC is activated by lowering the pH and the location of its putative proton activation site(s) still remain(s) unknown. To this end, every Asp, Glu, and His residue was mutated individually or in combination and investigated by electrophysiology. In addition to the mutational analysis, key mutations were structurally resolved to address whether particular residues contribute to proton sensing, or alternatively to GLIC-gating, independently of the side chain protonation. The data show that multiple residues located below the orthosteric site, notably E26, D32, E35, and D122 in the lower part of the extracellular domain (ECD), along with E222, H235, E243, and H277 in the transmembrane domain (TMD), alter GLIC activation. D122 and H235 were found to also alter GLIC expression. E35 is identified as a key proton-sensing residue, whereby neutralization of its side chain carboxylate stabilizes the active state. Thus, proton activation occurs allosterically to the orthosteric site, at the level of multiple loci with a key contribution of the coupling interface between the ECD and TMD.

Highlights

Pentameric ligand-gated ion channels are key players of neuronal communication
Pentameric ligand-gated ion channels are an important class of receptors that are involved in many neurological diseases
They promote either cell depolarization or hyperpolarization with the passive permeation of ions through an intrinsic channel, whose opening is stabilized by the binding of specific neurotransmitters. pentameric ligand-gated ion channel (pLGIC) are ubiquitously expressed in virtually all neurons, contribute to central nervous system functions, including sensory and motor processing, central autonomous control, memory and attention, sleep and wakefulness, reward, pain, anxiety, emotions, and cognition [1]

Summary

Introduction

Pentameric ligand-gated ion channels (pLGICs) are key players of neuronal communication They promote either cell depolarization or hyperpolarization with the passive permeation of ions through an intrinsic channel, whose opening is stabilized by the binding of specific neurotransmitters. At least one member of each major subfamily of vertebrate pLGICs has been structurally resolved in the recent years: a serotonergic receptor (5-HT3A, [2]) and a nicotinic acetylcholine receptor ([nAChR] α4β2-nAChR, [3]) from the cationic receptors, and a GABAergic receptor (β3-GABAA, [4]) and two glycinergic receptors ([GlyRs] α1- and α3-GlyRs, [5,6]) from the anionic receptors. The available structures of pLGICs support that the GLIC globally shares a common gating mechanism with its eukaryotic cousins, molecular details differ [1]

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