Sodium ions allosterically modulate the M2 muscarinic receptor

Sheli Friedman,Yair Ben-Chaim,Merav Tauber

doi:10.1038/s41598-020-68133-9

Sheli Friedman, Yair Ben-Chaim + Show 1 more

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https://doi.org/10.1038/s41598-020-68133-9

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Journal: Scientific Reports	Publication Date: Jul 7, 2020
Citations: 12	License type: open-access

Affiliation: Open University of Israel

Abstract

G protein coupled receptors (GPCRs) play a key role in the vast majority of cellular signal transduction processes. Previous experimental evidence has shown that sodium ion (Na+) allosterically modulate several class A GPCRs and theoretical studies suggested that the same also holds true for muscarinic receptors. Here we examined, using Xenopus oocytes as an expression system, the effect of Na+ on a prototypical GPCR, the M2 muscarinic receptor (M2R). We found that removal of extracellular Na+ resulted in a decrease in the potency of ACh toward the M2R and that a conserved aspartate in transmembrane domain 2 is crucial for this effect. We further show that this allosteric effect of Na+ does not underlie the voltage-dependence of this receptor.

Highlights

G protein coupled receptors (GPCRs) play a key role in the vast majority of cellular signal transduction processes
The binding of a ligand to a GPCR stabilizes an active conformation of the receptor, which in turn triggers the activation of G proteins, leading to a cascade of cellular responses
To investigate whether extracellular Na+ ([Na+]o) affect the potency of ACh toward the M2R we used, similar to previous studies[19], Xenopus Laevis oocytes as an expression system

Summary

Introduction

G protein coupled receptors (GPCRs) play a key role in the vast majority of cellular signal transduction processes. These biochemical studies were corroborated more recently by structural studies of some GPCRs, such as of the A2a adenosine receptor[5], the β1 adrenergic receptor[6] and the δ opioid receptor[7] These studies provided evidence for the existence of Na+ in a defined binding site located in the helical bundle of these receptors, with a conserved aspartate in position 2.50 (Ballesteros and Weinstein n umbering8) playing a role in Na+ binding. GPCRs have been shown to be regulated by membrane p otential[19,20,21,22,23,24] (reviewed in25) For two of these receptors, the M1R and the M2R, depolarization was found to induce charge movement, which was suggested to underlie the voltage-dependence of agonist b inding[26,27,28,29]. Recent studies have proposed that movement of N a+ from its binding site is the source of the charge movement associated currents in these receptor and thereby their voltage-dependence[17,18]

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