Illumination of a progressive allosteric mechanism mediating the glycine receptor activation

Pentameric ligand-gated ion channel mediate signal transduction at chemical synapses by transiting between resting and open states upon neurotransmitter binding. Here, we investigate the gating mechanism of the glycine receptor fluorescently labeled at the extracellular-transmembrane interface by voltage-clamp fluorometry (VCF). Fluorescence reports a glycine-elicited conformational change that precedes pore opening. Low concentrations of glycine, partial agonists or specific mixtures of glycine and strychnine trigger the full fluorescence signal while weakly activating the channel. Molecular dynamic simulations of a partial agonist bound-closed Cryo-EM structure show a highly dynamic nature: a marked structural flexibility at both the extracellular-transmembrane interface and the orthosteric site, generating docking properties that recapitulate VCF data. This work illuminates a progressive propagating transition towards channel opening, highlighting structural plasticity within the mechanism of action of allosteric effectors.

Automated summary

This study investigates the gating mechanism of the glycine receptor through voltage-clamp fluorometry (VCF). Fluorescence reports a glycine-induced conformational change that occurs before pore opening. Molecular dynamic simulations show the dynamic nature of a partial agonist bound-closed Cryo-EM structure, generating docking properties that recapitulate the VCF data. This research reveals the progressive propagating transition towards channel opening and highlights the structural plasticity within the mechanism of action of allosteric effectors.