Mapping a molecular link between allosteric inhibition and activation of the glycine receptor

Cys-loop ligand-gated ion channels mediate rapid neurotransmission throughout the central nervous system. They possess agonist recognition sites and allosteric sites where modulators regulate ion channel function. Using strychnine-sensitive glycine receptors, we identified a scaffold of hydrophobic residues enabling allosteric communication between glycine-agonist binding loops A and D, and the Zn2+-inhibition site. Mutating these hydrophobic residues disrupted Zn2+ inhibition, generating novel Zn2+-activated receptors and spontaneous channel activity. Homology modeling and electrophysiology revealed that these phenomena are caused by disruption to three residues on the '-' loop face of the Zn2+-inhibition site, and to D84 and D86, on a neighboring beta 3 strand, forming a Zn2+-activation site. We provide a new view for the activation of a Cys-loop receptor where, following agonist binding, the hydrophobic core and interfacial loops reorganize in a concerted fashion to induce downstream gating.