Molecular determinants for G protein βγ modulation of ionotropic glycine receptors

The ligand-gated ion channel superfamily plays a critical role in neuronal excitability. The functions of glycine receptor ( GlyR) and nicotinic acetylcholine receptor are modulated by G protein beta gamma subunits. The molecular determinants for this functional modulation, however, are still unknown. Studying mutant receptors, we identified two basic amino acid motifs within the large intracellular loop of the GlyR alpha(1) subunit that are critical for binding and functional modulation by G beta gamma. Mutations within these sequences demonstrated that all of the residues detected are important for G beta gamma modulation, although both motifs are necessary for full binding. Molecular modeling predicts that these sites are alpha-helixes near transmembrane domains 3 and 4, near to the lipid bilayer and highly electropositive. Our results demonstrate for the first time the sites for G protein beta gamma subunit modulation on GlyRs and provide a new framework regarding the ligand-gated ion channel superfamily regulation by intracellular signaling.