ANTAGONISM OF LIGAND-GATED ION CHANNEL RECEPTORS - 2 DOMAINS OF THE GLYCINE RECEPTOR ALPHA-SUBUNIT FORM THE STRYCHNINE-BINDING SITE

The inhibitory glycine receptor (GlyR) is a member of the ligand-gated ion channel receptor superfamily. Glycine activation of the receptor is antagonized by the convulsant alkaloid strychnine. Using in vitro mutagenesis and functional analysis of the cDNA encoding the al subunit of the human GlyR, we have identified several amino acid residues that form the strychnine-binding site. These residues were identified by transient expression of mutated cDNAs in mammalian (293) cells and examination of resultant [H-3]strychnine binding, glycine displacement of [H-3]strychnine, and electrophysiological responses to the application of glycine and strychnine. This mutational analysis revealed that residues from two separate domains within the alpha-1 subunit form the binding site for the antagonist strychnine. The first domain includes the amino acid residues Gly-160 and Tyr-161, and the second domain includes the residues Lys-200 and Tyr-202. These results, combined with analyses of other ligand-gated ion channel receptors, suggest a conserved tertiary structure and a common mechanism for antagonism in this receptor super family.