Structure of Ionotropic Glutamate Receptors

Abstract

By 1987, all of the major ligand-gated ion-channel families had succumbed to cloning efforts, with one notable exception, the glutamate receptors. Acetylcholine receptors had been cloned first, aided by the fact that these proteins bind α-bungarotoxin with high specificity and affinity, and that they are highly concentrated in the muscle tissue of the electric fish Torpedo californica and Torpedo marmorata. This had allowed protein purification followed by partial microsequencing (Devillers-Thiery et al. 1979; Raftery et al. 1980) as well as generation of antibodies (Tzartos and Lindstrom 1980). The resulting information and analytical tools, in turn, had been used to screen cDNA libraries with amino acid sequence-derived oligonucleotide probes and antibodies which, in 1982, had led to the isolation of the first cDNA clones for acetylcholine receptors (BALLIVET et al. 1982; Giraudat et al. 1982; Noda et al. 1982; Sumikawa et al. 1982). A glycine receptor cDNA had been isolated in 1987 by taking advantage of the specific high-affinity binding of the competitive antagonist strychnine to the receptor. This allowed isolation and partial microsequencing of a strychnine-binding protein (Pfeiffer et al. 1982), providing sequence information to construct specific oligonucleotide probes, which were then used to isolate the glycine receptor cDNA (Grenningloh et al. 1987). γ-Aminobutyric acid (GABA)A receptors were also cloned in 1987, via low-stringency hybridization screening based on oligonucleotide sequence derived from the partial amino acid sequence of a protein purified by benzodiazepine-affinity chromatography (Schofield et al. 1987).