The β Subunit Determines the Ion Selectivity of the GABAAReceptor
Journal of Biological Chemistry
The ␥-aminobutyric acid, type A (GABA A ) receptor is a chloride-conducting receptor composed of ␣, ␤, and ␥ subunits assembled in a pentameric structure forming a central pore. Each subunit has a large extracellular agonist binding domain and four transmembrane domains (M1-M4), with the second transmembrane (M2) domain lining the pore. Mutation of five amino acids in the M1-M2 loop of the ␤ 3 subunit to the corresponding amino acids of the ␣ 7 nicotinic acetylcholine subunit rendered the GABA
... rendered the GABA A receptor cation-selective upon coexpression with wild type ␣ 2 and ␥ 2 subunits. Similar mutations in the ␣ 2 or ␥ 2 subunits did not lead to such a change in ion selectivity. This suggests a unique role for the ␤ 3 subunit in determining the ion selectivity of the GABA A receptor. The pharmacology of the mutated GABA A receptor is similar to that of the wild type receptor, with respect to muscimol binding, Zn 2؉ and bicuculline sensitivity, flumazenil binding, and potentiation of GABA-evoked currents by diazepam. There was, however, an increase in GABA sensitivity (EC 50 ؍ 1.3 M) compared with the wild type receptor (EC 50 ؍ 6.4 M) and a loss of desensitization to GABA of the mutant receptor. . 1 The abbreviations used are: GABA A R, ␥-aminobutyric acid receptor; M2, second transmembrane domain; TBPS, tert-butylbicyclophosphorothionate; NMDG, N-methyl-D-glucosamine; GlyR, glycine receptor; nAChR, nicotinic acetylcholine receptor; 5-HT 3 R, subtype of the 5-hydroxytryptamine receptors; wt, wild type; LGIC, ligand-gated ion channel; CHO, Chinese hamster ovary cells.