TY - JOUR T1 - Agonist-specific Conformational Changes in the Structure of the α1-γ2 Subunit Interface of the GABA<sub>A</sub> Receptor JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.112.077875 SP - mol.112.077875 AU - Megan Eaton AU - You Bin Lim AU - John Bracamontes AU - Joseph H. Steinbach AU - Gustav Akk Y1 - 2012/05/09 UR - http://molpharm.aspetjournals.org/content/early/2012/05/09/mol.112.077875.abstract N2 - The GABAA receptor undergoes conformational changes upon the binding of agonist that lead to the opening of the channel gate and a flow of small anions across the cell membrane. Besides the transmitter GABA, allosteric ligands such as the general anesthetics pentobarbital and etomidate can activate the receptor. Here, we have investigated the agonist-specificity of structural changes in the extracellular domain of the receptor. We employed the substituted cysteine accessibility method and focused on the γ2(S195C) site (Loop F). We show that modification of the site with (2-sulfonatoethyl)methanethiosulfonate (MTSES) results in an enhanced response to GABA, indicating accessibility of the S195C residue in the resting receptor to the modifying agent. Coapplication of GABA or muscimol, but not gabazine, with MTSES prevented the effect suggesting that GABA and muscimol elicit a conformational change that reduces access to the γ2(S195C) site. Exposure of the receptors to MTSES in the presence of the allosteric activators pentobarbital and etomidate resulted in enhanced current response indicating accessibility and labeling of the γ2(S195C) site. However, comparison of the rates of modification indicated that labeling in the presence of etomidate was significantly faster than in the presence of pentobarbital, gabazine or in resting receptors. Modification of the β2(I180C) site resulted in a small reduction in current response. The effect was eliminated when GABA, gabazine or etomidate, but not pentobarbital, were coapplied with MTSES. We infer from the data that the structure of the α1-γ2 subunit interface undergoes agonist-specific conformational changes. ER -