Agonist-Specific Conformational Changes in the alpha 1-gamma 2 Subunit Interface of the GABA(A) Receptor

作者：Eaton Megan M; Lim You Bin; Bracamontes John; Steinbach Joe Henry; Akk Gustav^*

来源：Molecular Pharmacology, 2012, 82(2): 255-263.

DOI：10.1124/mol.112.077875

The GABA(A) 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 used the substituted cysteine accessibility method and focused on the gamma 2(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 resting receptor to the modifying agent. Coapplication of GABA or muscimol, but not of gabazine, with MTSES prevented the effect, suggesting that GABA and muscimol elicit a conformational change that reduces access to the gamma 2(S195C) site. Exposure of the receptors to MTSES in the presence of the allosteric activators pentobarbital and etomidate resulted in an enhanced current response indicating accessibility and labeling of the gamma 2(S195C) site. However, comparison of the rates of modification indicated that labeling in the presence of etomidate was significantly faster than that in the presence of pentobarbital or gabazine or in resting receptors. We infer from the data that the structure of the alpha 1-gamma 2 subunit interface undergoes agonist-specific conformational changes.

• 出版日期2012-8