title: Agonist-specific conformational changes in the α1-γ2 subunit interface of the GABA A receptor.
abstract: 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 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 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 γ2(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 γ2(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 α1-γ2 subunit interface undergoes agonist-specific conformational changes.
authors.affiliation: Department of Anesthesiology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110, USA. akk@morpheus.wustl.edu
authors.forename: Megan M
authors.initials: MM
authors.lastname: Eaton
authors.forename: You Bin
authors.initials: YB
authors.lastname: Lim
authors.forename: John
authors.initials: J
authors.lastname: Bracamontes
authors.forename: Joe Henry
authors.initials: JH
authors.lastname: Steinbach
authors.forename: Gustav
authors.initials: G
authors.lastname: Akk
mesh_terms: D000818:Animals; D005260:Female; D058785:GABA-A Receptor Agonists / Q000378:metabolism* / Q000494:pharmacology; D009154:Mutation; D011485:Protein Binding / Q000187:drug effects; D011487:Protein Conformation / Q000187:drug effects; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D011963:Receptors, GABA-A / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis; D005680:gamma-Aminobutyric Acid / Q000378:metabolism / Q000494:pharmacology
chemical_list: D058785:GABA-A Receptor Agonists; C546242:Gabra1 protein, rat; C546281:Gabrg2 protein, rat; D021122:Protein Subunits; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid