title: Interactions of L-3,5,3'-Triiodothyronine [corrected], Allopregnanolone, and Ivermectin with the GABAA Receptor: Evidence for Overlapping Intersubunit Binding Modes.
abstract: Structural mechanisms of modulation of γ-aminobutyric acid (GABA) type A receptors by neurosteroids and hormones remain unclear. The thyroid hormone L-3,5,3'-triiodothyronine (T3) inhibits GABAA receptors at micromolar concentrations and has common features with neurosteroids such as allopregnanolone (ALLOP). Here we use functional experiments on α2β1γ2 GABAA receptors expressed in Xenopus oocytes to detect competitive interactions between T3 and an agonist (ivermectin, IVM) with a crystallographically determined binding site at subunit interfaces in the transmembrane domain of a homologous receptor (glutamate-gated chloride channel, GluCl). T3 and ALLOP also show competitive effects, supporting the presence of both a T3 and ALLOP binding site at one or more subunit interfaces. Molecular dynamics (MD) simulations over 200 ns are used to investigate the dynamics and energetics of T3 in the identified intersubunit sites. In these simulations, T3 molecules occupying all intersubunit sites (with the exception of the α-β interface) display numerous energetically favorable conformations with multiple hydrogen bonding partners, including previously implicated polar/acidic sidechains and a structurally conserved deformation in the M1 backbone.
authors.affiliation: Department of Neuroscience, Thomas Jefferson University, Philadelphia, Pennsylvania, United States of America; Center for Computational and Integrative Biology, Rutgers University-Camden, Camden, New Jersey, United States of America.
authors.forename: Thomas
authors.initials: T
authors.lastname: Westergard
authors.affiliation: Center for Computational and Integrative Biology, Rutgers University-Camden, Camden, New Jersey, United States of America; Department of Physics, Rutgers University-Camden, Camden, New Jersey, United States of America.
authors.forename: Reza
authors.initials: R
authors.lastname: Salari
authors.affiliation: Center for Computational and Integrative Biology, Rutgers University-Camden, Camden, New Jersey, United States of America; Department of Biology, Rutgers University-Camden, Camden, New Jersey, United States of America.
authors.forename: Joseph V
authors.initials: JV
authors.lastname: Martin
authors.affiliation: Center for Computational and Integrative Biology, Rutgers University-Camden, Camden, New Jersey, United States of America; Department of Physics, Rutgers University-Camden, Camden, New Jersey, United States of America.
authors.forename: Grace
authors.initials: G
authors.lastname: Brannigan
mesh_terms: D000494:Allosteric Regulation / Q000187:drug effects; D000818:Animals; D001667:Binding, Competitive; D004347:Drug Interactions; D055724:Electrophysiological Phenomena / Q000187:drug effects; D005260:Female; D058787:GABA-A Receptor Antagonists / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D007559:Ivermectin / Q000378:metabolism* / Q000494:pharmacology; D008051:Lipid Bilayers / Q000378:metabolism; D062105:Molecular Docking Simulation; D056004:Molecular Dynamics Simulation; D011280:Pregnanolone / Q000378:metabolism* / Q000494:pharmacology; D011485:Protein Binding; D011487:Protein Conformation; D021122:Protein Subunits / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D011963:Receptors, GABA-A / Q000737:chemistry / Q000378:metabolism*; D013816:Thermodynamics; D014284:Triiodothyronine / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D058787:GABA-A Receptor Antagonists; D008051:Lipid Bilayers; D021122:Protein Subunits; D011963:Receptors, GABA-A; D014284:Triiodothyronine; D007559:Ivermectin; D011280:Pregnanolone