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This article is part of the supplement: 18th Scientific Symposium of the Austrian Pharmacological Society (APHAR)

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Understanding subtype-selective allosteric modulation of GABAA receptors

Roshan Puthenkalam, Zdravko Varagić, Pantea Mirheydari, Werner Sieghart and Margot Ernst*

Author Affiliations

Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University of Vienna, 1090 Vienna, Austria

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BMC Pharmacology and Toxicology 2012, 13(Suppl 1):A26  doi:10.1186/2050-6511-13-S1-A26

The electronic version of this article is the complete one and can be found online at:

Published:17 September 2012

© 2012 Puthenkalam et al; licensee BioMed Central Ltd.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The γ-aminobutyric acid type A (GABAA) receptors are the major inhibitory neurotransmitter receptors of the central nervous system. Benzodiazepine (Bz)-site ligands bind at the α/γ interface and can enhance GABA-induced Cl currents. The efficacy of certain benzodiazepines strongly depends on the type of α(1,2,3,5) subunits in the receptors. Functionally selective compounds for α2/3 can be anxiolytic without having the side effect of sedation. The molecular basis for functional selectivity is investigated in this work.


Two-electrode voltage-clamp electrophysiology recordings were performed in wild-type and mutated receptors expressed in Xenopus laevis oocytes. Modelling, docking and molecular dynamics simulation studies of α1γ2 and α3γ2-containing receptors were performed to understand Bz-ligand interaction with the different α subunits.


Electrophysiology recordings identified flumazenil as a null modulator in α1 and a weak plus modulator in α3-containing receptors. A sequence comparison between the α1 and α3 subunit revealed the residue R228 as unique for the α3 subunit among all α subunits. α3R228A-mutated receptors completely lost their ability to respond to flumazenil. This amino acid is part of the so-called loop C, a several-residues-spanning segment that forms part of the ligand-binding site with a highly variable sequence. The functionally α3-selective ligand flumazenil was docked into the α/γ interface. The flumazenil-bound state in the α1 subtype has already been studied previously [1] and was used for comparison. Our results indicate that the binding mode of flumazenil in α1 and α3-containing receptors is very similar.


The models made in this study show improved properties in certain variable segments that could not be resolved in the previously published models [1]. For understanding the role of α3R228, more models and docking computations have to be made on the basis of these improvements to explore possible conformations.


This project is funded by FWF W1232 Molecular Drug Targets and the Medical University of Vienna.


  1. Richter L, de Graaf C, Sieghart W, Varagic Z, Mörzinger M, de Esch IJ, Ecker GF, Ernst M: Diazepam-bound GABAA receptor models identify new benzodiazepine binding-site ligands.

    Nat Chem Biol 2012, 8:455-464. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL