Volume 13 Supplement 1

18th Scientific Symposium of the Austrian Pharmacological Society (APHAR)

Open Access

Understanding subtype-selective allosteric modulation of GABAAreceptors

  • Roshan Puthenkalam1,
  • Zdravko Varagić1,
  • Pantea Mirheydari1,
  • Werner Sieghart1 and
  • Margot Ernst1Email author
BMC Pharmacology and Toxicology201213(Suppl 1):A26

DOI: 10.1186/2050-6511-13-S1-A26

Published: 17 September 2012

Background

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.

Methods

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.

Results

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.

Conclusions

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.

Declarations

Acknowledgements

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

Authors’ Affiliations

(1)
Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University of Vienna

References

  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 CentralView ArticlePubMedGoogle Scholar

Copyright

© Puthenkalam et al; licensee BioMed Central Ltd. 2012

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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