Cryo-EM structure of the human α1β3γ2 GABAA receptor in a lipid bilayer

  • Nature. 2019 Jan;565(7740):516-520. doi: 10.1038/s41586-018-0833-4.
Duncan Laverty  1 ,  Rooma Desai  2 ,  Tomasz Uchański  3  4 ,  Simonas Masiulis  5 ,  Wojciech J Stec  2 ,  Tomas Malinauskas  6 ,  Jasenko Zivanov  5 ,  Els Pardon  3  4 ,  Jan Steyaert  3  4 ,  Keith W Miller  7 ,  A Radu Aricescu  8  9
Affiliations
  • 1. MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge, UK. [email protected].
  • 2. Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
  • 3. Structural Biology Brussels, Vrije Universiteit Brussel (VUB), Brussels, Belgium.
  • 4. VIB-VUB Center for Structural Biology, VIB, Brussels, Belgium.
  • 5. MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge, UK.
  • 6. Division of Structural Biology, Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK.
  • 7. Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA. [email protected].
  • 8. MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge, UK. [email protected].
  • 9. Division of Structural Biology, Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK. [email protected].
PMID: 30602789 DOI: 10.1038/s41586-018-0833-4
Abstract

Type A γ-aminobutyric acid (GABAA) receptors are pentameric ligand-gated ion channels and the main drivers of fast inhibitory neurotransmission in the vertebrate nervous system1,2. Their dysfunction is implicated in a range of neurological disorders, including depression, epilepsy and schizophrenia3,4. Among the numerous assemblies that are theoretically possible, the most prevalent in the brain are the α1β2/3γ2 GABAA receptors5. The β3 subunit has an important role in maintaining inhibitory tone, and the expression of this subunit alone is sufficient to rescue inhibitory synaptic transmission in β1-β3 triple knockout neurons6. So far, efforts to generate accurate structural models for heteromeric GABAA receptors have been hampered by the use of engineered receptors and the presence of detergents7-9. Notably, some recent cryo-electron microscopy reconstructions have reported 'collapsed' conformations8,9; however, these disagree with the structure of the prototypical pentameric ligand-gated ion channel the Torpedo nicotinic acetylcholine receptor10,11, the large body of structural work on homologous homopentameric receptor variants12 and the logic of an ion-channel architecture. Here we present a high-resolution cryo-electron microscopy structure of the full-length human α1β3γ2L-a major synaptic GABAA receptor isoform-that is functionally reconstituted in lipid nanodiscs. The receptor is bound to a positive allosteric modulator 'megabody' and is in a desensitized conformation. Each GABAA receptor pentamer contains two phosphatidylinositol-4,5-bisphosphate molecules, the head groups of which occupy positively charged pockets in the intracellular juxtamembrane regions of α1 subunits. Beyond this level, the intracellular M3-M4 loops are largely disordered, possibly because interacting post-synaptic proteins are not present. This structure illustrates the molecular principles of heteromeric GABAA receptor organization and provides a reference framework for future mechanistic investigations of GABAergic signalling and pharmacology.