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

Nature. 2019 Jan;565(7740):516-520. doi: 10.1038/s41586-018-0833-4. Epub 2019 Jan 2.

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Allosteric Regulation
  • Amino Acid Sequence
  • Binding Sites
  • Cryoelectron Microscopy*
  • Electric Conductivity
  • Humans
  • Lipid Bilayers / chemistry*
  • Models, Molecular
  • Molecular Docking Simulation
  • Nanostructures / chemistry
  • Nanostructures / ultrastructure
  • Phosphatidylinositol 4,5-Diphosphate / chemistry
  • Phosphatidylinositol 4,5-Diphosphate / metabolism
  • Protein Isoforms / chemistry
  • Protein Isoforms / metabolism
  • Protein Isoforms / ultrastructure
  • Protein Structure, Quaternary
  • Receptors, GABA-A / chemistry*
  • Receptors, GABA-A / metabolism
  • Receptors, GABA-A / ultrastructure*

Substances

  • Lipid Bilayers
  • Phosphatidylinositol 4,5-Diphosphate
  • Protein Isoforms
  • Receptors, GABA-A