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

Tijdschriftbijdrage - Tijdschriftartikel

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 system. Their dysfunction is implicated in a range of neurological disorders including depression, epilepsy and schizophrenia. Among the numerous assemblies that are theoretically possible, the most prevalent in the brain are the α1β2/3γ2 GABAA receptors. 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 neurons. 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 detergents. Notably, some recent cryo-electron microscopy reconstructions have reported ‘collapsed’ conformations; however, these disagree with the structure of the prototypical pentameric ligand-gated ion channel, the Torpedo nicotinic acetylcholine receptor, the large body of structural work on homologous homopentameric receptor variants 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 harbours 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.
Tijdschrift: Nature
ISSN: 0028-0836
Issue: 7740
Volume: 565
Pagina's: 516-520
Aantal pagina's: 5
Jaar van publicatie:2019
Trefwoorden:Allosteric Regulation, Amino Acid Sequence, Binding Sites, Cryoelectron Microscopy, Electric Conductivity, Humans, Lipid Bilayers/chemistry, Models, Molecular, Molecular Docking Simulation, Nanostructures/chemistry, Phosphatidylinositol 4,5-Diphosphate/chemistry, Protein Isoforms/chemistry, Protein Structure, Quaternary, Receptors, GABA-A/chemistry