Resolving native GABA_A receptor structures from the human brain

Type A GABA (γ-aminobutyric acid) receptors (GABA_A receptors) mediate most fast inhibitory signalling in the brain and are targets for drugs that treat epilepsy, anxiety, depression and insomnia and for anaesthetics^1,2. These receptors comprise a complex array of 19 related subunits, which form pentameric ligand-gated ion channels. The composition and structure of native GABA_A receptors in the human brain have been inferred from subunit localization in tissue^1,3, functional measurements and structural analysis from recombinant expression^4-7 and in mice⁸. However, the arrangements of subunits that co-assemble physiologically in native human GABA_A receptors remain unknown. Here we isolated α1 subunit-containing GABA_A receptors from human patients with epilepsy. Using cryo-electron microscopy, we defined a set of 12 native subunit assemblies and their 3D structures. We address inconsistencies between previous native and recombinant approaches, and reveal details of previously undefined subunit interfaces. Drug-like densities in a subset of these interfaces led us to uncover unexpected activity on the GABA_A receptor of antiepileptic drugs and resulted in localization of one of these drugs to the benzodiazepine-binding site. Proteomics and further structural analysis suggest interactions with the auxiliary subunits neuroligin 2 and GARLH4, which localize and modulate GABA_A receptors at inhibitory synapses. This work provides a structural foundation for understanding GABA_A receptor signalling and targeted pharmacology in the human brain.