Cryo-EM structure of the benzodiazepine-sensitive α1β1γ2S tri-heteromeric GABA receptor in complex with GABA.

Fast inhibitory neurotransmission in the mammalian nervous system is largely mediated by GABA(A) receptors, chloride-selective members of the superfamily of pentameric Cysloop receptors. Native GABA(A) receptors are heteromeric assemblies sensitive to many important drugs, from sedatives to anesthetics and anticonvulsant agents, with mutant forms of GABA(A) receptors implicated in multiple neurological diseases. Despite the profound importance of heteromeric GABA(A) receptors in neuroscience and medicine, they have proven recalcitrant to structure determination. Here we present the structure of a tri-heteromeric alpha 1 beta 1 gamma 2S(EM) GABA(A) receptor in complex with GABA, determined by single particle cryo-EM at 3.1 - 3.8 angstrom resolution, elucidating molecular principles of receptor assembly and agonist binding. Remarkable N-linked glycosylation on the alpha 1 subunit occludes the extracellular vestibule of the ion channel and is poised to modulate receptor assembly and perhaps ion channel gating. Our work provides a pathway to structural studies of heteromeric GABA(A) receptors and a framework for rational design of novel therapeutic agents.