Cryo-EM structure of the benzodiazepine-sensitive {alpha}1{beta}1{gamma}2 heterotrimeric GABAA receptor in complex with GABA illuminates mechanism of receptor assembly and agonist binding

Inhibitory neurotransmission in the mammalian nervous system is largely mediated by GABAA receptors, chloride-selective members of the superfamily of pentameric Cys-loop receptors. Native GABAA receptors are heteromeric assemblies sensitive to a tremendous array of important drugs, from sedatives to anesthetics and anticonvulsive agents, and mutant forms of GABAA receptors are implicated in multiple neurological diseases, including epilepsy. Despite the profound importance of heteromeric GABAA receptors in neuroscience and medicine, they have proven recalcitrant to structure determination. Here we present the structure of the triheteromeric 1{beta}1{gamma}2 GABAA receptor in complex with GABA, determined by single particle cryo-EM at 3.1-3.5 [A] resolution. The structure elucidates the molecular principles of receptor assembly and agonist binding as well as showing how remarkable N-linked glycosylation on the 1 subunit occludes the extracellular vestibule of the ion channel and is poised to modulate receptor gating and assembly. Our work provides a pathway to structural studies of heteromeric GABAA receptors and thus a framework for the rational design of novel therapeutic agents.