Cryo-EM structure of the benzodiazepine-sensitive α1β1γ2 heterotrimeric GABAA receptor in complex with GABA illuminates mechanism of receptor assembly and agonist binding

Abstract

Fast 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 many important drugs, from sedatives to anesthetics and anticonvulsive agents, with mutant forms of GABAA receptors 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}2EM GABAA receptor in complex with GABA, determined by single particle cryo-EM at 3.1-3.8 [A] resolution, elucidating the molecular principles of receptor assembly and agonist binding. Remarkable N-linked glycosylation on the 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 GABAA receptors and a framework for the rational design of novel therapeutic agents.