Pentameric ligand-gated ion channel ELIC is activated by GABA and modulated by benzodiazepines

Abstract

GABA A receptors are pentameric ligand-gated ion channels involved in fast inhibitory neurotransmission and are allosterically modulated by the anxiolytic, anticonvulsant, and sedative-hypnotic benzodiazepines. Here we show that the prokaryotic homolog ELIC also is activated by GABA and is modulated by benzodiazepines with effects comparable to those at GABA A receptors. Crystal structures reveal important features of GABA recognition and indicate that benzodiazepines, depending on their concentration, occupy two possible sites in ELIC. An intrasubunit site is adjacent to the GABA-recognition site but faces the channel vestibule. A second intersubunit site partially overlaps with the GABA site and likely corresponds to a low-affinity benzodiazepine-binding site in GABA A receptors that mediates inhibitory effects of the benzodiazepine flurazepam. Our study offers a structural view how GABA and benzodiazepines are recognized at a GABA-activated ion channel.

Subunit stoichiometry and arrangement in a heteromeric glutamate-gated chloride channel

“…1A). These Glu-binding sites are homologous to the neurotransmitter/agonist-binding sites of other Cys-loop receptors (1,2,24), bacterial homologs of Cys-loop receptors (25)(26)(27)(28)(29)(30), and ACh-binding proteins (31)(32)(33)(34).…”

Allosteric binding site in a Cys-loop receptor ligand-binding domain unveiled in the crystal structure of ELIC in complex with chlorpromazine

“…In this study, we take advantage of the ELIC, a prokaryote homolog of vertebrate Cys-loop receptors, which is activated by primary amine molecules, including GABA (36,37). The availability of several relatively high-resolution X-ray cocrystal structures of ELIC in complex with known ligands renders this channel a relevant model for the study of Cys-loop receptor modulation (36,(38)(39)(40)(41)(42).…”

Asymmetric perturbations of signalling oligomers

“…3 and a recent review of Nys et al, 2013). Even though these homopentamers have proven to be good pLGIC models (Spurny et al, 2012), crystallization in the presence of saturating ligand concentrations has resulted in XRC structures with open or closed pore states not compatible with the functional effects of cocrystallized ligands (Gonzalez-Gutierrez et al, 2012). Furthermore, the XRC structures have revealed a perplexing heterogeneity of inter-and intra-subunit binding cavities both for anaesthetics in the TM domain and for benzodiazepines in the EC domain (Spurny et al, 2012;Spurny et al, 2013).…”

“…Even though these homopentamers have proven to be good pLGIC models (Spurny et al, 2012), crystallization in the presence of saturating ligand concentrations has resulted in XRC structures with open or closed pore states not compatible with the functional effects of cocrystallized ligands (Gonzalez-Gutierrez et al, 2012). Furthermore, the XRC structures have revealed a perplexing heterogeneity of inter-and intra-subunit binding cavities both for anaesthetics in the TM domain and for benzodiazepines in the EC domain (Spurny et al, 2012;Spurny et al, 2013). For ELIC, a pharmacologically relevant model of GABA A R potentiation, in the presence of potentiating, low benzodiazepine concentrations, XRC has yielded a structure with occupancy of only one intrasubunit EC binding site adjacent to a GABA-binding interface (Spurny et al, 2012).…”

“…Furthermore, the XRC structures have revealed a perplexing heterogeneity of inter-and intra-subunit binding cavities both for anaesthetics in the TM domain and for benzodiazepines in the EC domain (Spurny et al, 2012;Spurny et al, 2013). For ELIC, a pharmacologically relevant model of GABA A R potentiation, in the presence of potentiating, low benzodiazepine concentrations, XRC has yielded a structure with occupancy of only one intrasubunit EC binding site adjacent to a GABA-binding interface (Spurny et al, 2012).…”