Influence of GABAA receptor α subunit isoforms on the benzodiazepine binding site

Abstract

Classical benzodiazepines, such as diazepam, interact with αxβ2γ2 GABAA receptors, x = 1, 2, 3, 5 and modulate their function. Modulation of different receptor isoforms probably results in selective behavioural effects as sedation and anxiolysis. Knowledge of differences in the structure of the binding pocket in different receptor isoforms is of interest for the generation of isoform-specific ligands. We studied here the interaction of the covalently reacting diazepam analogue 3-NCS with α1S204Cβ2γ2, α1S205Cβ2γ2 and α1T206Cβ2γ2 and with receptors containing the homologous mutations in α2β2γ2, α3β2γ2, α5β1/2γ2 and α6β2γ2. The interaction was studied using radioactive ligand binding and at the functional level using electrophysiological techniques. Both strategies gave overlapping results. Our data allow conclusions about the relative apposition of α1S204Cβ2γ2, α1S205Cβ2γ2 and α1T206Cβ2γ2 and homologous positions in α2, α3, α5 and α6 with C-atom adjacent to the keto-group in diazepam. Together with similar data on the C-atom carrying Cl in diazepam, they indicate that the architecture of the binding site for benzodiazepines differs in each GABAA receptor isoform α1β2γ2, α2β2γ2, α3β2γ2, α5β1/2γ2 and α6β2γ2. © 2012 Lüscher et al.