Influence of GABAA Receptor α Subunit Isoforms on the Benzodiazepine Binding Site

Classical benzodiazepines, such as diazepam, interact with alpha(x)beta(2)gamma(2) GABA(A) 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 alpha(1)S204C beta(2)gamma(2), alpha(1)S205C beta(2)gamma(2) and alpha(1)T206C beta(2)gamma(2) and with receptors containing the homologous mutations in alpha(2)beta(2)gamma(2), alpha(3)beta(2)gamma(2), alpha(5)beta(1/2)gamma(2) and alpha(6)beta(2)gamma(2). 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 alpha(1)S204C beta(2)gamma(2), alpha(1)S205C beta(2)gamma(2) and alpha(1)T206C beta(2)gamma(2) and homologous positions in alpha(2), alpha(3), alpha(5) and alpha(6) 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 alpha(1)beta(2)gamma(2), alpha(2)beta(2)gamma(2), alpha(3)beta(2)gamma(2), alpha(5)beta(1/2)gamma(2) and alpha(6)beta(2)gamma(2).