Mechanism of action of our key compound α5-SOP002
From computational modelling, we showed that α5-SOP002 docked into the interface of the α5 and γ2 subunits, indicating that it works via the benzodiazepine binding site (composed of a γ2 and either α1, α2, α3 or an α5 subunit of the GABAAR). Normally, binding of benzodiazepines to these sites causes a conformational change of the receptor increasing the receptor’s affinity for GABA, resulting in an enhanced inhibitory (hyperpolarising) effect mediated via Cl- flux (Sieghart, 1995). However, NAMs, such as α5-SOP002, when bound to the same GABAAR sub-typesdecrease the influx of Cl- which leads to depolarisation of the membrane and a decreased net inhibitory effect (Haefely et al., 1993). The data obtained from various HEK cell-lines constructed to contain specific GABAAR subunits and electrophysiological recordings performed, provided evidence to suggest that the developed compound, α5-SOP0002 specifically acted as a negative allosteric modulator at α5 GABAARs and had no effect on α1 or α2 subunit-containing GABAARs. However, this does not preclude an action of α5-SOP0002 as a NAM in native GABAARs where the synaptic colocalisation of the α subunits could result from a combination of the insertion of either two identical α subunits, or from insertion of a single receptor sub-type that contains two different α subunits. The α subunit that is adjacent to the γ2 subunit dominates the pharmacological profile of the receptor as suggested previously by binding studies on double immunopurified α1/α5 GABAARs (Araujo et al., 1999). Thus, we suggest that α5-SOP002 acts by specifically binding at the interface of α5 and γ2 subunits, which determines a unique pharmacological profile of this compound.