Figure 2.

Model structure indicating amino acid residues important for binding of CGS 9895 into the α⁺β⁻ interface. The structural model of the α⁺ side and the β⁻ side is based on the glutamate bound structure of the glutamate gated chloride channel (Hibbs and Gouaux, 2011), PDB entry 3RIF. This new template shares the highest sequence similarity with GABA_A receptors of all available homologous crystal structures. Modeller was used for modelling, VMD for visualization. (http://salilab.org/modeller/; http://www.ks.uiuc.edu/Research/vmd/) Residues used in steric hindrance experiments are shown in yellow label, and those affecting ligand potency or efficacy upon mutagenesis are shown in gray labels. All shown residues were individually mutated into cysteines. For α1S204C, α1V211C and β3Q64C the effect of CGS9895 on the mutant receptor was nearly unchanged, and cysteine modification with MTSEA-biotin drastically reduced ligand efficacy (Ramerstorfer et al., 2011). The mutations α1H101C and α1F99C induced a strong reduction of the ligand effect. Mutations α1S205C, α1T206C and β3A45C caused an increased potency of CGS 9895. These data strongly indicate that the binding site is structurally similar to the benzodiazepine binding site as identical or homologous residues are involved in ligand effects.