Fig. 4.

Epibatidine stabilization to the α2 ECD and comparison with homologous structures. (A and B) Close-up view of the aromatic cage. Residues are shown in green sticks, principal side backbone is colored in red and the complementary side is in cyan. Hydrogen bonds between residues and epibatidine are shown in black dashed lines (A), the 2Fo-Fc electron density contoured at 1.4-σ level attributed to epibatidine is shown in blue mesh (B). (C) Backbone superposition of a single subunit of α2 ECD (in green) with the other epibatidine-bound structures: α7-AChBP chimera (in cyan) and Ac-AChBP (in orange). Despite the similar conformation of loops A–C among the three structures, the epibatidine molecule (Epi) in α2-Epi structure is slightly rotated toward loop C. However, the overall binding motif is not altered.