Fig. 3. Orthosteric binding pocket of active α_2AAR bound to different agonists.

(A) Alignment of four structures of α_2AAR signaling complexes. (B) Superposition of Norepi, BRI, DEX, and OXY from cryo-EM structures. The imidazole moiety is highlighted by the dashed circle. (C to F) Detailed interactions of Norepi (C), BRI (D), DEX (E), and OXY (F) with α_2AAR. Residues within 4 Å of agonist are shown in sticks. The polar interactions are indicated by black dashed lines. (G) Superposition of the α_2AAR orthosteric binding pocket residues bound to four different agonists. (H and I) Concentration-response curves of different agonists for G protein activation (H) and β-arrestin-2 recruitment (I) for wild-type (wt) α_2AAR and receptor mutants D128^3.32A, Y431^7.43A, S215^5.42A, and Y409^6.55A, respectively. Except for the activation of D128^3.32A, which is normalized to DEX for G protein activation and relative to basal for arrestin recruitment, receptor activation is shown relative to the maximum effect of Norepi. Data are presented as means ± SEM of 3 to 11 independent experiments with repeats in duplicate.