Figure 2. Structural changes in the μOR stabilized by nucleotide-free G_i.

a, Comparison of inactive μOR (brown) and the G_i stabilized active state of μOR (green). b, Comparison of Nb39 and G_i stabilized active states of the μOR (blue and green, respectively). The structures are nearly identical except for a slight shift of TM6 towards TM7 in the G_i -bound state. c, Residues important for activation of the μOR show nearly identical conformations despite the difference in ligands. d, Comparison of G_s-stabilized β₂AR (orange) and G_i-stabilized μOR (green). While most transmembrane helices align well between the two receptors, TM6 is kinked further outward by 9Å in the β₂AR. Distance calculated between Cα of residue 6.29 (Ballesteros-Weinstein numbering) in TM6.