Figure 3. CB2 Activation by WIN 55,212–2.

(A) Superposition of the WIN 55,212–2 (cyan)-activated CB2 (magenta) complex with antagonist (AM10257, orange)-bound CB2 receptor (green) (PDB: 5ZTY, resolution: 2.8 Å).

(B) WIN 55,212–2 bound at the CB2 orthosteric pocket makes direct contacts with residues F117^3.36 and W258^6.48. The subtle rotation of F117^3.36 to interact with the 2,3-dihydro-[1,4]oxazino[2,3,4-hi]indole moiety of WIN 55,212–2 allows W258^6.48 to undergo a large rotation, with a consequent outward movement of the cytoplasmic end of TM6 that serves to create a cavity for G protein binding. Green cartoon: the inactive CB2 crystal structure (PDB: 5ZTY, resolution: 2.8 Å). Magenta cartoon: the active CB2 cryo-EM structure. There is relatively little rearrangement in residues V121^3.40, L201^5.50, and L254^6.44, different from the corresponding residue Pro^5.50 of β₂AR and μOR, which is involved in packing interactions with Ile^3.40 and Phe^6.44 during the activation of these GPCRs.

(C) The energy contribution of key residues involved in the binding pockets of inactive and active CB2. Green bars: calculated energy contributions of key residues based on the inactive CB2 crystal structure (PDB: 5ZTY). Magenta bars: calculated energy contributions of key residues using the active CB2 cryo-EM structure.