Fig. 5: The allosteric roles of ionic lock between TM3 and TM6 and cation-π microswitches between TM7/H8 and TM6 in the A2AR activation.

a, b In the inactive states the GDP-loaded Gαβγ and GPCR do not interact. The receptor undergoes a transition between two inactive states featured with ionic lock (DRY-E) switch between the helices TM3 and TM6. c Pre-coupled complex. The receptor and Gαβγ are evidently pre-coupled prior to be activated. d Upon partial agonist bindings, the receptor undergoes conformational rearrangement to form the S4 state to facilitate Cα5 to penetrate the binding cavity. e Upon the full agonist binding, the GPCR activation continues to proceed until the fully opened conformational complex is formed between the receptor and Gαβγ, resulting in a free nucleotide exchange. f After GTP binding, the Gαβγ will disengage the receptor and dissociate into the Gα and Gβγ. Of note, the allosteric switch from the inactive states to pre-coupled, active-like, and active states were modulated by the cation-π interactions between the TM7/H8 and TM6, in which R291 and R293 residues play critical roles in controlling the G protein cavity opening and regulating G protein hydrolysis.