Fig. 1.

Schematics of the GPCR-activation pathway. The receptor is activated upon binding of agonist (adrenaline in the case of the β₂AR), while the G protein is bound to GDP (studies showing conversion between the conformations of free G protein are mentioned in the main text). G protein binds to the activated receptor, undergoes the conformational changes required to facilitate exchange of GDP with GTP. The G protein is bound to GTP and then dissociates into the α-subunit and βγ-heterodimer, which elicit downstream signal transduction within the cell (e.g., increase or decrease of cAMP through activation or inhibition of adenylyl cyclase, respectively).