Figure 1. The classic β₂AR signalling pathway.

Binding of β₂-agonist to β₂AR induces a conformational change allowing the α-subunit of the G-protein to dissociate and bind to adenylyl cyclase. Adenylyl cyclase is thus activated and catalyses the formation of cyclic AMP (cAMP) from ATP. cAMP molecules bind to PKA which induces the dissociation of the catalytic and regulatory subunitsfrom each other. Once released, the PKA catalytic subunits phosphorylate and hence activate myriad cellular targets which results in airway smooth muscle relaxation and hence bronchodilation.