Fig. 3.

a Schematic representation of GPCR activation process. Upon agonist (red circle) binding, the receptor proceeds into a pre-activation state coupling with the G protein heterotrimer, where the exchange of GDP and GTP in G protein α subunit leads to G protein dissociation and mediate G protein signaling pathway. The phosphorylation of the receptor C-terminal tail by GRK binding promotes arrestin recruitment and signaling. When the antagonists (blue circle) bind, the receptor stabilizes in an inactive state. b Crosstalk of downstream pathway of Gs, Gq, Gi and arrestin