Fig. 4.

Class A GPCR activation. a Prominent outward bending of TM5 and TM6 opens the cytoplasmic pocket of inactive serotonin 5-HT2A receptor (orange, PDB 6A93) for the binding of G protein. Active 5-HT2A receptor (marine blue, PDB 6WHA). b Microswitches involved in 5-HT2A receptor activation. c Structural features of class C GPCRs. Inactive (PDB 7MTQ) and active metabotropic glutamate receptor 2 mGlu2R (PDB 7MTR). VFT extracellular venus flytrap domain, CRD cysteine-rich domain, TMD transmembrane domain, PAM positive allosteric modulator