Table showing some characteristics of family A–C GPCRs^a.

Feature	Family A	Family B	Family C	Reference
Transmembrane domains	All families possess seven transmembrane domains			31, 54 and 55
Orthosteric binding site	TM region	Extracellular loops, extracellular N-terminus, TM6	Extracellular N-terminus (VFTM, SUSHI)	12, 41, 55 and 56
Number of approved and marketed drugs	33	16	22	57
Motifs	All GPCRs share the D/E-R-Y/W motifs			30, 49 and 54
Number of conserved residues in TMD regions	25	33	94	55
Type of ligand	Small molecules, proteins, peptides	Proteins, peptides	Small molecules, cations, amino acids	31
Suitable as drug targets?	Yes, except the sensory receptors	Yes	Yes, except the sensory receptors	31

^aTM: transmembrane, GPCR(s): G-protein coupled receptor(s), VFTM: venus fly trap module, SUSHI: short consensus repeats.