The subfamily of class A rhodopsin-like receptors is by far the largest and most studied GPCR family. Most class A receptors have two Cys residues in extracellular loops (ELs) 1 and 2 that form a disulfide bridge, proline residues in the transmembrane (TM) regions, and a palmitoylated Cys residue in the C-terminal domain, forming putative intracellular loop four (IL4). All family A receptors have a conserved DRY motif in the proximal region of IL2.

Ref. Gether, U. Endocrine Reviews 2000, 21, 90–113.