Phylogenetic tree representation of the human GPCR superfamily constructed using sequence similarity within the seven-transmembrane region. Family members with determined structures are highlighted within the tree, and their binding pockets with the ligand, as captured in each of the distinct structures, are shown around the tree in the same orientation for ease of comparison. A2AAR (PDB code: 3EML), β1AR (2VT4), β2AR (2RH1), CXCR4 (3ODU), dopamine D3 (3PBL), δ-opioid (4EJ4), histamine H1 (3RZE), κ-opioid (4DJH), µ-opioid (4DKL), M2 muscarinic (3UON), M3 muscarinic (4DAJ), nociceptin/ophanin FQ peptide opioid (4EA3), rhodopsin (1GZM), sphingolipid S1P1 (3V2Y) receptors.