FIGURE 1

Phylogenetic analysis of all non-sensory human family A G protein-coupled receptors (GPCRs; adapted from Foord, 2007). The neighbour-joining method was used, after forced alignment according to common amino-acid motifs. Each line represents a GPCR; known and putative cannabinoid receptors and other receptors described in this review are identified. Clusters have been assigned to groups (Foord, 2007): group 1, the monoamine-like receptors; group 2, a diverse group containing opsins and glycoprotein/leucine-rich repeat (LRG) type as well as cannabinoid, prostaglandin and lipid receptors; group 3, brain/gut peptide receptors; group 4, chemokine receptors; and group 5, metabolic receptors including purinergic, thrombin and free-fatty acid receptors. Cross-species comparisons show that groups 4 and 5 are not found in nematodes and insects. Abbreviations: CNR1 and CNR2 are the genes encoding cannabinoid type 1 receptor (CB₁) and cannabinoid type 2 receptor (CB₂), respectively. EDG indicates the sphingolipid receptor cluster, which comprises LPA₁/EDG2, LPA₂/EDG4 and LPA₃/EDG7 and the sphingosine-1-phosphate (S1P) receptors (S1P₁ to S1P₅). LPA, lysophosphatidic acid.