Upon completion of the human genome project over 800 G protein-coupled receptor 1 (GPCR) genes, subdivided into five categories, were identified. These receptors sense a diverse array of stimuli, including peptides, ions, lipid analogues, light and odour, in a discriminating fashion. Subsequently, they transduce a signal from the ligand-receptor complex into numerous cellular responses. The importance of GPCRs is further reflected in the fact that they constitute the most common target for therapeutic drugs across a 2 wide range of human disorders. Phylogenetic analysis of GPCRs produced the...