TABLE 3

Classification of P2Y receptors into two subsets For P2Y_1,2,4,6, and ₁₁ receptors, amino acid residues reported in bold in TM6 and TM7 have been shown to be important for ligand binding in mutagenesis studies (Erb et al., 1995; Jiang et al., 1997b; Boarder and Webb, 2001; Jacobson et al., 2002; see also section V.). For P2Y_12,13, and ₁₄ receptors, direct evidence for the functional importance of the reported motifs in TM6 and TM7 is currently lacking. However, in a patient with a congenital bleeding disorder, a R-Q substitution in TM6 of the P2Y₁₂ receptor results in highly decreased receptor function (Cattaneo et al., 2003).