Amino acid residues conferring ligand binding properties of prostaglandin I and prostaglandin D receptors - Identification by site-directed mutagenesis

Using chimeras of the mouse prostaglandin (PG) I receptor (mIP) and the mou se PGD receptor (mDP), we previously revealed that the cyclopentane ring re cognition by these receptors is specified by a region from the first to thi rd transmembrane domain of each receptor; recognition by this region of mIP is broad, accommodating the D, E, and I types of cyclopentane rings, where as that of mDP binds the D type of PGs alone (Kobayashi, T., Kiriyama, M., Hirata, T., Hirata, M, Ushikubi, F., and Narumiya, S. (1997) J. Biol. Chem. 272, 15154-15160). In the present study, we performed a more detailed chim era analysis, and narrowed the domain for the ring recognition to a region from the first transmembrane domain to the first extracellular loop. One ch imera with the replacement of the second transmembrane domain and the first extracellular loop of mDP with that of mIP bound only iloprost. The amino acid substitutions in this chimera suggest that Ser(50) in the first transm embrane domain of mIP confers the broad ligand recognition of mIP and that Lys(75) and Leu(83) in the second transmembrane domain of mDP confer the hi gh affinity to PGD(2) and the strict specificity of ligand binding of mDP, respectively.