STRUCTURE AND FUNCTION OF PROSTANOID

There are five physiologically dominant prostaglandins which are all derived from arachadonic acid through cyc\ooxygenase pathway (l). These five metabolites, PGD2 , PGE2 , PGF2a, PGI2 , and TXA2 , produce their physiological effects through separate receptors, which have been defined as DP, EP, FP, IP and TP respectively (2). There is also further subdivision of the EP receptors into EP p EP2 , EP3 and EP4 (2). The cDNAs of all these receptors have been cloned (3). The primary structures of these prostanoid receptors reveal that they are members of the superfamily of G-protein coupled receptors that appear to have a single subunit structure containing seven transmembrane domains (TM) (4). Although these prostanoid receptors have been characterized biochemically as ligand binding activities for radiolabled prostaglandins and their analogues. the structure and function relationship of these receptors is virtually unknown. Judging from the similarity of the structures of prostaglandins, one would expect that these receptors exhibit high degree of amino acid conservation, especially in regions implicated in ligand binding and interactions with G-proteins. Other residues, whose role have remained obscure, are also conserved across virtually all members of this superfamily (5,6). We have successfully expressed the mouse EP3a receptor and the human TP receptor in insect cells using baculovirus system (7,8). This system has allowed us to explore the role of several conserved residues in the TM V to the TM VII of EP 3a and TP receptors where ligand binding is believed to occur and the role of N-glycosylation in ligand binding activity by site-directed mutagenesis.