The basis of prostaglandin synthesis in coral - Molecular cloning and expression of a cyclooxygenase from the Arctic soft coral Gersemia fruticosa

In vertebrates, the synthesis of prostaglandin hormones is catalyzed by cyc looxygenase (COX)-1, a constitutively expressed enzyme with physiological f unctions, and COX-2, induced in inflammation and cancer. Prostaglandins hav e been detected in high concentrations in certain corals, and previous evid ence suggested their biosynthesis through a lipoxygenase-allene oxide pathw ay. Here we describe the discovery of an ancestor of cyclooxygenases that i s responsible for prostaglandin biosynthesis in coral. Using a homology-bas ed polymerase chain reaction cloning strategy, the cDNA encoding a polypept ide with similar to 50% amino acid identity to both mammalian COX-1 and COX -2 was cloned and sequenced from the Arctic soft coral Gersemia fruticosa, Nearly all the amino acids essential for substrate binding and catalysis as determined in the mammalian enzymes are represented in coral COX: the arac hidonate-binding Arg(120) and Tyr(355) are present, as are the heme-coordin ating His(207), and His(338); the catalytic Tyr(385); and the target of asp irin attack, Ser(530). A key amino acid that determines the sensitivity to selective COX-2 inhibitors (Ile(523) in COX-1 and Val(523) in COX-2) is pre sent in coral COX as isoleucine. The conserved Glu(524), implicated in the binding of certain COX inhibitors, is represented as alanine, Expression of the G. fruticosa cDNA afforded a functional cyclooxygenase that converted exogenous arachidonic acid to prostaglandins. The biosynthesis was inhibite d by indomethacin, whereas the selective COX-2 inhibitor nimesulide was ine ffective. We conclude that the cyclooxygenase occurs widely in the animal k ingdom and that vertebrate COX-1 and COX-2 are evolutionary derivatives of the invertebrate precursor.