The basis of prostaglandin synthesis in coral: molecular cloning and expression of a cyclooxygenase from the Arctic soft coral Gersemia fruticosa.
of Bioorganic Chemistry, Institute of Chemistry, Tallinn Technical
University, Akadeemia tee 15, Tallinn 12618, Estonia.
In vertebrates, the synthesis of prostaglandin hormones is catalyzed by cyclooxygenase (COX)-1, a constitutively expressed enzyme with physiological functions, and COX-2,
induced in inflammation and cancer. Prostaglandins have been detected
in high concentrations in certain corals, and previous evidence
suggested their biosynthesis through a lipoxygenase-allene oxide
pathway. Here we describe the discovery of an ancestor of
cyclooxygenases that is responsible for prostaglandin
biosynthesis in coral. Using a homology-based polymerase chain reaction
cloning strategy, the cDNA encoding a polypeptide with approximately
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 arachidonate
- binding Arg(120) and Tyr(355) are present, as are the heme -
coordinating His(207) and His(388); the catalytic Tyr(385); and the
target of aspirin 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 present 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 inhibited by indomethacin, whereas the selective COX-2 inhibitor nimesulide was ineffective. We conclude that the cyclooxygenase occurs widely in the animal kingdom and that vertebrate COX-1 and COX-2 are evolutionary derivatives of the invertebrate precursor.