Characterisation of cavortin, the major haemolymph protein of the Pacific oyster (Crassostrea gigas)

Abstract Evidence suggests that members of the oyster genus Crassostrea share a common haemolymphprotein. Cavortin, the major haemolymph protein of the Pacific oyster (Crassostrea gigas), comprises 174 amino acid residues totalling 19.4 kDa and is rich in histidine and aspartic acid. The protein consists of a single Cu/Zn SOD (superoxide dismutase) derived domain showing homology to each of the three SOD‐like domains of pernin, the related 60 kDa protein from the green‐lipped mussel (Perna canaliculus). Despite some homology to Cu/Zn SOD sequences we found no compelling evidence that it has retained SOD function. Cavortin has affinity for several divalent cations, particularly iron. Each cavortin monomer is able to bind 8–11 iron ions, but can sequester considerably more iron, presumably by forming spheroid particles. The primary function of cavortin, like pernin, has been altered during the course of evolution, but has yet to be determined unambiguously. A likely role is as a metal ion chaperone.