A new phospholipase A2 isolated from the sea anemone Urticina crassicornis - its primary structure and phylogenetic classification.

Disulfide pairings and active site residues are highly conserved in secretory phospholipases A(2) (PLA(2)s). However, secretory PLA(2)s of marine invertebrates display some distinctive structural features. In this study, we report the isolation and characterization of a PLA(2) from the northern Pacific sea anemone, Urticina crassicornis (UcPLA(2)), containing a C27N substitution and a truncated C-terminal sequence. This novel cnidarian PLA(2) shares about 60% identity and almost 70% homology with two putative PLA(2)s identified in the starlet sea anemone (Nematostella vectensis) genome project. UcPLA(2) lacks hemolytic and neurotoxic activities. A search of available sequences revealed that Asn27-'type' PLA(2)s are present in a few other marine animal species, including some vertebrates. The possibility that the C27N replacement represents a structural adaptation for PLA(2) digestion/activity in the marine environment was not supported by experiments testing the influence of ionic strength on UcPLA(2) enzymatic activity. Because of the highly divergent sequences among invertebrate group I PLA(2)s, it is currently not possible to identify orthologous relationships. As the Asn27-containing PLA(2)s are scattered among the other invertebrate group I PLA(2)s, they do not constitute a new, monophyletic PLA(2) clade.