HALCURIN, A POLYPEPTIDE TOXIN FROM THE SEA-ANEMONE HALCURIAS SP, WITHA STRUCTURAL RESEMBLANCE TO TYPE-1 AND TYPE-2 TOXINS

The aqueous extract of the sea anemone Halcurias sp. belonging to the suborder Endocoelantheae was found to be potently lethal to crabs, alt hough it showed neither lethal activity in mice nor hemolytic activity . A polypeptide toxin (named halcurin) with a LD50 of 5.8 mu g/kg agai nst crabs was isolated by gel filtration on Sephadex G-50 and reverse- phase high-performance liquid chromatography on TSKgel ODS-120T. The c omplete amino acid sequence of halcurin comprising 47 residues was elu cidated by sequence analyses of the native molecule and its enzymatic fragment. Comparison with the known sea anemone polypeptide toxins (ty pes 1-3), which are all from members of the suborder Nynantheae, revea led a high sequence homology (49-74%) of halcurin with type 2 toxins. Also, halcurin has several residues conserved for only type toxins. Th ese results, together with the fact that Halcurias sp. is a more primi tive species than members of Nynantheae, suggest that type 1 and 2 tox ins have evolved from a common ancestor with a sequence more similar t o halcurin. (C) 1997 Elsevier Science Ltd.