Isolation and cDNA cloning of four peptide toxins from the sea anemone Heteractis aurora

Background: Sea anemones are well known to contain multiple peptide toxins. However, of more than 1100 species of sea anemones distributed worldwide, only a little over 50 have been studied for peptide toxins. Therefore, innumerable unique and novel peptide toxins remain to be discovered in unstudied sea anemones. Methods: Isolation of peptide toxins in the sea anemone Heteractis aurora was attempted by gel filtration and reverse-phase high performance liquid chromatography, using the toxicity to crabs as an index. The amino acid sequences of the isolated four toxins (Hau I-IV) and their precursors were determined using a combination of protein sequencing and cDNA cloning. Results: Hau I and IV were potently lethal to crabs, whereas Hau II and III were only paralytic. The precursor proteins of the four toxins were commonly composed of a signal peptide, a propart, and the remaining region including a mature peptide. Interestingly, four and two copies of the mature peptide were present in the precursor proteins of Hau II and III, respectively. Homology searches revealed that HauI (30 amino acid residues) is a novel peptide toxin, although it has the same cysteine pattern CXXC-C-C as the boundless beta-hairpin (BBH) family. Hau II (27 amino acid residues) and III (28 amino acid residues) were homologous with the BBH family, whereas Hau IV (49 amino acid residues) was a new member of the well-known type 1 sodium channel toxin family. Conclusion: This study showed that a novel class of toxin (Hau I), two BBH family toxins (Hau II and III), and a type 1 sodium channel toxin (Hau IV) are present in the toxin of the sea anemone H. aurora.