Isolation and Amino Acid Sequence of a Polypeptide Toxin from the Sea Anemone Radianthus crispus

Abstract

The aqueous extract of the sea anemone Radianthus crispus was potently lethal tocrabs but had no toxicity in mice. A polypeptide toxin (named Re I) was easily isolated by gel filtration on Sephadex G-50 and reverse-phase HPLC on TSKgel ODS-80Ts. Its minimum lethal dose against crabs was estimated to be 7.3 μg/kg. The complete amino acid sequence of Rc I was determined by sequence analyses of S-carboxamidomethylated toxin and its enzymatic fragments. Rc I comprises 47 amino acid residues and is characterized by the abundance of Asx, Gly, and half-Cys, the absence of Ala, Met, and Tyr, and the presence of an unusual amino acid, hydroxyproline. As compared with the sequences of the known sea anemone toxins, Rc I is ananalogue of type 1 toxins, showing an especially high homology with Cp I (89%) and Cp II (81%) from the Caribbean sea anemone Condylactis passiflora.