Complete amino acid sequence of tenebrosin‐C, a cardiac stimulatory and haemolytic protein from the sea anemone Actinia tenebrosa

The complete amino acid sequence of the cardiac stimulatory and haemolytic protein tenebrosin‐C, from the Australian sea anemone Actinia tenebrosa, has been determined by Edman degradation of the intact molecule and fragments produced by treatment of the polypeptide chain with cyanogen bromide and enzymatic cleavage with endoproteinase Asp‐N, thermolysin and trypsin. The molecule is a single‐chain polypeptide consisting of 179 amino acid residues with a calculated molecular mass of 19 797 Da. Tenebrosin‐C shows a high degree of amino acid sequence similarity (63%) with Stoichactis helianthus cytolysin III [Blumenthal, K. M. and Kem, W. R. (1983) J. Biol. Chem. 258, 5574–5581] and is identical to a partial sequence (90 residues) reported for equinatoxin, a cardiostimulatory and haemolytic protein isolated from the European sea anemone Actinia equina [Ferlan, I. and Jackson, K. (1983) Toxicon Suppl. 3, 141–144]. No amino acid sequence similarity was detected between tenebrosin‐C and other protein sequences stored in available databases. The predicted secondary structure of tenebrosin‐C suggests that it is a compact, highly structured molecule.