It is well established that sea anemones comprise a rich source of cytolytic toxins. The present study reports the isolation and characterization of a cytolysin obtained from the sea anemone Heteractis magnifica collected in the Andaman Islands of the Indian Ocean. The crude extract was screened for hemolytic activity by a blood agar plate method and a 6-mm zone of clearance was observed after incubation. The hemolytic property of the crude extract, tested by the microtiter plate method, revealed positive results at concentrations as low as 120 ng/mL. Furthermore, it was favored by alkaline pH and was stable up to 60°C. On the other hand, the hemolytic effect was abolished by the addition of human serum. Purification steps involved ammonium sulfate precipitation and subsequent desalting by dialysis, followed by anion- and cation-exchange chromatographies. The purified fractions displayed the presence of a 19-kDa cytolysin when analyzed by SDS-PAGE. The conserved region of the cytolysin (with 303 bp) was amplified by RT-PCR and was sequenced. The sequence showed maximum homology (97%) with the already reported cytolysins from other sea anemone species.

The unifying characteristic of cnidarians is the production of protein and polypeptide toxins. The present study describes the identification of a hemolytic toxin from the soft coral Sarcophyton trocheliophorum. The crude extract was highly cytotoxic (EC50 = 50 ng/mL) against human erythrocytes. It was also tested for hemolytic activity by the blood agar plate method, resulting in a hemolytic halo of 12 mm with 50 µg of protein. The stability of the venom under different physiological conditions was analyzed. The venom hemolytic activity was augmented by alkaline and neutral pH whereas it was reduced in acidic pH. The activity was stable up to 60º C. The hemolytic activity was completely abolished by the addition of serum and reduced significantly during frequent freezing-thawing cycles. Toxin purification was performed by ammonium sulfate precipitation and subsequently desalted by dialysis against 10 mM sodium phosphate buffer (pH 7.2), followed by anion exchange chromatography on DEAE cellulose column and gel filtration chromatography using Sephadex G-50 matrix. The purified active fractions possessed a prominent protein of approximately 45 kDa, as revealed by SDS-PAGE.