Isolation and characteristics of high molecular weight cytolysins from the sea anemone Radianthus macrodactylus

Three cytolytic toxins (RTX: RTX-A, RTX-S, and RTX-G) were isolated from the sea anemone Radianthus macrodactylus and characterized. The purification scheme involved hydrophobic chromatography on Polychrom-1, batch-chromatography on CM-23 cellulose, gel filtration on Akrilex P-4, cation-exchange chromatography on CM-32 cellulose, and HPLC on an ion-exchange Ultropac TSK CM-3SW column and a reversed-phase Silasorb C18 column. The molecular masses of RTXs (ca. 20 kDa) were determined by SDS-PAGE in a density gradient of PAG. They are highly basic polypeptides (pI of 9.8 for RTX-A and RTX-S and 10.5 for RTX-G) containing similar amino acid compositions with a high content of basic and hydrophobic residues and the absence of Cys residues. The hemolytic activities of RTX-A, RTX-S, and RTX-G were determined to be 3.5, 5.0, and 1.0 x 10(4) HU/mg, respectively. Exogenous sphingomyelin inhibits their action on the erythrocyte membrane. The N-terminal sequence of RTX-A was determined to be ALAGAIIAGAGL/KGLKI/FLIEVLGEG--V/NKVKI-.