A new cytolytic toxin, actinoporin RTX-S II, was isolated from the sea anemone Radianthus macrodactylus with a high degree of purity by a combination of gel filtration, ion-exchange and reverse-phase chromatography. RTX-S II has molecular mass of 19,280Da and isoelectric point of 10.0. The hemolytic activity of RTX-S II is inhibited by sphingomyelin. RTX-S II had an LD50 of 70 mg/kg, and is lacking in phospholipase activity. The amino acid composition of this protein contains a high amount of basic and non-polar amino acids and no cysteine. The N-terminal sequence of RTX-S II was determined. The partial amino acid sequence (141 aa) of RTX-S II was deduced based on the cDNA sequence obtained with two oligonucleotides encoding the N-terminal portion of RTX-S II and the internal conserved cytolysin peptide by PCR. A comparison of the RTX-S II cDNA sequence and the rtx-s II gene obtained with the same PCR primers indicates that they are 100% identical at the nucleotide level. It shows that no introns are present in the corresponding region of the rtx-s II gene. Multiple alignments of RTX-S II with known sequences of actinoporins show that RTX-S II is highly homologous to magnificalysin II from Heteractis magnifica. The predicted secondary structure of RTX-S II is predominantly anti-parallel β-structure, which is in good agreement with experimental data obtained from other sea anemones-actinoporins.
Bibliographical noteFunding Information:
The authors thank Dr I. Nazimov (Institute of Bioorganic Chemistry, the Russian Academy of Sciences, Moscow) for automated N-terminal amino acid sequence analyses of RTX-S II, and Mr A. Shvedov who translated this paper into English. This work was supported by the RFBR grant no. 02-04-49486, the program of Presidium of RAS “Molecular and cell biology” grant no. 03-1-0-05-002 and FEBRAS grant.
- Hemolytic activity
- Primary and secondary structures
- Sea anemones