Proposed nomenclature for cytolytic toxins of sea anemones

Purification and partial characterization of two cytolysins from a tropical sea anemone, Heteractis magnifica

Two cytolysins, designated as magnificalysins I and II, were purified from a tropical sea anemone, Heteractis magnifica (formerly Radianthus ritteri). The purification steps involved Sephadex G-50 and CM-Sepharose chromatography followed by Mono S and Phenyl-Superose Fast Protein Liquid Chromatography. The relative mol. wt of magnificalysins I and II, determined by SDS-PAGE, was approximately 19,000, while their isoelectric points, determined by isoelectric focusing in immobilized pH gradients, were 9.4 and 10.0, respectively. Those toxins were found to have haemolytic and lethal activities. The haemolytic activities of magnificalysins I and II were 3.6 x 10(4) HU/mg and 3.3 x 10(4) HU/mg, while their LD50 (i.v., mice) values were approximately 0.14 microgram/g and 0.32 microgram/g, respectively. The amino acid composition and N-terminal sequences of magnificalysins I and II were also obtained. They do not possess any cysteine or cystine residue, but are rich in basic and hydrophobic amino acids. The N-terminal amino acid sequences of magnificalysins I and II are ALAGTIIAGASLTFKILDEV and SAALAGTIIDGASLGFDILNKV, respectively. These are highly homologous to cytolysins from other sea anemones, particularly cytolysin III from Stichodactyla helianthus, a Caribbean anemone.

Relationship between the cytolysins tenebrosin-C from Actinia tenebrosa and equinatoxin II from Actinia equina

The chemical, physical and biological properties of the cytolysin tenebrosin-C from Actinia tenebrosa have been compared with those of equinatoxin II from Actinia equina. The two proteins are indistinguishable by reverse-phase and cation-exchange HPLC and capillary zone electrophoresis, and give similar peptide fragments upon cyanogen bromide cleavage (as judged by the chromatographic behaviour, ultraviolet absorption spectra, amino acid composition and N-terminal amino acid sequences of the peptides). Their cardiac stimulatory activities are identical, and their haemolytic activities are similar, with equinatoxin II having slightly greater activity. These data indicate that the two molecules are either identical in all 179 amino acid positions, or differ by no more than one or two residues. These findings are discussed in the context of the taxonomic relationship between the two species of sea anemone.

Biochemical and pharmacological studies of the mechanism of action of tenebrosin-C, a cardiac stimulatory and haemolytic protein from the sea anemone, Actinia tenebrosa

Tenebrosin-C is a protein of mol. wt 19,500 that displays potent cardiac stimulatory and haemolytic activities. Its haemolytic activity is inhibited by sphingomyelin but not phosphatidylcholine, and is not affected by Ca2+. The positive inotropic effect of tenebrosin-C on isolated guinea pig right atria is inhibited by the cyclooxygenase blockers indomethacin and aspirin, the lipoxygenase blocker and leukotriene antagonist RG5901, and the phospholipase A2 inhibitor mepacrine. This activity of tenebrosin-C therefore appears to be due to stimulation of the release of arachidonic acid and subsequent formation of prostaglandins and leukotrienes. Phospholipase A2-like activity was found with some tenebrosin-C preparations, but did not correlate with their positive inotropic or haemolytic activities and was too weak to account for either of these effects. Treatment of tenebrosin-C with various proteases in order to obtain active fragments showed that the protein is remarkably resistant to proteolysis.

Purification and characterisation of proteins with cardiac stimulatory and haemolytic activity from the anemone Actinia tenebrosa

Three new proteins with cardiac stimulatory and haemolytic activity, designated tenebrosins-A, -B and -C, have been purified from the Australian sea anemone Actinia tenebrosa. These proteins are basic (pI greater than or equal to 9.4), have mol. wt of about 20,000, and have very similar amino acid compositions and N-terminal amino acid sequences. None of the proteins contains cysteine or cystine residues. On isolated, spontaneously beating guinea pig atria they exhibit at 1-2 nM strong positive inotropic and slight to moderate chronotropic effects. In some cases a transient negative inotropic effect occurs prior to onset of the positive inotropic response. The proteins are also haemolytic, producing 50% haemolysis of guinea pig erythrocytes at concentrations similar to those showing positive inotropic effects.

Platelet aggregation induced by equinatoxin

Equinatoxin, isolated from Actinia equina, caused aggregation of washed rabbit platelets at a concentration as low as 0.01 ng/ml. ATP was released, but no formation of thromboxane B2 in challenged platelets. The aggregation was resistant to indomethacin or creatine phosphate/creatine phosphokinase or PAF antagonist. The aggregation was inhibited by imipramine, sodium nitroprusside, mepacrine, theophylline, prostaglandin E1 and EDTA. However, heparin and tetracaine were without any inhibitory effect. Verapamil suppressed both the aggregation and release reaction caused by equinatoxin in calcium concentrations from 0.01 to 15 mM. High concentrations of equinatoxin caused progressive cell lysis. It is concluded that equinatoxin-induced platelet aggregation is independent of ADP, thromboxane or PAF pathway. Phosphoinositide breakdown by phospholipase C is postulated to accomplish this phospholipase A2-independent platelet aggregation by equinatoxin.