Improved purification and enzymatic properties of a mixture of Sticholysin I and II: Isotoxins with hemolytic and phospholipase A2 activities from the sea anemone Stichodactyla helianthus

Sticholysin I and Sticholysin II (StI and StII) are two potent hemolysins which form pores in natural and model membranes at nanomolar concentrations. These proteins were purified from the aqueous extract of the sea anemone Stichodactyla helianthus, Ellis 1768, by gel filtration and ionic exchange chromatography. This procedure rendered StI and StII with high purity (purification factors: 36 and 50, respectively) but a low yield of hemolytic activity, HA (<3%). Additionally, these toxins exhibited very low phospholipase activity (10−3 U/mg of protein). In this work, a mixture StI-StII was obtained (yield >95%, with an increase in specific activity: 14 times) from the animal extract using an oxidized phospholipid-based affinity chromatographic matrix binding phospholipases. Cytolysin identification in the mixture was performed by immunoblotting and N-terminal sequence analyses. Phospholipase A2 (PLA2) activity of StI-StII was relatively high (1.85 U/mg) and dependent of Ca2+. The activity resulted optimum when was measured with the mostly unsaturated soybean phosphatidylcholine (PC), when compared to the less unsaturated egg PC or completely saturated dipalmitoyl PC, in the presence of 40 mM Ca2+ at pH 8.0. This Ca2+ concentration did not exert any effect on binding of StI-StII with soybean PC monolayers. Then, PLA2 activity seems not be required to binding to membranes.