Identification and characterization of a novel haemolytic and haemagglutinating bifunctional lectin from the coral Acropora millepora.

Two genes, AML-I and AML-II, have been reported to exhibit increased expression during the development of the coral Acropora millepora. They show amino acid sequence homology with CEL-III, a haemolytic lectin found in the sea cucumber Cucumaria echinata. CEL-III binds to carbohydrate chains on the surface of erythrocytes, forming heptameric pores in their membranes. To clarify the role of these proteins in coral, we identified and elucidated their functions. The carbohydrate-binding domains of them showed similar carbohydrate-binding specificity as that of CEL-III. AML-I showed haemagglutinating activity in erythrocytes, whereas AML-II can only be prepared as an aggregate and its function could not yet be determined. AML-IΔC and AML-IIΔC mutants were generated through deletion of the C-terminal extended amino acid residues of them relative to CEL-III. AML-IΔC showed haemolytic activity towards erythrocytes, whereas AML-IIΔC showed no activity. A tobacco etch virus (TEV) protease recognition site was inserted into the C-terminus of AML-I to regulate these activities. The haemagglutinating activity of AML-I was converted into haemolytic activity after TEV protease treatment. As a result, TEV protease could control the haemolytic and haemagglutinating activity of the lectin, which could be useful as an anticancer or antiviral drug because of its cytotoxic activity.