Purification, characterization and induction of a C-type lectin in the freshwater planarian Dugesia japonica

Lectins are important components of the immune defense system of invertebrates. Given their important functions, numerous investigations have been carried out on the characterization and function of lectins in invertebrates. However, lectin studies with the freshwater planarian, an evolutionarily important animal, are rare. In this paper, we demonstrate agglutination of glutaraldehyde treated erythrocytes by a lectin with preference for rabbit erythrocytes. The result of hemagglutinating activity inhibition assays with several carbohydrates showed the most potent inhibitor was maltose. A natural lectin from the crude homogenates of freshwater planarian Dugesia japonica was purified by single step affinity chromatography using amylose-coupled agarose. The purified protein appeared as one band with a molecular mass of 350 kDa in PAGE, and as one band, approximately 56 kDa, in SDS-PAGE. The purified lectin showed dependence on calcium. The activity of the purified lectin was inhibited at temperatures greater than 50 degrees C and showed a pH optimum between 5-8. The purified lectin also has binding activity to the Gram-negative bacteria E. coli, and the Gram-positive bacteria B. subtilis. Furthermore, the purified lectin obtained from injured and bacteria-induced planarians showed increased agglutinating activity against rabbit erythrocytes. These results suggest that the purified lectin may play an important role in the innate immunity of the freshwater planarian.