INTERACTION OF THE HEMOLYTIC LECTIN CEL-III FROM THE MARINE INVERTEBRATE CUCUMARIA-ECHINATA WITH THE ERYTHROCYTE-MEMBRANE

GEL-III is one of four Ca2+-dependent galactose/N-acetylgalactosamine (GalNAc)-binding lectins from the marine invertebrate Cucumaria echinata which exhibits hemolytic activity, especially toward rabbit and human erythrocytes. The hemolytic activity of GEL-III was also Ca2+-dependent and was found to be inhibited by galactose or GalNAc-containing carbohydrates, suggesting that the hemolysis was caused by GEL-III binding to specific carbohydrates on the erythrocyte membrane by Ca2+-dependent lectin activity, followed by partial destruction of the membrane. The activity of GEL-III was highest at 10 degrees C and decreased markedly with increasing temperature, unlike usual enzymatic reactions. The hemolytic activity of GEL-III increased with increasing pH from neutral to 10, but almost no hemolysis was observed below pH 6.5. Immunoblotting analysis of proteins from the erythrocyte membrane after treatment with GEL-III indicated that GEL-III aggregates were irreversibly bound to the membrane. When erythrocytes were incubated with GEL-III in the presence of dextran with molecular masses greater than 4 kDa, lysis was impeded considerably, while a concomitant release of ATP was detected from these osmotically protected cells. It was found that GEL-III released carboxyfluorescein from artificial globoside-containing lipid vesicles, and it is suggested that GEL-III is a novel pore-forming protein with the characteristics of a Ca2+-dependent lectin, which may act as a toxic protein to foreign microorganisms.