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 echina ta which exhibits hemolytic activity, especially toward rabbit and hum an erythrocytes. The hemolytic activity of GEL-III was also Ca2+-depen dent and was found to be inhibited by galactose or GalNAc-containing c arbohydrates, suggesting that the hemolysis was caused by GEL-III bind ing to specific carbohydrates on the erythrocyte membrane by Ca2+-depe ndent lectin activity, followed by partial destruction of the membrane . The activity of GEL-III was highest at 10 degrees C and decreased ma rkedly with increasing temperature, unlike usual enzymatic reactions. The hemolytic activity of GEL-III increased with increasing pH from ne utral to 10, but almost no hemolysis was observed below pH 6.5. Immuno blotting analysis of proteins from the erythrocyte membrane after trea tment 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, l ysis 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-formi ng protein with the characteristics of a Ca2+-dependent lectin, which may act as a toxic protein to foreign microorganisms.