| Research Abstract |
Structure and function of the carbohydrate-binding proteins (lectins) from a sea cucumber (Cucumaria echinata) and other marine invertebrates were investigated. Among four CaィイD12+ィエD1-dependent lectins from C. echinata, a galactose/N-acetylgalactosamine-specific lectin, CEL-III, exhibited strong hemolytic activity toward human and rabbit erythrocytes by forming ion-permeable pores in the cell membrane. In order to identify CEL-III receptor, membrane lipids were purified from human erythrocytes, and were assessed for their CEL-III receptor ability. As a result, glycolipids containing β-galactose or N-acetylgalactosamine at their nonreducing ends showed high affinity as well as effective receptor ability for CEL-III. Furthermore, it was also suggested that the receptor ability depends not only on the affinity for CEL-III, but also on the structure or length of the carbohydrate chains. On the other hand, chemical modification studies revealed that amino and carboxyl groups of CEL-III are involved in the hemolytic mechanism. Although modification of amino groups markedly reduced only hemolytic activity, modification of carboxyl groups led to decrease in both hemolytic and hemagglutinating activity of CEL-III. This suggests that some carboxyl groups are involved in one of two carbohydrate-binding sites of CEL-III. As a model of such a hemolytic lectin, novel protein conjugates consisting of lectins and amphiphilic α-helical peptides were also prepared. Since they exhibited hemolytic activity, depending on the carbohydrate-binding nature, these conjugates were suggested to interact with cell membrane after binding to the surface carbohydrate chains.
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