Purification, characterization and cDNA cloning of a lectin from the brittle star Ophioplocus japonicus

Lectins are carbohydrate-binding proteins that possess specific sugar-binding properties and are involved in various biological activities in different organisms. In this study, purification, characterization, and cDNA cloning of a brittle star lectin, designated as Ophioplocus japonicus agglutinin (OJA), were conducted. OJA was isolated from the brittle star O. japonicus by affinity chromatography on a Sephadex G-25 column, followed by ion-exchange chromatography on a Resource Q column. This lectin yielded distinct bands at approximately 176 or 17 kDa on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) under non-reducing or reducing conditions, respectively. It also exhibited Ca²⁺-dependent hemagglutination activity, which, however, was not affected by other metal cations, such as Ba²⁺, Co²⁺, Cu²⁺, Zn²⁺, Fe²⁺, Mg²⁺, and Mn²⁺. The OJA activity was strongly inhibited by glucose and xylose among the monosaccharides tested, and by bovine thyroglobulin among the glycoproteins tested. Cloning of the OJA cDNA revealed that its primary structure contained the C-type lectin domain (CTLD). The results of this study showed that OJA is an echinoderm-derived glucose/xylose-specific lectin that belongs to the C-type lectin superfamily.