Abstract
A galactose-specific carbohydrate-binding protein has been purified to homogeneity from the eggs and embryos of the sea urchin, Lytechinus variegatus. In the unfertilized egg, this carbohydrate-binding protein comprises 0.1% of the total protein. The carbohydrate-binding protein displays microheterogeneity with an average isoelectric point of 7.1 by 2D SDS-PAGE. It is a glycoprotein, composed of 5.6% carbohydrate, including mannose, galactose, glucose, glucosamine, and galactosamine. This carbohydrate-binding protein binds to galactose as well as to polymers of galactose and galactose-sulfate (carrageenan) and polymers of fucose and fucose-sulfate (fucoidan). The carbohydrate-binding protein demonstrates a preference for A- over B-type bonds. Results from 1D SDS-PAGE suggest the carbohydrate-binding protein is a dimer of molecular weight 214,000D composed of equal sub-units of 118,000D. The carbohydrate-binding protein is predominantly cytoplasmic as demonstrated by its solubility properties. A specific antiserum was raised against the carbohydrate-binding protein and used in the immunofluorescent localization of the carbohydrate-binding protein. Prior to fertilization, the carbohydrate-binding protein was located in uniformly distributed aggregates throughout the cytoplasm. After fertilization, the aggregates containing this carbohydrate-binding protein migrate to the cell cortex. The carbohydrate-binding protein purified from L. variegatus was found to have some degree of immunologic cross reactivity with a lectin purified from the sea urchin, Anthocidaris crassispina suggesting similar proteins exist in other invertebrate eggs.