Amino Acid Sequence and Molecular Characterization of a D-Galactoside-Specific Lectin Purified from Sea Urchin (Anthocidaris crassispina) Eggs

The complete amino acid sequence of a 11.5-kDa subunit of D-galactoside binding lectin purified from sea urchin (Anthocidaris crassispina) eggs is presented. The 105-residue sequence of the subunit was determined by analysis of the intact S-carbamoylmethylated protein and peptides generated by digestion with Achromobacter protease I or Staphylococcus aureus V8 protease. The lectin exists as a disulfide-linked homodimer of two subunits; the dimeric form is essential for hemagglutination activity. However, the monomeric form obtained by partial reduction retains the carbohydrate binding capacity. Neither Ca²⁺ nor SH reagent is essential for hemagglutination or carbohydrate binding. The sequence has no similarity to that of any known protein and apparently represents a new type of galactoside binding lectin.