Purification and characterization of β-galactoside binding lectin from frog (Rana catesbeiana) eggs

A β-galactoside-binding lectin, a homodimer composed of 14kDa subunits, was purified from unfertilized eggs of the frog Rana catesbeiana by asialofetuin-Sepharose 4B affinity column chromatography. The lectin was solubilized from eggs by addition of neither haptenic sugar nor detergent and showed a unique characteristic that it requires neither Ca⁺⁺ nor SH-reagent for its hemagglutination activity. However, the partial amino acid sequence indicated that the lectin belongs to a family of soluble 14kDa β-galactoside-binding lectins (14K-lectin) widely distributed in vertebrates and classified as S type lectins. These results indicate that a 14K-lectin is present as the free form in unfertilized frog eggs, presenting the first structural evidence for the presence of a soluble 14K-lectin in the amphibian eggs.