The fertilization layer mediated block to polyspermy in Xenopus laevis: isolation of the cortical granule lectin ligand.

The fertilization layer of Xenopus laevis eggs is formed by the cortical granule lectin binding to its ligand. The binding requires Ca2+, is specific for galactose, and functionally establishes a block to polyspermy at fertilization. We have designed a new enzyme-linked lectin assay for the cortical granule lectin (CGL) ligand which can detect the presence of the CGL ligand at a sensitivity of 1-2 ng/ml. This assay is specifically inhibited with galactose, 50% inhibition at 9.9 mM, and produces a linear response between 2 and 20 ng of jelly adsorbed to the microtiter plate. Using this assay, the CGL ligand was purified through gel filtration, anion-exchange, and CGL affinity chromatography. Hydrolysis of the purified CGL ligand with a series of exoglycosidases showed that a terminal alpha-galactose is the ligand structure required for recognition by CGL.