IDENTIFICATION OF A NEW SEA-URCHIN VITELLINE ENVELOPE SPERM BINDING GLYCOPROTEIN

The sea urchin egg vitelline envelope (VE) is composed of eight major glycopolypeptides that are heavily mannosylated and contain fucose and N-acetylglucosamine moieties based on lectin staining. In the present study, the macromolecular composition of the VE and the potential rol e of a purified VE glycoprotein in initial gamete binding was investig ated. The VE components were solubilized from the surface of intact, d ejellied eggs with dithiothreitol in divalent cation-free seawater, an d analyzed using native, reduced electrophoresis and immunoblotting. T hree major VE glycoproteins, VE-A, VE-B and VE-C, and one minor compon ent, VE-D, were identified with antisera against whole VE preparations and against glutaraldehyde-fixed, unfertilized eggs. The electrophore tically purified glycoproteins resolved into a common subunit doublet and one unique subunit each of decreasing size on blots oi sodium dode cylsulfate polyacrylamide gels. Lectin affinity chromatography was use d for analysis and purification of reduced VE components; a glycoprote in eluted from Con A columns with methyl-mannoside comigrated with VE- B when analyzed by immunoblotting. Whole VE preparations and VE-B obta ined from Con A columns were found to inhibit fertilization when prein cubated with sperm, thus directly establishing a role for VE-B in game te binding.