Characterization of the vitelline envelope of the sea urchin Strongylocentrotus purpuratus

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Abstract
The vitelline envelope (VE) is an extremely thin, acellular, proteinaceous coat that surrounds the extracellular surface of sea urchin eggs. Despite previous studies on VE composition, structure and function, our understanding to the envelope is still incomplete at the molecular level. We have isolated VE components from intact, unfertilized Strongylocentrotus purpuratus eggs by reduction with alkaline dithiothreitol-see water solutions and have characterized the macromolecules by SDS-PAGE. There were eight major glycoprotein bands, including two high molecular weight components at 265 and 300 kDa, and several minor components. We have revealed, by lectin blot analysis, that most components contain mannose, while a subset of glycoproteins contain fucose and N-acetylglucosamine; galactose and sialic acid were also detected. The components in the VE preparations were compared with cell surface complex preparations by immunoblot analysis, using antisera against a VE preparation, a 305 kDa electrophoretically purified VE glycoprotein and an extracellular portion of the sea urchin egg recombinant 350 kDa sperm receptor. Serum against the recombinant sperm receptor reacted with a component of approximately 350 kDa on blots, but did not react with the 300 kDa component found in VE preparations. Therefore, we suggest these two glycoproteins are not the same.