Isolation of a glycopeptide fraction from the surface of the sea urchin egg that inhibits sperm-egg binding and fertilization.

Abstract

The role of cell surface glycoproteins of the sea urchin egg in binding sperm was examined by studying the biological activity of glycopeptides derived from these glycoproteins. Glycopeptides were produced from egg surface glycoproteins by Pronase digestion. After fractionation by gel filtration the glycopeptides were tested for their ability to inhibit the binding of sperm to eggs, presumably by competing with the egg surface glycoproteins for binding sites on the sperm. One glycopeptide fraction with an apparent MW of .apprx. 6000 was a potent inhibitor of sperm-egg binding, and fertilization, even at nanomolar concentrations. This activity was heat stable and exerted its effect against the sperm and not the egg. Experiments with a radiolabeled form of the glycopeptide fraction directly demonstrated that at least 1 component of it bound to sperm. Specific binding of the radiolabeled glycopeptide occurred only to acrosome-reacted sperm. Because the isolated glycopeptide fraction has many of the characteristics expected of a biologically active fragment of an egg surface receptor for sperm, these findings are consistent with the idea that one or more glycoconjugates on the surface of the egg are involved in sperm binding.