Isolation and Partial Characterization of a Glycoprotein Complex with Sperm‐Receptor Activity from Ciona intestinalis Ovary1

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Abstract
Sperm-egg interaction in the ascidian Ciana intestinalis is mediated by a fucosyl-glycoprotein (FP) component of the egg vitelline coat. FP are responsible for sperm binding, sperm activation and the acrosome reaction. In this paper we report a detailed biochemical and functional characterization of FP purified from the ovaries by affinity chromatography. thic component with sperm receptor activity is a high molecular weight glycoprotein complex (>107) with a protein-carbohydrate ratio of 2:1, which inhibits the binding of the spermatozoa to the vitelline coat and induces sperm activation and the acrosome reaction. Exhaustive proteolytic digestion of FP yields high molecular weight glycopeptides (> 4×105), which contain N-acetylgalactosamine, fucose, galactose and rhamnose. These glycopeptides retain some receptor activity, thus raising the question of the involvement of the polypeptide backbone in the sperm-egg binding process. However, the glycopeptide fraction fails to induce the acrosome reaction: we suggest that the polypeptide fraction plays a role in the induction of sperm activation and the acrosome reaction.