Carbohydrate-Binding Proteins Involved in Gamete Interaction in the Pig

Abstract

An essential event in the complex, mulitstep process of mammalian species-specific fertilization is gamete recognition through specific complementary molecules located on the external surfaces of the spermatozoon and the oocyte (Lillie 1913; Yanagimachi 1988). Increasing evidence points out that sperm-egg recognitions and binding actually involve carbohydrate-protein interaction (Ahuja 1982; Huang et al. 1982; Macek and Shur 1988; Jones and Williams 1990; Miller and Ax 1990). Remarkably, this interaction has been conserved in the process of fertilization throughout the whole evolutionary scale (Dale 1991). Thus, inhibition experiments with a variety of polysaccharides show that mannose and fucose contain egg surface components of the marine brown alga Fucus, which interact with complementary carbohydrate-binding structures on the sperm cell surface (Bolwell et al. 1979). Similarly, Hoshi (1984) has presented evidence suggesting that sperm-egg binding in ascidians may be mediated by the enzyme a-fucosidase located on the sperm head. Moreover, the freshwater bivalve Unio spermatozoa bind to its homologous egg at a part of the oocyte surface that binds lectins, suggesting that the sperm receptors are also fucosylcontaining glycoproteins (Focarelli et al. 1988). In the sea urchin, the sperm specific protein, bindin, a 24 kDA major protein (Gao et al. 1986) associated with the inner acrosomal membrane and exposed during the acrosome reaction, mediates the adhesion to the egg’s vitelline layer by a lectin-like activity (Vacquier and Moy 1977; Glabe et al. 1982). Bindin has a strong affinity for sulfated, fucose-containing carbohydrate structures on proteoglycans of the egg surface (De Angelis and Gabel 1987). Sulfate esters of the vitelline coat and arginine residues of the sperm protein appear to be critical for the binding (De Angelis and Gable 1988; 1990).