Fertilization studies in the hamster : The role of cell-surface carbohydrates

The nature of complementary binding sites on the surfaces of hamster gametes has been analysed using mono- and oligosaccharides, glycoproteins and glycosidases in an in vitro system. The binding of capacitated spermatozoa to the zona pellucida was inhibited by several mono- and oligosaccharides related to fucose, galactose, and acetylated amino sugars, but not by unrelated sugars. Several glycoproteins with prosthetic carbohydrate groups rich in or terminated by galactose or N-acetylglucosamine residues were also potent inhibitors of fertilization. Of all the glucoproteins tested, two plasma glycoproteins, α₁-acid glycoproteins (orosomucoid) and fetuin were most effective. In their native form they were non-inhibitory but their desialylated (galactoseterminated) forms completely prevented the sperm-zona binding. Agalacto-orosomucoid with N-acetylglucosamine terminals also inhibited fertilization. The treatment of capacitated spermatozoa with α- -fucosidase, α- -galactosidase and β-N-acetylhexosaminidase, but not with other glycosidases, trypsin and arylsulphatase, resulted in the complete inhibition of fertilization. Inhibitory saccharides and glycosidases did not interfere with sperm motility and had no effect on sperm-oolemma fusion. The pretreatment of cumulus-free oocytes with these agents did not inhibit sperm zona pellucida binding either. These results provide evidence that sperm-zona pellucida binding is mediated by ligands on the sperm surface containing fucose, galactose, N-acetylglucosamine and N-acetylgalactosamine residues.