Calcium Ion-Independent Recognition of Sialyl and Nonsialyl N-Acetyllactosamine and Lex Structures by Boar Sperm

Abstract

Recognition of defined carbohydrate structures by boar sperm was studied on the basis of oligosaccharide structures of porcine zona pellucida glycoproteins so far elucidated. Boar sperm abundantly adhered to fetuin–Sepharose beads, moderately to asialofetuin–Sepharose beads, but not at all to galactosidase (β1-4-linkage-specific)-digested asialofetuin–Sepharose beads. The sperm also adhered to Lex oligosaccharide probe-coupled avidin–Sepharose beads. These adhesive activities were retained in the medium containing EDTA instead of calcium ion but abolished after induction of acrosome reaction by preincubation of sperm with calcium ionophore. Inhibition study of sperm adhesion to the beads by soluble ligands demonstrated that boar sperm express at least two kinds of carbohydrate recognition molecules, one recognizing both sialyl and nonsialyl N-acetyllactosamines but not the Lex structure and the other recognizing the Lex structure but not N-acetyllactosamines. Sperm binding to the zona pellucida on fixed porcine oocytes was inhibited by N-glycans of fetuin and their asialo form but not by the asialo, agalacto-N-glycans. Finally, dextran-based multivalent oligosaccharide polymers were prepared and their inhibitory activities in sperm–oocyte binding were examined. The result indicated that the polymer composed of fetuin N-glycans, its asialo-N-glycans, or lacto-N-fucopentaose III causes a remarkable inhibition at the oligosaccharide-based concentration of 50 μM. Thus, boar sperm are suggested to express multiple carbohydrate recognition molecules which may be involved in the sperm–egg interaction.