Participation of the nonreducing terminal ?-galactosyl residues of the neutral N-linked carbohydrate chains of porcine zona pellucida glycoproteins in sperm-egg binding

The zona pellucida (ZP) surrounding the mammalian oocyte is composed of three glycoprotein components (ZPA, ZPB, and ZPC). Mammalian sperm bind to carbohydrate chains of a ZP glycoprotein in the initial phase of fertilization. Sperm-ligand carbohydrate chains have been characterized in mouse, cow, and pig. In pigs, triantennary/tetraantennary neutral complex-type chains from ZPB/ZPC mixture possess stronger sperm-binding activity than those of biantennary chains (Kudo et al., 1998: Eur J Biochem 252:492–499). Most of these oligosaccharides have β-galactosyl residues at the nonreducing ends. This study used two in vitro competition assays to investigate the participation of the nonreducing terminal β-galactosyl residues of the ligand active chains in porcine sperm binding. The removal of the nonreducing terminal β-galactosyl residues from either the ligand active carbohydrate chains or endo-β-galactosidase-digested glycoproteins significantly reduced their inhibition of sperm–egg binding, indicating that the β-galactosyl residues at the nonreducing ends are involved in porcine sperm–egg binding. A correlation between the sperm-binding activity and in vitro fertilization rate is also presented. Mol. Reprod. Dev. 70: 222–227, 2005. © 2005 Wiley-Liss, Inc.