Defining oligosaccharide specificity for initial sperm-zona pellucida adhesion in the mouse

Abstract

The identity of the sperm surface protein(s) responsible for sperm‐zona pellucida binding in the mouse, as well as the characteristics of the oligosaccharide groups on zona pellucida glycoprotein 3 (ZP3) having ligand activity toward this receptor, remain controversial. Conflicting results from several groups have made interpretation of the current data difficult. By developing a quantitative binding assay to evaluate the molecular interactions between mammalian sperm and the zona pellucida during initial gamete interactions, we directly quantified sperm‐ZP binding interactions at the molecular level for the first time. The ZP binding assay demonstrated that live, capacitated mouse sperm bind solubilized 125I‐labeled ZP glycoproteins in a concentration‐dependent manner characterized by a rapid forward rate constant of 3.0 × 107 M−1 min−1. Following the initial characterization, the binding assay was used to examine the roles of the sperm surface enzymes galactosyltransferase (GalTase) and fucosyltransferase (FucTase) in sperm‐zone pellucida binding in the mouse. These data indicate that substrates for FucTase, but not for GalTase, inhibit sperm‐ZP binding, in contrast to earlier reports in which GalTase substrates significantly inhibited sperm binding to intact ZPs. A model is presented which resolves conflicting results between assays using intact ZPs and the results obtained here using soluble 125I‐ZPs. Assuming a complex binding/recognition site, monosaccharides that could occupy part of the binding site would have a dramatic effect on sperm‐ZP binding to the intact ZP, since they need only occupy the binding sites for a short time (∼ 100 msec) to disrupt binding. The current results suggest that the sperm ZP3 receptor binding site minimally recognizes the galβ1,3GlcNAc moiety also recognized by FucTases. The current data do not exclude the possibility that additional sugar residues form part of the ligand oligosaccharide group and are recognized by a yet‐to‐be‐identified sperm surface protein which serves as the ZP3 receptor. © 1996 Wiley‐Liss, Inc.

Murine Sperm-Zona Binding, A Fucosyl Residue Is Required for a High Affinity Sperm-binding Ligand

“…A Fucosyl Residue Is Required for an Oligosaccharide to Bind Acrosome-intact Sperm with High Affinity-The lack of inhibition of sperm-ZP binding with ␤GN-␤GN-GN is in agreement with published reports that in vitro sperm-ZP binding is not inhibited by free N-acetylglucosamine or by a tetraantennary oligosaccharide with four terminal N-acetylglucosaminyl residues (12,24). Additionally, our results are consistent with two independent reports that male mice that lack a functional ␤4GT gene are fertile (7,8).…”

“…A cell surface, calcium-dependent lectin with affinity for galactose has been described on sperm surface from mice, rats, and rabbits; in rabbits, this lectin has been shown to bind ZP3 (33)(34)(35). A sperm surface fucosyltransferase enzymatic activity has been identified and suggested to mediate sperm-ZP binding (24,36). However, we cannot exclude the possibility that these two oligosaccharide-binding sites on sperm represent unidentified receptors.…”

Reassessing the role of protein-carbohydrate complementarity during sperm-egg interactions in the mouse

“…Similar to that reported for sperm GalT, the great majority of FucT activity is confined to the sperm surface. The ability of substrates for α1,2 and α1,3/ 4 FucTs, such as Galβ1,4GlcNAc, to inhibit sperm-egg binding is consistent with a role for sperm FucT in recognition of ZP glycans (Litscher et al, 1995;Thaler and Cardullo, 1996;Johnston et al, 1998).…”

Molecular Interactions between Sperm and Oocytes in the Mouse

“…Although sp56 is believed to interact with the terminal galactose residues of ZP3, this molecule may be intra-acrosomal [27], and not present on the surface membrane, as originally reported [28]. Although little evidence is available to date, α -fucosyltransferase (FucTase) may also serve as a ZP3 receptor, because the substrates for FucTase, but not for GalTase, inhibit sperm-zona binding [29]. Following the acrosome reaction, it is necessary for sperm to remain tightly bound to the zona pellucida.…”