Defining oligosaccharide specificity for initial sperm-zona pellucida adhesion in the mouse.
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 x 10 (7)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 (approximately 100 msec) to disrupt binding. The current results suggest that the sperm ZP3 receptor binding site minimally recognizes the gal beta 1, 3-GlcNAc 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.
Thaler
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Department of Biology, University of California at Riverside 92521, USA.
Cardullo
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D000116:Acetylgalactosamine / Q000494:pharmacology*; D000117:Acetylglucosamine / Q000494:pharmacology*; D000818:Animals; D005260:Female; D005647:Fucosyltransferases / Q000378:metabolism; D005700:Galactosyltransferases / Q000378:metabolism; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009844:Oligosaccharides / Q000494:pharmacology*; D013084:Sperm-Ovum Interactions; D013094:Spermatozoa / Q000187:drug effects* / Q000378:metabolism; D015044:Zona Pellucida / Q000187:drug effects* / Q000378:metabolism
D009844:Oligosaccharides; D005647:Fucosyltransferases; D005700:Galactosyltransferases; D000116:Acetylgalactosamine; D000117:Acetylglucosamine