Characterization of zona pellucida glycoprotein 3 (ZP3) and ZP2 binding sites on acrosome-intact mouse sperm.
There is considerable evidence that mouse fertilization requires the binding of sperm to two of the three glycoproteins that form the zona pellucida (ZP), ZP3 and ZP2. Despite the biologic importance of this binding, no one has demonstrated that sperm express separate, saturable, and specific binding sites for ZP3 and for ZP2. Such a demonstration is a prerequisite for defining the distribution, numbers, affinities, and regulation of function of ZP3 and ZP2 binding sites on sperm. The experiments reported herein used fluorochrome-labeled ZP3 and ZP2 and quantitative image analysis to characterize the saturable binding of ZP3 and ZP2 to distinct sites on living, capacitated, acrosome-intact mouse sperm. Approximately 20% of the ZP3 binding sites were found over the acrosomal cap, and the remaining sites were located over the postacrosomal region of the head. In contrast, ZP2 binding sites were detected only over the postacrosomal region. Saturation analysis estimated numbers and affinities of the binding sites for ZP3 (B(max) approximately 185 000 sites per sperm; K(d) approximately 67 nM) and ZP2 (B(max) approximately 500 000 sites per sperm; K(d) approximately 200 nM). Use of unlabeled ZP3, ZP2, and ZP1 as competitive inhibitors of the binding of fluorochrome-labeled ZP3 and ZP2 demonstrated that ZP3 and ZP2 bound specifically to their respective sites on sperm. Finally, we demonstrate that extracellular calcium as well as capacitation and maturation of sperm are required for these sites to bind their respective ligands.
Kerr
Candace L
CL
Division of Reproductive Biology, Department of Biochemistry and Molecular Biology, The Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland 21205-2179, USA.
Hanna
William F
WF
Shaper
Joel H
JH
Wright
William W
WW
D000177:Acrosome / Q000502:physiology*; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002118:Calcium / Q000494:pharmacology; D004527:Egg Proteins / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D004822:Epididymis / Q000502:physiology; D005260:Female; D005456:Fluorescent Dyes; D006358:Hot Temperature; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D008813:Mice, Inbred ICR; D011956:Receptors, Cell Surface; D012995:Solubility; D013075:Sperm Capacitation; D013094:Spermatozoa / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D015044:Zona Pellucida / Q000737:chemistry; D000072216:Zona Pellucida Glycoproteins
D004527:Egg Proteins; D005456:Fluorescent Dyes; D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; D000072216:Zona Pellucida Glycoproteins; C000606519:Zp1 protein, mouse; C000606520:Zp2 protein, mouse; C000606521:Zp3 protein, mouse; D004533:Egtazic Acid; D002118:Calcium