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Lewis X-Containing Neoglycoproteins Mimic the Intrinsic Ability of Zona Pellucida Glycoprotein ZP3 to Induce the Acrosome Reaction in Capacitated Mouse Sperm¹

Division of Reproductive Biology,³ Department of Biochemistry and Molecular Biology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland 21205 The Johns Hopkins Kimmel Cancer Center and Department of Pharmacology and Molecular Sciences,⁴ Johns Hopkins University School of Medicine, Baltimore, Maryland 21231

The binding of zona pellucida (ZP) glycoprotein ZP3 to mouse sperm surface receptors is mediated by protein-carbohydrate interactions. Subsequently, ZP3 induces sperm to undergo the acrosome reaction, an obligatory step in fertilization. We have previously identified Lewis X (Le^x; Galß4[Fuc3]GlcNAc) as a potent inhibitor of in vitro sperm-ZP binding (Johnston et al. J Biol Chem 1998; 273:1888–1895). This glycan is recognized by 70% of the ZP3 binding sites on capacitated, acrosome-intact mouse sperm, whereas Lewis A (Le^a; Galß3[Fuc4]GlcNAc) is recognized by most of the remaining sites (Kerr et al. Biol Reprod 2004; 71:770–777). Herein, we test the hypothesis that Le^x- and Le^a-containing glycans, when clustered on a neoglycoprotein, bind ZP3 receptors on sperm and induce sperm to undergo the acrosome reaction via the same signaling pathways as ZP3. Results show that a Le^x-containing neoglycoprotein induced the acrosome reaction in a dose-dependent and capacitation-dependent manner. A Le^a-containing neoglycoprotein also induced sperm to undergo the acrosome reaction but was less potent than Le^x-containing neoglycoproteins. In contrast, neoglycoproteins containing ß4-lactosamine (Galß4GlcNAc), Lewis B (Fuc2Galß3[Fuc4]GlcNAc), and sialyl-Le^x glycans were inactive, as were four other neoglycoproteins with different nonfucosylated glycans. Consistent with these results, unconjugated Le^x- and Le^a-capped glycans were dose-dependent inhibitors, which at saturation, reduced the ZP-induced acrosome reaction by about 60% and 30%, respectively. Experiments utilizing pharmacological inhibitors suggest that induction of the acrosome reaction by solubilized ZP and Le^x- and Le^a-containing neoglycoproteins require the same calcium-dependent pathway. However, only the ZP-induced acrosome reaction requires a functional G_i protein. Thus, Le^x-containing neoglycoproteins bind to a major class of ZP3 receptors on capacitated sperm. A Le^a-containing neoglycoprotein binds a second ZP3 receptor but is a less-potent inducer of the acrosome reaction.

¹ This work was supported by National Institute for Child Health and Human Development (NICHD) 1 R01 HD-35699 and by the Johns Hopkins University Population Center (P30-HD-06268). W.F.H. and C.L.K. were supported in part by NICHD 5T32 HD-07276.

² Correspondence: William W. Wright, Johns Hopkins University Bloomberg School of Public Health, Department of Biochemistry and Molecular Biology, Room 3508, 615 N. Wolfe St., Baltimore, MD 21205. FAX: 410 614 2356; wwright1{at}jhem.jhmi.edu

This article has been cited by other articles:

				C. L. Kerr, W. F. Hanna, J. H. Shaper, and W. W. Wright Lewis X-Containing Glycans are Specific and Potent Competitive Inhibitors of the Binding of ZP3 to Complementary Sites on Capacitated, Acrosome-Intact Mouse Sperm Biol Reprod, September 1, 2004; 71(3): 770 - 777. [Abstract] [Full Text] [PDF]