The Contribution of d-Mannose, l-Fucose, N-Acetylglucosamine, and Selectin Residues on the Binding of Glycodelin Isoforms to Human Spermatozoa1

Abstract

Previous data showed that glycodelin-A from amniotic fluid and glycodelin-F from follicular fluid inhibited sperm-zona pellucida binding. Solubilized zona pellucida reduced the binding of glycodelin-F to sperm extract dose dependently. This study demonstrated that the zona pellucida proteins also reduced the binding of glycodelin-A to sperm extract. Ionophore-induced acrosome reaction reduced the binding of iodinated glycodelin-A and -F to sperm, indicating that the glycodelin-binding sites are on the outer acrosomal membrane or on the sperm plasma membrane overlying the acrosome. While the binding of glycodelin-A to sperm was suppressed by mannose and fucose neoglycoproteins, that of glycodelin-F was also reduced by acetylglucosamine neoglycoprotein. Pretreatment of sperm with inhibitors of mannosidase and acetylglucosaminidase reduced the binding of glycodelin-F to sperm. On the other hand, inhibitor of mannosidase but not of acetylglucosaminidase inhibited the binding of glycodelin-A. In a competition binding assay, mannosidase reduced both glycodelin-A and -F binding whereas acetylglucosaminidase reduced only glycodelin-F binding. While fucosidase reduced the binding of both glycodelins, fucosidase inhibitor was marginally active in suppressing the binding of glycodelins to human sperm. Among the selectins tested, only E-selectin had a slight inhibitory effect on the binding of glycodelin-A to sperm. The binding of glycodelin-F was unaffected by selectins and their antibodies. In conclusion, the binding of glycodelin-A to sperm involves mannose, fucose, and possibly E- selectin residues, while that of glycodelin-F involves mannose, fucose, and N-acetylglucosamine but not the selectin residue.

Glycodelin-A interacts with fucosyltransferase on human sperm plasma membrane to inhibit spermatozoa-zona pellucida binding

“…Its ability to bind to intact zona pellucida raises the possibility that it may be a zona pellucida glycoprotein receptor. This is in line with our previous conclusion that the glycodelin-A receptor is closely related to a zona pellucida glycoprotein receptor (Chiu et al, 2003b;Chiu et al, 2004).Apart from their usual intracellular location, FUT activities have been demonstrated on the cell surface of diverse cell types, such as prostatic epithelial cells (Marker et al, 2001) and rat Sertoli cells (Raychoudhury and Millette, 1997). It is generally believed that glycosyltransferases on the cell surface do not perform the glycosyltransferase function because of a lack of sugar nucleotide donors.…”

“…Deglycosylated glycodelin-A did not co-precipitate with recombinant and purified sperm FUTs (Fig. 6B), consistent with the previous observation that the interactions between glycodelin-A and spermatozoa were glycosylation dependent (Chiu et al, 2003b;Chiu et al, 2004). The addition of solubilized zona pellucida reduced the binding of The hemizona binding index (HZI) decreased in a dosedependent manner (Fig.…”

“…Moreover, in a cross-linking experiment, the glycodelin-A-FUT5 complex could only be obtained from spermatozoa, but not from fibroblasts, consistent with our previous finding that the binding of glycodelin is cell type-specific (Tse et al, 2002). The inability of deglycosylated glycodelin-A to coimmunoprecipitate with sperm FUT and recombinant FUT5 is also in line with the documented importance of carbohydrate moieties on spermatozoa-glycodelin interaction (Chiu et al, 2003b;Chiu et al, 2004). …”

More Than a Simple Lock and Key Mechanism: Unraveling the Intricacies of Sperm-Zona Pellucida Binding

“…Although sperm from GalT1 null mice bind poorly to ZP3 and fail to undergo a zona-induced acrosome reaction, they retain the ability to bind to the ovulated egg coat in vitro . In a similar vein, a number of zona pellucida binding molecules have been identified in human spermatozoa, including sperm autoantigenic protein 17 (SPA17) (Grizzi, et al, 2003), fucosyltransferase 5 (FUT5) (Chiu, et al, 2003a, Chiu, et al, 2004, and mannose binding receptor (Rosano, et al, 2007). However, further analyses of these receptor molecules have compromised their status as being the single molecule responsible for zona pellucida interaction (see Table 2).…”

“…Fucosyltransferase 5 (FUT5) Human  Localized to the acrosomal region of the sperm head  Pre-treatment of sperm with antibodies directed against FUT5 inhibits zona pellucida binding (Chiu, et al, 2003b, Chiu, et al, 2004 Milk fat globule-EGF factor 8 (MFGE8; p47; SED1)…”