Category Archives: Spermatozoa

Binding of Glycodelin Isoforms to Human Spermatozoa: DISCUSSION(9)

In summary, the binding of glycodelin-A to sperm involves mannose, fucose, and possibly E-selectin-binding residues, while that of glycodelin-F involves mannose, fucose, and N-acetylglucosamine. The reduction in glycodelin binding after acrosome reaction and the ability of the zona pellucida to displace glycodelin from sperm extract suggest a close relationship between glycodelin receptors and zona pellucida protein receptors. However, a difference in the requirement for the binding of glycodelin and zona pellu-cida to sperm is noted when comparing the present study with previous reports.

Binding of Glycodelin Isoforms to Human Spermatozoa: DISCUSSION(8)

DISCUSSION(8)

On the other hand, E-selectin had slight inhibitory effect on the binding of glycodelin-A to sperm. These results are consistent with previous conclusions that glycodelin-F and glycodelin-A have different oligosaccharide chains. However, the inability of anti-selectin antibody to affect the binding of glycodelin-A to sperm suggests that sperm protein(s) with selectin-like activity, but not selectin, is involved in the sperm binding. A similar conclusion was reached for the binding of sperm to the zona pellucida.

Binding of Glycodelin Isoforms to Human Spermatozoa: DISCUSSION(7)

Beta-1,4-galactosyltransferase is the best characterized potential sperm receptor for zona pellucida. It binds specifically to the N-terminal N-acetylglucosamine residues of ZP3 but not to the other zona pellucida proteins. The enzyme is present in the head region of all mammalian sperm studied, including human, consistent with a role in gamete recognition. Reagents blocking the activity of the enzyme, including UDP-Gal and alpha-lact-albumin, inhibit sperm-zona pellucida binding. In this study, both UDP-Gal and alpha-lactalbumin did not affect the binding of glycodelin-A and -F to human sperm.

Binding of Glycodelin Isoforms to Human Spermatozoa: DISCUSSION(6)

DISCUSSION(6)

Although N-ace-tylglucosaminidase also hydrolyses N-acetylgalactosamine residue, this monosaccharide residue is unlikely to be involved in the binding of glycodelin to sperm, as its neoglycoprotein did not affect glycodelin binding in the present study. This is consistent with previous observations that neither this monosaccharide nor its neoglycoprotein affects sperm-zona pellucida binding or acrosomal status of the human sperm in vitro. canadian neighbor pharmacy

Binding of Glycodelin Isoforms to Human Spermatozoa: DISCUSSION(5)

Rat, mouse, hamster, and human sperm possess mannosidase activity. Mannosidase binds and hydrolyses terminal mannose of N-linked oligosaccharides. Al-pha-mannosidase activity has been localized to the plasma membranes of rat, mouse, and human sperm. However, the exact mannosidase isoform on sperm remains to be identified. The importance of mannosyl residues in fertilization is demonstrated by the observation that incubation of mouse sperm with D-mannose results in a dose-dependent decrease in the number of sperm bound to the oocyte. Pretreatment of human sperm with D-mannose also inhibits sperm penetration through the zona.

Binding of Glycodelin Isoforms to Human Spermatozoa: DISCUSSION(4)

DISCUSSION(4)

This may make it more difficult for the neoglycoproteins to compete with glycodelin-F for the binding sites. It is also possible that the contribution of mannose and fucose residues in the binding of glycodelin-F to sperm is smaller than that in glycodelin-A sperm binding. The present data do not allow us to distinguish between these possibilities.

Binding of Glycodelin Isoforms to Human Spermatozoa: DISCUSSION(3)

The carbohydrate moieties of glycodelin-A and -F are critical for their zona-binding inhibitory activity as well as their binding on human sperm, and deglycosylated glycodelin loses such activities in vitro. Glycodelin-F has the same protein core as glycodelin-A, but their oligosaccharide chains are different. In the present study, we demonstrated that different sets of carbohydrate residues affected the binding of these glycodelin isoforms to sperm. While the binding of glycodelin-A appears to be affected by the mannose and fucose residues, that of glycodelin-F is influenced by N-acetylglucosamine in addition to fucose and mannose.

Binding of Glycodelin Isoforms to Human Spermatozoa: DISCUSSION(2)

DISCUSSION(2)

Neoglycoproteins are frequently used in studies on sperm-zona pellucida interactions, some of which mimic the action of ZP3 glycoprotein and induce acrosome reaction in capacitated mouse and human sperm. The acrosome reaction-inducing ability of neoglycoprotein and the reduction of glycodelin binding after acrosome reaction requires the use of fixed, instead of live, sperm for characterization of the glycodelin-binding sites on sperm using neoglycoproteins; otherwise, equilibrium binding would have been impossible to achieve.

Binding of Glycodelin Isoforms to Human Spermatozoa: DISCUSSION(1)

Solubilized zonae pellucidae protein dose-dependently reduces the binding of glycodelin-F to the sperm extract. This report demonstrates that zona pellucida proteins also reduce the binding of glycodelin-A to sperm extract. Glycodelin-A and -F form two and three complexes, respectively, with sperm extract. While the formation of two of the glycodelin-F complexes are inhibited by solubilized zona pellucida, only one of the glycodelin-A complexes is affected by the zona pellucida proteins. These observations are consistent with the binding kinetic experiments demonstrating that human sperm possess two receptors for glycodelin-F, one of which is common with gly-codelin-A.

Binding of Glycodelin Isoforms to Human Spermatozoa: RESULTS(5)

RESULTS(5)

Similar to glycodelin-A, mannosidase and fucosidase had the greatest inhibitory effect on glycodelin-F binding, with significant inhibition at a concentration of 0.5 |xg/ml (Fig. 7B). The corresponding inhibition at 3 |xg/ml was 51.7% ± 2.0% and 22.3% ± 4.2%. Unlike that of glycodelin-A, acetylglucosaminidase inhibited glycodelin-F binding dose dependently; the inhibition was 43.7% ± 2.8% at 3 |xg/ml. No inhibition was observed with galactosidase. At the concentrations employed, the glycosidases did not affect sperm viability, acrosomal status, and motility (data not shown).

Pages: 1 2 3 Next