Modulation of sperm acrosomal exocytosis by guanyl nucleotides and G-protein-modifier agents.
Mammalian sperm must undergo an exocytotic event during fertilization, the acrosome reaction (AR). This process is specifically induced by egg-surface glycoproteins and it involves guanine nucleotide binding proteins (G-proteins). Neoglycoproteins (NGP) with mannose or N-acetylglucosamine residues has been demonstrated to induce the AR in human sperm. Activators of G-proteins, like GTP gamma S, GppNHp, mastoparan and AlF4- were capable of inducing the AR, while other nucleotides or analogues did not. When sperm were preincubated with these agents and then with NGPs, only the G-protein inhibitor GDP beta S decreased the AR rate. The preincubation of sperm with Pertussis toxin resulted in the inhibition of NGP-induced AR, while no effect was observed with cholera toxin. Results indicate that direct activation of G-proteins is sufficient to elicit the AR, and the induction of the AR in human sperm is mediated by N-acetylglucosaminyl and mannosyl binding sites involving PTx-sensitive G-proteins similar to the induction by zona pellucida glycoproteins.
Brandelli
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Laboratorio de Bioquímica, ICTA, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brasil.
D000177:Acrosome / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D005089:Exocytosis / Q000187:drug effects*; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005944:Glucosamine / Q000031:analogs & derivatives / Q000378:metabolism; D006150:Guanine Nucleotides / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D008297:Male; D008358:Mannose / Q000378:metabolism; D006005:Phosphorylases / Q000037:antagonists & inhibitors; D013094:Spermatozoa / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D015044:Zona Pellucida / Q000378:metabolism / Q000502:physiology
D006150:Guanine Nucleotides; C098108:N-acetylglucopyranosylamine; D006005:Phosphorylases; D019204:GTP-Binding Proteins; D005944:Glucosamine; D008358:Mannose