THE POLYPEPTIDE BACKBONE OF RECOMBINANT HUMAN ZONA-PELLUCIDA GLYCOPROTEIN-3 INITIATES ACROSOMAL EXOCYTOSIS IN HUMAN SPERMATOZOA IN-VITRO

Human gamete interaction is of fundamental biological importance, yet the molecular interactions between spermatozoa and the zona pellucida are poorly understood. Suprisingly, the role of the polypeptide backbo ne of zona pellucida glycoprotein 3 (ZP3), the putative ligand for spe rmatozoa activation, has been largely overlooked. Purified recombinant human ZP3 was expressed in Escherichia coli as a C-terminal fusion to the dimeric glutathione S-transferase (GST) from Schistosoma japonicu m and was shown to induce acrosomal exocytosis in live, capacitated hu man spermatozoa. The level of exocytosis is comparable with that obtai ned using purified, glycosylated, recombinant human ZP3 [van Duin, M., Polman, J. E. M., DeBreet, I. T. M., Van Ginneken, K., Bunschoten, H. , Grootenhuis, A., Brindle, J. Aitken, R. J. (1994). Biol Reprod. 51, 607-617]. These data imply that the polypeptide chain of human ZP3 con tributes to recognition of spermatozoa during acrosomal exocytosis in vitro.