Background: Fertilization starts with the binding of the spermatozoa to the zona pellucida (ZP) of the oocyte. Such binding is a carbohydrate-mediated event and consists of a series of tightly regulated events. Molecular interactions between spermatozoon and ZP in human are not well characterized due to limited availability of oocytes for research. Our current technology cannot generate recombinant human ZP (hZP) glycoproteins with native glycosylation.
Methods and results: In this study, hZP glycoproteins, hZP2 (approximately 120 kDa), hZP3 (approximately 58 kDa) and hZP4 (approximately 65 kDa) were purified from ZP (purity >88%) by immunoaffinity columns. The binding sites of the purified native hZP3 and hZP4 were localized to the acrosome region of the capacitated human spermatozoa, and were lost after acrosome reaction. Purified human hZP2 bound to this region only in acrosome-reacted spermatozoa. Differential binding of the three glycoproteins to the post-acrosomal region and the midpiece of the spermatozoa was observed. In addition, hZP3, but not hZP2 and hZP4, induced hyperactivation. The stimulatory activity was dependent partly on N-linked glycosylation of hZP3.
Conclusions: This manuscript describes the biological activities of purified hZP glycoproteins from the native source for the first time.