Identification of Porcine Oocyte 55 kDa α and β Proteins within the Zona Pellucida Glycoprotein Families Indicates that Oocyte Sperm Receptor Activity is Associated with Different Zona Pellucida Proteins in Different Mammalian Species

Porcine zona pellucida (pZP) glycoprotein 55 kDa is composed of two core polypeptides, denominated alpha and beta. Sperm receptor activity has been shown to be associated with the oligosaccharide structures attached to the pZP55 alpha component. Here, we report a simple one-step HPLC procedure for the isolation of the alpha- and beta-components of the 55 kDa pZP proteins after enzymatic partial deglycosylation. N-Terminal sequence and protein chemical analysis of native proteins and of internal peptides from the alpha and the beta forms has established their homology with the rabbit 55 kDa zona pellucida glycoprotein and mouse ZP3, respectively. This, in turn, is relevant for a standardization of the ZP nomenclature in mammalian species. Moreover, our results imply that the sperm receptor activity in diverse mammalian species reside on oligosaccharide chains attached to nonhomologous zona pellucida glycoproteins. We hypothesize that acquisition of species-specific activity on the oocyte zona pellucida may thus be related to a species-specific glycosylation process.