Sperm-associated protein candidates for primary zona pellucida-binding molecules: structure-function correlations of...

The initial binding of mammalian spermatozoa and the zona pellucida of their homologous oocytes appears to be mediated by a protein-carbohydrate recognition mechanism. Subsequent protein-protein interaction triggers the acrosome reaction leading to sperm penetration. Spermatozoa possess a complement of surface-associated proteins that mediate interactions with the zona pellucida of the oocyte at fertilization. Both integral membrane and peripherally associated zona pellucida-interacting molecules have been described in a number of species. Some of these proteins have been shown to possess carbohydrate-binding activity and are therefore classified as candidates for primary gamete recognition molecules. The participation of any of these proteins in the in vivo situation is, however, a matter of debate. Here, we summarize current knowledge of the most thoroughly studied sperm-associated zona pellucida- and carbohydrate-binding molecules, paying special attention to recent evidence from our laboratories for considering sperm-adhesin AWN, and probably other members of its protein family, as a bona fide candidate for the primary gamete adhesion lectin.