Researchers have described how a secreted protease helps egg cells avoid being fertilized by more than one sperm. Because polyspermy disrupts embryonic development, oocytes take several steps to ensure they only fuse with a single sperm. One key step is to prevent additional sperm from binding to the surface of an already-fertilized egg, a blockade that involves the release of secretory granules and cleavage of the glycoprotein ZP2, a component of the zona pellucida matrix that surrounds eggs. ZP2 is cleaved upstream of two acidic amino acids, a cleavage site recognized by the astacin family of metalloendoproteases. Burkart et al. therefore investigated the function of ovastacin, an astacin family member expressed in oocytes.
