zona pellucida glycoprotein 3 (sperm receptor); The mammalian zona pellucida, which mediates species- specific sperm binding, induction of the acrosome reaction and prevents post-fertilization polyspermy, is composed of three to four glycoproteins, ZP1, ZP2, ZP3, and ZP4. ZP3 is essential for sperm binding and zona matrix formation (424 aa)