Zona pellucida sperm-binding protein 3 is a ZP module-containing protein. ZP3 is the glycoprotein in the zona pellucida most important for inducting the acrosome reaction of sperm cells at the beginning of fertilization. The zona pellucida (ZP) is composed of three or four glycoproteins (ZP1-4) with various functions during oogenesis, fertilization and preimplantation development. The protein is a major structural component of the ZP and functions in primary binding and stimulation of the sperm acrosome reaction. The nascent protein contains a N-terminal signal peptide sequence, a conserved "ZP domain" module, a consensus furin cleavage site (CFCS), a polymerization-blocking external hydrophobic patch (EHP), and a C-terminal transmembrane domain. Cleavage at the CFCS separates the mature protein from the EHP, allowing it to incorporate into nascent ZP filaments.