Component of the zona pellucida, an extracellular matrix surrounding oocytes which mediates sperm binding, induction of the acrosome reaction and prevents post-fertilization polyspermy. The zona pellucida is composed of 3 to 4 glycoproteins, ZP1, ZP2, ZP3, and ZP4. ZP2 may act as a secondary sperm receptor. Can form homopolymers that assemble into long fibers (in vitro). Polymers of ZP2 and ZP3 organized into long filaments cross-linked by ZP1 homodimers. Interacts with ZP3. Oocytes (at protein level). The ZP domain is involved in the polymerization of the ZP proteins to form the zona pellucida. Proteolytically cleaved before the transmembrane segment to yield the secreted ectodomain incorporated in the zona pellucida. Proteolytically cleaved in the N-terminal part by the metalloendopeptidase ASTL exocytosed from cortical granules after fertilization, yielding a N-terminal peptide of about 30 kDa which remains covalently attached to the C-terminal peptide via disulfide bond(s). This cleavage may play an important role in the post-fertilization block to polyspermy. Additional proteolytically cleavage of the N-terminal peptide of 30 kDa occurs in one-cell and two-cell embryos. N-glycosylated. O-glycosylated; contains sulfate-substituted glycans. Belongs to the ZP domain family. ZPA subfamily.