ZP3, also known as zona pellucida glycoprotein 3 or sperm receptor, is a glycoprotein encoded by the ZP3 gene and is a major structural component of the zona pellucida, an extracellular matrix that surrounds the oocyte and early embryo. It is crucial for sperm binding and induction of the acrosome reaction, which is essential for fertilization. In mice, ZP3 is the single zona pellucida protein sufficient and necessary for sperm binding in vitro, though it is insufficient for fertilization in vivo. In humans, ZP1, ZP3, and ZP4 all appear partially responsible for starting the acrosome reaction. The nascent ZP3 protein contains a N-terminal signal peptide sequence, a conserved ZP domain, a C-terminal consensus furin cleavage site, and a transmembrane domain. Furin cleavage is hypothesized to release the mature protein from the plasma membrane for incorporation into the zona pellucida matrix.
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