Zona Pellucida Binding Protein (ZPBP)

ZPBP is one of several proteins that are thought to participate in secondary binding between acrosome-reacted sperm and the egg-specific extracellular matrix, the zona pellucida.Katoh and Katoh (2003) determined that the deduced 351-amino acid ZPBP protein has no N-terminal signal peptide, but contains an N-terminal transmembrane domain and a long extracellular domain of almost 300 amino acids.The extracellular domain shares 38.1% identity with a homologous domain within ZPBP2, including 15 conserved Cys residues. Analysis of EST databases indicated that ZPBP mRNA was coexpressed with ZPBP2 mRNA in testis, germ cell tumor, and brain medulla.