Mammalian gametes recognize each other when the plasma membrane of the sperm head binds to the zona pellucida (ZP), an extracellular coat surrounding eggs. The zona pellucida is composed of four major glycoproteins expressed in oocytes, ZP1, ZP2, ZP3 and ZP4. Important receptors of zona pellucida on sperm are the zona pellucida binding proteins (ZPBPs). ZPBPs are suggested to play an essential role in sperm-egg interaction. ZPBP2 (zona pellucida binding protein 2), also known as ZPBPL, is a 338 amino acid secreted protein that belongs to the zona pellucida-binding protein Sp38 family. Mutations in the gene encoding ZPBP2 may cause subfertility. ZPBP2 exists as two alternatively spliced isoforms and is encoded by a gene located on human chromosome 17q12.