Multiple roles for PH-20 and fertilin in sperm-egg interactions

Using monoclonal antibodies that inhibit function, two cell surface proteins involved in gamete interactions were identified on guinea-pig sperm. Homologs of both the proteins have been identified in a number of mammalian species. One of the proteins, PH-20, has a function in sperm-zona binding and also has hyaluronidase activity. The other, named fertilin, is a heterodimer involved in sperm-egg membrane adhesion and also has a possible role in membrane fusion itself. Additionally, the precursor form of fertilin has potential metalloprotease activity. The functions of these proteins in gamete interactions range from the first physical contact between the sperm and cumulus cells to the final membrane interactions of sperm and egg leading to fusion.