Sperm surface membrane protein that may be involved in sperm-egg plasma membrane adhesion and fusion during fertilization. Could have a direct role in sperm-zona binding or migration of sperm from the uterus into the oviduct. Interactions with egg membrane could be mediated via binding between its disintegrin-like domain to one or more integrins receptors on the egg. This is a non catalytic metalloprotease-like protein. Expressed specifically in spermatogenic cells in the seminiferous cells. Not detected in fetal tissues. A tripeptide motif (FEE) within disintegrin-like domain could be involved in the binding to egg integrin receptor and thus could mediate sperm/egg binding. The prodomain and the metalloprotease domain are cleaved during the epididymal maturation of the spermatozoa. In mammals, exists as a heterodimer composed of an alpha and beta subunits. In human, fertilin subunit alpha is a pseudogene.