Fertilin protein mediates:
Fertilin, also known as ADAM1-ADAM2 heterodimer, is sperm surface metalloprotease-disintegrin expressed in testis and processed during epididymal maturation, localizing to posterior head and equatorial segment. Its disintegrin domain interacts with integrins on egg plasma membrane microvillar region, facilitating adhesion and promoting membrane apposition preceding fusion pore formation coordinated by Izumo1-Juno and CD9. Fertilin knockout sperm show reduced fusion efficiency despite normal zona penetration. It does not function in acrosome biogenesis, zona digestion or capacitation but specifically bridges gamete membranes, making it critical component of mammalian sperm-oolemma binding and fusion machinery evolutionarily conserved across rodents and primates.
Ref: Evans JP, Human Reproduction Update 2002: ADAM fertilin roles in sperm-egg adhesion and membrane fusion.