Practice question

Sperm-egg fusion depends on ADAM family proteins, particularly fertilin composed of ADAM1 and ADAM2 heterodimer concentrated on sperm membrane. After acrosome reaction equatorial segment exposes fertilin, which binds integrin alpha6beta1 on egg microvillar surface within CD9-enriched tetraspanin domains. This interaction stabilizes close apposition, promotes lipid bilayer merging and cytoplasmic continuity. While Izumo1-Juno provides primary adhesion, fertilin contributes fusogenic activity essential for completing membrane mixing and ensuring gamete coalescence during mammalian fertilization, subsequent zygote formation, activation cascade and monospermy establishment. This paradigm is central to understanding infertility and assisted fertilization.