Practice question

Membrane fusion between sperm and egg requires specialized fusogenic proteins beyond simple adhesion. Fertilin, heterodimer of ADAM1 and ADAM2 disintegrin containing metalloproteases on sperm equatorial segment, binds alpha6beta1 integrin on egg microvillar membrane organized by tetraspanin CD9 microdomains. Interaction following Izumo1-Juno adhesion stabilizes close apposition, lowers energy barrier for lipid merger and promotes mixing of outer leaflets. Genetic ablation reducing fertilin shows impaired binding-fusion. Hence fertilin contributes crucial binding-fusion activity ensuring gamete coalescence, cytoplasmic continuity, successful zygote formation during fertilization event, activation and developmental initiation.