Izumo sperm-egg fusion protein 1 (Izumo1)

Essential sperm cell-surface protein needed for fertilization by acting as a ligand for IZUMO1R/JUNO receptor on egg. The IZUMO1:IZUMO1R/JUNO interaction is a necessary adhesion event between sperm and egg that's required for fertilization but is not sufficient for cell fusion.

The ligand-receptor interaction probably doesn't act as a membrane'fusogen'. .