FOLR4, also know as Sperm-egg fusion protein Juno (IZUMO1R) is receptor for IZUMO1 present at the cell surface of oocytes (oolemma), which is essential for species-specific gamete recognition and fertilization. The IZUMO1:IZUMO1R/JUNO interaction is a necessary adhesion event between sperm and egg that is required for fertilization but is not sufficient for cell fusion. The ligand-receptor interaction probably does not act as a membrane 'fusogen'. Does not bind folate.