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8.A.55 The IZUMO Sperm-Egg Fusion Protein 1 (IZUMO1) Family 

Essential sperm cell-surface protein required 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 is required for fertilization but is not sufficient for cell fusion. The ligand-receptor interaction probably does not act as a membrane 'fusogen' (Klinovska et al. 2014).

References associated with 8.A.55 family:

Inoue, N., D. Hamada, H. Kamikubo, K. Hirata, M. Kataoka, M. Yamamoto, M. Ikawa, M. Okabe, and Y. Hagihara. (2013). Molecular dissection of IZUMO1, a sperm protein essential for sperm-egg fusion. Development 140: 3221-3229. 23824580
Klinovska, K., N. Sebkova, and K. Dvorakova-Hortova. (2014). Sperm-egg fusion: a molecular enigma of mammalian reproduction. Int J Mol Sci 15: 10652-10668. 24933635