IZUMO1
Domain
The extracellular domain assumes a distinct boomerang shape when not bound to IZUMO1R/JUNO (PubMed:27309818). Interaction with IZUMO1R/JUNO triggers a conformation change, so that the IZUMO1 extracellular domain assumes an upright conformation (PubMed:27309818).
The cytoplasmic C-terminus region is not essential for fertilization. It is however required for protein stability.
Function
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'. Acts a ligand for the human-specific oolemma epitope FCRL3/MAIA during fertilization (PubMed:36070373). FCRL3/MAIA replaces IZUMO1R/JUNO as IZUMO1 receptor after sperm-egg adhesion, which permits species-specific gamete fusion (PubMed:36070373).
Post-translational modifications
N-glycosylated. Glycosylation is not essential for fusion and for proper protein trafficking in sperm.
Phosphorylated. The cytoplasmic C-terminus is phosphorylated and undergoes phosphorylation changes during epididymal transit.
Sequence Similarities
Belongs to the Izumo family.
Tissue Specificity
Sperm-specific (at protein level) (PubMed:15759005, PubMed:36070373). Detectable on sperm surface only after the acrosome reaction (PubMed:15759005, PubMed:36070373).
Cellular localization
- Cell membrane
- Single-pass type I membrane protein
- Cytoplasmic vesicle
- Secretory vesicle
- Acrosome membrane
- Single-pass type I membrane protein
- Localizes initially to the acrosome membrane of the sperm head (both outer and inner acrosomal membranes) (PubMed:36070373). During the acrosome reaction, translocates to the plasma membrane (PubMed:15759005, PubMed:36070373).
Alternative names
Izumo sperm-egg fusion protein 1, Oocyte binding/fusion factor, Sperm-specific protein izumo, OBF, IZUMO1