Sperm protein required for fusion of sperm with the egg membrane during fertilization. Does not interact with sperm-egg fusion proteins IZUMO1 or IZUMO1R/JUNO. Following the acrosome reaction, relocalizes to the equatorial segment. Expressed exclusively in testis. Expression is first detected at postnatal day 21. Males are healthy, grossly normal and exhibit normal mating behavior but are infertile (PubMed:32484434, PubMed:32393636). Sperm are morphologically normal, exhibit normal motility and can penetrate the zona pellucida and bind to the oolemma but are unable to fuse with the egg membrane or penetrate into the ooplasm (PubMed:32484434, PubMed:32393636). No effect on location of sperm-egg fusion protein IZUMO1 (PubMed:32393636). Belongs to the TMEM95 family.