Plays a role in acrosome compaction and sperm morphogenesis. Is implicated in sperm-oocyte interaction during fertilization. First localized in acrosome granule, later migrates to the inner and outer acrosomal membrane (PubMed:19204925). Released after the acrosomal reaction (PubMed:17664285). Expressed in testis (at protein level) (PubMed:19204925). Expressed in male germ cells (PubMed:17664285). Barely detectable at 11 days postpartum (dpp), very strong signal from 20 dpp until adulthood (PubMed:19204925). Expressed from the mid-pachytene spermatocyte stage to the early elongating spermatid stage (PubMed:17664285, PubMed:19204925). N-glycosylated. Male mice are infertile with abnormal round-headed sperm morphology and no forward sperm motility. Belongs to the zona pellucida-binding protein Sp38 family.