Is implicated in sperm-oocyte interaction during fertilization. Released after the acrosomal reaction. Expressed specifically in male germ cells. Expressed from the mid-pachytene spermatocyte stage to the early elongating spermatid stage. N-glycosylated. Male mice are subfertile with sperm showing reduced ability to penetrate zona pellucida and displaying subtle morphological deformation, including shortened apical hook, smaller apical angle and bulges in acrosome region. Belongs to the zona pellucida-binding protein Sp38 family.