May have a role in sperm-egg fusion and maturation. Located in the lumen and epithelium of distal ductus efferentes and epididymal ducts, and on the postacrosomal region of the sperm head. Expressed in all the regions of the epididymis except the caput and is not detected in the testis, prostate, seminal vesicle, and brain. Belongs to the CRISP family.