Plays a role in the binding between sperm and oocytes. Component of epididymosomes, one type of membranous microvesicules which mediate the transfer of lipids and proteins to spermatozoa plasma membrane during epididymal maturation. Also a component of the CD9-positive microvesicules found in the cauda region. Located in the connecting piece of elongated spermatids and sperm. Also located in the apical region of the sperm head after sperm capacitation. Located on sperm equatorial segment and neck. Associated with epididymosomes from the caput and cauda epididymis. Highly expressed in testis. N-glycosylated. N-glycosylation decreases during the transit in the caput. Belongs to the CRISP family.