Binds in a species-specific manner to the zona pellucida of the egg. May be involved in gamete recognition and/or signaling. Probably forms covalent oligomers. Exclusively on the apical region of the sperm head. In testis, primarily in haploid spermatids. Not in lung, liver, heart, spleen, brain, kidney, epididymis. The MAM domains probably mediate sperm adhesion to the zona pellucida. During sperm migration through the reproductive tracts, the mucin-like domain might inhibit inappropriate trapping of spermatozoa or promoting adhesion to the oviductal isthmus. The VWFD domains 2 and 3 may mediate covalent oligomerization (By similarity to human intestinal mucin MUC2). The MAM domains and the mucin-like domains are missing from the zonadhesin that binds to the egg extracellular matrix. Processing might occur during sperm maturation and/or capacitation.