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. 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 domain 2 may mediate covalent oligomerization. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay.