AWN proteins mediate the binding of boar spermatozoa to component(s) of the egg's zona pellucida by a carbohydrate-binding mechanism. Awn proteins are secretory components of the male accessory glands being coated to the sperm surface at the time of ejaculation. They possess as well heparin-, serine-protease-inhibitor-binding capability. Predominantly localized on the membrane overlying the acrosomal cap region of the sperm head. Partial N-acetylation differentiates isoforms AWN-1 (not acetylated) and AWN-2 (acetylated). Belongs to the spermadhesin family.