Boar spermadhesins AQN-1 and AWN are sperm-associated acrosin inhibitor acceptor proteins.

Trypsin-like inhibitors secreted by the male accessory sex glands have been identified in the seminal plasma of every mammalian species so far investigated. They bind to acceptor molecules on the anterior part of ejaculated sperm, and are thought to play a role in the capacitation of spermatozoa stabilizing zona pellucida binding sites during sperm uterine passage, and then dissociating to allow sperm-egg's zona pellucida interaction. Here we report the identification of acrosin inhibitor acceptor molecules isolated from boar seminal plasma. These proteins, termed AQN-1 and AWN, belong to the recently described spermadhesin protein family, whose members have been implicated in sperm-zona pellucida recognition events. Thus, members of the spermadhesin family, although not possessing detectable enzymatic activity, show features of serine proteinases, and may be involved in both sperm capacitation and sperm-egg recognition and binding events.