A family of mammalian sperm proteins has been recently characterized [1,2]. The proteins that are currently known to belong to this family are:

• Pig spermadhesins AQN-1, AQN-3 and AWN-1. These proteins are synthesized by the sexual accessory glands and becomes attached to the sperm surface at the time of ejaculation. They bind to the ZP-glycoproteins and to heparin and seems to inhibit serine protease inhibitors.
• Bovine acidic seminal fluid protein (ASFP), which seems to be growth factor with effects on ovarian granulosa cells.
• Pig major seminal plasma glycoproteins PSP-I and PSP-II.
• Bovine seminal plasma protein Z13.

As shown in the following schematic representation these proteins, which have from 110 to 130 amino acid residues, contain four conserved cysteines involved in two disulfide bonds.

                +---------+           +---------+
                |         |           |         |
            xxxxCxxxxxxxxxCxxxxxxxxxxxCxxxxxxxxxCxxxxxxxxxxxxxxxxxx
                ************          ***********

'C': conserved cysteine involved in a disulfide bond.
'*': position of the patterns.

Structurally, the spermadhesins consist of a CUB domain [3] (see <PDOC00908>).