The active enzyme then functions in the lysis of the zona pellucida, thus facilitating penetration of the sperm through the innermost glycoprotein layers of the ovum.

It has been found through genetic knockout experiments that mouse spermatozoa lacking β-acrosin (the active protease) still have the ability to penetrate the zona pellucida.

β-acrosin demonstrates a high degree of sequence identity (70-80%) between boar, bull, rat, guinea pig, mouse, and human isoforms.

Proacrosin is first cleaved between Arg-22 and adjacent Valine to create a 22 residue light chain, and an active protease termed α-acrosin.

[11] The S1 pocket regulates acrosin's specificity for Arg and Lys substrates, with a conserved Trp-215 serving as a "gatekeeper" residue for the binding site entrance.

[3] An important structural element of β-acrosin is a highly charged patch (formed through both amino acids and post-translational modifications) on its surface region, that has been termed the "anion binding exosite.

[12] This structural feature is consistent with the secondary binding protein hypothesis, as charge-charge interactions would stabilize a protein-zona pellucida "tethering" complex.

[13] Further consistent with this structural hypothesis is the knowledge that suramin - a polysulfated drug (with substantial corresponding negative charge) has been found to inhibit sperm-zona pellucida binding.

Acrosin may represent as a uniquely druggable target due to its location and high cellular specificity.