Effect of recombinant boar beta-acrosin on sperm binding to intact zona pellucida during in vitro fertilization

In a previous paper we demonstrated that boar beta-acrosin recombinant prot eins were able to bind non-enzymatically to solubilized pig zona pellucida (ZP) glycoproteins, Here we report the participation of boar beta-acrosin i n the secondary binding of sperm to intact pig ZP, This was achieved by usi ng two boar recombinant proteins: beta-acrosin and a mutant of the catalyti c site, beta-acrosin Ser/Ala(222). Assays of binding between the iodinated recombinant beta-acrosin and whole ZP showed that this binding could be sat urated, was specific, and was stable over time. Using autoradiography, we d etermined that recombinant beta-acrosin bound on the entire surface of the ZP but initially was distributed heterogeneously. This suggests that the li gands for beta-acrosin may not be homogeneously distributed on the ZP. To s tudy the contribution of acrosin in sperm secondary binding to the ZP, we p reincubated in vitro-matured oocytes with these recombinant proteins and th en performed in vitro fertilization assays, Under the experimental conditio ns used, binding of beta-acrosin recombinant proteins did not block sperm p enetration. These results suggest that there may be other proteins that par ticipate in the secondary binding, and that these proteins may recognize li gands that are different from those blocked by beta-acrosin recombinant pro teins.