Effect of recombinant boar beta-acrosin on sperm binding to intact zona pellucida during in vitro fertilization
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Date
1999
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Abstract
In a previous paper we demonstrated that boar β-acrosin recombinant proteins were able to bind non-enzymatically to solubilized pig zona pellucida (ZP) glycoproteins. Here we report the participation of boar β-acrosin in the secondary binding of sperm to intact pig ZP. This was achieved by using two boar recombinant proteins: β-acrosin and a mutant of the catalytic site, β-acrosin Ser/Ala222. Assays of binding between the iodinated recombinant β-acrosin and whole ZP showed that this binding could be saturated, was specific, and was stable over time. Using autoradiography, we determined that recombinant β-acrosin bound on the entire surface of the ZP but initially was distributed heterogeneously. This suggests that the ligands for β-acrosin may not be homogeneously distributed on the ZP. To study the contribution of acrosin in sperm secondary binding to the ZP, we preincubated in vitro-matured oocytes with these recombinant proteins and then performed in vitro fertilization assays. Under the experimental conditions used, binding of β-acrosin recombinant proteins did not block sperm penetration. These results suggest that there may be other proteins that participate in the secondary binding, and that these proteins may recognize ligands that are different from those blocked by β-acrosin recombinant proteins.