Porcine Zona Pellucida: Association of Sperm Receptor Activity with the α-Glycoprotein Component of the Mr = 55,000 Family1

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Abstract
The immunogenicity and sperm receptor activity of five preparations of the major porcine zona pellucida glycoprotein family ZP3 (Mr = 55,000) were investigated. These included (1) ZP3, a chromatographically purified preparation of the 55,000 family; (2) ZP3.alpha., and (3) ZP3.beta., the two-component glycoproteins of the ZP3 family; (4) ZP3-EBGD, a partially deglycosylated preparation of ZP3 obtained by enzymatic treatment; and (5) ZP3-DG, a chemically deglycosylated preparation of ZP3. Titer studies using mouse and rabbit antisera prepared against each preparation yielded the following order of immunogenicity: ZP3 and ZP3.beta. > ZP3-EBGD and ZP3.alpha. > ZP3-DG, indicating that ZP3 becomes less immnogenic as more carbohydrate is removed. Pretreatment of intact zona with the various antisera prior to zona exposure to sperm resulted in an inhibition of sperm attachment to those zona treated with antibodies to ZP3, ZP3-EBGD, and ZP3.alpha.. Pretreatment of zona with antibodies to ZP3.beta. and ZP3-DG had no effect on sperm attachment. Studies involving pretreatment of boar sperm with the various ZP3 preparations prior to their use in a sperm-zona attachment assay and investigations involving displacement of the radiolabeled ZP3 preparations from sperm by unlabeled ZP3 preparations also yielded findings similar to the antibody studies. Collectively, these data indicate that ZP3.alpha. probably functions as a zona receptor for boar sperm and that carbohydrate has an important role in maintaining the functional integrity of the ZP3.alpha. glycoprotein.