A monoclonal antibody cross-reactive with porcine and human zona pellucida recognized the protein's steric structure

The epitopes recognized by two monoclonal antibodies (Nos. 1 and 2) against solubilized porcine zona pellucida (Zp) were chemically characterized. No. 1 reacts with porcine but not human Zp, whereas No. 2 not only reacts with both but also inhibits the binding of sperms to oocytes in the human system. By Western blotting, both No. 1 and No. 2 were found to react with a glycoprotein in the 55 kDa family of porcine Zp. Treatment of this protein with trypsin, sodium periodate, glycosidases and organic solvents, followed by measurement of its reactivity against No. 1 and No. 2 by competitive inhibition in an enzyme-linked immunosorbent assay (ELISA), found that the epitopes recognized by the two antibodies belonged to the peptide but not carbohydrate portion of the protein. The two epitopes were different in that the one recognized by No. 1 was resistant to protein denaturing conditions, whereas the other recognized by No. 2 was destroyed by such conditions. These results suggested that No. 1 recognized a porcine Zp-specific primary structure, while No. 2 recognized a steric structure of the protein which is similar in both human and porcine Zps.