STUDIES ON THE EPITOPE OF PIG ZONA-PELLUCIDA RECOGNIZED BY A FERTILIZATION-BLOCKING MONOCLONAL-ANTIBODY

Heat solubilized pig zona pellucida (pZP) was separated into four majo r glycoprotein families (pZP1, pZP2, pZP3, pZP4). Cloning of a full-le ngth cDNA coding for pZP1 revealed that the coding sequence for pZP4 w as immediately followed by the sequence for the amino-terminal residue of pZP2 and that they shared a significant similarity with mouse and human ZP2, which are considered to serve as a secondary sperm receptor in sperm-zona interactions. One of the monoclonal antibodies, mAb-5H4 , produced against pZP4 inhibited the binding of boar and human sperma tozoa to each of the homologous oocytes. The epitope recognized by mAb -5H4 was determined to be present on a 10 amino acid sequence of pZP1( 50-59) by using epitope mapping and analysis of chain flexibility of p ZP4. A synthetic 18mer peptide corresponding to pZP1(50-67) reacted wi th mAb-5H4, and mouse antisera raised to the synthetic 18mer peptide r ecognized intact pig zona pellucida and strongly inhibited the fertili zation of pig oocytes with boar spermatozoa in vitro. These results su ggest that the pZP4 peptide (50-59) identified as an epitope for mAb-5 H4 could be a promising candidate in the development of a contraceptiv e vaccine.