BINDING OF PIG SPERM RECEPTOR IN THE ZONA-PELLUCIDA TO THE BOAR SPERMACROSOME

Pig zona pellucida (ZP) contains three families of glycoproteins: PZP2 , PZP3 alpha and PZP3 beta. PZP3 alpha mediates the binding of the ZP to spermatozoa. In this study, the binding site of pig ZP on boar sper matozoa and the zona-binding proteins of boar spermatozoa were studied using chemically modified zona glycoproteins or anti-pig ZP antiserum . Endo-beta-galactosidase-digested PZP3 alpha (E beta G-PZP3 alpha), w hich is deficient in sulfated N-acetylpolylactosamine, as well as solu bilized ZP, bound to the acrosomal region of acrosome-damaged or parti ally acrosome-reacted spermatozoa. However, they did not bind to acros ome-intact or fully acrosome-reacted spermatozoa. Solubilized ZP did b ind to the acrosomal cap released upon acrosome reaction. In western b lot analyses, E beta G-PZP3 alpha bound to the sperm proteins with mol ecular masses similar to proacrosin-acrosin and the binding was inhibi ted by fucoidan and anti-pig acrosin antiserum. These results suggest that the binding site of solubilized pig ZP and E beta G-PZP3 alpha on spermatozoa is located mainly in the acrosomal matrix and on the memb ranous compartments in the acrosome and suggest that E beta G-PZP3 alp ha binds to proacrosin-acrosin. The binding of E beta G-PZP3 alpha to proacrosin-acrosin may be involved in the binding of the ZP to the acr osome of partially acrosome-reacted spermatozoa.