CHARACTERIZATION OF AWN-1 GLYCOSYLATED ISOFORMS HELPS DEFINE THE ZONA-PELLUCIDA AND SERINE PROTEINASE INHIBITOR-BINDING REGION ON BOAR SPERMADHESINS

Spermadhesin AWN-1 (14 kDa) belongs to a recently described family of boar sperm surface-associated proteins. AWN-1 is a multifunctional pro tein which possesses heparin-, serine proteinase inhibitor-, and zona pellucida glycoprotein-binding capability. Therefore it has been impli cated in sperm capacitation and sperm-oocyte attachment. Here, we repo rt the characterization of 22-25 kDa isoforms of AWN-1 isolated by hep arin-affinity chromatography, which fail to bind to zona pellucida gly coproteins or serine proteinase inhibitors. Our results show that the structure of the high and low molecular mass AWN-1 forms differ in tha t the former is N-glycosylated at Asp50 and truncated at the C-terminu s. The inability of the glycosylated AWN-1 molecules to bind ligands i s due solely to the presence of the oligosaccharide moieties, however. This indicates that glycosylation of AWN-1 may modulate its ligand-bi nding capabilities. On the other hand, the effect of glycosylation on ligand-binding suggests that both the zona pellucida- and the serine p roteinase inhibitor binding domain(s) may be located around the glycos ylation point.