Saccharide-binding properties of boar AQN spermadhesins and DQH sperm surface protein

Heparin-binding proteins BHB 2-BHB 5 were purified from boar seminal plasma by affinity chromatography on a heparin-polyacrylamide column and reversed phase HPLC. Three of the proteins, BHB 3-BHB 5, were found to be identical to spermadhesins AQN 1-AQN 3 isolated from boar spermatozoa. The lectin-like properties of the isolated proteins BHB 2-BHB 5 were studied using double-diffusion in agarose gel, enzyme-linked binding assay, and inhibition assays of erythroagglutinating activity. It was found that proteins BHB 3-BHB 5 (spermadhesins AQN 1-AQN 3) interacted with glycoproteins containing O-glycosidically bound oligosaccharide chains, but not with those containing only N-linked carbohydrate chains. The strongest interaction was observed between BHB 3 (AQN 1) and desialyzed bovine submaxillary gland mucin, the glycoprotein containing only O-glycosidically linked saccharides. No interaction of BHB 3-BHB 5 proteins with simple saccharides, their derivatives or acidic polysaccharides was observed. Both the hemagglutinating activity and saccharide-binding properties of BHB 2 protein were quite different. Agglutinating activity of human erythrocytes by BHB 2 protein was significantly higher than that by BHB 3-BHB 5 proteins (AQN spermadhesins). In contrast to AQN spermadhesins, BHB 2 protein (DQH sperm surface protein) interacted strongly with acidic polysaccharides and sialyzed glycoproteins, but no binding of desialyzed glycoproteins as well as N-acetyl-alpha-D-galactosaminyl-O-serine,simple monosaccharides and amino sugars was observed.