Spermadhesins of the AQN and AWN families, DQH sperm surface protein and HNK protein in the heparin-binding fraction of boar seminal plasma

Heparin-binding proteins (designated BHB-2-BHB-9) were isolated from boar seminal plasma by affinity chromatography on heparin immobilized on polyacrylamide gel, followed by reverse phase HPLC. According to their N-terminal amino acid sequences, BHB-3-BHB-5 belong to the AQN family of spermadhesins and BHB-7-BHB-9 to the AWN family. BHB-6 is composed of two different proteins. The dominant protein (14 kDa) has the N-terminal amino acid sequence HNKQEGRDHD that is identical to the sequence of human semenogelin at positions 85-94. The minor proteins (16 and 17 kDa) belong to the AWN family of spermadhesins. The 14 kDa HNK protein does not crossreact with antibodies against AQN or AWN spermadhesins. BHB-2 also binds to the acrosome of boar epididymal spermatozoa but has the N-terminal sequence DQH. Therefore, basic protein BHB-2 belongs to a new family of DQH sperm surface proteins that are homologous to the acidic proteins from bull and stallion seminal plasma, to the collagen binding domain II in fibronectin and to the leucocyte cell-cell adhesion regulator, but are not homologous to AQN or AWN spermadhesins. Nevertheless, anti-AQN-1 spermadhesin antibodies crossreact strongly with DQH protein. All boar heparin-binding proteins bind concanavalin A indicating their glycoprotein nature, which was proved by the detection of glucosamine and galactosamine residues in their molecules. Furthermore, spermadhesins interact with zona pellucida, protease inhibitors and a polyacrylamide derivative of heparin. Affinity chromatography experiments showed that the DQH protein bound to gelatin-agarose together with the AWN proteins and that the DQH protein and AQN-1 spermadhesin belong to the phosphoryl choline binding proteins.