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 b oar seminal plasma by affinity chromatography on heparin immobilized o n polyacrylamide gel, followed by reverse phase HPLC. According to the ir N-terminal amino acid sequences, BHB-3-BHB-5 belong to the AQN fami ly of spermadhesins and BHB-7-BHB-9 to the AWN family. BHB-6 is compos ed of two different proteins. The dominant protein (14 kDa) has the N- terminal amino acid sequence HNKQEGRDHD that is identical to the seque nce of human semenogelin at positions 85-94. The minor proteins (16 an d 17 kDa) belong to the AWN family of spermadhesins. The 14 kDa HNK pr otein does not crossreact with antibodies against AQN or AWN spermadhe sins. BHB-2 also binds to the acrosome of boar epididymal spermatozoa but has the N-terminal sequence DQH. Therefore, basic protein BHB-2 be longs to a new family of DQH sperm surface proteins that are homologou s to the acidic proteins from bull and stallion seminal plasma, to the collagen binding domain II in fibronectin and to the leucocyte cell-c ell adhesion regulator, but are not homologous to AQN or AWN spermadhe sins. Nevertheless, anti-AQN-1 spermadhesin antibodies crossreact stro ngly with DQH protein. All boar heparin-binding proteins bind concanav alin A indicating their glycoprotein nature, which was proved by the d etection of glucosamine and galactosamine residues in their molecules. Furthermore, spermadhesins interact with zona pellucida, protease inh ibitors and a polyacrylamide derivative of heparin. Affinity chromatog raphy experiments showed that the DQH protein bound to gelatin-agarose together with the AWN proteins and that the DQH protein and AQN-1 spe rmadhesin belong to the phosphoryl choline binding proteins.