Isolation and biochemical characterization of heparin‐binding proteins from boar seminal plasma: A dual role for spermadhesins in fertilization

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Abstract
Sperm surface‐coated heparin‐binding proteins originating from secretions of the male sexual accessory glands, are known to play a pivotal role as extrinsic regulatory factors during sperm capacitation in many mammalian species. They interact with glycosaminoglycans present in the female genital tract and enhance the subsequent zona pellucida‐induced acrosome reaction. We have isolated heparin‐binding proteins from boar seminal plasma by affinity chromatography on heparin–Sepharose and reverse‐phase HPLC. N‐Terminal sequence analysis of these proteins identified a boar counterpart of the bovine capacitation factors BSP‐A1/2 (also called PDC‐109) and BSP‐A3. Several carbohydrate‐ and zona pellucida‐binding proteins, which belong to the newly described spermadhesin family, were also identified as heparin‐binding proteins. Our results imply that, besides other capacitation factors, members of the spermadhesin family may play a dual role in sperm capacitation and fertilization in the pig.