Phosphorylcholine‐binding proteins from the seminal fluids of different species share antigenic determinants with the major proteins of bovine seminal plasma

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Abstract
The major proteins of bovine seminal plasma, BSP‐A1, BSP‐A2, BSP‐A3, and BSP‐30kDa (collectively named BSP proteins) bind to phospholipids containing the phosphorylcholine moiety. An affinity purification method using a p‐aminophenyl phosphorylcholine‐Agarose (PPC‐Agarose) affinity matrix was developed for their purification. In this study, we investigated the distribution of BSP‐like analogues in seminal fluid of the human, porcine, hamster, mouse, and rat using this affinity matrix. Alcohol precipitates of the seminal plasma/seminal vesicle secretions (SP/SVS) were further delipidated using isopropyl ether:n‐butanol (60:40). The protein preparations obtained were solubilized in a minimal volume of buffer A (50 mM Tris‐HCl, pH 7.4, 150 mM NaCl, 5 mM EDTA, 0.02% NaN3), dialyzed against the same buffer, and applied to a PPC‐Agarose column connected to a FPLC system. The unbound material was washed out and the adsorbed proteins eluted with buffer A containing 10 mM phosphorylcholine (PrC) and 10 M urea. The fractions were separated by SDS‐PAGE, stained or transferred onto a nitrocellulose membrane, and probed with rabbit polyclonal anti‐BSP antibodies. Anti‐BSP cross‐reacting proteins were detected in the seminal fluids of all the species investigated. Moreover, many of these proteins bound to the affinity matrix. The BSP proteins and their immunoreacting analogues appear to be ubiquitous in mammals and may possibly be involved in a common function such as in the modification of the lipid content of the sperm plasma membrane.