BINDING CHARACTERISTICS AND IMMUNOLOCALIZATION OF PORCINE SEMINAL PROTEIN, PSP-I

PSP-I, a 13 kDa protein purified from boar seminal plasma, was found t o have about 50% amino acid sequence homology with a family of zona pe llucida-binding proteins known as spermadhesins. These proteins are pr oduced by the accessory gland(s) of the male reproductive tract and co at the spermatozoa during ejaculation. In this study, we have investig ated the possible biological functions of PSP-I using a solid-phase pr otein binding assay and its site of synthesis using both Western blot and immunocytochemical analyses. PSP-I was found to bind a number of p roteins including endo-beta-galactosidase digested ZP3, soybean trypsi n inhibitor, IgA, IgG and alpha-casein, indicating that it may have mu ltiple functions. The protein or carbohydrate structures were not crit ical in the binding, since polyvinyl sulfate could effectively inhibit the binding of PSP-I to these proteins. Western blot analysis using s pecific antiserum to PSP-I showed that the protein was present in the seminal vesicle but not in the testes, epididymis or prostate. The pro tein was revealed by immunocytochemical analysis in the epithelium of seminal vesicles but not in the testes or the epididymis. It is conclu ded that PSP-I is synthesized by the epithelium of the seminal vesicle s, secreted into the semen during ejaculation, and may be involved in various reproductive functions, such as preventing premature acrosome reaction and immunosuppression. (C) 1993 Wiley-Liss, Inc.