Major proteins of bovine seminal plasma inhibit phospholipase A2

Abstract

We have recently shown that the major proteins of bovine seminal plasma, namely BSP-A1, BSP-A2, BSP-A3 and BSP-30-kDa (collectively called BSP proteins) bind to spermatozoa and that the binding sites on the plasma membrane of spermatozoa are choline phospholipids. In view of the fact that these phospholipids are substrates for phospholipase A2 (PLA2), a key enzyme in sperm capacitation and the acrosome reaction, the effect of BSP proteins on this enzyme activity was investigated. Since these BSP proteins are ubiquitous, the effect on pig pancreatic PLA2 was also studied. In contrast with control proteins, when preincubated with phosphatidylcholine as substrate, all BSP proteins inhibited both pancreatic and sperm PLA2 activity in a dose-dependent manner and in the presence of 1-6 microM BSP protein the enzyme activity was completely abolished. When phosphatidylethanolamine was used as substrate, only pancreatic PLA2 was inhibited. On the other hand, when the BSP proteins were preincubated with the enzyme followed by addition of substrate, a biphasic effect was observed; there was stimulation of enzyme activity below 1.3 microM BSP followed by an inhibition above this concentration. The inhibitory activity was trypsin-sensitive but heat-resistant. The effect of co-incubation of heparin, which is implicated in sperm capacitation and which also interacts with BSP proteins, was studied. Heparin (10 microM) had no effect on the PLA2 inhibitory activity exhibited by all BSP proteins. The PLA2 inhibitory effect exhibited by BSP proteins was abolished with excess substrate. The BSP proteins were adsorbed on PLA2-agarose and could be affinity cross-linked to the enzyme, indicating a direct interaction of enzyme with the inhibitor. These results suggest that these BSP proteins modulate PLA2 activity and therefore, phospholipid metabolism.

Male-specific Modification of Human CD52

“…High levels of secretory phospholipase A 2 have indeed been observed in seminal plasma samples of healthy donors as a product of the prostate (39). On the other hand, seminal plasma also contains potent phospholipase A 2 protein inhibitors (40,41), and it is not known whether the enzyme is active in ejaculates.…”

Interactions of spermatozoa with the female reproductive tract: inspiration for assisted reproduction

“…The PDC-109 protein reduces membrane fluidity and immobilises cholesterol in phospholipid membranes, including those of epididymal spermatozoa (Greube et al 2001;Müller et al 2002). In addition, PDC-109 can contribute to membrane stability by inhibiting the activity of phospholipase A 2 (Manjunath et al 1994;Soubreyrand and Manjunath 1997). Thus, PDC-109 may play a role in preserving bull sperm fertility while spermatozoa are stored in the reservoir.…”

Bovine seminal PDC-109 protein: An overview of biochemical and functional properties

“…1). Manjunath et al (1994) reported the purification and biochemical characterization of four GB-proteins and designated them as BSP-A1, BSP-A2, BSP-A3 and BSP-30-kDa. BSP-A1/-A2 or PDC-109 was named following the Ion-E x Chr.…”