Chemical and physical requirements for lipid extraction by bovine binder of sperm BSP1

Abstract

The bovine seminal plasma contains phosphocholine-binding proteins, which associate to sperm membranes upon ejaculation. These binder-of-sperm (BSP) proteins then induce a phospholipid and cholesterol efflux from these membranes. In this work, we determined physical and chemical parameters controlling this efflux by characterizing the lipid extraction induced by BSP1, the most abundant of BSP protein in bull seminal plasma, from model membranes with different composition. The model membranes were formed from binary mixtures of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) with 1-palmitoyl-2-hydroxy-sn-glycero-3-phosphocholine (Lyso-PC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoserine (POPS) or cholesterol. The modulation of BSP1-induced lipid extraction from membranes by their chemical composition and their physical properties brings us to propose a 3-step extraction mechanism. First, the protein associates with membranes via specific binding to phosphocholine groups. Second, BSP1 penetrates in the membrane, essentially in the external lipid leaflet. Third, BSP1 molecules solubilize a lipid patch coming essentially from the outer lipid leaflet, without any lipid specificity, to ultimately form small lipid/protein auto-assemblies. The stoichiometry of these complexes corresponds to 10-15 lipids per protein. It is also shown that fluid-phase membranes are more prone to BSP1-induced lipid extraction than gel-phase ones. The inhibition of the lipid extraction in this case appears to be related to the inhibition of the protein penetration in the membrane (step 2) and not to the protein association with PC head groups (step 1). These findings contribute to our understanding of the mechanism by which BSP1 modify the lipid composition of sperm membranes, a key event in sperm capacitation.

Assessment of binder of sperm protein 1 (BSP1) and heparin effects on in vitro capacitation and fertilization of bovine ejaculated and epididymal sperm

“…In the case of ejaculated sperm, treatments with BSP1 increased the rates over the time, but did not achieve the same rates induced by heparin. Therefore, BSP1 could be used for sperm capacitation but it requires more time to exert its effect when compared with heparin, as also shown by previous studies (Manjunath et al, 2002(Manjunath et al, , 2007Plante et al, 2012Plante et al, , 2014Therrien et al, 2013;Rodríguez-Villamil et al, 2016). The reason for this delayed effect of BSP1 is probably related to the time necessary for BSP1 to interact with and remove both cholesterol and phospholipids from sperm membrane (Thérien et al, 1999;Manjunath and Thérien, 2002;Manjunath et al, 2007;Therrien et al, 2013).…”

Genetic Diversity and Signatures of Selection for Thermal Stress in Cattle and Other Two Bos Species Adapted to Divergent Climatic Conditions

“…Three genes (BSP1, BSP3, and BSP5) related to fertilization and sperm capacitation were identified in scenario SCEN2, based on the heat adaptation candidate genes group. Manjunath and Thérien (2002) reported the binder of sperm protein (BSP) family as a key step to sperm capacitation in ejaculation, as BSP bind to sperm and induce efflux of membrane cholesterol and phospholipids (Therrien et al, 2013). The BSP family genes identified here might indicate that under heat stress these genes play an important role on sperm capacitation and consequently, bull fertility.…”

Melittin-Induced Lipid Extraction Modulated by the Methylation Level of Phosphatidylcholine Headgroups

“…Fluorescence measurements of the tryptophan at position 19 of melittin were conducted to investigate melittin binding to bilayers. We analyzed the extent of lipid extraction by melittin using a procedure analogous to one reported previously (37). We examined the composition of the lipid/peptide particles that resulted from the extraction, as well as that of the remaining bilayers, using liquid chromatography coupled with mass spectrometry (LC-MS) to determine any selectivity toward one lipid or another.…”