Factors Influencing the Chaperone-Like Activity of Major Proteins of Mammalian Seminal Plasma, Equine HSP-1/2 and Bovine PDC-109: Effect of Membrane Binding, pH and Ionic Strength

DSP-1, the major fibronectin type-II protein of donkey seminal plasma is a small heat-shock protein and exhibits chaperone-like activity against thermal and oxidative stress

Fibronectin type-II (FnII) proteins are major constituents in the seminal plasma of many mammals and play a crucial role in sperm capacitation. Additionally, the seminal FnII proteins from bull and horse exhibit chaperone-like activity (CLA), by acting as small heat shock proteins (shsps). The present work demonstrates that the major FnII protein of donkey seminal plasma, DSP-1 exhibits CLA with broad specificity and protects various client proteins such as alcohol dehydrogenase, lactate dehydrogenase and enolase against thermal and oxidative stress. Binding of phosphorylcholine (PrC) - the head group moiety of choline phospholipids, which are the physiological ligands of DSP-1 - decreased the CLA whereas binding of 1,2-dioleoyl-sn-glycero-3-phospholcholine (DOPC) increased the CLA. Biophysical studies suggested that these contrasting effects on the CLA by phosphorylcholine and diacyl phosphatidylcholine could be attributed to changes in the surface hydrophobicity of DSP-1 upon binding to these ligands. Interestingly, binding of PrC reduced DSP-1 tetramers to monomers with lower surface hydrophobicity, whereas binding to DOPC liposomes increased its surface hydrophobicity. These results, which demonstrate that DSP-1 exhibits CLA and functions as a molecular chaperone, expand the family of mammalian seminal FnII proteins that function as shsps.

Dexamethasone and azithromycin enhance goat sperm preservation quality by regulating lipid metabolism

Phospholipase A (PLA) in goat semen aggregates with egg yolk in semen diluent, leading to sperm death. The aim of this study is to address the issue of sperm death caused by the interaction between PLA and egg yolk, and to explore the protective effect and metabolic regulation mechanism of the combination of dexamethasone (DXMS) and azithromycin (AZM) on goat sperm under low temperature conditions. At a low temperature of 4 °C, different concentrations of DXMS were added to semen diluents containing 30 μg/mL AZM to detect the quality of goat sperm. The optimal concentration of DXMS was determined to be 20 μg/mL. On the 5th day of storage, antioxidant capacity, total cholesterol (TC) levels, energy metabolism, and metabolomics analysis were performed on the sperm of the 20 μg/mL DXMS group. The results showed that there was no aggregation caused by the interaction between PLA and egg yolk in the group containing 30 μg/mL AZM at 4 °C. 20 μg/mL DXMS significantly improved sperm motility, plasma membrane integrity, acrosome integrity, glutathione peroxidase (GPX) (P < 0.05), catalase (CAT) (P < 0.01), and superoxide dismutase (SOD) activity (P < 0.01). The content of reactive oxygen species (ROS) and Fe2+ significantly decreased (P < 0.01), while the content of ATP (P < 0.01) and TC (P < 0.05) significantly increased. Through metabolomics analysis, a total of 56 differential metabolites (P < 0.05) were screened, including 5a, 6-Anhydrotetracycline, Betamethasone, and 11-Dehydrocorticosterone, mainly enriched in 8 metabolic pathways (P < 0.05), including steroid hormone biosynthesis, glycerophospholipid metabolism, and choline metabolism in cancer. Among them, 5 metabolic pathways are related to lipid metabolism. The results indicate that AZM effectively inhibits the aggregation of PLA and yolk, and the combination of AZM and DXMS enhances the preservation quality of goat sperm during low-temperature preservation by regulating lipid metabolism.

Primary structure determination and physicochemical characterization of DSP-3, a phosphatidylcholine binding glycoprotein of donkey seminal plasma

Major proteins of the seminal plasma in a variety of mammals such as bovine PDC-109, equine HSP-1/2, and donkey DSP-1 contain fibronectin type-II (FnII) domains and are referred to as FnII family proteins. To further our understanding on these proteins, we carried out detailed studies on DSP-3, another FnII protein of donkey seminal plasma. High-resolution mass-spectrometric studies revealed that DSP-3 contains 106 amino acid residues and is heterogeneously glycosylated with multiple acetylations on the glycans. Interestingly, DSP-3 exhibits significantly higher homology to HSP-1 (104 identical residues) than DSP-1 (72 identical residues). Circular dichroism (CD) spectroscopic and differential scanning calorimetric (DSC) studies showed that DSP-3 unfolds at ~45 °C and binding of phosphorylcholine (PrC) - the head group moiety of choline phospholipids - increases the thermal stability. Analysis of DSC data suggested that unlike PDC-109 and DSP-1, which exist as mixtures of polydisperse oligomers, DSP-3 most likely exists as a monomer. Ligand binding studies monitoring changes in protein intrinsic fluorescence indicated that DSP-3 binds lyso-phosphatidylcholine (K_a = 1.08 × 10⁵ M^-1) with ~80-fold higher affinity than PrC (K_a = 1.39 × 10³ M^-1). Binding of DSP-3 to erythrocytes leads to membrane perturbation, suggesting that its binding to sperm plasma membrane could be physiologically significant.

Purification, molecular characterization and ligand binding properties of the major donkey seminal plasma protein DSP-1

Fibronectin type-II (FnII) family proteins are the major proteins in many mammalian species including bull, horse and pig. In the present study, a major FnII protein has been identified and isolated from donkey (Equus hemionus) seminal plasma, which we refer to as Donkey Seminal Plasma protein-1 (DSP-1). The amino acid sequence determined by mass spectrometry and computational modeling studies revealed that DSP-1 is homologous to other mammalian seminal plasma proteins, including bovine PDC-109 (also known as BSP-A1/A2) and equine HSP-1/2. High-resolution LC-MS analysis indicated that the protein is heterogeneously glycosylated and also contains multiple acetylations, occurring in the attached glycans. Structural and thermal stability studies on DSP-1 employing CD spectroscopy and differential scanning calorimetry showed that the protein unfolds at ~43 °C and binding to phosphorylcholine (PrC) - the head group moiety of choline phospholipids - increases its thermal stability. Intrinsic fluorescence titrations revealed that DSP-1 recognizes lyso-phosphatidylcholine with over 100-fold higher affinity than PrC. Further, interaction of DSP-1 with erythrocytes, a model cell membrane, revealed that DSP-1 binding is mediated by a specific interaction with choline phospholipids and results in membrane perturbation, suggesting that binding of this protein to sperm plasma membrane could be physiologically significant.

Differential proteome between ejaculate and epididymal sperm represents a key factor for sperm freezability in wild small ruminants

Epididymal sperm shows higher cryoresistance than ejaculated sperm. Although the sperm proteome seems to affect cell cryoresistance, studies aiming at identifying proteins involved in sperm freezing-tolerance are scarce. The aims of this study were to investigate differences of sperm freezability and proteome between epididymal and ejaculated sperm in three mountain ungulates: Iberian ibex, Mouflon and Chamois. Sperm samples were cryopreserved in straws by slow freezing. Tandem mass tag-labeled peptides from sperm samples were analyzed by high performance liquid chromatography coupled to a mass spectrometer in three technical replicates. The statistical analysis was done using the moderated t-test of the R package limma. Differences of freezability between both types of sperm were associated with differences of the proteome. Overall, epididymal sperm showed higher freezability than ejaculated sperm. Between 1490 and 1883 proteins were quantified in each species and type of sperm sample. Cross species comparisons revealed a total of 76 proteins that were more abundant in epididymal than in ejaculated sperm in the three species of study whereas 3 proteins were more abundant in ejaculated than epididymal sperm in the three species of study (adjusted P < 0.05; |log₂| fold-change > 0.5). Many of the proteins that were associated with higher cryoresistance are involved in stress response and redox homeostasis. In conclusion, marked changes of sperm proteome were detected between epididymal and ejaculated sperm. This work contributes to update the sperm proteome of small ruminants and to identify candidate markers of sperm freezability.

Heat SHOCK proteins in equine spermatozoa: Expression and correlation to kinetic and environmental parameters

Heat Shock Proteins are chaperones primary involved in the repair of cellular damages induced by temperature. The harmful effect of temperature on the male gonad is well known, on the contrary knowledge on the effects of the environment on semen quality are still insufficient. The aim of this paper was to learn more about the role of HSPs and the environment in modulating the physiology of equine male gonads. We showed a detailed analysis of equine semen characteristic and the expression level of three HSPs (60-70-90) over a one-year period analyzing the effects of temperature and humidity and the correlation among the different variables. We showed also that the interpretation of results depends strongly on the way in which data are assembled and analyzed, therefore we compared results obtained from three different ways of grouping: according to single months, to weather seasons and to mare reproductive periods. Results showed that the expression of the three HSPs is correlated to the environment through temperature and humidity and that it reaches the highest level in the breeding season and in summer. We found also that HSPs expression is correlated to some variables describing the quality of equine semen (concentration) and the kinetic of spermatozoa (total motility-MOT, %, average path velocity -VAP, μm/s- and lateral head displacement -ALH, μm). No correlation was found between HSPs expression and the mitochondrial membrane potential; while viability and HSP90 expression resulted positively correlated. The month-by-month analysis evidenced that in February equine semen has the highest kinetic characteristics (increased linearity -LIN, %-, straightness -STR, % -and average path velocity -VAP, μm/s) with the highest number of motile, progressive motile and rapid cells. These results may have a great impact in the comprehension of functional aspects of the physiology of equine semen and may have potential implications for breeders who want to understand the period (and/or month) of the year in which equine semen reaches the best characteristics with increased chances for better results in reproductive practice.

Preparation of Boronic Acid-Functionalized Silica Nanocomposites for Selective Enrichment of Glycoproteins

A facile method was developed for synthesis of boronic acid-functionalized silica nanocomposites (SiO₂ -BA) by 'thiol-ene' click reaction, where silica nanoparticles were synthesized by using tetraethoxysilane (TEOS) and γ-mercaptopropyl trimethoxysilane (γ-MPTS) as precursors. The morphology and structure properties of the resultant SiO₂ -BA were characterized by transmission electronic microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and Brunner-Emmet-Teller measurements (BET). The adsorption behavior of the SiO₂ -BA for glycoproteins was evaluated. Under the optimized conditions, the SiO₂ -BA exhibited higher adsorption capacity towards glycoproteins (ovalbumin, OVA, 7.64 μmol/g) than non-glycoproteins (bovine serum albumin, BSA, 0.83 μmol/g). In addition, the practicality of the SiO₂ -BA was further assessed by selective enrichment of glycoproteins from egg white samples.

Conserved core tryptophans of FnII domains are crucial for the membranolytic and chaperone-like activities of bovine seminal plasma protein PDC-109

The fibronectin type II (FnII) domain, present in diverse vertebrate proteins, plays crucial roles in several fundamental biological processes. PDC-109, the major bovine seminal plasma protein, contains two FnII domains that bind to choline phospholipids on sperm plasma membrane and induce lipid efflux crucial for successful fertilization. PDC-109 also exhibits chaperone-like activity and protects other proteins against various types of stress. Here, we show that a core tryptophan residue is highly conserved across species in the FnII domains. Mutation of conserved tryptophan residues W47, W93, and W106 in the FnII domains of PDC-109 to alanine leads to drastic decrease or complete abolition of membrane-binding and chaperone-like activities. These observations suggest that conserved tryptophans are important for the function of FnII proteins.