Bull Seminal Plasma Research Articles

Activity of IGF-binding proteins in seminal plasma of bulls: Effects on fertilization capacity in vivo and in vitro

Activity of IGF-binding proteins in seminal plasma of bulls: Effects on fertilization capacity in vivo and in vitro

Conformational features and thermal stability of bovine seminal plasma protein PDC-109 oligomers and phosphorylcholine-bound complexes.

At ejaculation, PDC-109, the major heparin-binding protein of bull seminal plasma, binds to the phosphorylcholine group of sperm lipids and modulates capacitation promoted by glycosaminoglycans during sperm residence in the female genital tract. Combination of size-exclusion chromatography, analytical ultracentrifugation, circular dichroism, Fourier-transform infrared spectroscopy, and differential scanning calorimetry has allowed us to biophysically characterize PDC-109 and its interaction with phosphorylcholine. PDC-109 can be regarded as a polydisperse molecule whose aggregation state can be modulated by the solute composition of its solution environment. Dissociation of PDC-109 oligomers occurs upon increasing the concentration of either NaCl, EDTA, CaCl2, or phosphorylcholine, suggesting that both ionic and hydrophobic interactions are responsible for the aggregation tendency of PDC-109 monomers. Dissociation processes are accompanied by exposure of peptide bonds to the solvent, changes in the environment of tyrosine and tryptophan residues, and a slight increase in the turn content at the expense of non-regular structure. Analysis of the heat-induced denaturation of PDC-109 oligomers revealed two melting transitions at about 36 degrees C (irreversible) and 55 degrees C (partially reversible) characterized by calorimetric enthalpy changes of 42 kJ/mol and 217 kJ/mol, respectively. These transitions could be assigned to the dissociation of oligomers and to the cooperative unfolding of PDC-109 monomers, respectively. The modulation of the aggregation state of PDC-109 by its molecular environment and by phosphorylcholine binding suggests possible mechanisms for capacitation mediated by the seminal plasma protein.

Crystallization and preliminary X-ray diffraction analysis of bovine seminal plasma PDC-109, a protein composed of two fibronectin type II domains.

PDC-109 is a 13 kDa glycoprotein and the major phosphorylcholine- and heparin-binding protein of bull seminal plasma. It is built by an acidic 23-residue N-terminal sequence followed by a tandem of fibronectin type II domains. Full-length PDC-109 was crystallized in complex with o-phosphorylcholine by vapor diffusion in sitting drops. Crystals grew to maximal size of 0.5 x 0.3 x 0.2 mm3, diffract x-rays beyond 2.6 A resolution, and belong to space group P321 with unit cell dimensions a = b = 93.6 A, c = 52.7 A.

Anti-Ca2+, Mg2+-Dependent Endonuclease Antibody Detects Specifically a Class of Chromatin-Bound Endonuclease

A polyclonal antibody against purified bull seminal plasma Ca2+, Mg2+-dependent endonuclease was raised in a rabbit. The antibody specifically cross-reacted with chromatin-bound Ca2+, Mg2+-dependent endonucleases from bovine thymus, human placenta, and bovine, rat and mouse liver in addition to the bovine seminal enzyme. The antibody did not cross-react with other endonucleases examined, including the acid-endonucleases from bovine thymus and liver, porcine spleen DNase II, micrococcal nuclease, and bovine pancreas DNase I, a known Ca2+and Mg2+requiring endonuclease. The present results indicate that this antibody specifically recognizes a class of so-called Ca2+, Mg2+-dependent endonuclease, which is localized in cell nuclei of various tissues and is probably involved in chromatin degradation during apoptosis. The antibody will be used to study the functional role of this class of endonuclease.

Thermodynamics of protein stability: A family of ribonucleases

Abstract

Surface changes of ram spermatozoa by adsorption of homologous and heterologous seminal plasma proteins revealed by partition in an aqueous two-phase system.

Ram spermatozoa freed from seminal plasma by a dextran 'swim-up' procedure were incubated with Tween 20 and fractionated into motile (PEG-rich) and stationary (dextran-rich) fractions by centrifugal countercurrent distribution (CCCD) in an aqueous dextran-Ficoll-polyethylene glycol (PEG) two-phase system. Increasing concentrations of Tween 20 resulted in greater amounts of extracted protein and lower cell viability. Addition of bull seminal plasma increased the proportion of live cells, whereas ram seminal plasma increased the proportion of stationary cells. Proteins isolated from each type of seminal plasma restored the CCCD profile of treated spermatozoa to the right, this effect being reduced when proteins were thermally denatured. Bovine serum albumin induced a slight displacement to the left. No restoration of profile was achieved when ram spermatozoa were exposed to proteins from bull seminal plasma in the presence of protein-free ram seminal plasma. Adsorption of seminal plasma proteins by spermatozoa previously stripped of surface proteins by exposure to detergent reversed the detergent effect on motility. The findings are consistent with the concept that ram seminal plasma contains a factor that interferes with protein adsorption on the cell surface and prevents the protective effect of seminal plasma proteins on maintenance of cell viability.

Reversion of thermic-shock effect on ram spermatozoa by adsorption of seminal plasma proteins revealed by partition in aqueous two-phase systems

Centrifugal counter-current distribution (CCCD) in a dextran, Ficoll, poly(ethylene glycol) two-phase system was used to study the effect of seminal plasma proteins on the partition behaviour of ram spermatozoa exposed to thermal shock. Ram spermatozoa freed from seminal plasma by a ‘swim-up’ procedure were submitted to thermal shock and fractionated by CCCD. Cell viability decreased from 68% to 18% after the treatment, showing a slight displacement of the cells from the right (where a higher enrichment of live cells is found) to the centre of the profile. A change of the distribution profile was shown in the presence of either ram or bull seminal plasma. Bull seminal plasma was able to move the profile to the right, whereas ram seminal plasma increased the proportion of cells with enhanced affinity for the lower dextran-rich phase. Plasma proteins isolated from both seminal plasmas moved the profile to the right. In addition, cell viability rose to 48% after the CCCD run in the presence of ram plasma proteins. This restoring effect was lost when ram plasma proteins were thermally denatured. Bovine serum albumin was not only unable to move the profile to the right but even promoted displacement of the profile to the left. This negative effect was also observed when proteins from bull seminal plasma were in the presence of protein-free ram seminal plasma. However, proteins isolated from ram seminal plasma still restored the profile in the presence of bull seminal plasma freed from proteins. The results presented here strongly suggest that seminal plasma proteins are absorbed by a spermatozoal surface previously exposed to thermic shock. These proteins would exert a highly specific protective effect on ram spermatozoa. In addition, in the ram seminal plasma there must be some factor which avoids this adsorption.

On the pH dependence of amide proton exchange rates in proteins

We have analyzed the pH dependencies of published amide proton exchange rates (kex) in three proteins: bovine pancreatic trypsin inhibitor (BPTI), bull seminal plasma proteinase inhibitor IIA (BUSI IIA), and calbindin D9K. The base-catalyzed exchange rate constants (kOH) of solvent exposed amides in BPTI are lower for residues with low peptide carbonyl exposure, showing that the environment around the carbonyl oxygen influences kOH. We also examined the possible importance of an exchange mechanism that involves formations of imidic acid intermediates along chains of hydrogen-bonded peptides in the three proteins. By invoking this "relayed imidic acid exchange mechanism," which should be essentially acid-catalyzed, we can explain the surprisingly high pHmin (the pH value at which kex reaches a minimum) found for the non-hydrogen-bonded amide protons in the beta-sheet in BPTI. The successive increase of pHmin along a chain of hydrogen-bonded peptides from the free amide to the free carbonyl, observed in BPTI, can be explained as an increasing contribution of the proposed mechanism in this direction of the chain. For BUSI IIA (pH 4-5) and calbindin D9K (pH 6-7) the majority of amide protons with negative pH dependence of kex are located in chains of hydrogen-bonded peptides; this situation is shown to be consistent with the proposed mechanism.

Spectrophotometric measurement of aspartate aminotransferase activity in mammalian and fish semen

The Karmen assay (Karmen, A., 1955. J. Clin. Invest., 34: 131–133) of aminotransferase activity as modified by the International Federation of Clinical Chemistry (Bergmeyer, H.U., Horder, M and Rej, R., 1986. J. Clin. Chem. Clin. Biochem., 24: 497–510) appeared to be useful for semen analysis, after a few additional modifications. The assay system does not work for neat bull seminal plasma; however, enzyme activity can be measured correctly in diluted samples. In many cases, slight inhibition of enzyme activity was observed at 240 mM of l-aspartate. For this reason, a lower concentration of this substrate should be used. The higher sensitivity of this modified Karmen method offers more accurate measurement of aspartate aminotransferase activity in semen as compared with the methods employed previously.

Reconstitution of 5'-nucleotidase of bull seminal plasma in spin-labeled liposomes.

Seminal plasma separated from freshly ejaculated bull semen contains vesicles with a 5'-nucleotidase activity incorporated as an ectoenzyme anchored by glycosyl phosphatidylinositol (GPI). After its extraction from bull seminal plasma vesicles, the protein was purified and reconstituted into hen egg yolk lecithin liposomes obtained through prolonged dialysis of buffered n-octylglucoside detergent solutions of lipid, protein and various effectors against detergent-free solutions. Gel filtration experiments showed that the enzyme incorporated into liposomes in a dimeric form with its two subunits linked by disulfide bridges. In the presence of reduced glutathione, the protein dissociated into monomers and failed to incorporate into liposomes. Electron spin resonance (ESR) experiments, performed with liposomes containing electron spin labels localized at the hydrophilic lipid headgroups (5-doxyl stearic acid) or in the hydrophobic lipid hydrocarbon chains (16-doxyl stearic acid), demonstrated that the incorporation of 5'-nucleotidase resulted in the immobilization of the spin probes. Furthermore, the spectral parameters obtained before and after treatment of 5'-nucleotidase-containing liposomes with phosphatidylinositol-specific phospholipase C (PI-PLC) indicated that the liposome membrane bilayer did not contain protein segments. This supports the well-known ecto-localization of 5'-nucleotidase and rules out a previously reported possibility of a proteic transmembrane anchoring of the enzyme.

Purification and characterization of β‐glucuronidase from bull seminal plasma and its role in fertilization

Bull seminal plasma contains high levels of beta-glucuronidase. The present study describes the isolation and characterization of beta-glucuronidase, and its role in fertilization. beta-glucuronidase was purified by ion exchange chromatography, saccharolactone-agarose affinity chromatography, and gel filtration. The specific activity of the purified enzyme was 4,414 mumoles/mg protein/min. The purified enzyme showed a single band on 7.5% PAGE. On SDS-PAGE, the enzyme appeared to consist of four identical subunits of M(r) 75,000 each. The apparent Km and Vmax for beta-glucuronidase were 0.4 mM and 5.7 mumol/min using phenolpthalein mono-beta-glucuronic acid as the substrate. beta-glucuronidase appeared to accelerate the cumulus dispersion in vitro.

Bovine seminal plasma ASFP: Localization of disulfide bridges and detection of three different isoelectric forms

Acidic seminal fluid protein (aSFP) is a major 13 kDa protein isolated from bull seminal plasma and characterized as a new growth factor which stimulates in vitro cell division and progesterone secretion by ovarian cells. Here, we establish that the four cysteines of oxidized aSFP form two disulfide bridges between nearest-neighbour residues. This pattern is conserved in boar spermadhesins, with which aSFP shares up to 50% amino acid sequence identity, and other proteins of the recently identified CUB domain family. Using isoelectric focusing in combination with sulfhydryl group-specific blotting, the three forms of aSFP were identified as completely oxidized (pI 4.7), partly reduced (pI 4.8) and fully reduced at pI 5.1. These results indicate that native aSFP possesses two pairs of cysteine residues of different reactivity. The observation that aSFP can protect sperm from oxidative damage might be explained by its reduction/oxidation behaviour.

Distribution of endogenous and exogenous 5'-nucleotidase on bovine spermatozoa.

A polyclonal rabbit antibody against 5'-nucleotidase purified from bull seminal plasma was used to localize the antigen on bovine spermatozoa. Spermatozoa taken from the ampulla of the vas deferens showed strong immunofluorescence at the anterior rim of the head portion. Evaluation of spermatozoa prepared from different segments of the seminal pathway indicated the presence of the antigen already in rete testis and epididymal spermatozoa. On cryostat sections of testis tissue a positive immunoreaction was found in the anterior head portion of elongated spermatids, but not in earlier forms of sperm development. This distribution corresponded with the enzyme activity and results of Western blotting in extracts of testicular and epididymal spermatozoa. Immunoelectron microscopy of ampullary spermatozoa using antibody detection with gold-labelled anti-rabbit IgG showed a clear-cut labelling of the plasma membrane in the acrosome region. Treatment of ampullary spermatozoa with 0.1% Triton X-100 did not completely remove the immunoreactive material from the acrosome, showing a very stable linkage of the protein to the plasma membrane. Treatment with phospholipase C from Bacillus thuringiensis, however, removed immunoreactive material from the plasma membrane, indicating its binding by a phosphoinositol anchor. Our findings show that endogenous 5'-nucleotidase is present on the plasma membrane covering the anterior head portion of bovine spermatozoa and indicate specialized functions during the acrosomal reaction. Soluble enzyme derived from seminal vesicle secretion covers the whole sperm surface during emission, but is not covalently bound. It provides generalized enzyme activity to the sperm surface in addition to the specialized area of the sperm head.

Immunolocalization and quantitation of acidic seminal fluid protein (aSFP) in ejaculated, swim-up, and capacitated bull spermatozoa.

Acidic seminal fluid protein (aSFP, 12.9 kDa), a major protein of bull seminal plasma, belongs to the spermadhesin protein family. Boar spermadhesins become bound to the sperm head's surface at ejaculation and are thought to play a role as capacitation factors and/or in gamete recognition and binding. Here, we have investigated the topographical distribution and fate of bovine spermadhesin aSFP during sperm capacitation in order to assess whether aSFP could be involved in similar aspects of the fertilization process as its boar homologous proteins. 5.7 +/- 2.1 x 10(6) molecules/spermatozoa were quantitated on the surface of fresh ejaculated and washed sperm. The binding site of aSFP was restricted to a thin coat at the apical part of the acrosomal cap. The amount of aSFP in swim-up sperm was 1.8 +/- 1.0 x 10(6) molecules/spermatozoa, but decreased dramatically to 22 +/- 10 x 10(3) and to undetectable levels after incubation of sperm for 1.5 h and 18 h, respectively, in capacitation medium. This indicates that the bull spermatozoa surface may be completely depleted of spermadhesin aSFP before spermatozoa reach the surroundings of the investing egg. Therefore, our results suggest that aSFP may act as a decapacitation factor on bull spermatozoa rather than as a zona pellucida binding molecule.

Fertility-Associated Proteins in Holstein Bull Seminal Plasma1

This study was undertaken to determine whether bovine seminal plasma contained protein markers associated with bull fertility, and whether these markers were of value in predicting bull fertility. Seminal plasma was obtained from 35 Holstein bulls of known fertility. Two-dimensional PAGE of seminal plasma samples indicated that two proteins (26 kDa, pI 6.2; 55 kDa, pI 4.5) predominated in higher-fertility bulls, and two proteins (16 kDa, pI 4.1; 16 kDa, pI 6.7) predominated in lower-fertility bulls. Densitometry data for these proteins in individual samples were combined for bulls grouped by fertility level. Average density of the 26-kDa protein was significantly greater in seminal plasma of high-fertility bulls, and high-fertility seminal plasma also contained more of the 55-kDa protein than that of average- and below average-fertility bulls. Below average- and low-fertility bull seminal plasma had significantly more of both 16-kDa proteins than that of average- and high-fertility bulls. A regression model was developed to predict bull fertility using the four fertility-associated protein densities. A plot of actual bull fertility versus that calculated by this model was linear and positively correlated (r = 0.89). These findings indicate that bull seminal plasma contains fertility-associated proteins that are predictive of bull fertility.

Bovine seminal ribonuclease produced from a synthetic gene

Bovine seminal ribonuclease (BS-RNase), a homolog of bovine pancreatic ribonuclease (RNase A), is isolated as a dimer in which the subunits are cross-linked by two disulfide bonds. In addition to this anomalous quaternary structure, the enzyme has extraordinary biological properties, such as antispermatogenic, antitumor, and immunosuppressive activities. The molecular bases for these properties are well-suited for exploration with the techniques of recombinant DNA. Accordingly, a gene encoding BS-RNase was designed based on criteria expected to maximize the translational efficiency of its mRNA in Escherichia coli. This gene was constructed from 12 synthetic oligonucleotides and expressed with the phage T7 system. The protein thus produced was insoluble and accumulated under optimal conditions to 15% of total cellular protein or 200 mg/liter of culture. Ribonuclease activity was generated by air oxidation of the reduced and denatured protein. Three forms of active BS-RNase were isolated by gel filtration chromatography: the well-characterized dimer and monomer and a previously uncharacterized form that migrated as a trimer. The ribonuclease activities of all three forms were equivalent to or higher than that of dimeric BS-RNase isolated from bull seminal plasma.

Localization and concentration of a new bioactive acetic seminal fluid protein (aSFP) in bulls (Bos taurus).

The concentration of the new bioactive acetic seminal fluid protein (aSFP) was determined in body fluids of bulls. An aSFP-specific radioimmunoassay was elaborated and established for routine measurement. No crossreaction of the aSFP antibody was found with other seminal plasma proteins and known growth factors. The 14 kDa aSFP was detected in secretions of ampulla and seminal vesicles by immunoblot analysis, but not in testis, epididymis or blood. Large quantities of aSFP were measured by radioimmunoassay in the fluid from the ampulla (2.6 +/- 0.3 mg ml-1) and seminal vesicles (3.0 +/- 0.4 mg ml-1). Immunohistochemistry techniques demonstrated that aSFP was localized mainly in the secretory epithelium of ampulla and seminal vesicles. Large amounts of aSFP (4.0 +/- 0.4 mg ml-1) were present in seminal plasma of bulls within a range of 1-7 mg ml-1, but aSFP could not be found on membranes of spermatozoa. Concentrations vary considerably among individuals, suggesting that aSFP may have a role in bovine reproduction.

Immunosuppressive and leucolytic effect of phospholipid binding protein in bull seminal plasma

Phospholipid binding protein (PBP) isolated from bull seminal vesicle fluid has a haemolytic effect in addition to immunosuppressive and leucolytic activities. Leucolysis of PBP is not rigidly dependent on haemolysis. Erythrocytes are more sensitive to PBP than leucocytes.

Structural and functional relationships in 5′-nucleotidase from bull seminal plasma. A Fourier transform infrared study

Fourier transform infrared spectroscopy (FTIR) was used to investigate the secondary structure of 5'-nucleotidase from bull seminal plasma (BSP). Spectra of protein in both D2O and H2O were analyzed by deconvolution and second derivative methods in order to observe the overlapping components of the amide I band. The protein, which is made up of two apparently identical subunits and which contains two zinc atoms, was studied in its native form, in the presence of dithiotreitol (DTT) and after removal of the two zinc atoms by means of nitrilotriacetic acid (NTA). Deconvolved and second derivative spectra of amide I band showed that the native protein contains mostly beta-sheet structure with a minor content of alpha-helix. The quantitative analysis of the amide I components was performed by a curve-fitting procedure which revealed 54% beta-sheet, 18% alpha-helix, 22% beta-turns and 6% unordered structure. The second derivative and deconvolved spectra of amide I band showed that no remarkable changes in the secondary structure of 5'-nucleotidase were induced by either DTT or NTA. These results were confirmed by the curve-fitting analysis where little or no changes occurred in the relative content of amide I components when the protein was treated with DTT or with NTA. Major changes, however, were observed in the thermal denaturation behavior of the protein. The native protein showed denaturation at temperatures between 70 and 75 degrees C, while the maximum of denaturation was observed between 65 and 70 degrees C and between 55 and 60 degrees C in the presence of NTA and DTT, respectively. The results obtained indicate that the two separate subunits of the protein have essentially the same secondary structure as that of the native enzyme.

Purification of 5′-nucleotidase from human seminal plasma

5′-Nucleotidase from human seminal plasma was purified to electrophoretic homogeneity and some of its kinetic and molecular properties compared with those of 5′-nucleotidase from bull seminal plasma. The purification of the enzyme was achieved by using the same affinity chromatography media (Con A-Sepharose and AMP-Agarose or ADP-Agarose) previously used for the purification of bull seminal plasma 5′-nucleotidase (Fini, C., Ipata, P.L., Palmerini, C.A. and Floridi, A. (1983) Biochim. Biophys. Acta 748, 405–412). However, in the present purification procedure no detergent was used as it had been necessary for the purification of the bovine enzyme. The experimental data reveal some main differences between these two enzymes; first, the human enzyme seems to be constituted of a single polypeptide chain of about 71 kDa, while the 5′-nucleotidase of bull seminal plasma, in non denaturing detergent solutions, is a homodimer of about 160 kDa. Another most remarkable difference is that the human enzyme does not seem to contain a phosphatidylinositol anchoring system like the one present in the bovine enzyme and in 5′-nucleotidase of different sources (Low, M.G. (1987) Biochem. J. 244, 1–13). Finally, the AMPase activity of 5′-nucleotidase from human seminal plasma is not affected by dithiothreitol which, on the contrary, is a powerful inhibitor of the bovine enzyme causing the dissociation of its subunits which are held together by disulphide bridges (Fini, C., Minelli, A., Camici, M. and Floridi, A. (1985) Biochem. Biophys. Acta 827, 403–409).