Thiol-disulfide proteins of stallion epididymal spermatozoa.

Thiol groups of cysteine residues represent redox centers involved in multiple biological functions. It has been postulated that changes in the redox status of mammalian epididymal spermatozoa contribute to the sperm maturation process. The present work shows the thiol-disulfide protein profile of stallion epididymal spermatozoa achieved by two-dimension electrophoresis and MALDI-TOF/TOF mass spectrometry of proteins labeled with a thiol-reactive fluorescent tag, monobromobimane. Our results have shown the formation of disulfide bonds in several sperm protein fractions during the epididymal maturation process. The majority of the oxidized thiol sperm proteins identified correspond to structural molecules of the flagellum (as the outer dense fiber-1 protein - ODF1), followed by glycolytic enzymes (as glyceraldehyde-3-phosphate dehydrogenase spermatogenic), antioxidant protectors (as glutathione S-transferase and phospholipid hydroperoxide glutathione peroxidase - PHGPx). The magnitude of the thiol oxidation differs between proteins, and was more drastic in polypeptides with molecular weights of up to 33kDa, identified as ODF1 and PHGPx. A kinase anchor protein, a voltage-dependent anion channel protein and a zona pellucida-binding protein were also found in the polypeptide samples that contained oxidized SH groups. These proteins may be modified or controlled by the mechanisms involved in the cysteine-redox changes, corroborating the belief that a correct degree of protein oxidation is required for the stabilization of sperm structure, protection against oxidative damage, induction of progressive sperm motility and fertilization.

Alpha-mannosidase activity in stallion epididymal fluid and spermatozoa.

The expression of α-D-mannosidase activity was fluorometrically and electrophoretically assessed in spermatozoa, epididymal fluid and homogenates of stallion epididymal tissue. Enzyme activity had regional differences; it was higher (P<0.05) in samples from the cauda epididymal region than in samples from the proximal caput region (largely composed of efferent ducts). Based on enzyme activity, as a function of pH of the assay substrate, electrophoretic analysis in native and native/SDS-PAGE conditions, and the effect of inhibitors or activators, we inferred the presence of at least two catalytically active forms of α-D-mannosidase. The neutral form of the enzyme (α-mannosidase II) was activated by Co2+, whereas the acid form (optimum pH 3.5 to 4.0) was sensitive to swainsonine (an inhibitor of α-mannosidase I), stabilized or stimulated by Zn2+, and not activated by Co2+ (activator of the neutral form). The activity of the acid form of the enzyme was highest in the epididymal fluid, where it seemed to be mainly in a secretory form. This form of the enzyme may have a role in plasma membrane remodeling associated with sperm maturation. In contrast, the activity of α-mannosidase II was higher in mature spermatozoa. It has been postulated that α-mannosidase II may act as a receptor in the recognition and binding of the complementary carbohydrate moieties present on the zona pellucida. With non-denaturing electrophoresis, α-D-mannosidase had an electrophoretic mobility of 0.35 and 0.24. When resolved by 1D and 2D SDS-PAGE (under denaturing conditions) the enzyme had a major protein band of molecular weight 154 kDa in spermatozoa and epididymal samples. Based on its properties under native conditions, we inferred that this enzyme might interact with other proteins and form transitory aggregates.

Acid phosphatase activity during the interaction of the nematophagous fungus Duddingtonia flagrans with the nematode Panagrellus sp.

The use of Duddingtonia flagrans, a nematode-trapping fungus, has been investigated as a biological control method against free living larvae of gastrointestinal nematodes of livestock animals. This fungus captures and infects the nematode by cuticle penetration, immobilization and digestion of the internal contents. It has been suggested that this sequence of events occurs by a combination of physical and enzymatical activities. This report characterizes the acid phosphatase activity during the interaction of D. flagrans with the free-living nematode Panagrellus sp. The optimum pH for the hydrolysis of the acid phosphatase substrate p-nitrophenyl phosphate was 2.2, 2.8 and 5.4 from D. flagrans alone and 2.2 and 5.4 for Panagrellus sp alone, fungus-nematode interaction in liquid medium and fungus-nematode interaction in solid medium. Different acid phosphatase activity bands were detected by SDS-PAGE. Maximum acid phosphatase activity of the fungus or nematode alone and of the fungus-nematode interaction occurred within 70min of incubation in the presence of the substrate 4-methylumbelliferyl phosphate. The activity of this enzyme was significantly higher for the fungus-nematode interaction when compared to the organisms alone, indicating a synergistic response. Furthermore, structures appeared in the hyphae after 30min, nematodes were observed adhered after 40min and many were captured by the typical fungus traps after 70min of interaction. The participation of acid phosphatase activity and its importance during the interaction of the fungus with the nematode were discussed.

Post-testicular changes in the density and distribution of intramembrane particles of stallion sperm surface domains.

Freeze-fracture replicas of stallion spermatozoa, collected from the proximal caput, corpus and cauda epididymides regions, were analyzed by electron microscopy to explore the distribution and density of intramembrane particles (IMP). Conspicuous differences in density and arrangement of the IMP were observed in the different topographical domains of mature and immature spermatozoa. A reduction of IMP, especially remarkable in the post-acrosomal domain, was observed in mature epididymal spermatozoa when compared with samples collected from ductuli efferentes. Some structural species-specific differences were also observed. The significance of these changes has not been determined, but remodeling of membrane components during developmental processes constitutes a fine control mechanism to ensure that key molecules are in the correct membrane position and during an appropriate timeframe to mediate fertilization.

Cloning and characterization of a cowpea seed lipid transfer protein cDNA: expression analysis during seed development and under fungal and cold stresses in seedlings' tissues.

Lipid transfer proteins (LTPs) are antimicrobial peptides (AMPs) involved in the defense of plants against pathogens. Our group has previously characterized and purified a LTP from cowpea (Vigna unguiculata (L.) Walp.) seeds which caused the inhibition of growth of fungal pathogens in vitro. The aim of this work was to obtain the cDNA encoding the cowpea LTP and after cloning, to use the cDNA as a probe for studying its expression profile during the development of cowpea seeds. In this work, the N-terminal sequence of the mature LTP peptide from cowpea was used to produce a degenerated oligonucleotide. This primer allowed the amplification of the LTP cDNA by RT-PCR from mRNA of cowpea seeds. The sequence analysis of the cloned cDNA, named VULTP, showed 494 bp which encoded a polypeptide of 91 amino acids. The deduced peptide presented high homology of similarity to plant LTPs of Vigna radiata var. radiate (94%), Prunus domestica (82%) and Zea mays (72%). The expression profile of the VULTP gene in cowpea was analyzed by Northern blot and revealed that the transcript is not accumulated in adult tissues. Conversely, VULTP mRNA is early and strongly accumulated during seed development. The results obtained to seedling of cowpea demonstrate that the VULTP gene presents differential expression in response to different stress. Further studies will be conducted to try to gain better understanding about the physiological role of this gene in cowpea.

Nuclear status of immature and mature stallion spermatozoa.

'The highly packed chromatin of mature spermatozoa results from replacement of somatic-like histones by highly basic arginine- and cysteine-rich protamines during spermatogenesis, with additional conformational changes in chromatin structure during epididymal transit. The objective of the present study was to compare the nuclear characteristics of immature and mature epididymal stallion spermatozoa, using a variety of experimental approaches. Resistance to in vitro decondensation of chromatin, following exposure to SDS-DTT and alkaline thioglycolate, increased significantly in mature spermatozoa. Evaluation of the thiol-disulfide status (monobromobimane labeling) demonstrated that immature cells obtained from ductulli efferentes contained mostly thiol groups, whereas these groups were oxidized in mature cells collected from the cauda epididymidis. Based on atomic absorption spectrophotometry, maturation of stallion spermatozoa was accompanied by a 60% reduction in the Zn(2+) content of sperm cells, concomitant with increased concentrations of this ion in epididymal fluid. Furthermore, the degree of disulfide bonding was inversely correlated with susceptibility of chromatin to acid denaturation (SCSA). Collectively, these data were consistent with the hypothesis that maturation of stallion spermatozoa involves oxidation of sulphydryl groups to form intra- and intermolecular disulfide links between adjacent protamines, with loss of zinc as an integral feature. These changes endow mechanical and chemical resistance to the nucleus, ensuring efficient transmission of the paternal genome at fertilization.

Protein purification from polyacrylamide gels by sonication extraction.

A protein purification procedure using sonication extraction from polyacrylamide gels (PAGE), which involves identification of a particular protein band and its excision, homogenization, sonication, and subsequent passage through a Sephadex G-25 minicolumn, is reported. Our results show a high degree of recovery regardless of the nature of the protein (soluble or membrane bound) or the characteristics of the gel (SDS-PAGE, native gels, or Tricine-SDS-PAGE). The percentage of recovery was dependent on the protein concentration applied in the gel. This technique is fast, gives high yield, provides good resolution, and can be used without any specialized equipment. The method was tested with a wide variety of membranes and soluble proteins and was found to give good results and to be applicable to different studies. The amino acid sequence of one of the purified proteins (Rf 0.45 stallion ejaculated sperm protein) was determined successfully.