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Query: UNIPROT:P36969 (phospholipid hydroperoxide glutathione peroxidase)
 344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Phospholipid hydroperoxide glutathione peroxidase (PHGPx; EC 1.11.1.12), a broad-spectrum thiol-dependent peroxidase, deserves renewed interest as a regulatory factor in various signaling cascades and as a structural protein in sperm cells. We present a first attempt to identify catalytic intermediates and derivatives of the selenoprotein by liquid chromatography coupled to electrospray tandem mass spectrometry (LC/ESI-MS/MS) and to explain observed specificities by molecular modeling. The ground state enzyme E proved to correspond to position 3-170 of the deduced porcine sequence with selenium being present as selenocysteine at position 46. The selenenic acid form, which is considered to be the first catalytic intermediate F formed by reaction with hydroperoxide, could not be identified. The second catalytic intermediate G was detected as Se-glutathionylated enzyme. This intermediate is generated in the reverse reaction where the active site selenol interacts with glutathione disulfide (GSSG). According to molecular models, specific binding of reduced glutathione (GSH) and of GSSG is inter alia facilitated by electrostatic attraction of Lys-48 and Lys-125. Polymerization of PHGPx is obtained under oxidizing conditions in the absence of low molecular weight thiols. Analysis of MS spectra revealed that the process is due to a selective reaction of Sec-46 with Cys-148' resulting in linear polymers representing dead-end intermediates (G'). FT Docking of PHGPx molecules allowed reactions of Sec-46 with either Cys-66', Cys-107', Cys-168' or Cys-148', the latter option being most likely as judged by the number of proposed intermediates with reasonable hydrogen bonds, interaction energies and interface areas. We conclude that the same catalytic principles, depending on the conditions, can drive the diverse actions of PHGPx, i.e. hydroperoxide reduction, GSSG reduction, S-derivatization and self-incorporation into biological structures.
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PMID:Versatility of selenium catalysis in PHGPx unraveled by LC/ESI-MS/MS. 1275 87

The selenoprotein phospholipid hydroperoxide glutathione peroxidase (PHGPx) is present in at least three different isoforms in testis: as a cytosolic, as a mitochondrial, and as a nuclear protein. We have recently shown that a sperm nucleus-specific glutathione peroxidase (snGPx) is identical to the mitochondrial and cytosolic forms of PHGPx apart from its N-terminus. This arginine-rich N-terminus of snGPx, reminiscent of protamines, is encoded by an alternative exon located in the first intron of the PHGPx gene and is responsible for nuclear localisation and chromatin binding of snGPx [Pfeifer et al., FASEB J. 15 (2001), pp. 1236-1238]. By using a combination of techniques including selective cloning of mRNA 5'-ends, RT-PCR, and S1 analyses, we provide evidence that the transcript encoding the nuclear form is generated by transcription initiation at an alternative promoter and not by alternative splicing. We show that the major transcription start region is located at -12 to -14 upstream of the AUG translation initiation site of the sperm nucleus-specific exon and lacks a TATA box. Two minor TATA-less transcription initiation sites are located at around -30 and -45. We have shown by in situ hybridisation that snGPx expression in testis, like protamine expression, is restricted to late stages of spermatogenesis whereas PHGPx expression is only found in spermatocytes and early spermatids. These findings have to be taken into account when studying either the differential regulation of PHGPx and snGPx expression in testis or the impact of putative mutations in snGPx on male fertility in man.
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PMID:Testis-specific expression of the nuclear form of phospholipid hydroperoxide glutathione peroxidase (PHGPx). 1275 92

The selenoprotein phospholipid hydroperoxide glutathione peroxidase (PHGPx) is highly expressed in testes under gonadotropin control. The expression patterns of PHGPx mRNA by 17beta-estradiol (E2) as an estrogen and tamoxifen (Tam) as an estrogen antagonist were investigated in the reproductive organs of male rats. Twelve-week-old male Sprague-Dawley rats were subcutaneously injected with E2 (7.5 microg/kg/day) or Tam (5 mg/kg/day) for 1 week. The E2 treatment significantly increased the levels of PHGPx mRNA in both testes and prostates, whereas the Tam treatment significantly decreased the levels of PHGPx mRNA, compared to the vehicle control (p<0.01). The treatment with E2 or Tam slightly decreased the levels of PHGPx mRNA in epididymides. In histopathological examination, severe vacuolization and depletion of germ cells in the seminiferous tubules, cell debris in the tubular lumen, and mild proliferative changes in interstitial tissues were observed in the testes of Tam-treated rats, whereas only mild spermatogonial proliferation was observed in the seminiferous tubules of E2-treated rats. There were no typical histopathological changes in the epididymides of any of the laboratory rats but mild epithelial proliferation in the prostates of E2- and Tam-treated rats. These results suggest that PHGPx mRNA expression may be influenced by estrogen in the male reproductive organs.
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PMID:Effects of 17beta-estradiol and tamoxifen on the selenoprotein phospholipid hydroperoxide glutathione peroxidase (PHGPx) mRNA expression in male reproductive organs of rats. 1496 15

PHGPx (phospholipid hydroperoxide glutathione peroxidase) is a selenoprotein present in at least three isoforms in testis: cytosolic, mitochondrial and nuclear. All of these derive from the same gene and are structurally related with the exception of the snPHGPx (sperm nucleus-specific form), which differs from the others due to the presence of an arginine-rich N-terminus. It has been demonstrated recently that this N-terminus is encoded by an alternative exon located in the first intron of the PHGPx gene. The expression of snPHGPx has been attributed either to an alternative pre-mRNA splicing or to the presence of a distinct promoter region. Nevertheless, the exact molecular mechanism by which the expression of snPHGPx occurs has not been demonstrated so far. Preliminary sequence analysis of the region located upstream of the alternative exon revealed some potential DNA-binding sites, one of which is specific to the binding of CREM (cAMP-response element modulator) transcription factors. By using electrophoretic mobility-shift assays, we demonstrated that both nuclear protein extract from highly purified rat spermatid cells and recombinant CREM-tau protein can specifically bind to this element. Furthermore, we cloned a 1059 bp comprising the intron and the alternative exon for snPHGPx in the pCAT3 reporter vector. By transient transfection experiments, we demonstrated that the expression of the transcription factor CREM-tau can induce the activation of the reporter gene in NIH-3T3 cell line. These results were confirmed by chromatin immunoprecipitation experiments performed on highly purified rat spermatid cells. On the basis of these results, we demonstrate that snPHGPx expression is mediated by the transcription factor CREM-tau, which acts as a cis-acting element localized in the first intron of the PHGPx gene.
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PMID:cAMP-response element modulator-tau activates a distinct promoter element for the expression of the phospholipid hydroperoxide/sperm nucleus glutathione peroxidase gene. 1522 22

Co-translational insertion of selenocysteine (Sec) into proteins in response to UGA codons is directed by selenocysteine insertion sequence (SECIS) elements. In known bacterial selenoprotein genes, SECIS elements are located in the coding regions immediately downstream of UGA codons. Here, we report that a distant SECIS element can also function in Sec insertion in bacteria provided that it is spatially close to the UGA codon. We expressed a mammalian phospholipid hydroperoxide glutathione peroxidase in Escherichia coli from a construct in which a natural E.coli SECIS element was located in the 3'-untranslated region (3'-UTR) and adjacent to a sequence complementary to the region downstream of the Sec UGA codon. Although the major readthrough event at the UGA codon was insertion of tryptophan, Sec was also incorporated and its insertion was dependent on the functional SECIS element in the UTR, base-pairing potential of the SECIS flanking region and the Sec UGA codon. These data provide important implications into evolution of SECIS elements and development of a system for heterologous expression of selenoproteins and show that in addition to the primary sequence arrangement between UGA codons and SECIS elements, their proximity within the tertiary structure can support Sec insertion in bacteria.
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PMID:Selenocysteine insertion directed by the 3'-UTR SECIS element in Escherichia coli. 1586 25

In the sperm nuclei, of mammalian species selenium has been found only in the form of sperm nuclei glutathione peroxidase (snGPx) where it is most likely bound to the chromatin of spermatozoa. Over 80% of selenium in sperm is bound to the selenoprotein phospholipid hydroperoxide glutathione peroxidase (PHGPx) in the midpiece of rat sperm. Zinc in sperm is mainly contained in the outer dense fiber (ODF) proteins of the flagella of mammalian spermatozoa. In the sperm nuclei, zinc is predominately located in the chromatin to the protamine proteins. In order to investigate if the insertion of zinc and selenium in sperm chromatin is regulated, the element concentrations were determined in equine spermatozoa and purified sperm nuclei. We found a significant positive correlation between the selenium concentration in equine spermatozoa and sperm nuclei. The same finding was obtained for the zinc concentration in spermatozoa and sperm nuclei. The results assume that the distribution of selenium and zinc in spermatozoa is regulated by cell signaling pathways and in this way determining the selenium and zinc amount in the chromatin of spermatozoa.
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PMID:Is the distribution of selenium and zinc in the sublocations of spermatozoa regulated? 1740 33

The role of selenium in male fertility is reviewed with special emphasis on selenoprotein P and phospholipid hydroperoxide glutathione peroxidase (GPx4) in spermiogenesis. Inverse genetics reveal that selenoprotein P is required for selenium supply to the testis. GPx4 is abundantly synthesized in spermatids. As a moonlighting protein it is transformed in the later stages of spermiogenesis from an active selenoperoxidase into a structural protein that becomes a constituent of the mitochondrial sheath of spermatozoa. The transformation is paralleled by loss of glutathione. Mechanistically, the process is an alternate substrate inactivation of GPx4 resulting from reactions of its selenenic form with thiols of GPx4 itself and other proteins. Circumstantial evidence and ongoing experimental genetics indicate that the mitochondrially expressed form of the GPx4 gene is the most relevant one in spermiogenesis, with the nuclear form being dispensable for fertility and the role of cytosolic GPx4 remaining unclear. Clinical data reveal a strong association of low sperm GPx4 with infertility. Thus, impaired GPx4 biosynthesis, due to selenium deficiency or to genetic defects in gpx4 itself or in proteins involved in Se distribution and selenoprotein biosynthesis, causes male infertility, but can also be an epiphenomenon due to any perturbation of testicular function.
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PMID:Selenium in mammalian spermiogenesis. 1793 12

Human selenium (Se) requirements are currently based on biochemical markers of Se status. In rats, tissue glutathione peroxidase-1 (Gpx1) mRNA levels can be used effectively to determine Se requirements; blood Gpx1 mRNA levels decrease in Se-deficient rats, so molecular biology-based markers have potential for human nutrition assessment. To study the efficacy of molecular biology markers for assessing Se status in humans, we conducted a longitudinal study on 39 subjects (age 45 +/- 11) in Reading, UK. Diet diaries (5 day) and blood were obtained from each subject at 2, 8, 17 and 23 weeks, and plasma Se, glutathione peroxidase (Gpx3) enzyme activity, and selenoprotein mRNA levels were determined. There were no significant longitudinal effects on Se biomarkers. Se intake averaged 48 +/- 14 microg/d. Plasma Se concentrations averaged 1.13 +/- 0.16 micromol/l. Plasma Se v. energy-corrected Se intake (ng Se/kJ/d) was significantly correlated, but neither Gpx3 activity v. Se intake (ng Se/kJ/d) nor Gpx3 activity v. plasma Se was significantly correlated. Collectively, this indicates that subjects were on the plateaus of the response curves. Selenoprotein mRNAs were quantitated in total RNA isolated from whole blood, but mRNA levels for Gpx1, selenoprotein H, and selenoprotein W (all highly regulated by Se in rodents), as well selenoprotein P, Gpx3, and phospholipid hydroperoxide glutathione peroxidase were also not significantly correlated with plasma Se. Thus selenoprotein molecular biomarkers, as well as traditional biochemical markers, are unable to further distinguish differences in Se status in these Se replete subjects. The efficacy of molecular biomarkers to detect Se deficiency needs to be tested in Se-deficient populations.
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PMID:Longitudinal selenium status in healthy British adults: assessment using biochemical and molecular biomarkers. 1859 87

The monomeric selenoprotein, phospholipid hydroperoxide glutathione peroxidase (GPx4) is an essential member of the antioxidant defense system. This paper describes the identification of two gpx4 genes (gpx4a and gpx4b) from somatic tissues of common carp (Cyprinus carpio). The two sequences exhibited 78% and 79% identity at the DNA and the predicted protein level, respectively. The gpx4a transcript was detected in all examined tissues of unstressed animals, with the highest level in the liver. The gpx4b expression was low relative to that of gpx4a in the liver, heart, muscle and brain, and was virtually undetected in the kidney. However, in the olfactory lobe gpx4b was expressed at a fairly high level, the ratio gpx4a/gpx4b being approximately 2:1. Cold shock and Cd(2+) exposure influenced the gpx4a expression to only a slight extent, whereas gpx4b was greatly down-regulated following Cd(2+) exposure.
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PMID:Identification of two phospholipid hydroperoxide glutathione peroxidase (gpx4) genes in common carp. 1934 79

The essential trace element selenium and polyunsaturated fatty acids (PUFA) have been used for the prevention of cancer. Both nutrients enhance the apoptosis of malignant cells and provide health benefits. However, an increased dietary intake of PUFA augments the susceptibility of lipid peroxidation and oxidative damage in many cells. So far, relatively few data are available about the interaction of selenium and PUFA in testis and thus a possible effect of both dietary components on the prevention of testicular cancer or on the apoptosis of testicular germ cells. Male germ cells in the rat contain most of the testicular phospholipid hydroperoxide glutathione peroxidase (PHGPx), mainly as the mitochondrial isoform of this selenoprotein (m-PHGPx). An experiment was therefore carried out to determine the action of fish oil, a nutrient rich in PUFA, on the testicular expression of PHGPx. Because the PHGPx formation remains nearly unchanged in the animals fed the PUFA-enriched diet, we conclude that no apoptosis of testicular germ cells is induced by an increased intake of this nutrient. The intake of fish oil in the selenium-deficient animal led to a markedly altered formation of several selenium-containing proteins, including sperm nuclei glutathione peroxidase (snGPx), also designated as the nuclear form of PHGPx (n-PHGPx), and a 10-kDa selenium-containing protein.
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PMID:Studies with regard to the apoptosis of testicular germ cells in rats fed a diet enriched with polyunsaturated Fatty acids. 1972 78


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