1,721,131 research outputs found
Redox Pioneer: Professor Regina Brigelius-Flohé
No full textDr. Regina Brigelius-Flohe (PhD 1978) is recognized here as redox pioneer because she has published an article on redox biology, as first author, that has been cited >1000 times, plus four articles cited >500 times, and a total of 30 articles cited >100 times. She obtained her doctorate in biochemistry at the Institute of Biochemistry of the University of Munster, Germany. She held positions in both, academia (Munster, Munich, Dusseldorf, Hannover, and Potsdam, Germany) and industry (Aachen, Germany). Dr. Brigelius-Flohe is the pioneer who, as head of the department of biochemistry of micronutrients of the German Institute of Human Nutrition (DIfE; Potsdam-Rehbrucke, Germany), worked out the metabolism of tocopherols and tocotrienols ("Key Finding 1"). She was the first to sequence glutathione peroxidase 4 (GPx4) ("Key Finding 2"), and unraveled the role of selenium, in particular of GPxs, in inflammation and carcinogenesis ("Key Finding 3"). Her contributions, thus, focused on serious biomedical problems such as nutrition, inflammation, and carcinogenesis. She has been a member of the scientific advisory board of the German Society of Biochemistry and Molecular Biology for 6 years and was president of SFRR-Europe in 2005-2006. She edited several books and serves on the editorial board of journals in the fields of nutrition, free radicals, and redox regulation. Antioxid. Redox Signal. 35, 000-000
When S is more convenient than Se: insights from GPx-7 kineticsWhen S is more convenient than Se: insights from GPx-7 kinetics
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Insight from GPxs structure and function
No full textThe multigene family of GPxs encodes for tetrameric and monomeric enzymes both containing either a selenocysteine (Sec) or cysteine (Cys) residue at the catalytic site. Monomeric GPxs carry deletions of the subunit interfaces. The Sec containing homologues are found in vertebrates, and, with a scattered presence, in lower organisms. These SecGPxs are either tetrameric or monomeric, as the mammalian GPx-1 and 4 respectively, and undergo a peroxidatic cycle where the selenenic acid derivative of Sec (SeOH), formed upon reaction with the peroxide, is reduced back at a fast rate by glutathione (GSH). On the other hand, terrestrial plants, insects, bacteria, fungi, do not encode for any SecGPxs, but for CysGPxs only. By analyzing more than 450 GPx sequences, we have found that the majority of these both carry a non-aligned ‘second’ Cys residue in the fourth helix and have a monomeric nature, being, in the latter respect, GPx-4 homologues. In these CysGPxs, the oxidized intermediate of the catalytic cycle is different from SecGPxs, being accounted for by a disulfide between the peroxidatic Cys and the ‘second’ Cys, thus acting as a ‘resolving’ Cys, as typically in peroxiredoxins. Conformation analysis suggests that the absence of tetrameric structure allows the loop flexibility required for the disulfide formation. Taking as a paradigm the Drosophila CysGPx, we have shown that the above features largely favor the reaction with Thioredoxin (Trx) over GSH. Thus, the majority of the CysGPxs sequences deposited in the data banks, in functional terms, must be referred to as Trx peroxidases. On the other hand, the functional role of the quantitatively minor tetrameric or monomeric CysGPxs sequences, lacking the resolving Cys, which, in vertebrates, are coexisting together with the SecGPxs, remains unresolved. GPxs are not redundant proteins. In yeast one of the above CysGPxs, GPX3, has been shown to be involved in the peroxide-dependent activation of the trascription factor Yap-1 (Toledano et al. TIBS 29, 351, (2004). While in mammals, GPx-1 appears the unique, real, glutathione peroxidase out of the five SecGPxs, the others might have different functions. In particular, GPx-4 is involved in the oxidation of protein thiol motifs taking place during sperm maturation
Defining the molecular bases for the thioredoxin peroxidase activity of glutathione peroxidases
No full textSelenium and male fertility
No full textSelenium in nutrition: historical milestones-Selenocysteine and eukaryotic selenocysteine-containing proteins -Mechanism of incorporation of Selenocysteine into proteins- Selenium and male fertility: historical milestones- Phospholipid hydroperoxide glutathione peroxidase (PHGPx or GPx4; E.C. 1. 11.1.12) as the major selenoperoxidase of testis germ cells and mitochondrial capsule of mature spermatozoa – Sperm PHGPx activity as a biomarker of fertility-Additional selenoproteins involved in spermatogenesis
Phospholipid Hydroperoxide Glutathione Peroxidase almost thirty years later
No full textPhospholipid hydroperoxide glutathione peroxidase (PHGPx), now known as GPx-4, was discovered in 1982 as a second glutathione peroxidase (GPx) distinct from GPx-1 because it could peculiarly protect membrane lipid peroxidation in the presence of Vitamin E. This cooperation was explained by the hydroperoxyl radical scavenging capacity of vitamin E and the reduction of membrane phosholipid hydroperoxide (PLOOH) by PHGPx.
Later, kinetic analysis indicated that in the presence of PCOOH, the oxidizing step of the catalytic cycle is very fast (measured k’+1 values of 107 M-1 s-1 for human and porcine GPx-4) while reduction is the rate-limiting step of the overall reaction. Comparison of k’+2 values suggests that, among the SecGPxs, PHGPx has the lowest reactivity with GSH. Indeed PHGPx reacts five times as fast with dithiothreitol than with GSH and almost equally fast with mercaptoethanol, when none of these thiols is accepted by GPx-1.
These early findings anticipated the broadest physiological role of this enzyme compared to the other GPxs that emerged year after year, and today is fully confirmed by k.o models. The vital role of GPx-4 could actually be ascribed to the enzyme antiperoxidant activity and was found definitely relevant for neurons. Intriguing enough, Vitamin E could to rescue the dead phenotype obtained in cells by switching off the expression of the GPx-4. On the other hand, the central role in fertility of GPx-4, allowing ‘moonlighting’ to a structural component of the sperm mitochondrial capsules by oxidizing specific protein thiols, can be ascribed to its broad thiol specificity.
In the meanwhile, CysGPx were discovered bearing the structural characteristics of PHGPx and found as efficient as their Sec-containing homologues in reducing hydroperoxides. The majority of these proteins, which indeed reduce efficiently PCOOH, are confined to the invertebrate and plant kingdom. Typically they contain a CR residue within a functional helix and are linked to the thioredoxin but not the GSH system. Some of them emerged for unespected novel roles such as peroxide sensing and gene activation.
All together these finding expand our apreciation of lipid peroxidation to a physiologically relevant phenomena, and qualify redox regulation is a complementary mechanism to the other most known post-translational modifications. In the present scenario, understanding the molecular details of these signaling cascades and defining the specific role of each individual GPx in this context is anticipated as extremely rewarding and full of surprises. Further, it appears indeed the ground for developing effective strategies to counteract major human pathological processes such as cancer and cerebral degeneration
Why selenium rather than sulphur catalysis in peroxidases? More we learn, less we understand it
No full textHydrogen peroxide is both a byproduct of oxygen utilization during respiration and a physiological oxidant, build up to faith pathogens and act as a chemical signal in signal transduction cascades. Irrespective of its final use, hydrogen peroxide has also to be quickly removed to prevent collateral damage. A pivotal enzyme for this is the Selenocysteine (Sec)-containing enzyme Glutathione Peroxidase (GPx1), the first discovered of a family encompassing to date eight mammalian proteins. The amazing catalytic efficiency is provided by the reactivity with hydrogen peroxide of the selenol at the active site, in turn attributed to its low pKa. This redox reaction is indeed much faster than the enzyme substrate interaction, giving rise to unusual non-saturation kinetics where the calculated rate constant for the oxidation of the active site selenol (k+1) is around 108 M-1 sec-1. This peculiar reactivity is assumed similar for the other SecGPxs, although careful kinetic data are available only for GPx1 and 4.
However, in the last years, new available information challenged the notion that the peculiar reactivity of GPxs can only be obtained when the redox moiety is selenol. First, a large number of GPxs have been identified in all living kingdoms, where the highly conserved active site contains a Cys residue in place of the redox-active Sec. As suggested by kinetic analysis of the Drosophila melanogaster variant (DmGPx), these CysGPxs are predicted only marginally less reactive with the hydroperoxide than the SecGPxs. Similarly, in peroxiredoxins, the oxidation of the peroxidatic Cys by hydrogen peroxide takes place with a k+1 in the range of 107 M-1 sec-1. Thus, apparently, when properly activated, a thiol can substitute for a selenol without affecting fast reduction of hydroperoxides. This raises the issue of the actual relevance of having a Sec residue in the active site.
Aiming to better define the constraints for Se or S activation at the active site of GPxs, we obtained an updated picture of the active site of these enzymes by analyzing more than 700 structures for sequence homology and molecular modeling. Data were implemented with activity measurement and kinetic analysis of the DmGPx as a model, where some conserved residues were substituted by site directed mutagenesis. Our results suggest that the thiol or the selenol is activated by H bonding to the nitrogens of three strongly conserved residues, namely Gln 80, Trp 135 and Asn 136, while computational calculation of pKa and kinetic analysis, suggest that the pKa of the redox moiety is less relevant than H bonding. The deduced reaction mechanism suggests that, instead, the polarization of the peroxidic substrate and protonation of the hydroxyl-leaving group play a major role in accelerating the peroxidatic reaction.
In conclusion, the previous notion that in nature Se is preferred to S just for a much faster reduction of hydroperoxides is not convincing anymore. Moreover, further complexity is added from phylogenetic analysis. While the ancestor of all GPxs is a CysGPx, and substitution of active site Cys with Sec is a relatively recent acquisition, for some GPxs an unexpected shift back to Cys is apparently taking place. In conclusion, from post-genomic acquisitions, unraveling the actual relevance about the use of Se rather than S in GPx catalysis, far from being clarified, appears more complex than before
Redox Pioneer: Professor Leopold Flohe
No full textLeopold Flohé is recognized here as a Redox Pioneer because has published a article on antioxidant/redox biology, as first author, that has been cited more than 1,000 times, and more than 20 articles have been cited more than 100 times. He obtained the medical doctorate at the Institute of Pharmacology and Toxicology at the University of Tübingen, Germany, in 1968. He held positions in both Academia (Tübingen, Aachen, and Braunschweig, Germany) and industry (Aachen). He is now operating the biotech company MOLISA in Magdeburg, Germany, while teaching as guest professor at the local university. Dr. Flohé is the pioneer who established the selenoprotein nature of glutathione peroxidase (GPx), the first and, for almost 10 years, the only selenoprotein known in animals. His work was pivotal to link the essential trace element selenium to metabolic processes, which led the Food and Drug Administration (FDA) to approve selenium supplementation for humans in 1980, and stimulated selenium biochemistry in general. In recent years, he embarked on investigating how pathogens protect themselves from oxidative killing. His inseminating studies on the thiol-dependent hydroperoxide metabolism of trypanosomatids and mycobacteria defined molecular drug targets, paving the way to new therapeutic strategies for neglected diseases affecting the people of developing countries
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