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Karolien Van Belle

Bio: Karolien Van Belle is an academic researcher from Vrije Universiteit Brussel. The author has contributed to research in topics: Arsenate reductase & Active site. The author has an hindex of 10, co-authored 14 publications receiving 557 citations. Previous affiliations of Karolien Van Belle include Flanders Institute for Biotechnology & VU University Amsterdam.

Papers
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Journal ArticleDOI
TL;DR: The catalytic mechanism for the reduction of arsenate to arsenite in Corynebacterium glutamicum is unraveled, paving the way for the study of redox mechanisms in actinobacteria.

91 citations

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TL;DR: Determination of the oxidized and reduced structures of mycoredoxin‐1, better understanding of the mycothiol‐dependent reactions in general, will likely give new insights in how M. tuberculosis survives oxidative stress in human macrophages.
Abstract: Summary To survive hostile conditions, the bacterial pathogen Mycobacterium tuberculosis produces millimolar concentrations of mycothiol as a redox buffer against oxidative stress. The reductases that couple the reducing power of mycothiol to redox active proteins in the cell are not known. We report a novel mycothiol-dependent reductase (mycoredoxin-1) with a CGYC catalytic motif. With mycoredoxin-1 and mycothiol deletion strains of Mycobacterium smegmatis, we show that mycoredoxin-1 and mycothiol are involved in the protection against oxidative stress. Mycoredoxin-1 acts as an oxidoreductase exclusively linked to the mycothiol electron transfer pathway and it can reduce S-mycothiolated mixed disulphides. Moreover, we solved the solution structures of oxidized and reduced mycoredoxin-1, revealing a thioredoxin fold with a putative mycothiol-binding site. With HSQC snapshots during electron transport, we visualize the reduction of oxidized mycoredoxin-1 as a function of time and find that mycoredoxin-1 gets S-mycothiolated on its N-terminal nucleophilic cysteine. Mycoredoxin-1 has a redox potential of −218 mV and hydrogen bonding with neighbouring residues lowers the pKa of its N-terminal nucleophilic cysteine. Determination of the oxidized and reduced structures of mycoredoxin-1, better understanding of mycothiol-dependent reactions in general, will likely give new insights in how M. tuberculosis survives oxidative stress in human macrophages.

83 citations

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TL;DR: Periplasmic ribonuclease I from Escherichia coli is presented as a new endogenous substrate for the study of oxidative protein folding and shows that DsbA is a sufficient catalyst for correct disulfide formation in vivo and in vitro.

80 citations

Journal ArticleDOI
TL;DR: The mechanism of pI258 arsenate reductase (ArsC) catalyzed arsenate reduction, involving its P-loop structural motif and three redox active cysteines, has been unraveled and Steady-state kinetics of ArsC mutants gives a view of the crucial residues for catalysis.
Abstract: The mechanism of pI258 arsenate reductase (ArsC) catalyzed arsenate reduction, involving its P-loop structural motif and three redox active cysteines, has been unraveled. All essential intermediates are visualized with x-ray crystallography, and NMR is used to map dynamic regions in a key disulfide intermediate. Steady-state kinetics of ArsC mutants gives a view of the crucial residues for catalysis. ArsC combines a phosphatase-like nucleophilic displacement reaction with a unique intramolecular disulfide bond cascade. Within this cascade, the formation of a disulfide bond triggers a reversible “conformational switch” that transfers the oxidative equivalents to the surface of the protein, while releasing the reduced substrate.

76 citations

Journal ArticleDOI
TL;DR: The active site proline in thioredoxin determines the driving potential for substrate reduction, and the oxidized form of wild-type Sa_Trx is far more stable than the reduced form over the whole temperature range.

71 citations


Cited by
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Journal ArticleDOI
TL;DR: The absence of a GSH-Grx system in some pathogenic bacteria such as Helicobacter pylori, Mycobacterium tuberculosis, and Staphylococcus aureus makes the bacterial Trx system essential for survival under oxidative stress, and provides an opportunity to kill these bacteria by targeting the TrxR-Trx system.

1,371 citations

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TL;DR: Resistance to silver compounds as determined by bacterial plasmids and genes has been defined by molecular genetics and the use of molecular epidemiological tools will establish the range and diversity of such resistance systems in clinical and non-clinical sources.
Abstract: Resistance to silver compounds as determined by bacterial plasmids and genes has been defined by molecular genetics. Silver resistance conferred by the Salmonella plasmid pMGH100 involves nine genes in three transcription units. A sensor/responder (SilRS) two-component transcriptional regulatory system governs synthesis of a periplasmic Ag(I)-binding protein (SilE) and two efflux pumps (a P-type ATPase (SilP) plus a three-protein chemiosmotic RND Ag(I)/H+ exchange system (SilCBA)). The same genes were identified on five of 19 additional IncH incompatibility class plasmids but thus far not on other plasmids. Of 70 random enteric isolates from a local hospital, isolates from catheters and other Ag-exposed sites, and total genomes of enteric bacteria, 10 have recognizable sil genes. The centrally located six genes are found and functional in the chromosome of Escherichia coli K-12, and also occur on the genome of E. coli O157:H7. The use of molecular epidemiological tools will establish the range and diversity of such resistance systems in clinical and non-clinical sources. Silver compounds are used widely as effective antimicrobial agents to combat pathogens (bacteria, viruses and eukaryotic microorganisms) in the clinic and for public health hygiene. Silver cations (Ag+) are microcidal at low concentrations and used to treat burns, wounds and ulcers. Ag is used to coat catheters to retard microbial biofilm development. Ag is used in hygiene products including face creams, ‘alternative medicine’ health supplements, supermarket products for washing vegetables, and water filtration cartridges. Ag is generally without adverse effects for humans, and argyria (irreversible discoloration of the skin resulting from subepithelial silver deposits) is rare and mostly of cosmetic concern.

1,257 citations

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TL;DR: The significance of GSH as a major factor in regulation of cell life, proliferation, and death, should be regarded as the integrated result of all these roles it can play.

1,234 citations

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TL;DR: Staphylococcus aureus can cause superficial skin infections and, occasionally, deep-seated infections that entail spread through the blood stream, and must rely primarily on cell-surface polymers and the ability to form a biolfilm to survive in the host.
Abstract: Staphylococcus aureus can cause superficial skin infections and, occasionally, deep-seated infections that entail spread through the blood stream. The organism expresses several factors that compromise the effectiveness of neutrophils and macrophages, the first line of defence against infection. S. aureus secretes proteins that inhibit complement activation and neutrophil chemotaxis or that lyse neutrophils, neutralizes antimicrobial defensin peptides, and its cell surface is modified to reduce their effectiveness. The organism can survive in phagosomes, express polysaccharides and proteins that inhibit opsonization by antibody and complement, and its cell wall is resistant to lysozyme. Furthermore, S. aureus expresses several types of superantigen that corrupt the normal humoral immune response, resulting in anergy and immunosuppression. In contrast, Staphylococcus epidermidis must rely primarily on cell-surface polymers and the ability to form a biolfilm to survive in the host.

1,204 citations

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TL;DR: The DNA sequencing and protein crystal structures have established the convergent evolution of three classes of arsenate reductases, which involve three cysteine thiols and S-As bond intermediates, so convergence evolution to similar mechanisms has taken place.
Abstract: Arsenic compounds have been abundant at near toxic levels in the environment since the origin of life. In response, microbes have evolved mechanisms for arsenic resistance and enzymes that oxidize As(III) to As(V) or reduce As(V) to As(III). Formation and degradation of organoarsenicals, for example methylarsenic compounds, occur. There is a global arsenic geocycle, where microbial metabolism and mobilization (or immobilization) are important processes. Recent progress in studies of the ars operon (conferring resistance to As(III) and As(V)) in many bacterial types (and related systems in Archaea and yeast) and new understanding of arsenite oxidation and arsenate reduction by respiratory-chain-linked enzyme complexes has been substantial. The DNA sequencing and protein crystal structures have established the convergent evolution of three classes of arsenate reductases (that is classes of arsenate reductases are not of common evolutionary origin). Proposed reaction mechanisms in each case involve three cysteine thiols and S–As bond intermediates, so convergent evolution to similar mechanisms has taken place.

660 citations