Mechanism of action of the glutaredoxins and their role in human lung diseases
1University of Oulu, Faculty of Science, Department of Biochemistry
2University of Oulu, Biocenter Oulu
3University of Oulu, Faculty of Medicine, Department of Internal Medicine
4Oulu University Hospital
5University of Helsinki, Faculty of Medicine
6University of Helsinki, Faculty of Medicine, Division of Pulmonary Diseases
|Online Access:||PDF Full Text (PDF, 1.1 MB)|
|Persistent link:|| http://urn.fi/urn:isbn:9789514285165
|Publish Date:|| 2007-07-31
|Thesis type:||Doctoral Dissertation
|Defence Note:||Academic dissertation to be presented, with the assent of the Faculty of Science of the University of Oulu, for public defence in Raahensali (Auditorium L10), Linnanmaa, on August 10th, 2007, at 12 noon
Docent Anna-Liisa Levonen
Professor John Mieyal
Glutaredoxins (Grx) are small thiol disulphide oxidoreductases with a conserved active site sequence -CXXC/S- and a glutathione (GSH) binding site. They catalyze the reduction of protein disulphides, preferring protein-GSH mixed disulphides as substrates. The accumulation of protein-GSH mixed disulphides has been observed during oxidative stress, where they may serve both a regulatory and an antioxidant function by protecting the enzymes from irreversible oxidation. Once oxidative stress has been removed the GSH-protein mixed disulphides are reduced by GSH or, more efficiently, by Grx.
The present study showed for the first time that Grx1 and Grx2 can be detected in healthy human lung. Highly specific expression of Grx1 was observed in alveolar macrophages, but it could also be detected from sputum supernatant. Grx1 levels in alveolar macrophages were lower in selected inflammatory diseases than in control lung samples. Grx1 was also mainly negative in the fibrotic areas in usual interstitial pneumonia, an aggressive fibrotic lung disease. Overall, the present study suggests that Grx1 is a potential redox modulatory protein regulating the intracellular as well as extracellular homeostasis of glutathionylated proteins and GSH not only in healthy lung, but also in inflammatory and fibrotic lung diseases.
In order to study the mechanism of action of glutaredoxins in vitro, a new real-time fluorescence-based method for measuring the deglutathionylation activity of glutaredoxins using a glutathionylated peptide as a substrate was developed. The first reaction intermediate in the deglutathionylation reaction was shown to be exclusively Grx-GSH mixed disulphide and this specificity was solely dependent on the unusual γ-linkage present in glutathione. The study also demonstrated the role of conserved residues in the proximity of proposed GSH binding site to the GSH binding specificity of E. coli Grx1. Opening the binding groove and removing charged residues enabled Grx to form more readily mixed disulfides with other molecules besides GSH. Different members of the PDI family showed considerably lower activity levels compared to glutaredoxins and, in contrast to the glutaredoxin-GSH mixed disulphide, the only intermediate in the PDI catalysed reaction was PDI-peptide mixed disulphide.
Acta Universitatis Ouluensis. A, Scientiae rerum naturalium
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