Reference : The Zinc Center Influences the Redox and Thermodynamic Properties of Escherichia coli...
Scientific journals : Article
Life sciences : Biochemistry, biophysics & molecular biology
http://hdl.handle.net/2268/13204
The Zinc Center Influences the Redox and Thermodynamic Properties of Escherichia coli Thioredoxin 2
English
El Hajjaji, Hayat [de Duve Institute, Université catholique de Louvain, B-1200 Brussels, Belgium]
Dumoulin, Mireille mailto [Université de Liège - ULg > Département des sciences de la vie > Enzymologie et repliement des protéines, Centre d'Ingénierie des Protéines > >]
Matagne, André mailto [Université de Liège - ULg > Département des sciences de la vie > Enzymologie et repliement des protéines, Centre d'Ingénierie des Protéines > >]
Colau, Didier [Ludwig Institute for Cancer Research, Université catholique de Louvain, B-1200 Brussels, Belgium]
Messens, Joris [Department of Molecular and Cellular Interactions, VIB, Structural Biology Brussels, Vrije Universiteit Brussel, B-1050 Brussels, Belgium]
Collet, Jean-Francois [de Duve Institute, Université catholique de Louvain, B-1200 Brussels, Belgium]
13-Feb-2009
Journal of Molecular Biology
Academic Press
386
1
60-71
Yes (verified by ORBi)
International
0022-2836
1089-8638
London
United Kingdom
[en] oxidative stress ; thioredoxin ; zinc
[fr] disulfide bonds ; cysteine
[en] Protein stability ; Thermodynamics ; Folding
[en] Thioredoxins are small, ubiquitous redox enzymes that reduce protein disulfide bonds by using a pair of cysteine residues present in a strictly conserved WCGPC catalytic motif. The Escherichia coli cytoplasm contains two thioredoxins, Trx1 and Trx2. Trx2 is special because it is induced under oxidative stress conditions and it has an additional N-terminal zinc-binding domain. We have determined the redox potential of Trx2, the pKa of the active site nucleophilic cysteine, as well as the stability of the oxidized and reduced form of the protein. Trx2 is more oxidizing than Trx1 (–221 mV versus –284 mV, respectively), which is in good agreement with the decreased value of the pKa of the nucleophilic cysteine (5.1 versus 7.1, respectively). The difference in stability between the oxidized and reduced forms of an oxidoreductase is the driving force to reduce substrate proteins. This difference is smaller for Trx2 (ΔΔG°H2O = 9 kJ/mol and ΔTm = 7. 4 °C) than for Trx1 (ΔΔG°H2O = 15 kJ/mol and ΔTm = 13 °C). Altogether, our data indicate that Trx2 is a significantly less reducing enzyme than Trx1, which suggests that Trx2 has a distinctive function. We disrupted the zinc center by mutating the four Zn2+-binding cysteines to serine. This mutant has a more reducing redox potential (–254 mV) and the pKa of its nucleophilic cysteine shifts from 5.1 to 7.1. The removal of Zn2+ also decreases the overall stability of the reduced and oxidized forms by 3.2 kJ/mol and 5.8 kJ/mol, respectively. In conclusion, our data show that the Zn2+-center of Trx2 fine-tunes the properties of this unique thioredoxin.
Researchers
http://hdl.handle.net/2268/13204

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