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Characterization of Escherichia coli null mutants for glutaredoxin 2
Alexios Vlamis-Gardikas1, Aristi Potamitou, Raz Zarivach
1Medical Nobel Institute for Biochemistry, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-171 77 Stockholm, Sweden.
The Journal of Biological Chemistry
|December 14, 2001
Summary
Escherichia coli glutaredoxin 2 (Grx2) plays a role in reducing protein disulfides and protecting cells against oxidants. Its absence increases sensitivity to oxidative stress and protein carbonylation.
Area of Science:
- Microbiology
- Biochemistry
- Molecular Biology
Background:
- Escherichia coli possesses three glutaredoxins (Grx1, Grx2, Grx3) involved in redox homeostasis.
- Grx2, unlike Grx1 and Grx3, does not donate hydrogen to ribonucleotide reductase.
- Understanding the specific roles of each glutaredoxin is crucial for elucidating cellular antioxidant responses.
Purpose of the Study:
- To investigate the function of Escherichia coli glutaredoxin 2 (Grx2) by creating a null mutant (grxB(-)).
- To explore the roles of Grx1, Grx2, and Grx3 in cytosolic disulfide reduction and cellular defense against oxidative stress.
- To examine the interplay between glutaredoxins, thioredoxins, and catalases in the antioxidant response.
Main Methods:
- Construction and characterization of grxB null mutants, individually and in combination with other mutations.
- Assay of leaderless alkaline phosphatase activity to assess cytosolic protein disulfide reduction.
- Measurement of cellular sensitivity to oxidants like hydrogen peroxide.
- Analysis of intracellular protein carbonylation levels.
- Enzyme activity assays for catalase and glutaredoxin.
Main Results:
- Null mutants for grxB or all three glutaredoxin genes showed viable growth with minor changes.
- Grx1 and Grx2, but not Grx3, were found to reduce cytosolic protein disulfides.
- grxB(-) cells exhibited increased sensitivity to hydrogen peroxide and other oxidants, with elevated protein carbonylation in stationary phase.
- Significant upregulation of catalase activity was observed in mutants lacking thioredoxin 1 and all three glutaredoxins.
- Glutaredoxin activity was upregulated in catalase-deficient strains with defects in the thioredoxin pathway.
Conclusions:
- Grx2 contributes to the reduction of cytosolic protein disulfides and cellular defense against oxidative stress.
- The expression of catalases is interconnected with the thioredoxin and glutaredoxin pathways in Escherichia coli's antioxidant response.
- Distinct roles for Grx1, Grx2, and Grx3 in redox homeostasis are highlighted, with Grx2 showing particular importance in oxidant defense.