Characterization of the redox properties of poplar glutaredoxin

The presence of glutaredoxins in plants is now well recognized, but their functions and natural substrates remain largely unknown. Recently, a poplar glutaredoxin has been biochemically characterized and several mutants have been engineered in order to explore its reactivity. This work focuses on some physiological functions of the enzyme. According to our findings, the poplar glutaredoxin can serve as an electron donor to the bacterial 3'-phosphoadenylylsulfate reductase as it supports both the catalysis by the enzyme in vitro and complements a methionine auxotroph strain of Escherichia coli. In addition, poplar glutaredoxin is able to reduce the Escherichia coli ribonucleotide reductase 1a (in vitro reduction of cytidine diphosphate). Although this glutaredoxin is described as an electron donor to a phloem-located peroxiredoxin, whose function is to detoxify hydroperoxides, we found that it does not directly reduce hydrogen peroxide or other alkyl hydroperoxides as described for yeast and rice glutaredoxins. However, the poplar glutaredoxin may be involved in the response to oxidative stress as its overexpression in Escherichia coli resulted in a higher resistance toward hydrogen peroxide, menadione, and tert-butyl hydroperoxide.