Glutaredoxins

Glutaredoxins are small enzymes of approximately one hundred amino-acid residues that are involved in the regulation of the redox status of multiple cellular substrates. They possess an active centre with either one or two cysteines separated by two amino acids and a C-terminal glutathione binding pocket.

Cysteines in glutathione, glutaredoxins and target proteins can occur in their reduced (-SH) or their oxidized forms (-S-S-; -S-S-Glutathione). Hydrogen can be transferred from glutathione to glutaredoxins and from glutaredoxins to target proteins. Under oxidative conditions, glutathione can be transferred from oxidized glutathione disulfide to target proteins (glutathionylation).

Under resting conditions, most of the glutathione is in its reduced form; still, proteins like NPR1 and TGA1 are in their oxidized form (Mou et al., 2003; Depres et al., 2003). After pathogen attack, further reduction of the cellular milieu occurs and at least NPR1 is reduced and thus activated through thioredoxins (Tada et al., 2008) which belong to the same superfamily of oxidoreductases as glutaredoxins. TGA1 is also reduced after treatment of plants with the defense hormone salicylic acid.

The role of the plant-specific glutaredoxins is poorly understood. They might control the redox state of specific substrates, like TGA transcription factors and TGA-interacting proteins.