The function of 2-Cys peroxiredoxins in chloroplast antioxidant defence

Abstract

The chloroplast 2-Cys peroxiredoxins are nuclear encoded peroxidases which reduce alkyl hydroperoxides and H2O2 at similar rates. Peroxide reduction takes place at a catalytic cysteine residue. Following oxidation to a sulfenic acid, it reacts with a second cysteine residue in the other subunit of the homodimeric enzyme and a disulfide bond is formed under release of one molecule of H2O. Regeneration of the active site takes place via enzymatic thiol/disulfide isomerisation. Based on in vitro data a thioredoxin-mediated regeneration pathway is postulated. In chloroplasts about 70 % of the protein is associated with the stromal site of stroma thylakoids. Analysis of Arabidopsis thaliana antisense suppression lines demonstrated that partial loss of 2-CP function caused increased degradation of chloroplast proteins and impaired photosynthesis. In young antisense plants the ascorbate pool was enlarged and highly oxidised. Expression and activity of monodehydroascorbate reductase and ascorbate peroxidase were increased, while the glutathione redox state and the activity and expression of glutathione linked enzymes were unaffected. At gene expression level, the 2-CP is under control of a redox signal. The transcript level rapidly decreases in response to a surplus of reduced ascorbate. Inhibitor studies indicate that a phosphorylation step is involved in the redox-regulation of gene expression.