Glutathionylation in the photosynthetic model organism Chlamydomonas reinhardtii: a proteomic survey

Protein glutathionylation is a redox post-translational modification occurring under oxidative stress conditions and playing a major role in cell regulation and signaling. This modification has been mainly studied in nonphotosynthetic organisms, whereas much less is known in photosynthetic organisms despite their important exposure to oxidative stress caused by changes in environmental conditions. We report a large scale proteomic analysis using biotinylated glutathione and streptavidin affinity chromatography that allowed identification of 225 glutathionylated proteins in the eukaryotic unicellular green alga Chlamydomonas reinhardtii. Moreover, 56 sites of glutathionylation were also identified after peptide affinity purification and tandem mass spectrometry. The targets identified belong to a wide range of biological processes and pathways, among which the Calvin-Benson cycle appears to be a major target. The glutathionylation of four enzymes of this cycle, phosphoribulokinase, glyceraldehyde-3-phosphate dehydrogenase, ribose-5-phosphate isomerase, and phosphoglycerate kinase was confirmed by Western blot and activity measurements. The results suggest that glutathionylation could constitute a major mechanism of regulation of the Calvin-Benson cycle under oxidative stress conditions.