Profound redox sensitivity of peptidyl-prolyl isomerase activity in Arabidopsis thylakoid lumen.

Proteomic, enzymatic, and mutant analyses revealed that peptidyl-prolyl isomerase (PPIase) activity in the chloroplast thylakoid lumen of Arabidopsis is determined by two immunophilins: AtCYP20-2 and AtFKBP13. These two enzymes are responsible for PPIase activity in both soluble and membrane-associated fractions of thylakoid lumen suggesting that other lumenal immunophilins are not active towards the peptide substrates. In thiol-reducing conditions PPIase activity of the isolated AtFKBP13 and of the total thylakoid lumen is suppressed several fold. Profound redox-dependence of PPIase activity implies oxidative activation of protein folding catalysis under oxidative stress and photosynthetic oxygen production in the thylakoid lumen of plant chloroplasts.