PPIases accelerate the folding of proteins. It catalyzes the cis-trans isomerization of proline imidic peptide bonds in oligopeptides. Required for the light-induced increase of thiol accumulation. Assists the folding or assembly of SAT1 enzyme to form the cysteine synthase complex. Links light and redox signals to the regulation of cysteine biosynthesis in response to stress. [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0) Binds cyclosporin A (CsA). CsA mediates some of its effects via an inhibitory action on PPIase. PPIase activity is optimal in reduced form and minimal in oxidized form. Reduction of the oxidized form is mediated by thioredoxin (TRX-M). Interacts with SAT1 and A.tumefaciens VirD2. Probably associated to membranes. A number of isoforms are produced. According to EST sequences. Ubiquitous, mostly expressed in leaves and flowers. Strongly induced by light. Hypersensitivity to high light and rose bengal. Belongs to the cyclophilin-type PPIase family.