Proteomics Uncovers Proteins Interacting Electrostatically with Thioredoxin in Chloroplasts

The ability of thioredoxin f to form an electrostatic (non-covalent) complex, earlier found with fructose-1,6-bisphosphatase, was extended to include 27 previously unrecognized proteins functional in 11 processes of chloroplasts. The proteins were identified by combining thioredoxin <i>f</i> affinity chromatography with proteomic analysis using tandem mass spectrometry. The results provide evidence that an association with thioredoxin enables the interacting protein to achieve an optimal conformation, so as to facilitate: (i) the transfer of reducing equivalents from the ferredoxin/ferredoxin—thioredoxin reductase complex to a target protein; (ii) in some cases, to enable the channeling of metabolite substrates; (iii) to function as a subunit in the formation of multienzyme complexes.