Ιn all living organisms, antioxidant defenses are largely orchestrated by the thioredoxin (Trx) and glutaredoxin(Grx) systems. The Trx system of Escherichia coli (E. coli) is comprised of Trx1 and Trx2, both reduced by thi-oredoxin reductase (TrxR). The Grx system consists of four Grxs (Grx1, Grx2, Grx3, and Grx4) all reduced by glu- tathione (GSH) except for Grx4, which is reduced by TrxR. Under normal conditions, the GSH reductase of theGrx system keeps GSH at its reduced state, while NADPH+ provides the electrons for all reductions in both theTrx and Grx systems. The role of the E. coli Trx system is widely known, while the established functions of the Grx system are mainly reflected in the ability of Grx1 to reduce ribonucleotide reductase Ia (RRIa). E. coli Grx3, (encoded by grxC) may also reduce RRIa in vitro but with slow kinetics. The molecule may account up to 0.4 % of total soluble protein and has been the subject of extensive structural studies. Its biological function however remains unknown. Herein, affinity chromatography with monothiol Grx3 was used to detect the interactions ofGrx3 with other proteins. Different types of interactions were identified (covalent, weak and strong non-cova- lent) that suggested novel functions for Grx3. In silico approaches were employed and gave a score 45 % for the selected interactions examined. Total protein extracts from the null mutant for grxC and the wild-type strain were also compared. The overall findings suggest that Grx3 is involved in various metabolic processes, protein synthesis, and stress responses expanding the recognized functions of Grx3 beyond the reduction of RRIa. This research was funded by the Hellenic Foundation for Research and Innovation (HFRI) under the “2nd Call for
H.F.R.I. Research Projects to Support Faculty Members & Researchers” (Project Number: 3352,
«Glutrxomics»).