Engineered mutated glutaredoxins mimicking peculiar plant class III glutaredoxins bind iron–sulfur centers and possess reductase activity

► The hydrophobic C-terminal end of class III glutaredoxins prevents their expression in Escherichia coli. ► Engineered class I glutaredoxins with a CCxC/S active site motif can bind iron–sulfur clusters and possess reductase activity. ► A genuine class III glutaredoxin devoid of the hydrophobic C-terminal end can also bind an iron–sulfur cluster. In order to gather biochemical information about class III glutaredoxins (CCxC/S active sites), the active sites of two poplar class I glutaredoxins, GrxC1 and C4, CGYC and CPYC, respectively, were transformed into CCMC or CCMS. All the recombinant mutated proteins bind [2Fe–2S] centers into holodimers, whereas monomeric apoforms possess glutathione-dependent reductase activity. The functionally important, hydrophobic GALWL C-terminal end, found in most class III glutaredoxins, prevents expression in Escherichia coli. Changing the C-terminal end of GrxS7.2, a genuine class III glutaredoxin, allowed purifying some holoproteins. These properties are discussed considering the documented function of class III glutaredoxins in development.