Analysis of the structure and function of YfcG from Escherichia coli reveals an efficient and unique disulfide bond reductase.

YfcG is one of eight glutathione (GSH) transferase homologues encoded in the Escherichia coli genome. The protein exhibits low or no GSH transferase activity toward a panel of electrophilic substrates. In contrast, it has a very robust disulfide-bond reductase activity toward 2-hydroxyethyldisulfide on par with mammalian and bacterial glutaredoxins. The structure of YfcG at 2.3 A-resolution from crystals grown in the presence of GSH reveals a molecule of glutathione disulfide in the active site. The crystallographic results and the lack of functional cysteine residues in the active site of YfcG suggests that the reductase activity is unique in that no sulfhydryl groups in the YfcG protein are covalently involved in the redox chemistry.