Biochemical characterization of the thioredoxin domain of Escherichia coliDsbE protein reveals a weak reductant

Thioredoxin (Trx) domain is a typical fold functioning in thiol/disulfide e xchange. DsbE protein is one of the Trx-domain containing proteins involved in electron transfer for cytochrome c maturation in the periplasm of Esche richia coli. The soluble C-terminal Trx domain of DsbE protein was overexpr essed and purified to homogeneity. We herein report biochemical characteriz ation of the structural and redox properties of this domain. During redox r eaction, the domain undergoes a structural transformation resulting in a mo re stable reduced form with a free energy difference (Delta DeltaG(Redox)) of ca. 5 kcal/mol, but the thiol/disulfide exchange exhibits very low react ivity. The standard redox potential (E-0') for the active thiol/disulfide i s -0.175 V and the pK(a) value of the active cysteine is around 6.8, indica ting that the domain acts as a weak reductant. This implies that the membra ne-anchored DsbE protein may provide driven reducing power for the redox re action in the thiol/disulfide exchange pathway. (C) 2001 Academic Press.