Thermodynamic Aspects of DsbD-Mediated Electron Transport

Abstract

DsbD from Escherichia coli transports electrons from cytoplasmic thioredoxin across the inner membrane to the periplasmic substrate proteins DsbC, DsbG and CcmG. DsbD consists of three domains: a periplasmic N-terminal domain, a central transmembrane domain (tmDsbD) and a periplasmic C-terminal domain. Each domain contains two essential cysteine residues that are required for electron transport. In contrast to the quinone reductase DsbB, HPLC analysis of the methanol/hexane extracts of purified DsbD revealed no presence of quinones, suggesting that the tmDsbD interacts with thioredoxin and the periplasmic C-terminal domain exclusively via disulfide exchange. We also demonstrate that a DsbD variant containing only the redox-active cysteine pair C163 and C285 in tmDsbD, reconstituted into liposomes, has a redox potential of − 0.246 V. The results show that all steps in the DsbD-mediated electron flow are thermodynamically favorable.