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Papers In Press, published online ahead of print July 15, 2005
Institute for Virus Research, Kyoto University, Kyoto 606-8507
Corresponding Author: kito{at}virus.kyoto-u.ac.jp
DsbB is a disulfide oxidoreductase present in the E. coli plasma membrane. Its cysteine pairs, Cys41-Cys44 and Cys104-Cys130, facing the periplasm, as well as the bound quinone molecules play crucial roles in oxidizing DsbA, the protein dithiol oxidant in the periplasm. In this study, we characterized quinone-free forms of DsbB prepared from mutant cells unable to synthesize ubiquinone and menaquinone. While such preparations lacked detectable quinones, previously reported lauroylsarcosine treatment was ineffective in removing DsbB-associated quinones. Moreover, DsbB-bound quinone was shown to contribute to the redox-dependent fluorescence changes observed with DsbB. Now we reconfirmed that redox potentials of cysteine pairs of quinone-free DsbB are lower than that of DsbA, as far as determined in dithiothreitol redox buffer. Nevertheless, the quinone-free DsbB was able to oxidize ~40% of DsbA in a 1:1 stoichiometric reaction, in which hemi-oxidized forms of DsbB having either pair of cysteines are generated. It was suggested that the DsbB-DsbA system is designed in such a way that specific interaction of the two components enables the thiol-disulfide exchanges in the "forward" direction. In addition, a minor fraction of quinone-free DsbB formed the DsbA-DsbB disulfide complex stably. Our results show that the rapid and the slow pathways of DsbA oxidation can proceed up to significant points, after which these reactions must be completed and recycled by quinones under physiological conditions. We discuss the significance of having such multiple reaction pathways for the DsbB-dependent DsbA oxidation.
J. Biol. Chem, 10.1074/jbc.M506189200
Submitted on June 7, 2005
Revised on July 11, 2005
Accepted on July 15, 2005
Reactivities of quinone-free DsbB from Escherichia coli
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