Arsenate reductase, mycothiol, and mycoredoxin concert thiol/disulfide exchange.

TitleArsenate reductase, mycothiol, and mycoredoxin concert thiol/disulfide exchange.
Publication TypeJournal Article
Year of Publication2009
AuthorsOrdóñez, E., K. Van Belle, G. Roos, S. De Galan, M. Letek, J. A. Gil, L. Wyns, L. M. Mateos, and J. Messens
JournalJ Biol Chem
Date Published2009 May 29
Type of Articleredox
KeywordsArsenate Reductases, Arsenates, Arsenites, Biocatalysis, Corynebacterium glutamicum, Cysteine, Disulfides, Electron Transport, Electrons, Genes, Bacterial, Glycopeptides, Inositol, Kinetics, Oxidation-Reduction, Substrate Specificity, Sulfhydryl Compounds

We identified the first enzymes that use mycothiol and mycoredoxin in a thiol/disulfide redox cascade. The enzymes are two arsenate reductases from Corynebacterium glutamicum (Cg_ArsC1 and Cg_ArsC2), which play a key role in the defense against arsenate. In vivo knockouts showed that the genes for Cg_ArsC1 and Cg_ArsC2 and those of the enzymes of the mycothiol biosynthesis pathway confer arsenate resistance. With steady-state kinetics, arsenite analysis, and theoretical reactivity analysis, we unraveled the catalytic mechanism for the reduction of arsenate to arsenite in C. glutamicum. The active site thiolate in Cg_ArsCs facilitates adduct formation between arsenate and mycothiol. Mycoredoxin, a redox enzyme for which the function was never shown before, reduces the thiol-arseno bond and forms arsenite and a mycothiol-mycoredoxin mixed disulfide. A second molecule of mycothiol recycles mycoredoxin and forms mycothione that, in its turn, is reduced by the NADPH-dependent mycothione reductase. Cg_ArsCs show a low specificity constant of approximately 5 m(-1) s(-1), typically for a thiol/disulfide cascade with nucleophiles on three different molecules. With the in vitro reconstitution of this novel electron transfer pathway, we have paved the way for the study of redox mechanisms in actinobacteria.

Alternate JournalJ. Biol. Chem.
PubMed ID19286650
PubMed Central IDPMC2685692
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