Arsenate reductase, mycothiol and mycoredoxin concert thiol/disulfide exchange

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Abstract:

We identified the first enzymes, which 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 defence 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 unravelled 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, forms arsenite and a mycothiol-mycoredoxin mixed disulfide. A second molecule of mycothiol recycles mycoredoxin and forms mycothione that on its turn is reduced by the NADPH-dependent mycothione reductase. Cg_ArsCs show a low specificity constant of ~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

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DA - 20090316
IS - 0021-9258 (Print)
LA - ENG
PT - JOURNAL ARTICLE