title: Arsenate reductase, mycothiol, and mycoredoxin concert thiol/disulfide exchange.
abstract: 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.
authors.affiliation: Department of Molecular Biology, Area of Microbiology, University of León, 24071 León, Spain.
authors.forename: Efrén
authors.initials: E
authors.lastname: Ordóñez
authors.forename: Karolien
authors.initials: K
authors.lastname: Van Belle
authors.forename: Goedele
authors.initials: G
authors.lastname: Roos
authors.forename: Sandra
authors.initials: S
authors.lastname: De Galan
authors.forename: Michal
authors.initials: M
authors.lastname: Letek
authors.forename: Jose A
authors.initials: JA
authors.lastname: Gil
authors.forename: Lode
authors.initials: L
authors.lastname: Wyns
authors.forename: Luis M
authors.initials: LM
authors.lastname: Mateos
authors.forename: Joris
authors.initials: J
authors.lastname: Messens
mesh_terms: D053502:Arsenate Reductases / Q000378:metabolism*; D001149:Arsenates / Q000378:metabolism; D018053:Arsenites / Q000378:metabolism; D055162:Biocatalysis; D048230:Corynebacterium glutamicum / Q000201:enzymology* / Q000235:genetics; D003545:Cysteine / Q000378:metabolism*; D004220:Disulfides / Q000378:metabolism*; D004579:Electron Transport; D004583:Electrons; D005798:Genes, Bacterial; D006020:Glycopeptides / Q000378:metabolism*; D007294:Inositol / Q000378:metabolism*; D007700:Kinetics; D010084:Oxidation-Reduction; D013379:Substrate Specificity; D013438:Sulfhydryl Compounds / Q000378:metabolism*
chemical_list: D001149:Arsenates; D018053:Arsenites; D004220:Disulfides; D006020:Glycopeptides; D013438:Sulfhydryl Compounds; C089265:mycothiol; D007294:Inositol; D053502:Arsenate Reductases; D003545:Cysteine; C015001:arsenite; C025657:arsenic acid