Regeneration mechanisms of arabidopsis thaliana methionine sulfoxide reductases B by glutaredoxins and thioredoxins
2009
Tarrago, Lionel | Laugier, Edith | Zaffagnini, Mirko | Marchand, Christophe | Le Maréchal, Pierre | Rouhier, Nicolas | Lemaire, Stéphane D. | Rey, Pascal
Methionine oxidation leads to the formation of S- and R-diastereomers of methionine sulfoxide (MetSO), which are reduced back to methionine by methionine sulfoxide reductases (MSRs) A and B, respectively.MSRBs are classified in two groups depending on the conservation of one or two redox-active Cys: 2-Cys MSRBs possess a catalytic Cys reducing MetSO and a resolving Cys allowing regeneration by thioredoxins (Trxs). The second type, 1-Cys MSRBs, possess only the catalytic Cys. The biochemical mechanisms involved in activity regeneration of 1-Cys MSRBs remain largely elusive. In the present work, we used recombinant plastidial Arabidopsis thaliana MSRB1 and MSRB2, as models for 1-Cys and 2-Cys MSRBs, respectively, to delineate the Trx- and glutaredoxindependent reduction mechanisms. Activity assays carried out using a series of cysteinic mutants, combined to measurement of free thiols under distinct oxidation states and to mass spectrometry experiments, show that the 2-Cys MSRB2 is reduced by Trx through a dithiol-disulfide exchange involving both redox-active Cys of the two partners. Regarding 1-Cys MSRB1, oxidation of the enzyme after substrate reduction leads to the formation of a stable sulfenic acid on the catalytic Cys, which is subsequently glutathionylated. The deglutathionylation of MSRB1 is achieved by both mono- and dithiol glutaredoxins (Grxs) and involves only their N-terminal conserved catalytic Cys. This study proposes a detailed mechanism of the regeneration of 1-Cys MSRB activity by Grxs, which likely constitute physiological reductants for this type of MSR.
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