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Methionine Sulfoxide Reduction and Assimilation in Escherichia coli: New Role for the Biotin Sulfoxide Reductase BisC

Benjamin Ezraty ,^, Julia Bos, Frédéric Barras,^* and Laurent Aussel

Laboratoire de Chimie Bactérienne, UPR9043, Institut Fédératif de Recherche Biologie Structurale et Microbiologie, Marseille, France

Received 26 August 2004/ Accepted 24 September 2004

Methionine ranks among the amino acids most sensitive to oxidation, which converts it to a racemic mixture of methionine-S-sulfoxide (Met-S-SO) and methionine-R-sulfoxide (Met-R-SO). The methionine sulfoxide reductases MsrA and MsrB reduce free and protein-bound MetSO, MsrA being specific for Met-S-SO and MsrB for Met-R-SO. In the present study, we report that an Escherichia coli metB₁ auxotroph lacking both msrA and msrB is still able to use either of the two MetSO enantiomers. This indicates that additional methionine sulfoxide reductase activities occur in E. coli. BisC, a poorly characterized biotin sulfoxide reductase, was identified as one of these new methionine sulfoxide reductases. BisC was purified and found to exhibit reductase activity with free Met-S-SO but not with free Met-R-SO as a substrate. Moreover, a metB₁ msrA msrB bisC strain of E. coli was unable to use Met-S-SO for growth, but it retained the ability to use Met-R-SO. Mass spectrometric analyses indicated that BisC is unable to reduce protein-bound Met-S-SO. Hence, this study shows that BisC has an essential role in assimilation of oxidized methionines. Moreover, this work provides the first example of an enzyme that reduces free MetSO while having no activity on peptide-bound MetSO residues.

Both authors contributed equally to this work.

Present address: Department of Biochemistry and Molecular Biology, University of Miami School of Medicine, Miami, FL 33101.

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