A Sulfenic Acid Enzyme Intermediate Is Involved in the Catalytic Mechanism of Peptide Methionine Sulfoxide Reductase fromEscherichia coli

• Published in: The Journal of biological chemistry Vol. 275; no. 46; pp. 35908 - 35913
• Main Authors: Boschi-Muller, Sandrine, Azza, Said, Sanglier-Cianferani, Sarah, Talfournier, François, Van Dorsselear, Alain, Branlant, Guy
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 17-11-2000; American Society for Biochemistry and Molecular Biology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M006137200

Methionine oxidation into methionine sulfoxide is known to be involved in many pathologies and to exert regulatory effects on proteins. This oxidation can be reversed by a ubiquitous monomeric enzyme, the peptide methionine sulfoxide reductase (MsrA), whose activity in vivo requires the thioredoxin-regenerating system. The proposed chemical mechanism ofEscherichia coli MsrA involves three Cys residues (positions 51, 198, and 206). A fourth Cys (position 86) is not important for catalysis. In the absence of a reducing system, 2 mol of methionine are formed per mole of enzyme for wild type and Cys-86 → Ser mutant MsrA, whereas only 1 mol is formed for mutants in which either Cys-198 or Cys-206 is mutated. Reduction of methionine sulfoxide is shown to proceed through the formation of a sulfenic acid intermediate. This intermediate has been characterized by chemical probes and mass spectrometry analyses. Together, the results support a three-step chemical mechanism in vivo: 1) Cys-51 attacks the sulfur atom of the sulfoxide substrate leading, via a rearrangement, to the formation of a sulfenic acid intermediate on Cys-51 and release of 1 mol of methionine/mol of enzyme; 2) the sulfenic acid is then reduced via a double displacement mechanism involving formation of a disulfide bond between Cys-51 and Cys-198, followed by formation of a disulfide bond between Cys-198 and Cys-206, which liberates Cys-51, and 3) the disulfide bond between Cys-198 and Cys-206 is reduced by thioredoxin-dependent recycling system process.