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Characterization of the Amino Acids from Neisseria meningitidis Methionine Sulfoxide Reductase B Involved in the Chemical Catalysis and Substrate Specificity of the Reductase Step

Abstract : Methionine sulfoxide reductases (Msrs) are antioxidant repair enzymes that catalyze the thioredoxin-dependent reduction of methionine sulfoxide back to methionine. The Msr family is composed of two structurally unrelated classes of enzymes named MsrA and MsrB, which display opposite stereoselectivities toward the S and R isomers of the sulfoxide function, respectively. Both classes of Msr share a similar three-step chemical mechanism involving first a reductase step that leads to the formation of a sulfenic acid intermediate. In this study, the invariant amino acids of Neisseria meningitidis MsrB involved in the reductase step catalysis and in substrate binding have been characterized by the structure-function relationship approach. Altogether the results show the following: 1) formation of the MsrB-substrate complex leads to an activation of the catalytic Cys-117 characterized by a decreased pKapp of ∼2.7 pH units; 2) the catalytic active MsrB form is the Cys-117-/His-103+ species with a pKapp of 6.6 and 8.3, respectively; 3) His-103 and to a lesser extent His-100, Asn-119, and Thr-26 (via a water molecule) participate in the stabilization of the polarized form of the sulfoxide function and of the transition state; and 4) Trp-65 is essential for the catalytic efficiency of the reductase step by optimizing the position of the substrate in the active site. A scenario for the reductase step is proposed and discussed in comparison with that of MsrA.
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Fabrice Neiers, Sanjiv Sonkaria, Alexandre Olry, Sandrine Boschi-Muller, Guy Branlant. Characterization of the Amino Acids from Neisseria meningitidis Methionine Sulfoxide Reductase B Involved in the Chemical Catalysis and Substrate Specificity of the Reductase Step. Journal of Biological Chemistry, American Society for Biochemistry and Molecular Biology, 2007, 282 (44), pp.32397-32405. ⟨10.1074/jbc.M704730200⟩. ⟨hal-01690652⟩

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