Characterization of the amino acids from Neisseria meningitidis methionine sulfoxide reductase B involved in the chemical catalysis and substrate specificity of the reductase step.
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 approximately 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.
Neiers
Fabrice
F
Maturation des ARN et Enzymologie Moléculaire, Unité Mixte de Recherche CNRS-UHP 7567, Nancy Université, Faculté des Sciences et Techniques, Boulevard des Aiguillettes, BP 239, 54506 Vandoeuvre-les-Nancy, France.
Sonkaria
Sanjiv
S
Olry
Alexandre
A
Boschi-Muller
Sandrine
S
Branlant
Guy
G
D002384:Catalysis; D007700:Kinetics; D051150:Methionine Sulfoxide Reductases; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009345:Neisseria meningitidis / Q000201:enzymology*; D010088:Oxidoreductases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D013379:Substrate Specificity
D010088:Oxidoreductases; D051150:Methionine Sulfoxide Reductases; C027219:methionine sulfoxide reductase