Peroxiredoxins (Prxs) catalyze the reduction of peroxides, a process of key relevance in a variety of cellular processes. The first step in the catalytic cycle of all Prxs is the oxidation of a cysteine residue to sulfenic acid, which occurs 103-107 times faster than in free cysteine. We present an experimental kinetics and hybrid QM/MM investigation to explore the reaction of Prxs with H2O2 using alkyl hydroperoxide reductase E from Mycobacterium tuberculosis as a Prx model. We report for the first time the reaction thermodynamical activation parameters of H2O2 reduction by a Prx, which show that the protein lowers significantly the activation enthalpy, with an unfavourable entropic effect, compared to the uncatalyzed reaction. The QM/MM simulations show that the remarkable catalytic effects responsible for the fast H2O2 reduction in Prxs are mainly due to an active-site arrangement, which establishes a complex hydrogen bond network activating both reactive species.

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Future work should be directed to establish the structural bases of the specificity of MSH-dependent enzymes, thus facilitating drug developments. Antioxid. Redox Signal. 28, 487-504.