A De Novo Heterodimeric Due Ferri Protein Minimizes the Release of Reactive Intermediates in Dioxygen-Dependent Oxidation
Metalloproteins utilize O2 as an oxidant, and they often achieve a 4-electron reduction without H2O2 or oxygen radical release. Several proteins have been designed to catalyze one or two-electron oxidative chemistry, but the de novo design of a protein that catalyzes the net 4-electron reduction of O2 has not been reported yet. We report the construction of a diiron-binding four-helix bundle, made up of two different covalently linked ?2 monomers, through click chemistry. Surprisingly, the prototype protein, DF-C1, showed a large divergence in its reactivity from earlier DFs (DF: due ferri, two iron). DFs release the quinone imine and free H2O2 in the oxidation of 4-aminophenol in the presence of O2, whereas FeIII-DF-C1 sequesters the quinone imine into the active site, and catalyzes inside the scaffold an oxidative coupling between oxidized and reduced 4-aminophenol. The asymmetry of the scaffold allowed a fine-engineering of the substrate binding pocket, that ensures selectivity.Not just a four-helix bundle: The use of a diiron-binding four-helix bundle scaffold with an asymmetric active site leads to an enhancement in selectivity of the iron-catalyzed oxidative coupling of phenols. The stabilization of the oxidized intermediate in the binding pocket enables the net four-electron O2 reduction, without release of any detectable H2O2.
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