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 H₂ O₂ 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 α₂ 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 H₂ O₂ in the oxidation of 4-aminophenol in the presence of O₂ , whereas Fe^III -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.