Exploring the catalytic potential of the 3-His mononuclear nonheme Fe(II) center: Discovery and characterization of an unprecedented maltol cleavage activity

摘要

Mononuclear nonheme iron enzymes (MNHEs) catalyze a range of very diverse reactions in O_2 metabolism, but they share a common principle active-site organization. To investigate a putative catalytic promiscuity of these enzymatic metal centers, we studied the reactivity of the 3-His ligated metal center of diketone cleaving enzyme (Dke1) toward non-native substrates, with a focus on alternative O_2 dependent reactions. From a screening approach, which aims at eliminating steric factors by including minimal substrate-substructures, three alternative, 'non-β-dicarbonyl-cleavage' reactions are identified, among them an unprecedented oxygenation of maltol. Maltol cleavage is characterized by steady state and fast kinetic measurements and shows an O_2 concentration dependent rate determining step k _(cat)/K_M(O_2) of 0.3 mM~(- 1) s ~(- 1) and a strict coupling of O_2 reduction and substrate oxidation. Furthermore, the catalytic potential of the 3-His metal center for O_2 dependent catechol ring-cleavage and phenylpyruvate oxidation (PP) is demonstrated.