Iron-dependent enzymes are prevalent in nature and participate in a wide range of biological redox activities. Frequently, high-valence iron intermediates are involved in the catalytic events of iron-dependent enzymes, especially when the activation of peroxide or molecular oxygen is involved. Building on the fundamental framework of iron-oxygen chemistry, these reactive intermediates constantly attract significant attention from the enzymology community. During the past few decades, tremendous efforts from a number of laboratories have been dedicated to the capture and characterization of these intermediates to improve mechanistic understandings. In 2008, an unprecedented bis-Fe(IV) intermediate was reported in a c-type di-heme enzyme, MauG, which is involved in the maturation of a tryptophan tryptophylquinone cofactor of methylamine dehydrogenase. This intermediate, though chemically equivalent to the well-characterized high-valence iron intermediates, such as compound I, compound ES, and Intermediate Q in methane monooxygenase, as well as the hypothetical Fe(V) species in Rieske non-heme oxygenases, is orders of magnitude more stable than these other high-valence species in the absence of its primary substrate. It has been recently discovered that the bis-Fe(IV) intermediate exhibits a unique near-IR absorption feature which has been attributed to a novel charge-resonance phenomenon. This mini-review compares the properties of MauG with structurally related enzymes, summarizes the current knowledge of this new high-valence iron intermediate, including its chemical origin and structural basis, explores the formation and consequences of charge-resonance, and recounts the long-range catalytic mechanism in which it participates. Biological strategies for storing oxidizing equivalents with iron ions are also discussed.

Bis-Fe(IV): Nature's sniper for long-range oxidation

248th National Meeting (2014)

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