Can a Mononuclear Iron(III)-Superoxo Active Site Catalyze the Decarboxylation of Dodecanoic Acid in UndA to Produce Biofuels?

Abstract

Decarboxylation of fatty acids is an important reaction in cell metabolism, but also has potential in biotechnology for the biosynthesis of hydrocarbons as biofuels. The recently discovered nonheme iron decarboxylase UndA is involved in the biosynthesis of 1-undecene from dodecanoic acid and using X-ray crystallography was assigned to be a mononuclear iron species. However, the work was contradicted by spectroscopic studies that suggested UndA to be more likely a dinuclear iron system. To resolve this controversy we decided to pursue a computational study on the reaction mechanism of fatty acid decarboxylation by UndA using iron(III)-superoxo and diiron(IV)-dioxo models. We tested several models with different protonation states of active site residues. Overall, however, the calculations imply that mononuclear iron(III)-superoxo is a sluggish oxidant of hydrogen atom abstraction reactions in UndA and will not be able to activate fatty acid residues by decarboxylation at room temperature. By contrast, a diiron-dioxo complex reacts with much lower hydrogen atom abstraction barriers and hence is a more likely oxidant in UndA.

Keywords: decarboxylation; density functional calculations; dioxygenases; nonheme iron; reaction mechanisms.