A thiocarbonate sink on the enzymatic energy landscape of aerobic CO oxidation? Answers from DFT and QM/MM models of Mo–Cu CO-dehydrogenases

We present a theoretical investigation providing key insights on a long-standing controversial issue that dominated the debate on carbon monoxide oxidation by Mo–Cu CO-dehydrogenases. Previous investigations gravitate around the possible occurrence of a thiocarbonate intermediate, that was repeatedly reported to behave as a thermodynamic sink on the catalytic energy landscape. By using a hierarchy of quantum mechanical and hybrid quantum/classical models of the enzyme, we show that no such energy sink is present on the catalytic energy profile. Consequent perspectives for the definition of a novel mechanistic proposal for the enzyme-catalyzed CO-oxidation are discussed in light of the recent literature.