Abstract
Carbon monoxide (CO) is a highly toxic gas to many living organisms. However, some microorganisms are able to use this molecule as the sole source of carbon and energy. Soil bacteria such as the aerobic Oligotropha carboxidovorans are responsible for the annual removal of about 2x108 tons of CO from the atmosphere. Detoxification through oxidation of CO to CO2 is enabled by the MoCu-dependent CO-dehydrogenase enzyme (MoCu-CODH) which—differently from other enzyme classes with similar function—retains its catalytic activity in the presence of atmospheric O2. In the last few years, targeted advancements have been described in the field of bioengineering and biomimetics, which is functional for future technological exploitation of the catalytic properties of MoCu-CODH and for the reproduction of its reactivity in synthetic complexes. Notably, a growing interest for the quantum chemical investigation of this enzyme has recently also emerged. This mini-review compiles the current knowledge of the MoCu-CODH catalytic cycle, with a specific focus on the outcomes of theoretical studies on this enzyme class. Rather controversial aspects from different theoretical studies will be highlighted, thus illustrating the challenges posed by this system as far as the application of density functional theory and hybrid quantum-classical methods are concerned.
Highlights
Reviewed by: Lubomir Rulisek, Institute of Organic Chemistry and Biochemistry (ASCR), Czechia Per E
Detoxification through oxidation of Carbon monoxide (CO) to CO2 is enabled by the MoCu-dependent CO-dehydrogenase enzyme (MoCu-CODH) which—differently from other enzyme classes with similar function—retains its catalytic activity in the presence of atmospheric O2
In the last few years, targeted advancements have been described in the field of bioengineering and biomimetics, which is functional for future technological exploitation of the catalytic properties of MoCu-CODH and for the reproduction of its reactivity in synthetic complexes
Summary
The first theoretical investigations of the catalytic activity of MoCu-CODH were carried out independently by two theoretical groups in 2005 (Hofmann et al, 2005; Siegbahn and Shestakov, 2005). Notwithstanding the shortcomings deriving from the choice of basis sets, both Siegbahn, Shestakov and their respective coworkers evidenced a surprisingly high stability for the thiocarbonate intermediate The presence of such a deep minimum on the energy landscape pertaining to the reaction mechanism was interpreted differently by the two groups. Hofmann and coworkers raised the possibility that the thiocarbonate adduct lies outside the catalytic cycle, in a deep potential energy well that would effectively slow down enzymatic activity (see Figure 2C) These authors further proposed that the constrains imposed by the protein matrix could prevent formation of such a stable offpath adduct, a hypothesis that— —was later discarded as a result of a theoretical study focused on this topic (Siegbahn, 2011). The occurrence of such large differences comes with little surprise, given the well-known shortcomings in binding energy calculations using quantum chemical models of coordination complexes and their ligands (Husch et al, 2018)
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