Theoretical hypothesis in a direct electron transfer between non-interacting Fe-S proteins within an artificial fusion

Abstract

Reduction of CO2 to formate utilizing formate dehydrogenases (FDHs) has been attempted biologically and electrochemically. However, the conversion efficiency is very low due to the low energy potential of electron donors and/or electron competition with other electron acceptors. To overcome such a low conversion efficiency, I focused on a direct electron transfer between two unrelated redox enzymes for the efficient reduction of CO2 and utilized the quantum mechanical magnetic properties of the [Fe-S] ([iron-sulfur]) cluster to develop a novel electron path. Using this electron path, we connected non-interacting carbon monoxide dehydrogenase and FDH, constructing a synthetic carbon monoxide:formate oxidoreductase as a single functional enzyme complex in the previous study. Here, a theoretical hypothesis that can explain the direct electron transfer phenomenon based on the magnetic properties of the [Fe-S] cluster is proposed.

Keywords: Fe-S protein; biorefinery; carbon monoxide:formate oxidoreductase; direct electron transfer; protein fusion; synthetic enzyme.

Figure 1.

Schematic representation of gene clusters and fusion combinations employed in constructing CFOR. (A) fdh3 and codh gene clusters in Thermococcus onnurineus. (B) Gene fusion combination of fdh3B:codhA and fdh3BC:codhA.

Figure 2.

Proposed mechanism of electron transfer within the Fe-S fusion protein by a hyperfine magnetic field. (A) Nonmagnetic state of [4Fe-4S] cluster (◇) in the oxidized state. (B) Reduction of distal-end [4Fe-4S] cluster in CodhA, generation of a hyperfine magnetic field. (C) Owing to the magnetic field, the ferromagnetic Fe atom in Fdh3B binds to CodhA and reduces CO₂ to formate by the synthetic electron path.