Redox Characterization of the Complex Molybdenum Enzyme Formate Dehydrogenase from Cupriavidus necator

Abstract

The oxygen-tolerant and molybdenum-dependent formate dehydrogenase FdsDABG from Cupriavidus necator is capable of catalyzing both formate oxidation to CO 2 and the reverse reaction (CO 2 reduction to formate) at neutral pH, which are both reactions of great importance to energy production and carbon capture. FdsDABG is replete with redox cofactors comprising seven Fe/S clusters, flavin mononucleotide, and a molybdenum ion coordinated by two pyranopterin dithiolene ligands. The redox potentials of these centers are described herein and assigned to specific cofactors using combinations of potential-dependent continuous wave and pulse EPR spectroscopy and UV/visible spectroelectrochemistry on both the FdsDABG holoenzyme and the FdsBG subcomplex. These data represent the first redox characterization of a complex metal dependent formate dehydrogenase and provide an understanding of the highly efficient catalytic formate oxidation and CO 2 reduction activity that are associated with the enzyme.

Selenium—More than Just a Fortuitous Sulfur Substitute in Redox Biology

“…Regardless of the physiological function and structural complexity, the reaction mechanism of the interconversion of formate and carbon dioxide (Equation (1)) is believed to be similar in all these selenocysteine- and cysteine-containing FDH and FMFDH enzymes. As originally proposed by Niks et al [ 61 ] for formate oxidation and shortly after also for carbon dioxide reduction by Maia et al [ 62 ], it is currently well established that formate oxidation and carbon dioxide reduction proceed through hydride transfer, with the oxidized and reduced active site sulfido group, Mo/W 6+ =S and Mo/W 4+ -SH, acting as the direct hydride acceptor and donor, respectively ( Figure 2 ) [ 63 , 64 , 65 , 66 ] (even though other atomic details of the reaction mechanism are not yet consensual; see, for example [ 67 ]). It is noteworthy that no direct role in the chemical transformations is presently ascribed to the selenocysteine or cysteine residue, in accordance with the existence of catalytically efficient SeCys enzymes and Cys enzymes (a similar situation occurs with molybdenum and tungsten).…”