Mechanism of Ni,Fe-containing Carbon Monoxide Dehydrogenases

• Applicant: Professor Dr. Holger Dobbek
• Subject Area: Biochemistry
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 578147562

Ni,Fe-containing carbon monoxide dehydrogenases (CODHs) catalyze the reversible oxidation of CO with water to CO2, two protons, and two electrons. Since CODHs can catalyze the reduction of CO₂ at low overpotentials, the active site and its Ni,Fe cluster serve as a model for the design of chemical catalysts for efficient CO₂ reduction. In the previous DFG project, we were able to elucidate key mechanistic aspects of Ni,Fe-containing carbon monoxide dehydrogenases (CODHs): (I) Structural analyses showed that O₂-induced inactivation of the active C cluster occurs via a multi-step process that ends with the loss of the Ni center. (II) Mutagenesis studies revealed a dual role of conserved residues in the second coordination sphere: they activate substrates and stabilize the metal cluster at the same time. (III) In addition, a novel hybrid Fe/S/O cluster was identified in a CODH homologue that does not exhibit CODH activity and illustrates the evolution and structural plasticity of this enzyme type. Finally, (IV) we achieved a breakthrough by combining crystallography and spectroscopic methods, which enabled us to determine the structures of the three catalytically relevant redox states (Cred1, Cint, Cred2) for the first time. Unexpectedly, the Cint state proved to be a key step in CO2 activation, with Ni playing a central, previously unknown role. These findings represent a paradigm shift in the role of Ni(I) for CODH catalysis, provide essential insights for the development of synthetic CO2 reduction catalysts - and form the basis for this project proposal. The aim of this project proposal is to elucidate in detail the reaction mechanism of CODHs. Building on the latest results, the three central redox states (Cred1, Cred2, Cint) will be systematically investigated. The focus will be on (i) the binding and activation of CO in the Cred1 state, (ii) the electronic structure and ligand chemistry of the Cred2 state, in which an activated form of CO2 is already bound, and (iii) the newly identified Cint state with a Ni(I) ion as the actual CO2 activating catalyst. In addition, contributions of the protein matrix and neighboring metal clusters to stabilization and reactivity will be investigated. To this end, we intend to continue combining protein biochemistry with crystallography and spectroscopic methods (IR, EPR, XAS) in order to develop a consistent reaction mechanism. The results promise fundamental insights into enzymatic CO2 reduction and provide design principles for the development of synthetic catalysts based on earth elements.

• DFG Programme: Research Grants