In nature, formate dehydrogenases (FDH), also known as CO2 reductases, have shown their ability to reversibly interconvert CO2 to formate (HCO2–), which makes them interesting in the field of CO2 capture and storage. O2-tolerant hydrogenases, on the other hand, are relevant for establishing hydrogen-based systems with potential applications in biotechnology. Therefore, understanding enzymatic HCO2– oxidation linked to H2 production and vice versa, can help developing systems for the sustainable generation of renewable chemical feedstocks and for H2 storage.
In this context, the UniSysCat groups of Silke Leimkühler, Oliver Lenz, Maria Andrea Mroginski and Ingo Zebger studied the coupling in solution of two O2-tolerant and physiologically unrelated enzymes: the FDH from Rhodobacter capsulatus and a membrane bound [NiFe]-hydrogenase (MBH) from Cupriavidus necator. To gain insights into the coupled reaction, in-situ IR spectroscopy was used to follow the absorptions of the different substrates and products of the FDH (i.e. CO2, HCO2–) and also to monitor the redox structural states of the MBH on the basis of the corresponding active site’s CO/CN stretching vibrations. Additionally, coarse-grained molecular dynamics (CGMD) computations allowed the study of potential interaction sites of the two enzymes without and in the presence of redox mediators. The coupling between both enzymes (strongly enhanced by the addition of redox mediators) was shown, as HCO2– oxidation to CO2 catalyzed by the FDH could induce H2 production by the MBH, which could be confirmed in independent gas chromatography (GC) studies. Hydration of CO2 to formate facilitated by the electrons provided by the MBH after H2-splitting could also be observed spectroscopically and corroborated in gas chromatography / mass spectrometry (GC/MS) assays. The CGMD results display low affinities for all studied enzyme/enzyme complexes, indicating that coupling occurs only during a random transient contact between the enzymes in buffered solutions. Computational analysis of the distances between mediator molecules and the enzyme complex revealed possible electron transfer (ET) pathways for the mediated coupled reaction.
This study represents a proof-of-concept approach that can be used in the future to develop novel coupled biocatalytic systems by identifying potential ET pathways.
More details can be found in the article “Coupling of the Catalytic Reactions of Formate Dehydrogenase and Hydrogenase in Solution: Insights from in situ IR Spectroscopy and Computations” by A.F.T. Waffo, M. Wu-Lu, S. Katz, S. Frielingsdorf, B.R. Duffus, J. Liedtke, S. Leimkühler, O. Lenz, K. Laun, M. A. Mroginski and I. Zebger. Online available in ChemCatChem 2024. https://doi.org/10.1002/cctc.202400794