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  • Perspective
  • Published:

Methanogenesis involves direct hydride transfer from H2 to an organic substrate

Abstract

Certain anaerobic microorganisms evolved a mechanism to use H2 as a reductant in their energy metabolisms. For these purposes, the microorganisms developed H2-activating enzymes, which are aspirational catalysts in a sustainable hydrogen economy. In the case of the hydrogenotrophic pathway performed by methanogenic archaea, 8e are extracted from 4H2 and used as reducing equivalents to convert CO2 into CH4. Under standard cultivation conditions, these archaea express [NiFe]-hydrogenases, which are Ni-dependent and Fe-dependent enzymes and heterolytically cleave H2 into 2H+ and 2e, the latter being supplied into the central metabolism. Under Ni-limiting conditions, F420-reducing [NiFe]-hydrogenases are downregulated and their functions are predominantly taken over by an upregulated [Fe]-hydrogenase. Unique in biology, this Fe-dependent hydrogenase cleaves H2 and directly transfers H to an imidazolium-containing substrate. [Fe]-hydrogenase activates H2 at an Fe cofactor ligated by two CO molecules, an acyl group, a pyridinol N atom and a cysteine thiolate as the central constituent. This Fe centre has inspired chemists to not only design synthetic mimics to catalytically cleave H2 in solution but also for incorporation into apo-[Fe]-hydrogenase to give semi-synthetic proteins. This Perspective describes the enzymes involved in hydrogenotrophic methanogenesis, with a focus on those performing the reduction steps. Of these, we describe [Fe]-hydrogenases in detail and cover recent progress in their synthetic modelling.

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Fig. 1: Methanogenesis from H2 and CO2.
Fig. 2: The reductions catalysed by Fwd, Mtd, Frh and Mcr.
Fig. 3: [Fe]-hydrogenase and its FeGP cofactor.
Fig. 4: The proposed mechanism of [Fe]-hydrogenase and key intermediates of [NiFe]-hydrogenases and [FeFe]-hydrogenases.
Fig. 5: Synthetic FeGP mimics enable [Fe]-hydrogenase reconstitution.

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Acknowledgements

This work was supported by grants from the Max Planck Society (to S.S., T.W. and U.E.) and the Deutsche Forschungsgemeinschaft (Iron-Sulfur for Life: SH 87/1-1, to S.S.).

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S.S. contributed to writing a draft and editing of the manuscript. G.H. contributed to drawing the figures. All authors contributed to discussing, writing and reviewing the manuscript before submission.

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Correspondence to Seigo Shima.

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Huang, G., Wagner, T., Ermler, U. et al. Methanogenesis involves direct hydride transfer from H2 to an organic substrate. Nat Rev Chem 4, 213–221 (2020). https://doi.org/10.1038/s41570-020-0167-2

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