Hydrogen-Producing Catalysts Based on Ferredoxin Scaffolds

Current attempts to transform our fossil fuel-based society into a sustainable one involve learning from and employing the biochemistry of nature. The process of photosynthesis is exemplary for utilizing sunlight as a regenerative energy source. Enzymes like hydrogenases, which reduce protons to molecular hydrogen (H₂) under ambient conditions, are model biocatalysts for generating sustainable, clean fuels. In green algae, photosynthesis and hydrogenases are coupled through ferredoxin, a small electron transfer protein. Here, it is shown that several plant-type ferredoxins can interact with a chemically synthesized active site cofactor analog of [FeFe]-hydrogenases in a way that allows comparably high H₂ evolution rates. UV-vis and Fourier-transform infrared spectroscopy indicate that the natural [2Fe-2S] clusters of the ferredoxin hosts must be absent for a functional interaction of polypeptide and cofactor mimic and that the apo-ferredoxins shield the H₂-producing cofactor from the solvent. The hybrid proteins exhibited higher O₂ tolerance than natural [FeFe]-hydrogenases and generated H₂ in light-dependent cascades based on photosystem I or the chemical photosensitizer proflavine. These features and the combination of natural hosts and cofactors might contribute to establishing sustainable light-dependent H₂ production systems.