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Deciphering catalytic mechanism of [FeFe]-hydrogenase by neutron crystallography

Applicant Jifu Duan, Ph.D.
Subject Area Structural Biology
Term from 2021 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 461338801
 
Final Report Year 2025

Final Report Abstract

[FeFe]-hydrogenases efficiently catalyze the reversible conversion of protons, electrons and dihydrogen (H2) employing their catalytic cofactor termed H-cluster. Catalytic turnover at the deeply buried H-cluster within protein matrix is achieved by concerted proton coupled electron transfer steps. To understand the fate of catalytically important hydrogen species binding to the H-cluster and the proton transfer pathway, neutron crystallography was proposed to be employed based on the well-established X-ray crystallography of in the hosting labs. Although the large-sized CpI ([FeFe]-hydrogenase from Clostridium pasteurianum) crystals (>0.1 mm3) were obtained, their diffraction capacity decreased to resolutions of 2.8-3.5 Å with high mosacity, indicating severe problems in crystal packing. Despite a lot of attempted efforts in optimization, large-sized CpI crystals suitable for neutron diffraction were not obtained in the end. More extensive screening for crystallization is needed in the future. In addition, the applicant has made other progress in structural studies on [FeFe]- hydrogenases. Extrinsic cyanide was demonstrated to directly bind at the open coordination site of the H-cluster. In the cyanide bound state, an alternative conformation of the proton transfer pathway was observed, possibly reflecting a second functional conformation of the proton transfer pathway. Formaldehyde was shown to react with the amine group of the H-cluster and the thiol group of the proton transfer pathway which both are catalytically very important for catalytic turnover, therefore providing a molecular mechanism about how formaldehyde inhibits [FeFe]-hydrogenases. A structural and functional understanding of the oxygen-stable [FeFe]-hydrogenase from Clostridium beijerinckii was obtained.

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