Investigations on the Role of Proton-Coupled Electron Transfer in Hydrogen Activation by [FeFe]-Hydrogenase

David Mulder, Paul King, Maurizio Bruschi, Claudio Greco, Evangeline Koonce, John Peters

Research output: Contribution to journalArticlepeer-review

98 Scopus Citations

Abstract

Proton-coupled electron transfer (PCET) is a fundamental process at the core of oxidation-reduction reactions for energy conversion. The [FeFe]-hydrogenases catalyze the reversible activation of molecular H2 through a unique metallocofactor, the H-cluster, which is finely tuned by the surrounding protein environment to undergo fast PCET transitions. The correlation of electronic and structural transitions at the H-cluster with proton-transfer (PT) steps has not been well-resolved experimentally. Here, we explore how modification of the conserved PT network via a Cys → Ser substitution at position 169 proximal to the H-cluster of Chlamydomonas reinhardtii [FeFe]-hydrogenase (CrHydA1) affects the H-cluster using electron paramagnetic resonance (EPR) and Fourier transform infrared (FTIR) spectroscopy. Despite a substantial decrease in catalytic activity, the EPR and FTIR spectra reveal different H-cluster catalytic states under reducing and oxidizing conditions. Under H2 or sodium dithionite reductive treatments, the EPR spectra show signals that are consistent with a reduced [4Fe-4S]H+ subcluster. The FTIR spectra showed upshifts of νCO modes to energies that are consistent with an increase in oxidation state of the [2Fe]H subcluster, which was corroborated by DFT analysis. In contrast to the case for wild-type CrHydA1, spectra associated with Hred and Hsred states are less populated in the Cys → Ser variant, demonstrating that the exchange of -SH with -OH alters how the H-cluster equilibrates among different reduced states of the catalytic cycle under steady-state conditions.

Original languageAmerican English
Pages (from-to)15394-15402
Number of pages9
JournalJournal of the American Chemical Society
Volume136
Issue number43
DOIs
StatePublished - 29 Oct 2014

Bibliographical note

Publisher Copyright:
© 2014 American Chemical Society.

NREL Publication Number

  • NREL/JA-2700-62666

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