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Title: CO-Bridged H-Cluster Intermediates in the Catalytic Mechanism of [FeFe]-Hydrogenase CaI

Journal Article · · Journal of the American Chemical Society
 [1];  [1];  [1];  [2];  [2]; ORCiD logo [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  2. Colorado School of Mines, Golden, CO (United States)
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The [FeFe]-hydrogenases ([FeFe] H2ases) catalyze reversible H2 activation at the H-cluster, which is composed of a [4Fe-4S]H subsite linked by a cysteine thiolate to a bridged, organometallic [2Fe-2S] ([2Fe]H) subsite. Profoundly different geometric models of the H-cluster redox states that orchestrate the electron/proton transfer steps of H2 bond activation have been proposed. We have examined this question in the [FeFe] H2ase I from Clostridium acetobutylicum (CaI) by Fourier-transform infrared (FTIR) spectroscopy with temperature annealing and H/D isotope exchange to identify the relevant redox states and define catalytic transitions. One-electron reduction of Hox led to formation of HredH+ ([4Fe-4S]H2+-FeI-FeI) and Hred' ([4Fe-4S]H1+-FeII-FeI), with both states characterized by low frequency μ-CO IR modes consistent with a fully bridged [2Fe]H. Similar μ-CO IR modes were also identified for HredH+ of the [FeFe] H2ase from Chlamydomonas reinhardtii (CrHydA1). The CaI proton-transfer variant C298S showed enrichment of an H/D isotope-sensitive μ-CO mode, a component of the hydride bound H-cluster IR signal, Hhyd. Equilibrating CaI with increasing amounts of NaDT, and probed at cryogenic temperatures, showed HredH+ was converted to Hhyd. Over an increasing temperature range from 10 to 260 K catalytic turnover led to loss of Hhyd and appearance of Hox, consistent with enzymatic turnover and H2 formation. The results show for CaI that the μ-CO of [2Fe]H remains bridging for all of the 'Hred' states and that HredH+ is on pathway to Hhyd and H2 evolution in the catalytic mechanism. Here, this provides a blueprint for designing small molecule catalytic analogs

Research Organization:
National Renewable Energy Laboratory (NREL), Golden, CO (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
AC36-08GO28308
OSTI ID:
1440310
Report Number(s):
NREL/JA-2700-71170
Journal Information:
Journal of the American Chemical Society, Vol. 140, Issue 24; ISSN 0002-7863
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 41 works
Citation information provided by
Web of Science

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Cited By (2)

Spectroscopic and biochemical insight into an electron-bifurcating [FeFe] hydrogenase journal December 2019
Spectroscopic and Computational Evidence that [FeFe] Hydrogenases Operate Exclusively with CO-Bridged Intermediates journal December 2019

Figures / Tables (7)

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
[FeFe]-hydrogenases
catalysis
catalytic transitions