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Volumen1847 (2)

Structural differences of oxidized iron-sulfur and nickel-iron cofactors in O-2-tolerant and O-2-sensitive hydrogenases studied by X-ray absorption spectroscopy

Autores:Oliver Sanganas , Oliver Lenz , Sebastien Dementin , Marc Rousset , Antonio López de Lacey, Michael Haumann
Grupos de investigación:BioElectroCatalisis
The class of [NiFe]-hydrogenases comprises oxygen-sensitive periplasmic (PH) and oxygen-tolerant membrane-bound (MBH) enzymes. For three PHs and four MBHs from six bacterial species, structural features of the nickel-iron active site of hydrogen turnover and of the iron-sulfur clusters functioning in electron transfer were determined using X-ray absorption spectroscopy (XAS). Fe-XAS indicated surplus oxidized iron and a lower number of similar to 2.7 angstrom Fe-Fe distances plus additional shorter and longer distances in the oxidized MBHs compared to the oxidized PHs. This supported a double-oxidized and modified proximal FeS cluster in all MBHs with an apparent trimer-plus-monomer arrangement of its four iron atoms, in agreement with crystal data showing a [4Fe3S] cluster instead of a [4Fe4S] cubane as in the PHs. Ni-XAS indicated coordination of the nickel by the thiol group sulfurs of four conserved cysteines and at least one iron-oxygen bond in both MBH and PH proteins. Structural differences of the oxidized inactive [NiFe] cofactor of MBHs in the Ni-B state compared to PHs in the Ni-A state included a similar to 0.05 angstrom longer Ni-O bond, a two times larger spread of the Ni-S bond lengths, and a similar to 0.1 angstrom shorter Ni-Fe distance. The modified proximal [4Fe3S] cluster, weaker binding of the Ni-Fe bridging oxygen species, and an altered localization of reduced oxygen species at the active site may each contribute to O-2 tolerance.
Palabras clave:[NiFe]-hydrogenase, O-2-tolerance, FeS cluster, [NiFe] active site, X-ray absorption spectroscopy
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