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Electronic structure of the unique [4Fe-3S] cluster in O2-tolerant hydrogenases characterized by 57Fe Mossbauer and EPR spectroscopy.


ABSTRACT: Iron-sulfur clusters are ubiquitous electron transfer cofactors in hydrogenases. Their types and redox properties are important for H(2) catalysis, but, recently, their role in a protection mechanism against oxidative inactivation has also been recognized for a [4Fe-3S] cluster in O(2)-tolerant group 1 [NiFe] hydrogenases. This cluster, which is uniquely coordinated by six cysteines, is situated in the proximity of the catalytic [NiFe] site and exhibits unusual redox versatility. The [4Fe-3S] cluster in hydrogenase (Hase) I from Aquifex aeolicus performs two redox transitions within a very small potential range, forming a superoxidized state above +200 mV vs. standard hydrogen electrode (SHE). Crystallographic data has revealed that this state is stabilized by the coordination of one of the iron atoms to a backbone nitrogen. Thus, the proximal [4Fe-3S] cluster undergoes redox-dependent changes to serve multiple purposes beyond classical electron transfer. In this paper, we present field-dependent (57)Fe-Mössbauer and EPR data for Hase I, which, in conjunction with spectroscopically calibrated density functional theory (DFT) calculations, reveal the distribution of Fe valences and spin-coupling schemes for the iron-sulfur clusters. The data demonstrate that the electronic structure of the [4Fe-3S] core in its three oxidation states closely resembles that of corresponding conventional [4Fe-4S] cubanes, albeit with distinct differences for some individual iron sites. The medial and distal iron-sulfur clusters have similar electronic properties as the corresponding cofactors in standard hydrogenases, although their redox potentials are higher.

SUBMITTER: Pandelia ME 

PROVIDER: S-EPMC3545817 | biostudies-other | 2013 Jan

REPOSITORIES: biostudies-other

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Electronic structure of the unique [4Fe-3S] cluster in O2-tolerant hydrogenases characterized by 57Fe Mossbauer and EPR spectroscopy.

Pandelia Maria-Eirini ME   Bykov Dmytro D   Izsak Robert R   Infossi Pascale P   Giudici-Orticoni Marie-Thérèse MT   Bill Eckhard E   Neese Frank F   Lubitz Wolfgang W  

Proceedings of the National Academy of Sciences of the United States of America 20121224 2


Iron-sulfur clusters are ubiquitous electron transfer cofactors in hydrogenases. Their types and redox properties are important for H(2) catalysis, but, recently, their role in a protection mechanism against oxidative inactivation has also been recognized for a [4Fe-3S] cluster in O(2)-tolerant group 1 [NiFe] hydrogenases. This cluster, which is uniquely coordinated by six cysteines, is situated in the proximity of the catalytic [NiFe] site and exhibits unusual redox versatility. The [4Fe-3S] cl  ...[more]

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