title: Characterization of a unique [FeS] cluster in the electron transfer chain of the oxygen tolerant [NiFe] hydrogenase from Aquifex aeolicus.
abstract: Iron-sulfur clusters are versatile electron transfer cofactors, ubiquitous in metalloenzymes such as hydrogenases. In the oxygen-tolerant Hydrogenase I from Aquifex aeolicus such electron "wires" form a relay to a diheme cytb, an integral part of a respiration pathway for the reduction of O(2) to water. Amino acid sequence comparison with oxygen-sensitive hydrogenases showed conserved binding motifs for three iron-sulfur clusters, the nature and properties of which were unknown so far. Electron paramagnetic resonance spectra exhibited complex signals that disclose interesting features and spin-coupling patterns; by redox titrations three iron-sulfur clusters were identified in their usual redox states, a [3Fe4S] and two [4Fe4S], but also a unique high-potential (HP) state was found. On the basis of (57)Fe Mössbauer spectroscopy we attribute this HP form to a superoxidized state of the [4Fe4S] center proximal to the [NiFe] site. The unique environment of this cluster, characterized by a surplus cysteine coordination, is able to tune the redox potentials and make it compliant with the [4Fe4S](3+) state. It is actually the first example of a biological [4Fe4S] center that physiologically switches between 3+, 2+, and 1+ oxidation states within a very small potential range. We suggest that the (1 + /2+) redox couple serves the classical electron transfer reaction, whereas the superoxidation step is associated with a redox switch against oxidative stress.
authors: Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim ad Ruhr, Germany.
authors: Maria-Eirini
authors: ME
authors: Pandelia
authors: Wolfgang
authors: W
authors: Nitschke
authors: Pascale
authors: P
authors: Infossi
authors: Marie-Thérèse
authors: MT
authors: Giudici-Orticoni
authors: Eckhard
authors: E
authors: Bill
authors: Wolfgang
authors: W
authors: Lubitz
mesh_terms: D000595:Amino Acid Sequence; D001419:Bacteria / Q000201:enzymology*; D004579:Electron Transport; D006864:Hydrogenase / Q000037:antagonists & inhibitors / Q000737:chemistry*; D007506:Iron-Sulfur Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry*; D058977:Molecular Sequence Annotation; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry* / Q000494:pharmacology
chemical_list: D007506:Iron-Sulfur Proteins; C043296:nickel-iron hydrogenase; D006864:Hydrogenase; D010100:Oxygen