title: Proton Coupled Electronic Rearrangement within the H-Cluster as an Essential Step in the Catalytic Cycle of [FeFe] Hydrogenases.
abstract: The active site of [FeFe] hydrogenases, the H-cluster, consists of a [4Fe-4S] cluster connected via a bridging cysteine to a [2Fe] complex carrying CO and CN-ligands as well as a bridging aza-dithiolate ligand (ADT) of which the amine moiety serves as a proton shuttle between the protein and the H-cluster. During the catalytic cycle, the two subclusters change oxidation states: [4Fe-4S]H2+⇔ [4Fe-4S]H+and [Fe(I)Fe(II)]H⇔ [Fe(I)Fe(I)]Hthereby enabling the storage of the two electrons needed for the catalyzed reaction 2H++ 2e-⇄ H2. Using FTIR spectro-electrochemistry on the [FeFe] hydrogenase from Chlamydomonas reinhardtii (CrHydA1) at different pH values, we resolve the redox and protonation events in the catalytic cycle and determine their intrinsic thermodynamic parameters. We show that the singly reduced state Hredof the H-cluster actually consists of two species: Hred= [4Fe-4S]H+- [Fe(I)Fe(II)]Hand HredH+= [4Fe-4S]H2+- [Fe(I)Fe(I)]H(H+) related by proton coupled electronic rearrangement. The two redox events in the catalytic cycle occur on the [4Fe-4S]Hsubcluster at similar midpoint-potentials (-375 vs -418 mV); the protonation event (Hred/HredH+) has a pKa≈ 7.2.
authors.affiliation: Max-Planck-Institut für Chemische Energiekonversion , Stiftstrasse 34-36, 45470 Mülheim/Ruhr, Germany.
authors.forename: Constanze
authors.initials: C
authors.lastname: Sommer
authors.affiliation: Max-Planck-Institut für Chemische Energiekonversion , Stiftstrasse 34-36, 45470 Mülheim/Ruhr, Germany.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Adamska-Venkatesh
authors.affiliation: Max-Planck-Institut für Chemische Energiekonversion , Stiftstrasse 34-36, 45470 Mülheim/Ruhr, Germany.
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Pawlak
authors.affiliation: Max-Planck-Institut für Chemische Energiekonversion , Stiftstrasse 34-36, 45470 Mülheim/Ruhr, Germany.
authors.forename: James A
authors.initials: JA
authors.lastname: Birrell
authors.affiliation: Max-Planck-Institut für Chemische Energiekonversion , Stiftstrasse 34-36, 45470 Mülheim/Ruhr, Germany.
authors.forename: Olaf
authors.initials: O
authors.lastname: Rüdiger
authors.affiliation: Max-Planck-Institut für Chemische Energiekonversion , Stiftstrasse 34-36, 45470 Mülheim/Ruhr, Germany.
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Reijerse
authors.affiliation: Max-Planck-Institut für Chemische Energiekonversion , Stiftstrasse 34-36, 45470 Mülheim/Ruhr, Germany.
authors.forename: Wolfgang
authors.identifier: 0000-0001-7059-5327
authors.initials: W
authors.lastname: Lubitz
mesh_terms: D055162:Biocatalysis; D016825:Chlamydomonas reinhardtii / Q000201:enzymology; D004583:Electrons; D006859:Hydrogen / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D006864:Hydrogenase / Q000737:chemistry / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000378:metabolism*; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D011522:Protons
chemical_list: D007506:Iron-Sulfur Proteins; D011522:Protons; D006859:Hydrogen; C118830:iron hydrogenase; D006864:Hydrogenase