title: Identification of a Catalytic Iron-Hydride at the H-Cluster of [FeFe]-Hydrogenase.
abstract: Hydrogenases couple electrochemical potential to the reversible chemical transformation of H2and protons, yet the reaction mechanism and composition of intermediates are not fully understood. In this Communication we describe the biophysical properties of a hydride-bound state (Hhyd) of the [FeFe]-hydrogenase from Chlamydomonas reinhardtii. The catalytic H-cluster of [FeFe]-hydrogenase consists of a [4Fe-4S] subcluster ([4Fe-4S]H) linked by a cysteine thiol to an azadithiolate-bridged 2Fe subcluster ([2Fe]H) with CO and CN-ligands. Mössbauer analysis and density functional theory (DFT) calculations show that Hhydconsists of a reduced [4Fe-4S]H+coupled to a diferrous [2Fe]Hwith a terminally bound Fe-hydride. The existence of the Fe-hydride in Hhydwas demonstrated by an unusually low Mössbauer isomer shift of the distal Fe of the [2Fe]Hsubcluster. A DFT model of Hhydshows that the Fe-hydride is part of a H-bonding network with the nearby bridging azadithiolate to facilitate fast proton exchange and catalytic turnover.
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory , Golden, Colorado 80401, United States.
authors.forename: David W
authors.initials: DW
authors.lastname: Mulder
authors.affiliation: Department of Chemistry, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States.
authors.forename: Yisong
authors.identifier: 0000-0002-4132-3565
authors.initials: Y
authors.lastname: Guo
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory , Golden, Colorado 80401, United States.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Ratzloff
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory , Golden, Colorado 80401, United States.
authors.forename: Paul W
authors.identifier: 0000-0001-5039-654X
authors.initials: PW
authors.lastname: King
mesh_terms: D055162:Biocatalysis; D016825:Chlamydomonas reinhardtii / Q000201:enzymology; D006864:Hydrogenase / Q000737:chemistry / Q000378:metabolism*; D007501:Iron / Q000737:chemistry / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D011522:Protons; D011789:Quantum Theory; D013816:Thermodynamics
chemical_list: D007506:Iron-Sulfur Proteins; D011522:Protons; D007501:Iron; C118830:iron hydrogenase; D006864:Hydrogenase