Activation Process of [NiFe] Hydrogenase Elucidated by High-Resolution X-Ray Analyses: Conversion of the Ready to the Unready State

Abstract

Hydrogenases catalyze oxidoreduction of molecular hydrogen and have potential applications for utilizing dihydrogen as an energy source. [NiFe] hydrogenase has two different oxidized states, Ni-A (unready, exhibits a lag phase in reductive activation) and Ni-B (ready). We have succeeded in converting Ni-B to Ni-A with the use of Na 2 S and O 2 and determining the high-resolution crystal structures of both states. Ni-B possesses a monatomic nonprotein bridging ligand at the Ni-Fe active site, whereas Ni-A has a diatomic species. The terminal atom of the bridging species of Ni-A occupies a similar position as C of the exogenous CO in the CO complex (inhibited state). The common features of the enzyme structures at the unready (Ni-A) and inhibited (CO complex) states are proposed. These findings provide useful information on the design of new systems of biomimetic dihydrogen production and fuel cell devices.

[NiFe] and [FeS] Cofactors in the Membrane-Bound Hydrogenase of Ralstonia eutropha Investigated by X-ray Absorption Spectroscopy: Insights into O2-Tolerant H2 Cleavage

“…Further O-atoms in the first coordination sphere of Ni were not detected. This rather excludes the presence of sulfenates (oxidized cysteines, CysSO) bound via their O-atom to Ni, which have been found in several crystal structures of oxidized Desulfovibrio H 2 ases (86)(87)(88).…”

Self-subunit Swapping Chaperone Needed for the Maturation of Multimeric Metalloenzyme Nitrile Hydratase by a Subunit Exchange Mechanism Also Carries Out the Oxidation of the Metal Ligand Cysteine Residues and Insertion of Cobalt

“…Cys-SOH and Cys-SO 2 H serve as catalytically essential redox centers, transient intermediates during peroxide reduction, sensors for the intracellular redox status, catalytic active sites, etc. (29,30,32,33). Compared with various proteins containing reactive cysteine residues, NHase and thiocyanate hydrolase have both post-translational oxidized Cys-SOH and Cys-SO 2 H in their active sites (8 -12, 26 -28); both cysteines play an important role in the catalytic reaction but do not play any catalytic redox role (29).…”

“…Oxidized cysteine residues Cys-SO 2 H or Cys-SOH are known to play roles in diverse processes, including signal transduction, oxygen metabolism and the oxidative stress response, transcription regulation, and metal coordination in various proteins such as NADH peroxidase (29,30), peroxiredoxins (31), hydrogenase (32,33), and so on (8 -12, 26 -28, 34). Among these enzymes, NHase and thiocyanate hydrolase are intriguing ones because they possess both Cys-SO 2 H and Cys-SOH as ligands of the metal center and neither residue plays any catalytic redox role at all (29).…”

Biohydrogen for a New Generation of H2/O2 Biofuel Cells: A Sustainable Energy Perspective

“…[90] Spectroscopic and electrochemical studies of O 2 -tolerant Hases revealed that only the Ni-B state was formed, [114] in which the redox state is Ni III Fe II , with a hydroxo ligand bridging the two metal atoms. [117] The formation of Ni-B is responsible for the decrease in the CV current as the potential reaches approximately À250 mV vs. Ag/AgCl ( Figure 4). This process is, however, reversible as shown by the increase in current in the reverse scan.…”