Role of the Metal Ion in Bio-Inspired Hydrogenase Models: Investigation of a Homodinuclear FeFe Complex vs Its Heterodinuclear NiFe Analogue (original) (raw)
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[FeFe]- and [NiFe]-hydrogenase diversity, mechanism, and maturation
Biochimica et biophysica acta. Molecular cell research, 2015
Fig. 2. Schematic representation of the structural variation of [FeFe]-hydrogenase homologs present in sequence databases as adapted from Meyer, 2007 and more recently Calusinska et al., 2010. The M1, M2, and M3, as reported by Meyer, 2007, correspond to monomeric enzymes with numbers indicating increasing size. "D" denotes a dimeric enzyme, "TR" denotes a trimeric enzyme, and "TE" denotes a tetrameric enzyme. Panel A illustrates the primary structural classes while panel B illustrates the remarkable structural variation within the M2 structural subclass.
2014
The HypC and HypD maturases are required for the biosynthesis of the Fe(CN)2CO cofactor in the large subunit of [NiFe]-hydrogenases. Using infrared spectroscopy we demonstrate that an anaerobically purified, Strep-tagged HypCD complex from Escherichia coli exhibits absorption bands characteristic of diatomic CO and CN− ligands as well as CO2. Metal and sulphide analyses revealed that along with the [4Fe–4S]2+ cluster in HypD, the complex has two additional oxygen-labile Fe ions. We prove that HypD cysteine 41 is required for the coordination of all three ligands. These findings suggest that the HypCD complex carries minimally the Fe(CN)2CO cofactor.
Hydrogen activation by [NiFe]-hydrogenases
Biochem. Soc. Trans., 2016
Hydrogenase-1 (Hyd-1) from Escherichia coli is a membrane-bound enzyme that catalyses the reversible oxidation of molecular H2. The active site contains one Fe and one Ni atom and several conserved amino acids including an arginine (Arg509), which interacts with two conserved aspartate residues (Asp118 and Asp574) forming an outer shell canopy over the metals. There is also a highly conserved glutamate (Glu28) positioned on the opposite side of the active site to the canopy. The mechanism of hydrogen activation has been dissected by site-directedmutagenesis to identify the catalytic base responsible for splitting molecular hydrogen and possible proton transfer pathways to/from the active site. Previous reported attempts to mutate residues in the canopy were unsuccessful, leading to an assumption of a purely structural role. Recent discoveries, however, suggest a catalytic requirement, for example replacing the arginine with lysine (R509K) leaves the structure virtually unchanged, but catalytic activity falls by more than 100-fold. Variants containing amino acid substitutions at either or both, aspartates retain significant activity. We now propose a new mechanism: heterolytic H2 cleavage is via a mechanism akin to that of a frustrated Lewis pair (FLP), where H2 is polarized by simultaneous binding to the metal(s) (the acid) and a nitrogen from Arg509 (the base).