Hydrogen activation by [NiFe]-hydrogenases.
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 (Arg(509)), which interacts with two conserved aspartate residues (Asp(118) and Asp(574)) forming an outer shell canopy over the metals. There is also a highly conserved glutamate (Glu(28)) positioned on the opposite side of the active site to the canopy. The mechanism of hydrogen activation has been dissected by site-directed mutagenesis 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 Arg(509) (the base).
Research Complex at Harwell, Rutherford Appleton Laboratory, Harwell Oxford, Didcot OX11 0FA, U.K. Simon.Phillips@rc-harwell.ac.uk stephen.carr@rc-harwell.ac.uk fraser.armstrong@chem.ox.ac.uk.
Stephen B
SB
Carr
Department of Chemistry, University of Oxford, Oxford OX1 3QR, U.K.
Rhiannon M
RM
Evans
Department of Chemistry, University of Oxford, Oxford OX1 3QR, U.K.
Emily J
EJ
Brooke
Department of Chemistry, University of Oxford, Oxford OX1 3QR, U.K.
Sara A M
SA
Wehlin
Department of Chemistry, University of Oxford, Oxford OX1 3QR, U.K.
Elena
E
Nomerotskaia
Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, U.K.
Frank
F
Sargent
Department of Chemistry, University of Oxford, Oxford OX1 3QR, U.K. Simon.Phillips@rc-harwell.ac.uk stephen.carr@rc-harwell.ac.uk fraser.armstrong@chem.ox.ac.uk.
Fraser A
FA
Armstrong
Research Complex at Harwell, Rutherford Appleton Laboratory, Harwell Oxford, Didcot OX11 0FA, U.K. Simon.Phillips@rc-harwell.ac.uk stephen.carr@rc-harwell.ac.uk fraser.armstrong@chem.ox.ac.uk.
Simon E V
SE
Phillips
D020134:Catalytic Domain; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D006859:Hydrogen / Q000378:metabolism*; D006864:Hydrogenase / Q000378:metabolism*; D010084:Oxidation-Reduction
D029968:Escherichia coli Proteins; D006859:Hydrogen; C043296:nickel-iron hydrogenase; D006864:Hydrogenase
crystal structure; frustrated Lewis pair; hydrogen splitting; hydrogenase; mutagenesis; protein film electrochemistry