Changing the ligation of the distal [4Fe4S] cluster in NiFe hydrogenase impairs inter- and intramolecular electron transfers.
In NiFe hydrogenases, electrons are transferred from the active site to the redox partner via a chain of three Iron-Sulfur clusters, and the surface-exposed [4Fe4S] cluster has an unusual His(Cys)3 ligation. When this Histidine (H184 in Desulfovibrio fructosovorans) is changed into a cysteine or a glycine, a distal cubane is still assembled but the oxidative activity of the mutants is only 1.5 and 3% of that of the WT, respectively. We compared the activities of the WT and engineered enzymes for H2 oxidation, H+ reduction and H/D exchange, under various conditions: (i) either with the enzyme directly adsorbed onto an electrode or using soluble redox partners, and (ii) in the presence of exogenous ligands whose binding to the exposed Fe of H184G was expected to modulate the properties of the distal cluster. Protein film voltammetry proved particularly useful to unravel the effects of the mutations on inter and intramolecular electron transfer (ET). We demonstrate that changing the coordination of the distal cluster has no effect on cluster assembly, protein stability, active-site chemistry and proton transfer; however, it slows down the first-order rates of ET to and from the cluster. All-sulfur coordination is actually detrimental to ET, and intramolecular (uphill) ET is rate determining in the glycine variant. This demonstrates that although [4Fe4S] clusters are robust chemical constructs, the direct protein ligands play an essential role in imparting their ability to transfer electrons.
Dementin
Sébastien
S
Laboratoire de Bioénergétique et Ingénierie des Protéines, CNRS UPR 9036, IBSM and Université de Provence, 31 chemin Joseph Aiguier, 13402 Marseille Cédex 20, France.
Belle
Valérie
V
Bertrand
Patrick
P
Guigliarelli
Bruno
B
Adryanczyk-Perrier
Géraldine
G
De Lacey
Antonio L
AL
Fernandez
Victor M
VM
Rousset
Marc
M
Léger
Christophe
C
D003901:Desulfovibrio / Q000201:enzymology / Q000235:genetics; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D006863:Hydrogen-Ion Concentration; D006864:Hydrogenase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D007093:Imidazoles / Q000737:chemistry / Q000378:metabolism; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D012996:Solutions
D007093:Imidazoles; D007506:Iron-Sulfur Proteins; D012996:Solutions; C029899:imidazole; C043296:nickel-iron hydrogenase; D006864:Hydrogenase