Does the environment around the H-cluster allow coordination of the pendant amine to the catalytic iron center in [FeFe] hydrogenases? Answers from theory.

Miyake, Toshiko; Bruschi, Maurizio; Cosentino, Ugo; Baffert, Carole; Fourmond, Vincent; Léger, Christophe; Moro, Giorgio; Gioia, Luca; Greco, Claudio

[FeFe] hydrogenases are H-evolving enzymes that feature a diiron cluster in their active site (the [2Fe] cluster). One of the iron atoms has a vacant coordination site that directly interacts with H, thus favoring its splitting in cooperation with the secondary amine group of a neighboring, flexible azadithiolate ligand. The vacant site is also the primary target of the inhibitor O. The [2Fe] cluster can span various redox states. The active-ready form (H) attains the FeFe state. States more oxidized than H were shown to be inactive and/or resistant to O. In this work, we used density functional theory to evaluate whether azadithiolate-to-iron coordination is involved in oxidative inhibition and protection against O, a hypothesis supported by recent results on biomimetic compounds. Our study shows that Fe-N(azadithiolate) bond formation is favored for an FeFe active-site model which disregards explicit treatment of the surrounding protein matrix, in line with the case of the corresponding FeFe synthetic system. However, the study of density functional theory models with explicit inclusion of the amino acid environment around the [2Fe] cluster indicates that the protein matrix prevents the formation of such a bond. Our results suggest that mechanisms other than the binding of the azadithiolate nitrogen protect the active site from oxygen in the so-called H state.

SUBSTITUENTS (Chemistry); CATALYSIS; HYDROGENASE; BINDING sites; COORDINATE covalent bond; DITHIOLATES; LIGANDS (Chemistry)

Journal of Biological Inorganic Chemistry (JBIC), 2013, Vol 18, Issue 6, p693

0949-8257

Academic Journal

10.1007/s00775-013-1014-4