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- Bruschi, Maurizio, et al.
(författare)
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Functionally Relevant Interplay between the Fe(4)S(4) Cluster and CN(-) Ligands in the Active Site of [FeFe]-Hydrogenases.
- 2010
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 132:14, s. 4992-4992
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Tidskriftsartikel (refereegranskat)abstract
- [FeFe]-hydrogenases are highly efficient H(2)-evolving metalloenzymes that include cyanides and carbonyls in the active site. The latter is an Fe(6)S(6) cluster (the so-called H-cluster) that can be subdivided into a binuclear portion carrying the CO and CN(-) groups and a tetranuclear subcluster. The fundamental role of cyanide ligands in increasing the basicity of the H-cluster has been highlighted previously. Here a more subtle but crucial role played by the two CN(-) ligands in the active site of [FeFe]-hydrogenases is disclosed. In fact, QM/MM calculations on all-atom models of the enzyme from Desulfovibrio desulfuricans show that the cyanide groups fine-tune the electronic and redox properties of the active site, affecting both the protonation regiochemistry and electron transfer between the two subclusters of the H-cluster. Despite the crucial role of cyanides in the protein active site, the currently available bioinspired electrocatalysts generally lack CN(-) groups in order to avoid competition between the latter and the catalytic metal centers for proton binding. In this respect, we show that a targeted inclusion of phosphine ligands in hexanuclear biomimetic clusters may restore the electronic and redox features of the wild-type H-cluster.
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2. |
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3. |
- Greco, Claudio, et al.
(författare)
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Isocyanide in Biochemistry? A Theoretical Investigation of the Electronic Effects and Energetics of Cyanide Ligand Protonation in [FeFe]-Hydrogenases
- 2011
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Ingår i: Chemistry: A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 17:6, s. 1954-1965
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Tidskriftsartikel (refereegranskat)abstract
- The presence of Fe-bound cyanide ligands in the active site of the proton-reducing enzymes [FeFe]-hydrogenases has led to the hypothesis that such Bronsted-Lowry bases could be protonated during the catalytic cycle, thus implying that hydrogen isocyanide (HNC) might have a relevant role in such crucial microbial metabolic paths. We present a hybrid quantum mechanical/molecular mechanical (QM/MM) study of the energetics of CN- protonation in the enzyme, and of the effects that cyanide protonation can have on [FeFe]-hydrogenase active sites. A detailed analysis of the electronic properties of the models and of the energy profile associated with H-2 evolution clearly shows that such protonation is dysfunctional for the catalytic process. However, the inclusion of the protein matrix surrounding the active site in our QM/MM models allowed us to demonstrate that the amino acid environment was finely selected through evolution, specifically to lower the Bronsted-Lowry basicity of the cyanide ligands. In fact, the conserved hydrogen-bonding network formed by these ligands and the neighboring amino acid residues is able to impede CN- protonation, as shown by the fact that the isocyanide forms of [FeFe]-hydrogenases do not correspond to stationary points on the enzyme QM/MM potential-energy surface.
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4. |
- Greco, Claudio, et al.
(författare)
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Mechanistic and Physiological Implications of the Interplay among Iron-Sulfur Clusters in [FeFe]-Hydrogenases. A QM/MM Perspective
- 2011
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 133:46, s. 18742-18749
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Tidskriftsartikel (refereegranskat)abstract
- Key stereoelectronic properties of Desulfovibrio desulfuricans [FeFe]-hydrogenase (DdH) were investigated by quantum mechanical description of its complete inorganic core, which includes a Fe6S6 active site (the H-cluster), as well as two ancillary Fe4S4 assemblies (the F and F' clusters). The partially oxidized, active-ready form of DdH is able to efficiently bind dihydrogen, thus starting H-2 oxidation catalysis. The calculations allow us to unambiguously assign a mixed Fe(H)Fe(I) state to the catalytic core of the active-ready enzyme and show that H-2 uptake exerts subtle, yet crucial influences on the redox properties of DdH. In fact, H-2 binding can promote electron transfer from the H-cluster to the solvent-exposed F'-cluster, thanks to a 50% decrease of the energy gap between the HOMO (that is localized on the H-cluster) and the LUMO (which is centered on the F'-cluster). Our results also indicate that the binding of the redox partners of DdH in proximity of its F'-cluster can trigger one-electron oxidation of the H-2-bound enzyme, a process that is expected to have an important role in H-2 activation. Our findings are analyzed not only from a mechanistic perspective, but also in consideration of the physiological role of DdH. In fact, this enzyme is known to be able to catalyze both the oxidation and the evolution of H-2, depending on the cellular metabolic requirements. Hints for the design of targeted mutations that could lead to the enhancement of the oxidizing properties of DdH are proposed and discussed.
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5. |
- Greco, Claudio, et al.
(författare)
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Probing the Effects of One-Electron Reduction and Protonation on the Electronic Properties of the Fe-S Clusters in the Active-Ready Form of [FeFe]-Hydrogenases. A QM/MM Investigation.
- 2011
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Ingår i: ChemPhysChem. - : Wiley. - 1439-7641 .- 1439-4235. ; 12:17, s. 3376-3382
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Tidskriftsartikel (refereegranskat)abstract
- A QM/MM investigation of the active-ready (Hox) form of [FeFe]-hydrogenase from D. desulfuricans, in which the electronic properties of all Fe-S clusters (H, F and F') have been simultaneously described using DFT, was carried out with the aim of disclosing a possible interplay between the H-cluster and the accessory iron-sulfur clusters in the initial steps of the catalytic process leading to H2 formation. It turned out that one-electron addition to the active-ready form leads to reduction of the F'-cluster and not of the H-cluster. Protonation of the H-cluster in Hox is unlikely, and in any case it would not trigger electron transfer from the accessory Fe4S4 clusters to the active site. Instead, one-electron reduction and protonation of the active-ready form trigger electron transfer within the protein, a key event in the catalytic cycle. In particular, protonation of the H-cluster after one-electron reduction of the enzyme lowers the energy of the lowest unoccupied molecular orbitals localized on the H-cluster to such an extent that a long-range electron transfer from the F'-cluster towards the H-cluster itself is allowed.
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6. |
- Greco, Claudio, et al.
(författare)
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Structural insights into the active-ready form of [FeFe]-Hydrogenase and mechanistic details of its inhibition by carbon monoxide
- 2007
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 46:18, s. 7256-7258
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Tidskriftsartikel (refereegranskat)abstract
- [FeFe]-Hydrogenases harbor a {2Fe3S} assembly bearing two CO and two CN- groups, a mu-CO ligand, and a vacant coordination site trans to the mu-CO group. Recent theoretical results obtained studying the isolated {2Fe3S} subsite indicated that one of the CN- ligands can easily move from the crystallographic position to the coordination site trans to the mu-CO group; such an isomerization would have a major impact on substrates and inhibitors binding regiochemistry and, consequently, on the catalytic mechanism. To shed light on this crucial issue, we have carried out hybrid QM/MM and free energy perturbation calculations on the whole enzyme, which demonstrate that the protein environment plays a crucial role and maintains the CN- group fixed in the position observed in the crystal structure; these results strongly support the hypothesis that the vacant coordination site trans to the mu-CO group has a crucial functional relevance both in the context of CO-mediated inhibition of the enzyme and in dihydrogen oxidation/evolution catalysis.
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