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| 2. |
- Ballmann, Joachim, et al.
(författare)
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Secondary bonding interactions in biomimetic [2Fe-2S] clusters
- 2008
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 47:5, s. 1586-1596
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Tidskriftsartikel (refereegranskat)abstract
- A series of synthetic [2Fe-2S] complexes with terminal thiophenolate ligands and tethered ether or thioether moieties has been prepared and investigated in order to provide models for the potential interaction of additional donor atoms with the Fe atoms in biological [2Fe-2S] clusters. X-ray crystal structures have been determined for six new complexes that feature appended Et (1(C)), OMe (1(O)), or SMe (1(S)) groups, or with a methylene group (2(C)), an ether-O (2(O)), or an thioether-S (2(S)) linking two aryl group. The latter two systems provide a constrained chelate arrangement that induces secondary bonding interactions with the ether-O and thioether-S, which is confirmed by density functional theory (DFT) calculations that also reveal significant spin density on those fifth donor atoms. Structural consequences of the secondary bonding interactions are analyzed in detail, and effects on the spectroscopic and electronic properties are probed by UV-vis, Mossbauer, and H-1 NMR spectroscopy, as well by SQUID measurements and cyclic voltammetry. The potential relevance of the findings for biological [2Fe-2S] sites is considered.
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| 3. |
- Kutin, Yuri, et al.
(författare)
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Divergent assembly mechanisms of the manganese/iron cofactors in R2lox and R2c proteins
- 2016
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 0162-0134 .- 1873-3344. ; 162, s. 164-177
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Tidskriftsartikel (refereegranskat)abstract
- A manganese/iron cofactor which performs multi-electron oxidative chemistry is found in two classes of ferritin-like proteins, the small subunit (R2) of dass Ic ribonucleotide reductase (R2c) and the R2-like ligand-binding oxidase (R2lox). It is undear how a heterodimeric Mn/Fe metallocofactor is assembled in these two related proteins as opposed to a homodimeric Fe/Fe cofactor, especially considering the structural similarity and proximity of the two metal-binding sites in both protein scaffolds and the similar first coordination sphere ligand preferences of Mn-II and Fe-II. Using EPR and Mfissbauer spectroscopies as well as X-ray anomalous dispersion, we examined metal loading and cofactor activation of both proteins in vitro (in solution). We find divergent cofactor assembly mechanisms for the two systems. In both cases, excess Mn-II promotes heterobimetallic cofactor assembly. In the absence of Fe-II, R2c cooperatively binds Mn-II at both metal sites, whereas R2lox does not readily bind Mn-II at either site. Heterometallic cofactor assembly is favored at substoichiometric Feu concentrations in R2lox. Fe-II and Mn-II likely bind to the protein in a stepwise fashion, with Feu binding to site 2 initiating cofactor assembly. In R2c, however, heterometallic assembly is presumably achieved by the displacement of Mn-II by Fe-II at site 2. The divergent metal loading mechanisms are correlated with the putative in vivo functions of R2c and R2lox, and most likely with the intracellular Mn-II/Fe-II concentrations in the host organisms from which they were isolated.
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| 4. |
- Lin, Po-Chi, et al.
(författare)
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A vertebrate-type ferredoxin domain in the Na+-translocating NADH dehydrogenase from Vibrio cholerae
- 2005
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 280:24, s. 22560-22563
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Tidskriftsartikel (refereegranskat)abstract
- The Na(+)-translocating NADH:quinone oxidoreductase from Vibrio cholerae contains a single Fe-S cluster localized in subunit NqrF. Here we study the electronic properties of the Fe-S center in a truncated version of the NqrF subunit comprising only its ferredoxin-like Fe-S domain. Mössbauer spectroscopy of the Fe-S domain in the oxidized state is consistent with a binuclear Fe-S cluster with tetrahedral sulfur coordination by the cysteine residues Cys(70), Cys(76), Cys(79), and Cys(111). Important sequence motifs surrounding these cysteines are conserved in the Fe-S domain and in vertebrate-type ferredoxins. The magnetic circular dichroism spectra of the photochemically reduced Fe-S domain exhibit a striking similarity to the magnetic circular dichroism spectra of vertebrate-type ferredoxins required for the in vivo assembly of iron-sulfur clusters. This study reveals a novel function for vertebrate-type [2Fe-2S] clusters as redox cofactors in respiratory dehydrogenases.
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| 5. |
- Pantazis, Dimitrios A, et al.
(författare)
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A new quantum chemical approach to the magnetic properties of oligonuclear transition-metal complexes : Application to a model for the Tetranuclear Manganese cluster of Photosystem II
- 2009
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Ingår i: Chemistry (Weinheim an der Bergstrasse, Germany). - Weinheim : WILEY-VCH Verlag GmbH & Co. KGaA. - 1521-3765 .- 0947-6539. ; 15:20, s. 5108-5123
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Tidskriftsartikel (refereegranskat)abstract
- The reliable correlation of structural features and magnetic or spectroscopic properties of oligonuclear transition-metal complexes is a critical requirement both for research into innovative magnetic materials and for elucidating the structure and function of many metalloenzymes. We have developed a novel method that for the first time enables the extraction of hyperfine coupling constants (HFCs) from broken-symmetry density functional theory (BS-DFT) calculations on clusters. Using the geometry-optimized tetranuclear manganese complex [Mn4O6(bpy)6]4+/3+ as a model, we first examine in detail the calculation of exchange coupling constants J through the BS-DFT approach. Complications arising from the indeterminacy of experimentally fitted J constants are identified and analyzed. It is found that only the energy levels derived from Hamiltonian diagonalization are a physically meaningful basis for comparing theory and experiment. Subsequently, the proposed theoretical scheme is applied to the calculation of 55Mn HFCs of the MnIII,IV,IV,IV state of the complex, which is similar to the S2 state of the oxygen-evolving complex (OEC) in photosystem II of oxygenic photosynthesis. The new approach performs reliably and accurately, and yields calculated HFCs that can be directly compared with experimental data. Finally, we carefully examine the dependence of HFC on the J value and draw attention to the sensitivity of the calculated values to the exchange coupling parameters. The proposed strategy extends naturally to hetero-oligonuclear clusters of arbitrary shape and nuclearity, and hence is of general validity and usefulness in the study of magnetic metal clusters. The successful application of the new approach presented here is a first step in the effort to establish correlations between the available spectroscopic information and the structural features of complex metalloenzymes like OEC.
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| 6. |
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| 7. |
- Türk, Karin, et al.
(författare)
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NADH oxidation by the Na+-translocating NADH : quinone oxidoreductase from Vibrio cholerae
- 2004
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 279:20, s. 21349-21355
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Tidskriftsartikel (refereegranskat)abstract
- The Na(+)-translocating NADH:quinone oxidoreductase from Vibrio cholerae is a six subunit enzyme containing four flavins and a single motif for the binding of a Fe-S cluster on its NqrF subunit. This study reports the production of a soluble variant of NqrF (NqrF') and its individual flavin and Fe-S-carrying domains using V. cholerae or Escherichia coli as expression hosts. NqrF' and the flavin domain each contain 1 mol of FAD/mol of enzyme and exhibit high NADH oxidation activity (20,000 micromol min(-1) mg(-1)). EPR, visible absorption, and circular dichroism spectroscopy indicate that the Fe-S cluster in NqrF' and its Fe-S domain is related to 2Fe ferredoxins of the vertebrate-type. The addition of NADH to NqrF' results in the formation of a neutral flavosemiquinone and a partial reduction of the Fe-S cluster. The NqrF subunit harbors the active site of NADH oxidation and acts as a converter between the hydride donor NADH and subsequent one-electron reaction steps in the Na(+)-translocating NADH:quinone oxidoreductase complex. The observed electron transfer NADH --> FAD --> [2Fe-2S] in NqrF requires positioning of the FAD and the Fe-S cluster in close proximity in accordance with a structural model of the subunit.
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