Crystal Structure of the Peroxo-diiron(III) Intermediate of Deoxyhypusine Hydroxylase, an Oxygenase Involved in Hypusination.

Deoxyhypusine hydroxylase (DOHH) is a non-heme diiron enzyme involved in the posttranslational modification of a critical lysine residue of eukaryotic translation initiation factor 5A (eIF-5A) to yield the unusual amino acid residue hypusine. This modification is essential for the role of eIF-5A in translation and in nuclear export of a group of specific mRNAs. The diiron center of human DOHH (hDOHH) forms a peroxo-diiron(III) intermediate (hDOHHperoxo) when its reduced form reacts with O2.

Ferric ion (hydr)oxo clusters in the "Venus flytrap" cleft of FbpA: Mössbauer, calorimetric and mass spectrometric studies.

Isothermal calorimetric studies of the binding of iron(III) citrate to ferric ion binding protein from Neisseria gonorrhoeae suggested the complexation of a tetranuclear iron(III) cluster as a single step binding event (apparent binding constant K(app) (ITC) = 6.0(5) × 10(5) M(-1)). High-resolution Fourier transform ion cyclotron resonance mass spectrometric data supported the binding of a tetranuclear oxo(hydroxo) iron(III) cluster of formula [Fe(4)O(2)(OH)(4)(H(2)O)(cit)](+) in the interdomain binding cleft of FbpA.

Interpretation of nuclear resonant vibrational spectra of rubredoxin using a combined quantum mechanics and molecular mechanics approach.

Nuclear resonant vibrational spectra of the reduced and oxidized form of a mutant of rubredoxin from Pyrococcus abyssii were measured and are compared with simulated spectra that were calculated by a combined quantum mechanics (QM) and molecular mechanics (MM) method. Density functional theory was used for the QM level. Calculations were performed for different models of rubredoxin.

Aspartate 141 is the fourth ligand of the oxygen-sensing [4Fe-4S]2+ cluster of Bacillus subtilis transcriptional regulator Fnr.

The Bacillus subtilis redox regulator Fnr controls genes of the anaerobic metabolism in response to low oxygen tension. An unusual structure for the oxygen-sensing [4Fe-4S](2+) cluster was detected by a combination of genetic experiments with UV-visible and Mössbauer spectroscopy. Asp-141 was identified as the fourth iron-sulfur cluster ligand besides three Cys residues.

Isoprenoid biosynthesis via the MEP pathway: in vivo Mössbauer spectroscopy identifies a [4Fe-4S]2+ center with unusual coordination sphere in the LytB protein.

The MEP pathway for the biosynthesis of isoprene units is present in most pathogenic bacteria, in the parasite responsible for malaria, and in plant plastids. This pathway is absent in animals and is accordingly a target for the development of antimicrobial drugs. LytB, also called IspH, the last enzyme of this pathway catalyzes the conversion of (E)-4-hydroxy-3-methylbut-2-enyl diphosphate (HMBPP) into a mixture of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) using an oxygen sensitive iron sulfur cluster.

Characterization of L-aspartate oxidase and quinolinate synthase from Bacillus subtilis.

NAD is an important cofactor and essential molecule in all living organisms. In many eubacteria, including several pathogens, the first two steps in the de novo synthesis of NAD are catalyzed by l-aspartate oxidase (NadB) and quinolinate synthase (NadA). Despite the important role played by these two enzymes in NAD metabolism, many of their biochemical and structural properties are still largely unknown.

A purple acidophilic di-ferric DNA ligase from Ferroplasma.

We describe here an extraordinary purple-colored DNA ligase, LigFa, from the acidophilic ferrous iron-oxidizing archaeon Ferroplasma acidiphilum, a di-ferric enzyme with an extremely low pH activity optimum. Unlike any other DNA ligase studied to date, LigFa contains two Fe(3+)-tyrosinate centers and lacks any requirement for either Mg(2+) or K(+) for activity. DNA ligases from closest phylogenetic and ecophysiological relatives have normal pH optima (6.

Crystallographic and spectroscopic studies of peroxide-derived myoglobin compound II and occurrence of protonated FeIV O.

High resolution crystal structures of myoglobin in the pH range 5.2-8.7 have been used as models for the peroxide-derived compound II intermediates in heme peroxidases and oxygenases.

Estimate of the vibrational contribution to the entropy change associated with the spin transition in the d4 systems [MnIII(pyrol)3tren] and [CrII(depe)2I2].

The vibrational contribution to DeltaS of the low-spin ((3)T(1)) to high-spin ((5)E) spin transition in two 3d(4) octahedral systems [Mn(III)(pyrol)(3)tren] and [Cr(depe)(2)I(2)] have been estimated by means of DFT calculations (B3LYP/CEP-31G) of the vibrational normal-modes frequencies. The obtained value at the transition temperature for the Mn(iii) complex is DeltaS(vib)(44 K) = 6.3 J K(-1) mol(-1), which is comparable with the proposed Jahn-Teller contribution of R ln3 = 9.

Vibrational spectrum of the spin crossover complex [Fe(phen)(2)(NCS)(2)] studied by IR and Raman spectroscopy, nuclear inelastic scattering and DFT calculations.

The vibrational modes of the low-spin and high-spin isomers of the spin crossover complex [Fe(phen)(2)(NCS)(2)] (phen = 1,10-phenanthroline) have been measured by IR and Raman spectroscopy and by nuclear inelastic scattering. The vibrational frequencies and normal modes and the IR and Raman intensities have been calculated by density functional methods. The vibrational entropy difference between the two isomers, DeltaS(vib), which is--together with the electronic entropy difference DeltaS(el)--the driving force for the spin-transition, has been determined from the measured and from the calculated frequencies.

A range of spin-crossover temperature T1/2>300 K results from out-of-sphere anion exchange in a series of ferrous materials based on the 4-(4-imidazolylmethyl)-2-(2-imidazolylmethyl)imidazole (trim) ligand, [Fe(trim)2]X2 (X=F, Cl, Br, I): comparison of experimental results with those derived from density functional theory calculations.

The synthesis and characterization of [FeII(trim)2]Cl2 (2), [FeII(trim)2]Br2MeOH (3), and [FeII(trim)2]I2MeOH (4), including the X-ray crystal structure determinations of 2 (50 and 293 K) and 4 (293 K), have been performed and their properties have been examined. In agreement with the magnetic susceptibility results, the Mössbauer data show the presence of high-spin (HS) to low-spin (LS) crossover with a range of T1/2 larger than 300 K (from approximately 20 K for [FeII(trim)2]F2 (1) to approximately 380 K for 4). All complexes in this series include the same [Fe(trim)2]2+ complex cation: the ligand field comprises a constant contribution from the trim ligands and a variable one originating from the out-of-sphere anions, which is transmitted to the metal center by the connecting imidazole rings and hydrogen bonds.

Bacillus subtilis Fnr senses oxygen via a [4Fe-4S] cluster coordinated by three cysteine residues without change in the oligomeric state.

The oxygen regulator Fnr is part of the regulatory cascade in Bacillus subtilis for the adaptation to anaerobic growth conditions. In vivo complementation experiments revealed the essential role of only three cysteine residues (C227, C230, C235) at the C-terminus of B. subtilis Fnr for the transcriptional activation of the nitrate reductase operon (narGHJI) and nitrite extrusion protein gene (narK) promoters.

The [Fe(III)[Fe(III)(L1)2]3] star-type single-molecule magnet.

Star-shaped complex [Fe(III)[Fe(III)(L1)2]3] (3) was synthesized starting from N-methyldiethanolamine H2L1 (1) and ferric chloride in the presence of sodium hydride. For 3, two different high-spin iron(III) ion sites were confirmed by Mössbauer spectroscopy at 77 K. Single-crystal X-ray structure determination revealed that 3 crystallizes with four molecules of chloroform, but, with only three molecules of dichloromethane.

Low-temperature EPR and Mössbauer spectroscopy of two cytochromes with His-Met axial coordination exhibiting HALS signals.

C-type cytochromes with histidine-methionine (His-Met) iron coordination play important roles in electron-transfer reactions and in enzymes. Low-temperature electron paramagnetic resonance (EPR) spectra of low-spin ferric cytochromes c can be divided into two groups, depending on the spread of g values: the normal rhombic ones with small g anisotropy and g(max) below 3.2, and those featuring large g anisotropy with g(max) between 3.

Synthesis and characterization of metal-centered, six-membered, mixed-valent, heterometallic wheels of iron, manganese, and indium.

Heptanuclear metal-centered, six-membered, mixed-valent, heterometallic wheels 1-3 of iron, manganese, and indium were prepared in a one-pot reaction from N-benzyldiethanolamine (H2L(1)), cesium carbonate, [PPh4]2[MnCl4], and FeCl3 or InCl3. All three complexes were characterized by the combination of elemental analysis, FAB mass spectroscopy, X-ray diffraction and cyclic voltammetry and in the case of 1 additionally by Mössbauer spectroscopy. In 1, four Mn(II) ions in the periphery are arranged in pairs alternating with one Fe(III) ion each, with an Fe(III) ion located in the center.

Models of the membrane-bound cytochromes: mössbauer spectra of crystalline low-spin ferriheme complexes having axial ligand plane dihedral angles ranging from 0 degree to 90 degrees.

Crystalline samples of four low-spin Fe(III) octaalkyltetraphenylporphyrinate and two low-spin Fe(III) tetramesitylporphyrinate complexes, all of which are models of the bis-histidine-coordinated cytochromes of mitochondrial complexes II, III, and IV and chloroplast complex b(6)f, and whose molecular structures and EPR spectra have been reported previously, have been investigated in detail by Mössbauer spectroscopy. The six complexes and the dihedral angles between axial ligand planes of each are [(TMP)Fe(1-MeIm)(2)]ClO(4) (0 degree), paral-[(OMTPP)Fe(1-MeIm)(2)]Cl (19.5 degrees), paral-[(TMP)Fe(5-MeHIm)(2)]ClO(4) (26 degrees, 30 degrees for two molecules in the unit cell whose EPR spectra overlap), [(OETPP)Fe(4-Me(2)NPy)(2)]Cl (70 degrees), perp-[(OETPP)Fe(1-MeIm)(2)]Cl (73 degrees), and perp-[(OMTPP)Fe(1-MeIm)(2)]Cl (90 degrees).

Spectroscopic characterization of the iron-oxo intermediate in cytochrome P450.

From analogy to chloroperoxidase from Caldariomyces fumago, it is believed that the electronic structure of the intermediate iron-oxo species in the catalytic cycle of cytochrome P450 corresponds to an iron(IV) porphyrin-pi-cation radical (compound I). However, our recent studies on P450cam revealed that after 8 ms a tyrosine radical and iron(IV) were formed in the reaction of ferric P450 with external oxidants in the shunt pathway. The present study on the heme domain of P450BM3 (P450BMP) shows a similar result.

Homo-/heterotrinuclear mixed-valent oxo-centered iron/nickel clusters-Mössbauer studies on internal electron-exchange processes.

In a one-pot reaction of N-(5-methylthiazole-2-yl)-thiazole-2-carboxamide HL2 (3) with iron(II) acetate in air, the homotrinuclear heteroleptic mixed-valent oxo-centered iron cluster [Fe(II)Fe(III)O(L2)3(OAc)3] (4) was formed. Exchange of iron(II) in 4 by nickel(II) afforded the heteronuclear cluster [Ni(II)Fe(III)O(L2)3(OAc)3] (6). To obtain crystals suitable for X-ray structure analyses, in 4 and 6, the OAc- co-ligands were exchanged by OBz- ligands to give [Fe(II)Fe2(III)O(L2)3(OBz)3] (5) and [Ni(II)Fe(III)O(L2)3(OBz)3] (7).

Radical S-adenosylmethionine enzyme coproporphyrinogen III oxidase HemN: functional features of the [4Fe-4S] cluster and the two bound S-adenosyl-L-methionines.

The S-adenosylmethionine (AdoMet) radical enzyme oxygen-independent coproporphyrinogen III oxidase HemN catalyzes the oxidative decarboxylation of coproporphyrinogen III to protoporphyrinogen IX during bacterial heme biosynthesis. The recently solved crystal structure of Escherichia coli HemN revealed the presence of an unusually coordinated iron-sulfur cluster and two molecules of AdoMet. EPR spectroscopy of the reduced iron-sulfur center in anaerobically purified HemN in the absence of AdoMet has revealed a [4Fe-4S](1+) cluster in two slightly different conformations.

Isoprenoid biosynthesis in chloroplasts via the methylerythritol phosphate pathway: the (E)-4-hydroxy-3-methylbut-2-enyl diphosphate synthase (GcpE) from Arabidopsis thaliana is a [4Fe-4S] protein.

The mevalonate-independent methylerythritol phosphate pathway is widespread in bacteria. It is also present in the chloroplasts of all phototrophic organisms. Whereas the first steps, are rather well known, GcpE and LytB, the enzymes catalyzing the last two steps have been much less investigated.

Molecular structure and vibrational spectra of spin-crossover complexes in solution and colloidal media: resonance Raman and time-resolved resonance Raman studies.

The spin-crossover system [Fe(btpa)](PF(6))(2) (btpa = N,N,N',N'-tetrakis(2-pyridylmethyl)-6,6'-bis(aminomethyl)-2,2'-bipyridine) and the predominantly low-spin species [Fe(b(bdpa))](PF(6))(2) ((b(bdpa) = N,N'-bis(benzyl)-N,N'-bis(2-pyridylmethyl)-6,6'-bis(aminomethyl)-2,2'-bipyridine) have been characterized by means of X-ray diffraction. The unit cell of [Fe(btpa)](PF(6))(2) contains two crystallographically independent molecules revealing octahedral low-spin and quasi-seven-coordinated high-spin structures. The unit cell of [Fe(b(bdpa))](PF(6))(2) contains two crystallographically independent molecules one of which corresponds to a low-spin structure, while the other reveals a disordering.

FhuF, part of a siderophore-reductase system.

FhuF is a cytoplasmic 2Fe-2S protein of Escherichia coli loosely associated with the cytoplasmic membrane. E. coli fhuF mutants showed reduced growth on plates with ferrioxamine B as the sole iron source, although siderophore uptake was not defective in transport experiments.

Tyrosine radical formation in the reaction of wild type and mutant cytochrome P450cam with peroxy acids: a multifrequency EPR study of intermediates on the millisecond time scale.

We report a multifrequency (9.6-, 94-, 190-, and 285-GHz) EPR study of a freeze-quenched intermediate obtained from reaction of substrate-free cytochrome P450cam (CYP101) and its Y96F and Y96F/Y75F mutants with peroxy acids. It is generally assumed that in such a shunt reaction an intermediate [Fe(IV)=O, porphyrin-pi-cation radical] is formed, which should be identical to the species in the natural reaction cycle.

Iron-binding characteristics of neuromelanin of the human substantia nigra.

The vulnerability of the dopaminergic neurons of the substantia nigra (SN) in Parkinson's disease has been related to the presence of the pigment neuromelanin (NM) in these neurons. It is hypothesised that NM may act as an endogenous storage molecule for iron, an interaction suggested to influence free radical production. The current study quantified and characterised the interaction between NM and iron.