David L Tierney

Miami University, Оксфорд, Ohio, United States

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Publications (72)391.08 Total impact

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    ABSTRACT: Scorpionate chemistry has long featured sandwich complexes with two trispyrazolylborate (Tp) or two bispyrazolylborate (Bp) ligands coordinated to a transition metal. Less common are complexes in which one Tp and one Bp ligand are coordinated to the metal. We report herein five such complexes of NiII, MnII, CoII, or FeII involving Tp and Bp ligands comprising either 3-phenyl-4-cyanopyrazole or 3-phenylpyrazole, as well as a related CoII complex with two Tp ligands, one of which is coordinated in a κ2 fashion. All complexes feature an agostic interaction with a B–H hydrogen atom.
    No preview · Article · Jan 2016 · Berichte der deutschen chemischen Gesellschaft
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    ABSTRACT: Metal ions in metallo-β-lactamases (MBLs) play a major role in catalysis. In this study we investigated the role of the metal ions in the Zn1 and Zn2 sites of MBL L1 during catalysis. A ZnCo (with Zn(II) in the invariant Zn1 site and Co(II) in the Zn2 site) analog of MBL L1 was prepared by using a biological incorporation method. Extended X-ray absorption fine structure (EXAFS) spectroscopic studies were used to confirm that the ZnCo analog was prepared. To study the roles of the Zn(II) and Co(II) ions during catalysis, rapid freeze quench (RFQ)-EXAFS studies were used to probe the reaction of the ZnCo-L1 analog with chromacef when quenched at 10 ms, 50 ms, and 100 ms. The L1-product complex was also analyzed with EXAFS spectroscopy. The data show that the Zn–Co distance is 3.49 Å in the resting enzyme and that this distance increases by 0.3 Å in the sample that was quenched at 10 ms. The average Zn–Co distance decreases at the other time points until reaching a distance of 3.58 Å in the L1-product complex. The data also show that a Co–S interaction is present in the 100 ms quenched sample and in the L1-product complex, which suggests that there is a significant rearrangement of product in the active site.
    Full-text · Article · Jan 2016 · Medicinal Chemistry Communication
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    ABSTRACT: In an effort to examine the relative position of a hairpin loop in New Delhi metallo-β-lactamase, NDM-1, during catalysis, rapid freeze quench double electron electron resonance (RFQ-DEER) spectroscopy was used. A doubly-labeled mutant of NDM-1, which had one spin label on the invariant loop at position 69 and another label at position 235, was prepared and characterized. The reaction of the doubly spin labeled mutant with chromacef was freeze quenched at 500 μs and 10 ms. DEER results showed that the average distance between labels decreased by 4 Å in the 500 μs quenched sample and by 2 Å in the 10 ms quenched sample, as compared to the distance in the unreacted enzyme, although the peaks corresponding to distance distributions were very broad. DEER spectra with the doubly spin labeled enzyme with two inhibitors showed that the distance between the loop residue at position 69 and the spin label at position 235 does not change upon inhibitor binding. This study suggests that the hairpin loop in NDM-1 moves over the metal ion during the catalysis and then moves back to its original position after hydrolysis, which is consistent with a previous hypothesis based on NMR solution studies on a related metallo-β-lactamase. This study also demonstrates that this loop motion occurs in the millisecond time domain.
    Full-text · Article · Oct 2015 · Journal of inorganic biochemistry
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    ABSTRACT: The hydrogen bonding ligand, 3-NH(t-butyl)-5-methyl-pyrazole, forms "scorpionate-like" first row transition metal complexes that are held together by hydrogen bonds rather than covalent bonds. The formulae of these complexes are (LH) n MX2, where n =3, 4; X=Cl, Br; and LH=3-NH(t-butyl)-5-methyl-pyrazole. The amino-substituted pyrazole can hydrogen bond via both the amino group and the pyrazole NH to form intramolecular NH to halide hydrogen bonds. These complexes have been well characterized and show a 3:1 ratio of ligand to metal for zinc and cobalt (1 and 2), and a 4:1 ratio of ligand to metal for manganese and nickel (3 and 4). The hydrogen bonding interactions appear to be stronger for the 3:1 complexes. The crystallographic and spectroscopic studies (EPR and NMR) have shown that these hydrogen-bonding interactions are strong enough to perturb metal halogen bond distances and, with non-hydrogen bonding solvents, the hydrogen bonds appear to hold these complexes together in solution.
    No preview · Article · Oct 2015 · Polyhedron
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    ABSTRACT: The [Ga(III)3(3,5-diCl-Sal-AHA)3(μ-OCH3)]− anion crystallizes with one K+ and one H3O+ counter ion between each pair of anions. The structure is analogous to the previously reported [Fe(III)3(3,5-diCl-Sal-AHA)3(μ-OCH3)]−, with each containing a M3O4 incomplete cubane at the base of a phenyl-derived pocket that surrounds a triply bridging methoxy group. The EPR spectrum of [Fe(III)3(3,5-diCl-Sal-AHA)3(μ-OCH3)]− at 4.5 K is complex with features near geff = 2, 4.3, and above 5. Only the 4.30 feature maintains intensity much above 30 K, and it persists to above 150 K. Room temperature magnetic susceptibility measurements indicate an average spin of S = 5/2 per trimer in both solid and solution. Both the Ga and Fe clusters are stable in methanol. However, the Ga complex slowly decomposes in 40% water or in the presence of EDTA, while the Fe cluster does not. Experiments with a mixed Fe/Ga solution show that the order of stability of the [M(III)3(3,5-diCl-Sal-AHA)3(μ-OCH3)]−, clusters in the presence of EDTA is M(III)3 = Fe3 > Fe2Ga > FeGa2 > Ga3. Metal or chelate exchange occurs very slowly (weeks to months) if at all. However, the μ3-methoxy bridge can be replaced by deuterated methoxy or a μ3-hydroxy bridge within hours to days.
    No preview · Article · Aug 2015 · Polyhedron
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    ABSTRACT: Cobalt is a metal contaminant at high temperature radioactive waste disposal sites. Past studies have largely focused on mesophilic microorganisms to remediate cobalt, despite the presence of thermophilic microorganisms at such sites. In this study, Methanothermobacter thermautotrophicus, a thermophilic methanogen, was used to reduce Co(III) in the form of [Co(III)-EDTA]−. Bioreduction experiments were conducted in a growth medium with H2/CO2 as a growth substrate at initial Co(III) concentrations of 1, 2, 4, 7, and 10 mM. At low Co(III) concentrations (< 4 mM), a complete reduction was observed within a week. Wet chemistry, X-ray absorption near-edge structure (XANES) and electron paramagnetic resonance (EPR) analyses were all consistent in revealing the reduction kinetics. However, at higher concentrations (7 and 10 mM) the reduction extents only reached 69.8% and 48.5%, respectively, likely due to the toxic effect of Co(III) to the methanogen cells as evidenced by a decrease in total cellular protein at these Co(III) concentrations. Methanogenesis was inhibited by Co(III) bioreduction, possibly due to impaired cell growth and electron diversion from CO2 to Co(III). Overall, our results demonstrated the ability of M. thermautotrophicus to reduce Co(III) to Co(II) and its potential application for remediating 60Co contaminant at high temperature subsurface radioactive waste disposal sites.
    Full-text · Article · Jun 2015 · Chemical Geology
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    ABSTRACT: Matrix metalloproteinase-1 (MMP-1) plays crucial roles in diseases-related physiologies and pathological processes in the human body. We report here solution studies of MMP-1, including characterization of a series of mutants designed to bind metal in either the catalytic site or the structural site (but not both). CD and fluorescence spectroscopy of the mutants demonstrate the importance of the structural Zn(II) to maintaining both secondary and tertiary structure, while UV-vis, NMR, EPR and EXAFS show its presence influences the catalytic metal ion's coordination number. The mutants allow us to demonstrate convincingly the preparation of a mixed-metal analog, CoCZnS-MMP-1, with Zn(II) in the structural site and Co(II) in the catalytic site. Stopped-flow fluorescence of the native, ZnCZnS-MMP-1, and the mixed-metal CoCZnS-MMP-1 analog, show that the internal fluorescence of a nearby Trp residue modulates with catalysis and can be used to monitor reactivity under a number of conditions.
    Full-text · Article · May 2015 · Biochemistry
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    ABSTRACT: Despite significant progress on iron reduction by thermophilic microorganisms, studies on their ability to reduce toxic metals are still limited, despite their common co-existence in high temperature environments (up to 70 °C). In this study, Methanothermobacter thermautotrophicus, an obligate thermophilic methanogen, was used to reduce hexavalent chromium. Experiments were conducted in a growth medium with H2/CO2 as substrate with various Cr6+ concentrations (0.2, 0.4, 1, 3, and 5 mM) in the form of potassium dichromate (K2Cr2O7). Time-course measurements of aqueous Cr6+ concentrations using 1,5-diphenylcarbazide colorimetric method showed complete reduction of the 0.2 and 0.4 mM Cr6+ solutions by this methanogen. However, much lower reduction extents of 43.6%, 13.0%, and 3.7% were observed at higher Cr6+ concentrations of 1, 3 and 5 mM, respectively. These lower extents of bioreduction suggest a toxic effect of aqueous Cr6+ to cells at this concentration range. At these higher Cr6+ concentrations, methanogenesis was inhibited and cell growth was impaired as evidenced by decreased total cellular protein production and live/dead cell ratio. Likewise, Cr6+ bioreduction rates decreased with increased initial concentrations of Cr6+ from 13.3 to 1.9 μM h-1. X-ray absorption near-edge structure (XANES) spectroscopy revealed a progressive reduction of soluble Cr6+ to insoluble Cr3+ precipitates, which was confirmed as amorphous chromium hydroxide by selected area electron diffraction pattern. However, a small fraction of reduced Cr occurred as aqueous Cr3+. Scanning and transmission electron microscope observations of M. thermautotrophicus cells after Cr6+ exposure suggest both extra- and intracellular chromium reduction mechanisms. Results of this study demonstrate the ability of M. thermautotrophicus cells to reduce toxic Cr6+ to less toxic Cr3+ and its potential application in metal bioremediation, especially at high temperature subsurface radioactive waste disposal sites, where the temperature may reach ∼70 °C.
    Full-text · Article · Nov 2014 · Geochimica et Cosmochimica Acta
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    ABSTRACT: This study examines metal binding to metallo-β-lactamase VIM-2, demonstrating the first successful preparation of a Co(II)-substituted VIM-2 analog. Spectroscopic studies of the half- and fully-metal loaded enzymes show that both Zn(II) and Co(II) bind cooperatively, where the major species present, regardless of stoichiometry, are apo- and di-Zn (or di-Co) enzymes. We determined the di-Zn VIM-2 structure to a resolution of 1.55 Å, and this structure supports results from spectroscopic studies. Kinetics, both steady-state and pre-steady-state, show that VIM-2 utilizes a mechanism that proceeds through a very short-lived anionic intermediate when chromacef is used as the substrate. Comparison with other B1 enzymes shows that those that bind Zn(II) cooperatively are better poised to protonate the intermediate on its formation, compared to those that bind Zn(II) non-cooperatively, which uniformly build up substantial amounts of the intermediate.
    Full-text · Article · Oct 2014 · Biochemistry
  • David L Tierney · Gerhard Schenk
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    ABSTRACT: In this mini-review, we briefly discuss the physical origin of x-ray absorption spectroscopy (XAS) before illustrating its application using dinuclear metallohydrolases as exemplary systems. The systems we have selected for illustrative purposes present a challenging problem for XAS, one that is ideal to demonstrate the potential of this methodology for structure/function studies of metalloenzymes in general. When the metal ion is redox active, XAS provides a sensitive measure of oxidation-state-dependent differences. When the metal ion is zinc, XAS is the only spectroscopic method that will provide easily accessible structural information in solution. In the case of heterodimetallic sites, XAS has the unique ability to interrogate each metal site independently in the same sample. One of the strongest advantages of XAS is its ability to examine metal ion site structures with crystallographic precision, without the need for a crystal. This is key for studying flexible metal ion sites, such as those described in the selected examples, because it allows one to monitor structural changes that occur during substrate turnover.
    No preview · Article · Sep 2014 · Biophysical Journal
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    ABSTRACT: Zinc finger proteins that bind Zn(II) using a Cys2His2 coordination motif within a ββα protein fold are the most abundant DNA binding transcription factor domains in eukaryotic systems. These classic zinc fingers are typically unfolded in the apo state and spontaneously fold into their functional ββα folds upon incorporation of Zn(II). These metal-induced protein folding events obscure the free energy cost of protein folding by coupling the protein folding and metal-ion binding thermodynamics. Herein, we determine the formation constant of a Cys2His2/ββα zinc finger domain, the C-terminal finger of the Wilms' tumor suppressor protein (WT1-4), for the purposes of determining its free energy cost of protein folding. Measurements of individual conditional dissociation constants, Kd values, at pH values from 5 to 9 were determined using fluorescence spectroscopy by direct or competition titration. Potentiometric titrations of apo-WT1-4 followed by NMR spectroscopy provided the intrinsic pKa values of the Cys2His2 residues, and corresponding potentiometric titrations of Zn(II)-WT1-4 followed by fluorescence spectroscopy yielded the effective pKa(eff) values of the Cys2His2 ligands bound to Zn(II). The Kd, pKa, and pKa(eff) values were combined in a minimal, complete equilibrium model to yield the pH-independent formation constant value for Zn(II)-WT1-4, Kf(ML) value of 7.5 × 10(12) M(-1), with a limiting Kd value of 133 fM. This shows that Zn(II) binding to the Cys2His2 site in WT1-4 provides at least -17.6 kcal/mol in driving force to fold the protein scaffold. A comparison of the conditional dissociation constants of Zn(II)-WT1-4 to those from the model peptide Zn(II)-GGG-Cys2His2 over the pH range 5.0 to 9.0 and a comparison of their pH-independent Kf(ML) values demonstrates that the free energy cost of protein folding in WT1-4 is less than +2.1 kcal/mol. These results validate our GGG model system for determining the cost of protein folding in natural zinc finger proteins and support the conclusion that the cost of protein folding in most zinc finger proteins is ≤+4.2 kcal/mol, a value that pales in comparison to the free energy contribution of Zn(II) binding, -17.6 kcal/mol.
    Preview · Article · Jun 2014 · Inorganic Chemistry
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    ABSTRACT: A mononuclear Cu(II) chlorodiketonate complex was prepared, characterized, and found to undergo oxidative aliphatic carbon-carbon bond cleavage within the diketonate unit upon exposure to O2 at ambient temperature. Mechanistic studies provide evidence for a dioxygenase-type carbon-carbon bond cleavage reaction pathway involving trione and hypochlorite intermediates. Significantly, the presence of a catalytic amount of chloride ion accelerates the oxygen activation step via the formation of a Cu-Cl species, which facilitates monodentate diketonate formation and lowers the barrier for O2 activation. The observed reactivity and chloride catalysis is relevant to Cu(II) halide catalyzed reactions in which diketonates are oxidatively cleaved using O2 as the terminal oxidant. The results of this study suggest that anion coordination can play a significant role in influencing copper-mediated oxygen activation in such systems.
    No preview · Article · May 2014 · Journal of the American Chemical Society
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    ABSTRACT: In an effort to characterize the roles of each metal ion in metallo-beta-lactamase NDM-1, heterodimetallic analogs (CoCo-, ZnCo-, and CoCd-) of the enzyme were generated and characterized. UV-visible, 1H NMR, EPR and EXAFS spectroscopies were used to confirm the fidelity of the metal substitutions, including the presence of a homogeneous, heterodimetallic cluster, with a single-atom bridge. This marks the first preparation of a metallo-beta-lactamase, selectively substituted with a paramagnetic metal ion, Co(II), in either the Zn1 (CoCd-NDM-1) or in the Zn2 site (ZnCo-NDM-1), as well as both (CoCo-NDM-1). We then used these metal-substituted forms of the enzyme to probe the reaction mechanism, using steady-state and stopped-flow kinetics, stopped-flow fluorescence and rapid-freeze-quench EPR. Both metal sites show significant effects on the kinetic constants, and both paramagnetic variants (CoCd- and ZnCo-NDM-1) showed significant structural changes on reaction with substrate. These changes are discussed in terms of a minimal kinetic mechanism that incorporates all of the data.
    Full-text · Article · Apr 2014 · Journal of the American Chemical Society
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    ABSTRACT: The binding of three closely related chelators: 5-hydroxy-2-methyl-4H-pyran-4-thione (allothiomaltol, ATM), 3-hydroxy-2-methyl-4H-pyran-4-thione (thiomaltol, TM), and 3-hydroxy-4H-pyran-4-thione (thiopyromeconic acid, TPMA) to the active site of human carbonic anhydrase II (hCAII) has been investigated. Two of these ligands display a monodentate mode of coordination to the active site Zn2+ ion in hCAII that is not recapitulated in model complexes of the enzyme active site. This unprecedented binding mode in the hCAII-thiomaltol complex has been characterized by both X-ray crystallography and X-ray spectroscopy. In addition, the steric restrictions of the active site force the ligands into a 'flattened' mode of coordination compared with inorganic model complexes. This change in geometry has been shown by density functional computations to significantly decrease the strength of the metal-ligand binding. Collectively, these data demonstrate that the mode of binding by small metal-binding groups (MBGs) can be significantly influenced by the protein active site. Diminishing the strength of the metal-ligand bond results in unconventional modes of metal coordination not found in typical coordination compounds or even carefully engineered active site models, and understanding these effects is critical to the rational design of inhibitors that target clinically relevant metalloproteins.
    Preview · Article · Mar 2014 · Journal of the American Chemical Society
  • Aliyar Mousavi · Amy R. Marts · David L. Tierney · Stephen E. Cabaniss
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    ABSTRACT: The structure of Zn(II) complexes with dissolved organic matter (DOM) is an important consideration in developing molecular-level models of Zn(II) speciation, but recent reports favoring the tetrahedral geometry differ from earlier findings that geometry was largely octahedral. In general, the presence of thiolate ligands favors the tetrahedral geometry, while O and N ligands favor the octahedral geometry. This work presents extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectroscopic results, indicating an octahedral geometry over the pH range of 5–9 for a freshwater DOM isolate. Changes in XANES derivatives as a function of pH can be explained in terms of ligand protonation and/or changing ligand groups. Tetrahedral Zn(II)–DOM geometry may be restricted to binding environments containing thiol groups.
    No preview · Article · Jan 2013 · Toxicological and Environmental Chemistry
  • David L Tierney
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    ABSTRACT: NMR paramagnetic relaxation enhancements (PREs) of a series of structurally-characterized, trigonal bistrispyrazolylborate (Tp) chelates of high-spin Co(II), spanning 100 - 850 MHz in field, are reported. Prior knowledge of the metal-nucleus distances allows numerical extraction of position-dependent electron spin relaxation rates (tc-1) from direct measurement of the individual PREs of the four symmetry distinct protons in Co(Tp)2, using available closed-form expressions. The data for this electronically complex system where spin-orbit coupling defines the ground state electronic structure are analyzed in terms of the Solomon-Bloembergen-Morgan (SBM) relations, as well as available zero-field splitting limit theories. A simple angular correction is shown to be sufficient to reconcile the individual tc(T) data for the four classes of protons. The data identify a previously unrecognized dynamic Jahn-Teller effect in these historically important complexes, with a barrier of ~ 230 cm-1, pointing to a level of dynamics in trispyrazolylborate chemistry that has not been described before, and further show that it is the Jahn-Teller that is responsible for the PREs in fluid solution. A field-dependent component is also identified for the two protons nearest g||, which is suggested to arise due to Zeeman mixing of excited state character into the ground level.
    No preview · Article · Oct 2012 · The Journal of Physical Chemistry A
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    ABSTRACT: Irradiation of 3-hydroxyflavonolato (3-Hfl) complexes of MnII, CoII, NiII and CuII (1–4) at 300 nm under aerobic conditions results in dioxygenase-type reactivity and the formation of the corresponding divalent metal O-benzoylsalicylato (O-bs) complexes 8–11 and CO. The latter were characterized by using multiple methods, including elemental analysis, X-ray crystallography, NMR and/or EPR spectroscopy, mass spectrometry and IR spectroscopy. Compounds 1–4 serve as catalysts for the photoinduced reactivity of 3-hydroxyflavonol (3-HflH) to produce O-benzoylsalicylic acid as the major product. Spectroscopic studies (UV/Vis and 1H NMR) show that each O-benzoylsalicylato complex 8–11 reacts with one equiv. of 3-hydroxyflavonol to regenerate 1–4 and enable turnover reactivity. Unlike what is observed for free 3-HflH, photoinduced reactions involving 1–4 and excess flavonol show only minor amounts of flavonol isomerization reactivity. These results indicate that the presence of a metal ion, whether under stoichiometric or catalytic conditions, facilitates the photoinduced degradation of 3-HflH to produce a carboxylic acid and CO as products.
    No preview · Article · Oct 2012 · Berichte der deutschen chemischen Gesellschaft
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    ABSTRACT: In an effort to biochemically characterize metallo-β-lactamase NDM-1, we cloned, overexpressed, purified, and characterized several maltose binding protein (MBP)-NDM-1 fusion proteins with different N-termini (full-length, Δ6, Δ21, and Δ36). All MBP-NDM-1 fusion proteins were soluble; however, only one, MBP-NDM-1Δ36, exhibited high activity and bound 2 equiv of Zn(II). Thrombin cleavage of this fusion protein resulted in the truncated NDM-1Δ36 variant, which exhibited a k(cat) of 16 s(-1) and a K(m) of 1.1 μM when using nitrocefin as a substrate, bound 2 equiv of Zn(II), and was monomeric in solution. Extended X-ray absorption fine structure studies of the NDM-1Δ36 variant indicate the average metal binding site for Zn(II) in this variant consists of four N/O donors (two of which are histidines) and 0.5 sulfur donor per zinc, with a Zn-Zn distance of 3.38 Å. This metal binding site is very similar to those of other metallo-β-lactamases that belong to the B1 subclass. Pre-steady-state kinetic studies using nitrocefin and chromacef and the NDM-1Δ36 variant indicate that the enzyme utilizes a kinetic mechanism similar to that used by metallo-β-lactamases L1 and CcrA, in which a reactive nitrogen anion is stabilized and its protonation is rate-limiting. While they are very different in terms of amino acid sequence, these studies demonstrate that NDM-1 is structurally and mechanistically very similar to metallo-β-lactamase CcrA.
    Full-text · Article · Apr 2012 · Biochemistry
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    ABSTRACT: To successfully establish an infection, Acinetobacter baumannii must overcome the iron starvation and oxidative stress imposed by the human host. Although previous studies have shown that ATCC 19606T cells acquire iron via the acinetobactin-mediated siderophore system, little is known about intracellular iron metabolism and its relation to oxidative stress in this pathogen. Screening of an insertion library resulted in the isolation of the ATCC 19606T derivative 1644, which was unable to grow in iron-chelated media. Rescue cloning and DNA sequencing showed that the insertion inactivated a gene coding for an NfuA Fe-S cluster protein ortholog, without any effect on the expression of the acinetobactin system. The nfuA mutant was also more sensitive to hydrogen peroxide and cumene hydroperoxide than the parental strain. The iron chelation- and oxidative-stress-deficient responses of this mutant were corrected when complemented with either the ATCC 19606T parental allele or the Escherichia coli MG1655 nfuA ortholog. Furthermore, electron paramagnetic resonance (EPR) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analyses showed that the ATCC 19606T NfuA ortholog has iron-binding properties compatible with the formation of [Fe-S] cluster protein. Ex vivo and in vivo assays using human epithelial cells and Galleria mellonella, respectively, showed that NfuA is critical for bacterial growth independent of their capacity to acquire iron or the presence of excess of free iron. Taken together, these observations indicate that the A. baumannii NfuA ortholog plays a role in intracellular iron utilization and protection from oxidative-stress responses that this pathogen could encounter during the infection of the human host.
    Full-text · Article · Mar 2012 · Journal of bacteriology
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    ABSTRACT: The tris(3-phenyl-5-methyl-1,2,4-triazolyl)borate (Ttz(Ph,Me)) ligand provides intermediate steric bulk and forms predominantly bis(ligand) complexes of the form M(Ttz(Ph,Me))(2) with first row divalent transition metals (1(M), M = Zn, Cu, Ni, Co, Fe, Mn). Due to ligand field effects that are greatest with Ni and Cu, ligand rearrangement is favored with these metals and Cu(Ttz(Ph,Me)*)(2) (1(Cu)*) and (Ttz(Ph,Me)*)Ni(Ttz(Ph,Me)) (1(Ni)*) were isolated by selective recrystallization and fully characterized (* indicates a rearranged Ttz ligand with Ph and Me in swapped positions in one triazole ring). For comparison with Co(Ttz(Ph,Me))(2), the less bulky analogs (Ttz(H,H))(2)Co (4) and (Ttz(Me,Me))(2)Co (5) were studied by NMR and EPR spectroscopy, and 5 was crystallographically characterized. These complexes allow for a study of how slight changes in structure and electron donor properties (for Ni and Cu), as well as dramatic changes in steric bulk (for Co), influence the physical properties; specifically there are significant changes in the UV-Vis, EPR and NMR spectra. Bis(ligand) complexes predominate with all metals, but (Ttz(Ph,Me))Ni(OH(2))Cl (2) and (Ttz(Ph,Me))ZnBr (3) were also isolated and these show that Ttz(Ph,Me) is coordinatively flexible.
    Full-text · Article · Mar 2012 · Dalton Transactions

Publication Stats

2k Citations
391.08 Total Impact Points

Institutions

  • 2005-2015
    • Miami University
      • Department of Chemistry and Biochemistry
      Оксфорд, Ohio, United States
  • 2006-2012
    • University of New Mexico
      • Department of Chemistry and Chemical Biology
      Albuquerque, New Mexico, United States
  • 2007
    • Columbia University
      • Department of Chemistry
      New York City, NY, United States
  • 2005-2006
    • University of Texas at Austin
      • Division of Medicinal Chemistry
      Austin, Texas, United States
  • 1998-2005
    • Northwestern University
      • • Department of Cell and Molecular Biology
      • • Department of Chemistry
      Evanston, Illinois, United States
    • Johns Hopkins University
      Baltimore, Maryland, United States
  • 2002
    • New University of Lisbon
      • Faculty of Sciences and Technology
      Caparica, Distrito de Setubal, Portugal
  • 1993-1996
    • University of Michigan
      • Department of Chemistry
      Ann Arbor, Michigan, United States
    • Concordia University–Ann Arbor
      Ann Arbor, Michigan, United States