1
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Heit YN, Sergentu DC, Autschbach J. Magnetic circular dichroism spectra of transition metal complexes calculated from restricted active space wavefunctions. Phys Chem Chem Phys 2019; 21:5586-5597. [DOI: 10.1039/c8cp07849a] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Multiconfigurational restricted active space (RAS) self-consistent field (SCF) or configuration interaction (CI) approaches, augmented with a treatment of spin–orbit coupling by state interaction, were used to calculate the magnetic circular dichroism , , and/or for closed- and open-shell transition metal complexes.
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Affiliation(s)
- Yonaton N. Heit
- Department of Chemistry
- University at Buffalo, State University of New York
- Buffalo
- USA
| | | | - Jochen Autschbach
- Department of Chemistry
- University at Buffalo, State University of New York
- Buffalo
- USA
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2
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Park K, Li N, Kwak Y, Srnec M, Bell CB, Liu LV, Wong SD, Yoda Y, Kitao S, Seto M, Hu M, Zhao J, Krebs C, Bollinger JM, Solomon EI. Peroxide Activation for Electrophilic Reactivity by the Binuclear Non-heme Iron Enzyme AurF. J Am Chem Soc 2017; 139:7062-7070. [PMID: 28457126 DOI: 10.1021/jacs.7b02997] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Binuclear non-heme iron enzymes activate O2 for diverse chemistries that include oxygenation of organic substrates and hydrogen atom abstraction. This process often involves the formation of peroxo-bridged biferric intermediates, only some of which can perform electrophilic reactions. To elucidate the geometric and electronic structural requirements to activate peroxo reactivity, the active peroxo intermediate in 4-aminobenzoate N-oxygenase (AurF) has been characterized spectroscopically and computationally. A magnetic circular dichroism study of reduced AurF shows that its electronic and geometric structures are poised to react rapidly with O2. Nuclear resonance vibrational spectroscopic definition of the peroxo intermediate formed in this reaction shows that the active intermediate has a protonated peroxo bridge. Density functional theory computations on the structure established here show that the protonation activates peroxide for electrophilic/single-electron-transfer reactivity. This activation of peroxide by protonation is likely also relevant to the reactive peroxo intermediates in other binuclear non-heme iron enzymes.
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Affiliation(s)
- Kiyoung Park
- Department of Chemistry, Stanford University , Stanford, California 94305-5080, United States.,Department of Chemistry, KAIST , Daejeon 34141, Republic of Korea
| | - Ning Li
- Department of Biochemistry and Molecular Biology, Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Yeonju Kwak
- Department of Chemistry, Stanford University , Stanford, California 94305-5080, United States
| | - Martin Srnec
- Department of Chemistry, Stanford University , Stanford, California 94305-5080, United States
| | - Caleb B Bell
- Department of Chemistry, Stanford University , Stanford, California 94305-5080, United States
| | - Lei V Liu
- Department of Chemistry, Stanford University , Stanford, California 94305-5080, United States
| | - Shaun D Wong
- Department of Chemistry, Stanford University , Stanford, California 94305-5080, United States
| | | | - Shinji Kitao
- Research Reactor Institute, Kyoto University , Kumatori-cho, Osaka 590-0494, Japan
| | - Makoto Seto
- Research Reactor Institute, Kyoto University , Kumatori-cho, Osaka 590-0494, Japan
| | - Michael Hu
- Advanced Photon Source, Argonne National Laboratory , Lemont, Illinois 60439, United States
| | - Jiyong Zhao
- Advanced Photon Source, Argonne National Laboratory , Lemont, Illinois 60439, United States
| | - Carsten Krebs
- Department of Biochemistry and Molecular Biology, Pennsylvania State University , University Park, Pennsylvania 16802, United States.,Department of Chemistry, Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - J Martin Bollinger
- Department of Biochemistry and Molecular Biology, Pennsylvania State University , University Park, Pennsylvania 16802, United States.,Department of Chemistry, Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Edward I Solomon
- Department of Chemistry, Stanford University , Stanford, California 94305-5080, United States.,Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory , Stanford, California 94309, United States
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3
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Gendron F, Fleischauer VE, Duignan TJ, Scott BL, Löble MW, Cary SK, Kozimor SA, Bolvin H, Neidig ML, Autschbach J. Magnetic circular dichroism of UCl6− in the ligand-to-metal charge-transfer spectral region. Phys Chem Chem Phys 2017. [DOI: 10.1039/c7cp02572f] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
We present a combined ab initio theoretical and experimental study of the magnetic circular dichroism (MCD) spectrum of the octahedral UCl6− complex ion in the UV-Vis spectral region.
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Affiliation(s)
- Frédéric Gendron
- Department of Chemistry
- University at Buffalo
- State University of New York
- Buffalo
- USA
| | | | - Thomas J. Duignan
- Department of Chemistry
- University at Buffalo
- State University of New York
- Buffalo
- USA
| | - Brian L. Scott
- Los Alamos National Laboratory
- Los Alamos
- New Mexico 87544
- USA
| | | | | | | | - Hélène Bolvin
- Laboratoire de Chimie et de Physique Quantiques
- 31062 Toulouse
- France
| | | | - Jochen Autschbach
- Department of Chemistry
- University at Buffalo
- State University of New York
- Buffalo
- USA
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4
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Solomon EI, Park K. Structure/function correlations over binuclear non-heme iron active sites. J Biol Inorg Chem 2016; 21:575-88. [PMID: 27369780 PMCID: PMC5010389 DOI: 10.1007/s00775-016-1372-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Accepted: 06/14/2016] [Indexed: 11/30/2022]
Abstract
Binuclear non-heme iron enzymes activate O2 to perform diverse chemistries. Three different structural mechanisms of O2 binding to a coupled binuclear iron site have been identified utilizing variable-temperature, variable-field magnetic circular dichroism spectroscopy (VTVH MCD). For the μ-OH-bridged Fe(II)2 site in hemerythrin, O2 binds terminally to a five-coordinate Fe(II) center as hydroperoxide with the proton deriving from the μ-OH bridge and the second electron transferring through the resulting μ-oxo superexchange pathway from the second coordinatively saturated Fe(II) center in a proton-coupled electron transfer process. For carboxylate-only-bridged Fe(II)2 sites, O2 binding as a bridged peroxide requires both Fe(II) centers to be coordinatively unsaturated and has good frontier orbital overlap with the two orthogonal O2 π* orbitals to form peroxo-bridged Fe(III)2 intermediates. Alternatively, carboxylate-only-bridged Fe(II)2 sites with only a single open coordination position on an Fe(II) enable the one-electron formation of Fe(III)-O2 (-) or Fe(III)-NO(-) species. Finally, for the peroxo-bridged Fe(III)2 intermediates, further activation is necessary for their reactivities in one-electron reduction and electrophilic aromatic substitution, and a strategy consistent with existing spectral data is discussed.
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Affiliation(s)
- Edward I Solomon
- Department of Chemistry, Stanford University, Stanford, CA, 94305-5080, USA.
| | - Kiyoung Park
- Department of Chemistry, Korea Advanced Institute of Science and Technology, Yuseong-gu, Daejeon, 34141, Republic of Korea
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5
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Knoot CJ, Kovaleva EG, Lipscomb JD. Crystal structure of CmlI, the arylamine oxygenase from the chloramphenicol biosynthetic pathway. J Biol Inorg Chem 2016; 21:589-603. [PMID: 27229511 PMCID: PMC4994471 DOI: 10.1007/s00775-016-1363-x] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Accepted: 05/16/2016] [Indexed: 11/28/2022]
Abstract
The diiron cluster-containing oxygenase CmlI catalyzes the conversion of the aromatic amine precursor of chloramphenicol to the nitroaromatic moiety of the active antibiotic. The X-ray crystal structures of the fully active, N-terminally truncated CmlIΔ33 in the chemically reduced Fe(2+)/Fe(2+) state and a cis μ-1,2(η (1):η (1))-peroxo complex are presented. These structures allow comparison with the homologous arylamine oxygenase AurF as well as other types of diiron cluster-containing oxygenases. The structural model of CmlIΔ33 crystallized at pH 6.8 lacks the oxo-bridge apparent from the enzyme optical spectrum in solution at higher pH. In its place, residue E236 forms a μ-1,3(η (1):η (2)) bridge between the irons in both models. This orientation of E236 stabilizes a helical region near the cluster which closes the active site to substrate binding in contrast to the open site found for AurF. A very similar closed structure was observed for the inactive dimanganese form of AurF. The observation of this same structure in different arylamine oxygenases may indicate that there are two structural states that are involved in regulation of the catalytic cycle. Both the structural studies and single crystal optical spectra indicate that the observed cis μ-1,2(η (1):η (1))-peroxo complex differs from the μ-η (1):η (2)-peroxo proposed from spectroscopic studies of a reactive intermediate formed in solution by addition of O2 to diferrous CmlI. It is proposed that the structural changes required to open the active site also drive conversion of the µ-1,2-peroxo species to the reactive form.
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Affiliation(s)
- Cory J Knoot
- Department of Biochemistry Molecular Biology and Biophysics and the Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN, 55455, USA
| | - Elena G Kovaleva
- Stanford Synchrotron Radiation Lightsource, 2575 Sand Hill Road, Menlo Park, CA, 94025, USA
| | - John D Lipscomb
- Department of Biochemistry Molecular Biology and Biophysics and the Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN, 55455, USA.
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Kwak Y, Schwartz JK, Huang VW, Boice E, Kurtz DM, Solomon EI. CD/MCD/VTVH-MCD Studies of Escherichia coli Bacterioferritin Support a Binuclear Iron Cofactor Site. Biochemistry 2015; 54:7010-8. [PMID: 26551523 DOI: 10.1021/acs.biochem.5b01033] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ferritins and bacterioferritins (Bfrs) utilize a binuclear non-heme iron binding site to catalyze oxidation of Fe(II), leading to formation of an iron mineral core within a protein shell. Unlike ferritins, in which the diiron site binds Fe(II) as a substrate, which then autoxidizes and migrates to the mineral core, the diiron site in Bfr has a 2-His/4-carboxylate ligand set that is commonly found in diiron cofactor enzymes. Bfrs could, therefore, utilize the diiron site as a cofactor rather than for substrate iron binding. In this study, we applied circular dichroism (CD), magnetic CD (MCD), and variable-temperature, variable-field MCD (VTVH-MCD) spectroscopies to define the geometric and electronic structures of the biferrous active site in Escherichia coli Bfr. For these studies, we used an engineered M52L variant, which is known to eliminate binding of a heme cofactor but to have very minor effects on either iron oxidation or mineral core formation. We also examined an H46A/D50A/M52L Bfr variant, which additionally disrupts a previously observed mononuclear non-heme iron binding site inside the protein shell. The spectral analyses define a binuclear and an additional mononuclear ferrous site. The biferrous site shows two different five-coordinate centers. After O2 oxidation and re-reduction, only the mononuclear ferrous signal is eliminated. The retention of the biferrous but not the mononuclear ferrous site upon O2 cycling supports a mechanism in which the binuclear site acts as a cofactor for the O2 reaction, while the mononuclear site binds the substrate Fe(II) that, after its oxidation to Fe(III), migrates to the mineral core.
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Affiliation(s)
- Yeonju Kwak
- Department of Chemistry, Stanford University , Stanford, California 94305, United States
| | - Jennifer K Schwartz
- Department of Chemistry, Stanford University , Stanford, California 94305, United States
| | - Victor W Huang
- Department of Chemistry, University of Texas at San Antonio , One UTSA Circle, San Antonio, Texas 78249, United States
| | - Emily Boice
- Department of Chemistry, University of Texas at San Antonio , One UTSA Circle, San Antonio, Texas 78249, United States
| | - Donald M Kurtz
- Department of Chemistry, University of Texas at San Antonio , One UTSA Circle, San Antonio, Texas 78249, United States
| | - Edward I Solomon
- Department of Chemistry, Stanford University , Stanford, California 94305, United States
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7
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Shahbazi-Raz F, Amani V, Noruzi EB, Safari N, Boča R, Titiš J, Notash B. Synthesis, characterization, electrochemical and magnetic study of mixed ligand mono iron and O-methoxy bridged diiron complexes. Inorganica Chim Acta 2015. [DOI: 10.1016/j.ica.2015.07.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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8
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Snyder RA, Betzu J, Butch SE, Reig AJ, DeGrado WF, Solomon EI. Systematic Perturbations of Binuclear Non-heme Iron Sites: Structure and Dioxygen Reactivity of de Novo Due Ferri Proteins. Biochemistry 2015; 54:4637-51. [PMID: 26154739 DOI: 10.1021/acs.biochem.5b00324] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
DFsc (single-chain due ferri) proteins allow for modeling binuclear non-heme iron enzymes with a similar fold. Three 4A → 4G variants of DFsc were studied to investigate the effects of (1) increasing the size of the substrate/solvent access channel (G4DFsc), (2) including an additional His residue in the first coordination sphere along with three additional helix-stabilizing mutations [3His-G4DFsc(Mut3)], and (3) the three helix-stabilizing mutations alone [G4DFsc(Mut3)] on the biferrous structures and their O2 reactivities. Near-infrared circular dichroism and magnetic circular dichroism (MCD) spectroscopy show that the 4A → 4G mutations increase coordination of the diiron site from 4-coordinate/5-coordinate to 5-coordinate/5-coordinate, likely reflecting increased solvent accessibility. While the three helix-stabilizing mutations [G4DFsc(Mut3)] do not affect the coordination number, addition of the third active site His residue [3His-G4DFsc(Mut3)] results in a 5-coordinate/6-coordinate site. Although all 4A→ 4G variants have significantly slower pseudo-first-order rates when reacting with excess O2 than DFsc (∼2 s(-1)), G4DFsc and 3His-G4DFsc(Mut3) have rates (∼0.02 and ∼0.04 s(-1)) faster than that of G4DFsc(Mut3) (∼0.002 s(-1)). These trends in the rate of O2 reactivity correlate with exchange coupling between the Fe(II) sites and suggest that the two-electron reduction of O2 occurs through end-on binding at one Fe(II) rather than through a peroxy-bridged intermediate. UV-vis absorption and MCD spectroscopies indicate that an Fe(III)Fe(III)-OH species first forms in all three variants but converts into an Fe(III)-μ-OH-Fe(III) species only in the 2-His forms, a process inhibited by the additional active site His ligand that coordinatively saturates one of the iron centers in 3His-G4DFsc(Mut3).
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Affiliation(s)
- Rae Ana Snyder
- †Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Justine Betzu
- ‡Department of Chemistry, Ursinus College, Collegeville, Pennsylvania 19426, United States
| | - Susan E Butch
- ‡Department of Chemistry, Ursinus College, Collegeville, Pennsylvania 19426, United States
| | - Amanda J Reig
- ‡Department of Chemistry, Ursinus College, Collegeville, Pennsylvania 19426, United States
| | - William F DeGrado
- §Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California 94143, United States
| | - Edward I Solomon
- †Department of Chemistry, Stanford University, Stanford, California 94305, United States.,∥Stanford Synchrotron Radiation Laboratory, Stanford University, SLAC, Menlo Park, California 94025, United States
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9
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Snyder RA, Butch SE, Reig AJ, DeGrado WF, Solomon EI. Molecular-Level Insight into the Differential Oxidase and Oxygenase Reactivities of de Novo Due Ferri Proteins. J Am Chem Soc 2015; 137:9302-14. [PMID: 26090726 DOI: 10.1021/jacs.5b03524] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Using the single-chain due ferri (DFsc) peptide scaffold, the differential oxidase and oxygenase reactivities of two 4A→4G variants, one with two histidines at the diiron center (G4DFsc) and the other with three histidines (3His-G4DFsc(Mut3)), are explored. By controlling the reaction conditions, the active form responsible for 4-aminophenol (4-AP) oxidase activity in both G4DFsc and 3His-G4DFsc(Mut3) is determined to be the substrate-bound biferrous site. Using circular dichroism (CD), magnetic CD (MCD), and variable-temperature, variable-field (VTVH) MCD spectroscopies, 4-AP is found to bind directly to the biferrous sites of the DF proteins. In G4DFsc, 4-AP increases the coordination of the biferrous site, while in 3His-G4DFsc(Mut3), the coordination number remains the same and the substrate likely replaces the additional bound histidine. This substrate binding enables a two-electron process where 4-AP is oxidized to benzoquinone imine and O2 is reduced to H2O2. In contrast, only the biferrous 3His variant is found to be active in the oxygenation of p-anisidine to 4-nitroso-methoxybenzene. From CD, MCD, and VTVH MCD, p-anisidine addition is found to minimally perturb the biferrous centers of both G4DFsc and 3His-G4DFsc(Mut3), indicating that this substrate binds near the biferrous site. In 3His-G4DFsc(Mut3), the coordinative saturation of one iron leads to the two-electron reduction of O2 at the second iron to generate an end-on hydroperoxo-Fe(III) active oxygenating species.
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Affiliation(s)
- Rae Ana Snyder
- †Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Susan E Butch
- ‡Department of Chemistry, Ursinus College, Collegeville, Pennsylvania 19426, United States
| | - Amanda J Reig
- ‡Department of Chemistry, Ursinus College, Collegeville, Pennsylvania 19426, United States
| | - William F DeGrado
- ⊥Department of Pharmaceutical Chemistry, University of California, San Francisco, California 94143, United States
| | - Edward I Solomon
- †Department of Chemistry, Stanford University, Stanford, California 94305, United States.,§Stanford Synchrotron Radiation Laboratory, SLAC, Stanford University, Menlo Park, California 94025, United States
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10
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Kwak Y, Schwartz JK, Haldar S, Behera RK, Tosha T, Theil EC, Solomon EI. Spectroscopic studies of single and double variants of M ferritin: lack of conversion of a biferrous substrate site into a cofactor site for O2 activation. Biochemistry 2014; 53:473-82. [PMID: 24397299 PMCID: PMC3985457 DOI: 10.1021/bi4013726] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
![]()
Ferritin has a binuclear non-heme
iron active site that functions
to oxidize iron as a substrate for formation of an iron mineral core.
Other enzymes of this class have tightly bound diiron cofactor sites
that activate O2 to react with substrate. Ferritin has
an active site ligand set with 1-His/4-carboxylate/1-Gln rather than
the 2-His/4-carboxylate set of the cofactor site. This ligand variation
has been thought to make a major contribution to this biferrous substrate
rather than cofactor site reactivity. However, the Q137E/D140H double
variant of M ferritin, has a ligand set that is equivalent to most
of the diiron cofactor sites, yet did not rapidly react with O2 or generate the peroxy intermediate observed in the cofactor
sites. Therefore, in this study, a combined spectroscopic methodology
of circular dichroism (CD)/magnetic CD (MCD)/variable temperature,
variable field (VTVH) MCD has been applied to evaluate the factors
required for the rapid O2 activation observed in cofactor
sites. This methodology defines the coordination environment of each
iron and the bridging ligation of the biferrous active sites in the
double and corresponding single variants of frog M ferritin. Based
on spectral changes, the D140H single variant has the new His ligand
binding, and the Q137E variant has the new carboxylate forming a μ-1,3
bridge. The spectra for the Q137E/D140H double variant, which has
the cofactor ligand set, however, reflects a site that is more coordinately
saturated than the cofactor sites in other enzymes including ribonucleotide
reductase, indicating the presence of additional water ligation. Correlation
of this double variant and the cofactor sites to their O2 reactivities indicates that electrostatic and steric changes in
the active site and, in particular, the hydrophobic nature of a cofactor
site associated with its second sphere protein environment, make important
contributions to the activation of O2 by the binuclear
non-heme iron enzymes.
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Affiliation(s)
- Yeonju Kwak
- Department of Chemistry, Stanford University , Stanford, California 94305, United States
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11
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Snyder RA, Bell CB, Diao Y, Krebs C, Bollinger JM, Solomon EI. Circular dichroism, magnetic circular dichroism, and variable temperature variable field magnetic circular dichroism studies of biferrous and mixed-valent myo-inositol oxygenase: insights into substrate activation of O2 reactivity. J Am Chem Soc 2013; 135:15851-63. [PMID: 24066857 DOI: 10.1021/ja406635k] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
myo-Inositol oxygenase (MIOX) catalyzes the 4e(-) oxidation of myo-inositol (MI) to D-glucuronate using a substrate activated Fe(II)Fe(III) site. The biferrous and Fe(II)Fe(III) forms of MIOX were studied with circular dichroism (CD), magnetic circular dichroism (MCD), and variable temperature variable field (VTVH) MCD spectroscopies. The MCD spectrum of biferrous MIOX shows two ligand field (LF) transitions near 10000 cm(-1), split by ~2000 cm(-1), characteristic of six coordinate (6C) Fe(II) sites, indicating that the modest reactivity of the biferrous form toward O2 can be attributed to the saturated coordination of both irons. Upon oxidation to the Fe(II)Fe(III) state, MIOX shows two LF transitions in the ~10000 cm(-1) region, again implying a coordinatively saturated Fe(II) site. Upon MI binding, these split in energy to 5200 and 11200 cm(-1), showing that MI binding causes the Fe(II) to become coordinatively unsaturated. VTVH MCD magnetization curves of unbound and MI-bound Fe(II)Fe(III) forms show that upon substrate binding, the isotherms become more nested, requiring that the exchange coupling and ferrous zero-field splitting (ZFS) both decrease in magnitude. These results imply that MI binds to the ferric site, weakening the Fe(III)-μ-OH bond and strengthening the Fe(II)-μ-OH bond. This perturbation results in the release of a coordinated water from the Fe(II) that enables its O2 activation.
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Affiliation(s)
- Rae Ana Snyder
- Department of Chemistry, Stanford University , Stanford, California 94305, United States
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12
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Aukema KG, Makris TM, Stoian SA, Richman JE, Münck E, Lipscomb JD, Wackett LP. Cyanobacterial aldehyde deformylase oxygenation of aldehydes yields n-1 aldehydes and alcohols in addition to alkanes. ACS Catal 2013; 3:2228-2238. [PMID: 24490119 PMCID: PMC3903409 DOI: 10.1021/cs400484m] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Aldehyde-deformylating oxygenase (ADO) catalyzes O2-dependent release of the terminal carbon of a biological substrate, octadecanal, to yield formate and heptadecane in a reaction that requires external reducing equivalents. We show here that ADO also catalyzes incorporation of an oxygen atom from O2 into the alkane product to yield alcohol and aldehyde products. Oxygenation of the alkane product is much more pronounced with C9-10 aldehyde substrates, so that use of nonanal as the substrate yields similar amounts of octane, octanal, and octanol products. When using doubly-labeled [1,2-13C]-octanal as the substrate, the heptane, heptanal and heptanol products each contained a single 13C-label in the C-1 carbons atoms. The only one-carbon product identified was formate. [18O]-O2 incorporation studies demonstrated formation of [18O]-alcohol product, but rapid solvent exchange prevented similar determination for the aldehyde product. Addition of [1-13C]-nonanol with decanal as the substrate at the outset of the reaction resulted in formation of [1-13C]-nonanal. No 13C-product was formed in the absence of decanal. ADO contains an oxygen-bridged dinuclear iron cluster. The observation of alcohol and aldehyde products derived from the initially formed alkane product suggests a reactive species similar to that formed by methane monooxygenase (MMO) and other members of the bacterial multicomponent monooxygenase family. Accordingly, characterization by EPR and Mössbauer spectroscopies shows that the electronic structure of the ADO cluster is similar, but not identical, to that of MMO hydroxylase component. In particular, the two irons of ADO reside in nearly identical environments in both the oxidized and fully reduced states, whereas those of MMOH show distinct differences. These favorable characteristics of the iron sites allow a comprehensive determination of the spin Hamiltonian parameters describing the electronic state of the diferrous cluster for the first time for any biological system. The nature of the diiron cluster and the newly recognized products from ADO catalysis hold implications for the mechanism of C-C bond cleavage.
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Affiliation(s)
- Kelly G. Aukema
- BioTechnology Institute University of Minnesota, St. Paul, Minnesota 55108
| | - Thomas M. Makris
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
| | - Sebastian A. Stoian
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213
| | - Jack E. Richman
- BioTechnology Institute University of Minnesota, St. Paul, Minnesota 55108
| | - Eckard Münck
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213
| | - John D. Lipscomb
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
| | - Lawrence P. Wackett
- BioTechnology Institute University of Minnesota, St. Paul, Minnesota 55108
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
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13
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Makris TM, Knoot CJ, Wilmot CM, Lipscomb JD. Structure of a dinuclear iron cluster-containing β-hydroxylase active in antibiotic biosynthesis. Biochemistry 2013; 52:6662-71. [PMID: 23980641 PMCID: PMC3826434 DOI: 10.1021/bi400845b] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A family of dinuclear iron cluster-containing oxygenases that catalyze β-hydroxylation tailoring reactions in natural product biosynthesis by nonribosomal peptide synthetase (NRPS) systems was recently described [Makris, T. M., Chakrabarti, M., Münck, E., and Lipscomb, J. D. (2010) Proc. Natl. Acad. Sci. U.S.A. 107, 15391-15396]. Here, the 2.17 Å X-ray crystal structure of the archetypal enzyme from the family, CmlA, is reported. CmlA catalyzes β-hydroxylation of l-p-aminophenylalanine during chloramphenicol biosynthesis. The fold of the N-terminal domain of CmlA is unlike any previously reported, but the C-terminal domain has the αββα fold of the metallo-β-lactamase (MBL) superfamily. The diiron cluster bound in the C-terminal domain is coordinated by an acetate, three His residues, two Asp residues, one Glu residue, and a bridging oxo moiety. One of the Asp ligands forms an unusual monodentate bridge. No other oxygen-activating diiron enzyme utilizes this ligation or the MBL protein fold. The N-terminal domain facilitates dimerization, but using computational docking and a sequence-based structural comparison to homologues, we hypothesize that it likely serves additional roles in NRPS recognition and the regulation of O2 activation.
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Affiliation(s)
| | | | - Carrie M. Wilmot
- Department of Biochemistry Molecular Biology and Biophysics and the Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455
| | - John D. Lipscomb
- Department of Biochemistry Molecular Biology and Biophysics and the Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455
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14
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Unexpected weak magnetic exchange coupling between haem and non-haem iron in the catalytic site of nitric oxide reductase (NorBC) from Paracoccus denitrificans1. Biochem J 2013; 451:389-94. [DOI: 10.1042/bj20121406] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Bacterial NOR (nitric oxide reductase) is a major source of the powerful greenhouse gas N2O. NorBC from Paracoccus denitrificans is a heterodimeric multi-haem transmembrane complex. The active site, in NorB, comprises high-spin haem b3 in close proximity with non-haem iron, FeB. In oxidized NorBC, the active site is EPR-silent owing to exchange coupling between FeIII haem b3 and FeBIII (both S=5/2). On the basis of resonance Raman studies [Moënne-Loccoz, Richter, Huang, Wasser, Ghiladi, Karlin and de Vries (2000) J. Am. Chem. Soc. 122, 9344–9345], it has been assumed that the coupling is mediated by an oxo-bridge and subsequent studies have been interpreted on the basis of this model. In the present study we report a VFVT (variable-field variable-temperature) MCD (magnetic circular dichroism) study that determines an isotropic value of J=−1.7 cm−1 for the coupling. This is two orders of magnitude smaller than that encountered for oxo-bridged diferric systems, thus ruling out this configuration. Instead, it is proposed that weak coupling is mediated by a conserved glutamate residue.
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15
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Bikas R, Hosseini-Monfared H, Zoppellaro G, Herchel R, Tucek J, Owczarzak AM, Kubicki M, Zboril R. Synthesis, structure, magnetic properties and theoretical calculations of methoxy bridged dinuclear iron(iii) complex with hydrazone based O,N,N-donor ligand. Dalton Trans 2013; 42:2803-12. [DOI: 10.1039/c2dt31751f] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
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16
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Electronic and geometric structures of the organophosphate-degrading enzyme from Agrobacterium radiobacter (OpdA). J Biol Inorg Chem 2011; 16:777-87. [PMID: 21487938 DOI: 10.1007/s00775-011-0779-6] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2010] [Accepted: 03/28/2011] [Indexed: 10/18/2022]
Abstract
The organophosphate-degrading enzyme from Agrobacterium radiobacter (OpdA) is a highly efficient catalyst for the degradation of pesticides and some nerve agents such as sarin. OpdA requires two metal ions for catalytic activity, and hydrolysis is initiated by a nucleophilic hydroxide that is bound to one of these metal ions. The precise location of this nucleophile has been contentious, with both a terminal and a metal-ion-bridging hydroxide as likely candidates. Here, we employed magnetic circular dichroism to probe the electronic and geometric structures of the Co(II)-reconstituted dinuclear metal center in OpdA. In the resting state the metal ion in the more secluded α site is five-coordinate, whereas the Co(II) in the solvent-exposed β site is predominantly six-coordinate with two terminal water ligands. Addition of the slow substrate diethyl 4-methoxyphenyl phosphate does not affect the α site greatly but lowers the coordination number of the β site to five. A reduction in the exchange coupling constant indicates that substrate binding also triggers a shift of the μ-hydroxide into a pseudoterminal position in the coordination sphere of either the α or the β metal ion. Mechanistic implications of these observations are discussed.
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17
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Krzystek J, Swenson DC, Zvyagin SA, Smirnov D, Ozarowski A, Telser J. Cobalt(II) “Scorpionate” Complexes as Models for Cobalt-Substituted Zinc Enzymes: Electronic Structure Investigation by High-Frequency and -Field Electron Paramagnetic Resonance Spectroscopy. J Am Chem Soc 2010; 132:5241-53. [PMID: 20329727 DOI: 10.1021/ja910766w] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- J. Krzystek
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, Dresden High Magnetic Field Laboratory (HLD), Forschungszentrum Dresden-Rossendorf, D-01314 Dresden, Germany, and Department of Biological, Chemical and Physical Sciences, Roosevelt University, Chicago, Illinois 60605
| | - Dale C. Swenson
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, Dresden High Magnetic Field Laboratory (HLD), Forschungszentrum Dresden-Rossendorf, D-01314 Dresden, Germany, and Department of Biological, Chemical and Physical Sciences, Roosevelt University, Chicago, Illinois 60605
| | - S. A. Zvyagin
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, Dresden High Magnetic Field Laboratory (HLD), Forschungszentrum Dresden-Rossendorf, D-01314 Dresden, Germany, and Department of Biological, Chemical and Physical Sciences, Roosevelt University, Chicago, Illinois 60605
| | - Dmitry Smirnov
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, Dresden High Magnetic Field Laboratory (HLD), Forschungszentrum Dresden-Rossendorf, D-01314 Dresden, Germany, and Department of Biological, Chemical and Physical Sciences, Roosevelt University, Chicago, Illinois 60605
| | - Andrew Ozarowski
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, Dresden High Magnetic Field Laboratory (HLD), Forschungszentrum Dresden-Rossendorf, D-01314 Dresden, Germany, and Department of Biological, Chemical and Physical Sciences, Roosevelt University, Chicago, Illinois 60605
| | - Joshua Telser
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, Dresden High Magnetic Field Laboratory (HLD), Forschungszentrum Dresden-Rossendorf, D-01314 Dresden, Germany, and Department of Biological, Chemical and Physical Sciences, Roosevelt University, Chicago, Illinois 60605
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18
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Hadler KS, Mitić N, Yip SHC, Gahan LR, Ollis DL, Schenk G, Larrabee JA. Electronic Structure Analysis of the Dinuclear Metal Center in the Bioremediator Glycerophosphodiesterase (GpdQ) from Enterobacter aerogenes. Inorg Chem 2010; 49:2727-34. [DOI: 10.1021/ic901950c] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Kieran S. Hadler
- School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia, Queensland, 4072, Australia
| | - Nataša Mitić
- School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia, Queensland, 4072, Australia
| | - Sylvia Hsu-Chen Yip
- Research School of Chemistry, Australian National University, Canberra, ACT, 0200, Australia
| | - Lawrence R Gahan
- School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia, Queensland, 4072, Australia
| | - David L. Ollis
- Research School of Chemistry, Australian National University, Canberra, ACT, 0200, Australia
| | - Gerhard Schenk
- School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia, Queensland, 4072, Australia
| | - James A. Larrabee
- Department of Chemistry and Biochemistry, Middlebury College, Middlebury, Vermont 05753
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19
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Larrabee JA, Johnson WR, Volwiler AS. Magnetic circular dichroism study of a dicobalt(II) complex with mixed 5- and 6-coordination: a spectroscopic model for dicobalt(II) hydrolases. Inorg Chem 2009; 48:8822-9. [PMID: 19691327 DOI: 10.1021/ic901000d] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The magnetic circular dichroism (MCD) study of [Co(2)(mu-OH)(mu-Ph(4)DBA)(TMEDA)(2)(OTf)], in which Ph(4)DBA is the dinucleating bis(carboxylate) ligand dibenzofuran-4,6-bis(diphenylacetate) and TMEDA is N,N,N',N'-tetramethylethylenediamine, is presented. This complex serves as an excellent spectroscopic model for a number of dicobalt(II) enzymes and proteins that have both the mu-hydroxo, mu-carboxylato bridging and asymmetric 6- and 5-coordination. The low-temperature MCD spectrum of the model complex shows bands at 490, 504, and 934 nm arising from d-d transitions on the 6-coordinate Co(II) and bands at 471, 522, 572, 594, and 638 nm arising from d-d transitions on the 5-coordinate Co(II). The most intense MCD bands are at 504 and 572 nm for 6- and 5-coordinate Co(II), respectively, and these two bands are found in the MCD spectra of dicobalt(II)-substituted methionine aminopeptidase from Escherichia coli (CoCoMetAP), glycerophosphodiesterase from Enterobacter aerogenes (CoCoGpdQ), aminopeptidase from Aeromonas proteolytica (CoCoAAP), and myohemerythrin from Themiste zostericola (CoCoMyoHry). These dicobalt(II)-substituted proteins are known to have one 5- and one 6-coordinate Co(II) bridged by one or two carboxylates and either a water or a hydroxide. The uncertainty of the bridging water's state of protonation is problematic, as this is a likely candidate for the attacking nucleophile in the dimetallohydrolases. Analysis of the variable-temperature variable-field (VTVH) MCD data determined that the Co(II) ions in the model complex are ferromagnetically coupled with a J of 3.0 cm(-1). A comparison of all dicobalt(II) complexes and dicobalt(II)-substituted protein active sites with the mu-hydroxo/aqua, mu-carboxylato bridging motif reveals that J is either zero or negative (antiferromagnetic) in the mu-aqua systems and positive (ferromagnetic) in the mu-hydroxo systems. It was also determined that the Co(II) ions in CoCoAAP and CoCoMyoHry are ferromagnetically coupled, each with a J of 3.4 cm(-1), which suggests that these ions have a mu-hydroxo bridging ligand.
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Affiliation(s)
- James A Larrabee
- Department of Chemistry and Biochemistry, Middlebury College, Middlebury, Vermont 05753, USA.
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20
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Jensen KP, Bell, CB, Clay MD, Solomon EI. Peroxo-Type Intermediates in Class I Ribonucleotide Reductase and Related Binuclear Non-Heme Iron Enzymes. J Am Chem Soc 2009; 131:12155-71. [DOI: 10.1021/ja809983g] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Kasper P. Jensen
- Department of Chemistry, Stanford University, 333 Campus Drive, Mudd Building, Stanford, California 94305-5080, and DTU-Chemistry, Technical University of Denmark, Building 207, DK 2800 Kgs. Lyngby, Denmark
| | - Caleb B. Bell,
- Department of Chemistry, Stanford University, 333 Campus Drive, Mudd Building, Stanford, California 94305-5080, and DTU-Chemistry, Technical University of Denmark, Building 207, DK 2800 Kgs. Lyngby, Denmark
| | - Michael D. Clay
- Department of Chemistry, Stanford University, 333 Campus Drive, Mudd Building, Stanford, California 94305-5080, and DTU-Chemistry, Technical University of Denmark, Building 207, DK 2800 Kgs. Lyngby, Denmark
| | - Edward I. Solomon
- Department of Chemistry, Stanford University, 333 Campus Drive, Mudd Building, Stanford, California 94305-5080, and DTU-Chemistry, Technical University of Denmark, Building 207, DK 2800 Kgs. Lyngby, Denmark
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21
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Martinho M, Xue G, Fiedler AT, Que L, Bominaar EL, Münck E. Mössbauer and DFT study of the ferromagnetically coupled diiron(IV) precursor to a complex with an Fe(IV)(2)O(2) diamond core. J Am Chem Soc 2009; 131:5823-30. [PMID: 19338307 DOI: 10.1021/ja8098917] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Recently, we reported the reaction of the (mu-oxo)diiron(III) complex 1 ([Fe(III)(2)(mu-O)(mu-O(2)H(3))(L)(2)](3+), L = tris(3,5-dimethyl-4-methoxypyridyl-2-methyl)amine) with 1 equiv of H(2)O(2) to yield a diiron(IV) intermediate, 2 (Xue, G.; Fiedler, A. T.; Martinho, M.; Munck, E.; Que, L., Jr. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 20615-20). Upon treatment with HClO(4), complex 2 converted to a species with an Fe(IV)(2)(mu-O)(2) diamond core that serves as the only synthetic model to date for the diiron(IV) core proposed for intermediate Q of soluble methane monooxygenase. Here we report detailed Mossbauer and density functional theory (DFT) studies of 2. The Mossbauer studies reveal that 2 has distinct Fe(IV) sites, a and b. Studies in applied magnetic fields show that the spins of sites a and b (S(a) = S(b) = 1) are ferromagnetically coupled to yield a ground multiplet with S = 2. Analysis of the applied field spectra of the exchange-coupled system yields for site b a set of parameters that matches those obtained for the mononuclear [LFe(IV)(O)(NCMe)](2+) complex, showing that site b (labeled Fe(O)) has a terminal oxo group. Using the zero-field splitting parameters of [LFe(IV)(O)(NCMe)](2+) for our analysis of 2, we obtained parameters for site a that closely resemble those reported for the nonoxo Fe(IV) complex [(beta-BPMCN)Fe(IV)(OH)(OO(t)Bu)](2+), suggesting that a (labeled Fe(OH)) coordinates a hydroxo group. A DFT optimization performed on 2 yielded an Fe-Fe distance of 3.39 A and an Fe-(mu-O)-Fe angle of 131 degrees , in good agreement with the results of our previous EXAFS study. The DFT calculations reproduce the Mossbauer parameters (A-tensors, electric field gradient, and isomer shift) of 2 quite well, including the observation that the largest components of the electric field gradients of Fe(O) and Fe(OH) are perpendicular. The ferromagnetic behavior of 2 seems puzzling given that the Fe-(mu-O)-Fe angle is large but can be explained by noting that the orbital structures of Fe(O) and Fe(OH) are such that the unpaired electrons at the two sites delocalize into orthogonal orbitals at the bridging oxygen, rationalizing the ferromagnetic behavior of 2. Thus, inequivalent coordinations at Fe(O) and Fe(OH) define magnetic orbitals favorable for ferromagnetic ineractions.
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Affiliation(s)
- Marlène Martinho
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
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22
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Wadman SH, Havenith RWA, Hartl F, Lutz M, Spek AL, van Klink GPM, van Koten G. Redox Chemistry and Electronic Properties of 2,3,5,6-Tetrakis(2-pyridyl)pyrazine-Bridged Diruthenium Complexes Controlled by N,C,N′-BisCyclometalated Ligands. Inorg Chem 2009; 48:5685-96. [PMID: 20507098 DOI: 10.1021/ic801897k] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
| | | | - František Hartl
- Homogeneous and Supramolecular Catalysis, Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands
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23
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Cappillino PJ, Tarves PC, Rowe GT, Lewis AJ, Harvey M, Rogge C, Stassinopoulos A, Lo W, Armstrong WH, Caradonna JP. Synthesis and characterization of a family of binuclear non-heme iron monooxygenase model compounds: Evidence for a “phenolate/amide carbonyl (PAC) shift” upon oxidation. Inorganica Chim Acta 2009. [DOI: 10.1016/j.ica.2008.09.036] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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24
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Shanmugam M, Doan PE, Lees NS, Stubbe J, Hoffman BM. Identification of protonated oxygenic ligands of ribonucleotide reductase intermediate X. J Am Chem Soc 2009; 131:3370-6. [PMID: 19220056 PMCID: PMC2789976 DOI: 10.1021/ja809223s] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We previously used a combination of continuous-wave (CW) and pulsed electron-nuclear double resonance (ENDOR) protocols to identify the types of protonated oxygen (OH(x)) species and their disposition within the Fe(III)/Fe(IV) cluster of intermediate X, the direct precursor of the essential diferric-tyrosyl radical cofactor of the beta2 subunit of Escherichia coli ribonucleotide reductase (RNR). We concluded that X contains the [(H(x)O)Fe(III)OFe(IV)] fragment (T model), and does not contain a mu-hydroxo bridge. When combined with a subsequent (17)O ENDOR study of X prepared with H(2)(17)O and with (17)O(2), the results led us to suggest that this fragment is the entire inorganic core of X. This has been questioned by recent reports, but these reports do not themselves agree on the core of X. One concluded that X possesses a di-mu-oxo Fe(III)/Fe(IV) core plus a terminal (H(2)O) bound to Fe(III) [e.g., Han, W.-G.; Liu, T.; Lovell, T.; Noodleman, L. J. Am. Chem. Soc. 2005, 127, 15778-15790]. The other [Mitic, N.; Clay, M. D.; Saleh, L.; Bollinger, J. M.; Solomon, E. I. J. Am. Chem. Soc. 2007, 129, 9049-9065] concluded that X contains only a single oxo bridge and postulated the presence of an additional hydroxo bridge plus a terminal hydroxyl bound to Fe(III). In this report we take advantage of improvements in 35 GHz pulsed ENDOR performance to reexamine the protonation state of oxygenic ligands of the inorganic core of X by directly probing the exchangeable proton(s) with (2)H pulsed ENDOR spectroscopy. These (2)H ENDOR measurements confirm that X contains an Fe(III)-bound terminal aqua ligand (H(x)O), but the spectra contain none of the features that would be required for the proton of a bridging hydroxyl. Thus, we confirm that X contains a terminal aqua (most likely hydroxo) ligand to Fe(III) in addition to one or two mu-oxo bridges but does not contain a mu-hydroxo bridge. The (2)H ENDOR measurements further demonstrate that this conclusion is applicable to both wild type and Y122F-beta2 mutant, and in fact we detect no difference between the properties of protons on the terminal oxygens in the two variants; likewise, (14)N ENDOR measurements of histidyl ligands bound to Fe show no difference between the two variants.
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Affiliation(s)
| | - Peter E. Doan
- Department of Chemistry, Northwestern University, Evanston, IL, 60208-3113
| | | | - JoAnne Stubbe
- Department of Chemistry, MIT, Cambridge, MA, 02139-4307
| | - Brian M. Hoffman
- Department of Chemistry, Northwestern University, Evanston, IL, 60208-3113
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Bell CB, Calhoun JR, Bobyr E, Wei PP, Hedman B, Hodgson KO, DeGrado WF, Solomon EI. Spectroscopic definition of the biferrous and biferric sites in de novo designed four-helix bundle DFsc peptides: implications for O2 reactivity of binuclear non-heme iron enzymes. Biochemistry 2009; 48:59-73. [PMID: 19090676 PMCID: PMC2660568 DOI: 10.1021/bi8016087] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
DFsc is a single chain de novo designed four-helix bundle peptide that mimics the core protein fold and primary ligand set of various binuclear non-heme iron enzymes. DFsc and the E11D, Y51L, and Y18F single amino acid variants have been studied using a combination of near-IR circular dichroism (CD), magnetic circular dichroism (MCD), variable temperature variable field MCD (VTVH MCD), and X-ray absorption (XAS) spectroscopies. The biferrous sites are all weakly antiferromagnetically coupled with mu-1,3 carboxylate bridges and one 4-coordinate and one 5-coordinate Fe, very similar to the active site of class I ribonucleotide reductase (R2) providing open coordination positions on both irons for dioxygen to bridge. From perturbations of the MCD and VTVH MCD the iron proximal to Y51 can be assigned as the 4-coordinate center, and XAS results show that Y51 is not bound to this iron in the reduced state. The two open coordination positions on one iron in the biferrous state would become occupied by dioxygen and Y51 along the O(2) reaction coordinate. Subsequent binding of Y51 functions as an internal spectral probe of the O(2) reaction and as a proton source that would promote loss of H(2)O(2). Coordination by a ligand that functions as a proton source could be a structural mechanism used by natural binuclear iron enzymes to drive their reactions past peroxo biferric level intermediates.
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Affiliation(s)
- Caleb B. Bell
- Department of Chemistry, Stanford University, Stanford, California 94305
| | - Jennifer R. Calhoun
- Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, Philadelphia, PA 19104
| | - Elena Bobyr
- Department of Chemistry, Stanford University, Stanford, California 94305
- Stanford Synchrotron Radiation Laboratory, Stanford University, SLAC, Menlo Park, 94025
| | - Pin-pin Wei
- Department of Chemistry, Stanford University, Stanford, California 94305
| | - Britt Hedman
- Department of Chemistry, Stanford University, Stanford, California 94305
- Stanford Synchrotron Radiation Laboratory, Stanford University, SLAC, Menlo Park, 94025
| | - Keith O. Hodgson
- Department of Chemistry, Stanford University, Stanford, California 94305
- Stanford Synchrotron Radiation Laboratory, Stanford University, SLAC, Menlo Park, 94025
| | - William F. DeGrado
- Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, Philadelphia, PA 19104
| | - Edward I. Solomon
- Department of Chemistry, Stanford University, Stanford, California 94305
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26
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Tomter AB, Bell CB, Røhr AK, Andersson KK, Solomon EI. Circular dichroism and magnetic circular dichroism studies of the biferrous site of the class Ib ribonucleotide reductase from Bacillus cereus: comparison to the class Ia enzymes. Biochemistry 2008; 47:11300-9. [PMID: 18831534 DOI: 10.1021/bi801212f] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The rate limiting step in DNA biosynthesis is the reduction of ribonucleotides to form the corresponding deoxyribonucleotides. This reaction is catalyzed by ribonucleotide reductases (RNRs) and is an attractive target against rapidly proliferating pathogens. Class I RNRs are binuclear non-heme iron enzymes and can be further divided into subclasses. Class Ia is found in many organisms, including humans, while class Ib has only been found in bacteria, notably some pathogens. Both Bacillus anthracis and Bacillus cereus encode class Ib RNRs with over 98% sequence identity. The geometric and electronic structure of the B. cereus diiron containing subunit (R2F) has been characterized by a combination of circular dichroism, magnetic circular dichroism (MCD) and variable temperature variable field MCD and is compared to class Ia RNRs. While crystallography has given several possible descriptions for the class Ib RNR biferrous site, the spectroscopically defined active site contains a 4-coordinate and a 5-coordinate Fe(II), weakly antiferromagnetically coupled via mu-1,3-carboxylate bridges. Class Ia biferrous sites are also antiferromagnetically coupled 4-coordinate and 5-coordinate Fe(II), however quantitatively differ from class Ib in bridging carboxylate conformation and tyrosine radical positioning relative to the diiron site. Additionally, the iron binding affinity in B. cereus RNR R2F is greater than class Ia RNR and provides the pathogen with a competitive advantage relative to host in physiological, iron-limited environments. These structural differences have potential for the development of selective drugs.
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Affiliation(s)
- Ane B Tomter
- Department of Molecular Biosciences, University of Oslo, PO Box 1041 Blindern, 0316 Oslo, Norway
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27
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Mitić N, Schwartz JK, Brazeau BJ, Lipscomb JD, Solomon EI. CD and MCD studies of the effects of component B variant binding on the biferrous active site of methane monooxygenase. Biochemistry 2008; 47:8386-97. [PMID: 18627173 PMCID: PMC2614212 DOI: 10.1021/bi800818w] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The multicomponent soluble form of methane monooxygenase (sMMO) catalyzes the oxidation of methane through the activation of O 2 at a nonheme biferrous center in the hydroxylase component, MMOH. Reactivity is limited without binding of the sMMO effector protein, MMOB. Past studies show that mutations of specific MMOB surface residues cause large changes in the rates of individual steps in the MMOH reaction cycle. To define the structural and mechanistic bases for these observations, CD, MCD, and VTVH MCD spectroscopies coupled with ligand-field (LF) calculations are used to elucidate changes occurring near and at the MMOH biferrous cluster upon binding of MMOB and the MMOB variants. Perturbations to both the CD and MCD are observed upon binding wild-type MMOB and the MMOB variant that similarly increases O 2 reactivity. MMOB variants that do not greatly increase O 2 reactivity fail to cause one or both of these changes. LF calculations indicate that reorientation of the terminal glutamate on Fe2 reproduces the spectral perturbations in MCD. Although this structural change allows O 2 to bridge the diiron site and shifts the redox active orbitals for good overlap, it is not sufficient for enhanced O 2 reactivity of the enzyme. Binding of the T111Y-MMOB variant to MMOH induces the MCD, but not CD changes, and causes only a small increase in reactivity. Thus, both the geometric rearrangement at Fe2 (observed in MCD) coupled with a more global conformational change that may control O 2 access (probed by CD), induced by MMOB binding, are critical factors in the reactivity of sMMO.
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Affiliation(s)
- Nataša Mitić
- Department of Chemistry, Stanford University, Stanford, California 94305
| | | | - Brian J. Brazeau
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
| | - John D. Lipscomb
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
| | - Edward I. Solomon
- Department of Chemistry, Stanford University, Stanford, California 94305
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28
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Schwartz JK, Liu XS, Tosha T, Theil EC, Solomon EI. Spectroscopic definition of the ferroxidase site in M ferritin: comparison of binuclear substrate vs cofactor active sites. J Am Chem Soc 2008; 130:9441-50. [PMID: 18576633 DOI: 10.1021/ja801251q] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Maxi ferritins, 24 subunit protein nanocages, are essential in humans, plants, bacteria, and other animals for the concentration and storage of iron as hydrated ferric oxide, while minimizing free radical generation or use by pathogens. Formation of the precursors to these ferric oxides is catalyzed at a nonheme biferrous substrate site, which has some parallels with the cofactor sites in other biferrous enzymes. A combination of circular dichroism (CD), magnetic circular dichroism (MCD), and variable-temperature, variable-field MCD (VTVH MCD) has been used to probe Fe(II) binding to the substrate active site in frog M ferritin. These data determined that the active site within each subunit consists of two inequivalent five-coordinate (5C) ferrous centers that are weakly antiferromagnetically coupled, consistent with a mu-1,3 carboxylate bridge. The active site ligand set is unusual and likely includes a terminal water bound to each Fe(II) center. The Fe(II) ions bind to the active sites in a concerted manner, and cooperativity among the sites in each subunit is observed, potentially providing a mechanism for the control of ferritin iron loading. Differences in geometric and electronic structure--including a weak ligand field, availability of two water ligands at the biferrous substrate site, and the single carboxylate bridge in ferritin--coincide with the divergent reaction pathways observed between this substrate site and the previously studied cofactor active sites.
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Affiliation(s)
- Jennifer K Schwartz
- Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California 94305, USA
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29
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Johansson FB, Bond AD, Nielsen UG, Moubaraki B, Murray KS, Berry KJ, Larrabee JA, McKenzie CJ. Dicobalt II−II, II−III, and III−III Complexes as Spectroscopic Models for Dicobalt Enzyme Active Sites. Inorg Chem 2008; 47:5079-92. [DOI: 10.1021/ic7020534] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Frank B. Johansson
- Department of Physics and Chemistry, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark, School of Chemistry, Building 23, Monash University, Clayton, Victoria Australia, Department of Chemistry and Biochemistry, Middlebury College, Middlebury, Vermont, U.S.A., and Westernport Secondary College, Hastings, Victoria, 3915, Australia
| | - Andrew D. Bond
- Department of Physics and Chemistry, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark, School of Chemistry, Building 23, Monash University, Clayton, Victoria Australia, Department of Chemistry and Biochemistry, Middlebury College, Middlebury, Vermont, U.S.A., and Westernport Secondary College, Hastings, Victoria, 3915, Australia
| | - Ulla Gro Nielsen
- Department of Physics and Chemistry, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark, School of Chemistry, Building 23, Monash University, Clayton, Victoria Australia, Department of Chemistry and Biochemistry, Middlebury College, Middlebury, Vermont, U.S.A., and Westernport Secondary College, Hastings, Victoria, 3915, Australia
| | - Boujemaa Moubaraki
- Department of Physics and Chemistry, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark, School of Chemistry, Building 23, Monash University, Clayton, Victoria Australia, Department of Chemistry and Biochemistry, Middlebury College, Middlebury, Vermont, U.S.A., and Westernport Secondary College, Hastings, Victoria, 3915, Australia
| | - Keith S. Murray
- Department of Physics and Chemistry, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark, School of Chemistry, Building 23, Monash University, Clayton, Victoria Australia, Department of Chemistry and Biochemistry, Middlebury College, Middlebury, Vermont, U.S.A., and Westernport Secondary College, Hastings, Victoria, 3915, Australia
| | - Kevin J. Berry
- Department of Physics and Chemistry, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark, School of Chemistry, Building 23, Monash University, Clayton, Victoria Australia, Department of Chemistry and Biochemistry, Middlebury College, Middlebury, Vermont, U.S.A., and Westernport Secondary College, Hastings, Victoria, 3915, Australia
| | - James A. Larrabee
- Department of Physics and Chemistry, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark, School of Chemistry, Building 23, Monash University, Clayton, Victoria Australia, Department of Chemistry and Biochemistry, Middlebury College, Middlebury, Vermont, U.S.A., and Westernport Secondary College, Hastings, Victoria, 3915, Australia
| | - Christine J. McKenzie
- Department of Physics and Chemistry, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark, School of Chemistry, Building 23, Monash University, Clayton, Victoria Australia, Department of Chemistry and Biochemistry, Middlebury College, Middlebury, Vermont, U.S.A., and Westernport Secondary College, Hastings, Victoria, 3915, Australia
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30
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Schwartz JK, Wei PP, Mitchell KH, Fox BG, Solomon EI. Geometric and electronic structure studies of the binuclear nonheme ferrous active site of toluene-4-monooxygenase: parallels with methane monooxygenase and insight into the role of the effector proteins in O2 activation. J Am Chem Soc 2008; 130:7098-109. [PMID: 18479085 DOI: 10.1021/ja800654d] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Multicomponent monooxygenases, which carry out a variety of highly specific hydroxylation reactions, are of great interest as potential biocatalysts in a number of applications. These proteins share many similarities in structure and show a marked increase in O2 reactivity upon addition of an effector component. In this study, circular dichroism (CD), magnetic circular dichroism (MCD), and variable-temperature, variable-field (VTVH) MCD have been used to gain spectroscopic insight into the Fe(II)Fe(II) active site in the hydroxylase component of Toluene-4 monoxygenase (T4moH) and the complex of T4moH bound by its effector protein, T4moD. These results have been correlated to spectroscopic data and density functional theory (DFT) calculations on MmoH and its interaction with MmoB. Together, these data provide further insight into the geometric and electronic structure of these biferrous active sites and, in particular, the perturbation associated with component B/D binding. It is found that binding of the effector protein changes the geometry of one iron center and orientation of its redox active orbital to accommodate the binding of O2 in a bridged structure for efficient 2-electron transfer that can form a peroxo intermediate.
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Affiliation(s)
- Jennifer K Schwartz
- Department of Chemistry, Stanford University, Stanford, California 94305, USA
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31
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Mití N, Clay MD, Saleh L, Bollinger JM, Solomon EI. Spectroscopic and electronic structure studies of intermediate X in ribonucleotide reductase R2 and two variants: a description of the FeIV-oxo bond in the FeIII-O-FeIV dimer. J Am Chem Soc 2007; 129:9049-65. [PMID: 17602477 PMCID: PMC2565590 DOI: 10.1021/ja070909i] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Spectroscopic and electronic structure studies of the class I Escherichia coli ribonucleotide reductase (RNR) intermediate X and three computationally derived model complexes are presented, compared, and evaluated to determine the electronic and geometric structure of the FeIII-FeIV active site of intermediate X. Rapid freeze-quench (RFQ) EPR, absorption, and MCD were used to trap intermediate X in R2 wild-type (WT) and two variants, W48A and Y122F/Y356F. RFQ-EPR spin quantitation was used to determine the relative contributions of intermediate X and radicals present, while RFQ-MCD was used to specifically probe the FeIII/FeIV active site, which displayed three FeIV d-d transitions between 16,700 and 22,600 cm(-1), two FeIV d-d spin-flip transitions between 23,500 and 24,300 cm(-1), and five oxo to FeIV and FeIII charge transfer (CT) transitions between 25,000 and 32,000 cm(-1). The FeIV d-d transitions were perturbed in the two variants, confirming that all three d-d transitions derive from the d-pi manifold. Furthermore, the FeIV d-pi splittings in the WT are too large to correlate with a bis-mu-oxo structure. The assignment of the FeIV d-d transitions in WT intermediate X best correlates with a bridged mu-oxo/mu-hydroxo [FeIII(mu-O)(mu-OH)FeIV] structure. The mu-oxo/mu-hydroxo core structure provides an important sigma/pi superexchange pathway, which is not present in the bis-mu-oxo structure, to promote facile electron transfer from Y122 to the remote FeIV through the bent oxo bridge, thereby generating the tyrosyl radical for catalysis.
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Affiliation(s)
- Nataša Mití
- Department of Chemistry, Stanford University, Stanford, California 94305
| | - Michael D. Clay
- Department of Chemistry, Stanford University, Stanford, California 94305
| | - Lana Saleh
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
| | - J. Martin Bollinger
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
| | - Edward I. Solomon
- Department of Chemistry, Stanford University, Stanford, California 94305
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32
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Pereira S, Cerqueira NMFSA, Fernandes PA, Ramos MJ. Computational studies on class I ribonucleotide reductase: understanding the mechanisms of action and inhibition of a cornerstone enzyme for the treatment of cancer. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2005; 35:125-35. [PMID: 16261381 DOI: 10.1007/s00249-005-0026-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2005] [Revised: 09/21/2005] [Accepted: 09/28/2005] [Indexed: 11/26/2022]
Abstract
This review provides a synthesis of recent work, using computational methods, on the action and inhibition mechanisms of class I ribonucleotide reductase (RNR). This enzyme catalyzes the rate-limiting step of the pathway for the synthesis of DNA monomers and, therefore, has long been regarded as an important target for therapies aiming to control pathologies that depend strongly on DNA replication. In fact, over the last years, several molecules, which are able to impair RNR activity by different mechanisms, have been applied effectively in anti-cancer, anti-viral and anti-parasite therapies. A better understanding of the chemical mechanisms involved in normal catalysis and in inhibition of the enzyme is important for the rational design of more specific and effective inhibitor compounds. To achieve this goal, computational methods, particularly quantum chemical calculations, have been used more and more frequently. The ever-growing capabilities of these methods together with undeniable advantages make it a stimulating area for research purposes.
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Affiliation(s)
- Susana Pereira
- REQUIMTE/Departamento de Química, Faculdade de Ciências do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal
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33
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Seth M, Ziegler T, Autschbach J. Ab initiocalculation of the C∕D ratio of magnetic circular dichroism. J Chem Phys 2005; 122:094112. [PMID: 15836117 DOI: 10.1063/1.1856453] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A procedure for calculating the magnetic circular dichroism C/D ratio from density functional theory calculations is discussed. The method is simplified considerably through the application of group theory and the irreducible-tensor method and only requires integrals of the magnetic dipole moment operator over a few orbitals and published tables of symmetry factors. The implementation of the method is tested through application to several small and medium-sized molecules.
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Affiliation(s)
- Michael Seth
- Department of Chemistry, University of Calgary, University Drive 2500, Calgary AB T2N-1N4, Canada
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34
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Lu S, Libby E, Saleh L, Xing G, Bollinger JM, Moënne-Loccoz P. Characterization of NO adducts of the diiron center in protein R2 of Escherichia coli ribonucleotide reductase and site-directed variants; implications for the O2 activation mechanism. J Biol Inorg Chem 2004; 9:818-27. [PMID: 15311337 DOI: 10.1007/s00775-004-0582-8] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2004] [Accepted: 07/06/2004] [Indexed: 11/30/2022]
Abstract
The R2 subunit of Escherichia coli ribonucleotide reductase contains a diiron site that reacts with O(2) to produce a tyrosine radical (Y122.). In wild-type R2 (R2-wt), the first observable reaction intermediate is a high-valent [Fe(III)-Fe(IV)] state called compound X, but in related diiron proteins such as methane monooxygenase, Delta(9)-desaturase, and ferritin, peroxodiiron(III) complexes have been characterized. Substitution of iron ligand D84 by E within the active site of R2 allows an intermediate (mu-1,2-peroxo)diiron species to accumulate. To investigate the possible involvement of a bridging peroxo species within the O(2) activation sequence of R2-wt, we have characterized the iron-nitrosyl species that form at the diiron sites in R2-wt, R2-D84E, and R2-W48F/D84E by using vibrational spectroscopy. Previous work has shown that the diiron center in R2-wt binds one NO per iron to form an antiferromagnetically coupled [(FeNO)(7)](2) center. In the wt and variant proteins, we also observe that both irons bind one NO to form a (FeNO)(7) dimer where both Fe-N-O units share a common vibrational signature. In the wt protein, nu(Fe-NO), delta(Fe-N-O), and nu(N-O) bands are observed at 445, 434 and 1742 cm(-1), respectively, while in the variant proteins the nu(Fe-NO) and delta(Fe-N-O) bands are observed approximately 10 cm(-1) higher and the nu(N-O) approximately 10 cm(-1) lower at 1735 cm(-1). These results demonstrate that all three proteins accommodate fully symmetric [(FeNO)(7)](2) species with two identical Fe-N-O units. The formation of equivalent NO adducts in the wt and variant proteins strongly favors the formation of a symmetric bridging peroxo intermediate during the O(2) activation process in R2-wt.
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Affiliation(s)
- Shen Lu
- Department of Environmental & Biomolecular Systems, OGI School of Science & Engineering, Oregon Health & Science University, Beaverton, OR 97006-8921, USA
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