1
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Kumar A, Usman M, Samanta D, Rath SP. Through Bridge Spin Coupling in Homo- and Heterobimetallic Porphyrin Dimers upon Stepwise Oxidations: A Spectroscopic and Theoretical Investigation. Chemistry 2021; 27:11428-11441. [PMID: 34061401 DOI: 10.1002/chem.202101384] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Indexed: 12/16/2022]
Abstract
We have described copper(II)-iron(III) and copper(II)-manganese(III) heterobimetallic porphyrin dimers and compared them with the corresponding homobimetallic analogs. UV-visible spectra are very distinct in the heterometallic species while electrochemical studies demonstrate that these species, as compared to the homobimetallic analog, are much easier to oxidize. Combined Mössbauer, EPR, NMR, magnetic and UV-visible spectroscopic studies show that upon 2e-oxidation of the heterobimetallic complexes only ring-centered oxidation occurs. The energy differences between HOMO and LUMO are linearly dependent with the low-energy NIR band obtained for the 2e-oxidized complexes. Also, strong electronic communication between two porphyrin rings through the bridge facilitates coupling between various unpaired spins present while the coupling model depends on the nature of metal ions used. While unpaired spins of Fe(III) and the porphyrin π-cation radical are strongly antiferromagnetically coupled, such coupling is rather weak between Mn(III) and a porphyrin π-cation radical. Moreover, the coupling between two π-cation radicals are much stronger in the 2e-oxidized complexes of dimanganese(III) and copper(II)-manganese(III) porphyrin dimers as compared to their diiron(III) and copper(II)-iron(III) analogs. Furthermore, coupling between the unpaired spins of a π-cation radical and copper(II) is much stronger in the 2e-oxidized complex of copper(II)-iron(III) porphyrin dimer as compared to its copper(II)-manganese(III) analog. The Mulliken spin density distributions in 2e-oxidized homo- and heterobimetallic complexes show symmetric and asymmetric spread between the two macrocycles, respectively. In both the 2e-oxidized heterobimetallic complexes, the Cu(II) porphyrin center acts as a charge donor while Fe(III)/Mn(III) porphyrin center act as a charge acceptor. The experimental observations are also strongly supported by DFT calculations.
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Affiliation(s)
- Amit Kumar
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Mohammad Usman
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Deepannita Samanta
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Sankar Prasad Rath
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
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2
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Weitz AC, Biswas S, Rizzolo K, Elliott S, Bominaar EL, Hendrich MP. Electronic State of the His/Tyr-Ligated Heme of BthA by Mössbauer and DFT Analysis. Inorg Chem 2020; 59:10223-10233. [PMID: 32602712 DOI: 10.1021/acs.inorgchem.0c01349] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The BthA protein from the microorganism Burkholderia thailandensis contains two hemes with axial His/OH2 and His/Tyr coordinations separated by the closest interheme distance of 14 Å. BthA has a similar structure and belongs to the same family of multiheme cytochrome c peroxidases as MauG, which performs long-range oxidation of the partner protein methylamine dehydrogenase. Magnetic Mössbauer spectroscopy of the diferric state of BthA corroborates previous structural work identifying a high-spin (His/OH2) peroxidatic heme and a low-spin (His/Tyr) electron transfer heme. Unlike MauG, addition of H2O2 fully converts the diferric form of BthA to a stable 2e- oxidized state, allowing a new assessment of this state. The peroxidatic heme is found to be oxidized to a canonical compound II, S = 1 oxoiron(IV) heme. In contrast, the electronic properties of the oxidized His/Tyr heme are puzzling. The isomer shift of the His/Tyr heme (0.17 mm/s) is close to that of the precursor S = 1/2 Fe3+ heme (0.21 mm/s) which suggests oxidation of the Tyr. However, the spin-dipolar hyperfine coupling constants are found here to be the same as those for the ferryl peroxidatic heme, indicating that the His/Tyr heme is also a compound II, S = 1 Fe4+ heme and ruling out oxidation of the Tyr. DFT calculations indicate that the unusually high isomer shift is not attributable to the rare axial His/Tyr heme coordination. The calculations are only compatible with spectroscopy for an unusually long Fe4+-OTyr distance, which is presumably under the influence of the protein environment of the His/Tyr heme moiety in the H2O2 oxidized state of the protein. The results offer new insights into how high valence intermediates can be tuned by the protein environment for performing long-range oxidation.
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Affiliation(s)
- Andrew C Weitz
- Department of Chemistry, Boston University, Boston, Massachusetts 02215, United States
| | - Saborni Biswas
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Kim Rizzolo
- Department of Chemistry, Boston University, Boston, Massachusetts 02215, United States
| | - Sean Elliott
- Department of Chemistry, Boston University, Boston, Massachusetts 02215, United States
| | - Emile L Bominaar
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Michael P Hendrich
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
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3
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Zhang Y. Computational Investigations of Heme Carbenes and Heme Carbene Transfer Reactions. Chemistry 2019; 25:13231-13247. [DOI: 10.1002/chem.201901984] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Revised: 06/19/2019] [Indexed: 12/15/2022]
Affiliation(s)
- Yong Zhang
- Department of Chemistry and Chemical Biology Stevens Institute of Technology 1 Castle Point on Hudson Hoboken NJ 07030 USA
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4
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Wei Y, Tinoco A, Steck V, Fasan R, Zhang Y. Cyclopropanations via Heme Carbenes: Basic Mechanism and Effects of Carbene Substituent, Protein Axial Ligand, and Porphyrin Substitution. J Am Chem Soc 2018; 140:1649-1662. [PMID: 29268614 PMCID: PMC5875692 DOI: 10.1021/jacs.7b09171] [Citation(s) in RCA: 89] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
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Catalytic carbene
transfer to olefins is a useful approach to synthesize
cyclopropanes, which are key structural motifs in many drugs and biologically
active natural products. While catalytic methods for olefin cyclopropanation
have largely relied on rare transition-metal-based catalysts, recent
studies have demonstrated the promise and synthetic value of iron-based
heme-containing proteins for promoting these reactions with excellent
catalytic activity and selectivity. Despite this progress, the mechanism
of iron-porphyrin and hemoprotein-catalyzed olefin cyclopropanation
has remained largely unknown. Using a combination of quantum chemical
calculations and experimental mechanistic analyses, the present study
shows for the first time that the increasingly useful C=C functionalizations
mediated by heme carbenes feature an FeII-based, nonradical,
concerted nonsynchronous mechanism, with early transition state character.
This mechanism differs from the FeIV-based, radical, stepwise
mechanism of heme-dependent monooxygenases. Furthermore, the effects
of the carbene substituent, metal coordinating axial ligand, and porphyrin
substituent on the reactivity of the heme carbenes was systematically
investigated, providing a basis for explaining experimental reactivity
results and defining strategies for future catalyst development. Our
results especially suggest the potential value of electron-deficient
porphyrin ligands for increasing the electrophilicity and thus the
reactivity of the heme carbene. Metal-free reactions were also studied
to reveal temperature and carbene substituent effects on catalytic
vs noncatalytic reactions. This study sheds new light into the mechanism
of iron-porphyrin and hemoprotein-catalyzed cyclopropanation reactions
and it is expected to facilitate future efforts toward sustainable
carbene transfer catalysis using these systems.
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Affiliation(s)
- Yang Wei
- Department of Chemistry and Chemical Biology, Stevens Institute of Technology , 1 Castle Point on Hudson, Hoboken, New Jersey 07030, United States of America
| | - Antonio Tinoco
- Department of Chemistry, University of Rochester , 120 Trustee Road, Rochester, New York 14627, United States of America
| | - Viktoria Steck
- Department of Chemistry, University of Rochester , 120 Trustee Road, Rochester, New York 14627, United States of America
| | - Rudi Fasan
- Department of Chemistry, University of Rochester , 120 Trustee Road, Rochester, New York 14627, United States of America
| | - Yong Zhang
- Department of Chemistry and Chemical Biology, Stevens Institute of Technology , 1 Castle Point on Hudson, Hoboken, New Jersey 07030, United States of America
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5
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Khade RL, Zhang Y. C-H Insertions by Iron Porphyrin Carbene: Basic Mechanism and Origin of Substrate Selectivity. Chemistry 2017; 23:17654-17658. [PMID: 29071754 DOI: 10.1002/chem.201704631] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Indexed: 11/09/2022]
Abstract
Recent experimental reports of heme carbene C-H insertions show promising results for sustainable chemistry due to good yield and selectivity, low cost of iron, and low/no toxicity of hemes. But mechanistic details are mostly unknown. Despite structural similarity and isoelectronic nature between heme carbene and the FeIV =O intermediate, our quantum chemical studies with detailed geometric and electronic information for the first time reveal an FeII -based, concerted, hydride-transfer mechanism, which is different from the FeIV -based stepwise hydrogen atom transfer mechanism for C-H functionalization by native heme enzymes. A trend of broad range experimental C-H insertion yields (0-88 %) of five different C-H bonds, including mostly non-functionalized moieties, was well reproduced. Results suggest that the substrate selectivity originates from the hydride formation capability. The predicted kinetic isotope effects were also in excellent agreement with experiment. Useful geometry, charge, and energy parameters well correlated with barriers were reported. These results provide the first theoretical evidence that carbene formation is the overall rate-limiting step, and suggest a key role of the formation of strong electrophilic heme carbene in developing heme-based C-H insertion catalysts and biocatalysts.
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Affiliation(s)
- Rahul L Khade
- Department of Chemistry and Chemical Biology, Stevens Institute of Technology, 1 Castle Point on Hudson, Hoboken, NJ 07030, USA
| | - Yong Zhang
- Department of Chemistry and Chemical Biology, Stevens Institute of Technology, 1 Castle Point on Hudson, Hoboken, NJ 07030, USA
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6
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Guchhait T, Sarkar S, Pandit YA, Rath SP. Probing Bis‐FeIVMauG: Isolation of Highly Reactive Radical Intermediates. Chemistry 2017; 23:10270-10275. [DOI: 10.1002/chem.201702321] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Indexed: 11/11/2022]
Affiliation(s)
- Tapas Guchhait
- Department of ChemistryIndian Institute of Technology Kanpur Kanpur 208016 India
| | - Sabyasachi Sarkar
- Department of ChemistryIndian Institute of Technology Kanpur Kanpur 208016 India
| | - Younis Ahmad Pandit
- Department of ChemistryIndian Institute of Technology Kanpur Kanpur 208016 India
| | - Sankar Prasad Rath
- Department of ChemistryIndian Institute of Technology Kanpur Kanpur 208016 India
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7
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Feng M, Ma Z, Crudup BF, Davidson VL. Properties of the high-spin heme of MauG are altered by binding of preMADH at the protein surface 40 Å away. FEBS Lett 2017; 591:1566-1572. [PMID: 28485817 DOI: 10.1002/1873-3468.12666] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2017] [Revised: 04/28/2017] [Accepted: 05/02/2017] [Indexed: 11/09/2022]
Abstract
The diheme enzyme MauG catalyzes oxidative post-translational modifications of a protein substrate, precursor protein of methylamine dehydrogenase (preMADH), that binds to the surface of MauG. The high-spin heme iron of MauG is located 40 Å from preMADH. The ferric heme is an equilibrium of five- and six-coordinate states. PreMADH binding increases the proportion of five-coordinate heme three-fold. On reaction of MauG with H2 O2 both hemes become FeIV . In the absence of preMADH the hemes autoreduce to ferric in a multistep process involving multiple electron and proton transfers. Binding of preMADH in the absence of catalysis alters the mechanism of autoreduction of the ferryl heme. Thus, substrate binding alters the environment in the distal heme pocket of the high-spin heme over very long distance.
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Affiliation(s)
| | - Zhongxin Ma
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL, USA
| | | | - Victor L Davidson
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL, USA
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8
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Ma Z, Williamson HR, Davidson VL. A Suicide Mutation Affecting Proton Transfers to High-Valent Hemes Causes Inactivation of MauG during Catalysis. Biochemistry 2016; 55:5738-5745. [PMID: 27622473 DOI: 10.1021/acs.biochem.6b00816] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In the absence of its substrate, the autoreduction of the high-valent bis-FeIV state of the hemes of MauG to the diferric state proceeds via a Compound I-like and then a Compound II-like intermediate. This process is coupled to oxidative damage to specific methionine residues and inactivation of MauG. The autoreduction of a P107V MauG variant, which is more prone to oxidative damage, proceeds directly from the bis-FeIV to the Compound II-like state with no detectable Compound I intermediate. Comparison of the crystal structures of native and P107V MauG reveals that this mutation alters the positions of amino acid residues in the heme site as well as the water network that delivers protons from the solvent to the hemes during their reduction. Kinetic, spectroscopic, and solvent kinetic isotope effect studies demonstrate that these changes in the heme site affect the protonation state of the ferryl heme and the relative efficiencies of two alternative pathways for the transfer of protons from solvent to the hemes. These changes enhance the rate of autoreduction of P107V MauG such that it competes with the catalytic reaction with substrate and causes the enzyme to inactivate itself during the steady-state reaction with H2O2 and its substrate. Thus, while this mutation has negligible effects on the initial steady-state kinetic parameters of MauG, it is a fatal mutation as it causes inactivation during catalysis.
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Affiliation(s)
- Zhongxin Ma
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida , Orlando, Florida 32827, United States
| | - Heather R Williamson
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida , Orlando, Florida 32827, United States
| | - Victor L Davidson
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida , Orlando, Florida 32827, United States
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9
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Arbelo-Lopez HD, Simakov NA, Smith JC, Lopez-Garriga J, Wymore T. Homolytic Cleavage of Both Heme-Bound Hydrogen Peroxide and Hydrogen Sulfide Leads to the Formation of Sulfheme. J Phys Chem B 2016; 120:7319-31. [DOI: 10.1021/acs.jpcb.6b02839] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Hector D. Arbelo-Lopez
- Chemistry
Department, University of Puerto Rico, Mayagüez Campus, Mayagüez 00681, Puerto Rico
| | - Nikolay A. Simakov
- Center
for Computational Research, University of Buffalo, Buffalo, New York 14203, United States
| | - Jeremy C. Smith
- UT/ORNL
Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6309, United States
- Department
of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Juan Lopez-Garriga
- Chemistry
Department, University of Puerto Rico, Mayagüez Campus, Mayagüez 00681, Puerto Rico
| | - Troy Wymore
- Department
of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee 37996, United States
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10
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Sil D, Dey S, Kumar A, Bhowmik S, Rath SP. Oxidation triggers extensive conjugation and unusual stabilization of two di-heme dication diradical intermediates: role of bridging group for electronic communication. Chem Sci 2015; 7:1212-1223. [PMID: 29910877 PMCID: PMC5975787 DOI: 10.1039/c5sc03120f] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2015] [Accepted: 10/26/2015] [Indexed: 11/21/2022] Open
Abstract
Synthetic analogs of diheme enzyme MauG have been reported. Unlike the bis-Fe(iv) state in MauG, the 2e-oxidation stabilizes two ferric hemes, each coupled with a porphyrin π-cation radical.
MauG is a diheme enzyme that utilizes two covalently bound c-type hemes to catalyse the biosynthesis of the protein-derived cofactor tryptophan tryptophylquinone. The two hemes are physically separated by 14.5 Å and a hole-hopping mechanism is proposed in which a tryptophan residue located between the hemes undergoes reversible oxidation and reduction to increase the effective electronic coupling element and enhance the rate of reversible electron transfer between the hemes in bis-Fe(iv) MauG. The present work describes the structure and spectroscopic investigation of 2e-oxidations of the synthetic diheme analogs in which two heme centers are covalently connected through a conjugated ethylene bridge that leads to the stabilization of two unusual trans conformations (U and P′ forms) with different and distinct spectroscopic and geometric features. Unlike in MauG, where the two oxidizing equivalents are distributed within the diheme system giving rise to the bis-Fe(iv) redox state, the synthetic analog stabilizes two ferric hemes, each coupled with a porphyrin cation radical, a scenario resembling the binuclear dication diradical complex. Interestingly, charge resonance-transition phenomena are observed here both in 1e and 2e-oxidised species from the same system, which are also clearly distinguishable by their relative position and intensity. Detailed UV-vis-NIR, X-ray, Mössbauer, EPR and 1H NMR spectroscopic investigations as well as variable temperature magnetic studies have unraveled strong electronic communications between two porphyrin π-cation radicals through the bridging ethylene group. The extensive π-conjugation also allows antiferromagnetic coupling between iron(iii) centers and porphyrin radical spins of both rings. DFT calculations revealed extended π-conjugation and H-bonding interaction as the major factors in controlling the stability of the conformers.
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Affiliation(s)
- Debangsu Sil
- Department of Chemistry , Indian Institute of Technology Kanpur , Kanpur-208016 , India . ;
| | - Soumyajit Dey
- Department of Chemistry , Indian Institute of Technology Kanpur , Kanpur-208016 , India . ;
| | - Amit Kumar
- Department of Chemistry , Indian Institute of Technology Kanpur , Kanpur-208016 , India . ;
| | - Susovan Bhowmik
- Department of Chemistry , Indian Institute of Technology Kanpur , Kanpur-208016 , India . ;
| | - Sankar Prasad Rath
- Department of Chemistry , Indian Institute of Technology Kanpur , Kanpur-208016 , India . ;
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11
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Roles of multiple-proton transfer pathways and proton-coupled electron transfer in the reactivity of the bis-FeIV state of MauG. Proc Natl Acad Sci U S A 2015; 112:10896-901. [PMID: 26283395 DOI: 10.1073/pnas.1510986112] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The high-valent state of the diheme enzyme MauG exhibits charge-resonance (CR) stabilization in which the major species is a bis-Fe(IV) state with one heme present as Fe(IV)=O and the other as Fe(IV) with axial heme ligands provided by His and Tyr side chains. In the absence of its substrate, the high-valent state is relatively stable and returns to the diferric state over several minutes. It is shown that this process occurs in two phases. The first phase is redistribution of the resonance species that support the CR. The second phase is the loss of CR and reduction to the diferric state. Thermodynamic analysis revealed that the rates of the two phases exhibited different temperature dependencies and activation energies of 8.9 and 19.6 kcal/mol. The two phases exhibited kinetic solvent isotope effects of 2.5 and 2.3. Proton inventory plots of each reaction phase exhibited extreme curvature that could not be fit to models for one- or multiple-proton transfers in the transition state. Each did fit well to a model for two alternative pathways for proton transfer, each involving multiple protons. In each case the experimentally determined fractionation factors were consistent with one of the pathways involving tunneling. The percent of the reaction that involved the tunneling pathway differed for the two reaction phases. Using the crystal structure of MauG it was possible to propose proton-transfer pathways consistent with the experimental data using water molecules and amino acid side chains in the distal pocket of the high-spin heme.
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12
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Shin S, Feng M, Li C, Williamson HR, Choi M, Wilmot CM, Davidson VL. A T67A mutation in the proximal pocket of the high-spin heme of MauG stabilizes formation of a mixed-valent FeII/FeIII state and enhances charge resonance stabilization of the bis-FeIV state. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1847:709-16. [PMID: 25896561 DOI: 10.1016/j.bbabio.2015.04.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2015] [Revised: 04/03/2015] [Accepted: 04/12/2015] [Indexed: 10/23/2022]
Abstract
The diheme enzyme MauG catalyzes a six-electron oxidation required for posttranslational modification of a precursor of methylamine dehydrogenase (preMADH) to complete the biosynthesis of its protein-derived tryptophan tryptophylquinone (TTQ) cofactor. One heme is low-spin with ligands provided by His205 and Tyr294, and the other is high-spin with a ligand provided by His35. The side chain methyl groups of Thr67 and Leu70 are positioned at a distance of 3.4Å on either side of His35, maintaining a hydrophobic environment in the proximal pocket of the high-spin heme and restricting the movement of this ligand. Mutation of Thr67 to Ala in the proximal pocket of the high-spin heme prevented reduction of the low-spin heme by dithionite, yielding a mixed-valent state. The mutation also enhanced the stabilization of the charge-resonance-transition of the high-valent bis-FeIV state that is generated by addition of H2O2. The rates of electron transfer from TTQ biosynthetic intermediates to the high-valent form of T67A MauG were similar to that of wild-type MauG. These results are compared to those previously reported for mutation of residues in the distal pocket of the high-spin heme that also affected the redox properties and charge resonance transition stabilization of the high-valent state of the hemes. However, given the position of residue 67, the structure of the variant protein and the physical nature of the T67A mutation, the basis for the effects of the T67A mutation must be different from those of the mutations of the residues in the distal heme pocket.
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Affiliation(s)
- Sooim Shin
- Department of Bioengineering and Biotechnology, College of Engineering, Chonnam National University, Chonnam, South Korea
| | - Manliang Feng
- Department of Chemistry, Tougaloo College, Tougaloo, MS 39174, USA
| | - Chao Li
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, St. Paul, MN 55108, USA
| | - Heather R Williamson
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32827, USA
| | - Moonsung Choi
- Department of Optometry, College of Energy and Biotechnology, Seoul National University of Science and Technology, Seoul 139-743, South Korea
| | - Carrie M Wilmot
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, St. Paul, MN 55108, USA
| | - Victor L Davidson
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32827, USA.
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13
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Khade RL, Fan W, Ling Y, Yang L, Oldfield E, Zhang Y. Iron porphyrin carbenes as catalytic intermediates: structures, Mössbauer and NMR spectroscopic properties, and bonding. Angew Chem Int Ed Engl 2014; 53:7574-8. [PMID: 24910004 DOI: 10.1002/anie.201402472] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2014] [Revised: 04/08/2014] [Indexed: 11/07/2022]
Abstract
Iron porphyrin carbenes (IPCs) are thought to be intermediates involved in the metabolism of various xenobiotics by cytochrome P450, as well as in chemical reactions catalyzed by metalloporphyrins and engineered P450s. While early work proposed IPCs to contain Fe(II), more recent work invokes a double-bond description of the iron-carbon bond, similar to that found in Fe(IV) porphyrin oxenes. Reported herein is the first quantum chemical investigation of IPC Mössbauer and NMR spectroscopic properties, as well as their electronic structures, together with comparisons to ferrous heme proteins and an Fe(IV) oxene model. The results provide the first accurate predictions of the experimental spectroscopic observables as well as the first theoretical explanation of their electrophilic nature, as deduced from experiment. The preferred resonance structure is Fe(II)←{:C(X)Y}(0) and not Fe(IV)={C(X)Y}(2-), a result that will facilitate research on IPC reactivities in various chemical and biochemical systems.
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Affiliation(s)
- Rahul L Khade
- Department of Chemistry, Chemical Biology, and Biomedical, Engineering, Stevens Institute of Technology, Castle Point on Hudson, Hoboken, NJ 07030 (USA)
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14
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Khade RL, Fan W, Ling Y, Yang L, Oldfield E, Zhang Y. Iron Porphyrin Carbenes as Catalytic Intermediates: Structures, Mössbauer and NMR Spectroscopic Properties, and Bonding. Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201402472] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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15
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Shin S, Yukl ET, Sehanobish E, Wilmot CM, Davidson VL. Site-directed mutagenesis of Gln103 reveals the influence of this residue on the redox properties and stability of MauG. Biochemistry 2014; 53:1342-9. [PMID: 24517455 PMCID: PMC3985960 DOI: 10.1021/bi5000349] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
The diheme enzyme MauG catalyzes
a six-electron oxidation that
is required for the posttranslational modification of a precursor
of methylamine dehydrogenase (preMADH) to complete the biosynthesis
of its protein-derived cofactor, tryptophan tryptophylquinone (TTQ).
Crystallographic and computational studies have implicated Gln103
in stabilizing the FeIV=O moiety of the bis-FeIV state by hydrogen bonding. The role of Gln103 was probed
by site-directed mutagenesis. Q103L and Q103E mutations resulted in
no expression and very little expression of the protein, respectively.
Q103A MauG exhibited oxidative damage when isolated. Q103N MauG was
isolated at levels comparable to that of wild-type MauG and exhibited
normal activity in catalyzing the biosynthesis of TTQ from preMADH.
The crystal structure of the Q103N MauG–preMADH complex suggests
that a water may mediate hydrogen bonding between the shorter Asn103
side chain and the FeIV=O moiety. The Q103N mutation
caused the two redox potentials associated with the diferric/diferrous
redox couple to become less negative, although the redox cooperativity
of the hemes of MauG was retained. Upon addition of H2O2, Q103N MauG exhibits changes in the absorbance spectrum in
the Soret and near-IR regions consistent with formation of the bis-FeIV redox state. However, the rate of spontaneous return of
the spectrum in the Soret region was 4.5-fold greater for Q103N MauG
than for wild-type MauG. In contrast, the rate of spontaneous decay
of the absorbance at 950 nm, which is associated with charge-resonance
stabilization of the high-valence state, was similar for wild-type
MauG and Q103N MauG. This suggests that as a consequence of the mutation
a different distribution of resonance structures stabilizes the bis-FeIV state. These results demonstrate that subtle changes in
the structure of the side chain of residue 103 can significantly affect
the overall protein stability of MauG and alter the redox properties
of the hemes.
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Affiliation(s)
- Sooim Shin
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida , Orlando, Florida 32827, United States
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16
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Shin S, Davidson VL. MauG, a diheme enzyme that catalyzes tryptophan tryptophylquinone biosynthesis by remote catalysis. Arch Biochem Biophys 2014; 544:112-8. [PMID: 24144526 PMCID: PMC3946517 DOI: 10.1016/j.abb.2013.10.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2013] [Revised: 10/03/2013] [Accepted: 10/08/2013] [Indexed: 11/30/2022]
Abstract
MauG contains two c-type hemes with atypical physical and catalytic properties. While most c-type cytochromes function simply as electron transfer mediators, MauG catalyzes the completion of tryptophan tryptophylquinone (TTQ)(1) biosynthesis within a precursor protein of methylamine dehydrogenase. This posttranslational modification is a six-electron oxidation that requires crosslinking of two Trp residues, oxygenation of a Trp residue and oxidation of the resulting quinol to TTQ. These reactions proceed via a bis-Fe(IV) state in which one heme is present as Fe(IV)O and the other is Fe(IV) with axial heme ligands provided by His and Tyr side chains. Catalysis does not involve direct contact between the protein substrate and either heme of MauG. Instead it is accomplished by remote catalysis using a hole hopping mechanism of electron transfer in which Trp residues of MauG are reversibly oxidized. In this process, long range electron transfer is coupled to the radical mediated chemical reactions that are required for TTQ biosynthesis.
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Affiliation(s)
- Sooim Shin
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32827, USA
| | - Victor L Davidson
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32827, USA.
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17
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Davidson VL, Wilmot CM. Posttranslational biosynthesis of the protein-derived cofactor tryptophan tryptophylquinone. Annu Rev Biochem 2013; 82:531-50. [PMID: 23746262 DOI: 10.1146/annurev-biochem-051110-133601] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Methylamine dehydrogenase (MADH) catalyzes the oxidative deamination of methylamine to formaldehyde and ammonia. Tryptophan tryptophylquinone (TTQ) is the protein-derived cofactor of MADH required for this catalytic activity. TTQ is biosynthesized through the posttranslational modification of two tryptophan residues within MADH, during which the indole rings of two tryptophan side chains are cross-linked and two oxygen atoms are inserted into one of the indole rings. MauG is a c-type diheme enzyme that catalyzes the final three reactions in TTQ formation. In total, this is a six-electron oxidation process requiring three cycles of MauG-dependent two-electron oxidation events using either H2O2 or O2. The MauG redox form responsible for the catalytic activity is an unprecedented bis-Fe(IV) species. The amino acids of MADH that are modified are ≈ 40 Å from the site where MauG binds oxygen, and the reaction proceeds by a hole hopping electron transfer mechanism. This review addresses these highly unusual aspects of the long-range catalytic reaction mediated by MauG.
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Affiliation(s)
- Victor L Davidson
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida 32827, USA.
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18
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Abu Tarboush N, Yukl ET, Shin S, Feng M, Wilmot CM, Davidson VL. Carboxyl group of Glu113 is required for stabilization of the diferrous and bis-Fe(IV) states of MauG. Biochemistry 2013; 52:6358-67. [PMID: 23952537 DOI: 10.1021/bi400905s] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The diheme enzyme MauG catalyzes a six-electron oxidation required for post-translational modification of a precursor of methylamine dehydrogenase (preMADH) to complete the biosynthesis of its protein-derived tryptophan tryptophylquinone (TTQ) cofactor. Crystallographic studies have implicated Glu113 in the formation of the bis-Fe(IV) state of MauG, in which one heme is Fe(IV)═O and the other is Fe(IV) with His-Tyr axial ligation. An E113Q mutation had no effect on the structure of MauG but significantly altered its redox properties. E113Q MauG could not be converted to the diferrous state by reduction with dithionite but was only reduced to a mixed valence Fe(II)/Fe(III) state, which is never observed in wild-type (WT) MauG. Addition of H2O2 to E113Q MauG generated a high valence state that formed more slowly and was less stable than the bis-Fe(IV) state of WT MauG. E113Q MauG exhibited no detectable TTQ biosynthesis activity in a steady-state assay with preMADH as the substrate. It did catalyze the steady-state oxidation of quinol MADH to the quinone, but 1000-fold less efficiently than WT MauG. Addition of H2O2 to a crystal of the E113Q MauG-preMADH complex resulted in partial synthesis of TTQ. Extended exposure of these crystals to H2O2 resulted in hydroxylation of Pro107 in the distal pocket of the high-spin heme. It is concluded that the loss of the carboxylic group of Glu113 disrupts the redox cooperativity between hemes that allows rapid formation of the diferrous state and alters the distribution of high-valence species that participate in charge-resonance stabilization of the bis-Fe(IV) redox state.
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Affiliation(s)
- Nafez Abu Tarboush
- Biochemistry and Physiology Department, College of Medicine, The University of Jordan , Amman, Jordan 11942
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19
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Abstract
Methylamine dehydrogenase (MADH) requires the cofactor tryptophan tryptophylquinone (TTQ) for activity. TTQ is a posttranslational modification that results from an 8-electron oxidation of two specific tryptophans in the MADH β-subunit. The final 6-electron oxidation is catalyzed by an unusual c-type di-heme enzyme, MauG. The di-ferric enzyme can react with H(2)O(2), but atypically for c-type hemes the di-ferrous enzyme can react with O(2) as well. In both cases, an unprecedented bis-Fe(IV) redox state is formed, composed of a ferryl heme (Fe(IV)=O) with the second heme as Fe(IV) stabilized by His-Tyr axial ligation. Bis-Fe(IV) MauG acts as a potent 2-electron oxidant. Catalysis is long-range and requires a hole hopping electron transfer mechanism. This review highlights the current knowledge and focus of research into this fascinating system.
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Affiliation(s)
- Carrie M Wilmot
- Department of Biochemistry, Molecular Biology and Biophysics, Minneapolis, Minnesota 55455, USA.
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20
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Ikezaki A, Takahashi M, Nakamura M. Equilibrium between Fe(IV) porphyrin and Fe(III) porphyrin radical cation: new insight into the electronic structure of high-valent iron porphyrin complexes. Chem Commun (Camb) 2013; 49:3098-100. [PMID: 23435760 DOI: 10.1039/c3cc40319j] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
UV-Vis, NMR, and Mössbauer studies have revealed that [Fe(TMP)(N3)2], showing the Mössbauer parameters quite similar to those of the ferryl species of MauG, CytP450BM3, Cyt P450CAM, and CPO, exists as equilibrium mixtures of Fe(IV) porphyrin and Fe(III) porphyrin radical cation.
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Affiliation(s)
- Akira Ikezaki
- Department of Chemistry, School of Medicine, Toho University, Otaku, Tokyo 143-8540, Japan.
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21
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Katigbak J, Zhang Y. Iron Binding Site in a Global Regulator in Bacteria - Ferric Uptake Regulator (Fur) Protein: Structure, Mössbauer Properties, and Functional Implication. J Phys Chem Lett 2012; 2012:3503-3508. [PMID: 23205186 PMCID: PMC3507992 DOI: 10.1021/jz301689b] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Fur protein plays key roles in regulating numerous genes in bacteria and is essential for intracellular iron concentration regulation. However, atomic level pictures of the iron binding site and its functional mechanism remain to be established. Here we present results of the first quantum chemical investigation of various first- and second-shell models and experimental Mössbauer data of E. Coli Fur, including 1) the first robust evidence that site 2 is the Fe binding site with a 3His/2Glu ligand set, being the first case in non-heme proteins, with computed Mössbauer data in excellent accord with experiment; 2) the first discovery of a conservative hydrogen bonding interaction in the iron binding site based on X-ray and homology structures; 3) the first atomic level hypothesis of active site reorganization upon iron concentration increase, triggering the conformational change needed for its function. These results shall facilitate structural and functional studies of Fur family proteins.
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22
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Zhang Y. Computational investigations of HNO in biology. J Inorg Biochem 2012; 118:191-200. [PMID: 23103077 DOI: 10.1016/j.jinorgbio.2012.09.023] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2012] [Revised: 09/01/2012] [Accepted: 09/27/2012] [Indexed: 10/27/2022]
Abstract
HNO (nitroxyl) has been found to have many physiological effects in numerous biological processes. Computational investigations have been employed to help understand the structural properties of HNO complexes and HNO reactivities in some interesting biologically relevant systems. The following computational aspects were reviewed in this work: 1) structural and energetic properties of HNO isomers; 2) interactions between HNO and non-metal molecules; 3) structural and spectroscopic properties of HNO metal complexes; 4) HNO reactions with biologically important non-metal systems; 5) involvement of HNO in reactions of metal complexes and metalloproteins. Results indicate that computational investigations are very helpful to elucidate interesting experimental phenomena and provide new insights into unique structural, spectroscopic, and mechanistic properties of HNO involvement in biology.
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Affiliation(s)
- Yong Zhang
- Department of Chemistry, Chemical Biology, and Biomedical Engineering, Stevens Institute of Technology, 1 Castle Point on Hudson, Hoboken, NJ 07030, USA.
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23
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Geometric and electronic structures of the His-Fe(IV)=O and His-Fe(IV)-Tyr hemes of MauG. J Biol Inorg Chem 2012; 17:1241-55. [PMID: 23053529 DOI: 10.1007/s00775-012-0939-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2012] [Accepted: 09/12/2012] [Indexed: 10/27/2022]
Abstract
Biosynthesis of the tryptophan tryptophylquinone (TTQ) cofactor activates the enzyme methylamine dehydrogenase. The diheme enzyme MauG catalyzes O-atom insertion and cross-linking of two Trp residues to complete TTQ synthesis. Solution optical and Mössbauer spectroscopic studies have indicated that the reactive form of MauG during turnover is an unusual bisFe(IV) intermediate, which has been formulated as a His-ligated ferryl heme [Fe(IV)=O] (heme A), and an Fe(IV) heme with an atypical His/Tyr ligation (heme B). In this study, Fe K-edge X-ray absorption spectroscopy and extended X-ray absorption fine structure studies have been combined with density functional theory (DFT) and time-dependent DFT methods to solve the geometric and electronic structures of each heme site in the MauG bisFe(IV) redox state. The ferryl heme site (heme A) is compared with the well-characterized compound I intermediate of cytochrome c peroxidase. Heme B is unprecedented in biology, and is shown to have a six-coordinate, S = 1 environment, with a short (1.85-Å) Fe-O(Tyr) bond. Experimentally calibrated DFT calculations are used to reveal a strong covalent interaction between the Fe and the O(Tyr) ligand of heme B in the high-valence form. A large change in the Fe-O(Tyr) bond distance on going from Fe(II) (2.02 Å) to Fe(III) (1.89 Å) to Fe(IV) (1.85 Å) signifies increasing localization of spin density on the tyrosinate ligand upon sequential oxidation of heme B to Fe(IV). As such, O(Tyr) plays an active role in attaining and stabilizing the MauG bisFe(IV) redox state.
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24
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Yukl ET, Wilmot CM. Cofactor biosynthesis through protein post-translational modification. Curr Opin Chem Biol 2012; 16:54-9. [PMID: 22387133 DOI: 10.1016/j.cbpa.2012.02.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2011] [Revised: 02/09/2012] [Accepted: 02/10/2012] [Indexed: 11/25/2022]
Abstract
Post-translational modifications of amino acids can be used to generate novel cofactors capable of chemistries inaccessible to conventional amino acid side chains. The biosynthesis of these sites often requires one or more enzyme or protein accessory factors, the functions of which are quite diverse and often difficult to isolate in cases where multiple enzymes are involved. Herein is described the current knowledge of the biosynthesis of urease and nitrile hydratase metal centers, pyrroloquinoline quinone, hypusine, and tryptophan tryptophylquinone cofactors along with the most recent work elucidating the functions of individual accessory factors in these systems. These examples showcase the breadth and diversity of this continually expanding field.
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Affiliation(s)
- Erik T Yukl
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, 321 Church St. SE, Minneapolis, MN 55455, United States
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25
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Davidson VL, Liu A. Tryptophan tryptophylquinone biosynthesis: a radical approach to posttranslational modification. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2012; 1824:1299-305. [PMID: 22314272 DOI: 10.1016/j.bbapap.2012.01.008] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2011] [Accepted: 01/17/2012] [Indexed: 11/20/2022]
Abstract
Protein-derived cofactors are formed by irreversible covalent posttranslational modification of amino acid residues. An example is tryptophan tryptophylquinone (TTQ) found in the enzyme methylamine dehydrogenase (MADH). TTQ biosynthesis requires the cross-linking of the indole rings of two Trp residues and the insertion of two oxygen atoms onto adjacent carbons of one of the indole rings. The diheme enzyme MauG catalyzes the completion of TTQ within a precursor protein of MADH. The preMADH substrate contains a single hydroxyl group on one of the tryptophans and no crosslink. MauG catalyzes a six-electron oxidation that completes TTQ assembly and generates fully active MADH. These oxidation reactions proceed via a high valent bis-Fe(IV) state in which one heme is present as Fe(IV)=O and the other is Fe(IV) with both axial heme ligands provided by amino acid side chains. The crystal structure of MauG in complex with preMADH revealed that catalysis does not involve direct contact between the hemes of MauG and the protein substrate. Rather it is accomplished through long-range electron transfer, which presumably generates radical intermediates. Kinetic, spectrophotometric, and site-directed mutagenesis studies are beginning to elucidate how the MauG protein controls the reactivity of the hemes and mediates the long range electron/radical transfer required for catalysis. This article is part of a Special Issue entitled: Radical SAM enzymes and Radical Enzymology.
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Affiliation(s)
- Victor L Davidson
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32827, USA.
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26
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Fu R, Gupta R, Geng J, Dornevil K, Wang S, Zhang Y, Hendrich MP, Liu A. Enzyme reactivation by hydrogen peroxide in heme-based tryptophan dioxygenase. J Biol Chem 2011; 286:26541-54. [PMID: 21632548 PMCID: PMC3143619 DOI: 10.1074/jbc.m111.253237] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2011] [Revised: 05/29/2011] [Indexed: 11/06/2022] Open
Abstract
An intriguing mystery about tryptophan 2,3-dioxygenase is its hydrogen peroxide-triggered enzyme reactivation from the resting ferric oxidation state to the catalytically active ferrous form. In this study, we found that such an odd Fe(III) reduction by an oxidant depends on the presence of L-Trp, which ultimately serves as the reductant for the enzyme. In the peroxide reaction with tryptophan 2,3-dioxygenase, a previously unknown catalase-like activity was detected. A ferryl species (δ = 0.055 mm/s and ΔE(Q) = 1.755 mm/s) and a protein-based free radical (g = 2.0028 and 1.72 millitesla linewidth) were characterized by Mössbauer and EPR spectroscopy, respectively. This is the first compound ES-type of ferryl intermediate from a heme-based dioxygenase characterized by EPR and Mössbauer spectroscopy. Density functional theory calculations revealed the contribution of secondary ligand sphere to the spectroscopic properties of the ferryl species. In the presence of L-Trp, the reactivation was demonstrated by enzyme assays and by various spectroscopic techniques. A Trp-Trp dimer and a monooxygenated L-Trp were both observed as the enzyme reactivation by-products by mass spectrometry. Together, these results lead to the unraveling of an over 60-year old mystery of peroxide reactivation mechanism. These results may shed light on how a metalloenzyme maintains its catalytic activity in an oxidizing environment.
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Affiliation(s)
- Rong Fu
- From the Department of Chemistry, Georgia State University, Atlanta, Georgia 30303
| | - Rupal Gupta
- the Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, and
| | - Jiafeng Geng
- From the Department of Chemistry, Georgia State University, Atlanta, Georgia 30303
| | - Kednerlin Dornevil
- From the Department of Chemistry, Georgia State University, Atlanta, Georgia 30303
| | - Siming Wang
- From the Department of Chemistry, Georgia State University, Atlanta, Georgia 30303
| | - Yong Zhang
- the Department of Chemistry, Chemical Biology, and Biomedical Engineering, Stevens Institute of Technology, Castle Point on Hudson, Hoboken, New Jersey 07030
| | - Michael P. Hendrich
- the Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, and
| | - Aimin Liu
- From the Department of Chemistry, Georgia State University, Atlanta, Georgia 30303
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27
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Yukl ET, Goblirsch BR, Davidson VL, Wilmot CM. Crystal structures of CO and NO adducts of MauG in complex with pre-methylamine dehydrogenase: implications for the mechanism of dioxygen activation. Biochemistry 2011; 50:2931-8. [PMID: 21355604 DOI: 10.1021/bi200023n] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
MauG is a diheme enzyme responsible for the post-translational formation of the catalytic tryptophan tryptophylquinone (TTQ) cofactor in methylamine dehydrogenase (MADH). MauG can utilize hydrogen peroxide, or molecular oxygen and reducing equivalents, to complete this reaction via a catalytic bis-Fe(IV) intermediate. Crystal structures of diferrous, Fe(II)-CO, and Fe(II)-NO forms of MauG in complex with its preMADH substrate have been determined and compared to one another as well as to the structure of the resting diferric MauG-preMADH complex. CO and NO each bind exclusively to the 5-coordinate high-spin heme with no change in ligation of the 6-coordinate low-spin heme. These structures reveal likely roles for amino acid residues in the distal pocket of the high-spin heme in oxygen binding and activation. Glu113 is implicated in the protonation of heme-bound diatomic oxygen intermediates in promoting cleavage of the O-O bond. Pro107 is shown to change conformation on the binding of each ligand and may play a steric role in oxygen activation by positioning the distal oxygen near Glu113. Gln103 is in a position to provide a hydrogen bond to the Fe(IV)═O moiety that may account for the unusual stability of this species in MauG.
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Affiliation(s)
- Erik T Yukl
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, 321 Church Street SE, Minneapolis, Minnesota 55455, United States
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28
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Ling Y, Khade RL, Zhang Y. Structural, EPR Superhyperfine, and NMR Hyperfine Properties of the Cu−Octarepeat Binding Site in the Prion Protein. J Phys Chem B 2011; 115:2663-70. [DOI: 10.1021/jp1119298] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Yan Ling
- Department of Chemistry and Biochemistry, University of Southern Mississippi, 118 College Drive #5043, Hattiesburg, Mississippi 39406, United States
| | - Rahul L. Khade
- Department of Chemistry and Biochemistry, University of Southern Mississippi, 118 College Drive #5043, Hattiesburg, Mississippi 39406, United States
| | - Yong Zhang
- Department of Chemistry and Biochemistry, University of Southern Mississippi, 118 College Drive #5043, Hattiesburg, Mississippi 39406, United States
- Department of Chemistry, Chemical Biology, and Biomedical Engineering, Stevens Institute of Technology, Castle Point on Hudson, Hoboken, New Jersey 07030, United States
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