1
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Rivera JJ, Trinh C, Kim JE. Photoinduced Electron Transfer from the Tryptophan Triplet State in Zn-Azurin. ACS PHYSICAL CHEMISTRY AU 2022; 3:63-73. [PMID: 36718260 PMCID: PMC9881450 DOI: 10.1021/acsphyschemau.2c00042] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Revised: 10/18/2022] [Accepted: 10/19/2022] [Indexed: 11/30/2022]
Abstract
Tryptophan is one of few residues that participates in biological electron transfer reactions. Upon substitution of the native Cu2+ center with Zn2+ in the blue-copper protein azurin, a long-lived tryptophan neutral radical can be photogenerated. We report the following quantum yield values for Zn-substituted azurin in the presence of the electron acceptor Cu(II)-azurin: formation of the tryptophan neutral radical (Φrad), electron transfer (ΦET), fluorescence (Φfluo), and phosphorescence (Φphos), as well as the efficiency of proton transfer of the cation radical (ΦPT). Increasing the concentration of the electron acceptor increased Φrad and ΦET values and decreased Φphos without affecting Φfluo. At all concentrations of the acceptor, the value of ΦPT was nearly unity. These observations indicate that the phosphorescent triplet state is the parent state of electron transfer and that nearly all electron transfer events lead to proton loss. Similar results regarding the parent state were obtained with a different electron acceptor, [Co(NH3)5Cl]2+; however, Stern-Volmer graphs revealed that [Co(NH3)5Cl]2+ was a more effective phosphorescence quencher (K SV = 230 000 M-1) compared to Cu(II)-azurin (K SV = 88 000 M-1). Competition experiments in the presence of both [Co(NH3)5Cl]2+ and Cu(II)-azurin suggested that [Co(NH3)5Cl]2+ is the preferred electron acceptor. Implications of these results in terms of quenching mechanisms are discussed.
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2
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Chaplin AK, Chicano TM, Hampshire BV, Wilson MT, Hough MA, Svistunenko DA, Worrall JAR. An Aromatic Dyad Motif in Dye Decolourising Peroxidases Has Implications for Free Radical Formation and Catalysis. Chemistry 2019; 25:6141-6153. [PMID: 30945782 DOI: 10.1002/chem.201806290] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2018] [Indexed: 01/27/2023]
Abstract
Dye decolouring peroxidases (DyPs) are the most recent class of heme peroxidase to be discovered. On reacting with H2 O2 , DyPs form a high-valent iron(IV)-oxo species and a porphyrin radical (Compound I) followed by stepwise oxidation of an organic substrate. In the absence of substrate, the ferryl species decays to form transient protein-bound radicals on redox active amino acids. Identification of radical sites in DyPs has implications for their oxidative mechanism with substrate. Using a DyP from Streptomyces lividans, referred to as DtpA, which displays low reactivity towards synthetic dyes, activation with H2 O2 was explored. A Compound I EPR spectrum was detected, which in the absence of substrate decays to a protein-bound radical EPR signal. Using a newly developed version of the Tyrosyl Radical Spectra Simulation Algorithm, the radical EPR signal was shown to arise from a pristine tyrosyl radical and not a mixed Trp/Tyr radical that has been widely reported in DyP members exhibiting high activity with synthetic dyes. The radical site was identified as Tyr374, with kinetic studies inferring that although Tyr374 is not on the electron-transfer pathway from the dye RB19, its replacement with a Phe does severely compromise activity with other organic substrates. These findings hint at the possibility that alternative electron-transfer pathways for substrate oxidation are operative within the DyP family. In this context, a role for a highly conserved aromatic dyad motif is discussed.
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Affiliation(s)
- Amanda K Chaplin
- Present address: Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge, CB2 1GA, UK
| | - Tadeo Moreno Chicano
- Present address: Department of Molecular Mechanisms, Max Planck Institute for Medical Research, Jahnstraße 29, 69120, Heidelberg, Germany
| | - Bethany V Hampshire
- Present address: Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
| | - Michael T Wilson
- School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK
| | - Michael A Hough
- School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK
| | - Dimitri A Svistunenko
- School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK
| | - Jonathan A R Worrall
- School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK
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3
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Tarpani L, Bellezza F, Sassi P, Gambucci M, Cipiciani A, Latterini L. New Insights into the Effects of Surface Functionalization on the Peroxidase Activity of Cytochrome c Adsorbed on Silica Nanoparticles. J Phys Chem B 2019; 123:2567-2575. [DOI: 10.1021/acs.jpcb.8b11762] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Affiliation(s)
- Luigi Tarpani
- Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, via Elce di Sotto, 8, 06123 Perugia, Italy
| | - Francesca Bellezza
- Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, via Elce di Sotto, 8, 06123 Perugia, Italy
| | - Paola Sassi
- Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, via Elce di Sotto, 8, 06123 Perugia, Italy
| | - Marta Gambucci
- Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, via Elce di Sotto, 8, 06123 Perugia, Italy
| | - Antonio Cipiciani
- Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, via Elce di Sotto, 8, 06123 Perugia, Italy
| | - Loredana Latterini
- Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, via Elce di Sotto, 8, 06123 Perugia, Italy
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4
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Juszczak LJ, Eisenberg AS. The Color of Cation-π Interactions: Subtleties of Amine-Tryptophan Interaction Energetics Allow for Radical-like Visible Absorbance and Fluorescence. J Am Chem Soc 2017; 139:8302-8311. [PMID: 28537725 DOI: 10.1021/jacs.7b03442] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Several peptides and a protein with an inter- or intramolecular cation-π interaction between tryptophan (Trp) and an amine cation are shown to absorb and fluoresce in the visible region of the spectrum. Titration of indole with sodium hydroxide or ammonium hydroxide yields an increasing visible fluorescence as well. Visible absorption and multipeaked fluorescence excitation spectra correlate with experimental absorption spectra and the vibrational modes of calculated absorption spectra for the neutral Trp radical. The radical character of the cation-indole interaction is predicted to stem from the electrostatic dislocation of indole highest occupied molecular orbital (HOMO) charge density toward the cation with a subsequent electronic transition from the HOMO-2 to the HOMO. Because this is a vertical transition, fluorescence is possible. Hydrogen bonding at the indole amine most likely stabilizes the radical-like state. These results provide new spectroscopic tools for the investigation of cation-π interactions in numerous biological systems, among them, proteins and their myriad ligands, and show that one, or at most, two, point mutations with natural amino acids are all that is required to impart visible fluorescence to proteins.
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Affiliation(s)
- Laura J Juszczak
- Chemistry Department, Brooklyn College, The City University of New York , New York, New York 11210, United States.,PhD programs in Chemistry and Biochemistry, The Graduate Center, The City University of New York , New York, New York 10016, United States
| | - Azaria S Eisenberg
- Chemistry Department, Brooklyn College, The City University of New York , New York, New York 11210, United States
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5
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Chaplin AK, Bernini C, Sinicropi A, Basosi R, Worrall JAR, Svistunenko DA. Tyrosine or Tryptophan? Modifying a Metalloradical Catalytic Site by Removal of the Cys-Tyr Cross-Link in the Galactose 6-Oxidase Homologue GlxA. Angew Chem Int Ed Engl 2017; 56:6502-6506. [DOI: 10.1002/anie.201701270] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2017] [Revised: 03/13/2017] [Indexed: 11/10/2022]
Affiliation(s)
- Amanda K. Chaplin
- School of Biological Sciences; University of Essex; Wivenhoe Park Colchester Essex CO4 3SQ (U K
| | - Caterina Bernini
- Department of Biotechnology, Chemistry and Pharmaceutical Sciences; University of Siena; Via A. Moro, 2 53100 Siena Italy
- CSGI, Consorzio per lo Sviluppo dei Sistemi a Grande Interfase; Via della Lastruccia 3 50019 Sesto Fiorentino Italy
| | - Adalgisa Sinicropi
- Department of Biotechnology, Chemistry and Pharmaceutical Sciences; University of Siena; Via A. Moro, 2 53100 Siena Italy
- CSGI, Consorzio per lo Sviluppo dei Sistemi a Grande Interfase; Via della Lastruccia 3 50019 Sesto Fiorentino Italy
| | - Riccardo Basosi
- Department of Biotechnology, Chemistry and Pharmaceutical Sciences; University of Siena; Via A. Moro, 2 53100 Siena Italy
- CSGI, Consorzio per lo Sviluppo dei Sistemi a Grande Interfase; Via della Lastruccia 3 50019 Sesto Fiorentino Italy
| | - Jonathan A. R. Worrall
- School of Biological Sciences; University of Essex; Wivenhoe Park Colchester Essex CO4 3SQ (U K
| | - Dimitri A. Svistunenko
- School of Biological Sciences; University of Essex; Wivenhoe Park Colchester Essex CO4 3SQ (U K
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6
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Chaplin AK, Bernini C, Sinicropi A, Basosi R, Worrall JAR, Svistunenko DA. Tyrosine or Tryptophan? Modifying a Metalloradical Catalytic Site by Removal of the Cys-Tyr Cross-Link in the Galactose 6-Oxidase Homologue GlxA. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201701270] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Amanda K. Chaplin
- School of Biological Sciences; University of Essex; Wivenhoe Park Colchester Essex CO4 3SQ (U K
| | - Caterina Bernini
- Department of Biotechnology, Chemistry and Pharmaceutical Sciences; University of Siena; Via A. Moro, 2 53100 Siena Italy
- CSGI, Consorzio per lo Sviluppo dei Sistemi a Grande Interfase; Via della Lastruccia 3 50019 Sesto Fiorentino Italy
| | - Adalgisa Sinicropi
- Department of Biotechnology, Chemistry and Pharmaceutical Sciences; University of Siena; Via A. Moro, 2 53100 Siena Italy
- CSGI, Consorzio per lo Sviluppo dei Sistemi a Grande Interfase; Via della Lastruccia 3 50019 Sesto Fiorentino Italy
| | - Riccardo Basosi
- Department of Biotechnology, Chemistry and Pharmaceutical Sciences; University of Siena; Via A. Moro, 2 53100 Siena Italy
- CSGI, Consorzio per lo Sviluppo dei Sistemi a Grande Interfase; Via della Lastruccia 3 50019 Sesto Fiorentino Italy
| | - Jonathan A. R. Worrall
- School of Biological Sciences; University of Essex; Wivenhoe Park Colchester Essex CO4 3SQ (U K
| | - Dimitri A. Svistunenko
- School of Biological Sciences; University of Essex; Wivenhoe Park Colchester Essex CO4 3SQ (U K
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Kathiresan M, English AM. LC-MS/MS suggests that hole hopping in cytochrome c peroxidase protects its heme from oxidative modification by excess H 2O 2. Chem Sci 2017; 8:1152-1162. [PMID: 28451256 PMCID: PMC5369544 DOI: 10.1039/c6sc03125k] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2016] [Accepted: 09/06/2016] [Indexed: 12/20/2022] Open
Abstract
We recently reported that cytochrome c peroxidase (Ccp1) functions as a H2O2 sensor protein when H2O2 levels rise in respiring yeast. The availability of its reducing substrate, ferrocytochrome c (CycII), determines whether Ccp1 acts as a H2O2 sensor or peroxidase. For H2O2 to serve as a signal it must modify its receptor so we employed high-performance LC-MS/MS to investigate in detail the oxidation of Ccp1 by 1, 5 and 10 M eq. of H2O2 in the absence of CycII to prevent peroxidase activity. We observe strictly heme-mediated oxidation, implicating sequential cycles of binding and reduction of H2O2 at Ccp1's heme. This results in the incorporation of ∼20 oxygen atoms predominantly at methionine and tryptophan residues. Extensive intramolecular dityrosine crosslinking involving neighboring residues was uncovered by LC-MS/MS sequencing of the crosslinked peptides. The proximal heme ligand, H175, is converted to oxo-histidine, which labilizes the heme but irreversible heme oxidation is avoided by hole hopping to the polypeptide until oxidation of the catalytic distal H52 in Ccp1 treated with 10 M eq. of H2O2 shuts down heterolytic cleavage of H2O2 at the heme. Mapping of the 24 oxidized residues in Ccp1 reveals that hole hopping from the heme is directed to three polypeptide zones rich in redox-active residues. This unprecedented analysis unveils the remarkable capacity of a polypeptide to direct hole hopping away from its active site, consistent with heme labilization being a key outcome of Ccp1-mediated H2O2 signaling. LC-MS/MS identification of the oxidized residues also exposes the bias of electron paramagnetic resonance (EPR) detection toward transient radicals with low O2 reactivity.
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Affiliation(s)
- Meena Kathiresan
- Concordia University Faculty of Arts and Science, and PROTEOhttp://www.proteo.ca/index.html , Chemistry and Biochemistry , Montreal , Canada .
| | - Ann M English
- Concordia University Faculty of Arts and Science, and PROTEOhttp://www.proteo.ca/index.html , Chemistry and Biochemistry , Montreal , Canada .
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Payne TM, Yee EF, Dzikovski B, Crane BR. Constraints on the Radical Cation Center of Cytochrome c Peroxidase for Electron Transfer from Cytochrome c. Biochemistry 2016; 55:4807-22. [PMID: 27499202 PMCID: PMC5689384 DOI: 10.1021/acs.biochem.6b00262] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The tryptophan 191 cation radical of cytochrome c peroxidase (CcP) compound I (Cpd I) mediates long-range electron transfer (ET) to cytochrome c (Cc). Here we test the effects of chemical substitution at position 191. CcP W191Y forms a stable tyrosyl radical upon reaction with peroxide and produces spectral properties similar to those of Cpd I but has low reactivity toward reduced Cc. CcP W191G and W191F variants also have low activity, as do redox ligands that bind within the W191G cavity. Crystal structures of complexes between Cc and CcP W191X (X = Y, F, or G), as well as W191G with four bound ligands reveal similar 1:1 association modes and heme pocket conformations. The ligands display structural disorder in the pocket and do not hydrogen bond to Asp235, as does Trp191. Well-ordered Tyr191 directs its hydroxyl group toward the porphyrin ring, with no basic residue in the range of interaction. CcP W191X (X = Y, F, or G) variants substituted with zinc-porphyrin (ZnP) undergo photoinduced ET with Cc(III). Their slow charge recombination kinetics that result from loss of the radical center allow resolution of difference spectra for the charge-separated state [ZnP(+), Cc(II)]. The change from a phenyl moiety at position 191 in W191F to a water-filled cavity in W191G produces effects on ET rates much weaker than the effects of the change from Trp to Phe. Low net reactivity of W191Y toward Cc(II) derives either from the inability of ZnP(+) or the Fe-CcP ferryl to oxidize Tyr or from the low potential of the resulting neutral Tyr radical.
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Affiliation(s)
- Thomas M. Payne
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, United States
| | - Estella F. Yee
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, United States
| | - Boris Dzikovski
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, United States,National Biomedical Center for Advanced ESR Technologies (ACERT), Cornell University, Ithaca 14850, USA
| | - Brian R. Crane
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, United States,To whom correspondence should be addressed , Tel (607) 254-8634 (B.R.C)
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Viglino E, Shaffer CJ, Tureček F. UV/Vis Action Spectroscopy and Structures of Tyrosine Peptide Cation Radicals in the Gas Phase. Angew Chem Int Ed Engl 2016; 55:7469-73. [DOI: 10.1002/anie.201602604] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2016] [Indexed: 12/25/2022]
Affiliation(s)
- Emilie Viglino
- Department of Chemistry University of Washington Seattle WA 98195 USA
| | | | - František Tureček
- Department of Chemistry University of Washington Seattle WA 98195 USA
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10
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Viglino E, Shaffer CJ, Tureček F. UV/Vis Action Spectroscopy and Structures of Tyrosine Peptide Cation Radicals in the Gas Phase. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201602604] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Emilie Viglino
- Department of Chemistry University of Washington Seattle WA 98195 USA
| | | | - František Tureček
- Department of Chemistry University of Washington Seattle WA 98195 USA
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11
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Larson BC, Pomponio JR, Shafaat HS, Kim RH, Leigh BS, Tauber MJ, Kim JE. Photogeneration and Quenching of Tryptophan Radical in Azurin. J Phys Chem B 2015; 119:9438-49. [PMID: 25625660 PMCID: PMC5092234 DOI: 10.1021/jp511523z] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Tryptophan and tyrosine can form radical intermediates that enable long-range, multistep electron transfer (ET) reactions in proteins. This report describes the mechanisms of formation and quenching of a neutral tryptophan radical in azurin, a blue-copper protein that contains native tyrosine (Y108 and Y72) and tryptophan (W48) residues. A long-lived neutral tryptophan radical W48• is formed upon UV-photoexcitation of a zinc(II)-substituted azurin mutant in the presence of an external electron acceptor. The quantum yield of W48• formation (Φ) depends upon the tyrosine residues in the protein. A tyrosine-deficient mutant, Zn(II)Az48W, exhibited a value of Φ = 0.080 with a Co(III) electron acceptor. A nearly identical quantum yield was observed when the electron acceptor was the analogous tyrosine-free, copper(II) mutant; this result for the Zn(II)Az48W:Cu(II)Az48W mixture suggests there is an interprotein ET path. A single tyrosine residue at one of the native positions reduced the quantum yield to 0.062 (Y108) or 0.067 (Y72). Wild-type azurin with two tyrosine residues exhibited a quantum yield of Φ = 0.045. These data indicate that tyrosine is able to quench the tryptophan radical in azurin.
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Affiliation(s)
- Bethany C. Larson
- Department of Chemistry and Biochemistry, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - Jennifer R. Pomponio
- Department of Chemistry and Biochemistry, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
| | | | - Rachel H. Kim
- Department of Chemistry and Biochemistry, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - Brian S. Leigh
- Department of Chemistry and Biochemistry, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - Michael J. Tauber
- Department of Chemistry and Biochemistry, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - Judy E. Kim
- Department of Chemistry and Biochemistry, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
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Baratto MC, Sinicropi A, Linde D, Sáez-Jiménez V, Sorace L, Ruiz-Duenas FJ, Martinez AT, Basosi R, Pogni R. Redox-Active Sites in Auricularia auricula-judae Dye-Decolorizing Peroxidase and Several Directed Variants: A Multifrequency EPR Study. J Phys Chem B 2015; 119:13583-92. [PMID: 26120933 DOI: 10.1021/acs.jpcb.5b02961] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Peroxide-activated Auricularia auricula-judae dye-decolorizing peroxidase (DyP) forms a mixed Trp377 and Tyr337 radical, the former being responsible for oxidation of the typical DyP substrates (Linde et al. Biochem. J., 2015, 466, 253-262); however, a pure tryptophanyl radical EPR signal is detected at pH 7 (where the enzyme is inactive), in contrast with the mixed signal observed at pH for optimum activity, pH 3. On the contrary, the presence of a second tyrosine radical (at Tyr147) is deduced by a multifrequency EPR study of a variety of simple and double-directed variants (including substitution of the above and other tryptophan and tyrosine residues) at different freezing times after their activation by H2O2 (at pH 3). This points out that subsidiary long-range electron-transfer pathways enter into operation when the main pathway(s) is removed by directed mutagenesis, with catalytic efficiencies progressively decreasing. Finally, self-reduction of the Trp377 neutral radical is observed when reaction time (before freezing) is increased in the absence of reducing substrates (from 10 to 60 s). Interestingly, the tryptophanyl radical is stable in the Y147S/Y337S variant, indicating that these two tyrosine residues are involved in the self-reduction reaction.
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Affiliation(s)
- Maria Camilla Baratto
- Department of Biotechnology, Chemistry and Pharmacy, University of Siena , I-53100 Siena, Italy
| | - Adalgisa Sinicropi
- Department of Biotechnology, Chemistry and Pharmacy, University of Siena , I-53100 Siena, Italy
| | - Dolores Linde
- Centro de Investigaciones Biológicas, CSIC , Ramiro de Maeztu 9, E-28040 Madrid, Spain
| | - Verónica Sáez-Jiménez
- Centro de Investigaciones Biológicas, CSIC , Ramiro de Maeztu 9, E-28040 Madrid, Spain
| | - Lorenzo Sorace
- Department of Chemistry, "Ugo Schiff" and INSTM RU, University of Florence , 50019 Sesto Fiorentino, Florence, Italy
| | | | - Angel T Martinez
- Centro de Investigaciones Biológicas, CSIC , Ramiro de Maeztu 9, E-28040 Madrid, Spain
| | - Riccardo Basosi
- Department of Biotechnology, Chemistry and Pharmacy, University of Siena , I-53100 Siena, Italy
| | - Rebecca Pogni
- Department of Biotechnology, Chemistry and Pharmacy, University of Siena , I-53100 Siena, Italy
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