1
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Gibbs CA, Ghazi N, Tao J, Warren JJ. An Investigation of the Influence of Tyrosine Local Interactions on Electron Hopping in a Model Protein. Molecules 2024; 29:350. [PMID: 38257263 PMCID: PMC10818705 DOI: 10.3390/molecules29020350] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Revised: 01/04/2024] [Accepted: 01/05/2024] [Indexed: 01/24/2024] Open
Abstract
Multi-step electron transfer reactions are important to the function of many cellular systems. The ways in which such systems have evolved to direct electrons along specific pathways are largely understood, but less so are the ways in which the reduction-oxidation potentials of individual redox sites are controlled. We prepared a series of three new artificial variants of Pseudomonas aeruginosa azurin where a tyrosine (Tyr109) is situated between the native Cu ion and a Ru(II) photosensitizer tethered to a histidine (His107). Arginine, glutamine, or methionine were introduced as position 122, which is near to Tyr109. We investigated the rate of CuI oxidation by a flash-quench generated Ru(III) oxidant over pH values from 5 to 9. While the identity of the residue at position 122 affects some of the physical properties of Tyr109, the rates of CuI oxidation are only weakly dependent on the identity of the residue at 122. The results highlight that more work is still needed to understand how non-covalent interactions of redox active groups are affected in redox proteins.
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Affiliation(s)
| | | | | | - Jeffrey J. Warren
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
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2
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Mostajabi Sarhangi S, Matyushov DV. Effect of Water Deuteration on Protein Electron Transfer. J Phys Chem Lett 2023; 14:723-729. [PMID: 36648391 DOI: 10.1021/acs.jpclett.2c03690] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Traditional theories of long-range protein electron transfer describe the reaction rate in terms of the tunneling distance and the reaction free energy. They do not recognize two physical effects: (i) local wetting of the active site by hydration water and (ii) protein identity affecting the rate through dynamics and flexibility. We find, by molecular dynamics simulations, a significant, ∼25 times, slowing down of the rate of protein electron transfer upon deuteration. H/D substitution changes the rate constant pre-exponential factor in the regime of electron transfer controlled by medium dynamics. Switching from light to heavy water increases the effective medium relaxation time. The effect is caused by both a global change in the flexibility of the protein backbone and locally stronger hydrogen bonds to charged residues.
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Affiliation(s)
- Setare Mostajabi Sarhangi
- School of Molecular Sciences and Department of Physics, Arizona State University, PO Box 871504, Tempe, Arizona85287-1504, United States
| | - Dmitry V Matyushov
- School of Molecular Sciences and Department of Physics, Arizona State University, PO Box 871504, Tempe, Arizona85287-1504, United States
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3
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Di Rocco G, Battistuzzi G, Borsari M, Bortolotti CA, Ranieri A, Sola M. The enthalpic and entropic terms of the reduction potential of metalloproteins: Determinants and interplay. Coord Chem Rev 2021. [DOI: 10.1016/j.ccr.2021.214071] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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4
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Pradhan B, Engelhard C, Van Mulken S, Miao X, Canters GW, Orrit M. Single electron transfer events and dynamical heterogeneity in the small protein azurin from Pseudomonas aeruginosa. Chem Sci 2019; 11:763-771. [PMID: 34123050 PMCID: PMC8146731 DOI: 10.1039/c9sc05405g] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2019] [Accepted: 11/25/2019] [Indexed: 01/07/2023] Open
Abstract
Monitoring the fluorescence of single-dye-labeled azurin molecules, we observed the reaction of azurin with hexacyanoferrate under controlled redox potential yielding data on the timing of individual (forward and backward) electron transfer (ET) events. Change-point analysis of the time traces demonstrates significant fluctuations of ET rates and of mid-point potential E 0. These fluctuations are a signature of dynamical heterogeneity, here observed on a 14 kDa protein, the smallest to date. By correlating changes in forward and backward reaction rates we found that 6% of the observed change events could be explained by a change in midpoint potential, while for 25% a change of the donor-acceptor coupling could explain the data. The remaining 69% are driven by variations in complex association constants or structural changes that cause forward and back ET rates to vary independently. Thus, the observed spread in individual ET rates could be related in a unique way to variations in molecular parameters. The relevance for the understanding of metabolic processes is briefly discussed.
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Affiliation(s)
- Biswajit Pradhan
- Huygens-Kamerlingh Onnes Laboratory, Leiden University 2300 RA Leiden Netherlands
| | | | | | - Xueyan Miao
- School of Public Health, Guilin Medical University 541004 Guilin China
| | - Gerard W Canters
- Huygens-Kamerlingh Onnes Laboratory, Leiden University 2300 RA Leiden Netherlands
| | - Michel Orrit
- Huygens-Kamerlingh Onnes Laboratory, Leiden University 2300 RA Leiden Netherlands
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5
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North ML, Wilcox DE. Shift from Entropic Cu 2+ Binding to Enthalpic Cu + Binding Determines the Reduction Thermodynamics of Blue Copper Proteins. J Am Chem Soc 2019; 141:14329-14339. [PMID: 31433629 DOI: 10.1021/jacs.9b06836] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The enthalpic and entropic components of Cu2+ and Cu+ binding to the blue copper protein azurin have been quantified with isothermal titration calorimetry (ITC) measurements and analysis, providing the first such experimental values for Cu+ binding to a protein. The high affinity of azurin for Cu2+ is entirely due to a very favorable binding entropy, while its even higher affinity for Cu+ is due to a favorable binding enthalpy and entropy. The binding thermodynamics provide insight into bond enthalpies at the blue copper site and entropic contributions from desolvation and proton displacement. These values were used in thermodynamic cycles to determine the enthalpic and entropic contributions to the free energy of reduction and thus the reduction potential. The reduction thermodynamics obtained with this method are in good agreement with previous results from temperature-dependent electrochemical measurements. The calorimetry method, however, provides new insight into contributions from the initial (oxidized) and final (reduced) states of the reduction. Since ITC measurements quantify the protons that are displaced upon metal binding, the proton transfer that is coupled with electron transfer is also determined with this method. Preliminary results for Cu2+ and Cu+ binding to the Phe114Pro variant of azurin demonstrate the insight about protein tuning of the reduction potential that is provided by the binding thermodynamics of each metal oxidation state.
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Affiliation(s)
- Molly L North
- Department of Chemistry , Dartmouth College , Hanover , New Hampshire 03755 , United States
| | - Dean E Wilcox
- Department of Chemistry , Dartmouth College , Hanover , New Hampshire 03755 , United States
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6
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Strianese M, Palm GJ, Kohlhause D, Ndamba LA, Tabares LC, Pellecchia C. Azurin and HS-
: Towards Implementation of a Sensor for HS-
Detection. Eur J Inorg Chem 2019. [DOI: 10.1002/ejic.201801399] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Maria Strianese
- Dipartimento di Chimica e Biologia “Adolfo Zambelli”; Università di Salerno; Via Giovanni Paolo II, 132 84084 Fisciano (SA) Italy
| | - Gottfried J. Palm
- Institute for Biochemistry; University of Greifswald; Felix-Hausdorff-Str. 4 17489 Greifswald Germany
| | - David Kohlhause
- Institute for Biochemistry; University of Greifswald; Felix-Hausdorff-Str. 4 17489 Greifswald Germany
| | - Lionel A. Ndamba
- Leiden; Leiden University; P.O. Box 9504 2300 RA Leiden Netherlands
| | - Leandro C. Tabares
- Institute for Integrative Biology of the Cell (I2BC); Department of Biochemistry, Biophysics and Structural Biology; Université Paris-Saclay, CEA, CNRS UMR 9198; 91198 Gif-sur-Yvette France
| | - Claudio Pellecchia
- Dipartimento di Chimica e Biologia “Adolfo Zambelli”; Università di Salerno; Via Giovanni Paolo II, 132 84084 Fisciano (SA) Italy
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7
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Sorrentino I, Gentil S, Nedellec Y, Cosnier S, Piscitelli A, Giardina P, Le Goff A. POXC Laccase from
Pleurotus ostreatus
: A High‐Performance Multicopper Enzyme for Direct Oxygen Reduction Reaction Operating in a Proton‐Exchange Membrane Fuel Cell. ChemElectroChem 2018. [DOI: 10.1002/celc.201801264] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
| | - Solène Gentil
- Univ. Grenoble AlpesCNRS, DCM 38000 Grenoble
- Univ. Grenoble AlpesCEA, CNRS, BIG-LCBM 38000 Grenoble France
| | | | | | | | - Paola Giardina
- Department of Chemical SciencesUniversity Federico II Naples Italy
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8
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Andreoni A, Sen S, Hagedoorn PL, Buma WJ, Aartsma TJ, Canters GW. Fluorescence Correlation Spectroscopy of Labeled Azurin Reveals Photoinduced Electron Transfer between Label and Cu Center. Chemistry 2018; 24:646-654. [PMID: 29064125 DOI: 10.1002/chem.201703733] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Indexed: 11/06/2022]
Abstract
Fluorescent labeling of biomacromolecules enjoys increasing popularity for structural, mechanistic, and microscopic investigations. Its success hinges on the ability of the dye to alternate between bright and dark states. Förster resonance energy transfer (FRET) is an important source of fluorescence modulation. Photo-induced electron transfer (PET) may occur as well, but is often considered only when donor and acceptor are in van der Waals contact. In this study, PET is shown between a label and redox centers in oxidoreductases, which may occur over large distances. In the small blue copper protein azurin, labeled with ATTO655, PET is observed when the label is at 18.5 Å, but not when it is at 29.1 Å from the Cu. For CuII , PET from label to Cu occurs at a rate of (4.8±0.3)×104 s-1 and back at (0.7±0.1)×103 s-1 . With CuI the numbers are (3.3±0.7)×106 s-1 and (1.0±0.1)×104 s-1 . Reorganization energies and electronic coupling elements are in the range of 0.8-1.2 eV and 0.02-0.5 cm-1 , respectively. These data are compatible with electron transfer (ET) along a through-bond pathway although transient complex formation followed by ET cannot be ruled out. The outcome of this study is a useful guideline for experimental designs in which oxidoreductases are labelled with fluorescent dyes, with particular attention to single molecule investigations. The labelling position for FRET can be optimized to avoid reactions like PET by evaluating the structure and thermodynamics of protein and label.
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Affiliation(s)
- Alessio Andreoni
- Leiden Institute of Physics, Leiden University, Niels Bohrweg 2, 2333CC, Leiden, The Netherlands.,Present address: National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
| | - Saptaswa Sen
- Leiden Institute of Physics, Leiden University, Niels Bohrweg 2, 2333CC, Leiden, The Netherlands.,Present address: AlbaNova University Center, Department of Applied Physics, KTH-Royal Institute of, Technology, 10691, Stockholm, Sweden
| | - Peter-Leon Hagedoorn
- TU Delft, Applied Sciences, Biotechnology, Building 58, Van der Maasweg 9, 2629 HZ, Delft, The Netherlands
| | - Wybren J Buma
- Van't Hoff Institute for Molecular Sciences, Science Park 904, P.O. Box 94157, 1090 GD, Amsterdam, The Netherlands
| | - Thijs J Aartsma
- Leiden Institute of Physics, Leiden University, Niels Bohrweg 2, 2333CC, Leiden, The Netherlands
| | - Gerard W Canters
- Leiden Institute of Physics, Leiden University, Niels Bohrweg 2, 2333CC, Leiden, The Netherlands
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9
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Lalaoui N, Le Goff A, Holzinger M, Cosnier S. Fully Oriented Bilirubin Oxidase on Porphyrin-Functionalized Carbon Nanotube Electrodes for Electrocatalytic Oxygen Reduction. Chemistry 2015; 21:16868-73. [DOI: 10.1002/chem.201502377] [Citation(s) in RCA: 73] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2015] [Indexed: 12/26/2022]
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10
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Akkilic N, Kamran M, Stan R, Sanghamitra NJM. Voltage-controlled fluorescence switching of a single redox protein. Biosens Bioelectron 2014; 67:747-51. [PMID: 25103339 DOI: 10.1016/j.bios.2014.07.051] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2014] [Revised: 07/14/2014] [Accepted: 07/22/2014] [Indexed: 02/07/2023]
Abstract
Heterogeneous electron transfer (ET) of the redox protein, wild-type azurin (wt-Az) from Pseudomonas aeruginosa, was monitored at the single-molecule (SM) level by fluorescence resonance energy transfer (FRET), one electron at a time. Azurin molecules were labeled with an organic fluorophore (Cy5), and the FRET-coupling between Cy5 and the redox center (copper) was used to study ET to a semi-transparent, 10nm thin gold electrode in an optical configuration. By using a confocal microscope and a bipotentiostat for control of the electrode potential, the oxidation and reduction processes of individual Az-Cy5 molecules were monitored. In the oxidized state of the redox center of the azurin molecule, the fluorescence emission of the covalently attached Cy5 was largely quenched by FRET ('off'-state), whereas the emission was recovered upon reduction ('on'-state). The work presented here, shows directly controlled single redox switching events of an individual redox protein and its thermodynamic dispersion. We show that the distribution of midpoint potentials (E0) of individual azurin molecules peaks at 45.7±0.5 mV with a full width at half maximum of 15 mV vs saturated calomel electrode (SCE).
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Affiliation(s)
- Namik Akkilic
- Leiden Institute of Physics, Huygens Laboratory, Leiden University, Leiden, The Netherlands.
| | - Muhammad Kamran
- Leiden Institute of Physics, Huygens Laboratory, Leiden University, Leiden, The Netherlands
| | - Razvan Stan
- Leiden Institute of Physics, Huygens Laboratory, Leiden University, Leiden, The Netherlands
| | - Nusrat J M Sanghamitra
- Leiden Institute of Physics, Huygens Laboratory, Leiden University, Leiden, The Netherlands
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11
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Wilson TD, Savelieff MG, Nilges MJ, Marshall NM, Lu Y. Kinetics of Copper Incorporation into a Biosynthetic Purple CuA Azurin: Characterization of Red, Blue, and a New Intermediate Species. J Am Chem Soc 2011; 133:20778-92. [DOI: 10.1021/ja205281t] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Affiliation(s)
- Tiffany D. Wilson
- Department of Chemistry, University of Illinois at Urbana—Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
| | - Masha G. Savelieff
- Department of Chemistry, University of Illinois at Urbana—Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
| | - Mark J. Nilges
- Department of Chemistry, University of Illinois at Urbana—Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
| | - Nicholas M. Marshall
- Department of Chemistry, University of Illinois at Urbana—Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
| | - Yi Lu
- Department of Chemistry, University of Illinois at Urbana—Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
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12
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Ullmann RT, Ullmann GM. Coupling of Protonation, Reduction, and Conformational Change in azurin from Pseudomonas aeruginosa Investigated with Free Energy Measures of Cooperativity. J Phys Chem B 2011; 115:10346-59. [DOI: 10.1021/jp204644h] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- R. Thomas Ullmann
- Structural Biology/Bioinformatics, University of Bayreuth, Universitätsstrasse 30, BGI, 95447 Bayreuth, Germany
| | - G. Matthias Ullmann
- Structural Biology/Bioinformatics, University of Bayreuth, Universitätsstrasse 30, BGI, 95447 Bayreuth, Germany
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13
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Li C, Sato K, Monari S, Salard I, Sola M, Banfield MJ, Dennison C. Metal-Binding Loop Length Is a Determinant of the pKa of a Histidine Ligand at a Type 1 Copper Site. Inorg Chem 2010; 50:482-8. [DOI: 10.1021/ic101413e] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Chan Li
- Institute for Cell and Molecular Biosciences, Medical School, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K
| | - Katsuko Sato
- Institute for Cell and Molecular Biosciences, Medical School, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K
| | - Stefano Monari
- Department of Chemistry, University of Modena and Reggio Emilia, Via Campi 183, 41125 Modena, Italy
| | - Isabelle Salard
- Institute for Cell and Molecular Biosciences, Medical School, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K
| | - Marco Sola
- Department of Chemistry, University of Modena and Reggio Emilia, Via Campi 183, 41125 Modena, Italy
| | - Mark J. Banfield
- Department of Biological Chemistry, John Innes Centre, Norwich NR4 7UH, U.K
| | - Christopher Dennison
- Institute for Cell and Molecular Biosciences, Medical School, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K
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14
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Active site loop dictates the thermodynamics of reduction and ligand protonation in cupredoxins. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2009; 1794:995-1000. [PMID: 19230853 DOI: 10.1016/j.bbapap.2009.02.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2008] [Revised: 01/28/2009] [Accepted: 02/03/2009] [Indexed: 11/21/2022]
Abstract
The thermodynamics of reduction and His ligand protonation have been determined for a range of loop-contraction variants of the electron transferring type 1 copper protein azurin (AZ). For AZPC, in which the native C-terminal loop containing the Cys, His and Met ligands has been replaced with the shorter sequence from plastocyanin (PC) and AZAMI, in which the even shorter amicyanin (AMI) loop has been inserted, the thermodynamics of reduction match those of the protein whose loop has been introduced which are different to the values for AZ. The enthalpic contribution to His ligand protonation, which is not observed in AZ, is similar in AZAMI and AMI. The thermodynamics of this process in AZPC are more dissimilar to those for PC. In the case of AZAMI-F, a variant possessing the (non natural) minimal loop that can bind a type 1 copper site, the reduction thermodynamics are intermediate between those of AZPC and AZAMI, whilst the thermodynamic data for His ligand protonation are very similar to those for AMI. The results for AZAMI and AZPC are primarily due to protein based enthalpic effects related to the interaction of the metal with permanent protein dipoles from the loop, and to the decreased loop length which favors His ligand protonation in the cuprous proteins. Entropic factors related to loop flexibility have little influence because of constraints imposed by metal coordination and the fact that the introduced loops pack well against the AZ scaffold. Thus, the host scaffold in general plays a minor thermodynamic role in both processes, although for AZAMI-F differences in the first and second coordination spheres influence the thermodynamics of reduction.
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15
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Elucidation of Electron- Transfer Pathways in Copper and Iron Proteins by Pulse Radiolysis Experiments. ACTA ACUST UNITED AC 2008. [DOI: 10.1002/9780470144428.ch1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/05/2023]
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16
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Gradinaru C, Crane BR. Comparison of intra- vs intermolecular long-range electron transfer in crystals of ruthenium-modified azurin. J Phys Chem B 2007; 110:20073-6. [PMID: 17034174 DOI: 10.1021/jp0644309] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Selective metal-ion incorporation and ligand substitution are employed to control whether electrons tunnel over intra- or intermolecular separations in crystals of P. aeruginosa azurin modified with Ru-polypyridine complexes. Cu(1+)-to-Ru3+ electron transfer (ET) across a specific protein-protein interface in the crystal lattice has a time constant 5-10 times longer than ET between the same donor and acceptor within a single protein (tauET = 5 vs 0.5-1.0 micros). Slower intermolecular ET agrees well with a longer distance between redox centers across the inter-protein (18.9 A) compared to the intra-protein separation (17.0 A) and indicates that the closest donor/acceptor pair dominates crystal ET. Lowering the crystal pH accelerates inter-protein ET (tauET = 1.0 micros) but not intra-protein ET. Faster inter-protein ET likely results from a pH-induced peptide bond flip that perturbs hydrogen bonding in the path between Ru and Cu centers on adjacent molecules.
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17
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Kuznetsova S, Zauner G, Schmauder R, Mayboroda OA, Deelder AM, Aartsma TJ, Canters GW. A Förster-resonance-energy transfer-based method for fluorescence detection of the protein redox state. Anal Biochem 2005; 350:52-60. [PMID: 16430854 DOI: 10.1016/j.ab.2005.11.036] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2005] [Revised: 11/23/2005] [Accepted: 11/25/2005] [Indexed: 11/21/2022]
Abstract
A method for fluorescence detection of a protein's redox state based on resonance energy transfer from an attached fluorescence label to the prosthetic group of the redox protein is described and tested for proteins containing three types of prosthetic groups: a type-1 copper site (azurin, amicyanin, plastocyanin, and pseudoazurin), a heme group (cytochrome c550), and a flavin mononucleotide (flavodoxin). This method permits one to reliably distinguish between reduced and oxidized proteins and to perform potentiometric titrations at submicromolar concentrations.
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Affiliation(s)
- Sofya Kuznetsova
- Leiden Institute of Chemistry-Gorlaeus Laboratories, Leiden University, The Netherlands
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18
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McEvoy JP, Foord JS. Direct electrochemistry of blue copper proteins at boron-doped diamond electrodes. Electrochim Acta 2005. [DOI: 10.1016/j.electacta.2004.11.043] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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19
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Zhang J, Guo SX, Bond AM, Honeychurch MJ, Oldham KB. Novel Kinetic and Background Current Selectivity in the Even Harmonic Components of Fourier Transformed Square-Wave Voltammograms of Surface-Confined Azurin. J Phys Chem B 2005; 109:8935-47. [PMID: 16852063 DOI: 10.1021/jp044614s] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Fourier transform analysis of ramped square-wave voltammograms indicates the availability of a novel form of kinetic selectivity for surface-confined electron-transfer processes. Thus, for all the even harmonic components, quasi-reversible processes are sensitive to the surface coverage, the reversible potential, the electron-transfer rate constant (k(0')), and the electron-transfer coefficient (alpha), as well as to the amplitude (DeltaE) and frequency (f) of the square wave and dc scan rate. Additionally, it is insensitive to background capacitance current. In contrast, reversible processes and background currents are predicted to be absent from the even harmonics and only detectable in the odd harmonic components. The square-wave voltammetry of the surface-confined quasi-reversible azurin process azurin[Cu(II)] + e(-) right arrow over left arrow azurin[Cu(I)] at a paraffin-impregnated graphite electrode has been employed as a model system to test theoretical predictions. Most voltammetric characteristics of the even harmonic components obtained from the Fourier analysis are consistent with electrode kinetic values of k(0') = 90 s(-1) and alpha = 0.48, although some nonideality possibly due to kinetic dispersion also is apparent. Conditions also have been determined under which a readily generated waveform constructed from the Fourier series of sine waves produces voltammograms that are essentially indistinguishable from those predicted when an ideal square wave is employed.
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Affiliation(s)
- Jie Zhang
- School of Chemistry, Monash University, Clayton, Victoria 3800, Australia
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20
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van den Bosch M, Swart M, Snijders JG, Berendsen HJC, Mark AE, Oostenbrink C, van Gunsteren WF, Canters GW. Calculation of the Redox Potential of the Protein Azurin and Some Mutants. Chembiochem 2005; 6:738-46. [PMID: 15747387 DOI: 10.1002/cbic.200400244] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Azurin from Pseudomonas aeruginosa is a small 128-residue, copper-containing protein. Its redox potential can be modified by mutating the protein. Free-energy calculations based on classical molecular-dynamics simulations of the protein and from mutants in aqueous solution at different pH values were used to compute relative redox potentials. The precision of the free-energy calculations with the lambda coupling-parameter approach is evaluated as function of the number and sequence of lambda values, the sampling time and initial conditions. It is found that the precision is critically dependent on the relaxation of hydrogen-bonding networks when changing the atomic-charge distribution due to a change of redox state or pH value. The errors in the free energies range from 1 to 10 k(B)T, depending on the type of process. Only qualitative estimates of the change in redox potential by protein mutation can be obtained.
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Affiliation(s)
- Marieke van den Bosch
- Leiden Institute of Chemistry, Gorlaeus Laboratories, Einsteinweg 55, 2333 CC Leiden, The Netherlands
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21
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Hwang HJ, Lu Y. pH-dependent transition between delocalized and trapped valence states of a CuA center and its possible role in proton-coupled electron transfer. Proc Natl Acad Sci U S A 2004; 101:12842-7. [PMID: 15326290 PMCID: PMC516483 DOI: 10.1073/pnas.0403473101] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2004] [Indexed: 11/18/2022] Open
Abstract
A pH-dependent transition between delocalized and trapped mixed valence states of an engineered CuA center in azurin has been investigated by UV-visible absorption and electron paramagnetic resonance spectroscopic techniques. At pH 7.0, the CuA azurin displays a typical delocalized mixed valence dinuclear [Cu(1.5)....Cu(1.5)] spectra with optical absorptions at 485, 530, and 760 nm, and with a seven-line EPR hyperfine. Upon lowering of the pH from 7.0 to 4.0, the absorption at 760 nm shifted to lower energy toward 810 nm, and a four-line EPR hyperfine, typical of a trapped valence, was observed. The pH-dependent transition is reversible because increasing the pH restores all delocalized spectral features. Lowering the pH resulted in not only a trapped valence state, but also a dramatically increased reduction potential of the Cu center (from 160 mV to 340 mV). Mutation of the titratable residues around the metal-binding site ruled out Glu-114 and identified the C-terminal histidine ligand (His-120) as a site of protonation, because the His120Ala mutation abolished the above pH-dependent transition. The corresponding histidine in cytochrome c oxidases is along a major electron transfer pathway from CuA center to heme a. Because the protonation of this histidine can result in an increased reduction potential that will prevent electron flow from the CuA to heme a, the CuA and the histidine may play an important role in regulating proton-coupled electron transfer.
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Affiliation(s)
- Hee Jung Hwang
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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22
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Guo S, Zhang J, Elton DM, Bond AM. Fourier Transform Large-Amplitude Alternating Current Cyclic Voltammetry of Surface-Bound Azurin. Anal Chem 2003. [DOI: 10.1021/ac034901c] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Sixuan Guo
- School of Chemistry, Monash University, Victoria 3800, Australia
| | - Jie Zhang
- School of Chemistry, Monash University, Victoria 3800, Australia
| | - Darrell M. Elton
- School of Chemistry, Monash University, Victoria 3800, Australia
| | - Alan M. Bond
- School of Chemistry, Monash University, Victoria 3800, Australia
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Jeuken LJ, Wisson LJ, Armstrong FA. The kinetics of a weakly electron-coupled proton transfer in azurin. Inorganica Chim Acta 2002. [DOI: 10.1016/s0020-1693(01)00809-x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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24
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Battistuzzi G, Borsari M, Canters GW, de Waal E, Loschi L, Warmerdam G, Sola M. Enthalpic and entropic contributions to the mutational changes in the reduction potential of azurin. Biochemistry 2001; 40:6707-12. [PMID: 11389584 DOI: 10.1021/bi010333o] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The changes in the reduction potential of Pseudomonas aeruginosa and Alcaligenes denitrificans azurins following point mutations and residue ionizations were factorized into the enthalpic and entropic contributions through variable temperature direct electrochemistry experiments. The effects on the reduction enthalpy due to changes in the first coordination sphere of the copper ion, as in the Met121Gln and Met121His variants of A. denitrificans azurin, insertion of a net charge and alteration in the solvation properties and electrostatic potential in proximity of the metal site, as in the Met44Lys and His35Leu variants of P. aeruginosa azurin, respectively, and proton uptake/release in wild-type and mutated species could invariably be accounted for on the basis of simple coordination chemistry and/or electrostatic considerations. The concomitant changes in reduction entropy were found in general to contribute to the E degrees ' variation to a lesser extent as compared to the enthalpy changes. However, their effects were by no means negligible and in some instances were found to heavily contribute to (or even become the main determinant of) the observed change in reduction potential. Several lines of evidence indicate that the entropic effects are notably influenced by reduction-induced solvent reorganization effects. In particular, protein reduction tends to be favored on entropic grounds with increasing exposure of the copper site to the solvent. Moreover, enthalpy-entropy compensation phenomena are invariably observed when residue mutation or pH-induced conformational changes modify the solvent accessibility of the metal site or alter the H-bonding network in the hydration shell of the molecule. Therefore, in these cases, caution must be used in making predictions of E degrees ' changes simply based on Coulombic or coordination chemistry arguments.
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Affiliation(s)
- G Battistuzzi
- Department of Chemistry, University of Modena and Reggio Emilia, Via Campi 183, 41100 Modena, Italy
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25
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Jeuken LJC, Armstrong FA. Electrochemical Origin of Hysteresis in the Electron-Transfer Reactions of Adsorbed Proteins: Contrasting Behavior of the “Blue” Copper Protein, Azurin, Adsorbed on Pyrolytic Graphite and Modified Gold Electrodes. J Phys Chem B 2001. [DOI: 10.1021/jp004283t] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Lars J. C. Jeuken
- Inorganic Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QR, England
| | - Fraser A. Armstrong
- Inorganic Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QR, England
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26
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Chowdhury A, Peteanu LA, Webb MA, Loppnow GR. Stark Spectroscopic Studies of Blue Copper Proteins: Azurin. J Phys Chem B 2000. [DOI: 10.1021/jp0025227] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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27
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Battistuzzi G, Borsari M, Loschi L, Righi F, Sola M. Redox Thermodynamics of Blue Copper Proteins. J Am Chem Soc 1999. [DOI: 10.1021/ja982126q] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Gianantonio Battistuzzi
- Contribution from the Department of Chemistry, University of Modena, Via Campi 183, 41100 Modena, Italy
| | - Marco Borsari
- Contribution from the Department of Chemistry, University of Modena, Via Campi 183, 41100 Modena, Italy
| | - Lodovica Loschi
- Contribution from the Department of Chemistry, University of Modena, Via Campi 183, 41100 Modena, Italy
| | - Fabio Righi
- Contribution from the Department of Chemistry, University of Modena, Via Campi 183, 41100 Modena, Italy
| | - Marco Sola
- Contribution from the Department of Chemistry, University of Modena, Via Campi 183, 41100 Modena, Italy
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28
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Spectroscopic characterization and kinetic studies of a novel plastocyanin from the green alga Ulva pertusa. Inorganica Chim Acta 1998. [DOI: 10.1016/s0020-1693(98)00228-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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29
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Webb MA, Loppnow GR. Protein Tuning of Excited-State Charge-Transfer Dynamics in Azurin. J Phys Chem B 1998. [DOI: 10.1021/jp982316n] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- M. Adam Webb
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
| | - Glen R. Loppnow
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
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30
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31
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32
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Villanueva ND, Chiang MY, Bocarsly JR. Copper Complexes Bearing Pendant, Protonatable Noncoordinating Groups: Synthesis, Characterization, and Protonation Chemistry. Inorg Chem 1998. [DOI: 10.1021/ic9703843] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Nydia D. Villanueva
- Departments of Chemistry, The University of Connecticut, Storrs, Connecticut 06269, and National Sun Yat-Sen University, Kaohsiung, Taiwan 804, Republic of China
| | - Michael Y. Chiang
- Departments of Chemistry, The University of Connecticut, Storrs, Connecticut 06269, and National Sun Yat-Sen University, Kaohsiung, Taiwan 804, Republic of China
| | - Jeffrey R. Bocarsly
- Departments of Chemistry, The University of Connecticut, Storrs, Connecticut 06269, and National Sun Yat-Sen University, Kaohsiung, Taiwan 804, Republic of China
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33
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Webb MA, Kwong CM, Loppnow GR. Excited-State Charge-Transfer Dynamics of Azurin, a Blue Copper Protein, from Resonance Raman Intensities. J Phys Chem B 1997. [DOI: 10.1021/jp970037e] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- M. Adam Webb
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
| | - Christine M. Kwong
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
| | - Glen R. Loppnow
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
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34
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Karlsson BG, Tsai LC, Nar H, Sanders-Loehr J, Bonander N, Langer V, Sjölin L. X-ray structure determination and characterization of the Pseudomonas aeruginosa azurin mutant Met121Glu. Biochemistry 1997; 36:4089-95. [PMID: 9100002 DOI: 10.1021/bi962416o] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The Met121Glu azurin mutant has been crystallized and the structure determined at a resolution of 2.3 A. In the crystal structure a carboxyl oxygen of Met121Glu is coordinated to the metal at a distance of 2.2 A. Single-crystal resonance Raman spectroscopy was used to show that the glutamic acid residue in the copper site was in the protonated state. Titration of this residue gives rise to a number of unusual, pH-dependent properties: as the pH is increased from 4 to 8, the S(Cys)-Cu ligand-to-metal charge transfer bands are blue shifted and their intensity ratio is reversed, the EPR signal changes from type 1 copper to a new form of protein-bound copper, and the redox potential changes from 370 to 180 mV. The spectroscopic changes in this pH interval are consistent with a two-state model. From the pH dependence of the optical and EPR spectra, pKa = 5.0 for the glutamic acid in the oxidized protein was determined.
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Affiliation(s)
- B G Karlsson
- Department of Biochemistry and Biophysics, Goteborg University, Sweden.
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35
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Sakurai T, Nose F, Fujiki T, Suzuki S. Reduction and Oxidation Processes of Blue Copper Proteins, Azurin, Pseudoazurin, Umecyanin, Stellacyanin, Plantacyanin, and Plastocyanin Approached by Cyclic and Potential Step Voltammetries. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 1996. [DOI: 10.1246/bcsj.69.2855] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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36
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37
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El-Shahawi MS, Smith WE. Spectroelectrochemistry of nickel(II) complexes of N,N′-bis(salicylaldehyde)–o-phenylenediamine and N,N-bis(2-hydroxy- 1-naphthaldehyde)–o-phenylenediamine using an optically transparent thin-layer electrode. Analyst 1994. [DOI: 10.1039/an9941900327] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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38
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Brischwein M, Scharf B, Engelhard M, Mäntele W. Analysis of the redox reaction of an archaebacterial copper protein, halocyanin, by electrochemistry and FTIR difference spectroscopy. Biochemistry 1993; 32:13710-7. [PMID: 8257705 DOI: 10.1021/bi00212a041] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Halocyanin is a recently discovered archaebacterial copper protein classified as "type I" small blue copper protein (Scharf, B., Ph.D. Thesis, University of Bochum, Germany). Its redox properties were investigated by a combination of protein electrochemical and spectroscopic techniques. Using electrochemical reactions in an ultrathin-layer electrochemical cell developed for UV/vis and IR spectroscopy, halocyanin could be quantitatively and reversibly oxidized and reduced. The titration of the absorption band at 600 nm can be perfectly described by a Nernst curve with n = 1 electron transferred; a quantitative fit yields a midpoint potential, Em, of 183 mV (vs SHE) at a pH of 7.3. The midpoint potential falls constantly from +333 mV at pH 4 to +119 mV at pH 10, with three regions around pH 4.5, 6.5, and 8.5 where the pH dependence is ca. -60 mV/pH unit, indicating the uptake of a proton with the reduction. By analogy with other small type I copper proteins, the three pK values suggested by the pH dependency of Em might be associated with three histidines which interact with the redox site. Electrochemically induced reduced-minus-oxidized Fourier transform infrared difference spectra in the 1800-1000 cm-1 range at neutral pH show a number of strong difference bands between ca. 1700 and 1600 cm-1 as well as smaller difference structures between 1600 and 1200 cm-1. The maximum amplitude of the difference bands--only ca. 1% of the amide-I absorption at ca. 1639 cm-1--indicates that only small protein rearrangements occur upon the redox transition.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M Brischwein
- Institut für Biophysik und Strahlenbiologie, Universität Freiburg, Germany
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39
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Van de Kamp M, Canters GW, Andrew CR, Sanders-Loehr J, Bender CJ, Peisach J. Effect of lysine ionization on the structure and electrochemical behaviour of the Met44-->Lys mutant of the blue-copper protein azurin from Pseudomonas aeruginosa. EUROPEAN JOURNAL OF BIOCHEMISTRY 1993; 218:229-38. [PMID: 8243468 DOI: 10.1111/j.1432-1033.1993.tb18369.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The structural and spectrochemical effects of the replacement of Met44 in the hydrophobic surface patch of azurin from Pseudomonas aeruginosa by a lysine residue were studied as a function of the ionization state of the lysine. In the pH range 5-8, the optical absorption, resonance Raman, EPR and electron spin-echo envelope modulation spectroscopic properties of wild-type and Met44-->Lys (M44K) azurin are very similar, indicating that the Cu-site geometry has been maintained. At higher pH, the deprotonation of Lys44 in M44K azurin (pKa 9-10) is accompanied by changes in the optical-absorption maxima (614 nm and 450 nm instead of 625 nm and 470 nm) and in the EPR gII value (2.298 instead of 2.241), indicative of a change in the bonding interactions of Cu at high pH. The strong pH dependence of the electron self-exchange rate of M44K azurin supports the assignment of Lys44 as the ionizable group and demonstrates the importance of the hydrophobic patch for electron transfer. The pH dependence of the midpoint potentials of wild-type and M44K azurin can be accounted for by the ionizations of His35 and His83 and by the additional electrostatic effect of the mutation.
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Affiliation(s)
- M Van de Kamp
- Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, The Netherlands
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40
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Germanas JP, Di Bilio AJ, Gray HB, Richards JH. Site saturation of the histidine-46 position in Pseudomonas aeruginosa azurin: characterization of the His46Asp copper and cobalt proteins. Biochemistry 1993; 32:7698-702. [PMID: 8394112 DOI: 10.1021/bi00081a014] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Cassette mutagenesis has been used to replace the copper ligand His46 of Pseudomonas aeruginosa azurin with 19 other amino acids and a stop codon. Several mutant proteins were expressed in Escherichia coli and isolated; however, only the variant in which His was replaced by Asp exhibited the spectral characteristics of a blue (type 1) center. The spectroscopic and electrochemical properties of this mutant protein show that the copper site is perturbed relative to wild-type azurin. The absorption spectrum of Cu(II)(His46Asp) azurin exhibits a S(Cys)-->Cu(II) band at 612 nm, as well as weaker features at approximately 300, 454, and approximately 850 nm; its EPR spectrum is rhombic (g parallel = 2.327(1), gx approximately 2.03, and gy approximately 2.07; A parallel = 22(2) x 10(-4), Ax approximately 46 x 10(-4), and Ay approximately 22 x 10(-4) cm-1). The reduction potential of the mutant (260 mV vs NHE at pH 8.5; 297 mV at pH 5.0) is lower than that of wild-type azurin (288 mV at pH 8.5; 349 mV at pH 5.0). The S(Cys)-->Co(II) absorption bands (approximately 300 and 362 nm) in Co(II)(His46Asp) azurin are strongly blue-shifted relative to those (330 and 375 nm) in the spectrum of the Co(II) (His46) protein, whereas the intensities of the ligand-field bands in the 500-650-nm region (epsilon approximately 100 M-1 cm-1) indicate a five-coordinate Co(II) environment.
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Affiliation(s)
- J P Germanas
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena 91125
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41
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Pascher T, Karlsson BG, Nordling M, Malmström BG, Vänngård T. Reduction potentials and their pH dependence in site-directed-mutant forms of azurin from Pseudomonas aeruginosa. EUROPEAN JOURNAL OF BIOCHEMISTRY 1993; 212:289-96. [PMID: 8383044 DOI: 10.1111/j.1432-1033.1993.tb17661.x] [Citation(s) in RCA: 128] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
A spectroelectrochemical method has been used to determine the reduction potential of the copper site in wild-type and 22 mutant forms of azurin from Pseudomonas aeruginosa at 25 degrees C and in the range pH 4-8; the effect of buffers and ionic strength on the potentials has also been studied. Amino-acid residues changed include Met121, which provides an S atom at a distance of about 0.3 nm from the metal, some amino acids in the hydrophobic patch, other residues believed to be important in electron transfer with physiological partners and some internal amino acids. The observed potentials span a range of about 300 mV. In all cases the potentials increase with decreasing pH, but the pKa values describing the pH dependence are essentially unchanged except in three mutants, where they change by pH 0.6-1.1 (up in one and down in two). The largest potential changes were found in some Met121 mutants, at which position large hydrophobic residues raise the potential, whereas negatively charged residues lower it; a decreased potential is also found in the Met121-->End mutant, which probably has H2O coordinated to the metal. Gly45 has its carbonyl group coordinated to copper, but the potential of Gly45-->Ala is close to that of the wild type. Some substitutions in the hydrophobic patch cause an increase in the potential, whereas substitutions involving His35 and Glu91 do not result in significant changes. No single mechanism for tuning the potential of the copper site can be discerned, but in many cases there are probably indirect effects of the protein conformation causing changes in metal-ligand interactions.
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Affiliation(s)
- T Pascher
- Department of Biochemistry and Biophysics, University of Göteborg, Sweden
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42
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Moratal JM, Salgado J, Donaire A, Jiménez HR, Castells J. 1D- and 2D-NMR studies of the pH effects on the metal-site geometry in nickel(II)–azurin from Pseudomonas aeruginosa. ACTA ACUST UNITED AC 1993. [DOI: 10.1039/c39930000110] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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43
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