1
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Liu N, Li L, Qin X, Li X, Xie Y, Chen X, Gao J. Theoretical Insights into the Generation Mechanism of the Tyr 122 Radical Catalyzed by Intermediate X in Class Ia Ribonucleotide Reductase. Inorg Chem 2023; 62:19498-19506. [PMID: 37987809 DOI: 10.1021/acs.inorgchem.3c02505] [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: 11/22/2023]
Abstract
Ribonucleotide reductase (RNR) catalyzes the reduction of ribonucleotides to deoxyribonucleotides in all organisms. There is an ∼35 Å long-range electron-hole transfer pathway during the catalytic process of class Ia RNR, which can be described as Tyr122β ↔ [Trp48β]? ↔ Tyr356β ↔ Tyr731α ↔ Tyr730α ↔ Cys439α. The formation of the Y122• radical initiates this long-range radical transfer process. However, the generation mechanism of Y122• is not yet clear due to confusion over the intermediate X structures. Based on the two reported X structures, we examined the possible mechanisms of Y122• generation by density functional theory (DFT) calculations. Our examinations revealed that the generation of the Y122• radical from the two different core structures of X was via a similar two-step reaction, with the first step of proton transfer for the formation of the proton receptor of Y122 and the second step of a proton-coupled long-range electron transfer reaction with the proton transfer from the Y122 hydroxyl group to the terminal hydroxide ligand of Fe1III and simultaneously electron transfer from the side chain of Y122 to Fe2IV. These findings provide an insight into the formation mechanism of Y122• catalyzed by the double-iron center of the β subunit of class Ia RNR.
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Affiliation(s)
- Nian Liu
- Chongqing Key Laboratory of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 401331, China
| | - Li Li
- Chongqing Key Laboratory of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 401331, China
| | - Xin Qin
- Chongqing Key Laboratory of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 401331, China
| | - Xin Li
- Chongqing Key Laboratory of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 401331, China
| | - Yuxin Xie
- Chongqing Key Laboratory of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 401331, China
| | - Xiaohua Chen
- Chongqing Key Laboratory of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 401331, China
| | - Jiali Gao
- Institute of Systems and Physical Biology, Shenzhen Bay Laboratory, Shenzhen 518055, China
- Department of Chemistry and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455, United States
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2
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Lebrette H, Srinivas V, John J, Aurelius O, Kumar R, Lundin D, Brewster AS, Bhowmick A, Sirohiwal A, Kim IS, Gul S, Pham C, Sutherlin KD, Simon P, Butryn A, Aller P, Orville AM, Fuller FD, Alonso-Mori R, Batyuk A, Sauter NK, Yachandra VK, Yano J, Kaila VRI, Sjöberg BM, Kern J, Roos K, Högbom M. Structure of a ribonucleotide reductase R2 protein radical. Science 2023; 382:109-113. [PMID: 37797025 PMCID: PMC7615503 DOI: 10.1126/science.adh8160] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2023] [Accepted: 08/30/2023] [Indexed: 10/07/2023]
Abstract
Aerobic ribonucleotide reductases (RNRs) initiate synthesis of DNA building blocks by generating a free radical within the R2 subunit; the radical is subsequently shuttled to the catalytic R1 subunit through proton-coupled electron transfer (PCET). We present a high-resolution room temperature structure of the class Ie R2 protein radical captured by x-ray free electron laser serial femtosecond crystallography. The structure reveals conformational reorganization to shield the radical and connect it to the translocation path, with structural changes propagating to the surface where the protein interacts with the catalytic R1 subunit. Restructuring of the hydrogen bond network, including a notably short O-O interaction of 2.41 angstroms, likely tunes and gates the radical during PCET. These structural results help explain radical handling and mobilization in RNR and have general implications for radical transfer in proteins.
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Affiliation(s)
- Hugo Lebrette
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Stockholm, Sweden
- Laboratoire de Microbiologie et Génétique Moléculaires, Centre de Biologie Intégrative, CNRS, Université Toulouse III, Toulouse, France
| | - Vivek Srinivas
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Stockholm, Sweden
| | - Juliane John
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Stockholm, Sweden
| | - Oskar Aurelius
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Stockholm, Sweden
- MAX IV Laboratory, Lund University, Lund, Sweden
| | - Rohit Kumar
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Stockholm, Sweden
| | - Daniel Lundin
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Stockholm, Sweden
| | - Aaron S. Brewster
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Asmit Bhowmick
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Abhishek Sirohiwal
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Stockholm, Sweden
| | - In-Sik Kim
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Sheraz Gul
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Cindy Pham
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Kyle D. Sutherlin
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Philipp Simon
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Agata Butryn
- Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot, United Kingdom
- Research Complex at Harwell, Harwell Science and Innovation Campus, Didcot, United Kingdom
| | - Pierre Aller
- Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot, United Kingdom
- Research Complex at Harwell, Harwell Science and Innovation Campus, Didcot, United Kingdom
| | - Allen M. Orville
- Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot, United Kingdom
- Research Complex at Harwell, Harwell Science and Innovation Campus, Didcot, United Kingdom
| | | | | | | | - Nicholas K. Sauter
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Vittal K. Yachandra
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Junko Yano
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Ville R. I. Kaila
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Stockholm, Sweden
| | - Britt-Marie Sjöberg
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Stockholm, Sweden
| | - Jan Kern
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Katarina Roos
- Department of Cell and Molecular Biology, Uppsala University, Uppsala, Sweden
| | - Martin Högbom
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Stockholm, Sweden
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3
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Yuan F, Su B, Yu Y, Wang J. Study and design of amino acid-based radical enzymes using unnatural amino acids. RSC Chem Biol 2023; 4:431-446. [PMID: 37292061 PMCID: PMC10246556 DOI: 10.1039/d2cb00250g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2022] [Accepted: 05/17/2023] [Indexed: 06/10/2023] Open
Abstract
Radical enzymes harness the power of reactive radical species by placing them in a protein scaffold, and they are capable of catalysing many important reactions. New native radical enzymes, especially those with amino acid-based radicals, in the category of non-heme iron enzymes (including ribonucleotide reductases), heme enzymes, copper enzymes, and FAD-radical enzymes have been discovered and characterized. We discussed recent research efforts to discover new native amino acid-based radical enzymes, and to study the roles of radicals in processes such as enzyme catalysis and electron transfer. Furthermore, design of radical enzymes in a small and simple scaffold not only allows us to study the radical in a well-controlled system and test our understanding of the native enzymes, but also allows us to create powerful enzymes. In the study and design of amino acid-based radical enzymes, the use of unnatural amino acids allows precise control of pKa values and reduction potentials of the residue, as well as probing the location of the radical through spectroscopic methods, making it a powerful research tool. Our understanding of amino acid-based radical enzymes will allow us to tailor them to create powerful catalysts and better therapeutics.
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Affiliation(s)
- Feiyan Yuan
- Institute of Biochemical Engineering, Key Laboratory of Medical Molecule Science and Pharmaceutical Engineering, Ministry of Industry and Information Technology, School of Chemistry and Chemical Engineering, Beijing Institute of Technology Beijing 102488 China
| | - Binbin Su
- Institute of Biochemical Engineering, Key Laboratory of Medical Molecule Science and Pharmaceutical Engineering, Ministry of Industry and Information Technology, School of Chemistry and Chemical Engineering, Beijing Institute of Technology Beijing 102488 China
| | - Yang Yu
- Institute of Biochemical Engineering, Key Laboratory of Medical Molecule Science and Pharmaceutical Engineering, Ministry of Industry and Information Technology, School of Chemistry and Chemical Engineering, Beijing Institute of Technology Beijing 102488 China
| | - Jiangyun Wang
- Laboratory of RNA Biology, Institute of Biophysics, Chinese Academy of Sciences Beijing 100101 China
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4
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Banerjee R, Srinivas V, Lebrette H. Ferritin-Like Proteins: A Conserved Core for a Myriad of Enzyme Complexes. Subcell Biochem 2022; 99:109-153. [PMID: 36151375 DOI: 10.1007/978-3-031-00793-4_4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Ferritin-like proteins share a common fold, a four α-helix bundle core, often coordinating a pair of metal ions. Although conserved, the ferritin fold permits a diverse set of reactions, and is central in a multitude of macromolecular enzyme complexes. Here, we emphasize this diversity through three members of the ferritin-like superfamily: the soluble methane monooxygenase, the class I ribonucleotide reductase and the aldehyde deformylating oxygenase. They all rely on dinuclear metal cofactors to catalyze different challenging oxygen-dependent reactions through the formation of multi-protein complexes. Recent studies using cryo-electron microscopy, serial femtosecond crystallography at an X-ray free electron laser source, or single-crystal X-ray diffraction, have reported the structures of the active protein complexes, and revealed unprecedented insights into the molecular mechanisms of these three enzymes.
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Affiliation(s)
- Rahul Banerjee
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN, USA
| | - Vivek Srinivas
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
| | - Hugo Lebrette
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden.
- Laboratoire de Microbiologie et Génétique Moléculaires (LMGM), Centre de Biologie Intégrative (CBI), CNRS, UPS, Université de Toulouse, Toulouse, France.
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5
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Ruskoski TB, Boal AK. The periodic table of ribonucleotide reductases. J Biol Chem 2021; 297:101137. [PMID: 34461093 PMCID: PMC8463856 DOI: 10.1016/j.jbc.2021.101137] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Revised: 08/20/2021] [Accepted: 08/26/2021] [Indexed: 12/30/2022] Open
Abstract
In most organisms, transition metal ions are necessary cofactors of ribonucleotide reductase (RNR), the enzyme responsible for biosynthesis of the 2'-deoxynucleotide building blocks of DNA. The metal ion generates an oxidant for an active site cysteine (Cys), yielding a thiyl radical that is necessary for initiation of catalysis in all RNRs. Class I enzymes, widespread in eukaryotes and aerobic microbes, share a common requirement for dioxygen in assembly of the active Cys oxidant and a unique quaternary structure, in which the metallo- or radical-cofactor is found in a separate subunit, β, from the catalytic α subunit. The first class I RNRs, the class Ia enzymes, discovered and characterized more than 30 years ago, were found to use a diiron(III)-tyrosyl-radical Cys oxidant. Although class Ia RNRs have historically served as the model for understanding enzyme mechanism and function, more recently, remarkably diverse bioinorganic and radical cofactors have been discovered in class I RNRs from pathogenic microbes. These enzymes use alternative transition metal ions, such as manganese, or posttranslationally installed tyrosyl radicals for initiation of ribonucleotide reduction. Here we summarize the recent progress in discovery and characterization of novel class I RNR radical-initiating cofactors, their mechanisms of assembly, and how they might function in the context of the active class I holoenzyme complex.
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Affiliation(s)
- Terry B Ruskoski
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, USA
| | - Amie K Boal
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, USA; Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania, USA.
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6
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Watson RA, Offenbacher AR, Barry BA. Detection of Catalytically Linked Conformational Changes in Wild-Type Class Ia Ribonucleotide Reductase Using Reaction-Induced FTIR Spectroscopy. J Phys Chem B 2021; 125:8362-8372. [PMID: 34289692 DOI: 10.1021/acs.jpcb.1c03038] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The enzyme, ribonucleotide reductase (RNR), is essential for DNA synthesis in all cells. The class Ia Escherichia coli RNR consists of two dimeric subunits, α2 and β2, which form an active but unstable heterodimer of dimers, α2β2. The structure of the wild-type form of the enzyme has been challenging to study due to the instability of the catalytic complex. A long-range proton-coupled electron-transfer (PCET) pathway facilitates radical migration from the Y122 radical-diiron cofactor in the β subunit to an active site cysteine, C439, in the α subunit to initiate the RNR chemistry. The PCET reactions and active site chemistry are spectroscopically masked by a rate-limiting, conformational gate. Here, we present a reaction-induced Fourier transform infrared (RIFTIR) spectroscopic method to monitor the mechanism of the active, wild-type RNR α2β2 complex. This method is employed to obtain new information about conformational changes accompanying RNR catalysis, including the role of carboxylate interactions, deprotonation, and oxidation of active site cysteines, and a detailed description of reversible secondary structural changes. Labeling of tyrosine revealed a conformationally active tyrosine in the β subunit, assigned to Y356β, which is part of the intersubunit PCET pathway. New insights into the roles of the inhibitors, azidoUDP and dATP, and the sensitivity of RIFTIR spectroscopy to detect subtle conformational motions arising from protein allostery are also presented.
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Affiliation(s)
- Ryan Atlee Watson
- Department of Chemistry and Biochemistry and the Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia, United States
| | - Adam R Offenbacher
- Department of Chemistry and Biochemistry and the Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia, United States.,Department of Chemistry, East Carolina University, Greenville, North Carolina, United States
| | - Bridgette A Barry
- Department of Chemistry and Biochemistry and the Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia, United States
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7
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Abstract
Electron-nuclear double resonance (ENDOR) measures the hyperfine interaction of magnetic nuclei with paramagnetic centers and is hence a powerful tool for spectroscopic investigations extending from biophysics to material science. Progress in microwave technology and the recent availability of commercial electron paramagnetic resonance (EPR) spectrometers up to an electron Larmor frequency of 263 GHz now open the opportunity for a more quantitative spectral analysis. Using representative spectra of a prototype amino acid radical in a biologically relevant enzyme, the [Formula: see text] in Escherichia coli ribonucleotide reductase, we developed a statistical model for ENDOR data and conducted statistical inference on the spectra including uncertainty estimation and hypothesis testing. Our approach in conjunction with 1H/2H isotopic labeling of [Formula: see text] in the protein unambiguously established new unexpected spectral contributions. Density functional theory (DFT) calculations and ENDOR spectral simulations indicated that these features result from the beta-methylene hyperfine coupling and are caused by a distribution of molecular conformations, likely important for the biological function of this essential radical. The results demonstrate that model-based statistical analysis in combination with state-of-the-art spectroscopy accesses information hitherto beyond standard approaches.
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8
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3-Nitrotyrosine and related derivatives in proteins: precursors, radical intermediates and impact in function. Essays Biochem 2020; 64:111-133. [PMID: 32016371 DOI: 10.1042/ebc20190052] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2019] [Revised: 12/30/2019] [Accepted: 01/03/2020] [Indexed: 12/22/2022]
Abstract
Oxidative post-translational modification of proteins by molecular oxygen (O2)- and nitric oxide (•NO)-derived reactive species is a usual process that occurs in mammalian tissues under both physiological and pathological conditions and can exert either regulatory or cytotoxic effects. Although the side chain of several amino acids is prone to experience oxidative modifications, tyrosine residues are one of the preferred targets of one-electron oxidants, given the ability of their phenolic side chain to undergo reversible one-electron oxidation to the relatively stable tyrosyl radical. Naturally occurring as reversible catalytic intermediates at the active site of a variety of enzymes, tyrosyl radicals can also lead to the formation of several stable oxidative products through radical-radical reactions, as is the case of 3-nitrotyrosine (NO2Tyr). The formation of NO2Tyr mainly occurs through the fast reaction between the tyrosyl radical and nitrogen dioxide (•NO2). One of the key endogenous nitrating agents is peroxynitrite (ONOO-), the product of the reaction of superoxide radical (O2•-) with •NO, but ONOO--independent mechanisms of nitration have been also disclosed. This chemical modification notably affects the physicochemical properties of tyrosine residues and because of this, it can have a remarkable impact on protein structure and function, both in vitro and in vivo. Although low amounts of NO2Tyr are detected under basal conditions, significantly increased levels are found at pathological states related with an overproduction of reactive species, such as cardiovascular and neurodegenerative diseases, inflammation and aging. While NO2Tyr is a well-established stable oxidative stress biomarker and a good predictor of disease progression, its role as a pathogenic mediator has been laboriously defined for just a small number of nitrated proteins and awaits further studies.
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9
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Kang G, Taguchi AT, Stubbe J, Drennan CL. Structure of a trapped radical transfer pathway within a ribonucleotide reductase holocomplex. Science 2020; 368:424-427. [PMID: 32217749 DOI: 10.1126/science.aba6794] [Citation(s) in RCA: 74] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2019] [Accepted: 03/16/2020] [Indexed: 12/27/2022]
Abstract
Ribonucleotide reductases (RNRs) are a diverse family of enzymes that are alone capable of generating 2'-deoxynucleotides de novo and are thus critical in DNA biosynthesis and repair. The nucleotide reduction reaction in all RNRs requires the generation of a transient active site thiyl radical, and in class I RNRs, this process involves a long-range radical transfer between two subunits, α and β. Because of the transient subunit association, an atomic resolution structure of an active α2β2 RNR complex has been elusive. We used a doubly substituted β2, E52Q/(2,3,5)-trifluorotyrosine122-β2, to trap wild-type α2 in a long-lived α2β2 complex. We report the structure of this complex by means of cryo-electron microscopy to 3.6-angstrom resolution, allowing for structural visualization of a 32-angstrom-long radical transfer pathway that affords RNR activity.
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Affiliation(s)
- Gyunghoon Kang
- Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge MA, USA.,Department of Biology, Massachusetts Institute of Technology, Cambridge MA, USA
| | - Alexander T Taguchi
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge MA, USA
| | - JoAnne Stubbe
- Department of Biology, Massachusetts Institute of Technology, Cambridge MA, USA. .,Department of Chemistry, Massachusetts Institute of Technology, Cambridge MA, USA
| | - Catherine L Drennan
- Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge MA, USA. .,Department of Biology, Massachusetts Institute of Technology, Cambridge MA, USA.,Department of Chemistry, Massachusetts Institute of Technology, Cambridge MA, USA
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10
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Offenbacher AR, Barry BA. A Proton Wire Mediates Proton Coupled Electron Transfer from Hydroxyurea and Other Hydroxamic Acids to Tyrosyl Radical in Class Ia Ribonucleotide Reductase. J Phys Chem B 2020; 124:345-354. [PMID: 31904962 DOI: 10.1021/acs.jpcb.9b08587] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Proton-coupled electron transfer (PCET) is fundamental to many important biological reactions, including solar energy conversion and DNA synthesis. For example, class Ia ribonucleotide reductases (RNRs) contain a tyrosyl radical-diiron cofactor with one aspartate ligand, D84. The tyrosyl radical, Y122•, in the β2 subunit acts as a radical initiator and oxidizes an active site cysteine in the α2 subunit. A transient quaternary α2/β2 complex is induced by substrate and effector binding. The hydroxamic acid, hydroxyurea (HU), reduces Y122• in a PCET reaction involving an electron and proton. This reaction is associated with the loss of activity, a conformational change at Y122, and a change in hydrogen bonding to the Fe1 ligand, D84. Here, we use isotopic labeling, solvent isotope exchange, proton inventories, and reaction-induced Fourier transform infrared (RIFT-IR) spectroscopy to show that the PCET reactions of hydroxamic acids are associated with a characteristic spectrum, which is assignable to electrostatic changes at nonligating aspartate residues. Notably, RIFT-IR spectroscopy reveals this characteristic spectrum when the effects of HU, hydroxylamine, and N-methylhydroxylamine are compared. A large solvent isotope effect is observed for each of the hydroxamic acid reactions, and proton inventories predict that the reactions are associated with the transfer of multiple protons in the transition state. The reduction of Y122• with 4-methoxyphenol does not lead to these characteristic carboxylate shifts and is associated with only a small solvent isotope effect. In addition to studies of the effects of hydroxamic acids on β2 alone, the reactions involving the quaternary α2β2 complex were also investigated. HU treatment of the quaternary complex, α2/β2/ATP/CDP, leads to a similar carboxylate shift spectrum, as observed with β2 alone. The use of globally labeled 13C chimeras (13C α2, 13C β2) confirms the assignment. Because the spectrum is sensitive to 13C β2 labeling, but not 13C α2 labeling, the quaternary complex spectrum is assigned to electrostatic changes in β2 carboxylate groups. Examination of the β2 X-ray structure reveals a hydrogen-bonded network leading from the protein surface to Y122. This predicted network includes nonligating aspartates, glutamate ligands to the iron cluster, and predicted crystallographically resolved water molecules. The network is similar when class Ia RNR structures from Escherichia coli, human, and mouse are compared. We propose that the PCET reactions of hydroxamic acids are mediated by a hydrogen-bonded proton wire in the β2 subunit.
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Affiliation(s)
- Adam R Offenbacher
- Department of Chemistry and Biochemistry and the Petit Institute for Bioengineering and Bioscience , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States.,Department of Chemistry , East Carolina University , Greenville , North Carolina 27858 , United States
| | - Bridgette A Barry
- Department of Chemistry and Biochemistry and the Petit Institute for Bioengineering and Bioscience , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States
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11
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Greene BL, Stubbe J, Nocera DG. Photochemical Rescue of a Conformationally Inactivated Ribonucleotide Reductase. J Am Chem Soc 2018; 140:15744-15752. [PMID: 30347141 DOI: 10.1021/jacs.8b07902] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Class Ia ribonucleotide reductase (RNR) of Escherichia coli contains an unusually stable tyrosyl radical cofactor in the β2 subunit (Y122•) necessary for nucleotide reductase activity. Upon binding the cognate α2 subunit, loaded with nucleoside diphosphate substrate and an allosteric/activity effector, a rate determining conformational change(s) enables rapid radical transfer (RT) within the active α2β2 complex from the Y122• site in β2 to the substrate activating cysteine residue (C439) in α2 via a pathway of redox active amino acids (Y122[β] ↔ W48[β]? ↔ Y356[β] ↔ Y731[α] ↔ Y730[α] ↔ C439[α]) spanning >35 Å. Ionizable residues at the α2β2 interface are essential in mediating RT, and therefore control activity. One of these mutations, E350X (where X = A, D, Q) in β2, obviates all RT, though the mechanism of control by which E350 mediates RT remains unclear. Herein, we utilize an E350Q-photoβ2 construct to photochemically rescue RNR activity from an otherwise inactive construct, wherein the initial RT event (Y122• → Y356) is replaced by direct photochemical radical generation of Y356•. These data present compelling evidence that E350 conveys allosteric information between the α2 and β2 subunits facilitating conformational gating of RT that specifically targets Y122• reduction, while the fidelity of the remainder of the RT pathway is retained.
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Affiliation(s)
- Brandon L Greene
- Department of Chemistry and Chemical Biology , Harvard University , Cambridge , Massachusetts 02138 , United States
| | | | - Daniel G Nocera
- Department of Chemistry and Chemical Biology , Harvard University , Cambridge , Massachusetts 02138 , United States
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12
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Gillet N, Elstner M, Kubař T. Coupled-perturbed DFTB-QM/MM metadynamics: Application to proton-coupled electron transfer. J Chem Phys 2018; 149:072328. [PMID: 30134697 DOI: 10.1063/1.5027100] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We present a new concept of free energy calculations of chemical reactions by means of extended sampling molecular dynamics simulations. Biasing potentials are applied on partial atomic charges, which may be combined with atomic coordinates either in a single collective variable or in multi-dimensional biasing simulations. The necessary additional gradients are obtained by solving coupled-perturbed equations within the approximative density-functional tight-binding method. The new computational scheme was implemented in a combination of Gromacs and Plumed. As a prospective application, proton-coupled electron transfer in a model molecular system is studied. Two collective variables are introduced naturally, one for the proton transfer and the other for the electron transfer. The results are in qualitative agreement with the extended free simulations performed for reference. Free energy minima as well as the mechanism of the process are identified correctly, while the topology of the transition region and the height of the energy barrier are only reproduced qualitatively. The application also illustrates possible difficulties with the new methodology. These may be inefficient sampling of spatial coordinates when atomic charges are biased exclusively and a decreased stability of the simulations. Still, the new approach represents a viable alternative for free energy calculations of a certain class of chemical reactions, for instance a proton-coupled electron transfer in proteins.
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Affiliation(s)
- Natacha Gillet
- Institute of Physical Chemistry, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
| | - Marcus Elstner
- Institute of Physical Chemistry, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
| | - Tomáš Kubař
- Institute of Physical Chemistry, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
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13
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Lee W, Kasanmascheff M, Huynh M, Quartararo A, Costentin C, Bejenke I, Nocera DG, Bennati M, Tommos C, Stubbe J. Properties of Site-Specifically Incorporated 3-Aminotyrosine in Proteins To Study Redox-Active Tyrosines: Escherichia coli Ribonucleotide Reductase as a Paradigm. Biochemistry 2018; 57:3402-3415. [PMID: 29630358 DOI: 10.1021/acs.biochem.8b00160] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
3-Aminotyrosine (NH2Y) has been a useful probe to study the role of redox active tyrosines in enzymes. This report describes properties of NH2Y of key importance for its application in mechanistic studies. By combining the tRNA/NH2Y-RS suppression technology with a model protein tailored for amino acid redox studies (α3X, X = NH2Y), the formal reduction potential of NH2Y32(O•/OH) ( E°' = 395 ± 7 mV at pH 7.08 ± 0.05) could be determined using protein film voltammetry. We find that the Δ E°' between NH2Y32(O•/OH) and Y32(O•/OH) when measured under reversible conditions is ∼300-400 mV larger than earlier estimates based on irreversible voltammograms obtained on aqueous NH2Y and Y. We have also generated D6-NH2Y731-α2 of ribonucleotide reductase (RNR), which when incubated with β2/CDP/ATP generates the D6-NH2Y731•-α2/β2 complex. By multifrequency electron paramagnetic resonance (35, 94, and 263 GHz) and 34 GHz 1H ENDOR spectroscopies, we determined the hyperfine coupling (hfc) constants of the amino protons that establish RNH2• planarity and thus minimal perturbation of the reduction potential by the protein environment. The amount of Y in the isolated NH2Y-RNR incorporated by infidelity of the tRNA/NH2Y-RS pair was determined by a generally useful LC-MS method. This information is essential to the utility of this NH2Y probe to study any protein of interest and is employed to address our previously reported activity associated with NH2Y-substituted RNRs.
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Affiliation(s)
| | - Müge Kasanmascheff
- Max Planck Institute for Biophysical Chemistry , Am Fassberg 11 , Göttingen , 37077 Germany
| | - Michael Huynh
- Department of Chemistry and Chemical Biology , Harvard University , 12 Oxford Street , Cambridge , Massachusetts 02138 United States
| | | | - Cyrille Costentin
- Department of Chemistry and Chemical Biology , Harvard University , 12 Oxford Street , Cambridge , Massachusetts 02138 United States.,Laboratoire d'Electrochimie Moléculaire, Unité Mixte de Recherche Université - CNRS No 7591 , Université Paris Diderot, Sorbonne Paris Cité , Bâtiment Lavoisier, 15 rue Jean de Baïf , 75205 Paris Cedex 13 , France
| | - Isabel Bejenke
- Max Planck Institute for Biophysical Chemistry , Am Fassberg 11 , Göttingen , 37077 Germany
| | - Daniel G Nocera
- Department of Chemistry and Chemical Biology , Harvard University , 12 Oxford Street , Cambridge , Massachusetts 02138 United States
| | - Marina Bennati
- Max Planck Institute for Biophysical Chemistry , Am Fassberg 11 , Göttingen , 37077 Germany
| | - Cecilia Tommos
- Department of Biochemistry and Biophysics , University of Pennsylvania Perelman School of Medicine , Philadelphia , Pennsylvania 19104 , United States
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14
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Ferrer-Sueta G, Campolo N, Trujillo M, Bartesaghi S, Carballal S, Romero N, Alvarez B, Radi R. Biochemistry of Peroxynitrite and Protein Tyrosine Nitration. Chem Rev 2018; 118:1338-1408. [DOI: 10.1021/acs.chemrev.7b00568] [Citation(s) in RCA: 292] [Impact Index Per Article: 48.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Gerardo Ferrer-Sueta
- Laboratorio
de Fisicoquímica Biológica, Facultad de
Ciencias, ‡Center for Free Radical and Biomedical Research, §Departamento de Bioquímica,
Facultad de Medicina, ∥Laboratorio de Enzimología, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
| | - Nicolás Campolo
- Laboratorio
de Fisicoquímica Biológica, Facultad de
Ciencias, ‡Center for Free Radical and Biomedical Research, §Departamento de Bioquímica,
Facultad de Medicina, ∥Laboratorio de Enzimología, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
| | - Madia Trujillo
- Laboratorio
de Fisicoquímica Biológica, Facultad de
Ciencias, ‡Center for Free Radical and Biomedical Research, §Departamento de Bioquímica,
Facultad de Medicina, ∥Laboratorio de Enzimología, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
| | - Silvina Bartesaghi
- Laboratorio
de Fisicoquímica Biológica, Facultad de
Ciencias, ‡Center for Free Radical and Biomedical Research, §Departamento de Bioquímica,
Facultad de Medicina, ∥Laboratorio de Enzimología, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
| | - Sebastián Carballal
- Laboratorio
de Fisicoquímica Biológica, Facultad de
Ciencias, ‡Center for Free Radical and Biomedical Research, §Departamento de Bioquímica,
Facultad de Medicina, ∥Laboratorio de Enzimología, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
| | - Natalia Romero
- Laboratorio
de Fisicoquímica Biológica, Facultad de
Ciencias, ‡Center for Free Radical and Biomedical Research, §Departamento de Bioquímica,
Facultad de Medicina, ∥Laboratorio de Enzimología, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
| | - Beatriz Alvarez
- Laboratorio
de Fisicoquímica Biológica, Facultad de
Ciencias, ‡Center for Free Radical and Biomedical Research, §Departamento de Bioquímica,
Facultad de Medicina, ∥Laboratorio de Enzimología, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
| | - Rafael Radi
- Laboratorio
de Fisicoquímica Biológica, Facultad de
Ciencias, ‡Center for Free Radical and Biomedical Research, §Departamento de Bioquímica,
Facultad de Medicina, ∥Laboratorio de Enzimología, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
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15
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Greene BL, Taguchi AT, Stubbe J, Nocera DG. Conformationally Dynamic Radical Transfer within Ribonucleotide Reductase. J Am Chem Soc 2017; 139:16657-16665. [PMID: 29037038 DOI: 10.1021/jacs.7b08192] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Ribonucleotide reductases (RNR) catalyze the reduction of nucleotides to deoxynucleotides through a mechanism involving an essential cysteine based thiyl radical. In the E. coli class 1a RNR the thiyl radical (C439•) is a transient species generated by radical transfer (RT) from a stable diferric-tyrosyl radical cofactor located >35 Å away across the α2:β2 subunit interface. RT is facilitated by sequential proton-coupled electron transfer (PCET) steps along a pathway of redox active amino acids (Y122β ↔ [W48β?] ↔ Y356β ↔ Y731α ↔ Y730α ↔ C439α). The mutant R411A(α) disrupts the H-bonding environment and conformation of Y731, ostensibly breaking the RT pathway in α2. However, the R411A protein retains significant enzymatic activity, suggesting Y731 is conformationally dynamic on the time scale of turnover. Installation of the radical trap 3-amino tyrosine (NH2Y) by amber codon suppression at positions Y731 or Y730 and investigation of the NH2Y• trapped state in the active α2:β2 complex by HYSCORE spectroscopy validate that the perturbed conformation of Y731 in R411A-α2 is dynamic, reforming the H-bond between Y731 and Y730 to allow RT to propagate to Y730. Kinetic studies facilitated by photochemical radical generation reveal that Y731 changes conformation on the ns-μs time scale, significantly faster than the enzymatic kcat. Furthermore, the kinetics of RT across the subunit interface were directly assessed for the first time, demonstrating conformationally dependent RT rates that increase from 0.6 to 1.6 × 104 s-1 when comparing wild type to R411A-α2, respectively. These results illustrate the role of conformational flexibility in modulating RT kinetics by targeting the PCET pathway of radical transport.
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Affiliation(s)
- Brandon L Greene
- Department of Chemistry and Chemical Biology, Harvard University , Cambridge, Massachusetts 02138, United States
| | - Alexander T Taguchi
- Department of Chemistry, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States
| | - JoAnne Stubbe
- Department of Chemistry, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States
| | - Daniel G Nocera
- Department of Chemistry and Chemical Biology, Harvard University , Cambridge, Massachusetts 02138, United States
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16
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Nick TU, Ravichandran KR, Stubbe J, Kasanmascheff M, Bennati M. Spectroscopic Evidence for a H Bond Network at Y 356 Located at the Subunit Interface of Active E. coli Ribonucleotide Reductase. Biochemistry 2017. [PMID: 28640584 DOI: 10.1021/acs.biochem.7b00462] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The reaction catalyzed by E. coli ribonucleotide reductase (RNR) composed of α and β subunits that form an active α2β2 complex is a paradigm for proton-coupled electron transfer (PCET) processes in biological transformations. β2 contains the diferric tyrosyl radical (Y122·) cofactor that initiates radical transfer (RT) over 35 Å via a specific pathway of amino acids (Y122· ⇆ [W48] ⇆ Y356 in β2 to Y731 ⇆ Y730 ⇆ C439 in α2). Experimental evidence exists for colinear and orthogonal PCET in α2 and β2, respectively. No mechanistic model yet exists for the PCET across the subunit (α/β) interface. Here, we report unique EPR spectroscopic features of Y356·-β, the pathway intermediate generated by the reaction of 2,3,5-F3Y122·-β2/CDP/ATP with wt-α2, Y731F-α2, or Y730F-α2. High field EPR (94 and 263 GHz) reveals a dramatically perturbed g tensor. [1H] and [2H]-ENDOR reveal two exchangeable H bonds to Y356·: a moderate one almost in-plane with the π-system and a weak one. DFT calculation on small models of Y· indicates that two in-plane, moderate H bonds (rO-H ∼1.8-1.9 Å) are required to reproduce the gx value of Y356· (wt-α2). The results are consistent with a model, in which a cluster of two, almost symmetrically oriented, water molecules provide the two moderate H bonds to Y356· that likely form a hydrogen bond network of water molecules involved in either the reversible PCET across the subunit interface or in H+ release to the solvent during Y356 oxidation.
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Affiliation(s)
- Thomas U Nick
- Research Group Electron-Spin Resonance Spectroscopy, Max Planck Institute for Biophysical Chemistry , 37077 Göttingen, Germany
| | - Kanchana R Ravichandran
- Department of Chemistry, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States
| | - JoAnne Stubbe
- Department of Chemistry, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States
| | - Müge Kasanmascheff
- Research Group Electron-Spin Resonance Spectroscopy, Max Planck Institute for Biophysical Chemistry , 37077 Göttingen, Germany
| | - Marina Bennati
- Research Group Electron-Spin Resonance Spectroscopy, Max Planck Institute for Biophysical Chemistry , 37077 Göttingen, Germany.,Department of Chemistry, University of Göttingen , 37077 Göttingen, Germany
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17
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Long-range proton-coupled electron transfer in the Escherichia coli class Ia ribonucleotide reductase. Essays Biochem 2017; 61:281-292. [PMID: 28487404 DOI: 10.1042/ebc20160072] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2017] [Revised: 03/31/2017] [Accepted: 04/03/2017] [Indexed: 11/17/2022]
Abstract
Escherichia coli class Ia ribonucleotide reductase (RNR) catalyzes the conversion of nucleotides to 2'-deoxynucleotides using a radical mechanism. Each turnover requires radical transfer from an assembled diferric tyrosyl radical (Y•) cofactor to the enzyme active site over 35 Å away. This unprecedented reaction occurs via an amino acid radical hopping pathway spanning two protein subunits. To study the mechanism of radical transport in RNR, a suite of biochemical approaches have been developed, such as site-directed incorporation of unnatural amino acids with altered electronic properties and photochemical generation of radical intermediates. The resulting variant RNRs have been investigated using a variety of time-resolved physical techniques, including transient absorption and stopped-flow UV-Vis spectroscopy, as well as rapid freeze-quench EPR, ENDOR, and PELDOR spectroscopic methods. The data suggest that radical transport occurs via proton-coupled electron transfer (PCET) and that the protein structure has evolved to manage the proton and electron transfer co-ordinates in order to prevent 'off-pathway' reactivity and build-up of oxidised intermediates. Thus, precise design and control over the factors that govern PCET is key to enabling reversible and long-range charge transport by amino acid radicals in RNR.
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18
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Lin Q, Parker MJ, Taguchi AT, Ravichandran K, Kim A, Kang G, Shao J, Drennan CL, Stubbe J. Glutamate 52-β at the α/β subunit interface of Escherichia coli class Ia ribonucleotide reductase is essential for conformational gating of radical transfer. J Biol Chem 2017; 292:9229-9239. [PMID: 28377505 DOI: 10.1074/jbc.m117.783092] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2017] [Revised: 04/02/2017] [Indexed: 11/06/2022] Open
Abstract
Ribonucleotide reductases (RNRs) catalyze the conversion of nucleoside diphosphate substrates (S) to deoxynucleotides with allosteric effectors (e) controlling their relative ratios and amounts, crucial for fidelity of DNA replication and repair. Escherichia coli class Ia RNR is composed of α and β subunits that form a transient, active α2β2 complex. The E. coli RNR is rate-limited by S/e-dependent conformational change(s) that trigger the radical initiation step through a pathway of 35 Å across the subunit (α/β) interface. The weak subunit affinity and complex nucleotide-dependent quaternary structures have precluded a molecular understanding of the kinetic gating mechanism(s) of the RNR machinery. Using a docking model of α2β2 created from X-ray structures of α and β and conserved residues from a new subclassification of the E. coli Ia RNR (Iag), we identified and investigated four residues at the α/β interface (Glu350 and Glu52 in β2 and Arg329 and Arg639 in α2) of potential interest in kinetic gating. Mutation of each residue resulted in loss of activity and with the exception of E52Q-β2, weakened subunit affinity. An RNR mutant with 2,3,5-trifluorotyrosine radical (F3Y122•) replacing the stable Tyr122• in WT-β2, a mutation that partly overcomes conformational gating, was placed in the E52Q background. Incubation of this double mutant with His6-α2/S/e resulted in an RNR capable of catalyzing pathway-radical formation (Tyr356•-β2), 0.5 eq of dCDP/F3Y122•, and formation of an α2β2 complex that is isolable in pulldown assays over 2 h. Negative stain EM images with S/e (GDP/TTP) revealed the uniformity of the α2β2 complex formed.
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Affiliation(s)
- Qinghui Lin
- From the Department of Pathology and Pathophysiology, Zhejiang University School of Medicine, Hangzhou 310058, China and
| | | | | | | | | | | | - Jimin Shao
- From the Department of Pathology and Pathophysiology, Zhejiang University School of Medicine, Hangzhou 310058, China and
| | - Catherine L Drennan
- the Departments of Chemistry and .,Biology, and.,Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
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19
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Ravichandran KR, Zong AB, Taguchi AT, Nocera DG, Stubbe J, Tommos C. Formal Reduction Potentials of Difluorotyrosine and Trifluorotyrosine Protein Residues: Defining the Thermodynamics of Multistep Radical Transfer. J Am Chem Soc 2017; 139:2994-3004. [PMID: 28171730 DOI: 10.1021/jacs.6b11011] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Redox-active tyrosines (Ys) play essential roles in enzymes involved in primary metabolism including energy transduction and deoxynucleotide production catalyzed by ribonucleotide reductases (RNRs). Thermodynamic characterization of Ys in solution and in proteins remains a challenge due to the high reduction potentials involved and the reactive nature of the radical state. The structurally characterized α3Y model protein has allowed the first determination of formal reduction potentials (E°') for a Y residing within a protein (Berry, B. W.; Martı́nez-Rivera, M. C.; Tommos, C. Proc. Natl. Acad. Sci. U. S. A. 2012, 109, 9739-9743). Using Schultz's technology, a series of fluorotyrosines (FnY, n = 2 or 3) was site-specifically incorporated into α3Y. The global protein properties of the resulting α3(3,5)F2Y, α3(2,3,5)F3Y, α3(2,3)F2Y and α3(2,3,6)F3Y variants are essentially identical to those of α3Y. A protein film square-wave voltammetry approach was developed to successfully obtain reversible voltammograms and E°'s of the very high-potential α3FnY proteins. E°'(pH 5.5; α3FnY(O•/OH)) spans a range of 1040 ± 3 mV to 1200 ± 3 mV versus the normal hydrogen electrode. This is comparable to the potentials of the most oxidizing redox cofactors in nature. The FnY analogues, and the ability to site-specifically incorporate them into any protein of interest, provide new tools for mechanistic studies on redox-active Ys in proteins and on functional and aberrant hole-transfer reactions in metallo-enzymes. The former application is illustrated here by using the determined α3FnY ΔE°'s to model the thermodynamics of radical-transfer reactions in FnY-RNRs and to experimentally test and support the key prediction made.
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Affiliation(s)
| | - Allan B Zong
- Department of Biochemistry and Biophysics, University of Pennsylvania Perelman School of Medicine , Philadelphia, Pennsylvania 19104, United States
| | | | - Daniel G Nocera
- Department of Chemistry and Chemical Biology, Harvard University , 12 Oxford Street, Cambridge, Massachusetts 02138, United States
| | | | - Cecilia Tommos
- Department of Biochemistry and Biophysics, University of Pennsylvania Perelman School of Medicine , Philadelphia, Pennsylvania 19104, United States
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20
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Ravichandran K, Minnihan EC, Lin Q, Yokoyama K, Taguchi AT, Shao J, Nocera DG, Stubbe J. Glutamate 350 Plays an Essential Role in Conformational Gating of Long-Range Radical Transport in Escherichia coli Class Ia Ribonucleotide Reductase. Biochemistry 2017; 56:856-868. [PMID: 28103007 DOI: 10.1021/acs.biochem.6b01145] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Escherichia coli class Ia ribonucleotide reductase (RNR) is composed of two subunits that form an active α2β2 complex. The nucleoside diphosphate substrates (NDP) are reduced in α2, 35 Å from the essential diferric-tyrosyl radical (Y122•) cofactor in β2. The Y122•-mediated oxidation of C439 in α2 occurs by a pathway (Y122 ⇆ [W48] ⇆ Y356 in β2 to Y731 ⇆ Y730 ⇆ C439 in α2) across the α/β interface. The absence of an α2β2 structure precludes insight into the location of Y356 and Y731 at the subunit interface. The proximity in the primary sequence of the conserved E350 to Y356 in β2 suggested its importance in catalysis and/or conformational gating. To study its function, pH-rate profiles of wild-type β2/α2 and mutants in which 3,5-difluorotyrosine (F2Y) replaces residue 356, 731, or both are reported in the presence of E350 or E350X (X = A, D, or Q) mutants. With E350, activity is maintained at the pH extremes, suggesting that protonated and deprotonated states of F2Y356 and F2Y731 are active and that radical transport (RT) can occur across the interface by proton-coupled electron transfer at low pH or electron transfer at high pH. With E350X mutants, all RNRs were inactive, suggesting that E350 could be a proton acceptor during oxidation of the interface Ys. To determine if E350 plays a role in conformational gating, the strong oxidants, NO2Y122•-β2 and 2,3,5-F3Y122•-β2, were reacted with α2, CDP, and ATP in E350 and E350X backgrounds and the reactions were monitored for pathway radicals by rapid freeze-quench electron paramagnetic resonance spectroscopy. Pathway radicals are generated only when E350 is present, supporting its essential role in gating the conformational change(s) that initiates RT and masking its role as a proton acceptor.
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Affiliation(s)
| | | | - Qinghui Lin
- Department of Pathology and Pathophysiology, Key Laboratory of Disease Proteomics of Zhejiang Province, Research Center for Air Pollution and Health, Zhejiang University School of Medicine , Hangzhou 310058, China
| | | | | | - Jimin Shao
- Department of Pathology and Pathophysiology, Key Laboratory of Disease Proteomics of Zhejiang Province, Research Center for Air Pollution and Health, Zhejiang University School of Medicine , Hangzhou 310058, China
| | - Daniel G Nocera
- Department of Chemistry and Chemical Biology, Harvard University , 12 Oxford Street, Cambridge, Massachusetts 02138, United States
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21
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Hu C, Yu Y, Wang J. Improving artificial metalloenzymes' activity by optimizing electron transfer. Chem Commun (Camb) 2017; 53:4173-4186. [DOI: 10.1039/c6cc09921a] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
This feature article discusses the strategies to optimize electron transfer efficiency, towards enhancing the activity of artificial metalloenzymes.
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Affiliation(s)
- Cheng Hu
- Laboratory of RNA Biology
- Institute of Biophysics
- Chinese Academy of Sciences
- Chaoyang District
- China
| | - Yang Yu
- Tianjin Institute of Industrial Biotechnology
- Chinese Academy of Sciences
- Tianjin 300308
- China
| | - Jiangyun Wang
- Laboratory of RNA Biology
- Institute of Biophysics
- Chinese Academy of Sciences
- Chaoyang District
- China
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22
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Biosynthetic approach to modeling and understanding metalloproteins using unnatural amino acids. Sci China Chem 2016. [DOI: 10.1007/s11426-016-0343-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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23
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Ravichandran KR, Taguchi AT, Wei Y, Tommos C, Nocera DG, Stubbe J. A >200 meV Uphill Thermodynamic Landscape for Radical Transport in Escherichia coli Ribonucleotide Reductase Determined Using Fluorotyrosine-Substituted Enzymes. J Am Chem Soc 2016; 138:13706-13716. [PMID: 28068088 PMCID: PMC5224885 DOI: 10.1021/jacs.6b08200] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
Escherichia coli class Ia ribonucleotide reductase
(RNR) converts ribonucleotides to deoxynucleotides. A diferric-tyrosyl
radical (Y122•) in one subunit (β2) generates
a transient thiyl radical in another subunit (α2) via long-range
radical transport (RT) through aromatic amino acid residues (Y122 ⇆ [W48] ⇆ Y356 in β2
to Y731 ⇆ Y730 ⇆ C439 in α2). Equilibration of Y356•, Y731•, and Y730• was recently observed using
site specifically incorporated unnatural tyrosine analogs; however,
equilibration between Y122• and Y356•
has not been detected. Our recent report of Y356•
formation in a kinetically and chemically competent fashion in the
reaction of β2 containing 2,3,5-trifluorotyrosine at Y122 (F3Y122•-β2) with α2, CDP
(substrate), and ATP (effector) has now afforded the opportunity to
investigate equilibration of F3Y122•
and Y356•. Incubation of F3Y122•-β2, Y731F-α2 (or Y730F-α2),
CDP, and ATP at different temperatures (2–37 °C) provides
ΔE°′(F3Y122•–Y356•) of 20 ± 10 mV at 25
°C. The pH dependence of the F3Y122•
⇆ Y356• interconversion (pH 6.8–8.0)
reveals that the proton from Y356 is in rapid exchange
with solvent, in contrast to the proton from Y122. Insertion
of 3,5-difluorotyrosine (F2Y) at Y356 and rapid
freeze-quench EPR analysis of its reaction with Y731F-α2,
CDP, and ATP at pH 8.2 and 25 °C shows F2Y356• generation by the native Y122•. FnY-RNRs (n = 2 and 3) together
provide a model for the thermodynamic landscape of the RT pathway
in which the reaction between Y122 and C439 is
∼200 meV uphill.
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Affiliation(s)
| | | | | | - Cecilia Tommos
- Department of Biochemistry and Biophysics, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States
| | - Daniel G Nocera
- Department of Chemistry and Chemical Biology, Harvard University , 12 Oxford Street, Cambridge, Massachusetts 02138, United States
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24
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Manbeck GF, Fujita E, Concepcion JJ. Proton-Coupled Electron Transfer in a Strongly Coupled Photosystem II-Inspired Chromophore–Imidazole–Phenol Complex: Stepwise Oxidation and Concerted Reduction. J Am Chem Soc 2016; 138:11536-49. [DOI: 10.1021/jacs.6b03506] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Gerald F. Manbeck
- Chemistry Division, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
| | - Etsuko Fujita
- Chemistry Division, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
| | - Javier J. Concepcion
- Chemistry Division, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
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25
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Oyala PH, Ravichandran KR, Funk MA, Stucky PA, Stich TA, Drennan CL, Britt RD, Stubbe J. Biophysical Characterization of Fluorotyrosine Probes Site-Specifically Incorporated into Enzymes: E. coli Ribonucleotide Reductase As an Example. J Am Chem Soc 2016; 138:7951-64. [PMID: 27276098 PMCID: PMC4929525 DOI: 10.1021/jacs.6b03605] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
![]()
Fluorinated tyrosines
(FnY’s, n = 2
and 3) have been site-specifically incorporated into E. coli class Ia ribonucleotide reductase (RNR) using the
recently evolved M. jannaschii Y-tRNA synthetase/tRNA
pair. Class Ia RNRs require four redox active Y’s, a stable
Y radical (Y·) in the β subunit (position 122 in E. coli), and three transiently oxidized Y’s (356
in β and 731 and 730 in α) to initiate the radical-dependent
nucleotide reduction process. FnY (3,5;
2,3; 2,3,5; and 2,3,6) incorporation in place of Y122-β
and the X-ray structures of each resulting β with a diferric
cluster are reported and compared with wt-β2 crystallized under
the same conditions. The essential diferric-FnY· cofactor is self-assembled from apo FnY-β2, Fe2+, and O2 to produce ∼1
Y·/β2 and ∼3 Fe3+/β2. The FnY· are stable and active in nucleotide
reduction with activities that vary from 5% to 85% that of wt-β2.
Each FnY·-β2 has been characterized
by 9 and 130 GHz electron paramagnetic resonance and high-field electron
nuclear double resonance spectroscopies. The hyperfine interactions
associated with the 19F nucleus provide unique signatures
of each FnY· that are readily distinguishable
from unlabeled Y·’s. The variability of the abiotic FnY pKa’s
(6.4 to 7.8) and reduction potentials (−30 to +130 mV relative
to Y at pH 7.5) provide probes of enzymatic reactions proposed to
involve Y·’s in catalysis and to investigate the importance
and identity of hopping Y·’s within redox active proteins
proposed to protect them from uncoupled radical chemistry.
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Affiliation(s)
- Paul H Oyala
- Department of Chemistry, University of California, Davis , One Shields Avenue, Davis, California 95616, United States
| | | | | | - Paul A Stucky
- Department of Chemistry, University of California, Davis , One Shields Avenue, Davis, California 95616, United States
| | - Troy A Stich
- Department of Chemistry, University of California, Davis , One Shields Avenue, Davis, California 95616, United States
| | - Catherine L Drennan
- Howard Hughes Medical Institute, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
| | - R David Britt
- Department of Chemistry, University of California, Davis , One Shields Avenue, Davis, California 95616, United States
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26
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Mahmoudi L, Kissner R, Nauser T, Koppenol WH. Electrode Potentials of l-Tryptophan, l-Tyrosine, 3-Nitro-l-tyrosine, 2,3-Difluoro-l-tyrosine, and 2,3,5-Trifluoro-l-tyrosine. Biochemistry 2016; 55:2849-56. [DOI: 10.1021/acs.biochem.6b00019] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Leila Mahmoudi
- Institute of Inorganic Chemistry,
Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, Zurich CH-8093, Switzerland
| | - Reinhard Kissner
- Institute of Inorganic Chemistry,
Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, Zurich CH-8093, Switzerland
| | - Thomas Nauser
- Institute of Inorganic Chemistry,
Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, Zurich CH-8093, Switzerland
| | - Willem H. Koppenol
- Institute of Inorganic Chemistry,
Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, Zurich CH-8093, Switzerland
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27
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Olshansky L, Stubbe J, Nocera DG. Charge-Transfer Dynamics at the α/β Subunit Interface of a Photochemical Ribonucleotide Reductase. J Am Chem Soc 2016; 138:1196-205. [PMID: 26710997 PMCID: PMC4924928 DOI: 10.1021/jacs.5b09259] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Ribonucleotide reductase (RNR) catalyzes the conversion of ribonucleotides to deoxyribonucleotides to provide the monomeric building blocks for DNA replication and repair. Nucleotide reduction occurs by way of multistep proton-coupled electron transfer (PCET) over a pathway of redox active amino acids spanning ∼35 Å and two subunits (α2 and β2). Despite the fact that PCET in RNR is rapid, slow conformational changes mask examination of the kinetics of these steps. As such, we have pioneered methodology in which site-specific incorporation of a [Re(I)] photooxidant on the surface of the β2 subunit (photoβ2) allows photochemical oxidation of the adjacent PCET pathway residue β-Y356 and time-resolved spectroscopic observation of the ensuing reactivity. A series of photoβ2s capable of performing photoinitiated substrate turnover have been prepared in which four different fluorotyrosines (FnYs) are incorporated in place of β-Y356. The FnYs are deprotonated under biological conditions, undergo oxidation by electron transfer (ET), and provide a means by which to vary the ET driving force (ΔG°) with minimal additional perturbations across the series. We have used these features to map the correlation between ΔG° and kET both with and without the fully assembled photoRNR complex. The photooxidation of FnY356 within the α/β subunit interface occurs within the Marcus inverted region with a reorganization energy of λ ≈ 1 eV. We also observe enhanced electronic coupling between donor and acceptor (HDA) in the presence of an intact PCET pathway. Additionally, we have investigated the dynamics of proton transfer (PT) by a variety of methods including dependencies on solvent isotopic composition, buffer concentration, and pH. We present evidence for the role of α2 in facilitating PT during β-Y356 photooxidation; PT occurs by way of readily exchangeable positions and within a relatively "tight" subunit interface. These findings show that RNR controls ET by lowering λ, raising HDA, and directing PT both within and between individual polypeptide subunits.
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Affiliation(s)
- Lisa Olshansky
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
- Department of Chemistry and Chemical Biology, 12 Oxford St., Harvard University, Cambridge, Massachusetts 02138, United States
| | - JoAnne Stubbe
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
| | - Daniel G. Nocera
- Department of Chemistry and Chemical Biology, 12 Oxford St., Harvard University, Cambridge, Massachusetts 02138, United States
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28
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Ravichandran KR, Minnihan EC, Wei Y, Nocera DG, Stubbe J. Reverse Electron Transfer Completes the Catalytic Cycle in a 2,3,5-Trifluorotyrosine-Substituted Ribonucleotide Reductase. J Am Chem Soc 2015; 137:14387-95. [PMID: 26492582 PMCID: PMC4678968 DOI: 10.1021/jacs.5b09189] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
![]()
Escherichia coli class Ia ribonucleotide reductase
is composed of two subunits (α and β), which form an α2β2
complex that catalyzes the conversion of nucleoside 5′-diphosphates
to deoxynucleotides (dNDPs). β2 contains the essential tyrosyl
radical (Y122•) that generates a thiyl
radical (C439•) in α2 where dNDPs
are made. This oxidation occurs over 35 Å through a pathway of
amino acid radical intermediates (Y122 → [W48] → Y356 in β2 to Y731 → Y730 → C439 in α2).
However, chemistry is preceded by a slow protein conformational change(s)
that prevents observation of these intermediates. 2,3,5-Trifluorotyrosine
site-specifically inserted at position 122 of β2 (F3Y•-β2) perturbs its conformation and the
driving force for radical propagation, while maintaining catalytic
activity (1.7 s–1). Rapid freeze–quench electron
paramagnetic resonance spectroscopy and rapid chemical-quench analysis
of the F3Y•-β2, α2, CDP,
and ATP (effector) reaction show generation of 0.5 equiv of Y356• and 0.5 equiv of dCDP, both at 30 s–1. In the absence of an external reducing system, Y356• reduction occurs concomitant with F3Y reoxidation (0.4 s–1) and subsequent to
oxidation of all α2s. In the presence of a reducing system,
a burst of dCDP (0.4 equiv at 22 s–1) is observed
prior to steady-state turnover (1.7 s–1). The [Y356•] does not change, consistent with rate-limiting
F3Y reoxidation. The data support a mechanism where Y122• is reduced and reoxidized on each turnover
and demonstrate for the first time the ability of a pathway radical
in an active α2β2 complex to complete the catalytic cycle.
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Affiliation(s)
| | | | | | - Daniel G Nocera
- Department of Chemistry and Chemical Biology, Harvard University , 12 Oxford Street, Cambridge, Massachusetts 02138, United States
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29
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Abstract
An enormous variety of biological redox reactions are accompanied by changes in proton content at enzyme active sites, in their associated cofactors, in substrates and/or products, and between protein interfaces. Understanding this breadth of reactivity is an ongoing chemical challenge. A great many workers have developed and investigated biomimetic model complexes to build new ways of thinking about the mechanistic underpinnings of such complex biological proton-coupled electron transfer (PCET) reactions. Of particular importance are those model reactions that involve transfer of one proton (H(+)) and one electron (e(-)), which is equivalent to transfer of a hydrogen atom (H(•)). In this Current Topic, we review key concepts in PCET reactivity and describe important advances in biomimetic PCET chemistry, with a special emphasis on research that has enhanced efforts to understand biological PCET reactions.
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Affiliation(s)
- Jeffrey J. Warren
- Simon Fraser University, Department of Chemistry, 8888 University Drive, Burnaby BC, Canada V5A 1S6
| | - James M. Mayer
- Yale University, Department of Chemistry, P.O. Box 208107, 225 Prospect Street, New Haven, CT 06520-8107
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30
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Gamiz-Hernandez AP, Magomedov A, Hummer G, Kaila VRI. Linear Energy Relationships in Ground State Proton Transfer and Excited State Proton-Coupled Electron Transfer. J Phys Chem B 2015; 119:2611-9. [DOI: 10.1021/jp508790n] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Affiliation(s)
- Ana P. Gamiz-Hernandez
- Department
Chemie, Technische Universität München (TUM) Lichtenbergstraße
4, D-85747 Garching, Germany
| | - Artiom Magomedov
- Department
Chemie, Technische Universität München (TUM) Lichtenbergstraße
4, D-85747 Garching, Germany
| | - Gerhard Hummer
- Department
of Theoretical Biophysics, Max Planck Institute of Biophysics, Max-von-Laue-Straße
3, 60438 Frankfurt
am Main, Germany
| | - Ville R. I. Kaila
- Department
Chemie, Technische Universität München (TUM) Lichtenbergstraße
4, D-85747 Garching, Germany
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31
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Williamson HR, Dow BA, Davidson VL. Mechanisms for control of biological electron transfer reactions. Bioorg Chem 2014; 57:213-221. [PMID: 25085775 PMCID: PMC4285783 DOI: 10.1016/j.bioorg.2014.06.006] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Revised: 06/17/2014] [Accepted: 06/20/2014] [Indexed: 10/25/2022]
Abstract
Electron transfer (ET) through and between proteins is a fundamental biological process. The rates and mechanisms of these ET reactions are controlled by the proteins in which the redox centers that donate and accept electrons reside. The protein influences the magnitudes of the ET parameters, the electronic coupling and reorganization energy that are associated with the ET reaction. The protein can regulate the rates of the ET reaction by requiring reaction steps to optimize the system for ET, leading to kinetic mechanisms of gated or coupled ET. Amino acid residues in the segment of the protein through which long range ET occurs can also modulate the ET rate by serving as staging points for hopping mechanisms of ET. Specific examples are presented to illustrate these mechanisms by which proteins control rates of ET reactions.
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Affiliation(s)
- Heather R Williamson
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32827, United States
| | - Brian A Dow
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32827, United States
| | - Victor L Davidson
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32827, United States.
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32
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Olshansky L, Pizano AA, Wei Y, Stubbe J, Nocera DG. Kinetics of hydrogen atom abstraction from substrate by an active site thiyl radical in ribonucleotide reductase. J Am Chem Soc 2014; 136:16210-6. [PMID: 25353063 PMCID: PMC4244835 DOI: 10.1021/ja507313w] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
Ribonucleotide
reductases (RNRs) catalyze the conversion of nucleotides
to deoxynucleotides in all organisms. Active E. coli class Ia RNR is an α2β2 complex
that undergoes reversible, long-range proton-coupled electron transfer
(PCET) over a pathway of redox active amino acids (β-Y122 → [β-W48] → β-Y356 → α-Y731 → α-Y730 → α-C439) that spans ∼35 Å.
To unmask PCET kinetics from rate-limiting conformational changes,
we prepared a photochemical RNR containing a [ReI] photooxidant
site-specifically incorporated at position 355 ([Re]-β2), adjacent to PCET pathway residue Y356 in β. [Re]-β2 was further modified by replacing Y356 with 2,3,5-trifluorotyrosine
to enable photochemical generation and spectroscopic observation of
chemically competent tyrosyl radical(s). Using transient absorption
spectroscopy, we compare the kinetics of Y· decay in the presence
of substrate and wt-α2, Y731F-α2 ,or C439S-α2, as well as with
3′-[2H]-substrate and wt-α2. We
find that only in the presence of wt-α2 and the unlabeled
substrate do we observe an enhanced rate of radical decay indicative
of forward radical propagation. This observation reveals that cleavage
of the 3′-C–H bond of substrate by the transiently formed
C439· thiyl radical is rate-limiting in forward PCET
through α and has allowed calculation of a lower bound for the
rate constant associated with this step of (1.4 ± 0.4) ×
104 s–1. Prompting radical propagation
with light has enabled observation of PCET events heretofore inaccessible,
revealing active site chemistry at the heart of RNR catalysis.
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Affiliation(s)
- Lisa Olshansky
- Department of Chemistry and Chemical Biology, Harvard University , 12 Oxford Street, Cambridge, Massachusetts 02138, United States
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33
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Barry BA. Reaction dynamics and proton coupled electron transfer: studies of tyrosine-based charge transfer in natural and biomimetic systems. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2014; 1847:46-54. [PMID: 25260243 DOI: 10.1016/j.bbabio.2014.09.003] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2014] [Revised: 08/27/2014] [Accepted: 09/10/2014] [Indexed: 11/25/2022]
Abstract
In bioenergetic reactions, electrons are transferred long distances via a hopping mechanism. In photosynthesis and DNA synthesis, the aromatic amino acid residue, tyrosine, functions as an intermediate that is transiently oxidized and reduced during long distance electron transfer. At physiological pH values, oxidation of tyrosine is associated with a deprotonation of the phenolic oxygen, giving rise to a proton coupled electron transfer (PCET) reaction. Tyrosine-based PCET reactions are important in photosystem II, which carries out the light-induced oxidation of water, and in ribonucleotide reductase, which reduces ribonucleotides to form deoxynucleotides. Photosystem II contains two redox-active tyrosines, YD (Y160 in the D2 polypeptide) and YZ (Y161 in the D1 polypeptide). YD forms a light-induced stable radical, while YZ functions as an essential charge relay, oxidizing the catalytic Mn₄CaO₅ cluster on each of four photo-oxidation reactions. In Escherichia coli class 1a RNR, the β2 subunit contains the radical initiator, Y122O•, which is reversibly reduced and oxidized in long range electron transfer with the α2 subunit. In the isolated E. coli β2 subunit, Y122O• is a stable radical, but Y122O• is activated for rapid PCET in an α2β2 substrate/effector complex. Recent results concerning the structure and function of YD, YZ, and Y122 are reviewed here. Comparison is made to recent results derived from bioengineered proteins and biomimetic compounds, in which tyrosine-based charge transfer mechanisms have been investigated. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems.
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Affiliation(s)
- Bridgette A Barry
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA; Petit Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, GA 30332, USA.
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34
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Wei Y, Mathies G, Yokoyama K, Chen J, Griffin R, Stubbe J. A chemically competent thiosulfuranyl radical on the Escherichia coli class III ribonucleotide reductase. J Am Chem Soc 2014; 136:9001-13. [PMID: 24827372 PMCID: PMC4073831 DOI: 10.1021/ja5030194] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2014] [Indexed: 11/28/2022]
Abstract
The class III ribonucleotide reductases (RNRs) are glycyl radical (G•) enzymes that provide the balanced pool of deoxynucleotides required for DNA synthesis and repair in many facultative and obligate anaerobic bacteria and archaea. Unlike the class I and II RNRs, where reducing equivalents for the reaction are delivered by a redoxin (thioredoxin, glutaredoxin, or NrdH) via a pair of conserved active site cysteines, the class III RNRs examined to date use formate as the reductant. Here, we report that reaction of the Escherichia coli class III RNR with CTP (substrate) and ATP (allosteric effector) in the absence of formate leads to loss of the G• concomitant with stoichiometric formation of a new radical species and a "trapped" cytidine derivative that can break down to cytosine. Addition of formate to the new species results in recovery of 80% of the G• and reduction of the cytidine derivative, proposed to be 3'-keto-deoxycytidine, to dCTP and a small amount of cytosine. The structure of the new radical has been identified by 9.5 and 140 GHz EPR spectroscopy on isotopically labeled varieties of the protein to be a thiosulfuranyl radical [RSSR2]•, composed of a cysteine thiyl radical stabilized by an interaction with a methionine residue. The presence of a stable radical species on the reaction pathway rationalizes the previously reported [(3)H]-(k(cat)/K(M)) isotope effect of 2.3 with [(3)H]-formate, requiring formate to exchange between the active site and solution during nucleotide reduction. Analogies with the disulfide anion radical proposed to provide the reducing equivalent to the 3'-keto-deoxycytidine intermediate by the class I and II RNRs provide further evidence for the involvement of thiyl radicals in the reductive half-reaction catalyzed by all RNRs.
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Affiliation(s)
- Yifeng Wei
- Departments of Chemistry and Biology and Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, United States
| | - Guinevere Mathies
- Departments of Chemistry and Biology and Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, United States
| | - Kenichi Yokoyama
- Departments of Chemistry and Biology and Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, United States
| | - Jiahao Chen
- Departments of Chemistry and Biology and Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, United States
| | - Robert
G. Griffin
- Departments of Chemistry and Biology and Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, United States
| | - JoAnne Stubbe
- Departments of Chemistry and Biology and Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, United States
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35
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Migliore A, Polizzi NF, Therien M, Beratan DN. Biochemistry and theory of proton-coupled electron transfer. Chem Rev 2014; 114:3381-465. [PMID: 24684625 PMCID: PMC4317057 DOI: 10.1021/cr4006654] [Citation(s) in RCA: 340] [Impact Index Per Article: 34.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Indexed: 02/01/2023]
Affiliation(s)
- Agostino Migliore
- Department
of Chemistry, Department of Biochemistry, and Department of Physics, Duke University, Durham, North Carolina 27708, United States
| | - Nicholas F. Polizzi
- Department
of Chemistry, Department of Biochemistry, and Department of Physics, Duke University, Durham, North Carolina 27708, United States
| | - Michael
J. Therien
- Department
of Chemistry, Department of Biochemistry, and Department of Physics, Duke University, Durham, North Carolina 27708, United States
| | - David N. Beratan
- Department
of Chemistry, Department of Biochemistry, and Department of Physics, Duke University, Durham, North Carolina 27708, United States
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36
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Offenbacher AR, Watson RA, Pagba CV, Barry BA. Redox-dependent structural coupling between the α2 and β2 subunits in E. coli ribonucleotide reductase. J Phys Chem B 2014; 118:2993-3004. [PMID: 24606240 DOI: 10.1021/jp501121d] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Ribonucleotide reductase (RNR) catalyzes the production of deoxyribonucleotides in all cells. In E. coli class Ia RNR, a transient α2β2 complex forms when a ribonucleotide substrate, such as CDP, binds to the α2 subunit. A tyrosyl radical (Y122O•)-diferric cofactor in β2 initiates substrate reduction in α2 via a long-distance, proton-coupled electron transfer (PCET) process. Here, we use reaction-induced FT-IR spectroscopy to describe the α2β2 structural landscapes, which are associated with dATP and hydroxyurea (HU) inhibition. Spectra were acquired after mixing E. coli α2 and β2 with a substrate, CDP, and the allosteric effector, ATP. Isotopic chimeras, (13)Cα2β2 and α2(13)Cβ2, were used to define subunit-specific structural changes. Mixing of α2 and β2 under turnover conditions yielded amide I (C═O) and II (CN/NH) bands, derived from each subunit. The addition of the inhibitor, dATP, resulted in a decreased contribution from amide I bands, attributable to β strands and disordered structures. Significantly, HU-mediated reduction of Y122O• was associated with structural changes in α2, as well as β2. To define the spectral contributions of Y122O•/Y122OH in the quaternary complex, (2)H4 labeling of β2 tyrosines and HU editing were performed. The bands of Y122O•, Y122OH, and D84, a unidentate ligand to the diferric cluster, previously identified in isolated β2, were observed in the α2β2 complex. These spectra also provide evidence for a conformational rearrangement at an additional β2 tyrosine(s), Yx, in the α2β2/CDP/ATP complex. This study illustrates the utility of reaction-induced FT-IR spectroscopy in the study of complex enzymes.
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Affiliation(s)
- Adam R Offenbacher
- School of Chemistry and Biochemistry and the Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology , Atlanta, Georgia 30332, United States
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37
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Ravichandran KR, Liang L, Stubbe J, Tommos C. Formal reduction potential of 3,5-difluorotyrosine in a structured protein: insight into multistep radical transfer. Biochemistry 2013; 52:8907-15. [PMID: 24228716 DOI: 10.1021/bi401494f] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
The reversible Y-O•/Y-OH redox properties of the α3Y model protein allow access to the electrochemical and thermodynamic properties of 3,5-difluorotyrosine. The unnatural amino acid has been incorporated at position 32, the dedicated radical site in α3Y, by in vivo nonsense codon suppression. Incorporation of 3,5-difluorotyrosine gives rise to very minor structural changes in the protein scaffold at pH values below the apparent pK (8.0±0.1) of the unnatural residue. Square-wave voltammetry on α3(3,5)F2Y provides an E°'(Y-O•/Y-OH) of 1026±4 mV versus the normal hydrogen electrode (pH 5.70±0.02) and shows that the fluoro substitutions lower the E°' by -30±3 mV. These results illustrate the utility of combining the optimized α3Y tyrosine radical system with in vivo nonsense codon suppression to obtain the formal reduction potential of an unnatural aromatic residue residing within a well-structured protein. It is further observed that the protein E°' values differ significantly from peak potentials derived from irreversible voltammograms of the corresponding aqueous species. This is notable because solution potentials have been the main thermodynamic data available for amino acid radicals. The findings in this paper are discussed relative to recent mechanistic studies of the multistep radical-transfer process in Escherichia coli ribonucleotide reductase site-specifically labeled with unnatural tyrosine residues.
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Affiliation(s)
- Kanchana R Ravichandran
- Department of Chemistry, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
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38
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Minnihan EC, Nocera DG, Stubbe J. Reversible, long-range radical transfer in E. coli class Ia ribonucleotide reductase. Acc Chem Res 2013; 46:2524-35. [PMID: 23730940 DOI: 10.1021/ar4000407] [Citation(s) in RCA: 200] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Ribonucleotide reductases (RNRs) catalyze the conversionof nucleotides to 2'-deoxynucleotides and are classified on the basis of the metallo-cofactor used to conduct this chemistry. The class Ia RNRs initiate nucleotide reduction when a stable diferric-tyrosyl radical (Y•, t1/2 of 4 days at 4 °C) cofactor in the β2 subunit transiently oxidizes a cysteine to a thiyl radical (S•) in the active site of the α2 subunit. In the active α2β2 complex of the class Ia RNR from E. coli , researchers have proposed that radical hopping occurs reversibly over 35 Å along a specific pathway comprised of redox-active aromatic amino acids: Y122• ↔ [W48?] ↔ Y356 in β2 to Y731 ↔ Y730 ↔ C439 in α2. Each step necessitates a proton-coupled electron transfer (PCET). Protein conformational changes constitute the rate-limiting step in the overall catalytic scheme and kinetically mask the detailed chemistry of the PCET steps. Technology has evolved to allow the site-selective replacement of the four pathway tyrosines with unnatural tyrosine analogues. Rapid kinetic techniques combined with multifrequency electron paramagnetic resonance, pulsed electron-electron double resonance, and electron nuclear double resonance spectroscopies have facilitated the analysis of stable and transient radical intermediates in these mutants. These studies are beginning to reveal the mechanistic underpinnings of the radical transfer (RT) process. This Account summarizes recent mechanistic studies on mutant E. coli RNRs containing the following tyrosine analogues: 3,4-dihydroxyphenylalanine (DOPA) or 3-aminotyrosine (NH2Y), both thermodynamic radical traps; 3-nitrotyrosine (NO2Y), a thermodynamic barrier and probe of local environmental perturbations to the phenolic pKa; and fluorotyrosines (FnYs, n = 2 or 3), dual reporters on local pKas and reduction potentials. These studies have established the existence of a specific pathway spanning 35 Å within a globular α2β2 complex that involves one stable (position 122) and three transient (positions 356, 730, and 731) Y•s. Our results also support that RT occurs by an orthogonal PCET mechanism within β2, with Y122• reduction accompanied by proton transfer from an Fe1-bound water in the diferric cluster and Y356 oxidation coupled to an off-pathway proton transfer likely involving E350. In α2, RT likely occurs by a co-linear PCET mechanism, based on studies of light-initiated radical propagation from photopeptides that mimic the β2 subunit to the intact α2 subunit and on [(2)H]-ENDOR spectroscopic analysis of the hydrogen-bonding environment surrounding a stabilized NH2Y• formed at position 730. Additionally, studies on the thermodynamics of the RT pathway reveal that the relative reduction potentials decrease according to Y122 < Y356 < Y731 ≈ Y730 ≤ C439, and that the pathway in the forward direction is thermodynamically unfavorable. C439 oxidation is likely driven by rapid, irreversible loss of water during the nucleotide reduction process. Kinetic studies of radical intermediates reveal that RT is gated by conformational changes that occur on the order of >100 s(-1) in addition to the changes that are rate-limiting in the wild-type enzyme (∼10 s(-1)). The rate constant of one of the PCET steps is ∼10(5) s(-1), as measured in photoinitiated experiments.
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Affiliation(s)
| | - Daniel G. Nocera
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States
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39
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Wörsdörfer B, Conner DA, Yokoyama K, Livada J, Seyedsayamdost M, Jiang W, Silakov A, Stubbe J, Bollinger JM, Krebs C. Function of the diiron cluster of Escherichia coli class Ia ribonucleotide reductase in proton-coupled electron transfer. J Am Chem Soc 2013; 135:8585-93. [PMID: 23676140 PMCID: PMC3869997 DOI: 10.1021/ja401342s] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The class Ia ribonucleotide reductase (RNR) from Escherichia coli employs a free-radical mechanism, which involves bidirectional translocation of a radical equivalent or "hole" over a distance of ~35 Å from the stable diferric/tyrosyl-radical (Y122(•)) cofactor in the β subunit to cysteine 439 (C439) in the active site of the α subunit. This long-range, intersubunit electron transfer occurs by a multistep "hopping" mechanism via formation of transient amino acid radicals along a specific pathway and is thought to be conformationally gated and coupled to local proton transfers. Whereas constituent amino acids of the hopping pathway have been identified, details of the proton-transfer steps and conformational gating within the β sununit have remained obscure; specific proton couples have been proposed, but no direct evidence has been provided. In the key first step, the reduction of Y122(•) by the first residue in the hopping pathway, a water ligand to Fe1 of the diferric cluster was suggested to donate a proton to yield the neutral Y122. Here we show that forward radical translocation is associated with perturbation of the Mössbauer spectrum of the diferric cluster, especially the quadrupole doublet associated with Fe1. Density functional theory (DFT) calculations verify the consistency of the experimentally observed perturbation with that expected for deprotonation of the Fe1-coordinated water ligand. The results thus provide the first evidence that the diiron cluster of this prototypical class Ia RNR functions not only in its well-known role as generator of the enzyme's essential Y122(•), but also directly in catalysis.
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Affiliation(s)
- Bigna Wörsdörfer
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA
| | - Denise A. Conner
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA
| | - Kenichi Yokoyama
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Jovan Livada
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA
| | | | - Wei Jiang
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA
| | - Alexey Silakov
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA
| | - JoAnne Stubbe
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - J. Martin Bollinger
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA
| | - Carsten Krebs
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA
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Offenbacher AR, Minnihan EC, Stubbe J, Barry BA. Redox-linked changes to the hydrogen-bonding network of ribonucleotide reductase β2. J Am Chem Soc 2013; 135:6380-3. [PMID: 23594029 PMCID: PMC3694779 DOI: 10.1021/ja3032949] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Ribonucleotide reductase (RNR) catalyzes conversion of nucleoside diphosphates (NDPs) to 2'-deoxynucleotides, a critical step in DNA replication and repair in all organisms. Class-Ia RNRs, found in aerobic bacteria and all eukaryotes, are a complex of two subunits: α2 and β2. The β2 subunit contains an essential diferric-tyrosyl radical (Y122O(•)) cofactor that is needed to initiate reduction of NDPs in the α2 subunit. In this work, we investigated the Y122O(•) reduction mechanism in Escherichia coli β2 by hydroxyurea (HU), a radical scavenger and cancer therapeutic agent. We tested the hypothesis that Y122OH redox reactions cause structural changes in the diferric cluster. Reduction of Y122O(•) was studied using reaction-induced FT-IR spectroscopy and [(13)C]aspartate-labeled β2. These Y122O(•) minus Y122OH difference spectra provide evidence that the Y122OH redox reaction is associated with a frequency change to the asymmetric vibration of D84, a unidentate ligand to the diferric cluster. The results are consistent with a redox-induced shift in H-bonding between Y122OH and D84 that may regulate proton-transfer reactions on the HU-mediated inactivation pathway in isolated β2.
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Affiliation(s)
- Adam R. Offenbacher
- Department of Chemistry and Biochemistry and the Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA 30332, USA
| | - Ellen C. Minnihan
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - JoAnne Stubbe
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Bridgette A. Barry
- Department of Chemistry and Biochemistry and the Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA 30332, USA
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Minnihan EC, Ando N, Brignole EJ, Olshansky L, Chittuluru J, Asturias FJ, Drennan CL, Nocera DG, Stubbe J. Generation of a stable, aminotyrosyl radical-induced α2β2 complex of Escherichia coli class Ia ribonucleotide reductase. Proc Natl Acad Sci U S A 2013; 110:3835-40. [PMID: 23431160 PMCID: PMC3593893 DOI: 10.1073/pnas.1220691110] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Ribonucleotide reductase (RNR) catalyzes the conversion of nucleoside diphosphates to deoxynucleoside diphosphates (dNDPs). The Escherichia coli class Ia RNR uses a mechanism of radical propagation by which a cysteine in the active site of the RNR large (α2) subunit is transiently oxidized by a stable tyrosyl radical (Y•) in the RNR small (β2) subunit over a 35-Å pathway of redox-active amino acids: Y122• ↔ [W48?] ↔ Y356 in β2 to Y731 ↔ Y730 ↔ C439 in α2. When 3-aminotyrosine (NH2Y) is incorporated in place of Y730, a long-lived NH2Y730• is generated in α2 in the presence of wild-type (wt)-β2, substrate, and effector. This radical intermediate is chemically and kinetically competent to generate dNDPs. Herein, evidence is presented that NH2Y730• induces formation of a kinetically stable α2β2 complex. Under conditions that generate NH2Y730•, binding between Y730NH2Y-α2 and wt-β2 is 25-fold tighter (Kd = 7 nM) than for wt-α2
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Affiliation(s)
| | - Nozomi Ando
- Departments of Chemistry and
- Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139; and
| | - Edward J. Brignole
- Departments of Chemistry and
- Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139; and
| | | | | | | | - Catherine L. Drennan
- Departments of Chemistry and
- Biology, and
- Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139; and
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Krebs C, Dassama LMK, Matthews ML, Jiang W, Price JC, Korboukh V, Li N, Bollinger JM. Novel Approaches for the Accumulation of Oxygenated Intermediates to Multi-Millimolar Concentrations. Coord Chem Rev 2013; 257:10.1016/j.ccr.2012.06.020. [PMID: 24368870 PMCID: PMC3870000 DOI: 10.1016/j.ccr.2012.06.020] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Metalloenzymes that utilize molecular oxygen as a co-substrate catalyze a wide variety of chemically difficult oxidation reactions. Significant insight into the reaction mechanisms of these enzymes can be obtained by the application of a combination of rapid kinetic and spectroscopic methods to the direct structural characterization of intermediate states. A key limitation of this approach is the low aqueous solubility (< 2 mM) of the co-substrate, O2, which undergoes further dilution (typically by one-third or one-half) upon initiation of reactions by rapid-mixing. This situation imposes a practical upper limit on [O2] (and therefore on the concentration of reactive intermediate(s) that can be rapidly accumulated) of ∼1-1.3 mM in such experiments as they are routinely carried out. However, many spectroscopic methods benefit from or require significantly greater concentrations of the species to be studied. To overcome this problem, we have recently developed two new approaches for the preparation of samples of oxygenated intermediates: (1) direct oxygenation of reduced metalloenzymes using gaseous O2 and (2) the in situ generation of O2 from chlorite catalyzed by the enzyme chlorite dismutase (Cld). Whereas the former method is applicable only to intermediates with half lives of several minutes, owing to the sluggishness of transport of O2 across the gas-liquid interface, the latter approach has been successfully applied to trap several intermediates at high concentration and purity by the freeze-quench method. The in situ approach permits generation of a pulse of at least 5 mM O2 within ∼ 1 ms and accumulation of O2 to effective concentrations of up to ∼ 11 mM (i.e. ∼ 10-fold greater than by the conventional approach). The use of these new techniques for studies of oxygenases and oxidases is discussed.
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Affiliation(s)
- Carsten Krebs
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
| | - Laura M. K. Dassama
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
| | - Megan L. Matthews
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802
| | - Wei Jiang
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
| | - John C. Price
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
| | - Victoria Korboukh
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802
| | - Ning Li
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
| | - J. Martin Bollinger
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
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43
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Dassama LMK, Jiang W, Varano PT, Pandelia ME, Conner DA, Xie J, Bollinger JM, Krebs C. Radical-translocation intermediates and hurdling of pathway defects in "super-oxidized" (Mn(IV)/Fe(IV)) Chlamydia trachomatis ribonucleotide reductase. J Am Chem Soc 2012; 134:20498-506. [PMID: 23157728 PMCID: PMC3931446 DOI: 10.1021/ja309468s] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A class I ribonucleotide reductase (RNR) uses either a tyrosyl radical (Y(•)) or a Mn(IV)/Fe(III) cluster in its β subunit to oxidize a cysteine residue ∼35 Å away in its α subunit, generating a thiyl radical that abstracts hydrogen (H(•)) from the substrate. With either oxidant, the inter-subunit "hole-transfer" or "radical-translocation" (RT) process is thought to occur by a "hopping" mechanism involving multiple tyrosyl (and perhaps one tryptophanyl) radical intermediates along a specific pathway. The hopping intermediates have never been directly detected in a Mn/Fe-dependent (class Ic) RNR nor in any wild-type (wt) RNR. The Mn(IV)/Fe(III) cofactor of Chlamydia trachomatis RNR assembles via a Mn(IV)/Fe(IV) intermediate. Here we show that this cofactor-assembly intermediate can propagate a hole into the RT pathway when α is present, accumulating radicals with EPR spectra characteristic of Y(•)'s. The dependence of Y(•) accumulation on the presence of substrate suggests that RT within this "super-oxidized" enzyme form is gated by the protein, and the failure of a β variant having the subunit-interfacial pathway Y substituted by phenylalanine to support radical accumulation implies that the Y(•)(s) in the wt enzyme reside(s) within the RT pathway. Remarkably, two variant β proteins having pathway substitutions rendering them inactive in their Mn(IV)/Fe(III) states can generate the pathway Y(•)'s in their Mn(IV)/Fe(IV) states and also effect nucleotide reduction. Thus, the use of the more oxidized cofactor permits the accumulation of hopping intermediates and the "hurdling" of engineered defects in the RT pathway.
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Affiliation(s)
- Laura M. K. Dassama
- Departments of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802
| | - Wei Jiang
- Departments of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802
| | - Paul T. Varano
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802
| | - Maria-Eirini Pandelia
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802
| | - Denise A. Conner
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802
| | - Jiajia Xie
- Departments of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802
| | - J. Martin Bollinger
- Departments of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802
| | - Carsten Krebs
- Departments of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802
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44
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Warren JJ, Lancaster KM, Richards JH, Gray HB. Inner- and outer-sphere metal coordination in blue copper proteins. J Inorg Biochem 2012; 115:119-26. [PMID: 22658756 PMCID: PMC3434318 DOI: 10.1016/j.jinorgbio.2012.05.002] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2012] [Revised: 04/30/2012] [Accepted: 05/01/2012] [Indexed: 10/28/2022]
Abstract
Blue copper proteins (BCPs) comprise classic cases of Nature's profound control over the electronic structures and chemical reactivity of transition metal ions. Early studies of BCPs focused on their inner coordination spheres, that is, residues that directly coordinate Cu. Equally important are the electronic and geometric perturbations to these ligands provided by the outer coordination sphere. In this tribute to Hans Freeman, we review investigations that have advanced the understanding of how inner-sphere and outer-sphere coordination affects biological Cu properties.
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Affiliation(s)
- Jeffrey J Warren
- Beckman Institute, California Institute of Technology, Pasadena, CA 91125, USA
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45
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Grilj J, Buchgraber P, Vauthey E. Excited-State Dynamics of Wurster’s Salts. J Phys Chem A 2012; 116:7516-22. [DOI: 10.1021/jp3045548] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Jakob Grilj
- Department
of Physical Chemistry and ‡Department of Organic Chemistry, University of Geneva, 30 quai Ernest-Ansermet, CH-1211
Geneva 4
| | - Philipp Buchgraber
- Department
of Physical Chemistry and ‡Department of Organic Chemistry, University of Geneva, 30 quai Ernest-Ansermet, CH-1211
Geneva 4
| | - Eric Vauthey
- Department
of Physical Chemistry and ‡Department of Organic Chemistry, University of Geneva, 30 quai Ernest-Ansermet, CH-1211
Geneva 4
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46
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Abstract
Biological redox machines require efficient transfer of electrons and holes for function. Reactions involving multiple tunneling steps, termed "hopping," often promote charge separation within and between proteins that is essential for energy storage and conversion. Here we show how semiclassical electron transfer theory can be extended to include hopping reactions: graphical representations (called hopping maps) of the dependence of calculated two-step reaction rate constants on driving force are employed to account for flow in a rhenium-labeled azurin mutant as well as in two structurally characterized redox enzymes, DNA photolyase and MauG. Analysis of the 35 Å radical propagation in ribonucleotide reductases using hopping maps shows that all tyrosines and tryptophans on the radical pathway likely are involved in function. We suggest that hopping maps can facilitate the design and construction of artificial photosynthetic systems for the production of fuels and other chemicals.
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Affiliation(s)
- Jeffrey J Warren
- Beckman Institute, California Institute of Technology, Mail Code 139-74, Pasadena, CA 91125, USA
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47
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Barry BA, Chen J, Keough J, Jenson D, Offenbacher A, Pagba C. Proton Coupled Electron Transfer and Redox Active Tyrosines: Structure and Function of the Tyrosyl Radicals in Ribonucleotide Reductase and Photosystem II. J Phys Chem Lett 2012; 3:543-554. [PMID: 22662289 PMCID: PMC3362996 DOI: 10.1021/jz2014117] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Proton coupled electron transfer (PCET) reactions are important in many biological processes. Tyrosine oxidation/reduction can play a critical role in facilitating these reactions. Two examples are photosystem II (PSII) and ribonucleotide reductase (RNR). RNR is essential in DNA synthesis in all organisms. In E. coli RNR, a tyrosyl radical, Y122(•), is required as a radical initiator. Photosystem II (PSII) generates molecular oxygen from water. In PSII, an essential tyrosyl radical, YZ(•), oxidizes the oxygen evolving center. However, the mechanisms, by which the extraordinary oxidizing power of the tyrosyl radical is controlled, are not well understood. This is due to the difficulty in acquiring high-resolution structural information about the radical state. Spectroscopic approaches, such as EPR and UV resonance Raman (UVRR), can give new information. Here, we discuss EPR studies of PCET and the PSII YZ radical. We also present UVRR results, which support the conclusion that Y122 undergoes an alteration in ring and backbone dihedral angle when it is oxidized. This conformational change results in a loss of hydrogen bonding to the phenolic oxygen. Our analysis suggests that access of water is an important factor in determining tyrosyl radical lifetime and function. TOC graphic.
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48
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Holder PG, Pizano AA, Anderson BL, Stubbe J, Nocera DG. Deciphering radical transport in the large subunit of class I ribonucleotide reductase. J Am Chem Soc 2012; 134:1172-80. [PMID: 22121977 DOI: 10.1021/ja209016j] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Incorporation of 2,3,6-trifluorotyrosine (F(3)Y) and a rhenium bipyridine ([Re]) photooxidant into a peptide corresponding to the C-terminus of the β protein (βC19) of Escherichia coli ribonucleotide reductase (RNR) allows for the temporal monitoring of radical transport into the α2 subunit of RNR. Injection of the photogenerated F(3)Y radical from the [Re]-F(3)Y-βC19 peptide into the surface accessible Y731 of the α2 subunit is only possible when the second Y730 is present. With the Y-Y established, radical transport occurs with a rate constant of 3 × 10(5) s(-1). Point mutations that disrupt the Y-Y dyad shut down radical transport. The ability to obviate radical transport by disrupting the hydrogen bonding network of the amino acids composing the colinear proton-coupled electron transfer pathway in α2 suggests a finely tuned evolutionary adaptation of RNR to control the transport of radicals in this enzyme.
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Affiliation(s)
- Patrick G Holder
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
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49
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50
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Yokoyama K, Smith AA, Corzilius B, Griffin RG, Stubbe J. Equilibration of tyrosyl radicals (Y356•, Y731•, Y730•) in the radical propagation pathway of the Escherichia coli class Ia ribonucleotide reductase. J Am Chem Soc 2011; 133:18420-32. [PMID: 21967342 PMCID: PMC3236566 DOI: 10.1021/ja207455k] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Escherichia coli ribonucleotide reductase is an α2β2 complex that catalyzes the conversion of nucleotides to deoxynucleotides using a diferric tyrosyl radical (Y(122)(•)) cofactor in β2 to initiate catalysis in α2. Each turnover requires reversible long-range proton-coupled electron transfer (PCET) over 35 Å between the two subunits by a specific pathway (Y(122)(•) ⇆ [W(48)?] ⇆ Y(356) within β to Y(731) ⇆ Y(730) ⇆ C(439) within α). Previously, we reported that a β2 mutant with 3-nitrotyrosyl radical (NO(2)Y(•); 1.2 radicals/β2) in place of Y(122)(•) in the presence of α2, CDP, and ATP catalyzes formation of 0.6 equiv of dCDP and accumulates 0.6 equiv of a new Y(•) proposed to be located on Y(356) in β2. We now report three independent methods that establish that Y(356) is the predominant location (85-90%) of the radical, with the remaining 10-15% delocalized onto Y(731) and Y(730) in α2. Pulsed electron-electron double-resonance spectroscopy on samples prepared by rapid freeze quench (RFQ) methods identified three distances: 30 ± 0.4 Å (88% ± 3%) and 33 ± 0.4 and 38 ± 0.5 Å (12% ± 3%) indicative of NO(2)Y(122)(•)-Y(356)(•), NO(2)Y(122)(•)-NO(2)Y(122)(•), and NO(2)Y(122)(•)-Y(731(730))(•), respectively. Radical distribution in α2 was supported by RFQ electron paramagnetic resonance (EPR) studies using Y(731)(3,5-F(2)Y) or Y(730)(3,5-F(2)Y)-α2, which revealed F(2)Y(•), studies using globally incorporated [β-(2)H(2)]Y-α2, and analysis using parameters obtained from 140 GHz EPR spectroscopy. The amount of Y(•) delocalized in α2 from these two studies varied from 6% to 15%. The studies together give the first insight into the relative redox potentials of the three transient Y(•) radicals in the PCET pathway and their conformations.
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Affiliation(s)
- Kenichi Yokoyama
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139–4307
| | - Albert A. Smith
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139–4307
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139–4307
| | - Björn Corzilius
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139–4307
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139–4307
| | - Robert G. Griffin
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139–4307
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139–4307
| | - JoAnne Stubbe
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139–4307
- Department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139–4307
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