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Kisgeropoulos EC, Gan YJ, Greer SM, Hazel JM, Shafaat HS. Pulsed Multifrequency Electron Paramagnetic Resonance Spectroscopy Reveals Key Branch Points for One- vs Two-Electron Reactivity in Mn/Fe Proteins. J Am Chem Soc 2022; 144:11991-12006. [PMID: 35786920 DOI: 10.1021/jacs.1c13738] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Traditionally, the ferritin-like superfamily of proteins was thought to exclusively use a diiron active site in catalyzing a diverse array of oxygen-dependent reactions. In recent years, novel redox-active cofactors featuring heterobimetallic Mn/Fe active sites have been discovered in both the radical-generating R2 subunit of class Ic (R2c) ribonucleotide reductases (RNRs) and the related R2-like ligand-binding oxidases (R2lox). However, the protein-specific factors that differentiate the radical reactivity of R2c from the C-H activation reactions of R2lox remain unknown. In this work, multifrequency pulsed electron paramagnetic resonance (EPR) spectroscopy and ligand hyperfine techniques in conjunction with broken-symmetry density functional theory calculations are used to characterize the molecular and electronic structures of two EPR-active intermediates trapped during aerobic assembly of the R2lox Mn/Fe cofactor. A MnIII(μ-O)(μ-OH)FeIII species is identified as the first EPR-active species and represents a common state between the two classes of redox-active Mn/Fe proteins. The species downstream from the MnIII(μ-O)(μ-OH)FeIII state exhibits unique EPR properties, including unprecedented spectral breadth and isotope-dependent g-tensors, which are attributed to a weakly coupled, hydrogen-bonded MnIII(μ-OH)FeIII species. This final intermediate precedes formation of the MnIII/FeIII resting state and is suggested to be relevant to understanding the endogenous reactivity of R2lox.
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Affiliation(s)
- Effie C Kisgeropoulos
- The Ohio State Biochemistry Program, The Ohio State University, 100 W 18th Avenue, Columbus, Ohio 43210, United States
| | - Yunqiao J Gan
- Department of Chemistry and Biochemistry, The Ohio State University, 100 W 18th Avenue, Columbus, Ohio 43210, United States
| | - Samuel M Greer
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, United States.,Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States
| | - Joseph M Hazel
- Department of Chemistry and Biochemistry, The Ohio State University, 100 W 18th Avenue, Columbus, Ohio 43210, United States
| | - Hannah S Shafaat
- The Ohio State Biochemistry Program, The Ohio State University, 100 W 18th Avenue, Columbus, Ohio 43210, United States.,Department of Chemistry and Biochemistry, The Ohio State University, 100 W 18th Avenue, Columbus, Ohio 43210, United States
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2
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Kisgeropoulos EC, Griese JJ, Smith ZR, Branca RMM, Schneider CR, Högbom M, Shafaat HS. Key Structural Motifs Balance Metal Binding and Oxidative Reactivity in a Heterobimetallic Mn/Fe Protein. J Am Chem Soc 2020; 142:5338-5354. [PMID: 32062969 DOI: 10.1021/jacs.0c00333] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Heterobimetallic Mn/Fe proteins represent a new cofactor paradigm in bioinorganic chemistry and pose countless outstanding questions. The assembly of the active site defies common chemical convention by contradicting the Irving-Williams series, while the scope of reactivity remains unexplored. In this work, the assembly and C-H bond activation process in the Mn/Fe R2-like ligand-binding oxidase (R2lox) protein is investigated using a suite of biophysical techniques, including time-resolved optical spectroscopy, global kinetic modeling, X-ray crystallography, electron paramagnetic resonance spectroscopy, protein electrochemistry, and mass spectrometry. Selective metal binding is found to be under thermodynamic control, with the binding sites within the apo-protein exhibiting greater MnII affinity than FeII affinity. The comprehensive analysis of structure and reactivity of wild-type R2lox and targeted primary and secondary sphere mutants indicate that the efficiency of C-H bond activation directly correlates with the Mn/Fe cofactor reduction potentials and is inversely related to divalent metal binding affinity. These findings suggest the R2lox active site is precisely tuned for achieving both selective heterobimetallic binding and high levels of reactivity and offer a mechanism to examine the means by which proteins achieve appropriate metal incorporation.
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Affiliation(s)
| | - Julia J Griese
- Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden.,Department of Cell and Molecular Biology, Uppsala University, SE-751 24 Uppsala, Sweden
| | | | - Rui M M Branca
- Department of Oncology-Pathology, Science for Life Laboratory, Karolinska Institutet, SE-171 21 Solna, Sweden
| | | | - Martin Högbom
- Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden
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Mebs S, Srinivas V, Kositzki R, Griese JJ, Högbom M, Haumann M. Fate of oxygen species from O 2 activation at dimetal cofactors in an oxidase enzyme revealed by 57Fe nuclear resonance X-ray scattering and quantum chemistry. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2019; 1860:148060. [PMID: 31394094 DOI: 10.1016/j.bbabio.2019.148060] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2019] [Revised: 07/30/2019] [Accepted: 08/02/2019] [Indexed: 10/26/2022]
Abstract
Oxygen (O2) activation is a central challenge in chemistry and catalyzed at prototypic dimetal cofactors in biological enzymes with diverse functions. Analysis of intermediates is required to elucidate the reaction paths of reductive O2 cleavage. An oxidase protein from the bacterium Geobacillus kaustophilus, R2lox, was used for aerobic in-vitro reconstitution with only 57Fe(II) or Mn(II) plus 57Fe(II) ions to yield [FeFe] or [MnFe] cofactors under various oxygen and solvent isotopic conditions including 16/18O and H/D exchange. 57Fe-specific X-ray scattering techniques were employed to collect nuclear forward scattering (NFS) and nuclear resonance vibrational spectroscopy (NRVS) data of the R2lox proteins. NFS revealed Fe/Mn(III)Fe(III) cofactor states and Mössbauer quadrupole splitting energies. Quantum chemical calculations of NRVS spectra assigned molecular structures, vibrational modes, and protonation patterns of the cofactors, featuring a terminal water (H2O) bound at iron or manganese in site 1 and a metal-bridging hydroxide (μOH-) ligand. A procedure for quantitation and correlation of experimental and computational NRVS difference signals due to isotope labeling was developed. This approach revealed that the protons of the ligands as well as the terminal water at the R2lox cofactors exchange with the bulk solvent whereas 18O from 18O2 cleavage is incorporated in the hydroxide bridge. In R2lox, the two water molecules from four-electron O2 reduction are released in a two-step reaction to the solvent. These results establish combined NRVS and QM/MM for tracking of iron-based oxygen activation in biological and chemical catalysts and clarify the reductive O2 cleavage route in an enzyme.
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Affiliation(s)
- Stefan Mebs
- Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Vivek Srinivas
- Department of Biochemistry and Biophysics, Stockholm University, Svante Arrhenius väg 16, 10691 Stockholm, Sweden
| | - Ramona Kositzki
- Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Julia J Griese
- Department of Cell and Molecular Biology, Structural Biology, Uppsala University, Box 596, 75124 Uppsala, Sweden
| | - Martin Högbom
- Department of Biochemistry and Biophysics, Stockholm University, Svante Arrhenius väg 16, 10691 Stockholm, Sweden
| | - Michael Haumann
- Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.
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4
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Kutin Y, Kositzki R, Branca RMM, Srinivas V, Lundin D, Haumann M, Högbom M, Cox N, Griese JJ. Chemical flexibility of heterobimetallic Mn/Fe cofactors: R2lox and R2c proteins. J Biol Chem 2019; 294:18372-18386. [PMID: 31591267 DOI: 10.1074/jbc.ra119.010570] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Revised: 10/04/2019] [Indexed: 11/06/2022] Open
Abstract
A heterobimetallic Mn/Fe cofactor is present in the R2 subunit of class Ic ribonucleotide reductases (R2c) and in R2-like ligand-binding oxidases (R2lox). Although the protein-derived metal ligands are the same in both groups of proteins, the connectivity of the two metal ions and the chemistry each cofactor performs are different: in R2c, a one-electron oxidant, the Mn/Fe dimer is linked by two oxygen bridges (μ-oxo/μ-hydroxo), whereas in R2lox, a two-electron oxidant, it is linked by a single oxygen bridge (μ-hydroxo) and a fatty acid ligand. Here, we identified a second coordination sphere residue that directs the divergent reactivity of the protein scaffold. We found that the residue that directly precedes the N-terminal carboxylate metal ligand is conserved as a glycine within the R2lox group but not in R2c. Substitution of the glycine with leucine converted the resting-state R2lox cofactor to an R2c-like cofactor, a μ-oxo/μ-hydroxo-bridged MnIII/FeIII dimer. This species has recently been observed as an intermediate of the oxygen activation reaction in WT R2lox, indicating that it is physiologically relevant. Cofactor maturation in R2c and R2lox therefore follows the same pathway, with structural and functional divergence of the two cofactor forms following oxygen activation. We also show that the leucine-substituted variant no longer functions as a two-electron oxidant. Our results reveal that the residue preceding the N-terminal metal ligand directs the cofactor's reactivity toward one- or two-electron redox chemistry, presumably by setting the protonation state of the bridging oxygens and thereby perturbing the redox potential of the Mn ion.
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Affiliation(s)
- Yury Kutin
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany
| | - Ramona Kositzki
- Institut für Experimentalphysik, Freie Universität Berlin, D-14195 Berlin, Germany
| | - Rui M M Branca
- Cancer Proteomics Mass Spectrometry, Department of Oncology-Pathology, Science for Life Laboratory, Karolinska Institute, Box 1031, SE-171 21 Solna, Sweden
| | - Vivek Srinivas
- Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Daniel Lundin
- Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Michael Haumann
- Institut für Experimentalphysik, Freie Universität Berlin, D-14195 Berlin, Germany
| | - Martin Högbom
- Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Nicholas Cox
- Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory 2601, Australia.
| | - Julia J Griese
- Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden; Department of Cell and Molecular Biology, Uppsala University, SE-751 24 Uppsala, Sweden.
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Griese JJ, Högbom M. Location-specific quantification of protein-bound metal ions by X-ray anomalous dispersion: Q-XAD. ACTA CRYSTALLOGRAPHICA SECTION D-STRUCTURAL BIOLOGY 2019; 75:764-771. [PMID: 31373575 DOI: 10.1107/s2059798319009926] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2019] [Accepted: 07/10/2019] [Indexed: 12/18/2022]
Abstract
Here, a method is described which exploits X-ray anomalous dispersion (XAD) to quantify mixtures of metal ions in the binding sites of proteins and can be applied to metalloprotein crystals of average quality. This method has successfully been used to study site-specific metal binding in a protein from the R2-like ligand-binding oxidase family which assembles a heterodinuclear Mn/Fe cofactor. While previously only the relative contents of Fe and Mn in each metal-binding site have been assessed, here it is shown that the method can be extended to quantify the relative occupancies of at least three different transition metals, enabling complex competition experiments. The number of different metal ions that can be quantified is only limited by the number of high-quality anomalous data sets that can be obtained from one crystal, as one data set has to be collected for each transition-metal ion that is present (or is suspected to be present) in the protein, ideally at the absorption edge of each metal. A detailed description of the method, Q-XAD, is provided.
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Affiliation(s)
- Julia J Griese
- Department of Biochemistry and Biophysics, Stockholm University, 106 91 Stockholm, Sweden
| | - Martin Högbom
- Department of Biochemistry and Biophysics, Stockholm University, 106 91 Stockholm, Sweden
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Schneider CR, Miller EK, Smith ZR, Shafaat HS. Electrochemical Investigation of R2lox, a Novel Class of Heterobimetallic Mn/Fe Protein. FASEB J 2019. [DOI: 10.1096/fasebj.2019.33.1_supplement.lb216] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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7
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Griese JJ, Kositzki R, Haumann M, Högbom M. Assembly of a heterodinuclear Mn/Fe cofactor is coupled to tyrosine-valine ether cross-link formation in the R2-like ligand-binding oxidase. J Biol Inorg Chem 2019; 24:211-221. [PMID: 30689052 PMCID: PMC6399176 DOI: 10.1007/s00775-019-01639-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2018] [Accepted: 01/18/2019] [Indexed: 11/28/2022]
Abstract
R2-like ligand-binding oxidases (R2lox) assemble a heterodinuclear Mn/Fe cofactor which performs reductive dioxygen (O2) activation, catalyzes formation of a tyrosine-valine ether cross-link in the protein scaffold, and binds a fatty acid in a putative substrate channel. We have previously shown that the N-terminal metal binding site 1 is unspecific for manganese or iron in the absence of O2, but prefers manganese in the presence of O2, whereas the C-terminal site 2 is specific for iron. Here, we analyze the effects of amino acid exchanges in the cofactor environment on cofactor assembly and metalation specificity using X-ray crystallography, X-ray absorption spectroscopy, and metal quantification. We find that exchange of either the cross-linking tyrosine or the valine, regardless of whether the mutation still allows cross-link formation or not, results in unspecific manganese or iron binding at site 1 both in the absence or presence of O2, while site 2 still prefers iron as in the wild-type. In contrast, a mutation that blocks binding of the fatty acid does not affect the metal specificity of either site under anoxic or aerobic conditions, and cross-link formation is still observed. All variants assemble a dinuclear trivalent metal cofactor in the aerobic resting state, independently of cross-link formation. These findings imply that the cross-link residues are required to achieve the preference for manganese in site 1 in the presence of O2. The metalation specificity, therefore, appears to be established during the redox reactions leading to cross-link formation.
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Affiliation(s)
- Julia J Griese
- Department of Biochemistry and Biophysics, Stockholm University, 106 91, Stockholm, Sweden. .,Department of Cell and Molecular Biology, Uppsala University, 751 24, Uppsala, Sweden.
| | - Ramona Kositzki
- Institut für Experimentalphysik, Freie Universität Berlin, 14195, Berlin, Germany
| | - Michael Haumann
- Institut für Experimentalphysik, Freie Universität Berlin, 14195, Berlin, Germany
| | - Martin Högbom
- Department of Biochemistry and Biophysics, Stockholm University, 106 91, Stockholm, Sweden.
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