1
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Janczak M, Vilhjálmsdóttir J, Ädelroth P. Proton transfer in cytochrome bd-I from E. coli involves Asp-105 in CydB. BIOCHIMICA ET BIOPHYSICA ACTA. BIOENERGETICS 2024; 1865:149489. [PMID: 39009175 DOI: 10.1016/j.bbabio.2024.149489] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2024] [Accepted: 06/27/2024] [Indexed: 07/17/2024]
Abstract
Cytochrome bds are bacterial terminal oxidases expressed under low oxygen conditions, and they are important for the survival of many pathogens and hence potential drug targets. The largest subunit CydA contains the three redox-active cofactors heme b558, heme b595 and the active site heme d. One suggested proton transfer pathway is found at the interface between the CydA and the other major subunit CydB. Here we have studied the O2 reduction mechanism in E. coli cyt. bd-I using the flow-flash technique and focused on the mechanism, kinetics and pathway for proton transfer. Our results show that the peroxy (P) to ferryl (F) transition, coupled to the oxidation of the low-spin heme b558 is pH dependent, with a maximum rate constant (~104 s-1) that is slowed down at higher pH. We assign this behavior to rate-limitation by internal proton transfer from a titratable residue with pKa ~ 9.7. Proton uptake from solution occurs with the same P➔F rate constant. Site-directed mutagenesis shows significant effects on catalytic turnover in the CydB variants Asp58B➔Asn and Asp105B➔Asn variants consistent with them playing a role in proton transfer. Furthermore, in the Asp105B➔Asn variant, the reactions up to P formation occur essentially as in the wildtype bd-I, but the P➔F transition is specifically inhibited, supporting a direct and specific role for Asp105B in the functional proton transfer pathway in bd-I. We further discuss the possible identity of the high pKa proton donor, and the conservation pattern of the Asp-105B in the cyt. bd superfamily.
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Affiliation(s)
- M Janczak
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
| | - J Vilhjálmsdóttir
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
| | - P Ädelroth
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden.
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2
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Electric fields control water-gated proton transfer in cytochrome c oxidase. Proc Natl Acad Sci U S A 2022; 119:e2207761119. [PMID: 36095184 PMCID: PMC9499568 DOI: 10.1073/pnas.2207761119] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Aerobic life is powered by membrane-bound enzymes that catalyze the transfer of electrons to oxygen and protons across a biological membrane. Cytochrome c oxidase (CcO) functions as a terminal electron acceptor in mitochondrial and bacterial respiratory chains, driving cellular respiration and transducing the free energy from O2 reduction into proton pumping. Here we show that CcO creates orientated electric fields around a nonpolar cavity next to the active site, establishing a molecular switch that directs the protons along distinct pathways. By combining large-scale quantum chemical density functional theory (DFT) calculations with hybrid quantum mechanics/molecular mechanics (QM/MM) simulations and atomistic molecular dynamics (MD) explorations, we find that reduction of the electron donor, heme a, leads to dissociation of an arginine (Arg438)-heme a3 D-propionate ion-pair. This ion-pair dissociation creates a strong electric field of up to 1 V Å-1 along a water-mediated proton array leading to a transient proton loading site (PLS) near the active site. Protonation of the PLS triggers the reduction of the active site, which in turn aligns the electric field vectors along a second, "chemical," proton pathway. We find a linear energy relationship of the proton transfer barrier with the electric field strength that explains the effectivity of the gating process. Our mechanism shows distinct similarities to principles also found in other energy-converting enzymes, suggesting that orientated electric fields generally control enzyme catalysis.
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3
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Blomberg MRA. Activation of O 2 and NO in heme-copper oxidases - mechanistic insights from computational modelling. Chem Soc Rev 2021; 49:7301-7330. [PMID: 33006348 DOI: 10.1039/d0cs00877j] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Heme-copper oxidases are transmembrane enzymes involved in aerobic and anaerobic respiration. The largest subgroup contains the cytochrome c oxidases (CcO), which reduce molecular oxygen to water. A significant part of the free energy released in this exergonic process is conserved as an electrochemical gradient across the membrane, via two processes, electrogenic chemistry and proton pumping. A deviant subgroup is the cytochrome c dependent NO reductases (cNOR), which reduce nitric oxide to nitrous oxide and water. This is also an exergonic reaction, but in this case none of the released free energy is conserved. Computational studies applying hybrid density functional theory to cluster models of the bimetallic active sites in the heme-copper oxidases are reviewed. To obtain a reliable description of the reaction mechanisms, energy profiles of the entire catalytic cycles, including the reduction steps have to be constructed. This requires a careful combination of computational results with certain experimental data. Computational studies have elucidated mechanistic details of the chemical parts of the reactions, involving cleavage and formation of covalent bonds, which have not been obtainable from pure experimental investigations. Important insights regarding the mechanisms of energy conservation have also been gained. The computational studies show that the reduction potentials of the active site cofactors in the CcOs are large enough to afford electrogenic chemistry and proton pumping, i.e. efficient energy conservation. These results solve a conflict between different types of experimental data. A mechanism for the proton pumping, involving a specific and crucial role for the active site tyrosine, conserved in all CcOs, is suggested. For the cNORs, the calculations show that the low reduction potentials of the active site cofactors are optimized for fast elimination of the toxic NO molecules. At the same time, the low reduction potentials lead to endergonic reduction steps with high barriers. To prevent even higher barriers, which would lead to a too slow reaction, when the electrochemical gradient across the membrane is present, the chemistry must occur in a non-electrogenic manner. This explains why there is no energy conservation in cNOR.
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Affiliation(s)
- Margareta R A Blomberg
- Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden.
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4
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Reed CJ, Lam QN, Mirts EN, Lu Y. Molecular understanding of heteronuclear active sites in heme-copper oxidases, nitric oxide reductases, and sulfite reductases through biomimetic modelling. Chem Soc Rev 2021; 50:2486-2539. [PMID: 33475096 PMCID: PMC7920998 DOI: 10.1039/d0cs01297a] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Heme-copper oxidases (HCO), nitric oxide reductases (NOR), and sulfite reductases (SiR) catalyze the multi-electron and multi-proton reductions of O2, NO, and SO32-, respectively. Each of these reactions is important to drive cellular energy production through respiratory metabolism and HCO, NOR, and SiR evolved to contain heteronuclear active sites containing heme/copper, heme/nonheme iron, and heme-[4Fe-4S] centers, respectively. The complexity of the structures and reactions of these native enzymes, along with their large sizes and/or membrane associations, make it challenging to fully understand the crucial structural features responsible for the catalytic properties of these active sites. In this review, we summarize progress that has been made to better understand these heteronuclear metalloenzymes at the molecular level though study of the native enzymes along with insights gained from biomimetic models comprising either small molecules or proteins. Further understanding the reaction selectivity of these enzymes is discussed through comparisons of their similar heteronuclear active sites, and we offer outlook for further investigations.
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Affiliation(s)
- Christopher J Reed
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urban, IL 61801, USA.
| | - Quan N Lam
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urban, IL 61801, USA
| | - Evan N Mirts
- Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA and Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Yi Lu
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urban, IL 61801, USA. and Department of Biochemistry, University of Illinois at Urbana-Champaign, Urban, IL 61801, USA and Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA and Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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5
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Melin F, Hellwig P. Redox Properties of the Membrane Proteins from the Respiratory Chain. Chem Rev 2020; 120:10244-10297. [DOI: 10.1021/acs.chemrev.0c00249] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Frederic Melin
- Chimie de la Matière Complexe UMR 7140, Laboratoire de Bioelectrochimie et Spectroscopie, CNRS-Université de Strasbourg, 1 rue Blaise Pascal, 67070 Strasbourg, France
| | - Petra Hellwig
- Chimie de la Matière Complexe UMR 7140, Laboratoire de Bioelectrochimie et Spectroscopie, CNRS-Université de Strasbourg, 1 rue Blaise Pascal, 67070 Strasbourg, France
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6
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Blomberg MRA. The mechanism for oxygen reduction in the C family cbb 3 cytochrome c oxidases - Implications for the proton pumping stoichiometry. J Inorg Biochem 2019; 203:110866. [PMID: 31706225 DOI: 10.1016/j.jinorgbio.2019.110866] [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: 08/05/2019] [Revised: 09/12/2019] [Accepted: 09/15/2019] [Indexed: 11/16/2022]
Abstract
Cytochrome c oxidases (CcOs) couple the exergonic reduction of molecular oxygen to proton pumping across the membrane in which they are embedded, thereby conserving a significant part of the free energy. The A family CcOs are known to pump four protons per oxygen molecule, while there is no consensus regarding the proton pumping stoichiometry for the C family cbb3 oxidases. Hybrid density functional theory is used here to investigate the catalytic mechanism for oxygen reduction in cbb3 oxidases. A surprising result is that the barrier for O O bond cleavage at the mixed valence reduction level seems to be too high compared to the overall reaction rate of the enzyme. It is therefore suggested that the O O bond is cleaved only after the first proton coupled reduction step, and that this reduction step most likely is not coupled to proton pumping. Furthermore, since the cbb3 oxidases have only one proton channel leading to the active site, it is proposed that the activated EH intermediate, suggested to be responsible for proton pumping in one of the reduction steps in the A family, cannot be involved in the catalytic cycle for cbb3, which results in the lack of proton pumping also in the E to R reduction step. In summary, the calculations indicate that only two protons are pumped per oxygen molecule in cbb3 oxidases. However, more experimental information on this divergent enzyme is needed, e.g. whether the flow of electrons resembles that in the other more well-studied CcO families.
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Affiliation(s)
- Margareta R A Blomberg
- Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden.
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7
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Ahn YO, Albertsson I, Gennis RB, Ädelroth P. Mechanism of proton transfer through the K C proton pathway in the Vibrio cholerae cbb 3 terminal oxidase. BIOCHIMICA ET BIOPHYSICA ACTA. BIOENERGETICS 2018; 1859:1191-1198. [PMID: 30251700 PMCID: PMC6260837 DOI: 10.1016/j.bbabio.2018.08.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2018] [Revised: 08/17/2018] [Accepted: 08/20/2018] [Indexed: 11/17/2022]
Abstract
The heme‑copper oxidases (HCuOs) are terminal components of the respiratory chain, catalyzing oxygen reduction coupled to the generation of a proton motive force. The C-family HCuOs, found in many pathogenic bacteria under low oxygen tension, utilize a single proton uptake pathway to deliver protons both for O2 reduction and for proton pumping. This pathway, called the KC-pathway, starts at Glu-49P in the accessory subunit CcoP, and connects into the catalytic subunit CcoN via the polar residues Tyr-(Y)-227, Asn (N)-293, Ser (S)-244, Tyr (Y)-321 and internal water molecules, and continues to the active site. However, although the residues are known to be functionally important, little is known about the mechanism and dynamics of proton transfer in the KC-pathway. Here, we studied variants of Y227, N293 and Y321. Our results show that in the N293L variant, proton-coupled electron transfer is slowed during single-turnover oxygen reduction, and moreover it shows a pH dependence that is not observed in wildtype. This suggests that there is a shift in the pKa of an internal proton donor into an experimentally accessible range, from >10 in wildtype to ~8.8 in N293L. Furthermore, we show that there are distinct roles for the conserved Y321 and Y227. In Y321F, proton uptake from bulk solution is greatly impaired, whereas Y227F shows wildtype-like rates and retains ~50% turnover activity. These tyrosines have evolutionary counterparts in the K-pathway of B-family HCuOs, but they do not have the same roles, indicating diversity in the proton transfer dynamics in the HCuO superfamily.
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Affiliation(s)
- Young O Ahn
- Department of Biochemistry and Biophysics, Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91 Stockholm, Sweden; Department of Biochemistry, University of Illinois at Urbana-Champaign, 600 S. Mathews Street, Urbana, IL 61801, USA
| | - Ingrid Albertsson
- Department of Biochemistry and Biophysics, Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Robert B Gennis
- Department of Biochemistry, University of Illinois at Urbana-Champaign, 600 S. Mathews Street, Urbana, IL 61801, USA
| | - Pia Ädelroth
- Department of Biochemistry and Biophysics, Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91 Stockholm, Sweden.
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8
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Wikström M, Krab K, Sharma V. Oxygen Activation and Energy Conservation by Cytochrome c Oxidase. Chem Rev 2018; 118:2469-2490. [PMID: 29350917 PMCID: PMC6203177 DOI: 10.1021/acs.chemrev.7b00664] [Citation(s) in RCA: 239] [Impact Index Per Article: 39.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
![]()
This review focuses on the type
A cytochrome c oxidases (CcO), which
are found in all mitochondria
and also in several aerobic bacteria. CcO catalyzes
the respiratory reduction of dioxygen (O2) to water by
an intriguing mechanism, the details of which are fairly well understood
today as a result of research for over four decades. Perhaps even
more intriguingly, the membrane-bound CcO couples
the O2 reduction chemistry to translocation of protons
across the membrane, thus contributing to generation of the electrochemical
proton gradient that is used to drive the synthesis of ATP as catalyzed
by the rotary ATP synthase in the same membrane. After reviewing the
structure of the core subunits of CcO, the active
site, and the transfer paths of electrons, protons, oxygen, and water,
we describe the states of the catalytic cycle and point out the few
remaining uncertainties. Finally, we discuss the mechanism of proton
translocation and the controversies in that area that still prevail.
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Affiliation(s)
- Mårten Wikström
- Institute of Biotechnology , University of Helsinki , P.O. Box 56 , Helsinki FI-00014 , Finland
| | - Klaas Krab
- Department of Molecular Cell Physiology , Vrije Universiteit , P.O. Box 7161 , Amsterdam 1007 MC , The Netherlands
| | - Vivek Sharma
- Institute of Biotechnology , University of Helsinki , P.O. Box 56 , Helsinki FI-00014 , Finland.,Department of Physics , University of Helsinki , P.O. Box 64 , Helsinki FI-00014 , Finland
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9
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Metabolic Reconstruction and Modeling Microbial Electrosynthesis. Sci Rep 2017; 7:8391. [PMID: 28827682 PMCID: PMC5566340 DOI: 10.1038/s41598-017-08877-z] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2017] [Accepted: 07/19/2017] [Indexed: 12/31/2022] Open
Abstract
Microbial electrosynthesis is a renewable energy and chemical production platform that relies on microbial cells to capture electrons from a cathode and fix carbon. Yet despite the promise of this technology, the metabolic capacity of the microbes that inhabit the electrode surface and catalyze electron transfer in these systems remains largely unknown. We assembled thirteen draft genomes from a microbial electrosynthesis system producing primarily acetate from carbon dioxide, and their transcriptional activity was mapped to genomes from cells on the electrode surface and in the supernatant. This allowed us to create a metabolic model of the predominant community members belonging to Acetobacterium, Sulfurospirillum, and Desulfovibrio. According to the model, the Acetobacterium was the primary carbon fixer, and a keystone member of the community. Transcripts of soluble hydrogenases and ferredoxins from Acetobacterium and hydrogenases, formate dehydrogenase, and cytochromes of Desulfovibrio were found in high abundance near the electrode surface. Cytochrome c oxidases of facultative members of the community were highly expressed in the supernatant despite completely sealed reactors and constant flushing with anaerobic gases. These molecular discoveries and metabolic modeling now serve as a foundation for future examination and development of electrosynthetic microbial communities.
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10
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Carvalheda CA, Pisliakov AV. On the role of subunit M in cytochrome cbb 3 oxidase. Biochem Biophys Res Commun 2017; 491:47-52. [PMID: 28694191 DOI: 10.1016/j.bbrc.2017.07.031] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2017] [Accepted: 07/06/2017] [Indexed: 10/19/2022]
Abstract
Cytochrome cbb3 (or C-type) oxidases are a highly divergent group and the least studied members of the heme-copper oxidases (HCOs) superfamily. HCOs couple the reduction of oxygen at the end of the respiratory chain to the active proton translocation across the membrane, contributing to establishment of an electrochemical gradient essential for ATP synthesis. Cbb3 oxidases exhibit unique structural and functional features and have an essential role in the metabolism of many clinically relevant human pathogens. Such characteristics make them a promising therapeutic target. Three subunits, N, O and P, comprise the core cbb3 complex, with N, the catalytic subunit, being highly conserved among all members of the HCO superfamily, including the A-type (aa3, mitochondrial-like) oxidases. An additional fourth subunit containing a single transmembrane (TM) helix was present in the first crystal structure of cbb3. This TM segment was recently proposed to be part of a novel protein CcoM, which was shown to have a putative role in the complex stability and assembly. In this work, we performed large-scale all-atom molecular dynamics simulations of the CcoNOPM complex to further characterize the interactions between subunit M and the core subunits and to determine whether the presence of the fourth subunit influences the water/proton channels previously described for the core complex. The previously proposed putative CcoNOPH complex is also assessed, and the potential functional redundancy of CcoM and CcoQ is discussed.
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Affiliation(s)
- Catarina A Carvalheda
- Computational Biology, School of Life Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH, United Kingdom; Physics, School of Science and Engineering, University of Dundee, Nethergate, Dundee, DD1 4HN, United Kingdom.
| | - Andrei V Pisliakov
- Computational Biology, School of Life Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH, United Kingdom; Physics, School of Science and Engineering, University of Dundee, Nethergate, Dundee, DD1 4HN, United Kingdom.
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11
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Bhagi-Damodaran A, Kahle M, Shi Y, Zhang Y, Ädelroth P, Lu Y. Insights Into How Heme Reduction Potentials Modulate Enzymatic Activities of a Myoglobin-based Functional Oxidase. Angew Chem Int Ed Engl 2017; 56:6622-6626. [PMID: 28470988 DOI: 10.1002/anie.201701916] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Indexed: 01/01/2023]
Abstract
Heme-copper oxidase (HCO) is a class of respiratory enzymes that use a heme-copper center to catalyze O2 reduction to H2 O. While heme reduction potential (E°') of different HCO types has been found to vary >500 mV, its impact on HCO activity remains poorly understood. Here, we use a set of myoglobin-based functional HCO models to investigate the mechanism by which heme E°' modulates oxidase activity. Rapid stopped-flow kinetic measurements show that increasing heme E°' by ca. 210 mV results in increases in electron transfer (ET) rates by 30-fold, rate of O2 binding by 12-fold, O2 dissociation by 35-fold, while decreasing O2 affinity by 3-fold. Theoretical calculations reveal that E°' modulation has significant implications on electronic charge of both heme iron and O2 , resulting in increased O2 dissociation and reduced O2 affinity at high E°' values. Overall, this work suggests that fine-tuning E°' in HCOs and other heme enzymes can modulate their substrate affinity, ET rate and enzymatic activity.
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Affiliation(s)
- Ambika Bhagi-Damodaran
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Maximilian Kahle
- Department of Biochemistry and Biophysics, Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-10691, Stockholm, Sweden
| | - Yelu Shi
- Department of Biomedical Engineering, Chemistry and Biological Sciences, Stevens Institute of Technology, Hoboken, New Jersey, NY, 07030, USA
| | - Yong Zhang
- Department of Biomedical Engineering, Chemistry and Biological Sciences, Stevens Institute of Technology, Hoboken, New Jersey, NY, 07030, USA
| | - Pia Ädelroth
- Department of Biochemistry and Biophysics, Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-10691, Stockholm, Sweden
| | - Yi Lu
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
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12
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Bhagi‐Damodaran A, Kahle M, Shi Y, Zhang Y, Ädelroth P, Lu Y. Insights Into How Heme Reduction Potentials Modulate Enzymatic Activities of a Myoglobin‐based Functional Oxidase. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201701916] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
| | - Maximilian Kahle
- Department of Biochemistry and Biophysics Arrhenius Laboratories for Natural Sciences Stockholm University SE-10691 Stockholm Sweden
| | - Yelu Shi
- Department of Biomedical Engineering, Chemistry and Biological Sciences Stevens Institute of Technology Hoboken, New Jersey NY 07030 USA
| | - Yong Zhang
- Department of Biomedical Engineering, Chemistry and Biological Sciences Stevens Institute of Technology Hoboken, New Jersey NY 07030 USA
| | - Pia Ädelroth
- Department of Biochemistry and Biophysics Arrhenius Laboratories for Natural Sciences Stockholm University SE-10691 Stockholm Sweden
| | - Yi Lu
- Department of Chemistry University of Illinois at Urbana-Champaign Urbana IL 61801 USA
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13
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Carvalheda CA, Pisliakov AV. Insights into proton translocation in cbb 3 oxidase from MD simulations. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2017; 1858:396-406. [PMID: 28259641 DOI: 10.1016/j.bbabio.2017.02.013] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 10/05/2016] [Revised: 02/03/2017] [Accepted: 02/27/2017] [Indexed: 01/18/2023]
Abstract
Heme-copper oxidases are membrane protein complexes that catalyse the final step of the aerobic respiration, namely the reduction of oxygen to water. The energy released during catalysis is coupled to the active translocation of protons across the membrane, which contributes to the establishment of an electrochemical gradient that is used for ATP synthesis. The distinctive C-type (or cbb3) cytochrome c oxidases, which are mostly present in proteobacteria, exhibit a number of unique structural and functional features, including high catalytic activity at low oxygen concentrations. At the moment, the functioning mechanism of C-type oxidases, in particular the proton transfer/pumping mechanism presumably via a single proton channel, is still poorly understood. In this work we used all-atom molecular dynamics simulations and continuum electrostatics calculations to obtain atomic-level insights into the hydration and dynamics of a cbb3 oxidase. We provide the details of the water dynamics and proton transfer pathways for both the "chemical" and "pumped" protons, and show that formation of protonic connections is strongly affected by the protonation state of key residues, namely H243, E323 and H337.
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Affiliation(s)
- Catarina A Carvalheda
- Computational Biology, School of Life Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH, United Kingdom; Physics, School of Sciences and Engineering, University of Dundee, Nethergate, Dundee, DD1 4HN, United Kingdom.
| | - Andrei V Pisliakov
- Computational Biology, School of Life Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH, United Kingdom; Physics, School of Sciences and Engineering, University of Dundee, Nethergate, Dundee, DD1 4HN, United Kingdom.
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14
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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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15
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Melin F, Xie H, Meyer T, Ahn YO, Gennis RB, Michel H, Hellwig P. The unusual redox properties of C-type oxidases. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1857:1892-1899. [PMID: 27664317 DOI: 10.1016/j.bbabio.2016.09.009] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2016] [Revised: 09/15/2016] [Accepted: 09/19/2016] [Indexed: 10/21/2022]
Abstract
Cytochrome cbb3 (also known as C-type) oxidases belong to the family of heme-copper terminal oxidases which couple at the end of the respiratory chain the reduction of molecular oxygen into water and the pumping of protons across the membrane. They are expressed most often at low pressure of O2 and they exhibit a low homology of sequence with the cytochrome aa3 (A-type) oxidases found in mitochondria. Their binuclear active site comprises a high-spin heme b3 associated with a CuB center. The protein also contains one low-spin heme b and 3 hemes c. We address here the redox properties of cbb3 oxidases from three organisms, Rhodobacter sphaeroides, Vibrio cholerae and Pseudomonas stutzeri by means of electrochemical and spectroscopic techniques. We show that the redox potential of the heme b3 exhibits a relatively low midpoint potential, as in related cytochrome c-dependent nitric oxide reductases. Potential implications for the coupled electron transfer and proton uptake mechanism of C-type oxidases are discussed.
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Affiliation(s)
- Frederic Melin
- Laboratoire de Bioélectrochimie et Spectroscopie, Chimie de la Matière Complexe, UMR 7140, Université de Strasbourg, 1 Rue Blaise Pascal, 67000 Strasbourg, France
| | - Hao Xie
- Max Planck Institute of Biophysics, Department of Molecular Membrane Biology, Max-von-Laue-Str. 3, D-60438 Frankfurt am Main, Germany
| | - Thomas Meyer
- Laboratoire de Bioélectrochimie et Spectroscopie, Chimie de la Matière Complexe, UMR 7140, Université de Strasbourg, 1 Rue Blaise Pascal, 67000 Strasbourg, France
| | - Young Ok Ahn
- Department of Biochemistry, University of Illinois at Urbana Champaign, USA
| | - Robert B Gennis
- Department of Biochemistry, University of Illinois at Urbana Champaign, USA
| | - Hartmut Michel
- Max Planck Institute of Biophysics, Department of Molecular Membrane Biology, Max-von-Laue-Str. 3, D-60438 Frankfurt am Main, Germany
| | - Petra Hellwig
- Laboratoire de Bioélectrochimie et Spectroscopie, Chimie de la Matière Complexe, UMR 7140, Université de Strasbourg, 1 Rue Blaise Pascal, 67000 Strasbourg, France.
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16
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Husband J, Aaron MS, Bains RK, Lewis AR, Warren JJ. Catalytic reduction of dioxygen with modified Thermus thermophilus cytochrome c552. J Inorg Biochem 2016; 157:8-14. [PMID: 26816109 DOI: 10.1016/j.jinorgbio.2016.01.023] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Revised: 12/23/2015] [Accepted: 01/18/2016] [Indexed: 10/22/2022]
Abstract
Efficient catalysis of the oxygen reduction reaction (ORR) is of central importance to function in fuel cells. Metalloproteins, such as laccase (Cu) or cytochrome c oxidase (Cu/Fe-heme) carry out the 4H(+)/4e(-) reduction quite efficiently, but using large, complex protein frameworks. Smaller heme proteins also can carry out ORR, but less efficiently. To gain greater insight into features that promote efficient ORR, we expressed, characterized, and investigated the electrochemical behavior of six new mutants of cytochrome c552 from Thermus thermophilus: V49S/M69A, V49T/M69A, L29D/V49S/M69A, P27A/P28A/L29D/V49S/M69A, and P27A/P28A/L29D/V49T/M69A. Mutation to V49 causes only minor shifts to Fe(III/II) reduction potentials (E°'), but introduction of Ser provides a hydrogen bond donor that slightly enhances oxygen reduction activity. Mutation of L29 to D induces small shifts in heme optical spectra, but not to E°' (within experimental error). Replacement of P27 and P28 with A in both positions induces a -50 mV shift in E°', again with small changes to the optical spectra. Both the optical spectra and reduction potentials have signatures consistent with peroxidase enzymes. The V49S and V49T mutations have the largest impact of ORR catalysis, suggesting that increased electron density at the Fe site does not improve O2 reduction chemistry.
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Affiliation(s)
- Jonathan Husband
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
| | - Michael S Aaron
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
| | - Rajneesh K Bains
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
| | - Andrew R Lewis
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
| | - Jeffrey J Warren
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada.
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17
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Lyons JA, Hilbers F, Caffrey M. Structure and Function of Bacterial Cytochrome c Oxidases. ADVANCES IN PHOTOSYNTHESIS AND RESPIRATION 2016. [DOI: 10.1007/978-94-017-7481-9_16] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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18
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Yu Y, Cui C, Liu X, Petrik ID, Wang J, Lu Y. A Designed Metalloenzyme Achieving the Catalytic Rate of a Native Enzyme. J Am Chem Soc 2015; 137:11570-3. [PMID: 26318313 PMCID: PMC4676421 DOI: 10.1021/jacs.5b07119] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
![]()
Terminal
oxidases catalyze four-electron reduction of oxygen to
water, and the energy harvested is utilized to drive the synthesis
of adenosine triphosphate. While much effort has been made to design
a catalyst mimicking the function of terminal oxidases, most biomimetic
catalysts have much lower activity than native oxidases. Herein we
report a designed oxidase in myoglobin with an O2 reduction
rate (52 s–1) comparable to that of a native cytochrome
(cyt) cbb3 oxidase (50 s–1) under identical conditions. We achieved this goal by engineering
more favorable electrostatic interactions between a functional oxidase
model designed in sperm whale myoglobin and its native redox partner,
cyt b5, resulting in a 400-fold electron
transfer (ET) rate enhancement. Achieving high activity equivalent
to that of native enzymes in a designed metalloenzyme offers deeper
insight into the roles of tunable processes such as ET in oxidase
activity and enzymatic function and may extend into applications such
as more efficient oxygen reduction reaction catalysts for biofuel
cells.
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Affiliation(s)
| | | | - Xiaohong Liu
- Laboratory of Non-coding RNA, Institute of Biophysics, Chinese Academy of Sciences , 15 Datun Road, Chaoyang District, Beijing 100101, P. R. China
| | | | - Jiangyun Wang
- Laboratory of Non-coding RNA, Institute of Biophysics, Chinese Academy of Sciences , 15 Datun Road, Chaoyang District, Beijing 100101, P. R. China
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19
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Ahn YO, Lee HJ, Kaluka D, Yeh SR, Rousseau DL, Ädelroth P, Gennis RB. The two transmembrane helices of CcoP are sufficient for assembly of the cbb3-type heme-copper oxygen reductase from Vibrio cholerae. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1847:1231-9. [PMID: 26116881 DOI: 10.1016/j.bbabio.2015.06.013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2015] [Revised: 06/17/2015] [Accepted: 06/23/2015] [Indexed: 10/23/2022]
Abstract
The C-family (cbb3) of heme-copper oxygen reductases are proton-pumping enzymes terminating the aerobic respiratory chains of many bacteria, including a number of human pathogens. The most common form of these enzymes contains one copy each of 4 subunits encoded by the ccoNOQP operon. In the cbb3 from Rhodobacter capsulatus, the enzyme is assembled in a stepwise manner, with an essential role played by an assembly protein CcoH. Importantly, it has been proposed that a transient interaction between the transmembrane domains of CcoP and CcoH is essential for assembly. Here, we test this proposal by showing that a genetically engineered form of cbb3 from Vibrio cholerae (CcoNOQP(X)) that lacks the hydrophilic domain of CcoP, where the two heme c moieties are present, is fully assembled and stable. Single-turnover kinetics of the reaction between the fully reduced CcoNOQP(X) and O2 are essentially the same as the wild type enzyme in oxidizing the 4 remaining redox-active sites. The enzyme retains approximately 10% of the steady state oxidase activity using the artificial electron donor TMPD, but has no activity using the physiological electron donor cytochrome c4, since the docking site for this cytochrome is presumably located on the absent domain of CcoP. Residue E49 in the hydrophobic domain of CcoP is the entrance of the K(C)-channel for proton input, and the E49A mutation in the truncated enzyme further reduces the steady state activity to less than 3%. Hence, the same proton channel is used by both the wild type and truncated enzymes.
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Affiliation(s)
- Young O Ahn
- Department of Biochemistry, University of Illinois, 600 S. Mathews Street, Urbana, IL 61801, USA
| | - Hyun Ju Lee
- Department of Biochemistry and Biophysics, Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Daniel Kaluka
- Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Syun-Ru Yeh
- Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Denis L Rousseau
- Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Pia Ädelroth
- Department of Biochemistry and Biophysics, Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Robert B Gennis
- Department of Biochemistry, University of Illinois, 600 S. Mathews Street, Urbana, IL 61801, USA.
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20
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Cytochrome cbb3 of Thioalkalivibrio is a Na+-pumping cytochrome oxidase. Proc Natl Acad Sci U S A 2015; 112:7695-700. [PMID: 26056262 DOI: 10.1073/pnas.1417071112] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cytochrome c oxidases (Coxs) are the basic energy transducers in the respiratory chain of the majority of aerobic organisms. Coxs studied to date are redox-driven proton-pumping enzymes belonging to one of three subfamilies: A-, B-, and C-type oxidases. The C-type oxidases (cbb3 cytochromes), which are widespread among pathogenic bacteria, are the least understood. In particular, the proton-pumping machinery of these Coxs has not yet been elucidated despite the availability of X-ray structure information. Here, we report the discovery of the first (to our knowledge) sodium-pumping Cox (Scox), a cbb3 cytochrome from the extremely alkaliphilic bacterium Thioalkalivibrio versutus. This finding offers clues to the previously unknown structure of the ion-pumping channel in the C-type Coxs and provides insight into the functional properties of this enzyme.
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21
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Arjona D, Wikström M, Ädelroth P. Nitric oxide is a potent inhibitor of the cbb(3)-type heme-copper oxidases. FEBS Lett 2015; 589:1214-8. [PMID: 25862499 DOI: 10.1016/j.febslet.2015.03.033] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2015] [Revised: 03/19/2015] [Accepted: 03/26/2015] [Indexed: 11/29/2022]
Abstract
C-type heme-copper oxidases terminate the respiratory chain in many pathogenic bacteria, and will encounter elevated concentrations of NO produced by the immune defense of the host. Thus, a decreased sensitivity to NO in C-type oxidases would increase the survival of these pathogens. Here we have compared the inhibitory effect of NO in C-type oxidases to that in the mitochondrial A-type. We show that O2-reduction in both the Rhodobacter sphaeroides and Vibrio cholerae C-type oxidases is strongly and reversibly inhibited by submicromolar NO, with an inhibition pattern similar to the A-type. Thus, NO tolerance in pathogens with a C-type terminal oxidase has to rely mainly on other mechanisms.
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Affiliation(s)
- Davinia Arjona
- Department of Biochemistry and Biophysics, The Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Mårten Wikström
- Helsinki Bioenergetics Group, Institute of Biotechnology, University of Helsinki, FI-00014 Helsinki, Finland
| | - Pia Ädelroth
- Department of Biochemistry and Biophysics, The Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91 Stockholm, Sweden.
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22
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Conformational coupling between the active site and residues within the K(C)-channel of the Vibrio cholerae cbb3-type (C-family) oxygen reductase. Proc Natl Acad Sci U S A 2014; 111:E4419-28. [PMID: 25288772 DOI: 10.1073/pnas.1411676111] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The respiratory chains of nearly all aerobic organisms are terminated by proton-pumping heme-copper oxygen reductases (HCOs). Previous studies have established that C-family HCOs contain a single channel for uptake from the bacterial cytoplasm of all chemical and pumped protons, and that the entrance of the K(C)-channel is a conserved glutamate in subunit III. However, the majority of the K(C)-channel is within subunit I, and the pathway from this conserved glutamate to subunit I is not evident. In the present study, molecular dynamics simulations were used to characterize a chain of water molecules leading from the cytoplasmic solution, passing the conserved glutamate in subunit III and extending into subunit I. Formation of the water chain, which controls the delivery of protons to the K(C)-channel, was found to depend on the conformation of Y241(Vc), located in subunit I at the interface with subunit III. Mutations of Y241(Vc) (to A/F/H/S) in the Vibrio cholerae cbb3 eliminate catalytic activity, but also cause perturbations that propagate over a 28-Å distance to the active site heme b3. The data suggest a linkage between residues lining the K(C)-channel and the active site of the enzyme, possibly mediated by transmembrane helix α7, which contains both Y241(Vc) and the active site cross-linked Y255(Vc), as well as two CuB histidine ligands. Other mutations of residues within or near helix α7 also perturb the active site, indicating that this helix is involved in modulation of the active site of the enzyme.
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23
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Sharma V, Wikström M. A structural and functional perspective on the evolution of the heme-copper oxidases. FEBS Lett 2014; 588:3787-92. [PMID: 25261254 DOI: 10.1016/j.febslet.2014.09.020] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2014] [Revised: 09/10/2014] [Accepted: 09/11/2014] [Indexed: 11/15/2022]
Abstract
The heme-copper oxidases (HCOs) catalyze the reduction of O2 to water, and couple the free energy to proton pumping across the membrane. HCOs are divided into three sub-classes, A, B and C, whose order of emergence in evolution has been controversial. Here we have analyzed recent structural and functional data on HCOs and their homologues, the nitric oxide reductases (NORs). We suggest that the C-type oxidases are ancient enzymes that emerged from the NORs. In contrast, the A-type oxidases are the most advanced from both structural and functional viewpoints, which we interpret as evidence for having evolved later.
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Affiliation(s)
- Vivek Sharma
- Department of Physics, Tampere University of Technology, PO Box 692, FI-33101 Tampere, Finland.
| | - Mårten Wikström
- Helsinki Bioenergetics Group, Institute of Biotechnology, University of Helsinki, FI-00014 Helsinki, Finland
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24
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Barile CJ, Tse ECM, Li Y, Sobyra TB, Zimmerman SC, Hosseini A, Gewirth AA. Proton switch for modulating oxygen reduction by a copper electrocatalyst embedded in a hybrid bilayer membrane. NATURE MATERIALS 2014; 13:619-23. [PMID: 24813418 DOI: 10.1038/nmat3974] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2013] [Accepted: 03/28/2014] [Indexed: 05/26/2023]
Abstract
Molecular switches gate many fundamental processes in natural and artificial systems. Here, we report the development of an electrochemical platform in which a proton carrier switches the activity of a catalyst. By incorporating an alkyl phosphate in the lipid layer of a hybrid bilayer membrane, we regulate proton transport to a Cu-based molecular oxygen reduction reaction catalyst. To construct this hybrid bilayer membrane system, we prepare an example of a synthetic Cu oxygen reduction reaction catalyst that forms a self-assembled monolayer on Au surfaces. We then embed this Cu catalyst inside a hybrid bilayer membrane by depositing a monolayer of lipid on the self-assembled monolayer. We envisage that this electrochemical system can give a unique mechanistic insight not only into the oxygen reduction reaction, but into proton-coupled electron transfer in general.
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Affiliation(s)
- Christopher J Barile
- 1] Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA [2]
| | - Edmund C M Tse
- 1] Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA [2]
| | - Ying Li
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - Thomas B Sobyra
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - Steven C Zimmerman
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - Ali Hosseini
- Department of Chemical and Materials Engineering, The University of Auckland, Auckland 1010, New Zealand
| | - Andrew A Gewirth
- 1] Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA [2] International Institute for Carbon Neutral Energy Research (WPI-I2CNER), Kyushu University, Fukuoka 812-8581, Japan
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25
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DeCoursey TE, Hosler J. Philosophy of voltage-gated proton channels. J R Soc Interface 2014; 11:20130799. [PMID: 24352668 PMCID: PMC3899857 DOI: 10.1098/rsif.2013.0799] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2013] [Accepted: 11/22/2013] [Indexed: 02/02/2023] Open
Abstract
In this review, voltage-gated proton channels are considered from a mainly teleological perspective. Why do proton channels exist? What good are they? Why did they go to such lengths to develop several unique hallmark properties such as extreme selectivity and ΔpH-dependent gating? Why is their current so minuscule? How do they manage to be so selective? What is the basis for our belief that they conduct H(+) and not OH(-)? Why do they exist in many species as dimers when the monomeric form seems to work quite well? It is hoped that pondering these questions will provide an introduction to these channels and a way to logically organize their peculiar properties as well as to understand how they are able to carry out some of their better-established biological functions.
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Affiliation(s)
- Thomas E. DeCoursey
- Department of Molecular Biophysics and Physiology, Rush University, 1750 West Harrison, Chicago, IL 60612, USA
| | - Jonathan Hosler
- Department of Biochemistry, University of Mississippi Medical Center, Jackson, MS 39216, USA
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26
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The K(C) channel in the cbb3-type respiratory oxygen reductase from Rhodobacter capsulatus is required for both chemical and pumped protons. J Bacteriol 2014; 196:1825-32. [PMID: 24563037 DOI: 10.1128/jb.00005-14] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The heme-copper superfamily of proton-pumping respiratory oxygen reductases are classified into three families (A, B, and C families) based on structural and phylogenetic analyses. Most studies have focused on the A family, which includes the eukaryotic mitochondrial cytochrome c oxidase as well as many bacterial homologues. Members of the C family, also called the cbb3-type oxygen reductases, are found only in prokaryotes and are of particular interest because of their presence in a number of human pathogens. All of the heme-copper oxygen reductases require proton-conducting channels to convey chemical protons to the active site for water formation and to convey pumped protons across the membrane. Previous work indicated that there is only one proton-conducting input channel (the K(C) channel) present in the cbb3-type oxygen reductases, which, if correct, must be utilized by both chemical protons and pumped protons. In this work, the effects of mutations in the K(C) channel of the cbb3-type oxygen reductase from Rhodobacter capsulatus were investigated by expressing the mutants in a strain lacking other respiratory oxygen reductases. Proton pumping was evaluated by using intact cells, and catalytic oxygen reductase activity was measured in isolated membranes. Two mutations, N346M and Y374F, severely reduced catalytic activity, presumably by blocking the chemical protons required at the active site. One mutation, T272A, resulted in a substantially lower proton-pumping stoichiometry but did not inhibit oxygen reductase activity. These are the first experimental data in support of the postulate that pumped protons are taken up from the bacterial cytoplasm through the K(C) channel.
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27
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Yu Y, Mukherjee A, Nilges MJ, Hosseinzadeh P, Miner KD, Lu Y. Direct EPR observation of a tyrosyl radical in a functional oxidase model in myoglobin during both H2O2 and O2 reactions. J Am Chem Soc 2014; 136:1174-1177. [PMID: 24383850 PMCID: PMC3955430 DOI: 10.1021/ja4091885] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Tyrosine is a conserved redox-active amino acid that plays important roles in heme-copper oxidases (HCO). Despite the widely proposed mechanism that involves a tyrosyl radical, its direct observation under O2 reduction conditions remains elusive. Using a functional oxidase model in myoglobin called F33Y-Cu(B)Mb that contains an engineered tyrosine, we report herein direct observation of a tyrosyl radical during both reactions of H2O2 with oxidized protein and O2 with reduced protein by electron paramagnetic resonance spectroscopy, providing a firm support for the tyrosyl radical in the HCO enzymatic mechanism.
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Affiliation(s)
- Yang Yu
- Center for Biophysics and Computational Biology, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801, United States
| | - Arnab Mukherjee
- Department of Chemistry, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801, United States
| | - Mark J. Nilges
- The Illinois EPR Research Center, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801, United States
| | - Parisa Hosseinzadeh
- Department of Biochemistry, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801, United States
| | - Kyle D. Miner
- Department of Biochemistry, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801, United States
| | - Yi Lu
- Center for Biophysics and Computational Biology, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801, United States
- Department of Chemistry, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801, United States
- Department of Biochemistry, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801, United States
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28
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Biochemical and biophysical characterization of the two isoforms of cbb3-type cytochrome c oxidase from Pseudomonas stutzeri. J Bacteriol 2013; 196:472-82. [PMID: 24214947 DOI: 10.1128/jb.01072-13] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The cbb3-type cytochrome c oxidases (cbb3-CcOs) are members of the heme-copper oxidase superfamily that couple the reduction of oxygen to translocation of protons across the membrane. The cbb3-CcOs are present only in bacteria and play a primary role in microaerobic respiration, being essential for nitrogen-fixing endosymbionts and for some human pathogens. As frequently observed in Pseudomonads, Pseudomonas stutzeri contains two independent ccoNO(Q)P operons encoding the two cbb3 isoforms, Cbb3-1 and Cbb3-2. While the crystal structure of Cbb3-1 from P. stutzeri was determined recently and cbb3-CcOs from other organisms were characterized functionally, less emphasis has been placed on the isoform-specific differences between the cbb3-CcOs. In this work, both isoforms were homologously expressed in P. stutzeri strains from which the genomic version of the respective operon was deleted. We purified both cbb3 isoforms separately by affinity chromatography and increased the yield of Cbb3-2 to a similar level as Cbb3-1 by replacing its native promoter. Mass spectrometry, UV-visible (UV-Vis) spectroscopy, differential scanning calorimetry, as well as oxygen reductase and catalase activity measurements were employed to characterize both cbb3 isoforms. Differences were found concerning the thermal stability and the presence of subunit CcoQ. However, no significant differences between the two isoforms were observed otherwise. Interestingly, a surprisingly high turnover of at least 2,000 electrons s(-1) and a high Michaelis-Menten constant (Km ~ 3.6 mM) using ascorbate-N,N,N',N'-tetramethyl-p-phenylenediamine dihydrochloride (TMPD) as the electron donor were characteristic for both P. stutzeri cbb3-CcOs. Our work provides the basis for further mutagenesis studies of each of the two cbb3 isoforms specifically.
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29
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Lee HJ, Ädelroth P. The heme-copper oxidase superfamily shares a Zn2+-binding motif at the entrance to a proton pathway. FEBS Lett 2013; 587:770-4. [PMID: 23399935 DOI: 10.1016/j.febslet.2013.01.069] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2012] [Revised: 01/30/2013] [Accepted: 01/31/2013] [Indexed: 11/17/2022]
Abstract
Heme-copper oxidases (HCuOs) catalyse the reduction of oxygen, using the liberated free energy to maintain a proton-motive force across the membrane. In the mitochondrial-like A-type HCuOs, binding of heavy metal ions at the surface of the protein inhibits proton transfer. In bacterial C-type oxidases, the entry point to the proton pathway is on an accessory subunit unrelated to any subunit in A-type HCuOs. Despite this, we show here that heavy metal ions such as Zn(2+) inhibit O2-reduction very similarly in C-type as in A-type HCuOs, and furthermore that the binding site shares the same Glu-His motif.
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Affiliation(s)
- Hyun Ju Lee
- Department of Biochemistry and Biophysics, The Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91 Stockholm, Sweden
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30
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Molecular dynamics simulations reveal proton transfer pathways in cytochrome C-dependent nitric oxide reductase. PLoS Comput Biol 2012; 8:e1002674. [PMID: 22956904 PMCID: PMC3431322 DOI: 10.1371/journal.pcbi.1002674] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2012] [Accepted: 07/22/2012] [Indexed: 01/25/2023] Open
Abstract
Nitric oxide reductases (NORs) are membrane proteins that catalyze the reduction of nitric oxide (NO) to nitrous oxide (N2O), which is a critical step of the nitrate respiration process in denitrifying bacteria. Using the recently determined first crystal structure of the cytochrome c-dependent NOR (cNOR) [Hino T, Matsumoto Y, Nagano S, Sugimoto H, Fukumori Y, et al. (2010) Structural basis of biological N2O generation by bacterial nitric oxide reductase. Science 330: 1666–70.], we performed extensive all-atom molecular dynamics (MD) simulations of cNOR within an explicit membrane/solvent environment to fully characterize water distribution and dynamics as well as hydrogen-bonded networks inside the protein, yielding the atomic details of functionally important proton channels. Simulations reveal two possible proton transfer pathways leading from the periplasm to the active site, while no pathways from the cytoplasmic side were found, consistently with the experimental observations that cNOR is not a proton pump. One of the pathways, which was newly identified in the MD simulation, is blocked in the crystal structure and requires small structural rearrangements to allow for water channel formation. That pathway is equivalent to the functional periplasmic cavity postulated in cbb3 oxidase, which illustrates that the two enzymes share some elements of the proton transfer mechanisms and confirms a close evolutionary relation between NORs and C-type oxidases. Several mechanisms of the critical proton transfer steps near the catalytic center are proposed. Denitrification is an anaerobic process performed by several bacteria as an alternative to aerobic respiration. A key intermediate step is catalyzed by the nitric oxide reductase (NOR) enzyme, which is situated in the cytoplasmic membrane. Proton delivery to the catalytic site inside NOR is an important part of its functioning. In this work we use molecular dynamics simulations to describe water distribution and to identify proton transfer pathways in cNOR. Our results reveal two channels from the periplasmic side of the membrane and none from the cytoplasmic side, indicating that cNOR is not a proton pump. It is our hope that these results will provide a basis for further experimental and computational studies aimed to understand details of the NOR mechanism. Furthermore, this work sheds light on the molecular evolution of respiratory enzymes.
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31
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Lee HJ, Reimann J, Huang Y, Ädelroth P. Functional proton transfer pathways in the heme–copper oxidase superfamily. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2012; 1817:537-44. [DOI: 10.1016/j.bbabio.2011.10.007] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2011] [Revised: 10/19/2011] [Accepted: 10/21/2011] [Indexed: 12/21/2022]
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