1
|
Siletsky SA. Investigation of the Mechanism of Membrane Potential Generation by Heme-Copper Respiratory Oxidases in a Real Time Mode. BIOCHEMISTRY. BIOKHIMIIA 2023; 88:1513-1527. [PMID: 38105021 DOI: 10.1134/s0006297923100085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2023] [Revised: 08/15/2023] [Accepted: 08/15/2023] [Indexed: 12/19/2023]
Abstract
Heme-copper respiratory oxidases are highly efficient molecular machines. These membrane enzymes catalyze the final step of cellular respiration in eukaryotes and many prokaryotes: the transfer of electrons from cytochromes or quinols to molecular oxygen and oxygen reduction to water. The free energy released in this redox reaction is converted by heme-copper respiratory oxidases into the transmembrane gradient of the electrochemical potential of hydrogen ions H+). Heme-copper respiratory oxidases have a unique mechanism for generating H+, namely, a redox-coupled proton pump. A combination of direct electrometric method for measuring the kinetics of membrane potential generation with the methods of prestationary kinetics and site-directed mutagenesis in the studies of heme-copper oxidases allows to obtain a unique information on the translocation of protons inside the proteins in real time. The review summarizes the data of studies employing time-resolved electrometry to decipher the mechanisms of functioning of these important bioenergetic enzymes.
Collapse
Affiliation(s)
- Sergei A Siletsky
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119991, Russia.
| |
Collapse
|
2
|
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.
Collapse
|
3
|
Identification of nosZ-expressing microorganisms consuming trace N 2O in microaerobic chemostat consortia dominated by an uncultured Burkholderiales. THE ISME JOURNAL 2022; 16:2087-2098. [PMID: 35676322 PMCID: PMC9381517 DOI: 10.1038/s41396-022-01260-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Revised: 05/23/2022] [Accepted: 05/27/2022] [Indexed: 12/12/2022]
Abstract
Microorganisms possessing N2O reductases (NosZ) are the only known environmental sink of N2O. While oxygen inhibition of NosZ activity is widely known, environments where N2O reduction occurs are often not devoid of O2. However, little is known regarding N2O reduction in microoxic systems. Here, 1.6-L chemostat cultures inoculated with activated sludge samples were sustained for ca. 100 days with low concentration (<2 ppmv) and feed rate (<1.44 µmoles h−1) of N2O, and the resulting microbial consortia were analyzed via quantitative PCR (qPCR) and metagenomic/metatranscriptomic analyses. Unintended but quantified intrusion of O2 sustained dissolved oxygen concentration above 4 µM; however, complete N2O reduction of influent N2O persisted throughout incubation. Metagenomic investigations indicated that the microbiomes were dominated by an uncultured taxon affiliated to Burkholderiales, and, along with the qPCR results, suggested coexistence of clade I and II N2O reducers. Contrastingly, metatranscriptomic nosZ pools were dominated by the Dechloromonas-like nosZ subclade, suggesting the importance of the microorganisms possessing this nosZ subclade in reduction of trace N2O. Further, co-expression of nosZ and ccoNO/cydAB genes found in the metagenome-assembled genomes representing these putative N2O-reducers implies a survival strategy to maximize utilization of scarcely available electron acceptors in microoxic environmental niches.
Collapse
|
4
|
Garg N, Taylor AJ, Pastorelli F, Flannery SE, Jackson PJ, Johnson MP, Kelly DJ. Genes Linking Copper Trafficking and Homeostasis to the Biogenesis and Activity of the cbb 3-Type Cytochrome c Oxidase in the Enteric Pathogen Campylobacter jejuni. Front Microbiol 2021; 12:683260. [PMID: 34248902 PMCID: PMC8267372 DOI: 10.3389/fmicb.2021.683260] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2021] [Accepted: 05/26/2021] [Indexed: 11/13/2022] Open
Abstract
Bacterial C-type haem-copper oxidases in the cbb 3 family are widespread in microaerophiles, which exploit their high oxygen-binding affinity for growth in microoxic niches. In microaerophilic pathogens, C-type oxidases can be essential for infection, yet little is known about their biogenesis compared to model bacteria. Here, we have identified genes involved in cbb 3-oxidase (Cco) assembly and activity in the Gram-negative pathogen Campylobacter jejuni, the commonest cause of human food-borne bacterial gastroenteritis. Several genes of unknown function downstream of the oxidase structural genes ccoNOQP were shown to be essential (cj1483c and cj1486c) or important (cj1484c and cj1485c) for Cco activity; Cj1483 is a CcoH homologue, but Cj1484 (designated CcoZ) has structural similarity to MSMEG_4692, involved in Qcr-oxidase supercomplex formation in Mycobacterium smegmatis. Blue-native polyacrylamide gel electrophoresis of detergent solubilised membranes revealed three major bands, one of which contained CcoZ along with Qcr and oxidase subunits. Deletion of putative copper trafficking genes ccoI (cj1155c) and ccoS (cj1154c) abolished Cco activity, which was partially restored by addition of copper during growth, while inactivation of cj0369c encoding a CcoG homologue led to a partial reduction in Cco activity. Deletion of an operon encoding PCu A C (Cj0909) and Sco (Cj0911) periplasmic copper chaperone homologues reduced Cco activity, which was partially restored in the cj0911 mutant by exogenous copper. Phenotypic analyses of gene deletions in the cj1161c-1166c cluster, encoding several genes involved in intracellular metal homeostasis, showed that inactivation of copA (cj1161c), or copZ (cj1162c) led to both elevated intracellular Cu and reduced Cco activity, effects exacerbated at high external Cu. Our work has therefore identified (i) additional Cco subunits, (ii) a previously uncharacterized set of genes linking copper trafficking and Cco activity, and (iii) connections with Cu homeostasis in this important pathogen.
Collapse
Affiliation(s)
- Nitanshu Garg
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield, United Kingdom
| | - Aidan J Taylor
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield, United Kingdom
| | - Federica Pastorelli
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield, United Kingdom
| | - Sarah E Flannery
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield, United Kingdom
| | - Phillip J Jackson
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield, United Kingdom
| | - Matthew P Johnson
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield, United Kingdom
| | - David J Kelly
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield, United Kingdom
| |
Collapse
|
5
|
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.
Collapse
Affiliation(s)
- Margareta R A Blomberg
- Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden.
| |
Collapse
|
6
|
Abstract
Bacteria power their energy metabolism using membrane-bound respiratory enzymes that capture chemical energy and transduce it by pumping protons or Na+ ions across their cell membranes. Recent breakthroughs in molecular bioenergetics have elucidated the architecture and function of many bacterial respiratory enzymes, although key mechanistic principles remain debated. In this Review, we present an overview of the structure, function and bioenergetic principles of modular bacterial respiratory chains and discuss their differences from the eukaryotic counterparts. We also discuss bacterial supercomplexes, which provide central energy transduction systems in several bacteria, including important pathogens, and which could open up possible avenues for treatment of disease.
Collapse
|
7
|
Muntyan MS, Morozov DA, Leonova YF, Ovchinnikova TV. Identification of Na+-Pumping Cytochrome Oxidase in the Membranes of Extremely Alkaliphilic Thioalkalivibrio Bacteria. BIOCHEMISTRY (MOSCOW) 2021; 85:1631-1639. [PMID: 33705300 DOI: 10.1134/s0006297920120147] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
For the first time, the functioning of the oxygen reductase Na+-pump (Na+-pumping cytochrome c oxidase of the cbb3-type) was demonstrated by examining the respiratory chain of the extremely alkaliphilic bacterium Thioalkalivibrio versutus [Muntyan, M. S., et al. (2015) Cytochrome cbb3 of Thioalkalivibrio is a Na+-pumping cytochrome oxidase, Proc. Natl. Acad. Sci. USA, 112, 7695-7700], a product of the ccoNOQP operon. In this study, we detected and identified this enzyme using rabbit polyclonal antibody against the predicted C-terminal amino acid sequence of its catalytic subunit. We found that this cbb3-type oxidase is synthesized in bacterial cells, where it is located in the membranes. The 48-kDa oxidase subunit (CcoN) is catalytic, while subunits CcoO and CcoP with molecular masses of 29 and 34 kDa, respectively, are cytochromes c. The theoretical pI values of the CcoN, CcoO, and CcoP subunits were determined. It was shown that parts of the CcoO and CcoP subunits exposed to the aqueous phase on the cytoplasmic membrane P-side are enriched with negatively charged amino acid residues, in contrast to the parts of the integral subunit CcoN adjacent to the aqueous phase. Thus, the Na+-pumping cytochrome c oxidase of T. versutus, both in function and in structure, demonstrates adaptation to extremely alkaline conditions.
Collapse
Affiliation(s)
- M S Muntyan
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119991, Russia.
| | - D A Morozov
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119991, Russia
| | - Y F Leonova
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997, Russia
| | - T V Ovchinnikova
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997, Russia
| |
Collapse
|
8
|
Calisto F, Sousa FM, Sena FV, Refojo PN, Pereira MM. Mechanisms of Energy Transduction by Charge Translocating Membrane Proteins. Chem Rev 2021; 121:1804-1844. [PMID: 33398986 DOI: 10.1021/acs.chemrev.0c00830] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Life relies on the constant exchange of different forms of energy, i.e., on energy transduction. Therefore, organisms have evolved in a way to be able to harvest the energy made available by external sources (such as light or chemical compounds) and convert these into biological useable energy forms, such as the transmembrane difference of electrochemical potential (Δμ̃). Membrane proteins contribute to the establishment of Δμ̃ by coupling exergonic catalytic reactions to the translocation of charges (electrons/ions) across the membrane. Irrespectively of the energy source and consequent type of reaction, all charge-translocating proteins follow two molecular coupling mechanisms: direct- or indirect-coupling, depending on whether the translocated charge is involved in the driving reaction. In this review, we explore these two coupling mechanisms by thoroughly examining the different types of charge-translocating membrane proteins. For each protein, we analyze the respective reaction thermodynamics, electron transfer/catalytic processes, charge-translocating pathways, and ion/substrate stoichiometries.
Collapse
Affiliation(s)
- Filipa Calisto
- Instituto de Tecnologia Química e Biológica-António Xavier, Universidade Nova de Lisboa, Av. da República EAN, 2780-157, Oeiras, Portugal.,BioISI-Biosystems & Integrative Sciences Institute, University of Lisboa, Faculty of Sciences, Campo Grande, 1749-016 Lisboa, Portugal
| | - Filipe M Sousa
- Instituto de Tecnologia Química e Biológica-António Xavier, Universidade Nova de Lisboa, Av. da República EAN, 2780-157, Oeiras, Portugal.,BioISI-Biosystems & Integrative Sciences Institute, University of Lisboa, Faculty of Sciences, Campo Grande, 1749-016 Lisboa, Portugal
| | - Filipa V Sena
- Instituto de Tecnologia Química e Biológica-António Xavier, Universidade Nova de Lisboa, Av. da República EAN, 2780-157, Oeiras, Portugal.,BioISI-Biosystems & Integrative Sciences Institute, University of Lisboa, Faculty of Sciences, Campo Grande, 1749-016 Lisboa, Portugal
| | - Patricia N Refojo
- Instituto de Tecnologia Química e Biológica-António Xavier, Universidade Nova de Lisboa, Av. da República EAN, 2780-157, Oeiras, Portugal
| | - Manuela M Pereira
- Instituto de Tecnologia Química e Biológica-António Xavier, Universidade Nova de Lisboa, Av. da República EAN, 2780-157, Oeiras, Portugal.,BioISI-Biosystems & Integrative Sciences Institute, University of Lisboa, Faculty of Sciences, Campo Grande, 1749-016 Lisboa, Portugal
| |
Collapse
|
9
|
Benoit SL, Maier RJ, Sawers RG, Greening C. Molecular Hydrogen Metabolism: a Widespread Trait of Pathogenic Bacteria and Protists. Microbiol Mol Biol Rev 2020; 84:e00092-19. [PMID: 31996394 PMCID: PMC7167206 DOI: 10.1128/mmbr.00092-19] [Citation(s) in RCA: 51] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Pathogenic microorganisms use various mechanisms to conserve energy in host tissues and environmental reservoirs. One widespread but often overlooked means of energy conservation is through the consumption or production of molecular hydrogen (H2). Here, we comprehensively review the distribution, biochemistry, and physiology of H2 metabolism in pathogens. Over 200 pathogens and pathobionts carry genes for hydrogenases, the enzymes responsible for H2 oxidation and/or production. Furthermore, at least 46 of these species have been experimentally shown to consume or produce H2 Several major human pathogens use the large amounts of H2 produced by colonic microbiota as an energy source for aerobic or anaerobic respiration. This process has been shown to be critical for growth and virulence of the gastrointestinal bacteria Salmonella enterica serovar Typhimurium, Campylobacter jejuni, Campylobacter concisus, and Helicobacter pylori (including carcinogenic strains). H2 oxidation is generally a facultative trait controlled by central regulators in response to energy and oxidant availability. Other bacterial and protist pathogens produce H2 as a diffusible end product of fermentation processes. These include facultative anaerobes such as Escherichia coli, S Typhimurium, and Giardia intestinalis, which persist by fermentation when limited for respiratory electron acceptors, as well as obligate anaerobes, such as Clostridium perfringens, Clostridioides difficile, and Trichomonas vaginalis, that produce large amounts of H2 during growth. Overall, there is a rich literature on hydrogenases in growth, survival, and virulence in some pathogens. However, we lack a detailed understanding of H2 metabolism in most pathogens, especially obligately anaerobic bacteria, as well as a holistic understanding of gastrointestinal H2 transactions overall. Based on these findings, we also evaluate H2 metabolism as a possible target for drug development or other therapies.
Collapse
Affiliation(s)
- Stéphane L Benoit
- Department of Microbiology, University of Georgia, Athens, Georgia, USA
| | - Robert J Maier
- Department of Microbiology, University of Georgia, Athens, Georgia, USA
| | - R Gary Sawers
- Institute of Microbiology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Chris Greening
- School of Biological Sciences, Monash University, Clayton, VIC, Australia
- Department of Microbiology, Monash Biomedicine Discovery Institute, Clayton, VIC, Australia
| |
Collapse
|
10
|
Borisov VB, Siletsky SA. Features of Organization and Mechanism of Catalysis of Two Families of Terminal Oxidases: Heme-Copper and bd-Type. BIOCHEMISTRY (MOSCOW) 2019; 84:1390-1402. [DOI: 10.1134/s0006297919110130] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
|
11
|
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.
Collapse
Affiliation(s)
- Margareta R A Blomberg
- Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden.
| |
Collapse
|
12
|
Taylor AJ, Kelly DJ. The function, biogenesis and regulation of the electron transport chains in Campylobacter jejuni: New insights into the bioenergetics of a major food-borne pathogen. Adv Microb Physiol 2019; 74:239-329. [PMID: 31126532 DOI: 10.1016/bs.ampbs.2019.02.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Campylobacter jejuni is a zoonotic Epsilonproteobacterium that grows in the gastrointestinal tract of birds and mammals, and is the most frequent cause of food-borne bacterial gastroenteritis worldwide. As an oxygen-sensitive microaerophile, C. jejuni has to survive high environmental oxygen tensions, adapt to oxygen limitation in the host intestine and resist host oxidative attack. Despite its small genome size, C. jejuni is a versatile and metabolically active pathogen, with a complex and highly branched set of respiratory chains allowing the use of a wide range of electron donors and alternative electron acceptors in addition to oxygen, including fumarate, nitrate, nitrite, tetrathionate and N- or S-oxides. Several novel enzymes participate in these electron transport chains, including a tungsten containing formate dehydrogenase, a Complex I that uses flavodoxin and not NADH, a periplasmic facing fumarate reductase and a cytochrome c tetrathionate reductase. This review presents an updated description of the composition and bioenergetics of these various respiratory chains as they are currently understood, including recent work that gives new insights into energy conservation during electron transport to various alternative electron acceptors. The regulation of synthesis and assembly of the electron transport chains is also discussed. A deeper appreciation of the unique features of the respiratory systems of C. jejuni may be helpful in informing strategies to control this important pathogen.
Collapse
Affiliation(s)
- Aidan J Taylor
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | - David J Kelly
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| |
Collapse
|
13
|
Gavrilov S, Podosokorskaya O, Alexeev D, Merkel A, Khomyakova M, Muntyan M, Altukhov I, Butenko I, Bonch-Osmolovskaya E, Govorun V, Kublanov I. Respiratory Pathways Reconstructed by Multi-Omics Analysis in Melioribacter roseus, Residing in a Deep Thermal Aquifer of the West-Siberian Megabasin. Front Microbiol 2017; 8:1228. [PMID: 28713355 PMCID: PMC5492636 DOI: 10.3389/fmicb.2017.01228] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Accepted: 06/16/2017] [Indexed: 01/19/2023] Open
Abstract
Melioribacter roseus, a representative of recently proposed Ignavibacteriae phylum, is a metabolically versatile thermophilic bacterium, inhabiting subsurface biosphere of the West-Siberian megabasin and capable of growing on various substrates and electron acceptors. Genomic analysis followed by inhibitor studies and membrane potential measurements of aerobically grown M. roseus cells revealed the activity of aerobic respiratory electron transfer chain comprised of respiratory complexes I and IV, and an alternative complex III. Phylogeny reconstruction revealed that oxygen reductases belonged to atypical cc(o/b)o3-type and canonical cbb3–type cytochrome oxidases. Also, two molybdoenzymes of M. roseus were affiliated either with Ttr or Psr/Phs clades, but not with typical respiratory arsenate reductases of the Arr clade. Expression profiling, both at transcripts and protein level, allowed us to assign the role of the terminal respiratory oxidase under atmospheric oxygen concentration for the cc(o/b)o3 cytochrome oxidase, previously proposed to serve for oxygen detoxification only. Transcriptomic analysis revealed the involvement of both molybdoenzymes of M. roseus in As(V) respiration, yet differences in the genomic context of their gene clusters allow to hypothesize about their distinct roles in arsenate metabolism with the ‘Psr/Phs’-type molybdoenzyme being the most probable candidate respiratory arsenate reductase. Basing on multi-omics data, the pathways for aerobic and arsenate respiration were proposed. Our results start to bridge the vigorously increasing gap between homology-based predictions and experimentally verified metabolic processes, what is especially important for understudied microorganisms of novel lineages from deep subsurface environments of Eurasia, which remained separated from the rest of the biosphere for several geological periods.
Collapse
Affiliation(s)
- Sergey Gavrilov
- Winogradsky Institute of Microbiology, Research Center of Biotechnology, Russian Academy of SciencesMoscow, Russia
| | - Olga Podosokorskaya
- Winogradsky Institute of Microbiology, Research Center of Biotechnology, Russian Academy of SciencesMoscow, Russia
| | - Dmitry Alexeev
- Saint Petersburg State University of Information Technologies, Mechanics and OpticsSt. Petersburg, Russia
| | - Alexander Merkel
- Winogradsky Institute of Microbiology, Research Center of Biotechnology, Russian Academy of SciencesMoscow, Russia
| | - Maria Khomyakova
- Winogradsky Institute of Microbiology, Research Center of Biotechnology, Russian Academy of SciencesMoscow, Russia
| | - Maria Muntyan
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State UniversityMoscow, Russia
| | - Ilya Altukhov
- Federal Research and Clinical Centre of Physico-Chemical MedicineMoscow, Russia.,Moscow Institute of Physics and TechnologyDolgoprudny, Russia
| | - Ivan Butenko
- Federal Research and Clinical Centre of Physico-Chemical MedicineMoscow, Russia
| | - Elizaveta Bonch-Osmolovskaya
- Winogradsky Institute of Microbiology, Research Center of Biotechnology, Russian Academy of SciencesMoscow, Russia
| | - Vadim Govorun
- Federal Research and Clinical Centre of Physico-Chemical MedicineMoscow, Russia.,Moscow Institute of Physics and TechnologyDolgoprudny, Russia
| | - Ilya Kublanov
- Winogradsky Institute of Microbiology, Research Center of Biotechnology, Russian Academy of SciencesMoscow, Russia.,Laboratory of Microbial Genomics, Immanuel Kant Baltic Federal UniversityKaliningrad, Russia
| |
Collapse
|
14
|
van der Stel AX, Boogerd FC, Huynh S, Parker CT, van Dijk L, van Putten JPM, Wösten MMSM. Generation of the membrane potential and its impact on the motility, ATP production and growth in Campylobacter jejuni. Mol Microbiol 2017; 105:637-651. [PMID: 28586527 DOI: 10.1111/mmi.13723] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Revised: 05/29/2017] [Accepted: 06/04/2017] [Indexed: 02/06/2023]
Abstract
The generation of a membrane potential (Δψ), the major constituent of the proton motive force (pmf), is crucial for ATP synthesis, transport of nutrients and flagellar rotation. Campylobacter jejuni harbors a branched electron transport chain, enabling respiration with different electron donors and acceptors. Here, we demonstrate that a relatively high Δψ is only generated in the presence of either formate as electron donor or oxygen as electron acceptor, in combination with an acceptor/donor respectively. We show the necessity of the pmf for motility and growth of C. jejuni. ATP generation is not only accomplished by oxidative phosphorylation via the pmf, but also by substrate-level phosphorylation via the enzyme AckA. In response to a low oxygen tension, C. jejuni increases the transcription and activity of the donor complexes formate dehydrogenase (FdhABC) and hydrogenase (HydABCD) as well as the transcription of the alternative respiratory acceptor complexes. Our findings suggest that in the gut of warm-blooded animals, C. jejuni depends on at least formate or hydrogen as donor (in the anaerobic lumen) or oxygen as acceptor (near the epithelial cells) to generate a pmf that sustains efficient motility and growth for colonization and pathogenesis.
Collapse
Affiliation(s)
| | - Fred C Boogerd
- Department of Molecular Cell Biology, VU University Amsterdam, Amsterdam, The Netherlands
| | - Steven Huynh
- Produce Safety and Microbiology Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Albany, CA, USA
| | - Craig T Parker
- Produce Safety and Microbiology Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Albany, CA, USA
| | - Linda van Dijk
- Department of Infectious Diseases and Immunology, Utrecht University, Utrecht, The Netherlands
| | - Jos P M van Putten
- Department of Infectious Diseases and Immunology, Utrecht University, Utrecht, The Netherlands
| | - Marc M S M Wösten
- Department of Infectious Diseases and Immunology, Utrecht University, Utrecht, The Netherlands
| |
Collapse
|
15
|
Bhagi-Damodaran A, Petrik I, Lu Y. Using Biosynthetic Models of Heme-Copper Oxidase and Nitric Oxide Reductase in Myoglobin to Elucidate Structural Features Responsible for Enzymatic Activities. Isr J Chem 2016; 56:773-790. [PMID: 27994254 PMCID: PMC5161413 DOI: 10.1002/ijch.201600033] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
In biology, a heme-Cu center in heme-copper oxidases (HCOs) is used to catalyze the four-electron reduction of oxygen to water, while a heme-nonheme diiron center in nitric oxide reductases (NORs) is employed to catalyze the two-electron reduction of nitric oxide to nitrous oxide. Although much progress has been made in biochemical and biophysical studies of HCOs and NORs, structural features responsible for similarities and differences within the two enzymatic systems remain to be understood. Here, we discuss the progress made in the design and characterization of myoglobin-based enzyme models of HCOs and NORs. In particular, we focus on use of these models to understand the structure-function relations between HCOs and NORs, including the role of nonheme metals, conserved amino acids in the active site, heme types and hydrogen-bonding network in tuning enzymatic activities and total turnovers. Insights gained from these studies are summarized and future directions are proposed.
Collapse
Affiliation(s)
| | - Igor Petrik
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL. 61801
| | - Yi Lu
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL. 61801
| |
Collapse
|
16
|
Menning KJ, Menon BB, Fox G, Scott KM. Dissolved inorganic carbon uptake in Thiomicrospira crunogena XCL-2 is Δp- and ATP-sensitive and enhances RubisCO-mediated carbon fixation. Arch Microbiol 2015; 198:149-59. [PMID: 26581415 DOI: 10.1007/s00203-015-1172-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2014] [Revised: 10/30/2015] [Accepted: 11/11/2015] [Indexed: 11/26/2022]
Abstract
The gammaproteobacterium Thiomicrospira crunogena XCL-2 is an aerobic sulfur-oxidizing hydrothermal vent chemolithoautotroph that has a CO2 concentrating mechanism (CCM), which generates intracellular dissolved inorganic carbon (DIC) concentrations much higher than extracellular, thereby providing substrate for carbon fixation at sufficient rate. This CCM presumably requires at least one active DIC transporter to generate the elevated intracellular concentrations of DIC measured in this organism. In this study, the half-saturation constant (K CO2) for purified carboxysomal RubisCO was measured (276 ± 18 µM) which was much greater than the K CO2 of whole cells (1.03 µM), highlighting the degree to which the CCM facilitates CO2 fixation under low CO2 conditions. To clarify the bioenergetics powering active DIC uptake, cells were incubated in the presence of inhibitors targeting ATP synthesis (DCCD) or proton potential (CCCP). Incubations with each of these inhibitors resulted in diminished intracellular ATP, DIC, and fixed carbon, despite an absence of an inhibitory effect on proton potential in the DCCD-incubated cells. Electron transport complexes NADH dehydrogenase and the bc 1 complex were found to be insensitive to DCCD, suggesting that ATP synthase was the primary target of DCCD. Given the correlation of DIC uptake to the intracellular ATP concentration, the ABC transporter genes were targeted by qRT-PCR, but were not upregulated under low-DIC conditions. As the T. crunogena genome does not include orthologs of any genes encoding known DIC uptake systems, these data suggest that a novel, yet to be identified, ATP- and proton potential-dependent DIC transporter is active in this bacterium. This transporter serves to facilitate growth by T. crunogena and other Thiomicrospiras in the many habitats where they are found.
Collapse
Affiliation(s)
- Kristy J Menning
- Department of Integrative Biology, University of South Florida, 4202 East Fowler Avenue, Tampa, FL, 33620, USA
| | - Balaraj B Menon
- Department of Chemistry and Biochemistry, The University of Southern Mississippi, Hattiesburg, MS, USA
- Schepens Eye Research Institute, Harvard Medical School, Boston, MA, USA
| | - Gordon Fox
- Department of Integrative Biology, University of South Florida, 4202 East Fowler Avenue, Tampa, FL, 33620, USA
| | - Kathleen M Scott
- Department of Integrative Biology, University of South Florida, 4202 East Fowler Avenue, Tampa, FL, 33620, USA.
| |
Collapse
|
17
|
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: 4] [Impact Index Per Article: 0.4] [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.
Collapse
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.
| |
Collapse
|
18
|
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.
Collapse
|
19
|
Lysine 362 in cytochrome c oxidase regulates opening of the K-channel via changes in pKA and conformation. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1837:1998-2003. [PMID: 25149865 DOI: 10.1016/j.bbabio.2014.08.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2014] [Revised: 08/09/2014] [Accepted: 08/12/2014] [Indexed: 11/21/2022]
Abstract
The metabolism of aerobic life uses the conversion of molecular oxygen to water as an energy source. This reaction is catalyzed by cytochrome e oxidase (CeO) consuming four electrons and four protons, which move along specific routes. While all four electrons are transferred via the same cofactors to the binuclear reaction center (BNC), the protons take two different routes in the A-type CeO, i.e., two of the four chemical protons consumed in the reaction arrive via the D-channel in the oxidative first half starting after oxygen binding. The other two chemical protons enter via the K-channel in the reductive second half of the reaction cycle. To date, the mechanism behind these separate proton transport pathways has not been understood. In this study, we propose a model that can explain the reaction-step specific opening and closing of the K-channel by conformational and pKA changes of its central lysine 362. Molecular dynamics simulations reveal an upward movement of Lys362 towards the BNC, which had already been supposed by several experimental studies. Redox state-dependent pKA calculations provide evidence that Lys362 may protonate transiently, thereby opening the K-channel only in the reductive second half of the reaction cycle. From our results, we develop a model that assigns a key role to Lys362 in the proton gating between the two proton input channels of the A-type CeO.
Collapse
|
20
|
Wikström M, Sharma V, Kaila VRI, Hosler JP, Hummer G. New Perspectives on Proton Pumping in Cellular Respiration. Chem Rev 2015; 115:2196-221. [DOI: 10.1021/cr500448t] [Citation(s) in RCA: 183] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Mårten Wikström
- Institute
of Biotechnology, University of Helsinki, Biocenter 3 (Viikinkaari 1), PB
65, Helsinki 00014, Finland
| | - Vivek Sharma
- Department
of Physics, Tampere University of Technology, Korkeakoulunkatu 3, Tampere 33720, Finland
| | - Ville R. I. Kaila
- Department
Chemie, Technische Universität München, Lichtenbergstraße 4, D-85748 Garching, Germany
| | - Jonathan P. Hosler
- Department
of Biochemistry, University of Mississippi Medical Center, Jackson, Mississippi 39216, United States
| | - Gerhard Hummer
- Department
of Theoretical Biophysics, Max Planck Institute of Biophysics, Max-von-Laue-Straße
3, 60438 Frankfurt
am Main, Germany
| |
Collapse
|
21
|
How cytochrome c oxidase can pump four protons per oxygen molecule at high electrochemical gradient. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2014; 1847:364-376. [PMID: 25529353 DOI: 10.1016/j.bbabio.2014.12.005] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2014] [Revised: 11/18/2014] [Accepted: 12/10/2014] [Indexed: 12/12/2022]
Abstract
Experiments have shown that the A-family cytochrome c oxidases pump four protons per oxygen molecule, also at a high electrochemical gradient. This has been considered a puzzle, since two of the reduction potentials involved, Cu(II) and Fe(III), were estimated from experiments to be too low to afford proton pumping at a high gradient. The present quantum mechanical study (using hybrid density functional theory) suggests a solution to this puzzle. First, the calculations show that the charge compensated Cu(II) potential for CuB is actually much higher than estimated from experiment, of the same order as the reduction potentials for the tyrosyl radical and the ferryl group, which are also involved in the catalytic cycle. The reason for the discrepancy between theory and experiment is the very large uncertainty in the experimental observations used to estimate the equilibrium potentials, mainly caused by the lack of methods for direct determination of reduced CuB. Second, the calculations show that a high energy metastable state, labeled EH, is involved during catalytic turnover. The EH state mixes the low reduction potential of Fe(III) in heme a3 with another, higher potential, here suggested to be that of the tyrosyl radical, resulting in enough exergonicity to allow proton pumping at a high gradient. In contrast, the corresponding metastable oxidized state, OH, is not significantly higher in energy than the resting state, O. Finally, to secure the involvement of the high energy EH state it is suggested that only one proton is taken up via the K-channel during catalytic turnover.
Collapse
|
22
|
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.
Collapse
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
| |
Collapse
|
23
|
Enzymatic characterization and in vivo function of five terminal oxidases in Pseudomonas aeruginosa. J Bacteriol 2014; 196:4206-15. [PMID: 25182500 DOI: 10.1128/jb.02176-14] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The ubiquitous opportunistic pathogen Pseudomonas aeruginosa has five aerobic terminal oxidases: bo(3)-type quinol oxidase (Cyo), cyanide-insensitive oxidase (CIO), aa3-type cytochrome c oxidase (aa3), and two cbb(3)-type cytochrome c oxidases (cbb(3)-1and cbb(3)-2). These terminal oxidases are differentially regulated under various growth conditions and are thought to contribute to the survival of this microorganism in a wide variety of environmental niches. Here, we constructed multiple mutant strains of P. aeruginosa that express only one aerobic terminal oxidase to investigate the enzymatic characteristics and in vivo function of each enzyme. The Km values of Cyo, CIO, and aa3 for oxygen were similar and were 1 order of magnitude higher than those of cbb(3)-1 and cbb(3)-2, indicating that Cyo, CIO, and aa3 are low-affinity enzymes and that cbb(3)-1 and cbb(3)-2 are high-affinity enzymes. Although cbb(3)-1 and cbb(3)-2 exhibited different expression patterns in response to oxygen concentration, they had similar Km values for oxygen. Both cbb(3)-1 and cbb(3)-2 utilized cytochrome c4 as the main electron donor under normal growth conditions. The electron transport chains terminated by cbb(3)-1 and cbb(3)-2 generate a proton gradient across the cell membrane with similar efficiencies. The electron transport chain of aa3 had the highest proton translocation efficiency, whereas that of CIO had the lowest efficiency. The enzymatic properties of the terminal oxidases reported here are partially in agreement with their regulatory patterns and may explain the environmental adaptability and versatility of P. aeruginosa.
Collapse
|
24
|
Rauhamäki V, Wikström M. The causes of reduced proton-pumping efficiency in type B and C respiratory heme-copper oxidases, and in some mutated variants of type A. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2014; 1837:999-1003. [PMID: 24583065 DOI: 10.1016/j.bbabio.2014.02.020] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2013] [Revised: 01/27/2014] [Accepted: 02/17/2014] [Indexed: 12/11/2022]
Abstract
The heme-copper oxidases may be divided into three categories, A, B, and C, which include cytochrome c and quinol-oxidising enzymes. All three types are known to be proton pumps and are found in prokaryotes, whereas eukaryotes only contain A-type cytochrome c oxidase in their inner mitochondrial membrane. However, the bacterial B- and C-type enzymes have often been reported to pump protons with an H(+)/e(-) ratio of only one half of the unit stoichiometry in the A-type enzyme. We will show here that these observations are likely to be the result of difficulties with the measuring technique together with a higher sensitivity of the B- and C-type enzymes to the protonmotive force that opposes pumping. We find that under optimal conditions the H(+)/e(-) ratio is close to unity in all the three heme-copper oxidase subfamilies. A higher tendency for proton leak in the B- and C-type enzymes may result from less efficient gating of a proton pump mechanism that we suggest evolved before the so-called D-channel of proton transfer. There is also a discrepancy between results using whole bacterial cells vs. phospholipid vesicles inlaid with oxidase with respect to the observed proton pumping after modification of the D-channel residue asparagine-139 (Rhodobacter sphaeroides numbering) to aspartate in A-type cytochrome c oxidase. This discrepancy might also be explained by a higher sensitivity of proton pumping to protonmotive force in the mutated variant. This article is part of a Special Issue entitled: 18th European Bioenergetic Conference.
Collapse
Affiliation(s)
- Virve Rauhamäki
- Institute of Biotechnology, University of Helsinki, Viikinkaari 1, 00014 Helsinki, Finland
| | - Mårten Wikström
- Institute of Biotechnology, University of Helsinki, Viikinkaari 1, 00014 Helsinki, Finland.
| |
Collapse
|
25
|
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.
Collapse
|
26
|
Blomberg MRA, Siegbahn PEM. Proton pumping in cytochrome c oxidase: energetic requirements and the role of two proton channels. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2014; 1837:1165-77. [PMID: 24418352 DOI: 10.1016/j.bbabio.2014.01.002] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2013] [Revised: 01/02/2014] [Accepted: 01/06/2014] [Indexed: 12/15/2022]
Abstract
Cytochrome c oxidase is a superfamily of membrane bound enzymes catalyzing the exergonic reduction of molecular oxygen to water, producing an electrochemical gradient across the membrane. The gradient is formed both by the electrogenic chemistry, taking electrons and protons from opposite sides of the membrane, and by proton pumping across the entire membrane. In the most efficient subfamily, the A-family of oxidases, one proton is pumped in each reduction step, which is surprising considering the fact that two of the reduction steps most likely are only weakly exergonic. Based on a combination of quantum chemical calculations and experimental information, it is here shown that from both a thermodynamic and a kinetic point of view, it should be possible to pump one proton per electron also with such an uneven distribution of the free energy release over the reduction steps, at least up to half the maximum gradient. A previously suggested pumping mechanism is developed further to suggest a reason for the use of two proton transfer channels in the A-family. Since the rate of proton transfer to the binuclear center through the D-channel is redox dependent, it might become too slow for the steps with low exergonicity. Therefore, a second channel, the K-channel, where the rate is redox-independent is needed. A redox-dependent leakage possibility is also suggested, which might be important for efficient energy conservation at a high gradient. A mechanism for the variation in proton pumping stoichiometry over the different subfamilies of cytochrome oxidase is also suggested. This article is part of a Special Issue entitled: 18th European Bioenergetic Conference.
Collapse
Affiliation(s)
- Margareta R A Blomberg
- Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden.
| | - Per E M Siegbahn
- Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden
| |
Collapse
|
27
|
Reply to Murali et al.: Proton translocation stoichiometry of cbb3-type cytochrome c oxidase. Proc Natl Acad Sci U S A 2012. [DOI: 10.1073/pnas.1207734109] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
|
28
|
Stoichiometry of proton pumping by the cbb3-type oxygen reductase in whole cells of Rhodobacter capsulatus at pH 7 is about 0.5 H+ per electron. Proc Natl Acad Sci U S A 2012; 109:E2144; author reply E2145. [PMID: 22761318 DOI: 10.1073/pnas.1207216109] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
|