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Fine Tuning of ROS, Redox and Energy Regulatory Systems Associated with the Functions of Chloroplasts and Mitochondria in Plants under Heat Stress. Int J Mol Sci 2023; 24:ijms24021356. [PMID: 36674866 PMCID: PMC9865929 DOI: 10.3390/ijms24021356] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2022] [Revised: 01/05/2023] [Accepted: 01/07/2023] [Indexed: 01/13/2023] Open
Abstract
Heat stress severely affects plant growth and crop production. It is therefore urgent to uncover the mechanisms underlying heat stress responses of plants and establish the strategies to enhance heat tolerance of crops. The chloroplasts and mitochondria are known to be highly sensitive to heat stress. Heat stress negatively impacts on the electron transport chains, leading to increased production of reactive oxygen species (ROS) that can cause damages on the chloroplasts and mitochondria. Disruptions of photosynthetic and respiratory metabolisms under heat stress also trigger increase in ROS and alterations in redox status in the chloroplasts and mitochondria. However, ROS and altered redox status in these organelles also activate important mechanisms that maintain functions of these organelles under heat stress, which include HSP-dependent pathways, ROS scavenging systems and retrograde signaling. To discuss heat responses associated with energy regulating organelles, we should not neglect the energy regulatory hub involving TARGET OF RAPAMYCIN (TOR) and SNF-RELATED PROTEIN KINASE 1 (SnRK1). Although roles of TOR and SnRK1 in the regulation of heat responses are still unknown, contributions of these proteins to the regulation of the functions of energy producing organelles implicate the possible involvement of this energy regulatory hub in heat acclimation of plants.
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Sweetman C, Selinski J, Miller TK, Whelan J, Day DA. Legume Alternative Oxidase Isoforms Show Differential Sensitivity to Pyruvate Activation. FRONTIERS IN PLANT SCIENCE 2022; 12:813691. [PMID: 35111186 PMCID: PMC8801435 DOI: 10.3389/fpls.2021.813691] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Accepted: 12/27/2021] [Indexed: 05/29/2023]
Abstract
Alternative oxidase (AOX) is an important component of the plant respiratory pathway, enabling a route for electrons that bypasses the energy-conserving, ROS-producing complexes of the mitochondrial electron transport chain. Plants contain numerous isoforms of AOX, classified as either AOX1 or AOX2. AOX1 isoforms have received the most attention due to their importance in stress responses across a wide range of species. However, the propensity for at least one isoform of AOX2 to accumulate to very high levels in photosynthetic tissues of all legumes studied to date, suggests that this isoform has specialized roles, but we know little of its properties. Previous studies with sub-mitochondrial particles of soybean cotyledons and roots indicated that differential expression of GmAOX1, GmAOX2A, and GmAOX2D across tissues might confer different activation kinetics with pyruvate. We have investigated this using recombinantly expressed isoforms of soybean AOX in a previously described bacterial system (Selinski et al., 2016, Physiologia Plantarum 157, 264-279). Pyruvate activation kinetics were similar between the two GmAOX2 isoforms but differed substantially from those of GmAOX1, suggesting that selective expression of AOX1 and 2 could determine the level of AOX activity. However, this alone cannot completely explain the differences seen in sub-mitochondrial particles isolated from different legume tissues and possible reasons for this are discussed.
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Affiliation(s)
- Crystal Sweetman
- College of Science and Engineering, Flinders University, Bedford Park, SA, Australia
| | - Jennifer Selinski
- Department of Plant Cell Biology, Botanical Institute, Christian-Albrecht University of Kiel, Kiel, Germany
| | - Troy K. Miller
- College of Science and Engineering, Flinders University, Bedford Park, SA, Australia
| | - James Whelan
- Department of Animal, Plant, and Soil Science, School of Soil Science, La Trobe University, Bundoora, VIC, Australia
| | - David A. Day
- College of Science and Engineering, Flinders University, Bedford Park, SA, Australia
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3
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Jethva J, Schmidt RR, Sauter M, Selinski J. Try or Die: Dynamics of Plant Respiration and How to Survive Low Oxygen Conditions. PLANTS (BASEL, SWITZERLAND) 2022; 11:plants11020205. [PMID: 35050092 PMCID: PMC8780655 DOI: 10.3390/plants11020205] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2021] [Revised: 01/07/2022] [Accepted: 01/11/2022] [Indexed: 05/09/2023]
Abstract
Fluctuations in oxygen (O2) availability occur as a result of flooding, which is periodically encountered by terrestrial plants. Plant respiration and mitochondrial energy generation rely on O2 availability. Therefore, decreased O2 concentrations severely affect mitochondrial function. Low O2 concentrations (hypoxia) induce cellular stress due to decreased ATP production, depletion of energy reserves and accumulation of metabolic intermediates. In addition, the transition from low to high O2 in combination with light changes-as experienced during re-oxygenation-leads to the excess formation of reactive oxygen species (ROS). In this review, we will update our current knowledge about the mechanisms enabling plants to adapt to low-O2 environments, and how to survive re-oxygenation. New insights into the role of mitochondrial retrograde signaling, chromatin modification, as well as moonlighting proteins and mitochondrial alternative electron transport pathways (and their contribution to low O2 tolerance and survival of re-oxygenation), are presented.
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Affiliation(s)
- Jay Jethva
- Department of Plant Developmental Biology and Plant Physiology, Faculty of Mathematics and Natural Sciences, Botanical Institute, Christian-Albrechts University, D-24118 Kiel, Germany; (J.J.); (M.S.)
| | - Romy R. Schmidt
- Department of Plant Biotechnology, Faculty of Biology, University of Bielefeld, D-33615 Bielefeld, Germany;
| | - Margret Sauter
- Department of Plant Developmental Biology and Plant Physiology, Faculty of Mathematics and Natural Sciences, Botanical Institute, Christian-Albrechts University, D-24118 Kiel, Germany; (J.J.); (M.S.)
| | - Jennifer Selinski
- Department of Plant Cell Biology, Botanical Institute, Faculty of Mathematics and Natural Sciences, Christian-Albrechts University, D-24118 Kiel, Germany
- Correspondence: ; Tel.: +49-(0)431-880-4245
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4
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Kaye Y, Huang W, Clowez S, Saroussi S, Idoine A, Sanz-Luque E, Grossman AR. The mitochondrial alternative oxidase from Chlamydomonas reinhardtii enables survival in high light. J Biol Chem 2018; 294:1380-1395. [PMID: 30510139 DOI: 10.1074/jbc.ra118.004667] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Revised: 10/24/2018] [Indexed: 01/07/2023] Open
Abstract
Photosynthetic organisms often experience extreme light conditions that can cause hyper-reduction of the chloroplast electron transport chain, resulting in oxidative damage. Accumulating evidence suggests that mitochondrial respiration and chloroplast photosynthesis are coupled when cells are absorbing high levels of excitation energy. This coupling helps protect the cells from hyper-reduction of photosynthetic electron carriers and diminishes the production of reactive oxygen species (ROS). To examine this cooperative protection, here we characterized Chlamydomonas reinhardtii mutants lacking the mitochondrial alternative terminal respiratory oxidases, CrAOX1 and CrAOX2. Using fluorescent fusion proteins, we experimentally demonstrated that both enzymes localize to mitochondria. We also observed that the mutant strains were more sensitive than WT cells to high light under mixotrophic and photoautotrophic conditions, with the aox1 strain being more sensitive than aox2 Additionally, the lack of CrAOX1 increased ROS accumulation, especially in very high light, and damaged the photosynthetic machinery, ultimately resulting in cell death. These findings indicate that the Chlamydomonas AOX proteins can participate in acclimation of C. reinhardtii cells to excess absorbed light energy. They suggest that when photosynthetic electron carriers are highly reduced, a chloroplast-mitochondria coupling allows safe dissipation of photosynthetically derived electrons via the reduction of O2 through AOX (especially AOX1)-dependent mitochondrial respiration.
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Affiliation(s)
- Yuval Kaye
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305.
| | - Weichao Huang
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | - Sophie Clowez
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | - Shai Saroussi
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | - Adam Idoine
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | - Emanuel Sanz-Luque
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | - Arthur R Grossman
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
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5
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Selinski J, Scheibe R, Day DA, Whelan J. Alternative Oxidase Is Positive for Plant Performance. TRENDS IN PLANT SCIENCE 2018; 23:588-597. [PMID: 29665989 DOI: 10.1016/j.tplants.2018.03.012] [Citation(s) in RCA: 84] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2017] [Revised: 03/15/2018] [Accepted: 03/22/2018] [Indexed: 05/02/2023]
Abstract
The alternative pathway of mitochondrial electron transport, which terminates in the alternative oxidase (AOX), uncouples oxidation of substrate from mitochondrial ATP production, yet plant performance is improved under adverse growth conditions. AOX is regulated at different levels. Identification of regulatory transcription factors shows that Arabidopsis thaliana AOX1a is under strong transcriptional suppression. At the protein level, the primary structure is not optimised for activity. Maximal activity requires the presence of various metabolites, such as tricarboxylic acid-cycle intermediates that act in an isoform-specific manner. In this opinion article we propose that the regulatory mechanisms that keep AOX activity suppressed, at both the gene and protein level, are positive for plant performance due to the flexible short- and long-term fine-tuning.
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Affiliation(s)
- Jennifer Selinski
- Department of Animal, Plant, and Soil Science, Australian Research Council Centre of Excellence in Plant Energy Biology, School of Life Science, La Trobe University Bundoora, VIC 3083, Australia.
| | - Renate Scheibe
- Division of Plant Physiology, Department of Biology/Chemistry, University of Osnabrueck, D-49069 Osnabrueck, Germany
| | - David A Day
- College of Science and Engineering, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia
| | - James Whelan
- Department of Animal, Plant, and Soil Science, Australian Research Council Centre of Excellence in Plant Energy Biology, School of Life Science, La Trobe University Bundoora, VIC 3083, Australia
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6
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Wang Y, Berkowitz O, Selinski J, Xu Y, Hartmann A, Whelan J. Stress responsive mitochondrial proteins in Arabidopsis thaliana. Free Radic Biol Med 2018; 122:28-39. [PMID: 29555593 DOI: 10.1016/j.freeradbiomed.2018.03.031] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/14/2017] [Revised: 03/05/2018] [Accepted: 03/16/2018] [Indexed: 12/27/2022]
Abstract
In the last decade plant mitochondria have emerged as a target, sensor and initiator of signalling cascades to a variety of stress and adverse growth conditions. A combination of various 'omic profiling approaches combined with forward and reverse genetic studies have defined how mitochondria respond to stress and the signalling pathways and regulators of these responses. Reactive oxygen species (ROS)-dependent and -independent pathways, specific metabolites, complex I dysfunction, and the mitochondrial unfolded protein response (UPR) pathway have been proposed to date. These pathways are regulated by kinases (sucrose non-fermenting response like kinase; cyclin dependent protein kinase E 1) and transcription factors from the abscisic acid-related, WRKY and NAC families. A number of independent studies have revealed that these mitochondrial signalling pathways interact with a variety of phytohormone signalling pathways. While this represents significant progress in the last decade there are more pathways to be uncovered. Post-transcriptional/translational regulation is also a likely determinant of the mitochondrial stress response. Unbiased analyses of the expression of genes encoding mitochondrial proteins in a variety of stress conditions reveal a modular network exerting a high degree of anterograde control. As abiotic and biotic stresses have significant impact on the yield of important crops such as rice, wheat and barley we will give an outlook of how knowledge gained in Arabidopsis may help to increase crop production and how emerging technologies may contribute.
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Affiliation(s)
- Yan Wang
- Department of Animal, Plant and Soil Sciences, Australian Research Council Centre of Excellence in Plant Energy Biology, School of Life Sciences, La Trobe University, Bundoora, Victoria, Australia
| | - Oliver Berkowitz
- Department of Animal, Plant and Soil Sciences, Australian Research Council Centre of Excellence in Plant Energy Biology, School of Life Sciences, La Trobe University, Bundoora, Victoria, Australia.
| | - Jennifer Selinski
- Department of Animal, Plant and Soil Sciences, Australian Research Council Centre of Excellence in Plant Energy Biology, School of Life Sciences, La Trobe University, Bundoora, Victoria, Australia
| | - Yue Xu
- Department of Animal, Plant and Soil Sciences, Australian Research Council Centre of Excellence in Plant Energy Biology, School of Life Sciences, La Trobe University, Bundoora, Victoria, Australia
| | - Andreas Hartmann
- Department of Animal, Plant and Soil Sciences, Australian Research Council Centre of Excellence in Plant Energy Biology, School of Life Sciences, La Trobe University, Bundoora, Victoria, Australia
| | - James Whelan
- Department of Animal, Plant and Soil Sciences, Australian Research Council Centre of Excellence in Plant Energy Biology, School of Life Sciences, La Trobe University, Bundoora, Victoria, Australia
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7
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Wanniarachchi VR, Dametto L, Sweetman C, Shavrukov Y, Day DA, Jenkins CLD, Soole KL. Alternative Respiratory Pathway Component Genes (AOX and ND) in Rice and Barley and Their Response to Stress. Int J Mol Sci 2018; 19:E915. [PMID: 29558397 PMCID: PMC5877776 DOI: 10.3390/ijms19030915] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2018] [Revised: 03/15/2018] [Accepted: 03/16/2018] [Indexed: 11/24/2022] Open
Abstract
Plants have a non-energy conserving bypass of the classical mitochondrial cytochrome c pathway, known as the alternative respiratory pathway (AP). This involves type II NAD(P)H dehydrogenases (NDs) on both sides of the mitochondrial inner membrane, ubiquinone, and the alternative oxidase (AOX). The AP components have been widely characterised from Arabidopsis, but little is known for monocot species. We have identified all the genes encoding components of the AP in rice and barley and found the key genes which respond to oxidative stress conditions. In both species, AOX is encoded by four genes; in rice OsAOX1a, 1c, 1d and 1e representing four clades, and in barley, HvAOX1a, 1c, 1d1 and 1d2, but no 1e. All three subfamilies of plant ND genes, NDA, NDB and NDC are present in both rice and barley, but there are fewer NDB genes compared to Arabidopsis. Cyanide treatment of both species, along with salt treatment of rice and drought treatment of barley led to enhanced expression of various AP components; there was a high level of co-expression of AOX1a and AOX1d, along with NDB3 during the stress treatments, reminiscent of the co-expression that has been well characterised in Arabidopsis for AtAOX1a and AtNDB2.
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Affiliation(s)
- Vajira R Wanniarachchi
- College of Science and Engineering, Flinders University of South Australia, GPO Box 5100, Adelaide, SA 5001, Australia.
| | - Lettee Dametto
- College of Science and Engineering, Flinders University of South Australia, GPO Box 5100, Adelaide, SA 5001, Australia.
| | - Crystal Sweetman
- College of Science and Engineering, Flinders University of South Australia, GPO Box 5100, Adelaide, SA 5001, Australia.
| | - Yuri Shavrukov
- College of Science and Engineering, Flinders University of South Australia, GPO Box 5100, Adelaide, SA 5001, Australia.
| | - David A Day
- College of Science and Engineering, Flinders University of South Australia, GPO Box 5100, Adelaide, SA 5001, Australia.
| | - Colin L D Jenkins
- College of Science and Engineering, Flinders University of South Australia, GPO Box 5100, Adelaide, SA 5001, Australia.
| | - Kathleen L Soole
- College of Science and Engineering, Flinders University of South Australia, GPO Box 5100, Adelaide, SA 5001, Australia.
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8
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Del-Saz NF, Ribas-Carbo M, McDonald AE, Lambers H, Fernie AR, Florez-Sarasa I. An In Vivo Perspective of the Role(s) of the Alternative Oxidase Pathway. TRENDS IN PLANT SCIENCE 2018; 23:206-219. [PMID: 29269217 DOI: 10.1016/j.tplants.2017.11.006] [Citation(s) in RCA: 93] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2017] [Revised: 10/18/2017] [Accepted: 11/15/2017] [Indexed: 05/02/2023]
Abstract
Despite intense research on the in vitro characterization of regulatory factors modulating the alternative oxidase (AOX) pathway, the regulation of its activity in vivo is still not fully understood. Advances concerning in vivo regulation of AOX based on the oxygen-isotope fractionation technique are reviewed, and regulatory factors that merit future research are highlighted. In addition, we review and discuss the main biological functions assigned to the plant AOX, and suggest future experiments involving in vivo activity measurements to test different hypothesized physiological roles.
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Affiliation(s)
- Néstor Fernández Del-Saz
- Grup de Recerca en Biologia de les Plantes en Condicions Mediterranies, Universitat de les Illes Balears, Carretera de Valldemossa Km 7.5, 07122 Palma de Mallorca, Spain
| | - Miquel Ribas-Carbo
- Grup de Recerca en Biologia de les Plantes en Condicions Mediterranies, Universitat de les Illes Balears, Carretera de Valldemossa Km 7.5, 07122 Palma de Mallorca, Spain
| | - Allison E McDonald
- Department of Biology, Wilfrid Laurier University, Science Building, 75 University Avenue West, Waterloo, ON N2L 3C5, Canada
| | - Hans Lambers
- School of Biological Sciences, University of Western Australia, 35 Stirling Highway, Crawley (Perth), Western Australia 6009, Australia
| | - Alisdair R Fernie
- Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany
| | - Igor Florez-Sarasa
- Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany.
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9
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Collakova E, Klumas C, Suren H, Myers E, Heath LS, Holliday JA, Grene R. Evidence for extensive heterotrophic metabolism, antioxidant action, and associated regulatory events during winter hardening in Sitka spruce. BMC PLANT BIOLOGY 2013; 13:72. [PMID: 23631437 PMCID: PMC3651351 DOI: 10.1186/1471-2229-13-72] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2012] [Accepted: 03/19/2013] [Indexed: 05/06/2023]
Abstract
BACKGROUND Cold acclimation in woody perennials is a metabolically intensive process, but coincides with environmental conditions that are not conducive to the generation of energy through photosynthesis. While the negative effects of low temperatures on the photosynthetic apparatus during winter have been well studied, less is known about how this is reflected at the level of gene and metabolite expression, nor how the plant generates primary metabolites needed for adaptive processes during autumn. RESULTS The MapMan tool revealed enrichment of the expression of genes related to mitochondrial function, antioxidant and associated regulatory activity, while changes in metabolite levels over the time course were consistent with the gene expression patterns observed. Genes related to thylakoid function were down-regulated as expected, with the exception of plastid targeted specific antioxidant gene products such as thylakoid-bound ascorbate peroxidase, components of the reactive oxygen species scavenging cycle, and the plastid terminal oxidase. In contrast, the conventional and alternative mitochondrial electron transport chains, the tricarboxylic acid cycle, and redox-associated proteins providing reactive oxygen species scavenging generated by electron transport chains functioning at low temperatures were all active. CONCLUSIONS A regulatory mechanism linking thylakoid-bound ascorbate peroxidase action with "chloroplast dormancy" is proposed. Most importantly, the energy and substrates required for the substantial metabolic remodeling that is a hallmark of freezing acclimation could be provided by heterotrophic metabolism.
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Affiliation(s)
- Eva Collakova
- Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, VA, 24061, USA
| | - Curtis Klumas
- Genetics, Bioinformatics and Computational Biology Program, Virginia Tech, Blacksburg, VA, 24061, USA
| | - Haktan Suren
- Genetics, Bioinformatics and Computational Biology Program, Virginia Tech, Blacksburg, VA, 24061, USA
- Department of Forest Resources and Environmental Conservation, Virginia Tech, Blacksburg, VA, 24061, USA
| | - Elijah Myers
- Genetics, Bioinformatics and Computational Biology Program, Virginia Tech, Blacksburg, VA, 24061, USA
| | - Lenwood S Heath
- Department of Computer Science, Virginia Tech, Blacksburg, VA, 24061, USA
| | - Jason A Holliday
- Department of Forest Resources and Environmental Conservation, Virginia Tech, Blacksburg, VA, 24061, USA
| | - Ruth Grene
- Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, VA, 24061, USA
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10
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Guerrero-Castillo S, Cabrera-Orefice A, Vázquez-Acevedo M, González-Halphen D, Uribe-Carvajal S. During the stationary growth phase, Yarrowia lipolytica prevents the overproduction of reactive oxygen species by activating an uncoupled mitochondrial respiratory pathway. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2011; 1817:353-62. [PMID: 22138628 DOI: 10.1016/j.bbabio.2011.11.007] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2011] [Revised: 11/08/2011] [Accepted: 11/09/2011] [Indexed: 12/01/2022]
Abstract
In the branched mitochondrial respiratory chain from Yarrowia lipolytica there are two alternative oxido-reductases that do not pump protons, namely an external type II NADH dehydrogenase (NDH2e) and the alternative oxidase (AOX). Direct electron transfer between these proteins is not coupled to ATP synthesis and should be avoided in most physiological conditions. However, under low energy-requiring conditions an uncoupled high rate of oxygen consumption would be beneficial, as it would prevent overproduction of reactive oxygen species (ROS). In mitochondria from high energy-requiring, logarithmic-growth phase cells, most NDH2e was associated to cytochrome c oxidase and electrons from NADH were channeled to the cytochromic pathway. In contrast, in the low energy requiring, late stationary-growth phase, complex IV concentration decreased, the cells overexpressed NDH2e and thus a large fraction of this enzyme was found in a non-associated form. Also, the NDH2e-AOX uncoupled pathway was activated and the state IV external NADH-dependent production of ROS decreased. Association/dissociation of NDH2e to/from complex IV is proposed to be the switch that channels electrons from external NADH to the coupled cytochrome pathway or allows them to reach an uncoupled, alternative, ΔΨ-independent pathway.
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11
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Interaction of purified alternative oxidase from thermogenic Arum maculatum with pyruvate. FEBS Lett 2010; 585:397-401. [PMID: 21187094 DOI: 10.1016/j.febslet.2010.12.026] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2010] [Revised: 12/06/2010] [Accepted: 12/16/2010] [Indexed: 10/18/2022]
Abstract
Plant alternative oxidase (AOX) activity in isolated mitochondria is regulated by carboxylic acids, but reaction and regulatory mechanisms remain unclear. We show that activity of AOX protein purified from thermogenic Arum maculatum spadices is sensitive to pyruvate and glyoxylate but not succinate. Rapid, irreversible AOX inactivation occurs in the absence of pyruvate, whether or not duroquinol oxidation has been initiated, and is insensitive to duroquinone. Our data indicate that pyruvate stabilises an active conformation of AOX, increasing the population of active protein in a manner independent of reducing substrate and product, and are thus consistent with an exclusive effect of pyruvate on the enzyme's apparent V(max).
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12
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Albury MS, Elliott C, Moore AL. Towards a structural elucidation of the alternative oxidase in plants. PHYSIOLOGIA PLANTARUM 2009; 137:316-27. [PMID: 19719482 DOI: 10.1111/j.1399-3054.2009.01270.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
In addition to the conventional cytochrome c oxidase, mitochondria of all plants studied to date contain a second cyanide-resistant terminal oxidase or alternative oxidase (AOX). The AOX is located in the inner mitochondrial membrane and branches from the cytochrome pathway at the level of the quinone pool. It is non-protonmotive and couples the oxidation of ubiquinone to the reduction of oxygen to water. For many years, the AOX was considered to be confined to plants, fungi and a small number of protists. Recently, it has become apparent that the AOX occurs in wide range of organisms including prokaryotes and a moderate number of animal species. In this paper, we provide an overview of general features and current knowledge available about the AOX with emphasis on structure, the active site and quinone-binding site. Characterisation of the AOX has advanced considerably over recent years with information emerging about the role of the protein, regulatory regions and functional sites. The large number of sequences available is now enabling us to obtain a clearer picture of evolutionary origins and diversity.
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Affiliation(s)
- Mary S Albury
- Division of Biochemistry and Biomedical Sciences, School of Life Sciences, University of Sussex, Falmer, Brighton BN19QG, UK
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13
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Costa JH, Cardoso HG, Campos MD, Zavattieri A, Frederico AM, Fernandes de Melo D, Arnholdt-Schmitt B. Daucus carota L.--an old model for cell reprogramming gains new importance through a novel expansion pattern of alternative oxidase (AOX) genes. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2009; 47:753-9. [PMID: 19372042 DOI: 10.1016/j.plaphy.2009.03.011] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2008] [Revised: 03/19/2009] [Accepted: 03/24/2009] [Indexed: 05/13/2023]
Abstract
The paper highlights Daucus carota L. as an ideal model to complement plant stress research on Arabidopsis thaliana L. Recently, alternative oxidase (AOX) is discussed as functional marker candidate for cell reprogramming upon stress. Carrot is the most studied species for cell reprogramming and our current research reveals that it is the only one that has expanded both AOX sub-family genes. We point to recently published, but not discussed results on conserved differences in the vicinity of the most active functional site of AOX1 and AOX2, which indicate the importance of studying AOX sequence polymorphism, structure and functionality. Thus, stress-inducible experimental systems of D. carota are especially appropriate to bring research on stress tolerance a significant step forward.
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Affiliation(s)
- J H Costa
- Department of Biochemistry and Molecular Biology, Federal University of Ceará, PO Box 6029, 60455-900, Fortaleza, Ceará, Brazil
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14
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A novel functional element in the N-terminal region of Arum concinnatum alternative oxidase is indispensable for catalytic activity of the enzyme in HeLa cells. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2009; 1797:20-8. [PMID: 19643077 DOI: 10.1016/j.bbabio.2009.07.006] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/01/2009] [Revised: 07/14/2009] [Accepted: 07/21/2009] [Indexed: 11/20/2022]
Abstract
Alternative oxidase (AOX) is a quinol-oxygen oxidoreductase, which is known to possess a dicarboxylate diiron reaction center held in structurally postulated alpha-helical bundle. However, little is known about the structural or functional features of its N-terminal region in any organism, with the exception of a regulatory cysteine residue (CysI) in angiosperm plants. Here, we show that transcripts of two AOX1 isozymes (AcoAOX1a and AcoAOX1b) are coexpressed in thermogenic appendices of Arum concinnatum, while their enzymatic activities seem to be distinct. Namely, AcoAOX1a, an abundantly expressed transcript in vivo, shows an apparent cyanide-insensitive and n-propyl gallate-sensitive respiration during ectopic expression of the protein in HeLa cells, whereas AcoAOX1b exhibits a lower transcript expression, and appears to be totally inactive as AOX at the protein level. Our functional analyses further reveal that an E83K substitution in AcoAOX1b, which is located far upstream of CysI in the N-terminal region, is the cause of this loss of function. These results suggest the presence of a naturally occurring inactive AOX homologue in thermogenic plants. Accordingly, our results further imply that the N-terminal region of the AOX protein functionally contributes to the dynamic activities of respiratory control within the mitochondria.
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15
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Grant N, Onda Y, Kakizaki Y, Ito K, Watling J, Robinson S. Two cys or not two cys? That is the question; alternative oxidase in the thermogenic plant sacred Lotus. PLANT PHYSIOLOGY 2009; 150:987-95. [PMID: 19386803 PMCID: PMC2689982 DOI: 10.1104/pp.109.139394] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2009] [Accepted: 04/13/2009] [Indexed: 05/05/2023]
Abstract
Sacred lotus (Nelumbo nucifera) regulates temperature in its floral chamber to 32 degrees C to 35 degrees C across ambient temperatures of 8 degrees C to 40 degrees C with heating achieved through high alternative pathway fluxes. In most alternative oxidase (AOX) isoforms, two cysteine residues, Cys(1) and Cys(2), are highly conserved and play a role in posttranslational regulation of AOX. Further control occurs via interaction of reduced Cys(1) with alpha-keto acids, such as pyruvate. Here, we report on the in vitro regulation of AOX isolated from thermogenic receptacle tissues of sacred lotus. AOX protein was mostly present in the reduced form, and only a small fraction could be oxidized with diamide. Cyanide-resistant respiration in isolated mitochondria was stimulated 4-fold by succinate but not pyruvate or glyoxylate. Insensitivity of the alternative pathway of respiration to pyruvate and the inability of AOX protein to be oxidized by diamide suggested that AOX in these tissues may lack Cys(1). Subsequently, we isolated two novel cDNAs for AOX from thermogenic tissues of sacred lotus, designated as NnAOX1a and NnAOX1b. Deduced amino acid sequences of both confirmed that Cys(1) had been replaced by serine; however, Cys(2) was present. This contrasts with AOXs from thermogenic Aroids, which contain both Cys(1) and Cys(2). An additional cysteine was present at position 193 in NnAOX1b. The significance of the sequence data for regulation of the AOX protein in thermogenic sacred lotus is discussed and compared with AOXs from other thermogenic and nonthermogenic species.
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Affiliation(s)
- Nicole Grant
- Institute for Conservation Biology, University of Wollongong, Wollongong, New South Wales 2522, Australia.
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16
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Wang J, Wang X, Liu C, Zhang J, Zhu C, Guo X. The NgAOX1a gene cloned from Nicotiana glutinosa is implicated in the response to abiotic and biotic stresses. Biosci Rep 2008; 28:259-66. [PMID: 18588517 DOI: 10.1042/bsr20080025] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
A novel gene, named NgAOX1a, was isolated from Nicotiana glutinosa by RT-PCR (reverse transcription-PCR). The full-length cDNA of NgAOX1a was 1448 bp, including a 1062-bp ORF (open reading frame), a 124 bp 5' UTR (untranslated region) and a 262 bp 3' UTR. The ORF encodes a 353-amino-acid protein which contains two conserved cysteine residues, four iron-binding motifs, five alpha-helix regions and six conserved histidine residues. The phylogenetic tree showed that NgAOX1a belongs to the AOX1 (alternative oxidase 1)-type group. Alignment analysis showed that NgAOX1a shares a high similarity with other known AOXs. Four exons and three introns were detected in the genomic DNA sequence, and Southern-blotting analysis suggested that NgAOX1a is a single-copy gene. A series of putative cis-acting elements were examined in the 5'-flanking region of NgAOX1a. Northern-blotting analysis showed that the transcript levels of NgAOX1a can be markedly accumulated when tobacco seedlings are treated with various abiotic stimuli, such as exogenous signalling molecules for plant defence response, salicylic acid and H(2)O(2), and the exogenous TCA (tricarboxylic acid) cycle metabolite citrate. However, it could be suppressed by abiotic stress, such as CoCl(2), an inhibitor of ethylene, which indicates that the expression of NgAOX1a may be regulated by ethylene. In addition, NgAOX1a can also be strongly induced by three viral pathogens, tobacco mosaic virus, potato virus X and potato virus Y. These results indicate that NgAOX1a may be involved in multi-signal transduction pathways and may play an important role in defence response.
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Affiliation(s)
- Jian Wang
- State Key Laboratory of Crop Biology, College of Life Sciences, Shandong Agricultural University, Tai'an, Shandong, 271018, People's Republic of China
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17
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McDonald AE. Alternative oxidase: an inter-kingdom perspective on the function and regulation of this broadly distributed 'cyanide-resistant' terminal oxidase. FUNCTIONAL PLANT BIOLOGY : FPB 2008; 35:535-552. [PMID: 32688810 DOI: 10.1071/fp08025] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2008] [Accepted: 07/11/2008] [Indexed: 06/11/2023]
Abstract
Alternative oxidase (AOX) is a terminal quinol oxidase located in the respiratory electron transport chain that catalyses the oxidation of quinol and the reduction of oxygen to water. However, unlike the cytochrome c oxidase respiratory pathway, the AOX pathway moves fewer protons across the inner mitochondrial membrane to generate a proton motive force that can be used to synthesise ATP. The energy passed to AOX is dissipated as heat. This appears to be very wasteful from an energetic perspective and it is likely that AOX fulfils some physiological function(s) that makes up for its apparent energetic shortcomings. An examination of the known taxonomic distribution of AOX and the specific organisms in which AOX has been studied has been used to explore themes pertaining to AOX function and regulation. A comparative approach was used to examine AOX function as it relates to the biochemical function of the enzyme as a quinol oxidase and associated topics, such as enzyme structure, catalysis and transcriptional expression and post-translational regulation. Hypotheses that have been put forward about the physiological function(s) of AOX were explored in light of some recent discoveries made with regard to species that contain AOX. Fruitful areas of research for the AOX community in the future have been highlighted.
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Affiliation(s)
- Allison E McDonald
- Department of Biology, The University of Western Ontario, Biological and Geological Sciences Building, London, Ontario N6A 5B7, Canada. Email
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18
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Onda Y, Kato Y, Abe Y, Ito T, Ito-Inaba Y, Morohashi M, Ito Y, Ichikawa M, Matsukawa K, Otsuka M, Koiwa H, Ito K. Pyruvate-sensitive AOX exists as a non-covalently associated dimer in the homeothermic spadix of the skunk cabbage, Symplocarpus renifolius. FEBS Lett 2007; 581:5852-8. [PMID: 18060878 DOI: 10.1016/j.febslet.2007.11.061] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2007] [Revised: 11/20/2007] [Accepted: 11/20/2007] [Indexed: 11/25/2022]
Abstract
The cyanide-resistant alternative oxidase (AOX) is a homodimeric protein whose activity can be regulated by the oxidation/reduction state and by alpha-keto acids. To further clarify the role of AOX in the skunk cabbage, Symplocarpus renifolius, we have performed expression and functional analyses of the encoding gene. Among the various tissues in the skunk cabbage, SrAOX transcripts were found to be specifically expressed in the thermogenic spadix. Moreover, our data demonstrate that the SrAOX protein exists as a non-covalently associated dimer in the thermogenic spadix, and is more sensitive to pyruvate than to other carboxylic acids. Our results suggest that the pyruvate-mediated modification of SrAOX activity plays a significant role in thermoregulation in the skunk cabbage.
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Affiliation(s)
- Yoshihiko Onda
- United Graduate School of Agricultural Science, Iwate University, Ueda, Morioka, Iwate 020 8550, Japan
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19
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Winger A, Millar A, Day D. Sensitivity of plant mitochondrial terminal oxidases to the lipid peroxidation product 4-hydroxy-2-nonenal (HNE). Biochem J 2006; 387:865-70. [PMID: 15689186 PMCID: PMC1135019 DOI: 10.1042/bj20042044] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
We have investigated the effect of the lipid peroxidation product, HNE (4-hydroxy-2-nonenal), on plant mitochondrial electron transport. In mitochondria isolated from Arabidopsis thaliana cell cultures, HNE inhibited succinate-dependent oxygen consumption via the Aox (alternative oxidase), but had minimal effect on respiration via Cox (cytochrome c oxidase). Maximal Cox activity, measured with reduced cytochrome c as substrate, was only slightly inhibited by high concentrations of HNE, at which Aox was completely inhibited. Incubation with HNE prevented dimerization of the Aox protein, suggesting that one site of modification was the conserved cysteine residue involved in dimerization and activation of this enzyme (Cys(I)). However, a naturally occurring isoform of Aox lacking Cys(I) and unable to be dimerized, LeAox1b from tomato (Lycopersicon esculentum), was equally sensitive to HNE inhibition, showing that other amino acid residues in Aox also interact with HNE. The presence of HNE in vivo in Arabidopsis cell cultures was also investigated. Induction of oxidative stress in the cell cultures by the addition of hydrogen peroxide, antimycin A or menadione, caused a significant increase in hydroxyalkenals (of which HNE is the most prominent). Western blotting of mitochondrial proteins with antibodies against HNE adducts, demonstrated significant modification of proteins during these treatments. The implications of these results for the response of plants to reactive oxygen species are discussed.
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Affiliation(s)
- Alison M. Winger
- Biochemistry and Molecular Biology, School of Biomedical and Chemical Sciences, The University of Western Australia, Crawley 6009, W.A., Australia
| | - A. Harvey Millar
- Biochemistry and Molecular Biology, School of Biomedical and Chemical Sciences, The University of Western Australia, Crawley 6009, W.A., Australia
| | - David A. Day
- Biochemistry and Molecular Biology, School of Biomedical and Chemical Sciences, The University of Western Australia, Crawley 6009, W.A., Australia
- To whom correspondence should be addressed. Present address: Faculty of Science, University of Sydney, Sydney, NSW 2006, Australia (email )
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20
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Umbach AL, Ng VS, Siedow JN. Regulation of plant alternative oxidase activity: A tale of two cysteines. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2006; 1757:135-42. [PMID: 16457775 DOI: 10.1016/j.bbabio.2005.12.005] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2005] [Revised: 12/14/2005] [Accepted: 12/19/2005] [Indexed: 11/21/2022]
Abstract
Two Cys residues, Cys(I) and Cys(II), are present in most plant alternative oxidases (AOXs). Cys(I) inactivates AOX by forming a disulfide bond with the corresponding Cys(I) residue on the adjacent subunit of the AOX homodimer. When reduced, Cys(I) associates with alpha-keto acids, such as pyruvate, to activate AOX, an effect mimicked by charged amino acid substitutions at the Cys(I) site. Cys(II) may also be a site of AOX activity regulation, through interaction with the small alpha-keto acid, glyoxylate. Comparison of Arabidopsis AOX1a (AtAOX1a) mutants with single or double substitutions at Cys(I) and Cys(II) confirmed that glyoxylate interacted with either Cys, while the effect of pyruvate (or succinate for AtAOX1a substituted with Ala at Cys(I)) was limited to Cys(I). A variety of Cys(II) substitutions constitutively activated AtAOX1a, indicating that neither the catalytic site nor, unlike at Cys(I), charge repulsion is involved. Independent effects at each Cys were suggested by lack of Cys(II) substitution interference with pyruvate stimulation at Cys(I), and close to additive activation at the two sites. However, results obtained using diamide treatment to covalently link the AtAOX1a subunits by the disulfide bond indicated that Cys(I) must be in the reduced state for activation at Cys(II) to occur.
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Affiliation(s)
- Ann L Umbach
- DCMB Group/Biology Department, Box 91000, Duke University, Durham, NC 27708-1000, USA.
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21
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Crichton PG, Affourtit C, Albury MS, Carré JE, Moore AL. Constitutive activity ofSauromatum guttatumalternative oxidase inSchizosaccharomyces pombeimplicates residues in addition to conserved cysteines in α-keto acid activation. FEBS Lett 2004; 579:331-6. [PMID: 15642340 DOI: 10.1016/j.febslet.2004.10.107] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2004] [Revised: 10/18/2004] [Accepted: 10/28/2004] [Indexed: 10/26/2022]
Abstract
Activity of the plant mitochondrial alternative oxidase (AOX) can be regulated by organic acids, notably pyruvate. To date, only two well-conserved cysteine residues have been implicated in this process. We report the functional expression of two AOX isozymes (Sauromatum guttatum Sg-AOX and Arabidopsis thaliana At-AOX1a) in Schizosaccharomyces pombe. Comparison of the response of these two isozymes to pyruvate in isolated yeast mitochondria and disrupted mitochondrial membranes reveals that in contrast to At-AOX1a, Sg-AOX activity is insensitive to pyruvate and appears to be in a constitutively active state. As both of these isozymes conserve the two cysteines, we propose that such contrasting behaviour must be a direct result of differences in their amino acid sequence and have subsequently identified novel candidate residues.
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Affiliation(s)
- Paul G Crichton
- Department of Biochemistry, School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, UK
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22
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Finnegan PM, Soole KL, Umbach AL. Alternative Mitochondrial Electron Transport Proteins in Higher Plants. PLANT MITOCHONDRIA: FROM GENOME TO FUNCTION 2004. [DOI: 10.1007/978-1-4020-2400-9_9] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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23
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Holtzapffel RC, Castelli J, Finnegan PM, Millar AH, Whelan J, Day DA. A tomato alternative oxidase protein with altered regulatory properties. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2003; 1606:153-62. [PMID: 14507436 DOI: 10.1016/s0005-2728(03)00112-9] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
We have investigated the expression and regulatory properties of the two alternative oxidase (Aox) proteins that are expressed in tomato (Lycopersicon esculentum L. Mill cv. Sweetie) after storage of green fruit at 4 degrees C. Four Aox genes were identified in the tomato genome, of which two (LeAox1a and LeAox1b) were demonstrated to be expressed in cold-treated fruit. The activity and regulatory properties of LeAox1a and LeAox1b were assayed after expression of each protein in yeast cells (Saccharomyces cerevisiae), proving that each is an active Aox protein. The LeAox1b protein was shown to have altered regulatory properties due to the substitution of a Ser for the highly conserved Cys(I) residue. LeAox1b could not form inactive disulfide-linked dimers and was activated by succinate instead of pyruvate. This is the first example of a dicot species expressing a natural Cys(I)/Ser isoform. The implications of the existence and expression of such Aox isoforms is discussed in the light of the hypothesised role for Aox in plant metabolism.
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Affiliation(s)
- Ruth C Holtzapffel
- Plant Molecular Biology Group, Biochemistry and Molecular Biology, School of Biomedical and Chemical Sciences, The University of Western Australia, 35 Stirling Highway, Crawley 6009, WA, Australia
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24
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Stenmark P, Nordlund P. A prokaryotic alternative oxidase present in the bacteriumNovosphingobium aromaticivorans. FEBS Lett 2003; 552:189-92. [PMID: 14527685 DOI: 10.1016/s0014-5793(03)00920-7] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The alternative oxidase (AOX) is a terminal oxidase present in the respiratory chain of all plants as well as some yeasts and trypanosomes, but has not previously been found in a prokaryote. We have identified an AOX homologue in Novosphingobium aromaticivorans, the first AOX found in a prokaryote. We have cloned the gene for the N. aromaticivorans AOX and showed it to have a terminal oxidase activity when heterologously expressed in Escherichia coli. We have also shown that this novel AOX is expressed in N. aromaticivorans cells, and that its expression level is greatly influenced by the oxygen level and carbon source of the growth media.
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Affiliation(s)
- Pål Stenmark
- Department of Biochemistry and Biophysics, Stockholm University, Roslagstullsbacken 15, Albanova University Center, SE-10691 Stockholm, Sweden
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25
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Abstract
Four proteins have been identified recently as diiron carboxylate proteins on the basis of conservation of six amino acids (four carboxylate residues and two histidines) constituting an iron-binding motif. Unlike previously identified proteins with this motif, biochemical studies indicate that each of these proteins is membrane bound, although homology modeling rules out a transmembrane mode of binding. Therefore, the predicted structure of each protein [the alternative oxidase (AOX), the plastid terminal oxidase (PTOX), the diiron 5-demethoxyquinone hydroxylase (DMQ hydroxylase), and the aerobic Mg-protoporphyrin IX monomethylester hydroxylase (MME hydroxylase)] is that of a protein bound monotopically to one leaflet of the membrane bilayer. Three of these enzymes utilize a quinol substrate, with two oxidizing the quinol (AOX and PTOX) and one hydroxylating it (DMQ hydroxylase). MME hydroxylase is involved in synthesis of the isocyclic ring of chlorophyll. Two enzymes are involved in respiration (AOX and, indirectly, the diiron DMQ hydroxylase through ubiquinone biosynthesis) and two in photosynthesis, through their roles in carotenoid and chlorophyll biosynthesis (PTOX and MME hydroxylase, respectively). We discuss what is known about each enzyme as well as our expectations based on their identification as interfacially bound proteins with a diiron carboxylate active site.
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Affiliation(s)
- Deborah A Berthold
- Department of Biochemistry and Biophysics, Arrhenius Laboratory for Natural Sciences, Stockholm University, Svante Arrhenius väg 12, SE-106 91 Stockholm, Sweden.
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26
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Berthold DA, Voevodskaya N, Stenmark P, Gräslund A, Nordlund P. EPR studies of the mitochondrial alternative oxidase. Evidence for a diiron carboxylate center. J Biol Chem 2002; 277:43608-14. [PMID: 12215444 DOI: 10.1074/jbc.m206724200] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The alternative oxidase (AOX) is a ubiquinol oxidase found in the mitochondrial respiratory chain of plants as well as some fungi and protists. It has been predicted to contain a coupled diiron center on the basis of a conserved sequence motif consisting of the proposed iron ligands, four glutamate and two histidine residues. However, this prediction has not been experimentally verified. Here we report the high level expression of the Arabidopsis thaliana alternative oxidase AOX1a as a maltose-binding protein fusion in Escherichia coli. Reduction and reoxidation of a sample of isolated E. coli membranes containing the alternative oxidase generated an EPR signal characteristic of a mixed-valent Fe(II)/Fe(III) binuclear iron center. The high anisotropy of the signal, the low value of the g-average tensor, and a small exchange coupling (-J) suggest that the iron center is hydroxo-bridged. A reduced membrane preparation yielded a parallel mode EPR signal with a g-value of about 15. In AOX containing a mutation of a putative glutamate ligand of the diiron center (E222A or E273A) the EPR signals are absent. These data provide evidence for an antiferromagnetic-coupled binuclear iron center, and together with the conserved sequence motif, identify the alternative oxidase as belonging to the growing family of diiron carboxylate proteins. The alternative oxidase is the first integral membrane protein in this family, and adds a new catalytic activity (ubiquinol oxidation) to this group of enzymatically diverse proteins.
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Affiliation(s)
- Deborah A Berthold
- Department of Biochemistry and Biophysics, Stockholm University Svante Arrhenius väg 16, Sweden.
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27
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Umbach AL, Gonzàlez-Meler MA, Sweet CR, Siedow JN. Activation of the plant mitochondrial alternative oxidase: insights from site-directed mutagenesis. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1554:118-28. [PMID: 12034477 DOI: 10.1016/s0005-2728(02)00219-0] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The homodimeric cyanide-resistant alternative oxidase of plant mitochondria reduces oxygen to water without forming ATP. Arabidopsis thaliana alternative oxidase AOX1a is stimulated by pyruvate or other alpha-keto acids associating with a regulatory cysteine at position 78, by succinate in a serine-78 mutant, and by site-directed mutation of position 78 to glutamate. The mechanism of activation was explored with additional amino acid substitutions made at Cys-78 in AOX1a, which was functionally expressed in Escherichia coli. Oxidases with positively charged substitutions (Lys and Arg) were insensitive to pyruvate or succinate but were more active than the wild type without pyruvate. Uncharged substitutions (Gln, Leu) produced an inactive enzyme. These results indicate that activation may be due to conformational changes caused by charge repulsion between the dimer subunits and not through a direct role of alpha-keto acids in catalysis. Oxygen isotope fractionation experiments suggest that the charge of the amino acid at position 78 also affects the entry of oxygen into the active site. Therefore, the N-terminal portion of the protein containing residue 78 can indirectly affect both catalysis at the diiron active site and the path of oxygen to that site. In addition, both positively and negatively substituted alternative oxidases were stimulated by glyoxylate, suggesting the presence of a second activation site, possibly Cys-128.
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Affiliation(s)
- Ann L Umbach
- DCMB Group/Biology Department, Box 91000, Duke University, Durham, NC 27708, USA.
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28
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Affourtit C, Albury MS, Crichton PG, Moore AL. Exploring the molecular nature of alternative oxidase regulation and catalysis. FEBS Lett 2002; 510:121-6. [PMID: 11801238 DOI: 10.1016/s0014-5793(01)03261-6] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Plant mitochondria contain a non-protonmotive alternative oxidase (AOX) that couples the oxidation of ubiquinol to the complete reduction of oxygen to water. In this paper we review theoretical and experimental studies that have contributed to our current structural and mechanistic understanding of the oxidase and to the clarification of the molecular nature of post-translational regulatory phenomena. Furthermore, we suggest a catalytic cycle for AOX that involves at least one transient protein-derived radical. The model is based on the reviewed information and on recent insights into the mechanisms of cytochrome c oxidase and the hydroxylase component of methane monooxygenase.
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Affiliation(s)
- Charles Affourtit
- Department of Biochemistry, University of Sussex, Falmer, Brighton BN1 9QG, UK.
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29
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Vanlerberghe GC, Ordog SH. Alternative Oxidase: Integrating Carbon Metabolism and Electron Transport in Plant Respiration. ADVANCES IN PHOTOSYNTHESIS AND RESPIRATION 2002. [DOI: 10.1007/0-306-48138-3_11] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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30
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Considine MJ, Daley DO, Whelan J. The expression of alternative oxidase and uncoupling protein during fruit ripening in mango. PLANT PHYSIOLOGY 2001; 126:1619-29. [PMID: 11500560 PMCID: PMC117161 DOI: 10.1104/pp.126.4.1619] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2001] [Accepted: 05/07/2001] [Indexed: 05/19/2023]
Abstract
The expression of alternative oxidase (Aox) and uncoupling proteins (Ucp) was investigated during ripening in mango (Mangifera indica) and compared with the expression of peroxisomal thiolase, a previously described ripening marker in mango. The multigene family for the Aox in mango was expressed differentially during ripening. Abundance of Aox message and protein both peaked at the ripe stage. Expression of the single gene for the Ucp peaked at the turning stage and the protein abundance peaked at the ripe stage. Proteins of the cytochrome chain peaked at the mature stage of ripening. The pattern of protein accumulation suggested that increases in cytochrome chain components played an important role in facilitating the climacteric burst of respiration and that the Aox and Ucp may play a role in post-climacteric senescent processes. Because both message and protein for the Aox and Ucp increased in a similar pattern, it suggests that their expression is not controlled in a reciprocal manner but may be active simultaneously.
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Affiliation(s)
- M J Considine
- Department of Biochemistry, The University of Western Australia, Nedlands, Western Australia 6907, Australia
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31
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Karaffa L, Váczy K, Sándor E, Biró S, Szentirmai A, Pócsi I. Cyanide-resistant alternative respiration is strictly correlated to intracellular peroxide levels in Acremonium chrysogenum. Free Radic Res 2001; 34:405-16. [PMID: 11328676 DOI: 10.1080/10715760100300341] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
A strict correlation between the intensity of the cyanide-resistant alternative respiratory pathway and the intracellular peroxide levels in the cephalosporin C producer filamentous fungus Acremonium chrysogenum was demonstrated. Intracellular peroxide levels increased in a dose-dependent manner after addition of H2O2 to the culture media. A similar phenomenon was observed due to the specific inhibition of catalase by salicylic acid. In both cases, cyanide-resistant respiration was markedly stimulated. On the other hand, both cyanide-resistant respiration and intracellular peroxide levels were effectively suppressed by the lipid peroxyl radical scavenger DL-alpha-tocopherol, which breaks lipid peroxidation chains effectively. Our findings firmly supported the assumption that there is a connection between the intracellular peroxide levels and the intensity of the alternative respiratory pathway in fungi.
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Affiliation(s)
- L Karaffa
- Department of Microbiology and Biotechnology Faculty of Sciences University of Debrecen P.O. Box 63, H-4010, Debrecen, Hungary.
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32
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Berthold DA, Andersson ME, Nordlund P. New insight into the structure and function of the alternative oxidase. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1460:241-54. [PMID: 11106766 DOI: 10.1016/s0005-2728(00)00149-3] [Citation(s) in RCA: 158] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The alternative oxidase is a ubiquinol oxidase found in plant mitochondria, as well as in the mitochondria of some fungi and protists. It catalyzes a cyanide-resistant reduction of oxygen to water without translocation of protons across the inner mitochondrial membrane, and thus functions as a non-energy-conserving member of the respiratory electron transfer chain. The active site of the alternative oxidase has been modelled as a diiron center within a four-helix bundle by Siedow et al. (FEBS Lett. 362 (1995) 10-14) and more recently by Andersson and Nordlund (FEBS Lett. 449 (1999) 17-22). The cloning of the Arabidopsis thaliana IMMUTANS (Im) gene, which encodes a plastid enzyme distantly related to the mitochondrial alternative oxidases (Wu et al. Plant Cell 11 (1999) 43-55; Carol et al. Plant Cell 11 (1999) 57-68), has now narrowed the range of possible ligands to the diiron center of the alternative oxidase. The Im protein sequence suggests a minor modification to the recent model of the active site of the alternative oxidase. This change moves an invariant tyrosine into a conserved hydrophobic pocket in the vicinity of the active site, in a position analogous to the long-lived tyrosine radical at the diiron center of ribonucleotide reductase, and similar to the tyrosines near the diiron center of bacterioferritin and rubrerythrin. The Im sequence and modified structural model yield a compelling picture of the alternative oxidase as a diiron carboxylate protein. The current status of the relationship of structure to function in the alternative oxidase is reviewed.
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Affiliation(s)
- D A Berthold
- Department of Biochemistry, Stockholm University, Svante Arrhenius vag 16, S-106 91, Stockholm, Sweden
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Joseph-Horne T, Babij J, Wood PM, Hollomon D, Sessions RB. New sequence data enable modelling of the fungal alternative oxidase and explain an absence of regulation by pyruvate. FEBS Lett 2000; 481:141-6. [PMID: 10996313 DOI: 10.1016/s0014-5793(00)01943-8] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Respiratory rates involving the alternative oxidase (AO) were studied in mitochondria from Tapesia acuformis. There was no evidence for regulation by pyruvate, in contrast with plant AO. The site of interaction of pyruvate with the plant AO is a conserved cysteine. The primary sequence was obtained for AO from Magnaporthe grisea and compared with four published sequences for fungal AO. In all cases this cysteine was absent. Sequence data were obtained for the C-terminal domain of a further five fungal AOs. In this region the fungal sequences were all consistent with a four-helix, di-iron binding structure as in the ferritin-fold family. A molecular model of this domain was deduced from the structure of Delta-9 desaturase. This is in general agreement with that developed for plant AOs, despite very low sequence identity between the two kingdoms. Further modelling indicated an appropriate active site for binding of ubiquinol, required in the AO redox reaction.
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Affiliation(s)
- T Joseph-Horne
- Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol, UK
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Siedow JN, Umbach AL. The mitochondrial cyanide-resistant oxidase: structural conservation amid regulatory diversity. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1459:432-9. [PMID: 11004460 DOI: 10.1016/s0005-2728(00)00181-x] [Citation(s) in RCA: 139] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Mitochondria from all plants, many fungi and some protozoa contain a cyanide-resistant, alternative oxidase that functions in parallel with cytochrome c oxidase as the terminal oxidase on the electron transfer chain. Characterization of the structural and potential regulatory features of the alternative oxidase has advanced considerably in recent years. The active site is proposed to contain a di-iron center belonging to the ribonucleotide reductase R2 family and modeling of a four-helix bundle to accommodate this active site within the C-terminal two-thirds of the protein has been carried out. The structural features of this active site are conserved among all known alternative oxidases. The post-translational regulatory features of the alternative oxidase are more variable among organisms. The plant oxidase is dimeric and can be stimulated by either alpha-keto acids or succinate, depending upon the presence or absence, respectively, of a critical cysteine residue found in a conserved block of amino acids in the N-terminal region of the plant protein. The fungal and protozoan alternative oxidases generally exist as monomers and are not subject to organic acid stimulation but can be stimulated by purine nucleotides. The origins of these diverse regulatory features remain unknown but are correlated with sequence differences in the N-terminal third of the protein.
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Affiliation(s)
- J N Siedow
- DCMB/Biology, Box 91000, Duke University, Durham, NC 27708-1000, USA.
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Umbach AL, Siedow JN. The cyanide-resistant alternative oxidases from the fungi Pichia stipitis and Neurospora crassa are monomeric and lack regulatory features of the plant enzyme. Arch Biochem Biophys 2000; 378:234-45. [PMID: 10860541 DOI: 10.1006/abbi.2000.1834] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Both plant and fungal mitochondria have cyanide-resistant alternative oxidases that use reductant from the mitochondrial ubiquinone pool to reduce oxygen to water in a reaction that conserves no energy for ATP synthesis. The dimeric plant alternative oxidase is relatively inactive when its subunits are linked by a disulfide bond. When this bond is reduced, the enzyme can then be stimulated by its activators, alpha-keto acids. A Cys in the N-terminal section of the protein is responsible for both of these features. We examined the alternative oxidases in mitochondria isolated from two fungi Neurospora crassa and Pichia stipitis for dimeric structure, ability to form an intermolecular disulfide, and sensitivity to alpha-keto acids. Neither of the two fungal alternative oxidases could be covalently linked by diamide, which induces disulfide bond formation between nearby Cys residues, nor could they be cross-linked by a Lys-specific reagent or glutaraldehyde at concentrations which cross-link the plant alternative oxidase dimer completely. Alternative oxidase activity in fungal mitochondria was not stimulated by the alpha-keto acids pyruvate and glyoxylate. Pyruvate did stimulate activity when succinate was the respiratory substrate, but this was not a direct effect on the alternative oxidase. In contrast, added GMP was a strong activator of fungal alternative oxidase activity. Analysis of plant and fungal alternative oxidase protein sequences revealed a unique domain of about 40 amino acids surrounding the regulatory Cys in the plant sequences that is not present in the fungal sequences. This domain may be where dimerization of the plant enzymes occurs. In contrast to plant enzymes, the fungal alternative oxidases studied here are monomeric and their activities are independent of alpha-keto acids.
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Affiliation(s)
- A L Umbach
- DCMB Group/Botany Department, Duke University, Durham, North Carolina 27708, USA
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