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Heidorn-Czarna M, Maziak A, Janska H. Protein Processing in Plant Mitochondria Compared to Yeast and Mammals. FRONTIERS IN PLANT SCIENCE 2022; 13:824080. [PMID: 35185991 PMCID: PMC8847149 DOI: 10.3389/fpls.2022.824080] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2021] [Accepted: 01/12/2022] [Indexed: 05/02/2023]
Abstract
Limited proteolysis, called protein processing, is an essential post-translational mechanism that controls protein localization, activity, and in consequence, function. This process is prevalent for mitochondrial proteins, mainly synthesized as precursor proteins with N-terminal sequences (presequences) that act as targeting signals and are removed upon import into the organelle. Mitochondria have a distinct and highly conserved proteolytic system that includes proteases with sole function in presequence processing and proteases, which show diverse mitochondrial functions with limited proteolysis as an additional one. In virtually all mitochondria, the primary processing of N-terminal signals is catalyzed by the well-characterized mitochondrial processing peptidase (MPP). Subsequently, a second proteolytic cleavage occurs, leading to more stabilized residues at the newly formed N-terminus. Lately, mitochondrial proteases, intermediate cleavage peptidase 55 (ICP55) and octapeptidyl protease 1 (OCT1), involved in proteolytic cleavage after MPP and their substrates have been described in the plant, yeast, and mammalian mitochondria. Mitochondrial proteins can also be processed by removing a peptide from their N- or C-terminus as a maturation step during insertion into the membrane or as a regulatory mechanism in maintaining their function. This type of limited proteolysis is characteristic for processing proteases, such as IMP and rhomboid proteases, or the general mitochondrial quality control proteases ATP23, m-AAA, i-AAA, and OMA1. Identification of processing protease substrates and defining their consensus cleavage motifs is now possible with the help of large-scale quantitative mass spectrometry-based N-terminomics, such as combined fractional diagonal chromatography (COFRADIC), charge-based fractional diagonal chromatography (ChaFRADIC), or terminal amine isotopic labeling of substrates (TAILS). This review summarizes the current knowledge on the characterization of mitochondrial processing peptidases and selected N-terminomics techniques used to uncover protease substrates in the plant, yeast, and mammalian mitochondria.
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Ghifari AS, Huang S, Murcha MW. The peptidases involved in plant mitochondrial protein import. JOURNAL OF EXPERIMENTAL BOTANY 2019; 70:6005-6018. [PMID: 31738432 DOI: 10.1093/jxb/erz365] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/01/2019] [Accepted: 08/08/2019] [Indexed: 05/17/2023]
Abstract
The endosymbiotic origin of the mitochondrion and the subsequent transfer of its genome to the host nucleus has resulted in intricate mechanisms of regulating mitochondrial biogenesis and protein content. The majority of mitochondrial proteins are nuclear encoded and synthesized in the cytosol, thus requiring specialized and dedicated machinery for the correct targeting import and sorting of its proteome. Most proteins targeted to the mitochondria utilize N-terminal targeting signals called presequences that are cleaved upon import. This cleavage is carried out by a variety of peptidases, generating free peptides that can be detrimental to organellar and cellular activity. Research over the last few decades has elucidated a range of mitochondrial peptidases that are involved in the initial removal of the targeting signal and its sequential degradation, allowing for the recovery of single amino acids. The significance of these processing pathways goes beyond presequence degradation after protein import, whereby the deletion of processing peptidases induces plant stress responses, compromises mitochondrial respiratory capability, and alters overall plant growth and development. Here, we review the multitude of plant mitochondrial peptidases that are known to be involved in protein import and processing of targeting signals to detail how their activities can affect organellar protein homeostasis and overall plant growth.
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Affiliation(s)
- Abi S Ghifari
- School of Molecular Sciences, The University of Western Australia, 35 Stirling Highway, Perth WA, Australia
- ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia, 35 Stirling Highway, Perth WA, Australia
| | - Shaobai Huang
- School of Molecular Sciences, The University of Western Australia, 35 Stirling Highway, Perth WA, Australia
- ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia, 35 Stirling Highway, Perth WA, Australia
| | - Monika W Murcha
- School of Molecular Sciences, The University of Western Australia, 35 Stirling Highway, Perth WA, Australia
- ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia, 35 Stirling Highway, Perth WA, Australia
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Plant mitochondrial protein import: the ins and outs. Biochem J 2018; 475:2191-2208. [PMID: 30018142 DOI: 10.1042/bcj20170521] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2018] [Revised: 06/19/2018] [Accepted: 06/21/2018] [Indexed: 01/29/2023]
Abstract
The majority of the mitochondrial proteome, required to fulfil its diverse range of functions, is cytosolically synthesised and translocated via specialised machinery. The dedicated translocases, receptors, and associated proteins have been characterised in great detail in yeast over the last several decades, yet many of the mechanisms that regulate these processes in higher eukaryotes are still unknown. In this review, we highlight the current knowledge of mitochondrial protein import in plants. Despite the fact that the mechanisms of mitochondrial protein import have remained conserved across species, many unique features have arisen in plants to encompass the developmental, tissue-specific, and stress-responsive regulation in planta. An understanding of unique features and mechanisms in plants provides us with a unique insight into the regulation of mitochondrial biogenesis in higher eukaryotes.
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Kolli R, Soll J, Carrie C. Plant Mitochondrial Inner Membrane Protein Insertion. Int J Mol Sci 2018; 19:E641. [PMID: 29495281 PMCID: PMC5855863 DOI: 10.3390/ijms19020641] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2018] [Revised: 02/20/2018] [Accepted: 02/22/2018] [Indexed: 02/06/2023] Open
Abstract
During the biogenesis of the mitochondrial inner membrane, most nuclear-encoded inner membrane proteins are laterally released into the membrane by the TIM23 and the TIM22 machinery during their import into mitochondria. A subset of nuclear-encoded mitochondrial inner membrane proteins and all the mitochondrial-encoded inner membrane proteins use the Oxa machinery-which is evolutionarily conserved from the endosymbiotic bacterial ancestor of mitochondria-for membrane insertion. Compared to the mitochondria from other eukaryotes, plant mitochondria have several unique features, such as a larger genome and a branched electron transport pathway, and are also involved in additional cellular functions such as photorespiration and stress perception. This review focuses on the unique aspects of plant mitochondrial inner membrane protein insertion machinery, which differs from that in yeast and humans, and includes a case study on the biogenesis of Cox2 in yeast, humans, two plant species, and an algal species to highlight lineage-specific similarities and differences. Interestingly, unlike mitochondria of other eukaryotes but similar to bacteria and chloroplasts, plant mitochondria appear to use the Tat machinery for membrane insertion of the Rieske Fe/S protein.
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Affiliation(s)
- Renuka Kolli
- Department of Biology I, Botany, Ludwig-Maximilians-Universität München, Großhaderner Strasse 2-4, D-82152 Planegg-Martinsried, Germany.
| | - Jürgen Soll
- Department of Biology I, Botany, Ludwig-Maximilians-Universität München, Großhaderner Strasse 2-4, D-82152 Planegg-Martinsried, Germany.
- Munich Center for Integrated Protein Science, CiPSM, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, D-81377 Munich, Germany.
| | - Chris Carrie
- Department of Biology I, Botany, Ludwig-Maximilians-Universität München, Großhaderner Strasse 2-4, D-82152 Planegg-Martinsried, Germany.
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Lee CP, Maksaev G, Jensen GS, Murcha MW, Wilson ME, Fricker M, Hell R, Haswell ES, Millar AH, Sweetlove LJ. MSL1 is a mechanosensitive ion channel that dissipates mitochondrial membrane potential and maintains redox homeostasis in mitochondria during abiotic stress. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2016; 88:809-825. [PMID: 27505616 PMCID: PMC5195915 DOI: 10.1111/tpj.13301] [Citation(s) in RCA: 58] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Revised: 08/04/2016] [Accepted: 08/05/2016] [Indexed: 05/18/2023]
Abstract
Mitochondria must maintain tight control over the electrochemical gradient across their inner membrane to allow ATP synthesis while maintaining a redox-balanced electron transport chain and avoiding excessive reactive oxygen species production. However, there is a scarcity of knowledge about the ion transporters in the inner mitochondrial membrane that contribute to control of membrane potential. We show that loss of MSL1, a member of a family of mechanosensitive ion channels related to the bacterial channel MscS, leads to increased membrane potential of Arabidopsis mitochondria under specific bioenergetic states. We demonstrate that MSL1 localises to the inner mitochondrial membrane. When expressed in Escherichia coli, MSL1 forms a stretch-activated ion channel with a slight preference for anions and provides protection against hypo-osmotic shock. In contrast, loss of MSL1 in Arabidopsis did not prevent swelling of isolated mitochondria in hypo-osmotic conditions. Instead, our data suggest that ion transport by MSL1 leads to dissipation of mitochondrial membrane potential when it becomes too high. The importance of MSL1 function was demonstrated by the observation of a higher oxidation state of the mitochondrial glutathione pool in msl1-1 mutants under moderate heat- and heavy-metal-stress. Furthermore, we show that MSL1 function is not directly implicated in mitochondrial membrane potential pulsing, but is complementary and appears to be important under similar conditions.
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Affiliation(s)
- Chun Pong Lee
- ARC Centre of Excellence in Plant Energy Biology, University of Western Australia, Bayliss Building M316, 35 Stirling Highway, Crawley, 6009, Western Australia, Australia
| | - Grigory Maksaev
- Department of Biology, Washington University in Saint Louis, One Brookings Drive, Mailcode 1137, Saint Louis, MO, 63130, USA
| | - Gregory S Jensen
- Department of Biology, Washington University in Saint Louis, One Brookings Drive, Mailcode 1137, Saint Louis, MO, 63130, USA
| | - Monika W Murcha
- ARC Centre of Excellence in Plant Energy Biology, University of Western Australia, Bayliss Building M316, 35 Stirling Highway, Crawley, 6009, Western Australia, Australia
| | - Margaret E Wilson
- Department of Biology, Washington University in Saint Louis, One Brookings Drive, Mailcode 1137, Saint Louis, MO, 63130, USA
| | - Mark Fricker
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK
| | - Ruediger Hell
- Department of Plant Molecular Biology, Centre for Organismal Studies, University of Heidelberg, Im Neuenheimer Feld 360, D-69120, Heidelberg, Germany
| | - Elizabeth S Haswell
- Department of Biology, Washington University in Saint Louis, One Brookings Drive, Mailcode 1137, Saint Louis, MO, 63130, USA
| | - A Harvey Millar
- ARC Centre of Excellence in Plant Energy Biology, University of Western Australia, Bayliss Building M316, 35 Stirling Highway, Crawley, 6009, Western Australia, Australia
| | - Lee J Sweetlove
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK
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Murcha MW, Kmiec B, Kubiszewski-Jakubiak S, Teixeira PF, Glaser E, Whelan J. Protein import into plant mitochondria: signals, machinery, processing, and regulation. JOURNAL OF EXPERIMENTAL BOTANY 2014; 65:6301-35. [PMID: 25324401 DOI: 10.1093/jxb/eru399] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The majority of more than 1000 proteins present in mitochondria are imported from nuclear-encoded, cytosolically synthesized precursor proteins. This impressive feat of transport and sorting is achieved by the combined action of targeting signals on mitochondrial proteins and the mitochondrial protein import apparatus. The mitochondrial protein import apparatus is composed of a number of multi-subunit protein complexes that recognize, translocate, and assemble mitochondrial proteins into functional complexes. While the core subunits involved in mitochondrial protein import are well conserved across wide phylogenetic gaps, the accessory subunits of these complexes differ in identity and/or function when plants are compared with Saccharomyces cerevisiae (yeast), the model system for mitochondrial protein import. These differences include distinct protein import receptors in plants, different mechanistic operation of the intermembrane protein import system, the location and activity of peptidases, the function of inner-membrane translocases in linking the outer and inner membrane, and the association/regulation of mitochondrial protein import complexes with components of the respiratory chain. Additionally, plant mitochondria share proteins with plastids, i.e. dual-targeted proteins. Also, the developmental and cell-specific nature of mitochondrial biogenesis is an aspect not observed in single-celled systems that is readily apparent in studies in plants. This means that plants provide a valuable model system to study the various regulatory processes associated with protein import and mitochondrial biogenesis.
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Affiliation(s)
- Monika W Murcha
- Australian Research Council Centre of Excellence in Plant Energy Biology, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia, 6009, Australia
| | - Beata Kmiec
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, SE-10691 Stockholm, Sweden
| | - Szymon Kubiszewski-Jakubiak
- Australian Research Council Centre of Excellence in Plant Energy Biology, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia, 6009, Australia
| | - Pedro F Teixeira
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, SE-10691 Stockholm, Sweden
| | - Elzbieta Glaser
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, SE-10691 Stockholm, Sweden
| | - James Whelan
- Australian Research Council Centre of Excellence in Plant Energy Biology, School of Life Science, La Trobe University, Bundoora, Victoria, 3086, Australia
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Murcha MW, Wang Y, Narsai R, Whelan J. The plant mitochondrial protein import apparatus - the differences make it interesting. Biochim Biophys Acta Gen Subj 2013; 1840:1233-45. [PMID: 24080405 DOI: 10.1016/j.bbagen.2013.09.026] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Revised: 09/17/2013] [Accepted: 09/18/2013] [Indexed: 12/25/2022]
Abstract
BACKGROUND Mitochondria play essential roles in the life and death of almost all eukaryotic cells, ranging from single-celled to multi-cellular organisms that display tissue and developmental differentiation. As mitochondria only arose once in evolution, much can be learned from studying single celled model systems such as yeast and applying this knowledge to other organisms. However, two billion years of evolution have also resulted in substantial divergence in mitochondrial function between eukaryotic organisms. SCOPE OF REVIEW Here we review our current understanding of the mechanisms of mitochondrial protein import between plants and yeast (Saccharomyces cerevisiae) and identify a high level of conservation for the essential subunits of plant mitochondrial import apparatus. Furthermore, we investigate examples whereby divergence and acquisition of functions have arisen and highlight the emerging examples of interactions between the import apparatus and components of the respiratory chain. MAJOR CONCLUSIONS After more than three decades of research into the components and mechanisms of mitochondrial protein import of plants and yeast, the differences between these systems are examined. Specifically, expansions of the small gene families that encode the mitochondrial protein import apparatus in plants are detailed, and their essential role in seed viability is revealed. GENERAL SIGNIFICANCE These findings point to the essential role of the inner mitochondrial protein translocases in Arabidopsis, establishing their necessity for seed viability and the crucial role of mitochondrial biogenesis during germination. This article is part of a Special Issue entitled Frontiers of Mitochondrial Research.
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Affiliation(s)
- Monika W Murcha
- ARC Centre of Excellence in Plant Energy Biology, Bayliss Building M316, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia.
| | - Yan Wang
- ARC Centre of Excellence in Plant Energy Biology, Bayliss Building M316, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia
| | - Reena Narsai
- ARC Centre of Excellence in Plant Energy Biology, Bayliss Building M316, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia; Computational Systems Biology, Bayliss Building M316, The University of Western Australia, 35 Stirling Highway, Crawley 6009, Western Australia, Australia
| | - James Whelan
- ARC Centre of Excellence in Plant Energy Biology, Bayliss Building M316, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia; Department of Botany, School of Life Science, La Trobe University, Bundoora 3086, Victoria, Australia
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Zhang B, Carrie C, Ivanova A, Narsai R, Murcha MW, Duncan O, Wang Y, Law SR, Albrecht V, Pogson B, Giraud E, Van Aken O, Whelan J. LETM proteins play a role in the accumulation of mitochondrially encoded proteins in Arabidopsis thaliana and AtLETM2 displays parent of origin effects. J Biol Chem 2012; 287:41757-73. [PMID: 23043101 PMCID: PMC3516725 DOI: 10.1074/jbc.m112.383836] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2012] [Revised: 10/01/2012] [Indexed: 11/06/2022] Open
Abstract
The Arabidopsis thaliana genome contains two genes with homology to the mitochondrial protein LETM1 (leucine zipper-EF-hand-containing transmembrane protein). Inactivation of both genes, Atletm1 and Atletm2, together is lethal. Plants that are hemizygous for AtLETM2 and homozygous for Atletm1 (letm1(-/-) LETM2(+/-)) displayed a mild retarded growth phenotype during early seedling growth. It was shown that accumulation of mitochondrial proteins was reduced in hemizygous (letm1(-/-) LETM2(+/-)) plants. Examination of respiratory chain proteins by Western blotting, blue native PAGE, and enzymatic activity assays revealed that the steady state level of ATP synthase was reduced in abundance, whereas the steady state levels of other respiratory chain proteins remained unchanged. The absence of a functional maternal AtLETM2 allele in an Atletm1 mutant background resulted in early seed abortion. Reciprocal crosses revealed that maternally, but not paternally, derived AtLETM2 was absolutely required for seed development. This requirement for a functional maternal allele of AtLETM2 was confirmed using direct sequencing of reciprocal crosses of Col-0 and Ler accessions. Furthermore, AtLETM2 promoter β-glucuronidase constructs displayed exclusive maternal expression patterns.
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Affiliation(s)
- Botao Zhang
- From the Australian Research Council Centre of Excellence in Plant Energy Biology and
| | - Chris Carrie
- From the Australian Research Council Centre of Excellence in Plant Energy Biology and
| | - Aneta Ivanova
- From the Australian Research Council Centre of Excellence in Plant Energy Biology and
| | - Reena Narsai
- From the Australian Research Council Centre of Excellence in Plant Energy Biology and
- Centre for Computational Systems Biology, Bayliss Building M316 University of Western Australia, 35 Stirling Highway, Crawley 6009, Western Australia, Australia and
| | - Monika W. Murcha
- From the Australian Research Council Centre of Excellence in Plant Energy Biology and
| | - Owen Duncan
- From the Australian Research Council Centre of Excellence in Plant Energy Biology and
| | - Yan Wang
- From the Australian Research Council Centre of Excellence in Plant Energy Biology and
| | - Simon R. Law
- From the Australian Research Council Centre of Excellence in Plant Energy Biology and
| | - Verónica Albrecht
- the Australian Research Council Centre of Excellence in Plant Energy Biology, Research School of Biology, Australian National University, Acton 2601, Australian Capital Territory, Australia
| | - Barry Pogson
- the Australian Research Council Centre of Excellence in Plant Energy Biology, Research School of Biology, Australian National University, Acton 2601, Australian Capital Territory, Australia
| | - Estelle Giraud
- From the Australian Research Council Centre of Excellence in Plant Energy Biology and
| | - Olivier Van Aken
- From the Australian Research Council Centre of Excellence in Plant Energy Biology and
| | - James Whelan
- From the Australian Research Council Centre of Excellence in Plant Energy Biology and
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Duncan O, Murcha MW, Whelan J. Unique components of the plant mitochondrial protein import apparatus. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2012; 1833:304-13. [PMID: 22406071 DOI: 10.1016/j.bbamcr.2012.02.015] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2012] [Revised: 02/21/2012] [Accepted: 02/23/2012] [Indexed: 10/28/2022]
Abstract
The basic mitochondrial protein import apparatus was established in the earliest eukaryotes. Over the subsequent course of evolution and the divergence of the plant, animal and fungal lineages, this basic import apparatus has been modified and expanded in order to meet the specific needs of protein import in each kingdom. In the plant kingdom, the arrival of the plastid complicated the process of protein trafficking and is thought to have given rise to the evolution of a number of unique components that allow specific and efficient targeting of mitochondrial proteins from their site of synthesis in the cytosol, to their final location in the organelle. This includes the evolution of two unique outer membrane import receptors, plant Translocase of outer membrane 20 kDa subunit (TOM20) and Outer membrane protein of 64 kDa (OM64), the loss of a receptor domain from an ancestral import component, Translocase of outer membrane 22 kDa subunit (TOM22), evolution of unique features in the disulfide relay system of the inter membrane space, and the addition of an extra membrane spanning domain to another ancestral component of the inner membrane, Translocase of inner membrane 17 kDa subunit (TIM17). Notably, many of these components are encoded by multi-gene families and exhibit differential sub-cellular localisation and functional specialisation. This article is part of a Special Issue entitled: Protein Import and Quality Control in Mitochondria and Plastids.
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Affiliation(s)
- Owen Duncan
- ARC Centre of Excellence in Plant Energy Biology, Bayliss Building M316, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia
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Carrie C, Giraud E, Duncan O, Xu L, Wang Y, Huang S, Clifton R, Murcha M, Filipovska A, Rackham O, Vrielink A, Whelan J. Conserved and novel functions for Arabidopsis thaliana MIA40 in assembly of proteins in mitochondria and peroxisomes. J Biol Chem 2010; 285:36138-48. [PMID: 20829360 DOI: 10.1074/jbc.m110.121202] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The disulfide relay system of the mitochondrial intermembrane space has been extensively characterized in Saccharomyces cerevisiae. It contains two essential components, Mia40 and Erv1. The genome of Arabidopsis thaliana contains a single gene for each of these components. Although insertional inactivation of Erv1 leads to a lethal phenotype, inactivation of Mia40 results in no detectable deleterious phenotype. A. thaliana Mia40 is targeted to and accumulates in mitochondria and peroxisomes. Inactivation of Mia40 results in an alteration of several proteins in mitochondria, an absence of copper/zinc superoxide dismutase (CSD1), the chaperone for superoxide dismutase (Ccs1) that inserts copper into CSD1, and a decrease in capacity and amount of complex I. In peroxisomes the absence of Mia40 leads to an absence of CSD3 and a decrease in abnormal inflorescence meristem 1 (Aim1), a β-oxidation pathway enzyme. Inactivation of Mia40 leads to an alteration of the transcriptome of A. thaliana, with genes encoding peroxisomal proteins, redox functions, and biotic stress significantly changing in abundance. Thus, the mechanistic operation of the mitochondrial disulfide relay system is different in A. thaliana compared with other systems, and Mia40 has taken on new roles in peroxisomes and mitochondria.
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Affiliation(s)
- Chris Carrie
- Australian Research Council Centre of Excellence in Plant Energy Biology, University of Western Australia, Crawley, Western Australia 6009, Australia
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Pudelski B, Kraus S, Soll J, Philippar K. The plant PRAT proteins - preprotein and amino acid transport in mitochondria and chloroplasts. PLANT BIOLOGY (STUTTGART, GERMANY) 2010; 12 Suppl 1:42-55. [PMID: 20712620 DOI: 10.1111/j.1438-8677.2010.00357.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The membrane proteins of the plant preprotein and amino acid transporter (PRAT) superfamily all share common structural elements, such as four membrane-spanning alpha-helices. Interestingly they display diverse localisation to outer and inner membranes of chloroplasts and mitochondria. Furthermore, they fulfil different functions in preprotein translocation as well as amino acid transport across these membranes. This review summarises current knowledge on precursor protein import and amino acid transport in plastids and mitochondria and provides an overview of the distinct tasks and features of members of the PRAT superfamily in the model plant Arabidopsis thaliana.
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Affiliation(s)
- B Pudelski
- Biochemie und Physiologie der Pflanzen, Department Biologie I, Botanik, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
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Lister R, Carrie C, Duncan O, Ho LHM, Howell KA, Murcha MW, Whelan J. Functional definition of outer membrane proteins involved in preprotein import into mitochondria. THE PLANT CELL 2007; 19:3739-59. [PMID: 17981999 PMCID: PMC2174869 DOI: 10.1105/tpc.107.050534] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
The role of plant mitochondrial outer membrane proteins in the process of preprotein import was investigated, as some of the principal components characterized in yeast have been shown to be absent or evolutionarily distinct in plants. Three outer membrane proteins of Arabidopsis thaliana mitochondria were studied: TOM20 (translocase of the outer mitochondrial membrane), METAXIN, and mtOM64 (outer mitochondrial membrane protein of 64 kD). A single functional Arabidopsis TOM20 gene is sufficient to produce a normal multisubunit translocase of the outer membrane complex. Simultaneous inactivation of two of the three TOM20 genes changed the rate of import for some precursor proteins, revealing limited isoform subfunctionalization. Inactivation of all three TOM20 genes resulted in severely reduced rates of import for some but not all precursor proteins. The outer membrane protein METAXIN was characterized to play a role in the import of mitochondrial precursor proteins and likely plays a role in the assembly of beta-barrel proteins into the outer membrane. An outer mitochondrial membrane protein of 64 kD (mtOM64) with high sequence similarity to a chloroplast import receptor was shown to interact with a variety of precursor proteins. All three proteins have domains exposed to the cytosol and interacted with a variety of precursor proteins, as determined by pull-down and yeast two-hybrid interaction assays. Furthermore, inactivation of one resulted in protein abundance changes in the others, suggesting functional redundancy. Thus, it is proposed that all three components directly interact with precursor proteins to participate in early stages of mitochondrial protein import.
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Affiliation(s)
- Ryan Lister
- Australian Research Council Centre of Excellence in Plant Energy Biology, University of Western Australia, Crawley 6009, Western Australia, Australia
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Howell KA, Cheng K, Murcha MW, Jenkin LE, Millar AH, Whelan J. Oxygen initiation of respiration and mitochondrial biogenesis in rice. J Biol Chem 2007; 282:15619-31. [PMID: 17383966 DOI: 10.1074/jbc.m609866200] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Rice growth under aerobic and anaerobic conditions allowed aspects of mitochondrial biogenesis to be identified as dependent on or independent of an oxygen signal. Analysis of transcripts encoding mitochondrial components found that a subset of these genes respond to oxygen (defined as aerobic), whereas others are relatively unaffected by oxygen availability. Mitochondria formed during growth in anaerobic conditions had reduced protein levels of tricarboxylic acid cycle components and cytochrome-containing complexes of the respiratory chain and repressed respiratory functionality. In general, the capacity of the general import pathway was found to be significantly lower in mitochondria isolated from tissue grown under anaerobic conditions, whereas the carrier import pathway capacity was not affected by changes in oxygen availability. Transcript levels of genes encoding components of the protein import apparatus were generally not affected by the absence of oxygen, and their protein abundance was severalfold higher in mitochondria isolated from anaerobically grown tissue. However, both transcript and protein abundances of the subunits of the mitochondrial processing peptidase, which in plants is integrated into the cytochrome bc(1) complex, were repressed under anaerobic conditions. Therefore, in this system, an increase in import capacity is correlated with an increase in the abundance of the cytochrome bc(1) complex, which is ultimately dependent on the presence of oxygen, providing a link between the respiratory chain and protein import apparatus.
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Affiliation(s)
- Katharine A Howell
- Australian Research Council Centre of Excellence in Plant Energy Biology, University of Western Australia, Perth, Western Australia 6009, Australia
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Carrie C, Murcha MW, Millar AH, Smith SM, Whelan J. Nine 3-ketoacyl-CoA thiolases (KATs) and acetoacetyl-CoA thiolases (ACATs) encoded by five genes in Arabidopsis thaliana are targeted either to peroxisomes or cytosol but not to mitochondria. PLANT MOLECULAR BIOLOGY 2007; 63:97-108. [PMID: 17120136 DOI: 10.1007/s11103-006-9075-1] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2006] [Accepted: 08/10/2006] [Indexed: 05/12/2023]
Abstract
The sub-cellular location of enzymes of fatty acid beta-oxidation in plants is controversial. In the current debate the role and location of particular thiolases in fatty acid degradation, fatty acid synthesis and isoleucine degradation are important. The aim of this research was to determine the sub-cellular location and hence provide information about possible functions of all the putative 3-ketoacyl-CoA thiolases (KAT) and acetoacetyl-CoA thiolases (ACAT) in Arabidopsis. Arabidopsis has three genes predicted to encode KATs, one of which encodes two polypeptides that differ at the N-terminal end. Expression in Arabidopsis cells of cDNAs encoding each of these KATs fused to green fluorescent protein (GFP) at their C-termini showed that three are targeted to peroxisomes while the fourth is apparently cytosolic. The four KATs are also predicted to have mitochondrial targeting sequences, but purified mitochondria were unable to import any of the proteins in vitro. Arabidopsis also has two genes encoding a total of five different putative ACATs. One isoform is targeted to peroxisomes as a fusion with GFP, while the others display no targeting in vivo as GFP fusions, or import into isolated mitochondria. Analysis of gene co-expression clusters in Arabidopsis suggests a role for peroxisomal KAT2 in beta-oxidation, while KAT5 co-expresses with genes of the flavonoid biosynthesis pathway and cytosolic ACAT2 clearly co-expresses with genes of the cytosolic mevalonate biosynthesis pathway. We conclude that KATs and ACATs are present in the cytosol and peroxisome, but are not found in mitochondria. The implications for fatty acid beta-oxidation and for isoleucine degradation in mitochondria are discussed.
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Affiliation(s)
- Chris Carrie
- ARC Centre of Excellence in Plant Energy Biology, University of Western Australia, MCS building M316, 35 Stirling Highway, Crawley, 6009, WA, Australia
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15
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Zara V, Dolce V, Capobianco L, Ferramosca A, Papatheodorou P, Rassow J, Palmieri F. Biogenesis of eel liver citrate carrier (CIC): negative charges can substitute for positive charges in the presequence. J Mol Biol 2006; 365:958-67. [PMID: 17113102 DOI: 10.1016/j.jmb.2006.10.077] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2006] [Revised: 10/20/2006] [Accepted: 10/21/2006] [Indexed: 11/22/2022]
Abstract
A family of structurally related carrier proteins mediates the flux of metabolites across the mitochondrial inner membrane. Differently from most other mitochondrial proteins, members of the carrier family are synthesized without an amino-terminal targeting sequence. However, in some mammalian and plant species, representatives were identified that carry a positively charged presequence. To obtain data on a carrier protein from lower vertebrates, we determined the primary structure of eel mitochondrial citrate carrier (CIC) and investigated its import pathway into the target organelle. The protein carries a cleavable presequence of 20 amino acids, including two positively charged residues. The cleavage site is recognized by a magnesium-dependent peptidase in the intermembrane space. The presequence is dispensable both for targeting and translocation, but prior to import into mitochondria, significantly increases the solubility of the precursor protein. This effect is completely retained if the positive charges are exchanged with negative charges. Following this observation, we found that several carrier proteins appear to carry non-cleavable presequences that may similarly act as charged intramolecular chaperones.
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Affiliation(s)
- Vincenzo Zara
- Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Università di Lecce, Via Provinciale Lecce-Monteroni, I-73100 Lecce, Italy.
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16
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Elhafez D, Murcha MW, Clifton R, Soole KL, Day DA, Whelan J. Characterization of Mitochondrial Alternative NAD(P)H Dehydrogenases in Arabidopsis: Intraorganelle Location and Expression. ACTA ACUST UNITED AC 2006; 47:43-54. [PMID: 16258072 DOI: 10.1093/pcp/pci221] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The intramitochondrial location of putative type II NAD(P)H dehydrogenases (NDs) in Arabidopsis was investigated by measuring the ability of isolated mitochondria to take up precursor proteins generated from cDNAs using an in vitro translation system. The mature proteins of NDA1, NDA2 and NDC1 were judged to be located on the inside of the inner membrane because they were protected from protease added after the mitochondrial outer membrane had been ruptured. In contrast, NDB1, NDB2 and NDB4 were not protected from protease digestion in mitochondria with ruptured outer membranes and were deemed to be located on the outside of the inner membrane. Expression of all ND genes was measured using quantitative reverse transcription-PCR (RT-PCR) to determine transcript abundance, and compared with expression of alternative oxidase, uncoupler proteins and selected components of the oxidative phosphorylation complexes. NDA1 and NDB2 were the most prominently expressed members in a variety of tissues, and were up-regulated in the early daytime in a diurnal manner. Analysis of array data suggested that NDA1 clustered closest to the gene encoding the P-subunit of glycine decarboxylase. Taken together with the diurnal regulation of NDA1 observed here and in other studies, this suggests that NDA1 plays a role in integrating metabolic activities of chloroplasts and mitochondria. NDA2, NDB2 and Aox1a were up-regulated in a coordinated manner under various treatments, potentially forming a complete respiratory chain capable of oxidizing matrix and cytosolic NAD(P)H. NDB1 and NDC1 were down-regulated under the same conditions and may be regarded as housekeeping genes.
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Affiliation(s)
- Dina Elhafez
- ARC Centre of Excellence in Plant Energy Biology, CMS Building M310, The University of Western Australia, Crawley
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17
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Howell KA, Millar AH, Whelan J. Ordered assembly of mitochondria during rice germination begins with pro-mitochondrial structures rich in components of the protein import apparatus. PLANT MOLECULAR BIOLOGY 2006; 60:201-23. [PMID: 16429260 DOI: 10.1007/s11103-005-3688-7] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2005] [Accepted: 10/03/2005] [Indexed: 05/06/2023]
Abstract
Mitochondrial maturation during imbibition of rice embryos follows the transition of unstructured double membrane bound pro-mitochondria to the typical cristae-rich mitochondrial structures observed in mature plant cells. During the first 48 h following imbibition, an ordered increase in the abundance of transcripts encoding mitochondrial proteins was observed. Co-incident with these changes in transcript levels was dynamic and rapid changes in mitochondrial protein content and mitochondrial function. Proteins representing components of the mitochondrial protein import apparatus are strikingly abundant in dry seeds, and a functional import apparatus was shown to operate 2 h after imbibition. Interestingly, this import process was best driven by the oxidation of NADH from outside the mitochondrial inner membrane. In later developmental stages the capacity for matrix organic acid metabolism was evident, accompanied by the appearance of proteins for TCA cycle components, and coordination of electron transport chain assembly through components encoded in both mitochondrial and nuclear genomes. Together these events provide new insights into the understanding of mitochondrial maturation and the nature of pro-mitochondrial structures in plant cells.
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Affiliation(s)
- Katharine A Howell
- ARC Centre of Excellence in Plant Energy Biology, CMS Building M310, University of Western Australia, 35 Stirling Hwy, Perth, WA 6009, Australia
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Zara V, Ferramosca A, Papatheodorou P, Palmieri F, Rassow J. Import of rat mitochondrial citrate carrier (CIC) at increasing salt concentrations promotes presequence binding to import receptor Tom20 and inhibits membrane translocation. J Cell Sci 2005; 118:3985-95. [PMID: 16129883 DOI: 10.1242/jcs.02526] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mitochondria contain a family of related carrier proteins that mediate transport of metabolites across the mitochondrial inner membrane. All members of this family are synthesized in the cytosol. We characterized the interactions of newly synthesized rat citrate carrier (CIC) precursor protein (pCIC) with the components of the mitochondrial protein import machinery. pCIC contains both a positively charged presequence of 13 amino acids and internal targeting sequences. We found that the pCIC presequence does not interfere with the import pathway and merely acts as an internal chaperone in the cytosol. Under conditions of increased ionic strength, the pCIC presequence binds to the import receptor Tom20 and accumulates at the mitochondrial surface, thereby delaying pCIC translocation across the mitochondrial outer membrane. Similarly, the presequence of the bovine phosphate carrier (PiC) precursor protein (pPiC) is arrested at the mitochondrial surface when salt concentrations are elevated. We conclude that presequences can only act as mediators of mitochondrial protein import if they allow rapid release from import receptor sites. Release from receptors sites may be rate-limiting in translocation.
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Affiliation(s)
- Vincenzo Zara
- Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Università di Lecce, I-73100 Lecce, Italy.
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Lister R, Hulett JM, Lithgow T, Whelan J. Protein import into mitochondria: origins and functions today (review). Mol Membr Biol 2005; 22:87-100. [PMID: 16092527 DOI: 10.1080/09687860500041247] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Mitochondria are organelles derived from alpha-proteobacteria over the course of one to two billion years. Mitochondria from the major eukaryotic lineages display some variation in functions and coding capacity but sequence analysis demonstrates them to be derived from a single common ancestral endosymbiont. The loss of assorted functions, the transfer of genes to the nucleus, and the acquisition of various 'eukaryotic' proteins have resulted in an organelle that contains approximately 1000 different proteins, with most of these proteins imported into the organelle across one or two membranes. A single translocase in the outer membrane and two translocases in the inner membrane mediate protein import. Comparative sequence analysis and functional complementation experiments suggest some components of the import pathways to be directly derived from the eubacterial endosymbiont's own proteins, and some to have arisen 'de novo' at the earliest stages of 'mitochondrification' of the endosymbiont. A third class of components appears lineage-specific, suggesting they were incorporated into the process of protein import long after mitochondria was established as an organelle and after the divergence of the various eukaryotic lineages. Protein sorting pathways inherited from the endosymbiont have been co-opted and play roles in intraorganelle protein sorting after import. The import apparatus of animals and fungi show significant similarity to one another, but vary considerably to the plant apparatus. Increasing complexity in the eukaryotic lineage, i.e., from single celled to multi-cellular life forms, has been accompanied by an expansion in genes encoding each component, resulting in small gene families encoding many components. The functional differences in these gene families remain to be elucidated, but point to a mosaic import apparatus that can be regulated by a variety of signals.
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Affiliation(s)
- Ryan Lister
- Plant Molecular Biology Group, School of Biomedical and Chemical Sciences, The University of Western Australia, Crawley, Western Australia, Australia
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20
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Murcha MW, Millar AH, Whelan J. The N-terminal cleavable extension of plant carrier proteins is responsible for efficient insertion into the inner mitochondrial membrane. J Mol Biol 2005; 351:16-25. [PMID: 15992825 DOI: 10.1016/j.jmb.2005.06.004] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2005] [Revised: 06/01/2005] [Accepted: 06/01/2005] [Indexed: 10/25/2022]
Abstract
A subset of mitochondrial carrier proteins from plants contain a cleavable N-terminal extension. We have used a reconstituted protein import assay system into intermembrane space-depleted mitochondria to study the role of the cleavable extension in the carrier import pathway. Insertion of carrier proteins into the inner membrane can be stimulated by the addition of a soluble intermembrane space fraction isolated from plant mitochondria. Greater stimulation of import of the adenine nucleotide carrier (ANT) and phosphate carrier (Pic), which contain N-terminal cleavable extensions, was observed compared to the import of the oxoglutarate malate carrier (OMT), which does not contain a cleavable extension. Removal of the N-terminal cleavable extension from ANT and Pic resulted in loss of stimulation of insertion into the inner membrane. Conversely, addition of the N-terminal extension from ANT or Pic to OMT resulted in significantly enhanced insertion into the inner membrane. The polytopic inner membrane proteins TIM17 and TIM23 that are imported via the carrier import pathway contain no cleavable extension, displayed high-level stimulation of insertion into the inner membrane by addition of the intermembrane space fraction. Addition of the N-terminal cleavable extension from carrier proteins to TIM23 enhanced insertion of TIM23 into the inner membrane even in the absence of the soluble intermembrane space fraction. Together, these results demonstrate that the cleavable N-terminal extensions present on carrier proteins from plants are required for efficient insertion into the inner mitochondrial membrane, and that they can stimulate insertion of any carrier-like protein into the inner membrane.
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Affiliation(s)
- Monika W Murcha
- ARC Centre of Excellence in Plant Energy Biology, CMS Building M310, The University of Western Australia, Crawley 6009, WA, Australia
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Murcha MW, Rudhe C, Elhafez D, Adams KL, Daley DO, Whelan J. Adaptations required for mitochondrial import following mitochondrial to nucleus gene transfer of ribosomal protein S10. PLANT PHYSIOLOGY 2005; 138:2134-44. [PMID: 16040655 PMCID: PMC1183401 DOI: 10.1104/pp.105.062745] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The minimal requirements to support protein import into mitochondria were investigated in the context of the phenomenon of ongoing gene transfer from the mitochondrion to the nucleus in plants. Ribosomal protein 10 of the small subunit is encoded in the mitochondrion in soybean and many other angiosperms, whereas in several other species it is nuclear encoded and thus must be imported into the mitochondrial matrix to function. When encoded by the nuclear genome, it has adopted different strategies for mitochondrial targeting and import. In lettuce (Lactuca sativa) and carrot (Daucus carota), Rps10 independently gained different N-terminal extensions from other genes, following transfer to the nucleus. (The designation of Rps10 follows the following convention. The gene is indicated in italics. If encoded in the mitochondrion, it is rps10; if encoded in the nucleus, it is Rps10.) Here, we show that the N-terminal extensions of Rps10 in lettuce and carrot are both essential for mitochondrial import. In maize (Zea mays), Rps10 has not acquired an extension upon transfer but can be readily imported into mitochondria. Deletion analysis located the mitochondrial targeting region to the first 20 amino acids. Using site directed mutagenesis, we changed residues in the first 20 amino acids of the mitochondrial encoded soybean (Glycine max) rps10 to the corresponding amino acids in the nuclear encoded maize Rps10 until import was achieved. Changes were required that altered charge, hydrophobicity, predicted ability to form an amphipathic alpha-helix, and generation of a binding motif for the outer mitochondrial membrane receptor, translocase of the outer membrane 20. In addition to defining the changes required to achieve mitochondrial localization, the results demonstrate that even proteins that do not present barriers to import can require substantial changes to acquire a mitochondrial targeting signal.
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Affiliation(s)
- Monika W Murcha
- Australian Research Council Centre of Excellence in Plant Energy Biology, University of Western Australia, Crawley 6009, Western Australia
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22
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Ståhl A, Nilsson S, Lundberg P, Bhushan S, Biverståhl H, Moberg P, Morisset M, Vener A, Mäler L, Langel U, Glaser E. Two novel targeting peptide degrading proteases, PrePs, in mitochondria and chloroplasts, so similar and still different. J Mol Biol 2005; 349:847-60. [PMID: 15893767 DOI: 10.1016/j.jmb.2005.04.023] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2004] [Revised: 04/01/2005] [Accepted: 04/05/2005] [Indexed: 10/25/2022]
Abstract
Two novel metalloproteases from Arabidopsis thaliana, termed AtPrePI and AtPrePII, were recently identified and shown to degrade targeting peptides in mitochondria and chloroplasts using an ambiguous targeting peptide. AtPrePI and AtPrePII are classified as dually targeted proteins as they are targeted to both mitochondria and chloroplasts. Both proteases harbour an inverted metal binding motif and belong to the pitrilysin subfamily A. Here we have investigated the subsite specificity of AtPrePI and AtPrePII by studying their proteolytic activity against the mitochondrial F(1)beta pre-sequence, peptides derived from the F(1)beta pre-sequence as well as non-mitochondrial peptides and proteins. The degradation products were analysed, identified by MALDI-TOF spectrometry and superimposed on the 3D structure of the F(1)beta pre-sequence. AtPrePI and AtPrePII cleaved peptides that are in the range of 10 to 65 amino acid residues, whereas folded or longer unfolded peptides and small proteins were not degraded. Both proteases showed preference for basic amino acids in the P(1) position and small, uncharged amino acids or serine residues in the P'(1) position. Interestingly, both AtPrePI and AtPrePII cleaved almost exclusively towards the ends of the alpha-helical elements of the F(1)beta pre-sequence. However, AtPrePI showed a preference for the N-terminal amphiphilic alpha-helix and positively charged amino acid residues and degraded the F(1)beta pre-sequence into 10-16 amino acid fragments, whereas AtPrePII did not show any positional preference and degraded the F(1)beta pre-sequence into 10-23 amino acid fragments. In conclusion, despite the high sequence identity between AtPrePI and AtPrePII and similarities in cleavage specificities, cleavage site recognition differs for both proteases and is context and structure dependent.
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Affiliation(s)
- Annelie Ståhl
- Department of Biochemistry and Biophysics, The Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91 Stockholm, Sweden.
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Murcha MW, Elhafez D, Millar AH, Whelan J. The C-terminal region of TIM17 links the outer and inner mitochondrial membranes in Arabidopsis and is essential for protein import. J Biol Chem 2005; 280:16476-83. [PMID: 15722347 DOI: 10.1074/jbc.m413299200] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The translocase of the inner membrane 17 (AtTIM17-2) protein from Arabidopsis has been shown to link the outer and inner mitochondrial membranes. This was demonstrated by several approaches: (i) In vitro organelle import assays indicated the imported AtTIM17-2 protein remained protease accessible in the outer membrane when inserted into the inner membrane. (ii) N-terminal and C-terminal tagging indicated that it was the C-terminal region that was located in the outer membrane. (iii) Antibodies raised to the C-terminal 100 amino acids recognize a 31-kDa protein from purified mitochondria, but cross-reactivity was abolished when mitochondria were protease-treated to remove outer membrane-exposed proteins. Antibodies to AtTIM17-2 inhibited import of proteins via the general import pathway into outer membrane-ruptured mitochondria, but did not inhibit protein import via the carrier import pathway. Together these results indicate that the C-terminal region of AtTIM17-2 is exposed on the outer surface of the outer membrane, and the C-terminal region is essential for protein import into mitochondria.
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Affiliation(s)
- Monika W Murcha
- Plant Molecular Biology Group, School of Biomedical and Chemicals Sciences, University of Western Australia, 35 Stirling Highway, Crawley 6009, Western Australia, Australia
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