151
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Complementing structural information of modular proteins with small angle neutron scattering and contrast variation. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2008; 37:603-11. [DOI: 10.1007/s00249-008-0278-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2007] [Revised: 01/18/2008] [Accepted: 01/22/2008] [Indexed: 11/25/2022]
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152
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Hayden CA, Bosco G. Comparative genomic analysis of novel conserved peptide upstream open reading frames in Drosophila melanogaster and other dipteran species. BMC Genomics 2008; 9:61. [PMID: 18237443 PMCID: PMC2276209 DOI: 10.1186/1471-2164-9-61] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2007] [Accepted: 02/01/2008] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Upstream open reading frames (uORFs) are elements found in the 5'-region of an mRNA transcript, capable of regulating protein production of the largest, or major ORF (mORF), and impacting organismal development and growth in fungi, plants, and animals. In Drosophila, approximately 40% of transcripts contain upstream start codons (uAUGs) but there is little evidence that these are translated and affect their associated mORF. RESULTS Analyzing 19,389 Drosophila melanogaster transcript annotations and 666,153 dipteran EST sequences we have identified 44 putative conserved peptide uORFs (CPuORFs) in Drosophila melanogaster that show evidence of negative selection, and therefore are likely to be translated. Transcripts with CPuORFs constitute approximately 0.3% of the total number of transcripts, a similar frequency to the Arabidopsis genome, and have a mean length of 70 amino acids, much larger than the mean length of plant CPuORFs (40 amino acids). There is a statistically significant clustering of CPuORFs at cytological band 57 (p = 10-5), a phenomenon that has never been described for uORFs. Based on GO term and Interpro domain analyses, genes in the uORF dataset show a higher frequency of ORFs implicated in mitochondrial import than the genome-wide frequency (p < 0.01) as well as methyltransferases (p < 0.02). CONCLUSION Based on these data, it is clear that Drosophila contain putative CPuORFs at frequencies similar to those found in plants. They are distinguished, however, by the type of mORF they tend to associate with, Drosophila CPuORFs preferentially occurring in transcripts encoding mitochondrial proteins and methyltransferases. This provides a basis for the study of CPuORFs and their putative regulatory role in mitochondrial function and disease.
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Affiliation(s)
- Celine A Hayden
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, AZ 85721, USA.
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153
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Chapter 5 New Insights into the Mechanism of Precursor Protein Insertion into the Mitochondrial Membranes. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2008; 268:147-90. [DOI: 10.1016/s1937-6448(08)00805-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/10/2023]
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154
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Ivanova E, Ball M, Lu H. Zinc binding of Tim10: Evidence for existence of an unstructured binding intermediate for a zinc finger protein. Proteins 2008; 71:467-75. [DOI: 10.1002/prot.21713] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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155
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The direct route: a simplified pathway for protein import into the mitochondrion of trypanosomes. Trends Cell Biol 2008; 18:12-8. [DOI: 10.1016/j.tcb.2007.09.009] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2007] [Revised: 09/09/2007] [Accepted: 09/14/2007] [Indexed: 01/23/2023]
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156
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Ivanova E, Jowitt TA, Lu H. Assembly of the Mitochondrial Tim9–Tim10 Complex: A Multi-step Reaction with Novel Intermediates. J Mol Biol 2008; 375:229-39. [DOI: 10.1016/j.jmb.2007.10.037] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2007] [Revised: 09/28/2007] [Accepted: 10/13/2007] [Indexed: 11/25/2022]
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157
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Milenkovic D, Müller J, Stojanovski D, Pfanner N, Chacinska A. Diverse mechanisms and machineries for import of mitochondrial proteins. Biol Chem 2007; 388:891-7. [PMID: 17696772 DOI: 10.1515/bc.2007.097] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Mitochondria are ubiquitous organelles that play an essential role in energy conversion and biosynthetic pathways in eukaryotic cells. Most mitochondrial proteins must be imported from the cytosol and sorted into one of the four mitochondrial subcompartments, the outer membrane, the intermembrane space, the inner membrane and the matrix. Studies in recent years revealed a remarkable diversity of mechanisms and machineries that are required for the import of proteins into mitochondria. At least four different pathways for the sorting and assembly of nuclear-encoded mitochondrial proteins have been identified.
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Affiliation(s)
- Dusanka Milenkovic
- Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany
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158
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Alcock FH, Grossmann JG, Gentle IE, Likić VA, Lithgow T, Tokatlidis K. Conserved substrate binding by chaperones in the bacterial periplasm and the mitochondrial intermembrane space. Biochem J 2007; 409:377-87. [PMID: 17894549 DOI: 10.1042/bj20070877] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Mitochondria were derived from intracellular bacteria and the mitochondrial intermembrane space is topologically equivalent to the bacterial periplasm. Both compartments contain ATP-independent chaperones involved in the transport of hydrophobic membrane proteins. The mitochondrial TIM (translocase of the mitochondrial inner membrane) 10 complex and the periplasmic chaperone SurA were examined in terms of evolutionary relation, structural similarity, substrate binding specificity and their function in transporting polypeptides for insertion into membranes. The two chaperones are evolutionarily unrelated; structurally, they are also distinct both in their characteristics, as determined by SAXS (small-angle X-ray scattering), and in pairwise structural comparison using the distance matrix alignment (DALILite server). Despite their structural differences, SurA and the TIM10 complex share a common binding specificity in Pepscan assays of substrate proteins. Comprehensive analysis of the binding on a total of 1407 immobilized 13-mer peptides revealed that the TIM10 complex, like SurA, does not bind hydrophobic peptides generally, but that both chaperones display selectivity for peptides rich in aromatic residues and with net positive charge. This common binding specificity was not sufficient for SurA to completely replace TIM10 in yeast cells in vivo. In yeast cells lacking TIM10, when SurA is targeted to the intermembrane space of mitochondria, it binds translocating substrate proteins, but fails to completely transfer the substrate to the translocase in the mitochondrial inner membrane. We suggest that SurA was incapable of presenting substrates effectively to the primitive TOM (translocase of the mitochondrial outer membrane) and TIM complexes in early mitochondria, and was replaced by the more effective small Tim chaperone.
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Affiliation(s)
- Felicity H Alcock
- Institute of Molecular Biology and Biotechnology, Foundation of Research and Technology Hellas, PO Box 1385, 71110 Heraklion, Crete, Greece
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159
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Kutik S, Guiard B, Meyer HE, Wiedemann N, Pfanner N. Cooperation of translocase complexes in mitochondrial protein import. ACTA ACUST UNITED AC 2007; 179:585-91. [PMID: 17998403 PMCID: PMC2080918 DOI: 10.1083/jcb.200708199] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Most mitochondrial proteins are synthesized in the cytosol and imported into one of the four mitochondrial compartments: outer membrane, intermembrane space, inner membrane, and matrix. Each compartment contains protein complexes that interact with precursor proteins and promote their transport. These translocase complexes do not act as independent units but cooperate with each other and further membrane complexes in a dynamic manner. We propose that a regulated coupling of translocases is important for the coordination of preprotein translocation and efficient sorting to intramitochondrial compartments.
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Affiliation(s)
- Stephan Kutik
- Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, and 2Fakultät für Biologie, Universität Freiburg, 79104 Freiburg, Germany
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160
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Khalimonchuk O, Winge DR. Function and redox state of mitochondrial localized cysteine-rich proteins important in the assembly of cytochrome c oxidase. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2007; 1783:618-28. [PMID: 18070608 DOI: 10.1016/j.bbamcr.2007.10.016] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2007] [Revised: 10/22/2007] [Accepted: 10/30/2007] [Indexed: 11/16/2022]
Abstract
The cytochrome c oxidase (CcO) complex of the mitochondrial respiratory chain exists within the mitochondrial inner membrane (IM). The biogenesis of the complex is a multi-faceted process requiring multiple assembly factors that function on both faces of the IM. Formation of the two copper centers of CcO occurs within the intermembrane space (IMS) and is dependent on assembly factors with critical cysteinyl thiolates. Two classes of assembly factors exist, one group being soluble IMS proteins and the second class being proteins tethered to the IM. A common motif in the soluble assembly factors is a duplicated Cx(9)C sequence motif. Since mitochondrial respiration is a major source of reactive oxygen species, control of the redox state of mitochondrial proteins is an important process. This review documents the role of these cysteinyl CcO assembly factors within the IMS and the necessity of redox control in their function.
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Affiliation(s)
- Oleh Khalimonchuk
- University of Utah Health Sciences Center, Department of Medicine, Salt Lake City, Utah 84132, USA
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161
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A role for cytochrome c and cytochrome c peroxidase in electron shuttling from Erv1. EMBO J 2007; 26:4801-11. [PMID: 17972915 DOI: 10.1038/sj.emboj.7601909] [Citation(s) in RCA: 137] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2007] [Accepted: 10/10/2007] [Indexed: 11/08/2022] Open
Abstract
Erv1 is a flavin-dependent sulfhydryl oxidase in the mitochondrial intermembrane space (IMS) that functions in the import of cysteine-rich proteins. Redox titrations of recombinant Erv1 showed that it contains three distinct couples with midpoint potentials of -320, -215, and -150 mV. Like all redox-active enzymes, Erv1 requires one or more electron acceptors. We have generated strains with erv1 conditional alleles and employed biochemical and genetic strategies to facilitate identifying redox pathways involving Erv1. Here, we report that Erv1 forms a 1:1 complex with cytochrome c and a reduced Erv1 can transfer electrons directly to the ferric form of the cytochrome. Erv1 also utilized molecular oxygen as an electron acceptor to generate hydrogen peroxide, which is subsequently reduced to water by cytochrome c peroxidase (Ccp1). Oxidized Ccp1 was in turn reduced by the Erv1-reduced cytochrome c. By coupling these pathways, cytochrome c and Ccp1 function efficiently as Erv1-dependent electron acceptors. Thus, we propose that Erv1 utilizes diverse pathways for electron shuttling in the IMS.
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162
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Müller JM, Milenkovic D, Guiard B, Pfanner N, Chacinska A. Precursor oxidation by Mia40 and Erv1 promotes vectorial transport of proteins into the mitochondrial intermembrane space. Mol Biol Cell 2007; 19:226-36. [PMID: 17978092 DOI: 10.1091/mbc.e07-08-0814] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The mitochondrial intermembrane space contains chaperone complexes that guide hydrophobic precursor proteins through this aqueous compartment. The chaperones consist of hetero-oligomeric complexes of small Tim proteins with conserved cysteine residues. The precursors of small Tim proteins are synthesized in the cytosol. Import of the precursors requires the essential intermembrane space proteins Mia40 and Erv1 that were proposed to form a relay for disulfide formation in the precursor proteins. However, experimental evidence for a role of Mia40 and Erv1 in the oxidation of intermembrane space precursors has been lacking. We have established a system to directly monitor the oxidation of precursors during import into mitochondria and dissected distinct steps of the import process. Reduced precursors bind to Mia40 during translocation into mitochondria. Both Mia40 and Erv1 are required for formation of oxidized monomers of the precursors that subsequently assemble into oligomeric complexes. Whereas the reduced precursors can diffuse back into the cytosol, the oxidized precursors are retained in the intermembrane space. Thus, oxidation driven by Mia40 and Erv1 determines vectorial transport of the precursors into the mitochondrial intermembrane space.
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Affiliation(s)
- Judith M Müller
- Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Universität Freiburg, D-79104 Freiburg, Germany
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163
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Grumbt B, Stroobant V, Terziyska N, Israel L, Hell K. Functional characterization of Mia40p, the central component of the disulfide relay system of the mitochondrial intermembrane space. J Biol Chem 2007; 282:37461-70. [PMID: 17959605 DOI: 10.1074/jbc.m707439200] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mia40p and Erv1p are components of a translocation pathway for the import of cysteine-rich proteins into the intermembrane space of mitochondria. We have characterized the redox behavior of Mia40p and reconstituted the disulfide transfer system of Mia40p by using recombinant functional C-terminal fragment of Mia40p, Mia40C, and Erv1p. Oxidized Mia40p contains three intramolecular disulfide bonds. One disulfide bond connects the first two cysteine residues in the CPC motif. The second and the third bonds belong to the twin CX(9)C motif and bridge the cysteine residues of two CX(9)C segments. In contrast to the stabilizing disulfide bonds of the twin CX(9)C motif, the first disulfide bond was easily accessible to reducing agents. Partially reduced Mia40C generated by opening of this bond as well as fully reduced Mia40C were oxidized by Erv1p in vitro. In the course of this reaction, mixed disulfides of Mia40C and Erv1p were formed. Reoxidation of fully reduced Mia40C required the presence of the first two cysteine residues in Mia40C. However, efficient reoxidation of a Mia40C variant containing only the cysteine residues of the twin CX(9)C motif was observed when in addition to Erv1p low amounts of wild type Mia40C were present. In the reconstituted system the thiol oxidase Erv1p was sufficient to transfer disulfide bonds to Mia40C, which then could oxidize the variant of Mia40C. In summary, we reconstituted a disulfide relay system consisting of Mia40C and Erv1p.
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Affiliation(s)
- Barbara Grumbt
- Adolf-Butenandt-Institut für Physiologische Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse 5, 81377, München, Germany
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164
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Stojanovski D, Müller JM, Milenkovic D, Guiard B, Pfanner N, Chacinska A. The MIA system for protein import into the mitochondrial intermembrane space. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2007; 1783:610-7. [PMID: 17996737 DOI: 10.1016/j.bbamcr.2007.10.004] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2007] [Revised: 10/05/2007] [Accepted: 10/15/2007] [Indexed: 01/20/2023]
Abstract
When thinking of the mitochondrial intermembrane space we envisage a small compartment that is bordered by the mitochondrial outer and inner membranes. Despite this somewhat simplified perception the intermembrane space has remained a central focus in mitochondrial biology. This compartment accommodates many proteinaceous factors that play critical roles in mitochondrial and cellular metabolism, including the regulation of programmed cell death and energy conversion. The mechanism by which intermembrane space proteins are transported into the organelle and folded remained largely unknown until recently. In pursuit of the answer to this question a novel machinery, the Mitochondrial Intermembrane Space Assembly machinery, exploiting a unique regulated thiol-disulfide exchange mechanism has been revealed. This exciting discovery has not only put in place novel concepts for the biogenesis of intermembrane space precursors but also raises important implications on the mechanisms involved in the generation and transfer of disulfide bonds.
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Affiliation(s)
- Diana Stojanovski
- Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany
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165
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Abstract
About 10% to 15% of the nuclear genes of eukaryotic organisms encode mitochondrial proteins. These proteins are synthesized in the cytosol and recognized by receptors on the surface of mitochondria. Translocases in the outer and inner membrane of mitochondria mediate the import and intramitochondrial sorting of these proteins; ATP and the membrane potential are used as energy sources. Chaperones and auxiliary factors assist in the folding and assembly of mitochondrial proteins into their native, three-dimensional structures. This review summarizes the present knowledge on the import and sorting of mitochondrial precursor proteins, with a special emphasis on unresolved questions and topics of current research.
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Affiliation(s)
- Walter Neupert
- Institut für Physiologische Chemie, Universität München, 81377 München, Germany.
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166
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Abstract
Mitochondria cannot be made de novo but replicate by a mechanism of recruitment of new proteins, which are added to preexisting subcompartments. Although mitochondria have their own DNA, more than 98% of the total protein complement of the organelle is encoded by the nuclear genome. Mitochondrial biogenesis requires a coordination of expression of two genomes and therefore cross talk between the nucleus and mitochondria. In mammals, regulation of mitochondrial biogenesis and proliferation is influenced by external factors, such as nutrients, hormones, temperature, exercise, hypoxia, and aging. This complexity points to the existence of a coordinated and tightly regulated network connecting different pathways. Communications are also required for eliciting mitochondrial responses to specific stress pathways. This review covers the mechanisms of mitochondrial biogenesis and the way cells respond to external signals to maintain mitochondrial function and cellular homeostasis.
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Affiliation(s)
- Michael T Ryan
- Department of Biochemistry, La Trobe University, Melbourne 3086, Australia.
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167
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Baker MJ, Frazier AE, Gulbis JM, Ryan MT. Mitochondrial protein-import machinery: correlating structure with function. Trends Cell Biol 2007; 17:456-64. [PMID: 17825565 DOI: 10.1016/j.tcb.2007.07.010] [Citation(s) in RCA: 158] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2007] [Revised: 07/03/2007] [Accepted: 07/03/2007] [Indexed: 11/16/2022]
Abstract
Most mitochondrial proteins are synthesized in the cytosol, translocated into the organelle and directed along specific sorting pathways. Over the past 20 years, >30 proteins have been identified as having key roles in mitochondrial protein import. Recently, the elucidation of the structures of several import components has provided fresh insight into the import process. Here, we review the different pathways involved in sorting proteins into mitochondrial subcompartments. Along the way, we highlight the available structural information about the protein-import machinery and discuss how these structures correlate with previously ascribed functions. Future challenges for the cell biologists will be to use this structural information to test specific hypotheses addressing the molecular mechanisms of mitochondrial protein import.
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Affiliation(s)
- Michael J Baker
- Department of Biochemistry, La Trobe University, Melbourne 3086, Australia
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168
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Sideris DP, Tokatlidis K. Oxidative folding of small Tims is mediated by site-specific docking onto Mia40 in the mitochondrial intermembrane space. Mol Microbiol 2007; 65:1360-73. [PMID: 17680986 DOI: 10.1111/j.1365-2958.2007.05880.x] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Oxidative folding in the mitochondrial intermembrane space (IMS) is crucial for the import of certain cysteine-rich IMS proteins. The essential proteins Mia40 and Erv1 are key components for this mechanism functioning as a disulphide protein cascade that is functionally linked to the respiratory chain by shuttling electrons onto CytC. The subunits of the chaperone complex Tim9-Tim10 require Mia40 for their biogenesis. Previously, it was shown that the four cysteines of Tim10 are crucial for folding and assembly, that they are connected intramolecularly into an inner and an outer disulphide bridge, and that the inner disulphide has a more prominent role in these processes. Here we show that interaction with Mia40 is a site-specific event: (i) the N-terminal first cysteine of the precursor is crucial for docking onto Mia40 via a mixed disulphide; (ii) release is triggered by disulphide pairing of the C-terminal cysteine onto the N-terminal one; and (iii) formation of the inner disulphide between the second and third cysteines apparently precedes the release reaction and is critical for assembly with Tim9. The Tim10-Mia40 interaction is independent of divalent cations, any other mitochondrial proteins or membranes, and is shown to occur efficiently in organello and in vitro.
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Affiliation(s)
- Dionisia P Sideris
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology Hellas (IMBB-FORTH), Heraklion 71110, Crete, Greece
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169
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Milenkovic D, Gabriel K, Guiard B, Schulze-Specking A, Pfanner N, Chacinska A. Biogenesis of the Essential Tim9–Tim10 Chaperone Complex of Mitochondria. J Biol Chem 2007; 282:22472-80. [PMID: 17553782 DOI: 10.1074/jbc.m703294200] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mitochondrial intermembrane space (IMS) contains an essential machinery for protein import and assembly (MIA). Biogenesis of IMS proteins involves a disulfide relay between precursor proteins, the cysteine-rich IMS protein Mia40 and the sulfhydryl oxidase Erv1. How precursor proteins are specifically directed to the IMS has remained unknown. Here we systematically analyzed the role of cysteine residues in the biogenesis of the essential IMS chaperone complex Tim9-Tim10. Although each of the four cysteines of Tim9, as well as of Tim10, is required for assembly of the chaperone complex, only the most amino-terminal cysteine residue of each precursor is critical for translocation across the outer membrane and interaction with Mia40. Mia40 selectively recognizes cysteine-containing IMS proteins in a site-specific manner in organello and in vitro. Our results indicate that Mia40 acts as a trans receptor in the biogenesis of mitochondrial IMS proteins.
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Affiliation(s)
- Dusanka Milenkovic
- Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Universität Freiburg, D-79104 Freiburg, Germany
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170
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Vergnolle MAS, Alcock FH, Petrakis N, Tokatlidis K. Mutation of conserved charged residues in mitochondrial TIM10 subunits precludes TIM10 complex assembly, but does not abolish growth of yeast cells. J Mol Biol 2007; 371:1315-24. [PMID: 17618651 DOI: 10.1016/j.jmb.2007.06.025] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2007] [Revised: 05/25/2007] [Accepted: 06/11/2007] [Indexed: 11/16/2022]
Abstract
The Saccharomyces cerevisiae TIM10 complex (TIM10c) is an ATP-independent chaperone of the mitochondrial intermembrane space, involved in transport of polytopic membrane proteins. The complex is an alpha(3)beta(3) hexamer of Tim9 and Tim10 subunits. We have generated specific mutations in charged residues in the central core domain of each subunit delineated by the characteristic twin CX(3)C motif, and investigated the effect of these mutations on subunit folding, complex assembly and TIM10 function in vitro and in vivo. Any combination of mutations that included a specific glutamate residue, conserved in all known Tim9 and Tim10 sequences, abolished assembly of the TIM10 complex. In vivo complementation analyses using a MET3-TIM10 strain that is selectively inactivated for the expression of wild-type Tim10 showed that (i) an N-terminal deleted version of Tim10 that was previously shown to be defective in substrate binding is lethal under all conditions, but (ii) the charged residues mutant of Tim10 that is defective in assembly with Tim9 can restore growth in glucose, but not in non-fermentable carbon sources. These data suggest that formation of the hexamer is beneficial but not vital for TIM10 function, whilst the N-terminal substrate-binding region of Tim10 is essential in vivo.
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171
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Sanjuán Szklarz LK, Kozjak-Pavlovic V, Vögtle FN, Chacinska A, Milenkovic D, Vogel S, Dürr M, Westermann B, Guiard B, Martinou JC, Borner C, Pfanner N, Meisinger C. Preprotein Transport Machineries of Yeast Mitochondrial Outer Membrane Are not Required for Bax-induced Release of Intermembrane Space Proteins. J Mol Biol 2007; 368:44-54. [PMID: 17335847 DOI: 10.1016/j.jmb.2007.01.016] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2006] [Revised: 12/22/2006] [Accepted: 01/04/2007] [Indexed: 10/23/2022]
Abstract
The mitochondrial outer membrane contains protein import machineries, the translocase of the outer membrane (TOM) and the sorting and assembly machinery (SAM). It has been speculated that TOM or SAM are required for Bax-induced release of intermembrane space (IMS) proteins; however, experimental evidence has been scarce. We used isolated yeast mitochondria as a model system and report that Bax promoted an efficient release of soluble IMS proteins while preproteins were still imported, excluding an unspecific damage of mitochondria. Removal of import receptors by protease treatment did not inhibit the release of IMS proteins by Bax. Yeast mutants of each Tom receptor and the Tom40 channel were not impaired in Bax-induced protein release. We analyzed a large collection of mutants of mitochondrial outer membrane proteins, including SAM, fusion and fission components, but none of these components was required for Bax-induced protein release. The released proteins included complexes up to a size of 230 kDa. We conclude that Bax promotes efficient release of IMS proteins through the outer membrane of yeast mitochondria while the inner membrane remains intact. Inactivation of the known protein import and sorting machineries of the outer membrane does not impair the function of Bax at the mitochondria.
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Affiliation(s)
- Luiza K Sanjuán Szklarz
- Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany
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172
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Bohnert M, Pfanner N, van der Laan M. A dynamic machinery for import of mitochondrial precursor proteins. FEBS Lett 2007; 581:2802-10. [PMID: 17376437 DOI: 10.1016/j.febslet.2007.03.004] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2007] [Accepted: 03/04/2007] [Indexed: 10/23/2022]
Abstract
Mitochondria contain approximately 1000 different proteins, which are located in four different compartments, outer membrane, inner membrane, intermembrane space and matrix. The vast majority of these proteins has to be imported from the cytosol. Therefore, sophisticated molecular machineries have evolved that mediate protein translocation across or insertion into mitochondrial membranes and subsequent assembly into multi-subunit complexes. While the initial entry of virtually all mitochondrial proteins is mediated by the general import pore of the outer membrane, at least four different downstream pathways are dedicated to import and assembly of proteins into a specific compartment.
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Affiliation(s)
- Maria Bohnert
- Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany
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173
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Herrmann JM, Köhl R. Catch me if you can! Oxidative protein trapping in the intermembrane space of mitochondria. ACTA ACUST UNITED AC 2007; 176:559-63. [PMID: 17312024 PMCID: PMC2064014 DOI: 10.1083/jcb.200611060] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The intermembrane space (IMS) of mitochondria, the compartment that phylogenetically originated from the periplasm of bacteria, contains machinery to catalyze the oxidative folding of proteins (Mesecke, N., N. Terziyska, C. Kozany, F. Baumann, W. Neupert, K. Hell, and J.M. Herrmann. 2005. Cell. 121:1059-1069; Rissler, M., N. Wiedemann, S. Pfannschmidt, K. Gabriel, B. Guiard, N. Pfanner, and A. Chacinska. 2005. J. Mol. Biol. 353: 485-492; Tokatlidis, K. 2005. Cell. 121:965-96). This machinery introduces disulfide bonds into newly imported precursor proteins, thereby locking them in a folded conformation. Because folded proteins cannot traverse the translocase of the outer membrane, this stably traps the proteins in the mitochondria. The principle of protein oxidation in the IMS presumably has been conserved from the bacterial periplasm and has been adapted during evolution to drive the vectorial translocation of proteins from the cytosol into the mitochondria.
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Affiliation(s)
- Johannes M Herrmann
- Department of Cell Biology, University of Kaiserslautern, 67663 Kaiserslautern, Germany.
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174
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Terziyska N, Grumbt B, Bien M, Neupert W, Herrmann JM, Hell K. The sulfhydryl oxidase Erv1 is a substrate of the Mia40-dependent protein translocation pathway. FEBS Lett 2007; 581:1098-102. [PMID: 17336303 DOI: 10.1016/j.febslet.2007.02.014] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2006] [Revised: 01/31/2007] [Accepted: 02/08/2007] [Indexed: 11/26/2022]
Abstract
The thiol oxidase Erv1 and the redox-regulated receptor Mia40/Tim40 are components of a disulfide relay system which mediates import of proteins into the intermembrane space (IMS) of mitochondria. Here we report that Erv1 requires Mia40 for its import into mitochondria. After passage across the translocase of the mitochondrial outer membrane Erv1 interacts via disulfide bonds with Mia40. Erv1 does not contain twin "CX(3)C" or twin "CX(9)C" motifs which are crucial for import of typical substrates of this pathway and it does not need two "CX(2)C" motifs for import into mitochondria. Thus, Erv1 represents an unusual type of substrate of the Mia40-dependent import pathway.
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Affiliation(s)
- Nadia Terziyska
- Adolf-Butenandt-Institut für Physiologische Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse 5, D-81377 München, Germany
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175
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Satrústegui J, Pardo B, Del Arco A. Mitochondrial Transporters as Novel Targets for Intracellular Calcium Signaling. Physiol Rev 2007; 87:29-67. [PMID: 17237342 DOI: 10.1152/physrev.00005.2006] [Citation(s) in RCA: 209] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Ca2+signaling in mitochondria is important to tune mitochondrial function to a variety of extracellular stimuli. The main mechanism is Ca2+entry in mitochondria via the Ca2+uniporter followed by Ca2+activation of three dehydrogenases in the mitochondrial matrix. This results in increases in mitochondrial NADH/NAD ratios and ATP levels and increased substrate uptake by mitochondria. We review evidence gathered more than 20 years ago and recent work indicating that substrate uptake, mitochondrial NADH/NAD ratios, and ATP levels may be also activated in response to cytosolic Ca2+signals via a mechanism that does not require the entry of Ca2+in mitochondria, a mechanism depending on the activity of Ca2+-dependent mitochondrial carriers (CaMC). CaMCs fall into two groups, the aspartate-glutamate carriers (AGC) and the ATP-Mg/Picarriers, also named SCaMC (for short CaMC). The two mammalian AGCs, aralar and citrin, are members of the malate-aspartate NADH shuttle, and citrin, the liver AGC, is also a member of the urea cycle. Both types of CaMCs are activated by Ca2+in the intermembrane space and function together with the Ca2+uniporter in decoding the Ca2+signal into a mitochondrial response.
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Affiliation(s)
- Jorgina Satrústegui
- Departamento de Biología Molecular Centro de Biología Molecular "Severo Ochoa" UAM-CSIC, Facultad de Ciencias, Universidad Autónoma, Madrid, Spain.
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176
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MacKenzie JA, Payne RM. Mitochondrial protein import and human health and disease. Biochim Biophys Acta Mol Basis Dis 2006; 1772:509-23. [PMID: 17300922 PMCID: PMC2702852 DOI: 10.1016/j.bbadis.2006.12.002] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2006] [Revised: 12/06/2006] [Accepted: 12/07/2006] [Indexed: 12/31/2022]
Abstract
The targeting and assembly of nuclear-encoded mitochondrial proteins are essential processes because the energy supply of humans is dependent upon the proper functioning of mitochondria. Defective import of mitochondrial proteins can arise from mutations in the targeting signals within precursor proteins, from mutations that disrupt the proper functioning of the import machinery, or from deficiencies in the chaperones involved in the proper folding and assembly of proteins once they are imported. Defects in these steps of import have been shown to lead to oxidative stress, neurodegenerative diseases, and metabolic disorders. In addition, protein import into mitochondria has been found to be a dynamically regulated process that varies in response to conditions such as oxidative stress, aging, drug treatment, and exercise. This review focuses on how mitochondrial protein import affects human health and disease.
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Affiliation(s)
- James A MacKenzie
- Department of Biological Sciences, 133 Piez Hall, State University of New York at Oswego, Oswego, NY 13126, USA.
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177
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Stirling PC, Bakhoum SF, Feigl AB, Leroux MR. Convergent evolution of clamp-like binding sites in diverse chaperones. Nat Struct Mol Biol 2006; 13:865-70. [PMID: 17021621 DOI: 10.1038/nsmb1153] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Molecular chaperones have evolved diverse tertiary and quaternary structures to stabilize non-native polypeptides and facilitate their transition to the native state. Indeed, different families of chaperones lack sequence similarity, and few are represented ubiquitously in all three domains of life. Despite their discrete evolutionary paths, recent crystal structures reveal that many chaperones use seemingly convergent strategies to bind non-native proteins. This crystallographic evidence shows, or strongly suggests, that chaperones including prefoldin, Skp, trigger factor, Hsp40 and Hsp90 have clamp-like structural features used to grip substrate proteins. We explore the notion that clamp-like structures are evolutionarily favored by both ATP-dependent and ATP-independent molecular chaperones. Presumably, clamps present a multivalent binding surface ideal for protecting unstable protein conformers until they reach the native state or are transferred to another component of the folding machinery.
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Affiliation(s)
- Peter C Stirling
- Department of Molecular Biology and Biochemistry, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, V5A 1S6, Canada
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178
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Davis AJ, Alder NN, Jensen RE, Johnson AE. The Tim9p/10p and Tim8p/13p complexes bind to specific sites on Tim23p during mitochondrial protein import. Mol Biol Cell 2006; 18:475-86. [PMID: 17122363 PMCID: PMC1783793 DOI: 10.1091/mbc.e06-06-0546] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The import of polytopic membrane proteins into the mitochondrial inner membrane (IM) is facilitated by Tim9p/Tim10p and Tim8p/Tim13p protein complexes in the intermembrane space (IMS). These complexes are proposed to act as chaperones by transporting the hydrophobic IM proteins through the aqueous IMS and preventing their aggregation. To examine the nature of this interaction, Tim23p molecules containing a single photoreactive cross-linking probe were imported into mitochondria in the absence of an IM potential where they associated with small Tim complexes in the IMS. On photolysis and immunoprecipitation, a probe located at a particular Tim23p site (27 different locations were examined) was found to react covalently with, in most cases, only one of the small Tim proteins. Tim8p, Tim9p, Tim10p, and Tim13p were therefore positioned adjacent to specific sites in the Tim23p substrate before its integration into the IM. This specificity of binding to Tim23p strongly suggests that small Tim proteins do not function solely as general chaperones by minimizing the exposure of nonpolar Tim23p surfaces to the aqueous medium, but may also align a folded Tim23p substrate in the proper orientation for delivery and integration into the IM at the TIM22 translocon.
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Affiliation(s)
- Alison J. Davis
- *Department of Molecular and Cellular Medicine, Texas A&M University System Health Science Center, College Station, TX 77843-1114
| | - Nathan N. Alder
- *Department of Molecular and Cellular Medicine, Texas A&M University System Health Science Center, College Station, TX 77843-1114
| | - Robert E. Jensen
- Department of Cell Biology and Anatomy, The Johns Hopkins University School of Medicine, Baltimore, MD 21205; and
| | - Arthur E. Johnson
- *Department of Molecular and Cellular Medicine, Texas A&M University System Health Science Center, College Station, TX 77843-1114
- Departments of Chemistry and
- Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843
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179
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Albrecht R, Rehling P, Chacinska A, Brix J, Cadamuro SA, Volkmer R, Guiard B, Pfanner N, Zeth K. The Tim21 binding domain connects the preprotein translocases of both mitochondrial membranes. EMBO Rep 2006; 7:1233-8. [PMID: 17099692 PMCID: PMC1794701 DOI: 10.1038/sj.embor.7400828] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2006] [Revised: 08/11/2006] [Accepted: 09/08/2006] [Indexed: 11/08/2022] Open
Abstract
Proteins destined for the mitochondrial matrix are imported by the translocase of the outer membrane--the TOM complex--and the presequence translocase of the inner membrane--the TIM23 complex. At present, there is no structural information on components of the presequence translocase. Tim21, a subunit of the presequence translocase consisting of a membrane anchor and a carboxy-terminal domain exposed to the intermembrane space, directly connects the TOM and TIM23 complexes by binding to the intermembrane space domain of the Tom22 receptor. We crystallized the binding domain of Tim21 of Saccharomyces cerevisiae and determined its structure at 1.6 A resolution. The Tim21 structure represents a new alpha/beta-mixed protein fold with two alpha-helices flanked by an extended eight-stranded beta-sheet. We also identified a core sequence of Tom22 that binds to Tim21. Furthermore, negatively charged amino-acid residues of Tom22 are important for binding to Tim21. Here we suggest a mechanism for the TOM-TIM interaction.
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Affiliation(s)
- Reinhard Albrecht
- Max-Planck-Institut für Biochemie, Abteilung Membranbiochemie, Am Klopferspitz 18, D-82512 Martinsried, Germany
- Max-Planck-Institut für Entwicklungsbiologie, Abteilung Protein Evolution, Spemannstraße 35/I, D-72076 Tübingen, Germany
| | - Peter Rehling
- Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Universität Freiburg, Hermann-Herder-Straße 7, D-79104 Freiburg, Germany
| | - Agnieszka Chacinska
- Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Universität Freiburg, Hermann-Herder-Straße 7, D-79104 Freiburg, Germany
| | - Jan Brix
- Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Universität Freiburg, Hermann-Herder-Straße 7, D-79104 Freiburg, Germany
| | - Sergio A Cadamuro
- Max-Planck-Institut für Biochemie, Laboratory of Bioorganic Chemistry, Am Klopferspitz 18, D-82512 Martinsried, Germany
| | - Rudolf Volkmer
- Institut für Medizinische Immunologie, Charité—Universitätsmedizin Berlin, Hessische Straße 3–4, D-10115 Berlin, Germany
| | - Bernard Guiard
- Centre de Génétique Moléculaire, CNRS, Avenue de la Terrasse—Bât. 26, F-91190 Gif-sur-Yvette, France
| | - Nikolaus Pfanner
- Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Universität Freiburg, Hermann-Herder-Straße 7, D-79104 Freiburg, Germany
- Tel: +49 761 2035224; Fax: +49 761 2035261; E-mail:
| | - Kornelius Zeth
- Max-Planck-Institut für Biochemie, Abteilung Membranbiochemie, Am Klopferspitz 18, D-82512 Martinsried, Germany
- Max-Planck-Institut für Entwicklungsbiologie, Abteilung Protein Evolution, Spemannstraße 35/I, D-72076 Tübingen, Germany
- Tel: +49 7071 601 323; Fax: +49 7071 601 349; E-mail:
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180
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Gabriel K, Milenkovic D, Chacinska A, Müller J, Guiard B, Pfanner N, Meisinger C. Novel mitochondrial intermembrane space proteins as substrates of the MIA import pathway. J Mol Biol 2006; 365:612-20. [PMID: 17095012 DOI: 10.1016/j.jmb.2006.10.038] [Citation(s) in RCA: 130] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2006] [Revised: 10/06/2006] [Accepted: 10/09/2006] [Indexed: 10/24/2022]
Abstract
Mitochondria consist of four compartments, the outer membrane, intermembrane space (IMS), inner membrane and the matrix. Most mitochondrial proteins are synthesized as precursors in the cytosol and have to be imported into these compartments. While the protein import machineries of the outer membrane, inner membrane and matrix have been investigated in detail, a specific mitochondrial machinery for import and assembly of IMS proteins, termed MIA, was identified only recently. To date, only a very small number of substrate proteins of the MIA pathway have been identified. The substrates contain characteristic cysteine motifs, either a twin Cx(3)C or a twin Cx(9)C motif. The largest MIA substrates known possess a molecular mass of 11 kDa, implying that this new import pathway has a very small size limit. Here, we have compiled a list of Saccharomyces cerevisiae proteins with a twin Cx(9)C motif and identified three IMS proteins that were previously localized to incorrect cellular compartments by tagging approaches. Mdm35, Mic14 (YDR031w) and Mic17 (YMR002w) require the two essential subunits, Mia40 and Erv1, of the MIA machinery for their localization in the mitochondrial IMS. With a molecular mass of 14 kDa and 17 kDa, respectively, Mic14 and Mic17 are larger than the known MIA substrates. Remarkably, the precursor of Erv1 itself is imported via the MIA pathway. As Erv1 has a molecular mass of 22 kDa and a twin Cx(2)C motif, this study demonstrates that the MIA pathway can transport substrates that are twice as large as the substrates known to date and is not limited to proteins with twin Cx(3)C or Cx(9)C motifs. However, tagging of MIA substrates can interfere with their subcellular localization, indicating that the proper localization of mitochondrial IMS proteins requires the characterization of the authentic untagged proteins.
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Affiliation(s)
- Kipros Gabriel
- Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany
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181
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Fan ACY, Bhangoo MK, Young JC. Hsp90 functions in the targeting and outer membrane translocation steps of Tom70-mediated mitochondrial import. J Biol Chem 2006; 281:33313-24. [PMID: 16968702 DOI: 10.1074/jbc.m605250200] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Tom70 import receptor on the mitochondrial outer membrane specifically recognizes Hsp90 and Hsc70, a critical step for the import of mitochondrial preproteins, the targeting of which depends on these cytosolic chaperones. To analyze the role of Hsp90 in mitochondrial import, the effects of the Hsp90 inhibitors geldanamycin and novobiocin were compared. Geldanamycin occludes the N-terminal ATP-binding site of Hsp90, whereas novobiocin targets the C-terminal region of the chaperone. Here, novobiocin was found to inhibit preprotein import and, in particular, targeting to the purified cytosolic fragment of Tom70. Hsp90 cross-linking to preprotein and coprecipitation of Hsp90 with Tom70 were both impaired by novobiocin. Overall, novobiocin treatment increased preprotein aggregation, contributing to reduced import competence. In contrast, geldanamycin had no apparent effect on preprotein interactions with Hsp90, formation of preprotein-chaperone complexes, Hsp90 docking onto Tom70, or preprotein association with the outer membrane. Instead, geldanamycin impaired formation of preprotein import intermediates at the outer membrane. This suggests a novel active role for Hsp90 in import steps subsequent to Tom70 targeting. Our results outline the mechanisms of Hsp90 function in preprotein targeting and transport.
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Affiliation(s)
- Anna C Y Fan
- Department of Biochemistry, McGill University, Montréal, Québec H3G 1Y6, Canada
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182
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Meisinger C, Wiedemann N, Rissler M, Strub A, Milenkovic D, Schönfisch B, Müller H, Kozjak V, Pfanner N. Mitochondrial Protein Sorting. J Biol Chem 2006; 281:22819-26. [PMID: 16760475 DOI: 10.1074/jbc.m602679200] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mitochondrial outer membrane contains two distinct machineries for protein import and protein sorting that function in a sequential manner: the general translocase of the outer membrane (TOM complex) and the sorting and assembly machinery (SAM complex), which is dedicated to beta-barrel proteins. The SAM(core) complex consists of three subunits, Sam35, Sam37, and Sam50, that can associate with a fourth subunit, the morphology component Mdm10, to form the SAM(holo) complex. Whereas the SAM(core) complex is required for the biogenesis of all beta-barrel proteins, Mdm10 and the SAM(holo) complex play a selective role in beta-barrel biogenesis by promoting assembly of Tom40 but not of porin. We report that Tom7, a conserved subunit of the TOM complex, functions in an antagonistic manner to Mdm10 in biogenesis of Tom40 and porin. We show that Tom7 promotes segregation of Mdm10 from the SAM(holo) complex into a low molecular mass form. Upon deletion of Tom7, the fraction of Mdm10 in the SAM(holo) complex is significantly increased, explaining the opposing functions of Tom7 and Mdm10 in beta-barrel sorting. Thus the role of Tom7 is not limited to the TOM complex. Tom7 functions in mitochondrial protein biogenesis by a new mechanism, segregation of a sorting component, leading to a differentiation of beta-barrel assembly.
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Affiliation(s)
- Chris Meisinger
- Institut für Biochemie und Molekularbiologie and the Fakultät für Biologie, Universität Freiburg, 79104 Freiburg
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183
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Dolezal P, Likic V, Tachezy J, Lithgow T. Evolution of the molecular machines for protein import into mitochondria. Science 2006; 313:314-8. [PMID: 16857931 DOI: 10.1126/science.1127895] [Citation(s) in RCA: 422] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
In creating mitochondria some 2 billion years ago, the first eukaryotes needed to establish protein import machinery in the membranes of what was a bacterial endosymbiont. Some of the preexisting protein translocation apparatus of the endosymbiont appears to have been commandeered, including molecular chaperones, the signal peptidase, and some components of the protein-targeting machinery. However, the protein translocases that drive protein import into mitochondria have no obvious counterparts in bacteria, making it likely that these machines were created de novo. The presence of similar translocase subunits in all eukaryotic genomes sequenced to date suggests that all eukaryotes can be considered descendants of a single ancestor species that carried an ancestral "protomitochondria."
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Affiliation(s)
- Pavel Dolezal
- Department of Biochemistry & Molecular Biology, University of Melbourne, Parkville 3010, Australia
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184
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Matsufuji Y, Nakagawa T, Ito T, Fujimura S, Chikui M, Miyaji T, Tomizuka N. Molecular characterization of theTim9 homologue from the methylotrophic yeastPichia methanolica. Yeast 2006; 23:701-6. [PMID: 16845686 DOI: 10.1002/yea.1385] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
In this paper we describe molecular characterization of the TIM9 gene encoding the essential mitochondrial inner-membrane protein in the methylotrophic yeast Pichia methanolica. PmTIM9 contains two exons corresponding to a gene product of 89 amino acid residues and a 140 bp intron. The deduced amino acid sequence exhibited high identity to those of other yeast Tim9ps, and possessed two CX(3)C motifs that contained two cysteine residues conserved among small Tim family proteins. Moreover, PmTIM9 had the ability to partially suppress the temperature sensitivity of Saccharomyces cerevisiae strain tim9-3, suggesting that PmTIM9 is a functional homologue of the ScTIM9 gene.
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Affiliation(s)
- Yoshimi Matsufuji
- Department of Food Science and Technology, Faculty of Bioindustry, Tokyo University of Agriculture, 196 Yasaka, Abashiri, Hokkaido 099-2493, Japan
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185
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de Marcos-Lousa C, Sideris DP, Tokatlidis K. Translocation of mitochondrial inner-membrane proteins: conformation matters. Trends Biochem Sci 2006; 31:259-67. [PMID: 16616497 DOI: 10.1016/j.tibs.2006.03.006] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2005] [Revised: 02/15/2006] [Accepted: 03/23/2006] [Indexed: 10/24/2022]
Abstract
Most of the mitochondrial inner-membrane proteins are generated without a presequence and their targeting depends on inadequately defined internal segments. Despite the numerous components of the import machinery identified by proteomics, the properties of hydrophobic import substrates remain poorly understood. Recent studies support several principles for these membrane proteins: first, they become organized into partially assembled forms within the translocon; second, they present noncontiguous targeting signals; and third, they induce conformational changes in translocase subunits, thereby mediating "assembly on demand" of the import machinery. It is possible that the energy needed for these proteins to pass across the outer membrane, to travel through the intermembrane space and to target the inner-membrane surface is provided by conformational changes involving import components that seem to have natively unfolded structures. Such structural malleability might render some of the translocase subunits more adept at driving the protein import process.
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Affiliation(s)
- Carine de Marcos-Lousa
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology (IMBB-FORTH), PO Box 1385, Heraklion 71110, Crete, Greece
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186
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Abstract
The first high-resolution structure of a mitochondrial translocase complex, the Tim9-Tim10 chaperone, is reported by Webb et al. (2006) in a recent issue of Molecular Cell, providing important insight in the transport of hydrophobic proteins through the aqueous intermembrane space and the mechanisms of protein assembly.
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Affiliation(s)
- Nils Wiedemann
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany
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