1
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Structural basis of Tom20 and Tom22 cytosolic domains as the human TOM complex receptors. Proc Natl Acad Sci U S A 2022; 119:e2200158119. [PMID: 35733257 PMCID: PMC9245660 DOI: 10.1073/pnas.2200158119] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Mitochondrial preproteins synthesized in cytosol are imported into mitochondria by a multisubunit translocase of the outer membrane (TOM) complex. Functioned as the receptor, the TOM complex components, Tom 20, Tom22, and Tom70, recognize the presequence and further guide the protein translocation. Their deficiency has been linked with neurodegenerative diseases and cardiac pathology. Although several structures of the TOM complex have been reported by cryoelectron microscopy (cryo-EM), how Tom22 and Tom20 function as TOM receptors remains elusive. Here we determined the structure of TOM core complex at 2.53 Å and captured the structure of the TOM complex containing Tom22 and Tom20 cytosolic domains at 3.74 Å. Structural analysis indicates that Tom20 and Tom22 share a similar three-helix bundle structural feature in the cytosolic domain. Further structure-guided biochemical analysis reveals that the Tom22 cytosolic domain is responsible for binding to the presequence, and the helix H1 is critical for this binding. Altogether, our results provide insights into the functional mechanism of the TOM complex recognizing and transferring preproteins across the mitochondrial membrane.
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2
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Wang W, Chen X, Zhang L, Yi J, Ma Q, Yin J, Zhuo W, Gu J, Yang M. Atomic structure of human TOM core complex. Cell Discov 2020; 6:67. [PMID: 33083003 PMCID: PMC7522991 DOI: 10.1038/s41421-020-00198-2] [Citation(s) in RCA: 47] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Accepted: 07/20/2020] [Indexed: 12/22/2022] Open
Abstract
The translocase of the outer mitochondrial membrane (TOM) complex is the main entry gate for mitochondrial precursor proteins synthesized on cytosolic ribosomes. Here we report the single-particle cryo-electron microscopy (cryo-EM) structure of the dimeric human TOM core complex (TOM-CC). Two Tom40 β-barrel proteins, connected by two Tom22 receptor subunits and one phospholipid, form the protein-conducting channels. The small Tom proteins Tom5, Tom6, and Tom7 surround the channel and have notable configurations. The distinct electrostatic features of the complex, including the pronounced negative interior and the positive regions at the periphery and center of the dimer on the intermembrane space (IMS) side, provide insight into the preprotein translocation mechanism. Further, two dimeric TOM complexes may associate to form tetramer in the shape of a parallelogram, offering a potential explanation into the unusual structural features of Tom subunits and a new perspective of viewing the import of mitochondrial proteins.
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Affiliation(s)
- Wenhe Wang
- Ministry of Education Key Laboratory of Protein Science, Beijing Advanced Innovation Center for Structural Biology & Frontier Research Center for Biological Structure, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, 100084 Beijing, China
| | - Xudong Chen
- Ministry of Education Key Laboratory of Protein Science, Beijing Advanced Innovation Center for Structural Biology & Frontier Research Center for Biological Structure, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, 100084 Beijing, China
| | - Laixing Zhang
- Ministry of Education Key Laboratory of Protein Science, Beijing Advanced Innovation Center for Structural Biology & Frontier Research Center for Biological Structure, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, 100084 Beijing, China
| | - Jingbo Yi
- Ministry of Education Key Laboratory of Protein Science, Beijing Advanced Innovation Center for Structural Biology & Frontier Research Center for Biological Structure, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, 100084 Beijing, China
| | - Qingxi Ma
- Ministry of Education Key Laboratory of Protein Science, Beijing Advanced Innovation Center for Structural Biology & Frontier Research Center for Biological Structure, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, 100084 Beijing, China
| | - Jian Yin
- Ministry of Education Key Laboratory of Protein Science, Beijing Advanced Innovation Center for Structural Biology & Frontier Research Center for Biological Structure, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, 100084 Beijing, China
| | - Wei Zhuo
- Ministry of Education Key Laboratory of Protein Science, Beijing Advanced Innovation Center for Structural Biology & Frontier Research Center for Biological Structure, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, 100084 Beijing, China
| | - Jinke Gu
- Ministry of Education Key Laboratory of Protein Science, Beijing Advanced Innovation Center for Structural Biology & Frontier Research Center for Biological Structure, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, 100084 Beijing, China
| | - Maojun Yang
- Ministry of Education Key Laboratory of Protein Science, Beijing Advanced Innovation Center for Structural Biology & Frontier Research Center for Biological Structure, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, 100084 Beijing, China
- School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030 Hubei China
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3
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Di Maio R, Barrett PJ, Hoffman EK, Barrett CW, Zharikov A, Borah A, Hu X, McCoy J, Chu CT, Burton EA, Hastings TG, Greenamyre JT. α-Synuclein binds to TOM20 and inhibits mitochondrial protein import in Parkinson's disease. Sci Transl Med 2016; 8:342ra78. [PMID: 27280685 PMCID: PMC5016095 DOI: 10.1126/scitranslmed.aaf3634] [Citation(s) in RCA: 377] [Impact Index Per Article: 47.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2016] [Accepted: 05/17/2016] [Indexed: 12/16/2022]
Abstract
α-Synuclein accumulation and mitochondrial dysfunction have both been strongly implicated in the pathogenesis of Parkinson's disease (PD), and the two appear to be related. Mitochondrial dysfunction leads to accumulation and oligomerization of α-synuclein, and increased levels of α-synuclein cause mitochondrial impairment, but the basis for this bidirectional interaction remains obscure. We now report that certain posttranslationally modified species of α-synuclein bind with high affinity to the TOM20 (translocase of the outer membrane 20) presequence receptor of the mitochondrial protein import machinery. This binding prevented the interaction of TOM20 with its co-receptor, TOM22, and impaired mitochondrial protein import. Consequently, there were deficient mitochondrial respiration, enhanced production of reactive oxygen species, and loss of mitochondrial membrane potential. Examination of postmortem brain tissue from PD patients revealed an aberrant α-synuclein-TOM20 interaction in nigrostriatal dopaminergic neurons that was associated with loss of imported mitochondrial proteins, thereby confirming this pathogenic process in the human disease. Modest knockdown of endogenous α-synuclein was sufficient to maintain mitochondrial protein import in an in vivo model of PD. Furthermore, in in vitro systems, overexpression of TOM20 or a mitochondrial targeting signal peptide had beneficial effects and preserved mitochondrial protein import. This study characterizes a pathogenic mechanism in PD, identifies toxic species of wild-type α-synuclein, and reveals potential new therapeutic strategies for neuroprotection.
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Affiliation(s)
- Roberto Di Maio
- Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh, Pittsburgh, PA 15213, USA. Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA. Ri.MED Foundation, Palermo, Italy
| | - Paul J Barrett
- Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh, Pittsburgh, PA 15213, USA. Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Eric K Hoffman
- Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh, Pittsburgh, PA 15213, USA. Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Caitlyn W Barrett
- Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh, Pittsburgh, PA 15213, USA. Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Alevtina Zharikov
- Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh, Pittsburgh, PA 15213, USA. Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA. Geriatric Research Education and Clinical Center, VA Pittsburgh Healthcare System, Pittsburgh, PA 15240, USA
| | - Anupom Borah
- Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh, Pittsburgh, PA 15213, USA. Department of Life Science and Bioinformatics, Assam University, Silchar 788011, India
| | - Xiaoping Hu
- Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh, Pittsburgh, PA 15213, USA. Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Jennifer McCoy
- Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh, Pittsburgh, PA 15213, USA. Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Charleen T Chu
- Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh, Pittsburgh, PA 15213, USA. Department of Pathology, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Edward A Burton
- Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh, Pittsburgh, PA 15213, USA. Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA. Geriatric Research Education and Clinical Center, VA Pittsburgh Healthcare System, Pittsburgh, PA 15240, USA
| | - Teresa G Hastings
- Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh, Pittsburgh, PA 15213, USA. Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - J Timothy Greenamyre
- Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh, Pittsburgh, PA 15213, USA. Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA. Geriatric Research Education and Clinical Center, VA Pittsburgh Healthcare System, Pittsburgh, PA 15240, USA.
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4
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Characterization of the membrane-inserted C-terminus of cytoprotective BCL-XL. Protein Expr Purif 2016; 122:56-63. [PMID: 26923059 DOI: 10.1016/j.pep.2016.02.010] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2015] [Revised: 02/01/2016] [Accepted: 02/17/2016] [Indexed: 02/03/2023]
Abstract
BCL-XL is a dominant inhibitor of apoptosis and a significant anti-cancer drug target. Endogenous BCL-XL is integral to the mitochondrial outer membrane (MOM). BCL-XL reconstituted in detergent-free lipid bilayer nanodiscs is anchored to the nanodisc lipid bilayer membrane by tight association of its C-terminal tail, while the N-terminal head retains the canonical structure determined for water-soluble, tail-truncated BCL-XL, with the surface groove solvent-exposed and available for BH3 ligand binding. To better understand the conformation and dynamics of this key region of BCL-XL we have developed methods for isolating the membrane-embedded C-terminal tail from its N-terminal head and for preparing protein suitable for structural and biochemical studies. Here, we outline the methods for sample preparation and characterization and describe previously unreported structural and dynamics features. We show that the C-terminal tail of BCL-XL forms a transmembrane α-helix that retains a significant degree of conformational dynamics. We also show that the presence of the intact C-terminus destabilizes the soluble state of the protein, and that the small fraction of soluble recombinant protein produced in Escherichia coli is susceptible to proteolytic degradation of C-terminal residues beyond M218. This finding impacts the numerous previous studies where recombinant soluble BCL-XL was presumed to be full-length. Nevertheless, the majority of recombinant BCL-XL produced in E. coli is insoluble and protected from proteolysis. This protein retains the complete C-terminal tail and can be reconstituted in lipid bilayers in a folded and active state.
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5
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Wang X, Patel ND, Hui D, Pal R, Hafez MM, Sayed-Ahmed MM, Al-Yahya AA, Michaelis EK. Gene expression patterns in the hippocampus during the development and aging of Glud1 (Glutamate Dehydrogenase 1) transgenic and wild type mice. BMC Neurosci 2014; 15:37. [PMID: 24593767 PMCID: PMC3973933 DOI: 10.1186/1471-2202-15-37] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2013] [Accepted: 02/24/2014] [Indexed: 11/22/2022] Open
Abstract
Background Extraneuronal levels of the neurotransmitter glutamate in brain rise during aging. This is thought to lead to synaptic dysfunction and neuronal injury or death. To study the effects of glutamate hyperactivity in brain, we created transgenic (Tg) mice in which the gene for glutamate dehydrogenase (Glud1) is over-expressed in neurons and in which such overexpression leads to excess synaptic release of glutamate. In this study, we analyzed whole genome expression in the hippocampus, a region important for learning and memory, of 10 day to 20 month old Glud1 and wild type (wt) mice. Results During development, maturation and aging, both Tg and wt exhibited decreases in the expression of genes related to neurogenesis, neuronal migration, growth, and process elongation, and increases in genes related to neuro-inflammation, voltage-gated channel activity, and regulation of synaptic transmission. Categories of genes that were differentially expressed in Tg vs. wt during development were: synaptic function, cytoskeleton, protein ubiquitination, and mitochondria; and, those differentially expressed during aging were: synaptic function, vesicle transport, calcium signaling, protein kinase activity, cytoskeleton, neuron projection, mitochondria, and protein ubiquitination. Overall, the effects of Glud1 overexpression on the hippocampus transcriptome were greater in the mature and aged than the young. Conclusions Glutamate hyperactivity caused gene expression changes in the hippocampus at all ages. Some of these changes may result in premature brain aging. The identification of these genomic expression differences is important in understanding the effects of glutamate dysregulation on neuronal function during aging or in neurodegenerative diseases.
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Affiliation(s)
- Xinkun Wang
- Higuchi Biosciences Center, University of Kansas, 2099 Constant Ave,, Lawrence, KS 66047, USA.
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6
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Kriechbaumer V, Abell BM. Chloroplast envelope protein targeting fidelity is independent of cytosolic components in dual organelle assays. FRONTIERS IN PLANT SCIENCE 2012; 3:148. [PMID: 22783268 PMCID: PMC3384937 DOI: 10.3389/fpls.2012.00148] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2012] [Accepted: 06/14/2012] [Indexed: 05/22/2023]
Abstract
The general mechanisms of intracellular protein targeting are well established, and depend on a targeting sequence in the protein, which is recognized by a targeting factor. Once a membrane protein is delivered to the correct organelle its targeting sequence can be recognized by receptors and a translocase, leading to membrane insertion. However, the relative contribution of each step for generating fidelity and efficiency of the overall process has not been systematically addressed. Here, we use tail-anchored (TA) membrane proteins in cell-free competitive targeting assays to chloroplasts to show that targeting can occur efficiently and with high fidelity in the absence of all cytosolic components, suggesting that chloroplast envelope protein targeting is primarily dependent on events at the outer envelope. Efficiency of targeting was increased by the addition of complete cytosol, and by Hsp70 or Hsp90, depending on the protein, but none of these cytosolic components influenced the fidelity of targeting. Our results suggest that the main role of targeting factors in chloroplast localization is to increase targeting efficiency by maintaining recognition competency at the outer envelope.
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Affiliation(s)
| | - Ben M. Abell
- *Correspondence: Ben M. Abell, Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S1 1WB, UK. e-mail:
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7
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Gessmann D, Flinner N, Pfannstiel J, Schlösinger A, Schleiff E, Nussberger S, Mirus O. Structural elements of the mitochondrial preprotein-conducting channel Tom40 dissolved by bioinformatics and mass spectrometry. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2011; 1807:1647-57. [DOI: 10.1016/j.bbabio.2011.08.006] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2011] [Revised: 08/12/2011] [Accepted: 08/17/2011] [Indexed: 11/27/2022]
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8
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Zhang Y, Baaden M, Yan J, Shao J, Qiu S, Wu Y, Ding Y. The Molecular Recognition Mechanism for Superoxide Dismutase Presequence Binding to the Mitochondrial Protein Import Receptor Tom20 from Oryza sativa Involves an LRTLA Motif. J Phys Chem B 2010; 114:13839-46. [DOI: 10.1021/jp103547s] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Yubo Zhang
- Key Laboratory of Ministry of Education for Plant Developmental Biology, College of Life Sciences, Wuhan University, Wuhan 430072, P. R. China, Institut de Biologie Physico-Chimique, Laboratoire de Biochimie Théorique, CNRS UPR 9080, 13, rue Pierre et Marie Curie, F-75005 Paris, France, and State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, P. R. China
| | - Marc Baaden
- Key Laboratory of Ministry of Education for Plant Developmental Biology, College of Life Sciences, Wuhan University, Wuhan 430072, P. R. China, Institut de Biologie Physico-Chimique, Laboratoire de Biochimie Théorique, CNRS UPR 9080, 13, rue Pierre et Marie Curie, F-75005 Paris, France, and State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, P. R. China
| | - Junjie Yan
- Key Laboratory of Ministry of Education for Plant Developmental Biology, College of Life Sciences, Wuhan University, Wuhan 430072, P. R. China, Institut de Biologie Physico-Chimique, Laboratoire de Biochimie Théorique, CNRS UPR 9080, 13, rue Pierre et Marie Curie, F-75005 Paris, France, and State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, P. R. China
| | - Jinzhen Shao
- Key Laboratory of Ministry of Education for Plant Developmental Biology, College of Life Sciences, Wuhan University, Wuhan 430072, P. R. China, Institut de Biologie Physico-Chimique, Laboratoire de Biochimie Théorique, CNRS UPR 9080, 13, rue Pierre et Marie Curie, F-75005 Paris, France, and State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, P. R. China
| | - Su Qiu
- Key Laboratory of Ministry of Education for Plant Developmental Biology, College of Life Sciences, Wuhan University, Wuhan 430072, P. R. China, Institut de Biologie Physico-Chimique, Laboratoire de Biochimie Théorique, CNRS UPR 9080, 13, rue Pierre et Marie Curie, F-75005 Paris, France, and State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, P. R. China
| | - Yingliang Wu
- Key Laboratory of Ministry of Education for Plant Developmental Biology, College of Life Sciences, Wuhan University, Wuhan 430072, P. R. China, Institut de Biologie Physico-Chimique, Laboratoire de Biochimie Théorique, CNRS UPR 9080, 13, rue Pierre et Marie Curie, F-75005 Paris, France, and State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, P. R. China
| | - Yi Ding
- Key Laboratory of Ministry of Education for Plant Developmental Biology, College of Life Sciences, Wuhan University, Wuhan 430072, P. R. China, Institut de Biologie Physico-Chimique, Laboratoire de Biochimie Théorique, CNRS UPR 9080, 13, rue Pierre et Marie Curie, F-75005 Paris, France, and State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, P. R. China
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9
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Bohnsack MT, Schleiff E. The evolution of protein targeting and translocation systems. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2010; 1803:1115-30. [DOI: 10.1016/j.bbamcr.2010.06.005] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2010] [Revised: 05/26/2010] [Accepted: 06/11/2010] [Indexed: 11/28/2022]
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10
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Synthesis and biophysical characterization of stabilized alpha-helices of BCL-2 domains. Methods Enzymol 2008; 446:369-86. [PMID: 18603134 DOI: 10.1016/s0076-6879(08)01622-4] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Rational design of compounds to mimic the functional domains of BCL-2 family proteins requires chemical reproduction of the biologic complexity afforded by the relatively large and folded surfaces of BCL-2 homology (BH) domain peptide alpha-helices. Because the intermolecular handshakes of BCL-2 proteins are so critical to controlling cellular fate, we undertook the development of a toolbox of peptidic ligands that harness the natural potency and specificity of BH alpha-helices to interrogate and potentially medicate the deregulated apoptotic pathways of human disease. To overcome the classic deficiencies of peptide reagents, including loss of bioactive structure in solution, rapid proteolytic degradation in vivo, and cellular impermeability, we developed a new class of compounds based on hydrocarbon stapling of BH3 death domain peptides. Here we describe the chemical synthesis of Stabilized Alpha-Helices of BCL-2 domains or SAHBs, and the analytical methods used to characterize their secondary structure, proteolytic stability, and cellular penetrance.
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11
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Bhangoo MK, Tzankov S, Fan AC, Dejgaard K, Thomas DY, Young JC. Multiple 40-kDa heat-shock protein chaperones function in Tom70-dependent mitochondrial import. Mol Biol Cell 2007; 18:3414-28. [PMID: 17596514 PMCID: PMC1951752 DOI: 10.1091/mbc.e07-01-0088] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Mitochondrial preproteins that are imported via the translocase of the mitochondrial outer membrane (Tom)70 receptor are complexed with cytosolic chaperones before targeting to the mitochondrial outer membrane. The adenine nucleotide transporter (ANT) follows this pathway, and its purified mature form is identical to the preprotein. Purified ANT was reconstituted with chaperones in reticulocyte lysate, and bound proteins were identified by mass spectrometry. In addition to 70-kDa heat-shock cognate protein (Hsc70) and 90-kDa heat-shock protein (Hsp90), a specific subset of cochaperones were found, but no mitochondria-specific targeting factors were found. Interestingly, three different Hsp40-related J-domain proteins were identified: DJA1, DJA2, and DJA4. The DJAs bound preproteins to different extents through their C-terminal regions. DJA dominant-negative mutants lacking the N-terminal J-domains impaired mitochondrial import. The mutants blocked the binding of Hsc70 to preprotein, but with varying efficiency. The DJAs also showed significant differences in activation of the Hsc70 ATPase and Hsc70-dependent protein refolding. In HeLa cells, the DJAs increased new protein folding and mitochondrial import, although to different extents. No single DJA was superior to the others in all aspects, but each had a profile of partial specialization. The Hsp90 cochaperones p23 and Aha1 also regulated Hsp90-preprotein interactions. We suggest that multiple cochaperones with similar yet partially specialized properties cooperate in optimal chaperone-preprotein complexes.
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Affiliation(s)
- Melanie K. Bhangoo
- Department of Biochemistry, McGill University, Montreal, QC, H3G 1Y6, Canada
| | - Stefan Tzankov
- Department of Biochemistry, McGill University, Montreal, QC, H3G 1Y6, Canada
| | - Anna C.Y. Fan
- Department of Biochemistry, McGill University, Montreal, QC, H3G 1Y6, Canada
| | - Kurt Dejgaard
- Department of Biochemistry, McGill University, Montreal, QC, H3G 1Y6, Canada
| | - David Y. Thomas
- Department of Biochemistry, McGill University, Montreal, QC, H3G 1Y6, Canada
| | - Jason C. Young
- Department of Biochemistry, McGill University, Montreal, QC, H3G 1Y6, Canada
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12
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Roman I, Figys J, Steurs G, Zizi M. Hunting interactomes of a membrane protein: obtaining the largest set of voltage-dependent anion channel-interacting protein epitopes. Mol Cell Proteomics 2006; 5:1667-80. [PMID: 16735301 DOI: 10.1074/mcp.t600009-mcp200] [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] [Indexed: 11/06/2022] Open
Abstract
The identification of epitopes involved in protein-protein interactions is essential for understanding protein structure and function. Large scale efforts, although identifying the interactions, did not always yield these epitopes, could not confirm most of the known interactions, and seemed particularly unsuccessful for native intrinsic membrane proteins. We have developed a fluidics-based approach (non-steady-state kinetics) to obtain the broadest set of the epitopes interacting with a given target and applied it to a phage display methodology optimized for membrane proteins. Phages expressing a liver cDNA library were screened against a membrane protein (voltage-dependent anion channel) reconstituted into liposomes and captured on a chip surface. The controlled fluidics was obtained by a surface plasmon resonance (SPR) device that combined the advantages of working with minute reaction volumes and non-equilibrium conditions. We demonstrated selective enrichment of binders and could even select for different binding affinities by fractionation of the selected outputs at various elution times. With voltage-dependent anion channel as bait (a mitochondrial channel critical for cellular metabolism and apoptosis) we found at least 40% of its already reported ligands and independently confirmed 55 novel functional interactions, some of which fully blocked the channel. This highly efficient approach is generally applicable for any protein and could be automated and scaled up even without the use of a SPR device. The epitopes directly identified by this method are useful not only for unraveling interactomes but also for drug design and therapeutics.
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Affiliation(s)
- Inge Roman
- Department of Physiology (FYSP), Vrije Universiteit Brussel (VUB), 1090 Brussels, Belgium
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13
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Esaki M, Shimizu H, Ono T, Yamamoto H, Kanamori T, Nishikawa SI, Endo T. Mitochondrial Protein Import. J Biol Chem 2004; 279:45701-7. [PMID: 15337763 DOI: 10.1074/jbc.m404591200] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Protein translocation across the outer mitochondrial membrane is mediated by the translocator called the TOM (translocase of the outer mitochondrial membrane) complex. The TOM complex possesses two presequence binding sites on the cytosolic side (the cis site) and on the intermembrane space side (the trans site). Here we analyzed the requirement of presequence elements and subunits of the TOM complex for presequence binding to the cis and trans sites of the TOM complex. The N-terminal 14 residues of the presequence of subunit 9 of F(0)-ATPase are required for binding to the trans site. The interaction between the presequence and the cis site is not sufficient to anchor the precursor protein to the TOM complex. Tom7 constitutes or is close to the trans site and has overlapping functions with the C-terminal intermembrane space domain of Tom22 in the mitochondrial protein import.
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Affiliation(s)
- Masatoshi Esaki
- Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya, Japan
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14
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Walensky LD, Kung AL, Escher I, Malia TJ, Barbuto S, Wright RD, Wagner G, Verdine GL, Korsmeyer SJ. Activation of apoptosis in vivo by a hydrocarbon-stapled BH3 helix. Science 2004; 305:1466-70. [PMID: 15353804 PMCID: PMC1360987 DOI: 10.1126/science.1099191] [Citation(s) in RCA: 1034] [Impact Index Per Article: 51.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
BCL-2 family proteins constitute a critical control point for the regulation of apoptosis. Protein interaction between BCL-2 members is a prominent mechanism of control and is mediated through the amphipathic alpha-helical BH3 segment, an essential death domain. We used a chemical strategy, termed hydrocarbon stapling, to generate BH3 peptides with improved pharmacologic properties. The stapled peptides, called "stabilized alpha-helix of BCL-2 domains" (SAHBs), proved to be helical, protease-resistant, and cell-permeable molecules that bound with increased affinity to multidomain BCL-2 member pockets. A SAHB of the BH3 domain from the BID protein specifically activated the apoptotic pathway to kill leukemia cells. In addition, SAHB effectively inhibited the growth of human leukemia xenografts in vivo. Hydrocarbon stapling of native peptides may provide a useful strategy for experimental and therapeutic modulation of protein-protein interactions in many signaling pathways.
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MESH Headings
- Alkenes
- Animals
- Apoptosis
- BH3 Interacting Domain Death Agonist Protein
- Bridged-Ring Compounds/chemical synthesis
- Bridged-Ring Compounds/chemistry
- Bridged-Ring Compounds/metabolism
- Bridged-Ring Compounds/pharmacology
- Carrier Proteins/chemistry
- Cell Division/drug effects
- Cell Line, Tumor
- Cell Membrane/metabolism
- Cytochromes c/metabolism
- Dose-Response Relationship, Drug
- Endosomes/metabolism
- Humans
- Jurkat Cells
- Leukemia, Experimental/drug therapy
- Leukemia, Experimental/pathology
- Leukemic Infiltration
- Mice
- Mice, SCID
- Mitochondria, Liver/drug effects
- Mitochondria, Liver/metabolism
- Molecular Mimicry
- Neoplasm Transplantation
- Peptide Fragments/chemistry
- Peptides/chemical synthesis
- Peptides/chemistry
- Peptides/metabolism
- Peptides/pharmacology
- Protein Binding
- Protein Engineering
- Protein Structure, Secondary
- Protein Structure, Tertiary
- Proto-Oncogene Proteins/chemistry
- Proto-Oncogene Proteins c-bcl-2/metabolism
- Transplantation, Heterologous
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Affiliation(s)
- Loren D Walensky
- Howard Hughes Medical Institute, Department of Pediatric Hematology/Oncology and Children's Hospital Boston, Massachusetts, USA
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15
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Vial S, Lu H, Allen S, Savory P, Thornton D, Sheehan J, Tokatlidis K. Assembly of Tim9 and Tim10 into a functional chaperone. J Biol Chem 2002; 277:36100-8. [PMID: 12138093 DOI: 10.1074/jbc.m202310200] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The TIM10 complex is localized in the mitochondrial intermembrane space and mediates insertion of hydrophobic proteins at the inner membrane. We have characterized TIM10 assembly and analyzed the structural properties of its subunits, Tim9 and Tim10. Both proteins are alpha-helical with a protease-resistant central domain, and each self-associates to form mainly dimers and trimers in solution. Tim9 and Tim10 bound to one another with submicromolar affinity in equimolar amounts and assembled in a stable, significantly extended complex that was indistinguishable from the native mitochondrial TIM10 complex. Importantly, the reconstituted TIM10 complex is functional because it bound to the physiological substrate ADP/ATP carrier and displayed chaperone activity in refolding the model substrate firefly luciferase. These data demonstrate that the individual subunits can exist as independent, dynamically self-associating proteins. Assembly into the thermodynamically stable hexameric complex is necessary for the TIM10 chaperone function.
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Affiliation(s)
- Sarah Vial
- School of Biological Sciences and The Wellcome Trust Centre for Cell Matrix Research, University of Manchester, Manchester M13 9PT, United Kingdom
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16
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Endo T, Kohda D. Functions of outer membrane receptors in mitochondrial protein import. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1592:3-14. [PMID: 12191763 DOI: 10.1016/s0167-4889(02)00259-8] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Most mitochondrial proteins are synthesized in the cytosol as precursor proteins and are imported into mitochondria. The targeting signals for mitochondria are encoded in the presequences or in the mature parts of the precursor proteins, and are decoded by the receptor sites in the translocator complex in the mitochondrial outer membrane. The recently determined NMR structure of the general import receptor Tom20 in a complex with a presequence peptide reveals that, although the amphiphilicity and positive charges of the presequence is essential for the import ability of the presequence, Tom20 recognizes only the amphiphilicity, but not the positive charges. This leads to a new model that different features associated with the mitochondrial targeting sequence of the precursor protein can be recognized by the mitochondrial protein import system in different steps during the import.
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Affiliation(s)
- Toshiya Endo
- Department of Chemistry, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, 464-8602, Japan.
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17
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Hoogenraad NJ, Ward LA, Ryan MT. Import and assembly of proteins into mitochondria of mammalian cells. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1592:97-105. [PMID: 12191772 DOI: 10.1016/s0167-4889(02)00268-9] [Citation(s) in RCA: 137] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Most of our knowledge regarding the process of protein import into mitochondria has come from research employing fungal systems. This review outlines recent advances in our understanding of this process in mammalian cells. In particular, we focus on the characterisation of cytosolic molecular chaperones that are involved in binding to mitochondrial-targeted preproteins, as well as the identification of both conserved and novel subunits of the import machineries of the outer and inner mitochondrial membranes. We also discuss diseases associated with defects in import and assembly of mitochondrial proteins and what is currently known about the regulation of import in mammals.
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18
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Müller A, Rassow J, Grimm J, Machuy N, Meyer TF, Rudel T. VDAC and the bacterial porin PorB of Neisseria gonorrhoeae share mitochondrial import pathways. EMBO J 2002; 21:1916-29. [PMID: 11953311 PMCID: PMC125974 DOI: 10.1093/emboj/21.8.1916] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The human pathogen Neisseria gonorrhoeae induces host cell apoptosis during infection by delivering the outer membrane protein PorB to the host cell's mitochondria. PorB is a pore-forming beta-barrel protein sharing several features with the mitochondrial voltage-dependent anion channel (VDAC), which is involved in the regulation of apoptosis. Here we show that PorB of pathogenic Neisseria species produced by host cells is efficiently targeted to mitochondria. Imported PorB resides in the mitochondrial outer membrane and forms multimers with similar sizes as in the outer bacterial membrane. The mitochondria completely lose their membrane potential, a characteristic previously observed in cells infected with gonococci or treated with purified PorB. Closely related bacterial porins of non-pathogenic Neisseria mucosa or Escherichia coli remain in the cytosol. Import of PorB into mitochondria in vivo is independent of a linear signal sequence. Insertion of PorB into the mitochondrial outer membrane in vitro depends on the activity of Tom5, Tom20 and Tom40, but is independent of Tom70. Our data show that human VDAC and bacterial PorB are imported into mitochondria by a similar mechanism.
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Affiliation(s)
| | - Joachim Rassow
- Max Planck Institute for Infection Biology, Department of Molecular Biology, Schumannstrasse 21/22, D-10117 Berlin,
University of Hohenheim, Department of Microbiology, Garbenstrasse 30, D-70593 Stuttgart-Hohenheim and Max Delbrück Centrum für Molekulare Medizin, Abteilung Zellbiologie, Robert-Rössle-Strasse 10, D-13092 Berlin, Germany Corresponding author e-mail:
| | - Jan Grimm
- Max Planck Institute for Infection Biology, Department of Molecular Biology, Schumannstrasse 21/22, D-10117 Berlin,
University of Hohenheim, Department of Microbiology, Garbenstrasse 30, D-70593 Stuttgart-Hohenheim and Max Delbrück Centrum für Molekulare Medizin, Abteilung Zellbiologie, Robert-Rössle-Strasse 10, D-13092 Berlin, Germany Corresponding author e-mail:
| | | | - Thomas F. Meyer
- Max Planck Institute for Infection Biology, Department of Molecular Biology, Schumannstrasse 21/22, D-10117 Berlin,
University of Hohenheim, Department of Microbiology, Garbenstrasse 30, D-70593 Stuttgart-Hohenheim and Max Delbrück Centrum für Molekulare Medizin, Abteilung Zellbiologie, Robert-Rössle-Strasse 10, D-13092 Berlin, Germany Corresponding author e-mail:
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19
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Mukhopadhyay A, Avramova LV, Weiner H. Tom34 unlike Tom20 does not interact with the leader sequences of mitochondrial precursor proteins. Arch Biochem Biophys 2002; 400:97-104. [PMID: 11913975 DOI: 10.1006/abbi.2002.2777] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Tom20 and Tom34 are mammalian liver proteins previously identified by others to be components of the mitochondrial import translocation apparatus. It has been shown that Tom20 interacts with the leader sequence of nuclear coded matrix space precursor proteins. Here we show with recombinantly expressed Tom proteins that Tom34 binds the mature portion of the precursor and not the leader. Both these Tom proteins inhibited the import of newly translated precursor of aldehyde dehydrogenase in an in vitro assay. Only Tom20 inhibited the import of a fusion protein of the leader of aldehyde dehydrogenase attached to dihydrofolate reductase. Antibodies against Tom20 coprecipitated both the precursor of aldehyde dehydrogenase (pALDH) and of dihydrofolate reductase (pA-DHFR). Antibodies against Tom34 interacted only when the mature portion of aldehyde dehydrogenase was present. Similar import inhibition patterns were found when other precursor and chimeric constructs we investigated. When Tom34-green fluorescence protein was transfected to HeLa cells it was observed that Tom34 was found through out the cell. It is concluded from our observation that Tom34 is a cytosolic protein, whose role appeared to be to interact with mature portion of some preproteins and may keep them in an unfolded, import compatible state.
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Affiliation(s)
- Abhijit Mukhopadhyay
- Department of Biochemistry, Purdue University, 1153 Biochemistry Building, West Lafayette, Indiana 47907-1153, USA
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20
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Edmonson AM, Mayfield DK, Vervoort V, DuPont BR, Argyropoulos G. Characterization of a human import component of the mitochondrial outer membrane, TOMM70A. CELL COMMUNICATION & ADHESION 2002; 9:15-27. [PMID: 12200962 DOI: 10.1080/15419060212186] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Functional mitochondria require up to 1000 proteins to function properly, with 99% synthesized as precursors in the cytoplasm and transported into the mitochondria with the aid of cytosolic chaperones and mitochondrial translocators (import components). Proteins to be imported are chaperoned to the mitochondria by the cytosolic heat shock protein (cHSP70) and are immediately pursued by Translocators of the Outer Membrane (TOMs), followed by transient interactions of the unfolded proteins with Translocators of the Inner Membrane (TIMs). In the present study, we describe a human gene, TOMM70A, orthologous to the yeast Tom70 import component. TOMM70A is ubiquitously expressed in human tissues, maps on chromosome 3q13.1-q13.2 and consists of 12 coding exons spanning over 37 kb. TOMM70A localizes in the mitochondria of COS-7 cells, and in organello import assays confirmed its presence in the Outer Mitochondrial membrane (OM) of rat liver mitochondria. TOMM70A could play a significant role in the import of nuclear-encoded mitochondrial proteins with internal targeting sites such as ADP/ATP carriers and the uncoupling proteins.
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Affiliation(s)
- Angela M Edmonson
- Department of Medicine, Medical University of South Carolina, Charleston, SC 29403, USA
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21
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Krimmer T, Rapaport D, Ryan MT, Meisinger C, Kassenbrock CK, Blachly-Dyson E, Forte M, Douglas MG, Neupert W, Nargang FE, Pfanner N. Biogenesis of porin of the outer mitochondrial membrane involves an import pathway via receptors and the general import pore of the TOM complex. J Cell Biol 2001; 152:289-300. [PMID: 11266446 PMCID: PMC2199606 DOI: 10.1083/jcb.152.2.289] [Citation(s) in RCA: 127] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Porin, also termed the voltage-dependent anion channel, is the most abundant protein of the mitochondrial outer membrane. The process of import and assembly of the protein is known to be dependent on the surface receptor Tom20, but the requirement for other mitochondrial proteins remains controversial. We have used mitochondria from Neurospora crassa and Saccharomyces cerevisiae to analyze the import pathway of porin. Import of porin into isolated mitochondria in which the outer membrane has been opened is inhibited despite similar levels of Tom20 as in intact mitochondria. A matrix-destined precursor and the porin precursor compete for the same translocation sites in both normal mitochondria and mitochondria whose surface receptors have been removed, suggesting that both precursors utilize the general import pore. Using an assay established to monitor the assembly of in vitro-imported porin into preexisting porin complexes we have shown that besides Tom20, the biogenesis of porin depends on the central receptor Tom22, as well as Tom5 and Tom7 of the general import pore complex (translocase of the outer mitochondrial membrane [TOM] core complex). The characterization of two new mutant alleles of the essential pore protein Tom40 demonstrates that the import of porin also requires a functional Tom40. Moreover, the porin precursor can be cross-linked to Tom20, Tom22, and Tom40 on its import pathway. We conclude that import of porin does not proceed through the action of Tom20 alone, but requires an intact outer membrane and involves at least four more subunits of the TOM machinery, including the general import pore.
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Affiliation(s)
- Thomas Krimmer
- Institute for Biochemistry and Molecular Biology, University of Freiburg, D-79104 Freiburg, Germany
- Faculty for Biology, University of Freiburg, D-79104 Freiburg, Germany
| | - Doron Rapaport
- Institute for Physiological Chemistry, Munich University, D-80336 Munich, Germany
| | - Michael T. Ryan
- Institute for Biochemistry and Molecular Biology, University of Freiburg, D-79104 Freiburg, Germany
| | - Chris Meisinger
- Institute for Biochemistry and Molecular Biology, University of Freiburg, D-79104 Freiburg, Germany
| | - C. Kenneth Kassenbrock
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599
| | | | - Michael Forte
- Oregon Health Sciences University, Portland, Oregon 97201
| | - Michael G. Douglas
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599
| | - Walter Neupert
- Institute for Physiological Chemistry, Munich University, D-80336 Munich, Germany
| | - Frank E. Nargang
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada
| | - Nikolaus Pfanner
- Institute for Biochemistry and Molecular Biology, University of Freiburg, D-79104 Freiburg, Germany
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22
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Brix J, Ziegler GA, Dietmeier K, Schneider-Mergener J, Schulz GE, Pfanner N. The mitochondrial import receptor Tom70: identification of a 25 kDa core domain with a specific binding site for preproteins. J Mol Biol 2000; 303:479-88. [PMID: 11054285 DOI: 10.1006/jmbi.2000.4120] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The mitochondrial import receptor of 70 kDa, Tom70, preferentially recognizes precursors of membrane proteins with internal targeting signals. We report the identification of a stably folded 25 kDa core domain located in the middle portion of Tom70 that contains two of the seven tetratricopeptide repeat motifs of the receptor. The core domain binds non-cleavable and cleavable preproteins carrying internal targeting signals with a specificity indistinguishable from the full-length receptor. Competition studies indicate that both types of preproteins interact with overlapping binding sites of the core domain and that at least one additional interaction site is present in the full-length receptor. We suggest a model of Tom70 function in import of membrane proteins whereby a hydrophobic preprotein concomitantly interacts with several binding sites of the receptor.
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Affiliation(s)
- J Brix
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, Freiburg, D-79104, Germany
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23
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Grey JY, Connor MK, Gordon JW, Yano M, Mori M, Hood DA. Tom20-mediated mitochondrial protein import in muscle cells during differentiation. Am J Physiol Cell Physiol 2000; 279:C1393-400. [PMID: 11029287 DOI: 10.1152/ajpcell.2000.279.5.c1393] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mitochondrial biogenesis is accompanied by an increased expression of components of the protein import machinery, as well as increased import of proteins destined for the matrix. We evaluated the role of the outer membrane receptor Tom20 by varying its expression and measuring changes in the import of malate dehydrogenase (MDH) in differentiating C2C12 muscle cells. Cells transfected with Tom20 had levels that were twofold higher than in control cells. Labeling of cells followed by immunoprecipitation of MDH revealed equivalent increases in MDH import. This parallelism between import rate and Tom20 levels was also evident as a result of thyroid hormone treatment. Using antisense oligodeoxynucleotides, we inhibited Tom20 expression by 40%, resulting in 40-60% reductions in MDH import. In vitro assays also revealed that import into the matrix was more sensitive to Tom20 inhibition than import into the outer membrane. These data indicate a close relationship between induced changes in Tom20 and the import of a matrix protein, suggesting that Tom20 is involved in determining the kinetics of import. However, this relationship was dissociated during normal differentiation, since the expression of Tom20 remained relatively constant, whereas imported MDH increased 12-fold. Thus Tom20 is important in determining import during organelle biogenesis, but other mechanisms (e.g., intramitochondrial protein degradation or nuclear transcription) likely also play a role in establishing the final mitochondrial phenotype during normal muscle differentiation.
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Affiliation(s)
- J Y Grey
- Department of Biology, York University, Toronto, Ontario, Canada M3J 1P3
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24
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Yano M, Hoogenraad N, Terada K, Mori M. Identification and functional analysis of human Tom22 for protein import into mitochondria. Mol Cell Biol 2000; 20:7205-13. [PMID: 10982837 PMCID: PMC86274 DOI: 10.1128/mcb.20.19.7205-7213.2000] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mitochondria have a receptor complex in the outer membrane which recognizes and translocates mitochondrial proteins synthesized in the cytosol. We report here the identification and functional analysis of human Tom22 (hTom22). hTom22 has an N-terminal negatively charged region exposed to the cytosol, a putative transmembrane region, and a C-terminal intermembrane space region with little negative charge. Tom22 forms a complex with Tom20, and its cytosolic domain functions as an import receptor as in fungi. An import inhibition assay, using pre-ornithine transcarbamylase (pOTC) derivatives and a series of hTom22 deletion mutants, showed that the C-terminal segment of the cytosolic domain is important for presequence binding, whereas the N-terminal domain is important for binding to the mature portion of pOTC. No evidence for pOTC interaction with the Tom22 intermembrane space domain was obtained. Binding studies revealed that the presequence is critical for pOTC binding to Tom20, whereas both the presequence and mature portion are important for binding to Tom22. A cell-free immunoprecipitation assay indicated that an internal segment of the Tom22 cytosolic domain is important for interaction with Tom20.
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Affiliation(s)
- M Yano
- Department of Molecular Genetics, Kumamoto University School of Medicine, Kumamoto 860-0811, Japan
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25
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Stan T, Ahting U, Dembowski M, Künkele KP, Nussberger S, Neupert W, Rapaport D. Recognition of preproteins by the isolated TOM complex of mitochondria. EMBO J 2000; 19:4895-902. [PMID: 10990453 PMCID: PMC314223 DOI: 10.1093/emboj/19.18.4895] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
A multisubunit complex in the mitochondrial outer membrane, the TOM complex, mediates targeting and membrane translocation of nuclear-encoded preproteins. We have isolated the TOM holo complex, containing the preprotein receptor components Tom70 and Tom20, and the TOM core complex, which lacks these receptors. The interaction of recombinant mitochondrial preproteins with both types of soluble TOM complex was analyzed. Preproteins bound efficiently in a specific manner to the isolated complexes in the absence of chaperones and lipids in a bilayer structure. Using fluorescence correlation spectroscopy, a dissociation constant in the nanomolar range was determined. The affinity was lower when the preprotein was stabilized in its folded conformation. Following the initial binding, the presequence was transferred into the translocation pore in a step that required unfolding of the mature part of the preprotein. This translocation step was also mediated by protease-treated TOM holo complex, which contains almost exclusively Tom40. Thus, the TOM core complex, consisting of Tom40, Tom22, Tom6 and Tom7, is a molecular machine that can recognize and partially translocate mitochondrial precursor proteins.
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Affiliation(s)
- T Stan
- Institut für Physiologische Chemie der Universität München, Goethestrabetae 33, D-80336 München, Germany
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26
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Schleiff E, McBride H. The central matrix loop drives import of uncoupling protein 1 into mitochondria. J Cell Sci 2000; 113 ( Pt 12):2267-72. [PMID: 10825298 DOI: 10.1242/jcs.113.12.2267] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The uncoupling protein (UCP1) is a carrier protein of the inner mitochondrial membrane spanning the bilayer six times. It does not contain a typical amino-terminal targeting signal and the mechanism of targeting and insertion is unknown. Here we focus on the biogenesis of UCP1 by analysing the import signals contained within the three repeated units of the protein. The amino-terminal third of the protein can mediate insertion into the outer membrane and therefore acts as artificial targeting signal when fused to DHFR. However, in the context of full-length UCP, the targeting information contained within the first repeated unit is not sufficient to trigger insertion into the outer membrane. Deletion of either the first or third repeated unit from UCP1 did not reduce import into the inner membrane and bound to the outer membrane receptor protein hTom20 with the characteristics of full-length UCP1. Deletion of the second repeat of UCP1 completely abolished all import into the mitochondria. Consistent with this, the central repeat alone was efficiently imported to the inner membrane and bound hTom20 with the characteristics of UCP1. We conclude that the site for binding hTom20 is within the central repeat and that this domain contains the complete targeting signal for directing UCP1 to the inner membrane.
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Affiliation(s)
- E Schleiff
- Department of Biochemistry, McGill University Montreal, Montreal, Canada, H3G 1Y6.
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27
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Abstract
The mitochondrial protein import machinery specifically recognizes many different preproteins lacking a consensus sequence. The three-dimensional structure of an import receptor complexed to an amino-terminal targeting 'presequence' provides exciting insight into the molecular mechanism of signal recognition.
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Affiliation(s)
- N Pfanner
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Germany.
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28
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Abe Y, Shodai T, Muto T, Mihara K, Torii H, Nishikawa S, Endo T, Kohda D. Structural basis of presequence recognition by the mitochondrial protein import receptor Tom20. Cell 2000; 100:551-60. [PMID: 10721992 DOI: 10.1016/s0092-8674(00)80691-1] [Citation(s) in RCA: 399] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Most mitochondrial proteins are synthesized in the cytosol as precursor proteins with a cleavable N-terminal presequence and are imported into mitochondria. We report here the NMR structure of a general import receptor, rat Tom20, in a complex with a presequence peptide derived from rat aldehyde dehydrogenase. The cytosolic domain of Tom20 forms an all alpha-helical structure with a groove to accommodate the presequence peptide. The bound presequence forms an amphiphilic helical structure with hydrophobic leucines aligned on one side to interact with a hydrophobic patch in the Tom20 groove. Although the positive charges of the presequence are essential for import ability, presequence binding to Tom20 is mediated mainly by hydrophobic rather than ionic interactions.
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Affiliation(s)
- Y Abe
- Department of Structural Biology, Biomolecular Engineering Research Institute, Suita, Osaka, Japan
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29
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Schleiff E. Signals and receptors--the translocation machinery on the mitochondrial surface. J Bioenerg Biomembr 2000; 32:55-66. [PMID: 11768763 DOI: 10.1023/a:1005512412404] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Most proteins involved in mitochondrial biogenesis are encoded by the genome of the nucleus. They are synthesized in the cytosol and have to be transported toward and, subsequently, imported into the organelle. This targeting and import process is initiated by the specific mitochondrial targeting signal, which differs pending on the final localization of the protein. The preprotein will be recognized by cytosolic proteins, which function in transport toward the mitochondria and in maintaining the import competent state of the preprotein. The precursor will be transferred onto a multicomponent complex on the outer mitochondrial membrane, formed by receptor proteins and the general insertion pore (GIP). Some proteins are directly sorted into the outer membrane whereas the majority will be transported over the outer membrane through the import channel followed by further distribution of those proteins.
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Affiliation(s)
- E Schleiff
- Department of Biochemistry, McGill University, Montreal, Canada.
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30
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Rivera IL, Shore GC, Schleiff E. Cloning and characterization of a 35-kDa mouse mitochondrial outer membrane protein MOM35 with high homology to Tom40. J Bioenerg Biomembr 2000; 32:111-21. [PMID: 11768756 DOI: 10.1023/a:1005524815130] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We have cloned a 35-kDa protein from a mouse cDNA library with a 25% overall amino acid identity to yTom40 and 27% identity to nTom40. This homolog toTom40 was named MOM35. It contains two possible start codons 36 amino acids apart from each other. Both the long and the short version of MOM35 can be imported in vitro into mouse mitochondria. The identified protein is imported into the outer mitochondrial membrane and comprises a trypsin-resistance pattern similar to that of nTom40. Tom40 of N. crassa, S. cerevisiae, and the protein identified herein contains a highly conserved region with possible physiological importance. Subsequent investigation has revealed that this region interacts specifically in vitro with preproteins proposed to be imported by a Tom40-dependent pathway.
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Affiliation(s)
- I L Rivera
- Department of Biochemistry, McGill University, Montreal Quebec, Canada
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31
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Ryan MT, Wagner R, Pfanner N. The transport machinery for the import of preproteins across the outer mitochondrial membrane. Int J Biochem Cell Biol 2000; 32:13-21. [PMID: 10661891 DOI: 10.1016/s1357-2725(99)00114-4] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
In order for proteins to be imported into subcellular compartments, they must first traverse the organellar membranes. In mitochondria, hydrophilic protein channels in both the outer and inner membranes serve such a purpose. Recently, the channel protein of the outer mitochondrial membrane was identified to be Tom40. Tom40 is found in a high molecular weight complex termed the general import pore (GIP) complex where it is tightly associated with the receptor protein Tom22 along with Tom7, Tom6 and Tom5. Tom7 and Tom6 seem to modulate the dynamics of the GIP complex while Tom5 is involved in preprotein transfer from receptors to Tom40. The receptor proteins Tom70 and Tom20 associate with this complex in a weaker manner where they are involved in the initial recognition of preproteins. This review focuses on the identification and characterisation of the transport machinery of the outer mitochondrial membrane and how they are involved in the co-ordination and regulation of events required for the translocation of preproteins into mitochondria.
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Affiliation(s)
- M T Ryan
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Germany
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32
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Voos W, Martin H, Krimmer T, Pfanner N. Mechanisms of protein translocation into mitochondria. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1422:235-54. [PMID: 10548718 DOI: 10.1016/s0304-4157(99)00007-6] [Citation(s) in RCA: 122] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Mitochondrial biogenesis utilizes a complex proteinaceous machinery for the import of cytosolically synthesized preproteins. At least three large multisubunit protein complexes, one in the outer membrane and two in the inner membrane, have been identified. These translocase complexes cooperate with soluble proteins from the cytosol, the intermembrane space and the matrix. The translocation of presequence-containing preproteins through the outer membrane channel includes successive electrostatic interactions of the charged mitochondrial targeting sequence with a chain of import components. Translocation across the inner mitochondrial membrane utilizes the energy of the proton motive force of the inner membrane and the hydrolysis of ATP. The matrix chaperone system of the mitochondrial heat shock protein 70 forms an ATP-dependent import motor by interaction with the polypeptide chain in transit and components of the inner membrane translocase. The precursors of integral inner membrane proteins of the metabolite carrier family interact with newly identified import components of the intermembrane space and are inserted into the inner membrane by a second translocase complex. A comparison of the full set of import components between the yeast Sacccharomyces cerevisiae and the nematode Caenorhabditis elegans demonstrates an evolutionary conservation of most components of the mitochondrial import machinery with a possible greater divergence for the import pathway of the inner membrane carrier proteins.
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Affiliation(s)
- W Voos
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Str. 7, D-79104, Freiburg, Germany.
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Schleiff E, Heard TS, Weiner H. Positively charged residues, the helical conformation and the structural flexibility of the leader sequence of pALDH are important for recognition by hTom20. FEBS Lett 1999; 461:9-12. [PMID: 10561487 DOI: 10.1016/s0014-5793(99)01415-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Tom20, a mitochondrial outer membrane receptor necessary for protein translocation, was found to interact specifically with mitochondrial preproteins. The interaction of proteins containing an N-terminal matrix targeting signal was enhanced in an hydrophobic environment and the dependence of this interaction on the alpha helical conformation of the presequence was postulated. In order to test this hypothesis and to gain insights about the features of a matrix targeting signal necessary to be recognized by the receptor machinery including Tom20, the interaction of pALDH and signal sequence mutants to Tom20 in the absence and presence of a hydrophobic environment was investigated. Here we present evidence to show that in a hydrophobic environment the interaction between Tom20 and the leader sequence is strongly dependent on the positive charges within the signal sequence as well as on the flexibility of this signal.
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Affiliation(s)
- E Schleiff
- Department of Biochemistry, McGill University, Montreal, Que., Canada
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34
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Schleiff E, Khanna R, Orlicky S, Vrielink A. Expression, purification, and in vitro characterization of the human outer mitochondrial membrane receptor human translocase of the outer mitochondrial membrane 20. Arch Biochem Biophys 1999; 367:95-103. [PMID: 10375404 DOI: 10.1006/abbi.1999.1240] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In order to investigate the biochemical properties of the mitochondrial outer membrane receptor, hTom20, involved in protein recognition, the cytosolic domain of this receptor was overexpressed and purified to homogeneity. A four-step purification including the purification of thrombin is described as well as an analysis of the function of the highly purified hTom20 protein. The receptor was concentrated and the subsequent aggregation behavior was investigated in order to understand the function of the single cysteine in the cytosolic domain as well as the function of the proposed "glutamine face" for the structure of the protein. It was found that specific dimerization of the cytosolic domain of hTom20 is necessary in order to prevent aggregation of the protein. In addition, the cysteine and the glutamine face are important for the stability of the protein. We propose that the function of the cysteine is to promote dimerization as found in the absence of dithiothreitol.
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Affiliation(s)
- E Schleiff
- Department of Biochemistry, McGill University, 3655 Drummond, Montreal, H3G 1Y6, Canada.
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36
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Brix J, Rüdiger S, Bukau B, Schneider-Mergener J, Pfanner N. Distribution of binding sequences for the mitochondrial import receptors Tom20, Tom22, and Tom70 in a presequence-carrying preprotein and a non-cleavable preprotein. J Biol Chem 1999; 274:16522-30. [PMID: 10347216 DOI: 10.1074/jbc.274.23.16522] [Citation(s) in RCA: 174] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Preproteins destined for mitochondria either are synthesized with amino-terminal signal sequences, termed presequences, or possess internal targeting information within the protein. The preprotein translocase of the outer mitochondrial membrane (designated Tom) contains specific import receptors. The cytosolic domains of three import receptors, Tom20, Tom22, and Tom70, have been shown to interact with preproteins. Little is known about the internal targeting information in preproteins and the distribution of binding sequences for the three import receptors. We have studied the binding of the purified cytosolic domains of Tom20, Tom22, and Tom70 to cellulose-bound peptide scans derived from a presequence-carrying cleavable preprotein, cytochrome c oxidase subunit IV, and a non-cleavable preprotein with internal targeting information, the phosphate carrier. All three receptor domains are able to bind efficiently to linear 13-mer peptides, yet with different specificity. Tom20 preferentially binds to presequence segments of subunit IV. Tom22 binds to segments corresponding to the carboxyl-terminal part of the presequence and the amino-terminal part of the mature protein. Tom70 does not bind efficiently to any region of subunit IV. In contrast, Tom70 and Tom20 bind to multiple segments within the phosphate carrier, yet the amino-terminal region is excluded. Both charged and uncharged peptides derived from the phosphate carrier show specific binding properties for Tom70 and Tom20, indicating that charge is not a critical determinant of internal targeting sequences. This feature contrasts with the crucial role of positively charged amino acids in presequences. Our results demonstrate that linear peptide segments of preproteins can serve as binding sites for all three receptors with differential specificity and imply different mechanisms for translocation of cleavable and non-cleavable preproteins.
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Affiliation(s)
- J Brix
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany
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37
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Schleiff E, Silvius JR, Shore GC. Direct membrane insertion of voltage-dependent anion-selective channel protein catalyzed by mitochondrial Tom20. J Cell Biol 1999; 145:973-8. [PMID: 10352015 PMCID: PMC2133124 DOI: 10.1083/jcb.145.5.973] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Insertion of newly synthesized proteins into or across the mitochondrial outer membrane is initiated by import receptors at the surface of the organelle. Typically, this interaction directs the precursor protein into a preprotein translocation pore, comprised of Tom40. Here, we show that a prominent beta-barrel channel protein spanning the outer membrane, human voltage- dependent anion-selective channel (VDAC), bypasses the requirement for the Tom40 translocation pore during biogenesis. Insertion of VDAC into the outer membrane is unaffected by plugging the translocation pore with a partially translocated matrix preprotein, and mitochondria containing a temperature-sensitive mutant of Tom40 insert VDAC at the nonpermissive temperature. Synthetic liposomes harboring the cytosolic domain of the human import receptor Tom20 efficiently insert newly synthesized VDAC, resulting in transbilayer transport of ATP. Therefore, Tom20 transforms newly synthesized cytosolic VDAC into a transmembrane channel that is fully integrated into the lipid bilayer.
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Affiliation(s)
- E Schleiff
- Department of Biochemistry, McGill University, Montreal, Quebec, Canada H3G 1Y6
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38
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Künkele KP, Juin P, Pompa C, Nargang FE, Henry JP, Neupert W, Lill R, Thieffry M. The isolated complex of the translocase of the outer membrane of mitochondria. Characterization of the cation-selective and voltage-gated preprotein-conducting pore. J Biol Chem 1998; 273:31032-9. [PMID: 9813001 DOI: 10.1074/jbc.273.47.31032] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The complex of the translocase mitochondrial outer membrane (TOM), mediates recognition, unfolding, and translocation of preproteins. We have used a combination of biochemical and electrophysiological methods to study the properties of the preprotein-conducting pore of the purified TOM complex. The pore is cation-selective and voltage-gated. It shows three main conductance levels with characteristic slow and fast kinetics transitions to states of lower conductance following application of transmembrane voltages. These electrical properties distinguish it from the mitochondrial voltage-dependent anion channel (porin) and are identical to those of the previously described peptide-sensitive channel. Binding of antibodies to the C terminus of Tom40 on the intermembrane space side of the outer membrane modifies the channel properties and allows determination of the orientation of the channel within the lipid bilayer. Mitochondrial presequence peptides specifically interact with the pore and decrease the ion flow through the channel in a voltage-dependent manner. We propose that the presequence-induced closures of the pore are related to structural alterations of the TOM complex observed during the various stages of preprotein movement across the mitochondrial outer membrane.
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Affiliation(s)
- K P Künkele
- Institut für Physiologische Chemie, Physikalische Biochemie und Zellbiologie der Universität München, Goethestrasse 33, 80336 Munich, Federal Republic of Germany
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39
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Dekker PJ, Ryan MT, Brix J, Müller H, Hönlinger A, Pfanner N. Preprotein translocase of the outer mitochondrial membrane: molecular dissection and assembly of the general import pore complex. Mol Cell Biol 1998; 18:6515-24. [PMID: 9774667 PMCID: PMC109237 DOI: 10.1128/mcb.18.11.6515] [Citation(s) in RCA: 200] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The preprotein translocase of the outer mitochondrial membrane (Tom) is a multisubunit machinery containing receptors and a general import pore (GIP). We have analyzed the molecular architecture of the Tom machinery. The receptor Tom22 stably associates with Tom40, the main component of the GIP, in a complex with a molecular weight of approximately 400,000 ( approximately 400K), while the other receptors, Tom20 and Tom70, are more loosely associated with this GIP complex and can be found in distinct subcomplexes. A yeast mutant lacking both Tom20 and Tom70 can still form the GIP complex when sufficient amounts of Tom22 are synthesized. Besides the essential proteins Tom22 and Tom40, the GIP complex contains three small subunits, Tom5, Tom6, and Tom7. In mutant mitochondria lacking Tom6, the interaction between Tom22 and Tom40 is destabilized, leading to the dissociation of Tom22 and the generation of a subcomplex of approximately 100K containing Tom40, Tom7, and Tom5. Tom6 is required to promote but not to maintain a stable association between Tom22 and Tom40. The following conclusions are suggested. (i) The GIP complex, containing Tom40, Tom22, and three small Tom proteins, forms the central unit of the outer membrane import machinery. (ii) Tom20 and Tom70 are not essential for the generation of the GIP complex. (iii) Tom6 functions as an assembly factor for Tom22, promoting its stable association with Tom40.
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Affiliation(s)
- P J Dekker
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, D-79104 Freiburg, Germany
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40
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Yano M, Kanazawa M, Terada K, Takeya M, Hoogenraad N, Mori M. Functional analysis of human mitochondrial receptor Tom20 for protein import into mitochondria. J Biol Chem 1998; 273:26844-51. [PMID: 9756929 DOI: 10.1074/jbc.273.41.26844] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mitochondrial import receptor translocase of the outer membrane of mitochondria (Tom20) consists of five segments, an N-terminal membrane-anchor segment, a linker segment rich in charged amino acids, a tetratricopeptide repeat motif, a glutamine-rich segment, and a C-terminal segment. To assess the role of each segment, four C-terminally truncated mutants of the human receptor (hTom20) were constructed, and the effect of their overexpression in COS-7 cells was analyzed. Expression of a mutant lacking the tetratricopeptide repeat motif inhibited preornithine transcarbamylase (pOTC) import to the same extent as the wild-type receptor. Thus, overexpression of the membrane-anchor and the linker segments is sufficient for the inhibition of import. Expression of either the wild-type receptor or a mutant lacking the C-terminal end of 20 amino acid residues stimulated import of pOTC-green fluorescent protein (GFP), a fusion protein in which the presequene of pOTC was fused to green fluorescent protein. On the other hand, expression of mutants lacking either the glutamine-rich segment or larger deletions inhibited pOTC-GFP import. In vitro import of pOTC was inhibited by the wild-type hTom20 and the mutant lacking the C-terminal end, but much less strongly by the mutant lacking the glutamine-rich segment. On the other hand, import of pOTC-GFP was little affected by any of the forms of hTom20. In binding assays, pOTC binding to hTom20 was only moderately decreased by the deletion of the glutamine-rich segment, whereas pOTC-GFP binding was completely lost by this deletion. Binding of pOTCN-GFP a construct that contains an additional 58 N-terminal residues of mature OTC, resembled that of pOTC. All of these results indicate that the region 106-125 containing the glutamine-rich segment of hTom20 is essential for binding and import stimulation in vivo of pOTC-GFP and for inhibition of in vitro import of pOTC. The results also indicate that this region is important for mitochondrial aggregation. The different behaviors of pOTC and the pOTC-GFP chimera toward hTom20 mutants is explicable on the basis of the conformation of the precursor proteins.
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Affiliation(s)
- M Yano
- Department of Molecular Genetics, Kumamoto University School of Medicine, Kumamoto 862, Japan.
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41
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Schleiff E, Turnbull JL. Functional and structural properties of the mitochondrial outer membrane receptor Tom20. Biochemistry 1998; 37:13043-51. [PMID: 9748309 DOI: 10.1021/bi9807456] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Tom20 is an outer mitochondrial membrane protein that functions as a component of the import receptor complex for cytoplasmically synthesized mitochondrial precursor proteins. The human homologue, hTom20, consists of an N-terminal membrane anchor region predicted between aa5-25 and a soluble cytosolic domain from aa30 to 145. To analyze the properties of hTom20, we have expressed several truncations of the cytosolic domain as fusion proteins with glutathione S-transferase. Our studies reveal that the cytosolic region of hTom20 is a monomeric protein in solution containing two domains which are involved in different functions of the receptor. The N-terminal region is involved in membrane binding (aa30-60) and recognition of the cleavable matrix targeting signals (aa50-90). In addition, we have demonstrated that the receptor recognizes the alpha-helical state of the matrix targeting signal. The dissociation constant for this interaction in the presence of a detergent which induces this secondary structure is 0.6 microM, one-fifth the value in the absence of detergent. In aqueous solution, the region between aa30 and 60 is loosely folded and stabilized against proteolytic cleavage by interaction with detergents or a matrix targeting signal. Our work further shows that the remainder of the cytosolic domain of hTom20, aa60-145, is a compactly folded globular domain containing a region (aa90-145) that is critical for the recognition of proteins bearing internal signal sequences such as the uncoupling protein and porin.
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Affiliation(s)
- E Schleiff
- Department of Biochemistry, McGill University, Montreal, Canada.
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42
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Rapaport D, Künkele KP, Dembowski M, Ahting U, Nargang FE, Neupert W, Lill R. Dynamics of the TOM complex of mitochondria during binding and translocation of preproteins. Mol Cell Biol 1998; 18:5256-62. [PMID: 9710610 PMCID: PMC109111 DOI: 10.1128/mcb.18.9.5256] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Translocation of preproteins across the mitochondrial outer membrane is mediated by the TOM complex. This complex consists of receptor components for the initial contact with preproteins at the mitochondrial surface and membrane-embedded proteins which promote transport and form the translocation pore. In order to understand the interplay between the translocating preprotein and the constituents of the TOM complex, we analyzed the dynamics of the TOM complex of Neurospora crassa and Saccharomyces cerevisiae mitochondria by following the structural alterations of the essential pore component Tom40 during the translocation of preproteins. Tom40 exists in a homo-oligomeric assembly and dynamically interacts with Tom6. The Tom40 assembly is influenced by a block of negatively charged amino acid residues in the cytosolic domain of Tom22, indicating a cross-talk between preprotein receptors and the translocation pore. Preprotein binding to specific sites on either side of the outer membrane (cis and trans sites) induces distinct structural alterations of Tom40. To a large extent, these changes are mediated by interaction with the mitochondrial targeting sequence. We propose that such targeting sequence-induced adaptations are a critical feature of translocases in order to facilitate the movement of preproteins across cellular membranes.
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Affiliation(s)
- D Rapaport
- Institut für Physiologische Chemie, Physikalische Biochemie und Zellbiologie der Universität München, 80336 Munich, Germany
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Komiya T, Rospert S, Koehler C, Looser R, Schatz G, Mihara K. Interaction of mitochondrial targeting signals with acidic receptor domains along the protein import pathway: evidence for the 'acid chain' hypothesis. EMBO J 1998; 17:3886-98. [PMID: 9670006 PMCID: PMC1170724 DOI: 10.1093/emboj/17.14.3886] [Citation(s) in RCA: 134] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Mitochondrial precursor proteins with basic targeting signals may be transported across the outer membrane by sequential binding to acidic receptor sites of increasing affinity. To test this 'acid chain' hypothesis, we assayed the interaction of mitochondrial precursors with three acidic receptor domains: the cytosolic domain of Tom20 and the intermembrane space domain of Tom22 and Tim23. The apparent affinity and salt resistance of precursor binding increased in the order Tom20<Tom22 (internal)<Tim23. Precursor binding to the three acidic receptor domains and to the pure cytosolic domain of Tom70 was inhibited by excess targeting peptide, but not by an equally basic control peptide. In this membrane-free and defined system, a precursor pre-bound to the Tom70 or Tom20 domain was transferred efficiently to the Tim23 domain. Transfer was stimulated by the internal Tom22 domain and was much less efficient in the reverse direction. Precursors destined for the outer membrane bound only to Tom20, but not to the internal Tom22 or the Tim23 domain, and a precursor destined for the inner membrane bound only to the Tom20 and the internal Tom22 domain, but not to the Tim23 domain. These results suggest that specific and sequential binding of a targeting signal to strategically situated acidic receptors delivers a precursor across the outer membrane and contributes to intramitochondrial sorting of imported proteins.
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Affiliation(s)
- T Komiya
- Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Fukuoka 812, Japan
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44
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Palmisano A, Zara V, Hönlinger A, Vozza A, Dekker PJ, Pfanner N, Palmieri F. Targeting and assembly of the oxoglutarate carrier: general principles for biogenesis of carrier proteins of the mitochondrial inner membrane. Biochem J 1998; 333 ( Pt 1):151-8. [PMID: 9639574 PMCID: PMC1219567 DOI: 10.1042/bj3330151] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
We have studied the targeting and assembly of the 2-oxoglutarate carrier (OGC), an integral inner-membrane protein of mitochondria. The precursor of OGC, synthesized without a cleavable presequence, is transported into mitochondria in an ATP- and membrane potential-dependent manner. Import of the mammalian OGC occurs efficiently into both mammalian and yeast mitochondria. Targeting of OGC reveals a clear dependence on the mitochondrial surface receptor Tom70 (the 70 kDa subunit of the translocase of the outer mitochondrial membrane), whereas a cleavable preprotein depends on Tom20 (the 20 kDa subunit), supporting a model of specificity differences of the receptors and the existence of distinct targeting pathways to mitochondria. The assembly of minute amounts of OGC imported in vitro to the dimeric form can be monitored by blue native electrophoresis of digitonin-lysed mitochondria. The assembly of mammalian OGC and fungal ADP/ATP carrier occurs with high efficiency in both mammalian and yeast mitochondria. These findings indicate a dynamic behaviour of the carrier dimers in the mitochondrial inner membrane and suggest a high conservation of the assembly reactions from mammals to fungi.
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Affiliation(s)
- A Palmisano
- Dipartimento Farmaco-Biologico, Università di Bari, Via E. Orabona 4, I-70125 Bari, Italy
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45
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Nargang FE, Rapaport D, Ritzel RG, Neupert W, Lill R. Role of the negative charges in the cytosolic domain of TOM22 in the import of precursor proteins into mitochondria. Mol Cell Biol 1998; 18:3173-81. [PMID: 9584158 PMCID: PMC108899 DOI: 10.1128/mcb.18.6.3173] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
TOM22 is an essential mitochondrial outer membrane protein required for the import of precursor proteins into the organelles. The amino-terminal 84 amino acids of TOM22 extend into the cytosol and include 19 negatively and 6 positively charged residues. This region of the protein is thought to interact with positively charged presequences on mitochondrial preproteins, presumably via electrostatic interactions. We constructed a series of mutant derivatives of TOM22 in which 2 to 15 of the negatively charged residues in the cytosolic domain were changed to their corresponding amido forms. The mutant constructs were transformed into a sheltered Neurospora crassa heterokaryon bearing a tom22::hygromycin R disruption in one nucleus. All constructs restored viability to the disruption-carrying nucleus and gave rise to homokaryotic strains containing mutant tom22 alleles. Isolated mitochondria from three representative mutant strains, including the mutant carrying 15 neutralized residues (strain 861), imported precursor proteins at efficiencies comparable to those for wild-type organelles. Precursor binding studies with mitochondrial outer membrane vesicles from several of the mutant strains, including strain 861, revealed only slight differences from binding to wild-type vesicles. Deletion mutants lacking portions of the negatively charged region of TOM22 can also restore viability to the disruption-containing nucleus, but mutants lacking the entire region cannot. Taken together, these data suggest that an abundance of negative charges in the cytosolic domain of TOM22 is not essential for the binding or import of mitochondrial precursor proteins; however, other features in the domain are required.
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Affiliation(s)
- F E Nargang
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9.
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46
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Affiliation(s)
- M Mori
- Department of Molecular Genetics, Kumamoto University School of Medicine, Kuhonji 4-24-1, Kumamoto 862, Japan.
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47
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Ng FW, Shore GC. Bcl-XL cooperatively associates with the Bap31 complex in the endoplasmic reticulum, dependent on procaspase-8 and Ced-4 adaptor. J Biol Chem 1998; 273:3140-3. [PMID: 9452422 DOI: 10.1074/jbc.273.6.3140] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Bap31 is a polytopic integral membrane protein of the endoplasmic reticulum and forms a complex with Bcl-2/Bcl-XL and procaspase-8 (Ng, F. W. H., Nguyen, M., Kwan, T., Branton, P. E., Nicholson, W. D., Cromlish, J. A., and Shore, G. C. (1997) J. Cell Biol. 139, 327-338). In co-transfected human cells, procaspase-8 is capable of interacting with Ced-4, an important adaptor molecule in Caenorhabditis elegans that binds to and activates the C. elegans procaspase, proCed-3. Here, we show that the predicted death effector homology domain within the cytosolic region of Bap31 interacts with Ced-4 and contributes to recruitment of procaspase-8. Bcl-XL, which binds directly but weakly to the polytopic transmembrane region of Bap31, indirectly and cooperatively associates with the Bap31 cytosolic domain, dependent on the presence of procaspase-8 and Ced-4. Ced-4Deltac does not interact with Bcl-XL but rather displaces it from Bap31, suggesting that an endogenous Ced-4-like adaptor is a normal constituent of the Bap31 complex and is required for stable association of Bcl-XL with Bap31 in vivo. These findings indicate that Bap31 is capable of recruiting essential components of a core death regulatory machinery.
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Affiliation(s)
- F W Ng
- Department of Biochemistry, McGill University, Montreal, Quebec H3G 1Y6, Canada
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