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Falvo S, Grillo G, Latino D, Chieffi Baccari G, Di Fiore MM, Venditti M, Petito G, Santillo A. Potential role of mitochondria and endoplasmic reticulum in the response elicited by D-aspartate in TM4 Sertoli cells. Front Cell Dev Biol 2024; 12:1438231. [PMID: 39105170 PMCID: PMC11298366 DOI: 10.3389/fcell.2024.1438231] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2024] [Accepted: 07/04/2024] [Indexed: 08/07/2024] Open
Abstract
D-Aspartic Acid (D-Asp) affects spermatogenesis by enhancing the biosynthesis of the sex steroid hormones acting either through the hypothalamus-pituitary-testis axis or directly on Leydig cells. Recently, in vitro studies have also demonstrated the direct effects of D-Asp on the proliferation and/or activity of germ cells. However, although D-Asp is present in Sertoli cells (SC), the specific role of the amino acid in these cells remains unknown. This study investigated the effects of D-Asp on the proliferation and activity of TM4 SC, focusing on the mitochondrial compartment and its association with the endoplasmic reticulum (ER). We found that D-Asp enhanced the proliferation and activity of TM4 cells as evidenced by the activation of ERK/Akt/PCNA pathway and the increase in the protein levels of the androgen receptor. Furthermore, D-Asp reduced both the oxidative stress and apoptotic process. An increase in mitochondrial functionality and dynamics, as well as a reduction in ER stress, were also found in D-Asp-treated TM4 cells. It is known that mitochondria are closely associated with ER to form the Mitochondrial-Associated Endoplasmic Reticulum Membranes (MAM), the site of calcium ions and lipid transfer from ER to the mitochondria, and vice versa. The data demonstrated that D-Asp induced stabilization of MAM in TM4 cells. In conclusion, this study is the first to demonstrate a direct effect of D-Asp on SC activity and to clarify the cellular/molecular mechanism underlying these effects, suggesting that D-Asp could stimulate spermatogenesis by improving the efficiency of SC.
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Affiliation(s)
- Sara Falvo
- Department of Environmental Biological and Pharmaceutical Sciences and Technologies, University of Campania Luigi Vanvitelli, Caserta, Italy
| | - Giulia Grillo
- Department of Environmental Biological and Pharmaceutical Sciences and Technologies, University of Campania Luigi Vanvitelli, Caserta, Italy
| | - Debora Latino
- Department of Environmental Biological and Pharmaceutical Sciences and Technologies, University of Campania Luigi Vanvitelli, Caserta, Italy
| | - Gabriella Chieffi Baccari
- Department of Environmental Biological and Pharmaceutical Sciences and Technologies, University of Campania Luigi Vanvitelli, Caserta, Italy
| | - Maria Maddalena Di Fiore
- Department of Environmental Biological and Pharmaceutical Sciences and Technologies, University of Campania Luigi Vanvitelli, Caserta, Italy
| | - Massimo Venditti
- Department of Experimental Medicine, University of Campania Luigi Vanvitelli, Naples, Italy
| | - Giuseppe Petito
- Department of Environmental Biological and Pharmaceutical Sciences and Technologies, University of Campania Luigi Vanvitelli, Caserta, Italy
| | - Alessandra Santillo
- Department of Environmental Biological and Pharmaceutical Sciences and Technologies, University of Campania Luigi Vanvitelli, Caserta, Italy
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2
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Latino D, Venditti M, Falvo S, Grillo G, Santillo A, Messaoudi I, Ben Rhouma M, Minucci S, Chieffi Baccari G, Di Fiore MM. Steroidogenesis Upregulation through Mitochondria-Associated Endoplasmic Reticulum Membranes and Mitochondrial Dynamics in Rat Testes: The Role of D-Aspartate. Cells 2024; 13:523. [PMID: 38534366 DOI: 10.3390/cells13060523] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2024] [Revised: 03/14/2024] [Accepted: 03/14/2024] [Indexed: 03/28/2024] Open
Abstract
Mitochondria-Associated Endoplasmic Reticulum Membranes (MAMs) mediate the communication between the Endoplasmic Reticulum (ER) and the mitochondria, playing a fundamental role in steroidogenesis. This study aimed to understand how D-aspartate (D-Asp), a well-known stimulator of testosterone biosynthesis and spermatogenesis, affects the mechanism of steroidogenesis in rat testes. Our results suggested that D-Asp exerts this function through MAMs, affecting lipid trafficking, calcium signaling, ER stress, and mitochondrial dynamics. After 15 days of oral administration of D-Asp to rats, there was an increase in both antioxidant enzymes (SOD and Catalase) and in the protein expression levels of ATAD3A, FACL4, and SOAT1, which are markers of lipid transfer, as well as VDAC and GRP75, which are markers of calcium signaling. Additionally, there was a decrease in protein expression levels of GRP78, a marker of aging that counteracts ER stress. The effects of D-Asp on mitochondrial dynamics strongly suggested its active role as well. It induced the expression levels of proteins involved in fusion (MFN1, MFN2, and OPA1) and in biogenesis (NRF1 and TFAM), as well as in mitochondrial mass (TOMM20), and decreased the expression level of DRP1, a crucial mitochondrial fission marker. These findings suggested D-Asp involvement in the functional improvement of mitochondria during steroidogenesis. Immunofluorescent signals of ATAD3A, MFN1/2, TFAM, and TOMM20 confirmed their localization in Leydig cells showing an intensity upgrade in D-Asp-treated rat testes. Taken together, our results demonstrate the involvement of D-Asp in the steroidogenesis of rat testes, acting at multiple stages of both MAMs and mitochondrial dynamics, opening new opportunities for future investigation in other steroidogenic tissues.
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Affiliation(s)
- Debora Latino
- Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, University of Campania 'Luigi Vanvitelli', 81100 Caserta, Italy
| | - Massimo Venditti
- Department of Experimental Medicine, Section Human Physiology and Integrated Biological Functions, University of Campania 'Luigi Vanvitelli', 80138 Napoli, Italy
| | - Sara Falvo
- Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, University of Campania 'Luigi Vanvitelli', 81100 Caserta, Italy
| | - Giulia Grillo
- Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, University of Campania 'Luigi Vanvitelli', 81100 Caserta, Italy
| | - Alessandra Santillo
- Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, University of Campania 'Luigi Vanvitelli', 81100 Caserta, Italy
| | - Imed Messaoudi
- LR11ES41: Génetique, Biodiversité et Valorisation des Bioressources, Institut Supérieur de Biotechnologie, Université de Monastir, Monastir 5000, Tunisia
| | - Mariem Ben Rhouma
- LR11ES41: Génetique, Biodiversité et Valorisation des Bioressources, Institut Supérieur de Biotechnologie, Université de Monastir, Monastir 5000, Tunisia
| | - Sergio Minucci
- Department of Experimental Medicine, Section Human Physiology and Integrated Biological Functions, University of Campania 'Luigi Vanvitelli', 80138 Napoli, Italy
| | - Gabriella Chieffi Baccari
- Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, University of Campania 'Luigi Vanvitelli', 81100 Caserta, Italy
| | - Maria Maddalena Di Fiore
- Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, University of Campania 'Luigi Vanvitelli', 81100 Caserta, Italy
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3
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Latino D, Chieffi Baccari G, Di Fiore MM, Cioffi F, Venditti M, Giacco A, Santillo A. Autophagy and mitochondrial damage in the testis of high-fat diet fed rats. Gen Comp Endocrinol 2022; 328:114104. [PMID: 35973585 DOI: 10.1016/j.ygcen.2022.114104] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/23/2022] [Revised: 08/05/2022] [Accepted: 08/11/2022] [Indexed: 11/18/2022]
Abstract
High-fat diet (HFD) affects the physiology of reproduction in males, and many studies have investigated its detrimental effects. In this study, we investigated the cellular response induced by an HFD in the rat testis, focusing on the mitochondrial compartment. After five weeks of HFD, an increase in the levels of malondialdehyde and of reduced form of glutathione in the rat testis indicated an increase in lipid peroxidation. The results showed an increase in autophagy, apoptosis, and mitochondrial damage in the testis of HFD rats. We found a decrease in the protein expression of mitochondrial antioxidant enzymes, such as catalase and SOD2. Immunohistochemical analysis revealed a decrease in the immunofluorescent signal of SOD2, mainly in the spermatogonia and spermatocytes of HFD rats. HFD-induced mitochondrial damage caused a reduction in mitochondria, as evidenced by a decrease in the protein expression of TOM20, a mitochondrial outer membrane receptor. Consistently, HFD enhanced the levels of the PINK1 protein, a mitophagy marker, suggesting the removal of damaged mitochondria under these conditions. Induction of mtDNA damage and repair was stronger in the HFD rat testis. Finally, we found a decrease in the mtDNA copy number and expression of the POLG enzyme, which is involved in mtDNA replication. In conclusion, our results showed that autophagy and apoptosis are activated in the testis of HFD rats as a survival strategy to cope with oxidative stress. Furthermore, HFD-induced oxidative stress affects the mitochondria, inducing mtDNA damage and mtDNA copy number reduction. Mitophagy and mtDNA repair mechanisms might represent a mitochondrial adaptive response.
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Affiliation(s)
- Debora Latino
- Dipartimento di Scienze e Tecnologie Ambientali, Biologiche e Farmaceutiche, Università degli studi della Campania "Luigi Vanvitelli", Caserta, Italy
| | - Gabriella Chieffi Baccari
- Dipartimento di Scienze e Tecnologie Ambientali, Biologiche e Farmaceutiche, Università degli studi della Campania "Luigi Vanvitelli", Caserta, Italy
| | - Maria Maddalena Di Fiore
- Dipartimento di Scienze e Tecnologie Ambientali, Biologiche e Farmaceutiche, Università degli studi della Campania "Luigi Vanvitelli", Caserta, Italy
| | - Federica Cioffi
- Dipartimento di Scienze e Tecnologie, Università degli studi del Sannio, Benevento, Italy
| | - Massimo Venditti
- Dipartimento di Medicina Sperimentale, Università degli studi della Campania "Luigi Vanvitelli", Caserta, Italy
| | - Antonia Giacco
- Dipartimento di Scienze e Tecnologie, Università degli studi del Sannio, Benevento, Italy
| | - Alessandra Santillo
- Dipartimento di Scienze e Tecnologie Ambientali, Biologiche e Farmaceutiche, Università degli studi della Campania "Luigi Vanvitelli", Caserta, Italy.
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4
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Walter C, Marada A, Suhm T, Ernsberger R, Muders V, Kücükköse C, Sánchez-Martín P, Hu Z, Aich A, Loroch S, Solari FA, Poveda-Huertes D, Schwierzok A, Pommerening H, Matic S, Brix J, Sickmann A, Kraft C, Dengjel J, Dennerlein S, Brummer T, Vögtle FN, Meisinger C. Global kinome profiling reveals DYRK1A as critical activator of the human mitochondrial import machinery. Nat Commun 2021; 12:4284. [PMID: 34257281 PMCID: PMC8277783 DOI: 10.1038/s41467-021-24426-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Accepted: 06/15/2021] [Indexed: 11/21/2022] Open
Abstract
The translocase of the outer mitochondrial membrane TOM constitutes the organellar entry gate for nearly all precursor proteins synthesized on cytosolic ribosomes. Thus, TOM presents the ideal target to adjust the mitochondrial proteome upon changing cellular demands. Here, we identify that the import receptor TOM70 is targeted by the kinase DYRK1A and that this modification plays a critical role in the activation of the carrier import pathway. Phosphorylation of TOM70Ser91 by DYRK1A stimulates interaction of TOM70 with the core TOM translocase. This enables transfer of receptor-bound precursors to the translocation pore and initiates their import. Consequently, loss of TOM70Ser91 phosphorylation results in a strong decrease in import capacity of metabolite carriers. Inhibition of DYRK1A impairs mitochondrial structure and function and elicits a protective transcriptional response to maintain a functional import machinery. The DYRK1A-TOM70 axis will enable insights into disease mechanisms caused by dysfunctional DYRK1A, including autism spectrum disorder, microcephaly and Down syndrome.
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Affiliation(s)
- Corvin Walter
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
- Faculty of Biology, University of Freiburg, Freiburg, Germany
| | - Adinarayana Marada
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Tamara Suhm
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Ralf Ernsberger
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Vera Muders
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Cansu Kücükköse
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
- Faculty of Biology, University of Freiburg, Freiburg, Germany
| | - Pablo Sánchez-Martín
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Zehan Hu
- Department of Biology, University of Fribourg, Fribourg, Switzerland
| | - Abhishek Aich
- Department of Cellular Biochemistry, University Medical Center Göttingen, Göttingen, Germany
- Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen, Göttingen, Germany
| | - Stefan Loroch
- Leibniz Institut für Analytische Wissenschaften - ISAS - e.V., Dortmund, Germany
| | | | - Daniel Poveda-Huertes
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Alexandra Schwierzok
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Henrike Pommerening
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Stanka Matic
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Jan Brix
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Albert Sickmann
- Leibniz Institut für Analytische Wissenschaften - ISAS - e.V., Dortmund, Germany
| | - Claudine Kraft
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
- CIBSS - Centre for Integrative Biological Signalling Studies, University of Freiburg, Freiburg, Germany
| | - Jörn Dengjel
- Department of Biology, University of Fribourg, Fribourg, Switzerland
| | - Sven Dennerlein
- Department of Cellular Biochemistry, University Medical Center Göttingen, Göttingen, Germany
| | - Tilman Brummer
- Institute of Molecular Medicine, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany
- BIOSS Centre for Biological Signalling Studies, University of Freiburg, Freiburg, Germany
- German Cancer Consortium DKTK Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - F-Nora Vögtle
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
- CIBSS - Centre for Integrative Biological Signalling Studies, University of Freiburg, Freiburg, Germany.
- Center for Molecular Biology of Heidelberg University (ZMBH), Heidelberg, Germany.
| | - Chris Meisinger
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
- CIBSS - Centre for Integrative Biological Signalling Studies, University of Freiburg, Freiburg, Germany.
- BIOSS Centre for Biological Signalling Studies, University of Freiburg, Freiburg, Germany.
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5
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Rout S, Oeljeklaus S, Makki A, Tachezy J, Warscheid B, Schneider A. Determinism and contingencies shaped the evolution of mitochondrial protein import. Proc Natl Acad Sci U S A 2021; 118:e2017774118. [PMID: 33526678 PMCID: PMC8017667 DOI: 10.1073/pnas.2017774118] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mitochondrial protein import requires outer membrane receptors that evolved independently in different lineages. Here we used quantitative proteomics and in vitro binding assays to investigate the substrate preferences of ATOM46 and ATOM69, the two mitochondrial import receptors of Trypanosoma brucei The results show that ATOM46 prefers presequence-containing, hydrophilic proteins that lack transmembrane domains (TMDs), whereas ATOM69 prefers presequence-lacking, hydrophobic substrates that have TMDs. Thus, the ATOM46/yeast Tom20 and the ATOM69/yeast Tom70 pairs have similar substrate preferences. However, ATOM46 mainly uses electrostatic, and Tom20 hydrophobic, interactions for substrate binding. In vivo replacement of T. brucei ATOM46 by yeast Tom20 did not restore import. However, replacement of ATOM69 by the recently discovered Tom36 receptor of Trichomonas hydrogenosomes, while not allowing for growth, restored import of a large subset of trypanosomal proteins that lack TMDs. Thus, even though ATOM69 and Tom36 share the same domain structure and topology, they have different substrate preferences. The study establishes complementation experiments, combined with quantitative proteomics, as a highly versatile and sensitive method to compare in vivo preferences of protein import receptors. Moreover, it illustrates the role determinism and contingencies played in the evolution of mitochondrial protein import receptors.
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Affiliation(s)
- Samuel Rout
- Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern, CH-3012 Bern, Switzerland
| | - Silke Oeljeklaus
- Biochemistry and Functional Proteomics, Institute of Biology II, Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany
- Signalling Research Centres BIOSS and CIBSS, University of Freiburg, 79104 Freiburg, Germany
| | - Abhijith Makki
- Department of Parasitology, Faculty of Science, Charles University, BIOCEV, 12843 Prague, Czech Republic
| | - Jan Tachezy
- Department of Parasitology, Faculty of Science, Charles University, BIOCEV, 12843 Prague, Czech Republic
| | - Bettina Warscheid
- Biochemistry and Functional Proteomics, Institute of Biology II, Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany;
| | - André Schneider
- Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern, CH-3012 Bern, Switzerland;
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6
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Cytosolic Events in the Biogenesis of Mitochondrial Proteins. Trends Biochem Sci 2020; 45:650-667. [DOI: 10.1016/j.tibs.2020.04.001] [Citation(s) in RCA: 52] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2020] [Revised: 03/18/2020] [Accepted: 04/02/2020] [Indexed: 01/08/2023]
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7
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Trcka F, Durech M, Vankova P, Vandova V, Simoncik O, Kavan D, Vojtesek B, Muller P, Man P. The interaction of the mitochondrial protein importer TOMM34 with HSP70 is regulated by TOMM34 phosphorylation and binding to 14-3-3 adaptors. J Biol Chem 2020; 295:8928-8944. [PMID: 32371396 PMCID: PMC7335785 DOI: 10.1074/jbc.ra120.012624] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2020] [Revised: 04/28/2020] [Indexed: 01/17/2023] Open
Abstract
Translocase of outer mitochondrial membrane 34 (TOMM34) orchestrates heat shock protein 70 (HSP70)/HSP90-mediated transport of mitochondrial precursor proteins. Here, using in vitro phosphorylation and refolding assays, analytical size-exclusion chromatography, and hydrogen/deuterium exchange MS, we found that TOMM34 associates with 14-3-3 proteins after its phosphorylation by protein kinase A (PKA). PKA preferentially targeted two serine residues in TOMM34: Ser93 and Ser160, located in the tetratricopeptide repeat 1 (TPR1) domain and the interdomain linker, respectively. Both of these residues were necessary for efficient 14-3-3 protein binding. We determined that phosphorylation-induced structural changes in TOMM34 are further augmented by binding to 14-3-3, leading to destabilization of TOMM34's secondary structure. We also observed that this interaction with 14-3-3 occludes the TOMM34 interaction interface with ATP-bound HSP70 dimers, which leaves them intact and thereby eliminates an inhibitory effect of TOMM34 on HSP70-mediated refolding in vitro In contrast, we noted that TOMM34 in complex with 14-3-3 could bind HSP90. Both TOMM34 and 14-3-3 participated in cytosolic precursor protein transport mediated by the coordinated activities of HSP70 and HSP90. Our results provide important insights into how PKA-mediated phosphorylation and 14-3-3 binding regulate the availability of TOMM34 for its interaction with HSP70.
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Affiliation(s)
- Filip Trcka
- Regional Centre for Applied Molecular Oncology, Masaryk Memorial Cancer Institute, Brno, Czech Republic
| | - Michal Durech
- Regional Centre for Applied Molecular Oncology, Masaryk Memorial Cancer Institute, Brno, Czech Republic
| | - Pavla Vankova
- BioCeV, Institute of Microbiology of the Czech Academy of Sciences, Vestec, Czech Republic; Department of Biochemistry, Faculty of Science, Charles University, Prague, Czech Republic
| | - Veronika Vandova
- Regional Centre for Applied Molecular Oncology, Masaryk Memorial Cancer Institute, Brno, Czech Republic
| | - Oliver Simoncik
- Regional Centre for Applied Molecular Oncology, Masaryk Memorial Cancer Institute, Brno, Czech Republic
| | - Daniel Kavan
- BioCeV, Institute of Microbiology of the Czech Academy of Sciences, Vestec, Czech Republic; Department of Biochemistry, Faculty of Science, Charles University, Prague, Czech Republic
| | - Borivoj Vojtesek
- Regional Centre for Applied Molecular Oncology, Masaryk Memorial Cancer Institute, Brno, Czech Republic
| | - Petr Muller
- Regional Centre for Applied Molecular Oncology, Masaryk Memorial Cancer Institute, Brno, Czech Republic.
| | - Petr Man
- BioCeV, Institute of Microbiology of the Czech Academy of Sciences, Vestec, Czech Republic.
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8
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Aghazadeh Y, Venugopal S, Martinez-Arguelles DB, Boisvert A, Blonder J, Papadopoulos V. Identification of Sec23ip, Part of 14-3-3γ Protein Network, as a Regulator of Acute Steroidogenesis in MA-10 Leydig Cells. Endocrinology 2020; 161:5686882. [PMID: 31875919 PMCID: PMC7007878 DOI: 10.1210/endocr/bqz036] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/13/2019] [Accepted: 12/18/2019] [Indexed: 02/07/2023]
Abstract
Testosterone production occurs in the Leydig cells of the testes and is essential for virilization, development, reproduction, and quality of life. Although the steroidogenic proteins involved in cholesterol conversion to testosterone (T) are well characterized, the causes of reduced T during fetal, neonatal, and adult life remain uncertain. It is well established that normal cellular function is achieved through fine-tuning of multiple rather than single protein networks. Our objective was to use mass spectrometry (MS)-based proteomics to identify which cellular pathways, other than the steroidogenic machinery, influence testosterone production in MA-10 mouse tumor Leydig cells. The 14-3-3 family of scaffolds mediate protein-protein interactions facilitating the crosstalk between protein networks. We previously showed that in MA-10 cells, 14-3-3γ is a critical regulator of steroidogenesis. Therefore, identifying proteins that interact with 14-3-3γ during steroidogenesis could provide clues into the other networks involved. Using liquid chromatography (LC)-MS, we identified 688 proteins that interact with 14-3-3γ and thus potentially impact MA-10 cell steroidogenesis. The identified proteins belong to multiple protein networks, including endoplasmic reticulum-Golgi cargo sorting and vesicle biogenesis, micro ribonucleic acid-induced gene silencing, inflammation, and vesicle trafficking, to name a few. We found that silencing one of the candidates, Sec23ip, a protein known to be involved in vesicle trafficking, resulted in decreased steroidogenesis. We further showed that in Sec23ip-silenced MA-10 cells, cholesterol mobilization from the cytoplasmic membrane to mitochondria is impaired. Taken together these data suggest that Sec23ip is involved in cholesterol trafficking to supply cholesterol for acute steroidogenesis through its interactions with 14-3-3γ.
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Affiliation(s)
- Yasaman Aghazadeh
- The Research Institute of the McGill University Health Centre and the Department of Medicine, McGill University, 1001 Decarie Boulevard, Montreal, Quebec, Canada
- Present address: McEwen Stem Cell Center & Toronto General Hospital Research Institute, University Health Network, Toronto, Ontario M5G 1L7, Canada
| | - Sathvika Venugopal
- The Research Institute of the McGill University Health Centre and the Department of Medicine, McGill University, 1001 Decarie Boulevard, Montreal, Quebec, Canada
| | - Daniel Benjamin Martinez-Arguelles
- The Research Institute of the McGill University Health Centre and the Department of Medicine, McGill University, 1001 Decarie Boulevard, Montreal, Quebec, Canada
| | - Annie Boisvert
- The Research Institute of the McGill University Health Centre and the Department of Medicine, McGill University, 1001 Decarie Boulevard, Montreal, Quebec, Canada
| | - Josip Blonder
- Cancer Research Technology Program, Frederick National Laboratory for Cancer Research, sponsored by the National Cancer Institute, 8560 Progress Drive, Frederick, Maryland
| | - Vassilios Papadopoulos
- The Research Institute of the McGill University Health Centre and the Department of Medicine, McGill University, 1001 Decarie Boulevard, Montreal, Quebec, Canada
- Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, 1985 Zonal Ave, Los Angeles, California
- Correspondence: Vassilios Papadopoulos, Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, 1985 Zonal Ave, Los Angeles, California 90089, USA. E-mail:
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9
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Becker T, Song J, Pfanner N. Versatility of Preprotein Transfer from the Cytosol to Mitochondria. Trends Cell Biol 2019; 29:534-548. [PMID: 31030976 DOI: 10.1016/j.tcb.2019.03.007] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2019] [Revised: 03/27/2019] [Accepted: 03/28/2019] [Indexed: 11/16/2022]
Abstract
Mitochondrial biogenesis requires the import of a large number of precursor proteins from the cytosol. Although specific membrane-bound preprotein translocases have been characterized in detail, it was assumed that protein transfer from the cytosol to mitochondria mainly involved unselective binding to molecular chaperones. Recent findings suggest an unexpected versatility of protein transfer to mitochondria. Cytosolic factors have been identified that bind to selected subsets of preproteins and guide them to mitochondrial receptors in a post-translational manner. Cotranslational import processes are emerging. Mechanisms for crosstalk between protein targeting to mitochondria and other cell organelles, in particular the endoplasmic reticulum (ER) and peroxisomes, have been uncovered. We discuss how a network of cytosolic machineries and targeting pathways promote and regulate preprotein transfer into mitochondria.
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Affiliation(s)
- Thomas Becker
- Institute of Biochemistry and Molecular Biology, Centre for Biochemistry and Molecular Cell Research (ZBMZ), Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany; Centre for Integrative Biological Signaling Studies (CIBSS), University of Freiburg, 79104 Freiburg, Germany.
| | - Jiyao Song
- Institute of Biochemistry and Molecular Biology, Centre for Biochemistry and Molecular Cell Research (ZBMZ), Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany
| | - Nikolaus Pfanner
- Institute of Biochemistry and Molecular Biology, Centre for Biochemistry and Molecular Cell Research (ZBMZ), Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany; Centre for Integrative Biological Signaling Studies (CIBSS), University of Freiburg, 79104 Freiburg, Germany.
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10
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Wang H, Cheung F, Stoll AC, Rockwell P, Figueiredo-Pereira ME. Mitochondrial and calcium perturbations in rat CNS neurons induce calpain-cleavage of Parkin: Phosphatase inhibition stabilizes pSer 65Parkin reducing its calpain-cleavage. Biochim Biophys Acta Mol Basis Dis 2019; 1865:1436-1450. [PMID: 30796971 DOI: 10.1016/j.bbadis.2019.02.016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Revised: 02/04/2019] [Accepted: 02/18/2019] [Indexed: 02/07/2023]
Abstract
Mitochondrial impairment and calcium (Ca++) dyshomeostasis are associated with Parkinson's disease (PD). When intracellular ATP levels are lowered, Ca++-ATPase pumps are impaired causing cytoplasmic Ca++ to be elevated and calpain activation. Little is known about the effect of calpain activation on Parkin integrity. To address this gap, we examined the effects of mitochondrial inhibitors [oligomycin (Oligo), antimycin and rotenone] on endogenous Parkin integrity in rat midbrain and cerebral cortical cultures. All drugs induced calpain-cleavage of Parkin to ~36.9/43.6 kDa fragments. In contrast, treatment with the proinflammatory prostaglandin J2 (PGJ2) and the proteasome inhibitor epoxomicin induced caspase-cleavage of Parkin to fragments of a different size, previously shown by others to be triggered by apoptosis. Calpain-cleaved Parkin was enriched in neuronal mitochondrial fractions. Pre-treatment with the phosphatase inhibitor okadaic acid prior to Oligo-treatment, stabilized full-length Parkin phosphorylated at Ser65, and reduced calpain-cleavage of Parkin. Treatment with the Ca++ ionophore A23187, which facilitates Ca++ transport across the plasma membrane, mimicked the effect of Oligo by inducing calpain-cleavage of Parkin. Removing extracellular Ca++ from the media prevented oligomycin- and ionophore-induced calpain-cleavage of Parkin. Computational analysis predicted that calpain-cleavage of Parkin liberates its UbL domain. The phosphagen cyclocreatine moderately mitigated Parkin cleavage by calpain. Moreover, the pituitary adenylate cyclase activating peptide (PACAP27), which stimulates cAMP production, prevented caspase but not calpain-cleavage of Parkin. Overall, our data support a link between Parkin phosphorylation and its cleavage by calpain. This mechanism reflects the impact of mitochondrial impairment and Ca++-dyshomeostasis on Parkin integrity and could influence PD pathogenesis.
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Affiliation(s)
- Hu Wang
- Department of Biological Sciences, Hunter College and Graduate Center, City University of New York, NY 10065, USA
| | - Fanny Cheung
- Department of Biological Sciences, Hunter College and Graduate Center, City University of New York, NY 10065, USA
| | - Anna C Stoll
- Department of Biological Sciences, Hunter College and Graduate Center, City University of New York, NY 10065, USA
| | - Patricia Rockwell
- Department of Biological Sciences, Hunter College and Graduate Center, City University of New York, NY 10065, USA
| | - Maria E Figueiredo-Pereira
- Department of Biological Sciences, Hunter College and Graduate Center, City University of New York, NY 10065, USA.
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11
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The Glutamate Dehydrogenase Pathway and Its Roles in Cell and Tissue Biology in Health and Disease. BIOLOGY 2017; 6:biology6010011. [PMID: 28208702 PMCID: PMC5372004 DOI: 10.3390/biology6010011] [Citation(s) in RCA: 100] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/15/2016] [Revised: 01/10/2017] [Accepted: 01/16/2017] [Indexed: 02/07/2023]
Abstract
Glutamate dehydrogenase (GDH) is a hexameric enzyme that catalyzes the reversible conversion of glutamate to α-ketoglutarate and ammonia while reducing NAD(P)⁺ to NAD(P)H. It is found in all living organisms serving both catabolic and anabolic reactions. In mammalian tissues, oxidative deamination of glutamate via GDH generates α-ketoglutarate, which is metabolized by the Krebs cycle, leading to the synthesis of ATP. In addition, the GDH pathway is linked to diverse cellular processes, including ammonia metabolism, acid-base equilibrium, redox homeostasis (via formation of fumarate), lipid biosynthesis (via oxidative generation of citrate), and lactate production. While most mammals possess a single GDH1 protein (hGDH1 in the human) that is highly expressed in the liver, humans and other primates have acquired, via duplication, an hGDH2 isoenzyme with distinct functional properties and tissue expression profile. The novel hGDH2 underwent rapid evolutionary adaptation, acquiring unique properties that enable enhanced enzyme function under conditions inhibitory to its ancestor hGDH1. These are thought to provide a biological advantage to humans with hGDH2 evolution occurring concomitantly with human brain development. hGDH2 is co-expressed with hGDH1 in human brain, kidney, testis and steroidogenic organs, but not in the liver. In human cerebral cortex, hGDH1 and hGDH2 are expressed in astrocytes, the cells responsible for removing and metabolizing transmitter glutamate, and for supplying neurons with glutamine and lactate. In human testis, hGDH2 (but not hGDH1) is densely expressed in the Sertoli cells, known to provide the spermatids with lactate and other nutrients. In steroid producing cells, hGDH1/2 is thought to generate reducing equivalents (NADPH) in the mitochondria for the biosynthesis of steroidal hormones. Lastly, up-regulation of hGDH1/2 expression occurs in cancer, permitting neoplastic cells to utilize glutamine/glutamate for their growth. In addition, deregulation of hGDH1/2 is implicated in the pathogenesis of several human disorders.
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12
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Revisiting trends on mitochondrial mega-channels for the import of proteins and nucleic acids. J Bioenerg Biomembr 2016; 49:75-99. [DOI: 10.1007/s10863-016-9662-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Accepted: 04/25/2016] [Indexed: 12/14/2022]
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13
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Kathiresan M, English AM. Targeted proteomics identify metabolism-dependent interactors of yeast cytochrome c peroxidase: implications in stress response and heme trafficking. Metallomics 2016; 8:434-43. [PMID: 26980054 DOI: 10.1039/c5mt00330j] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Recently we discovered that cytochrome c peroxidase (Ccp1) functions primarily as a mitochondrial H2O2 sensor and heme donor in yeast cells. When cells switch their metabolism from fermentation to respiration mitochondrial H2O2 levels spike, and overoxidation of its polypeptide labilizes Ccp1's heme. A large pool of heme-free Ccp1 exits the mitochondria and enters the nucleus and vacuole. To gain greater insight into the mechanisms of Ccp1's H2O2-sensing and heme-donor functions during the cell's different metabolic states, here we use glutathione-S-transferase (GST) pulldown assays, combined with 1D gel electrophoresis and mass spectrometry to probe for interactors of apo- and holoCcp1 in extracts from 1 d fermenting and 7 d stationary-phase respiring yeast. We identified Ccp1's peroxidase cosubstrate Cyc1 and 28 novel interactors of GST-apoCcp1 and GST-holoCcp1 including mitochondrial superoxide dismutase 2 (Sod2) and cytosolic Sod1, the mitochondrial transporter Pet9, the three yeast isoforms of glyceraldehyde-3-phosphate dehydrogenase (Tdh3/2/1), heat shock proteins including Hsp90 and Hsp70, and the main peroxiredoxin in yeast (Tsa1) as well as its cosubstrate, thioreoxin (Trx1). These new interactors expand the scope of Ccp1's possible roles in stress response and in heme trafficking and suggest several new lines of investigation. Furthermore, our targeted proteomics analysis underscores the limitations of large-scale interactome studies that found only 4 of the 30 Ccp1 interactors isolated here.
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Affiliation(s)
- M Kathiresan
- PROTEO and the Department of Chemistry and Biochemistry, Concordia University, 7141 Sherbrooke St West, Montreal, Quebec, Canada H4B 1R6.
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14
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Mani J, Meisinger C, Schneider A. Peeping at TOMs-Diverse Entry Gates to Mitochondria Provide Insights into the Evolution of Eukaryotes. Mol Biol Evol 2015; 33:337-51. [PMID: 26474847 DOI: 10.1093/molbev/msv219] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Mitochondria are essential for eukaryotic life and more than 95% of their proteins are imported as precursors from the cytosol. The targeting signals for this posttranslational import are conserved in all eukaryotes. However, this conservation does not hold true for the protein translocase of the mitochondrial outer membrane that serves as entry gate for essentially all precursor proteins. Only two of its subunits, Tom40 and Tom22, are conserved and thus likely were present in the last eukaryotic common ancestor. Tom7 is found in representatives of all supergroups except the Excavates. This suggests that it was added to the core of the translocase after the Excavates segregated from all other eukaryotes. A comparative analysis of the biochemically and functionally characterized outer membrane translocases of yeast, plants, and trypanosomes, which represent three eukaryotic supergroups, shows that the receptors that recognize the conserved import signals differ strongly between the different systems. They present a remarkable example of convergent evolution at the molecular level. The structural diversity of the functionally conserved import receptors therefore provides insight into the early evolutionary history of mitochondria.
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Affiliation(s)
- Jan Mani
- Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland
| | - Chris Meisinger
- Institut für Biochemie und Molekularbiologie, ZBMZ and BIOSS Centre for Biological Signalling Studies, Universität Freiburg, Freiburg, Germany
| | - André Schneider
- Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland
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15
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Aghazadeh Y, Papadopoulos V. The role of the 14-3-3 protein family in health, disease, and drug development. Drug Discov Today 2015; 21:278-87. [PMID: 26456530 DOI: 10.1016/j.drudis.2015.09.012] [Citation(s) in RCA: 188] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2015] [Revised: 09/21/2015] [Accepted: 09/29/2015] [Indexed: 11/18/2022]
Abstract
14-3-3 proteins regulate intracellular signaling pathways, such as signal transduction, protein trafficking, cell cycle, and apoptosis. In addition to the ubiquitous roles of 14-3-3 isoforms, unique tissue-specific functions are also described for each isoform. Owing to their role in regulating cell cycle, protein trafficking, and steroidogenesis, 14-3-3 proteins are prevalent in human diseases, such as cancer, neurodegeneration, and reproductive disorders, and, therefore, serve as valuable drug targets. In this review, we summarize the role of 14-3-3 proteins in normal and disease states, with a focus on 14-3-3γ and ɛ. We also discuss drug compounds targeting 14-3-3 proteins and their potential therapeutic uses.
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Affiliation(s)
- Yasaman Aghazadeh
- The Research Institute of the McGill University Health Centre, Montreal, QC H4A 3J1, Canada; Department of Medicine, McGill University, Montreal, QC H3G 1A4, Canada
| | - Vassilios Papadopoulos
- The Research Institute of the McGill University Health Centre, Montreal, QC H4A 3J1, Canada; Department of Medicine, McGill University, Montreal, QC H3G 1A4, Canada; Department of Pharmacology and Therapeutics, McGill University, Montreal, QC H3G 1Y6, Canada; Department of Biochemistry, McGill University, Montreal, QC H3G 1Y6, Canada.
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16
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Kuszak AJ, Jacobs D, Gurnev PA, Shiota T, Louis JM, Lithgow T, Bezrukov SM, Rostovtseva TK, Buchanan SK. Evidence of Distinct Channel Conformations and Substrate Binding Affinities for the Mitochondrial Outer Membrane Protein Translocase Pore Tom40. J Biol Chem 2015; 290:26204-17. [PMID: 26336107 DOI: 10.1074/jbc.m115.642173] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2015] [Indexed: 12/14/2022] Open
Abstract
Nearly all mitochondrial proteins are coded by the nuclear genome and must be transported into mitochondria by the translocase of the outer membrane complex. Tom40 is the central subunit of the translocase complex and forms a pore in the mitochondrial outer membrane. To date, the mechanism it utilizes for protein transport remains unclear. Tom40 is predicted to comprise a membrane-spanning β-barrel domain with conserved α-helical domains at both the N and C termini. To investigate Tom40 function, including the role of the N- and C-terminal domains, recombinant forms of the Tom40 protein from the yeast Candida glabrata, and truncated constructs lacking the N- and/or C-terminal domains, were functionally characterized in planar lipid membranes. Our results demonstrate that each of these Tom40 constructs exhibits at least four distinct conductive levels and that full-length and truncated Tom40 constructs specifically interact with a presequence peptide in a concentration- and voltage-dependent manner. Therefore, neither the first 51 amino acids of the N terminus nor the last 13 amino acids of the C terminus are required for Tom40 channel formation or for the interaction with a presequence peptide. Unexpectedly, substrate binding affinity was dependent upon the Tom40 state corresponding to a particular conductive level. A model where two Tom40 pores act in concert as a dimeric protein complex best accounts for the observed biochemical and electrophysiological data. These results provide the first evidence for structurally distinct Tom40 conformations playing a role in substrate recognition and therefore in transport function.
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Affiliation(s)
| | - Daniel Jacobs
- From the Laboratories of Molecular Biology and Program in Physical Biology, NICHD, National Institutes of Health, Bethesda, Maryland 20892
| | - Philip A Gurnev
- Program in Physical Biology, NICHD, National Institutes of Health, Bethesda, Maryland 20892, the Physics Department, University of Massachusetts, Amherst, Massachusetts 01003, and
| | - Takuya Shiota
- the Department of Microbiology, Monash University, Melbourne 3800, Victoria, Australia
| | | | - Trevor Lithgow
- the Department of Microbiology, Monash University, Melbourne 3800, Victoria, Australia
| | - Sergey M Bezrukov
- Program in Physical Biology, NICHD, National Institutes of Health, Bethesda, Maryland 20892
| | - Tatiana K Rostovtseva
- Program in Physical Biology, NICHD, National Institutes of Health, Bethesda, Maryland 20892,
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17
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A presequence-binding groove in Tom70 supports import of Mdl1 into mitochondria. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2015; 1853:1850-9. [PMID: 25958336 DOI: 10.1016/j.bbamcr.2015.04.021] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2015] [Revised: 04/23/2015] [Accepted: 04/30/2015] [Indexed: 11/21/2022]
Abstract
The translocase of the outer mitochondrial membrane (TOM complex) is the general entry gate into mitochondria for almost all imported proteins. A variety of specific receptors allow the TOM complex to recognize targeting signals of various precursor proteins that are transported along different import pathways. Aside from the well-characterized presequence receptors Tom20 and Tom22 a third TOM receptor, Tom70, binds proteins of the carrier family containing multiple transmembrane segments. Here we demonstrate that Tom70 directly binds to presequence peptides using a dedicated groove. A single point mutation in the cavity of this pocket (M551R) reduces the presequence binding affinity of Tom70 ten-fold and selectively impairs import of the presequence-containing precursor Mdl1 but not the ADP/ATP carrier (AAC). Hence Tom70 contributes to the presequence import pathway by recognition of the targeting signal of the Mdl1 precursor.
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18
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Aghazadeh Y, Zirkin BR, Papadopoulos V. Pharmacological regulation of the cholesterol transport machinery in steroidogenic cells of the testis. VITAMINS AND HORMONES 2015; 98:189-227. [PMID: 25817870 DOI: 10.1016/bs.vh.2014.12.006] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Reduced serum testosterone (T), or hypogonadism, is estimated to affect about 5 million American men, including both aging and young men. Low serum T has been linked to mood changes, worsening cognition, fatigue, depression, decreased lean body mass and bone mineral density, increased visceral fat, metabolic syndrome, decreased libido, and sexual dysfunction. Administering exogenous T, known as T-replacement therapy (TRT), reverses many of the symptoms of low T levels. However, this treatment can result in luteinizing hormone suppression which, in turn, can lead to reduced sperm numbers and infertility, making TRT inappropriate for men who wish to father children. Additionally, TRT may result in supraphysiologic T levels, skin irritation, and T transfer to others upon contact; and there may be increased risk of prostate cancer and cardiovascular disease, particularly in aging men. Therefore, the development of alternate therapies for treating hypogonadism would be highly desirable. To do so requires greater understanding of the series of steps leading to T formation and how they are regulated, and the identification of key steps that are amenable to pharmacological modulation so as to induce T production. We review herein our current understanding of mechanisms underlying the pharmacological induction of T formation in hypogonadal testis.
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Affiliation(s)
- Yasaman Aghazadeh
- The Research Institute of the McGill University Health Centre, Montreal, Quebec, Canada; Department of Medicine, McGill University, Montreal, Quebec, Canada
| | - Barry R Zirkin
- Department of Biochemistry and Molecular Biology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland, USA
| | - Vassilios Papadopoulos
- The Research Institute of the McGill University Health Centre, Montreal, Quebec, Canada; Department of Medicine, McGill University, Montreal, Quebec, Canada; Department of Biochemistry, McGill University, Montreal, Quebec, Canada; Department of Pharmacology & Therapeutics, McGill University, Montreal, Quebec, Canada.
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19
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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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20
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Nargang FE, Adames K, Rüb C, Cheung S, Easton N, Nargang CE, Chae MS. Identification of genes required for alternative oxidase production in the Neurospora crassa gene knockout library. G3 (BETHESDA, MD.) 2012; 2:1345-56. [PMID: 23173086 PMCID: PMC3484665 DOI: 10.1534/g3.112.004218] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/14/2012] [Accepted: 09/04/2012] [Indexed: 01/22/2023]
Abstract
The alternative oxidase (AOX) of Neurospora crassa transfers electrons from ubiquinol to oxygen. The enzyme is not expressed under normal conditions. However, when the function of the standard electron transport chain is compromised, AOX is induced, providing cells with a means to continue respiration and growth. Induction of the enzyme represents a form of retrograde regulation because AOX is encoded by a nuclear gene that responds to signals produced from inefficiently functioning mitochondria. To identify genes required for AOX expression, we have screened the N. crassa gene knockout library for strains that are unable to grow in the presence of antimycin A, an inhibitor of complex III of the standard electron transport chain. From the 7800 strains containing knockouts of different genes, we identified 62 strains that have reduced levels of AOX when grown under conditions known to induce the enzyme. Some strains have virtually no AOX, whereas others have only a slight reduction of the protein. A broad range of seemingly unrelated functions are represented in the knockouts. For example, we identified transcription factors, kinases, the mitochondrial import receptor Tom70, three subunits of the COP9 signalosome, a monothiol glutaredoxin, and several hypothetical proteins as being required for wild-type levels of AOX production. Our results suggest that defects in many signaling or metabolic pathways have a negative effect on AOX expression and imply that complex systems control production of the enzyme.
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Affiliation(s)
- Frank E Nargang
- Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada.
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21
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Aghazadeh Y, Rone MB, Blonder J, Ye X, Veenstra TD, Hales DB, Culty M, Papadopoulos V. Hormone-induced 14-3-3γ adaptor protein regulates steroidogenic acute regulatory protein activity and steroid biosynthesis in MA-10 Leydig cells. J Biol Chem 2012; 287:15380-94. [PMID: 22427666 DOI: 10.1074/jbc.m112.339580] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Cholesterol is the sole precursor of steroid hormones in the body. The import of cholesterol to the inner mitochondrial membrane, the rate-limiting step in steroid biosynthesis, relies on the formation of a protein complex that assembles at the outer mitochondrial membrane called the transduceosome. The transduceosome contains several mitochondrial and cytosolic components, including the steroidogenic acute regulatory protein (STAR). Human chorionic gonadotropin (hCG) induces de novo synthesis of STAR, a process shown to parallel maximal steroid production. In the hCG-dependent steroidogenic MA-10 mouse Leydig cell line, the 14-3-3γ protein was identified in native mitochondrial complexes by mass spectrometry and immunoblotting, and its levels increased in response to hCG treatment. The 14-3-3 proteins bind and regulate the activity of many proteins, acting via target protein activation, modification and localization. In MA-10 cells, cAMP induces 14-3-3γ expression parallel to STAR expression. Silencing of 14-3-3γ expression potentiates hormone-induced steroidogenesis. Binding motifs of 14-3-3γ were identified in components of the transduceosome, including STAR. Immunoprecipitation studies demonstrate a hormone-dependent interaction between 14-3-3γ and STAR that coincides with reduced 14-3-3γ homodimerization. The binding site of 14-3-3γ on STAR was identified to be Ser-194 in the STAR-related sterol binding lipid transfer (START) domain, the site phosphorylated in response to hCG. Taken together, these results demonstrate that 14-3-3γ negatively regulates steroidogenesis by binding to Ser-194 of STAR, thus keeping STAR in an unfolded state, unable to induce maximal steroidogenesis. Over time 14-3-3γ homodimerizes and dissociates from STAR, allowing this protein to induce maximal mitochondrial steroid formation.
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Affiliation(s)
- Yasaman Aghazadeh
- The Research Institute of the McGill University Health Centre and the Department of Medicine, McGill University, Montreal, Quebec H3G 1A4, Canada
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22
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Midzak A, Rone M, Aghazadeh Y, Culty M, Papadopoulos V. Mitochondrial protein import and the genesis of steroidogenic mitochondria. Mol Cell Endocrinol 2011; 336:70-9. [PMID: 21147195 PMCID: PMC3057322 DOI: 10.1016/j.mce.2010.12.007] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/19/2010] [Revised: 12/03/2010] [Accepted: 12/05/2010] [Indexed: 11/23/2022]
Abstract
The principal site of regulation of steroid hormone biosynthesis is the transfer of cholesterol from the outer to inner mitochondrial membrane. Hormonal stimulation of steroidogenic cells promotes this mitochondrial lipid import through a multi-protein complex, termed the transduceosome, spanning the two membranes. The transduceosome complex is assembled from multiple proteins, such as the steroidogenic acute regulatory (STAR) protein and translocator protein (TSPO), and requires their targeting to the mitochondria for transduceosome function. The vast majority of mitochondrial proteins, including those participating in cholesterol import, are encoded in the nucleus. Their subsequent mitochondrial incorporation is performed through a series of protein import machineries located in the outer and inner mitochondrial membranes. Here we review our current knowledge of the mitochondrial cholesterol import machinery of the transduceosome. This is complemented with descriptions of mitochondrial protein import machineries and mechanisms by which these machineries assemble the transduceosome in steroidogenic mitochondria.
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Affiliation(s)
- Andrew Midzak
- Research Institute of the McGill University Health Centre, McGill University, Montreal, Quebec, H3G 1A4, Canada
- Department of Medicine, McGill University, Montreal, Quebec, H3G 1A4, Canada
| | - Malena Rone
- Research Institute of the McGill University Health Centre, McGill University, Montreal, Quebec, H3G 1A4, Canada
- Department of Medicine, McGill University, Montreal, Quebec, H3G 1A4, Canada
| | - Yassaman Aghazadeh
- Research Institute of the McGill University Health Centre, McGill University, Montreal, Quebec, H3G 1A4, Canada
- Department of Medicine, McGill University, Montreal, Quebec, H3G 1A4, Canada
| | - Martine Culty
- Research Institute of the McGill University Health Centre, McGill University, Montreal, Quebec, H3G 1A4, Canada
- Department of Medicine, McGill University, Montreal, Quebec, H3G 1A4, Canada
- Department of Pharmacology & Therapeutics, McGill University, Montreal, Quebec, H3G 1A4, Canada
| | - Vassilios Papadopoulos
- Research Institute of the McGill University Health Centre, McGill University, Montreal, Quebec, H3G 1A4, Canada
- Department of Medicine, McGill University, Montreal, Quebec, H3G 1A4, Canada
- Department of Pharmacology & Therapeutics, McGill University, Montreal, Quebec, H3G 1A4, Canada
- Department of Biochemistry, McGill University, Montreal, Quebec, H3G 1A4, Canada
- Correspondence at The Research Institute of the McGill University Health Center, Montreal General Hospital, 1650 Cedar Avenue, C10-148, Montreal, Quebec H3G 1A4, Canada. Tel: 514-934-1934 ext. 44580; Fax: 514-934-8261;
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Rimmer KA, Foo JH, Ng A, Petrie EJ, Shilling PJ, Perry AJ, Mertens HDT, Lithgow T, Mulhern TD, Gooley PR. Recognition of mitochondrial targeting sequences by the import receptors Tom20 and Tom22. J Mol Biol 2010; 405:804-18. [PMID: 21087612 DOI: 10.1016/j.jmb.2010.11.017] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2010] [Revised: 11/04/2010] [Accepted: 11/09/2010] [Indexed: 01/16/2023]
Abstract
The Tom20 and Tom22 receptor subunits of the TOM (translocase of the outer mitochondrial membrane) complex recognize N-terminal presequences of proteins that are to be imported into the mitochondrion. In plants, Tom20 is C-terminally anchored in the mitochondrial membrane, whereas Tom20 is N-terminally anchored in animals and fungi. Furthermore, the cytosolic domain of Tom22 in plants is smaller than its animal/fungal counterpart and contains fewer acidic residues. Here, NMR spectroscopy was used to explore presequence interactions with the cytosolic regions of receptors from the plant Arabidopsis thaliana and the fungus Saccharomyces cerevisiae (i.e., AtTom20, AtTom22, and ScTom22). It was found that AtTom20 possesses a discontinuous bidentate hydrophobic binding site for presequences. The presequences on plant mitochondrial proteins comprise two or more hydrophobic binding regions to match this bidentate site. NMR data suggested that while these presequences bind to ScTom22, they do not bind to AtTom22. AtTom22, however, binds to AtTom20 at the same binding site as presequences, suggesting that this domain competes with the presequences of imported proteins, thereby enabling their progression along the import pathway.
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Affiliation(s)
- Kieran A Rimmer
- Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, Australia
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Endo T, Yamano K. Transport of proteins across or into the mitochondrial outer membrane. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2010; 1803:706-14. [DOI: 10.1016/j.bbamcr.2009.11.007] [Citation(s) in RCA: 99] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2009] [Revised: 11/11/2009] [Accepted: 11/17/2009] [Indexed: 11/30/2022]
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25
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Tom20 mediates localization of mRNAs to mitochondria in a translation-dependent manner. Mol Cell Biol 2010; 30:284-94. [PMID: 19858288 DOI: 10.1128/mcb.00651-09] [Citation(s) in RCA: 129] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
mRNAs encoding mitochondrial proteins are enriched in the vicinity of mitochondria, presumably to facilitate protein transport. A possible mechanism for enrichment may involve interaction of the translocase of the mitochondrial outer membrane (TOM) complex with the precursor protein while it is translated, thereby leading to association of polysomal mRNAs with mitochondria. To test this hypothesis, we isolated mitochondrial fractions from yeast cells lacking the major import receptor, Tom20, and compared their mRNA repertoire to that of wild-type cells by DNA microarrays. Most mRNAs encoding mitochondrial proteins were less associated with mitochondria, yet the extent of decrease varied among genes. Analysis of several mRNAs revealed that optimal association of Tom20 target mRNAs requires both translating ribosomes and features within the encoded mitochondrial targeting signal. Recently, Puf3p was implicated in the association of mRNAs with mitochondria through interaction with untranslated regions. We therefore constructed a tom20 Delta puf3 Delta double-knockout strain, which demonstrated growth defects under conditions where fully functional mitochondria are required. Mislocalization effects for few tested mRNAs appeared stronger in the double knockout than in the tom20 Delta strain. Taken together, our data reveal a large-scale mRNA association mode that involves interaction of Tom20p with the translated mitochondrial targeting sequence and may be assisted by Puf3p.
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26
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Yamamoto H, Fukui K, Takahashi H, Kitamura S, Shiota T, Terao K, Uchida M, Esaki M, Nishikawa SI, Yoshihisa T, Yamano K, Endo T. Roles of Tom70 in import of presequence-containing mitochondrial proteins. J Biol Chem 2009; 284:31635-46. [PMID: 19767391 DOI: 10.1074/jbc.m109.041756] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Mitochondrial protein traffic requires precise recognition of the mitochondrial targeting signals by the import receptors on the mitochondrial surface including a general import receptor Tom20 and a receptor for presequence-less proteins, Tom70. Here we took a proteome-wide approach of mitochondrial protein import in vitro to find a set of presequence-containing precursor proteins for recognition by Tom70. The presequences of the Tom70-dependent precursor proteins were recognized by Tom20, whereas their mature parts exhibited Tom70-dependent import when attached to the presequence of Tom70-independent precursor proteins. The mature parts of the Tom70-dependent precursor proteins have the propensity to aggregate, and the presence of the receptor domain of Tom70 prevents their aggregate formation. Therefore Tom70 plays the role of a docking site for not only cytosolic chaperones but also aggregate-prone substrates to maintain their solubility for efficient transfer to downstream components of the mitochondrial import machineries.
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Affiliation(s)
- Hayashi Yamamoto
- Department of Chemistry, Graduate School of Science, Japan Science and Technology Agency, Research Centre for Material Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
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27
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Emelyanov VV. Mitochondrial Porin VDAC 1 Seems to Be Functional in Rickettsial Cells. Ann N Y Acad Sci 2009; 1166:38-48. [DOI: 10.1111/j.1749-6632.2009.04513.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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28
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Mills RD, Trewhella J, Qiu TW, Welte T, Ryan TM, Hanley T, Knott RB, Lithgow T, Mulhern TD. Domain Organization of the Monomeric Form of the Tom70 Mitochondrial Import Receptor. J Mol Biol 2009; 388:1043-58. [DOI: 10.1016/j.jmb.2009.03.070] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2009] [Revised: 03/24/2009] [Accepted: 03/30/2009] [Indexed: 11/28/2022]
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29
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Perry AJ, Rimmer KA, Mertens HDT, Waller RF, Mulhern TD, Lithgow T, Gooley PR. Structure, topology and function of the translocase of the outer membrane of mitochondria. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2008; 46:265-74. [PMID: 18272380 DOI: 10.1016/j.plaphy.2007.12.012] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2007] [Indexed: 05/09/2023]
Abstract
Proteins destined for the mitochondria required the evolution of specific and efficient molecular machinery for protein import. The subunits of the import translocases of the inner membrane (TIM) appear homologous and conserved amongst species, however the components of the translocase of the outer membrane (TOM) show extensive differences between species. Recently, bioinformatic and structural analysis of Tom20, an important receptor subunit of the TOM complex, suggests that this protein complex arose from different ancestors for plants compared to animals and fungi, but has subsequently converged to provide similar functions and analogous structures. Here we review the current knowledge of the TOM complex, the function and structure of the various subunits that make up this molecular machine.
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Affiliation(s)
- Andrew J Perry
- Department of Biochemistry and Molecular Biology, Bio21 Institute of Biotechnology and Molecular Science, University of Melbourne, Parkville, Victoria 3010, Australia
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30
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Abstract
We established a novel combinatorial method of laser microdissection system and immunoblot analysis in combination with a novel unfolding chaperone (oligomeric Aip2p/Dld2p) that enables us to examine the molecular profile of proteins in the microscopic regions of interest. As a model system for analyzing inclusion bodies associated with various diseases such as Alzheimer's disease, Parkinson's disease, and prion diseases including bovine spongiform encephalopathy (BSE), we applied this novel method to examine brain samples of patients with Pick's disease, a type of progressive presenile dementia with intraneuronal lesions denoted as Pick bodies (PBs) whose major structural components are tau proteins. After boiling in Laemmli's sample buffer according to the established immunoblotting procedures, 500-2000 PBs were initially applied onto SDS-PAGE gels; however, only faint signals were obtained. Remarkably, only one Pick body was sufficient to illustrate an immunoblot signal; this indicates that pretreatment with oligomeric Aip2p/Dld2p enhances the immunoblot sensitivity by more than a 100-fold. This unprecedented property of laser microdissection combined with oligomeric Aip2p/Dld2p may have further potential applications. For example, a number of proteomic strategies for such inclusion bodies depend on liquid chromatography-tandem mass spectrometry (LC-MS/MS); however, sample preparation methods typically involve the use of detergents and chaotropic agents that often interfere with chromatographic separation and/or electrospray ionization. However, the use of oligomeric Aip2p/Dld2p would not interfere with the LC-MS/MS procedures. Therefore, it might significantly facilitate nanoscale analysis, which is often hindered by the aggregation property of the target proteins present under various analytical conditions, particularly, when the sample protein is present in minor quantities.
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Affiliation(s)
- Naomi S Hachiya
- Department of Neurophysiology, Tokyo Medical University 6-1-1 Shinjuku, Shinjuku-ku Tokyo 160-8402, Japan
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31
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Bushell SR, Bottomley SP, Rossjohn J, Beddoe T. Tracking the Unfolding Pathway of a Multirepeat Protein via Tryptophan Scanning. J Biol Chem 2006; 281:24345-50. [PMID: 16803880 DOI: 10.1074/jbc.m602966200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The tetratricopeptide repeat (TPR) is a degenerate 34-amino acid repeating motif that forms a repeating helix-turn-helix structure and is a well characterized mediator of protein-protein interactions. Recently, a biophysical investigation on one naturally occurring TPR protein, Tom70, found that the mitochondrial receptor displayed an unusual three-state unfolding pathway, distinct from the two-state model usually displayed by TPR proteins. To investigate this unusual behavior, we undertook a tryptophan-scanning analysis of Tom70, where both native and engineered tryptophan residues are used as fluorescent reporters to monitor the range of local and global unfolding events that comprise the unfolding pathway of Tom70. Specifically, seven Tom70 variants were constructed, each with a single tryptophan residue in each of the seven TPR repeats of Tom70. By combining equilibrium and kinetic fluorescent unfolding assays, with circular dichroism experiments, our study reveals that the unusual folding pathway of Tom70 is a consequence of the unfolding of two separate, autonomous TPR arrays, with the less stable region appearing to account for the low structural stability of Tom70.
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Affiliation(s)
- Simon R Bushell
- Protein Crystallography Unit, Australian Research Council Centre of Excellence in Structural and Functional Microbial Genomics, Clayton, Victoria 3800, Australia
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32
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Chan NC, Likić VA, Waller RF, Mulhern TD, Lithgow T. The C-terminal TPR Domain of Tom70 Defines a Family of Mitochondrial Protein Import Receptors Found only in Animals and Fungi. J Mol Biol 2006; 358:1010-22. [PMID: 16566938 DOI: 10.1016/j.jmb.2006.02.062] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2005] [Revised: 02/21/2006] [Accepted: 02/23/2006] [Indexed: 11/15/2022]
Abstract
In fungi and animals the translocase in the outer mitochondrial membrane (TOM complex) consists of multiple components including the receptor subunit Tom70. Genome sequence analyses suggest no Tom70 receptor subunit exists in plants or protozoans, raising questions about its ancestry, function and the importance of its activity. Here we characterise the relationships within the Tom70 family of proteins. We find that in both fungi and animals, a conserved domain structure exists within the Tom70 family, with a transmembrane segment followed by 11 tetratricopeptide repeat motifs organised in three distinct domains. The C-terminal domain of Tom70 is highly conserved, and crucial for the import of hydrophobic substrate proteins, including those with and those without N-terminal presequences. Tom70 likely arose after fungi and animals diverged from other eukaryote lineages including plants, and subsequent gene duplication gave rise to a paralogue specific to the Saccharomyces group of yeasts. In animals and in fungi, Tom70 plays a fundamental role in the import of precursor proteins, by assisting relatively hydrophobic regions of substrate proteins into the translocation channel in the outer mitochondrial membrane. Proteins that function equivalently to Tom70 may have arisen independently in plants and protists.
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Affiliation(s)
- Nickie C Chan
- Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville 3010, Australia
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33
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Puri N, Lai-Zhang J, Meier S, Mueller DM. Expression of bovine F1-ATPase with functional complementation in yeast Saccharomyces cerevisiae. J Biol Chem 2005; 280:22418-24. [PMID: 15817482 DOI: 10.1074/jbc.m411113200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mitochondrial F(1)F(0)-ATP synthase is a multimeric enzyme complex composed of at least 16 unique peptides with an overall molecular mass of approximately 600 kDa. F(1)-ATPase is composed of alpha(3)beta(3)gammadeltaepsilon with an overall molecular mass of 370 kDa. The genes encoding bovine F(1)-ATPase have been expressed in a quintuple yeast Saccharomyces cerevisiae deletion mutant (DeltaalphaDeltabetaDeltagammaDeltadeltaDeltaepsilon). This strain expressing bovine F(1) is unable to grow on medium containing a non-fermentable carbon source (YPG), indicating that the enzyme is non-functional. However, daughter strains were easily selected for growth on YPG medium and these were evolved for improved growth on YPG medium. The evolution of the strains was presumably due to mutations, but mutations in the genes encoding the subunits of the bovine F(1)-ATPase were not required for the ability of the cell to grow on YPG medium. The bovine enzyme expressed in yeast was partially purified to a specific activity of about half of that of the enzyme purified from bovine heart mitochondria. These results indicate that the molecular machinery required for the assembly of the mitochondrial ATP synthase is conserved from bovine and yeast and suggest that yeast may be useful for the expression, mutagenesis, and analysis of the mammalian F(1)- or F(1)F(0)-ATP synthase.
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Affiliation(s)
- Neeti Puri
- Department of Biochemistry and Molecular Biology, Rosalind Franklin University of Medicine and Science, The Chicago Medical School, 3333 Greenbay Road, North Chicago, IL 60064, USA
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34
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Likić VA, Perry A, Hulett J, Derby M, Traven A, Waller RF, Keeling PJ, Koehler CM, Curran SP, Gooley PR, Lithgow T. Patterns that Define the Four Domains Conserved in Known and Novel Isoforms of the Protein Import Receptor Tom20. J Mol Biol 2005; 347:81-93. [PMID: 15733919 DOI: 10.1016/j.jmb.2004.12.057] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2004] [Revised: 12/17/2004] [Accepted: 12/27/2004] [Indexed: 11/22/2022]
Abstract
Tom20 is the master receptor for protein import into mitochondria. Analysis of motifs present in Tom20 sequences from fungi and animals found several highly conserved regions, including features of the transmembrane segment, the ligand-binding domain and functionally important flexible segments at the N terminus and the C terminus of the protein. Hidden Markov model searches of genome sequence data revealed novel isoforms of Tom20 in vertebrate and invertebrate animals. A three-dimensional comparative model of the novel type I Tom20, based on the structurally characterized type II isoform, shows important differences in the amino acid residues lining the ligand-binding groove, where the type I protein from animals is more similar to the fungal form of Tom20. Given that the two receptor types from mouse interact with the same set of precursor protein substrates, comparative analysis of the substrate-binding site provides unique insight into the mechanism of substrate recognition. No Tom20-related protein was found in genome sequence data from plants or protozoans, suggesting the receptor Tom20 evolved after the split of animals and fungi from the main lineage of eukaryotes.
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Affiliation(s)
- Vladimir A Likić
- Russell Grimwade School of Biochemistry and Molecular Biology, University of Melbourne, Melbourne 3010, Australia
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35
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Mihara K, Omura T. Cytoplasmic chaperones in precursor targeting to mitochondria: the role of MSF and hsp 70. Trends Cell Biol 2005; 6:104-8. [PMID: 15157486 DOI: 10.1016/0962-8924(96)81000-2] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Despite extensive study since the early 1980s, the mechanism by which newly synthesized protein precursors are unfolded in the cytoplasm and targeted correctly to the mitochondrial surface prior to translocation through the mitochondrial membranes is understood poorly. Recently, an N-ethylmaleimide (NEM)-sensitive cytoplasmic factor called mitochondrial import stimulation factor (MSF), which catalyses the ATP-dependent unfolding of precursor proteins, was described. Unlike the more general chaperone proteins of the hsp70 families, MSF not only unfolds proteins but also targets the unfolded precursor proteins to the mitochondria. Here, Mihara and Omura summarize what is known about MSF and speculate on how it, and other cytoplasmic factors, may be involved in mitochondrial import.
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Affiliation(s)
- K Mihara
- Dept of Molecular Biology, Graduate School of Medical Science, Fukuoka 812, Japan
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36
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Hachiya NS, Sakasegawa Y, Sasaki H, Jozuka A, Tsukita S, Kaneko K. Oligomeric Aip2p/Dld2p modifies the protein conformation of both properly folded and misfolded substrates in vitro. Biochem Biophys Res Commun 2004; 323:339-44. [PMID: 15351742 DOI: 10.1016/j.bbrc.2004.08.098] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2004] [Indexed: 10/26/2022]
Abstract
Oligomeric actin-interacting protein 2 (Aip2p) [Nat. Struct. Biol. 2 (1995) 28]/D-lactate dehydrogenase protein 2 (Dld2p) [Yeast 15 (1999) 1377, Biochem. Biophys. Res. Commun. 295 (2002) 910] exhibits the unique grapple-like structure with an ATP-dependent opening [Biochem. Biophys. Res. Commun. 320 (2004) 1271], which is required for the F-actin conformation modifying activity in vitro and in vivo [Biochem. Biophys. Res. Commun. 319 (2004) 78]. To further investigate the molecular nature of oligomeric Aip2p/Dld2p, the substrate specificity of its binding and protein conformation modifying activity was examined. In the presence of 1mM ATP or AMP-PNP, oligomeric Aip2p/Dld2p bound to all substrates so far examined, and modified the conformation of actin, DNase I, the mature form of invertase, prepro-alpha-factor, pro-alpha-factor, and mitochondrial superoxide dismutase, as determined by the trypsin susceptibility assay. Of note, the activity could modify even the conformation of pathogenic highly aggregated polypeptides, such as recombinant prion protein in beta-sheet form, alpha-synuclein, and amyloid beta (1-42) in the presence of ATP. The in vivo protein conformation modifying activity, however, depends on the growth stage; the most significant substrate modification activity was observed in yeast cells at the log phase, suggesting the presence of a cofactor/s in yeast cells, where F-actin is supposed to be a major target in vivo. These data further support our previous notion that the oligomeric Aip2p/Dld2p may belong to an unusual class of molecular chaperones [Biochem. Biophys. Res. Commun. 320 (2004) 1271], which can target both properly folded and misfolded proteins in an ATP-dependent manner in vitro.
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Affiliation(s)
- Naomi S Hachiya
- Department of Cortical Function Disorders, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo 187-8502, Japan
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37
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Hachiya NS, Sakasegawa Y, Sasaki H, Jozuka A, Tsukita S, Kaneko K. Oligomeric Aip2p/Dld2p forms a novel grapple-like structure and has an ATP-dependent F-actin conformation modifying activity in vitro. Biochem Biophys Res Commun 2004; 320:1271-6. [PMID: 15249227 DOI: 10.1016/j.bbrc.2004.06.082] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2004] [Indexed: 10/26/2022]
Abstract
In order to investigate the molecular mechanism of the F-actin conformation modifying activity [Biochem. Biophys. Res. Commun. 319 (2004) 78] of actin-interacting protein 2 (Aip2p) [Nat. Struct. Biol. 2 (1995) 28]/D-lactate dehydrogenase protein 2 (Dld2p) [Yeast 15 (1999) 1377; Biochem. Biophys. Res. Commun. 295 (2002) 910], the ultrastructure and the regulatory mechanism of the activity were further examined. Interestingly, a novel oligomeric grapple-like structure of 10-12 subunits with an ATP-dependent opening was observed. ATP regulates the opening and closing of the "gate" that forms the opening within oligomeric Aip2p/Dld2p, where binding to the substrate occurs while in the open form. In the presence of ATP (open state of oligomeric Aip2p/Dld2p), oligomeric Aip2p/Dld2p bound the F-actin fiber within the opening, whereas in the absence of ATP (closed state of oligomeric Aip2p/Dld2p), no binding was observed. Simultaneously, the oligomeric Aip2p/Dld2p increased the trypsin susceptibility of F-actin in an ATP-dependent manner. Use of the non-hydrolyzable ATP analogue AMP-PNP yielded similar results to those observed with ATP, suggesting that ATP binding rather than ATP hydrolysis is required for the protein conformation modifying reaction of oligomeric Aip2p/Dld2p. Endogenous Aip2p/Dld2p purified from Saccharomyces cerevisiae also exhibited such protein conformation modifying activity, but monomeric Aip2p/Dld2p with a C-terminal coiled-coil region-truncation failed to exhibit the activity. These data suggest that the oligomerization of Aip2p/Dld2p, which exhibits the unique grapple-like structure with an ATP-dependent opening, is required for the F-actin conformation modifying activity.
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Affiliation(s)
- Naomi S Hachiya
- Department of Cortical Function Disorders, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo, Japan
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38
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Hachiya NS, Sakasegawa Y, Jozuka A, Tsukita S, Kaneko K. Interaction of d-lactate dehydrogenase protein 2 (Dld2p) with F-actin: implication for an alternative function of Dld2p. Biochem Biophys Res Commun 2004; 319:78-82. [PMID: 15158445 DOI: 10.1016/j.bbrc.2004.04.146] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2004] [Indexed: 11/22/2022]
Abstract
D-Lactate dehydrogenase protein 2 [Yeast 15 (1999) 1377; Biochem. Biophys. Res. Commun. 295 (2002) 910] was initially identified as the actin interacting protein 2 (Aip2p) using a two-hybrid screen to search for proteins that interact with actin [Nat. Struct. Biol. 2 (1995) 28], but no other evidence indicating an interaction between Aip2p and actin cytoskeleton has been reported so far. During our search for the protein conformation modifying activity, we serendipitously identified Aip2p isolated from Saccharomyces cerevisiae as exhibiting an interaction with F-actin both in vitro and in vivo. Incubation with Aip2p facilitated the formation of the circular form of F-actin in vitro, which exhibited an aberrant trypsin susceptibility. Overexpression of Aip2p induced multi-buds in yeast cells, whereas reduced expression interfered with the formation of the cleavage furrow for the cell division, which was rescued by the introduction of wild-type Aip2p. While Aip2p-treated F-actin in the circular form was negligibly stained by rhodamine-labeled phalloidin (rhodamine-phalloidin) in vitro, rhodamine-phalloidin staining profiles in actin interacting protein 2 gene (AIP2)-modified cells suggested a correlation between the conformation of F-actin and the expression of Aip2p in vivo. AIP2-deleted cells became sensitive to osmotic conditions, a hallmark of actin dysfunction. Finally, immunoprecipitation of yeast cells using anti-Aip2p antibody demonstrated that Aip2p associates with actin. These properties suggest that Aip2p may interact with F-actin in vivo and play an important role in the yeast cell morphology.
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Affiliation(s)
- Naomi S Hachiya
- Department of Cortical Function Disorders, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo, Japan
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39
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Asai T, Takahashi T, Esaki M, Nishikawa SI, Ohtsuka K, Nakai M, Endo T. Reinvestigation of the requirement of cytosolic ATP for mitochondrial protein import. J Biol Chem 2004; 279:19464-70. [PMID: 15001571 DOI: 10.1074/jbc.m401291200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Protein import into mitochondria requires the energy of ATP hydrolysis inside and/or outside mitochondria. Although the role of ATP in the mitochondrial matrix in mitochondrial protein import has been extensively studied, the role of ATP outside mitochondria (external ATP) remains only poorly characterized. Here we developed a protocol for depletion of external ATP without significantly reducing the import competence of precursor proteins synthesized in vitro with reticulocyte lysate. We tested the effects of external ATP on the import of various precursor proteins into isolated yeast mitochondria. We found that external ATP is required for maintenance of the import competence of mitochondrial precursor proteins but that, once they bind to mitochondria, the subsequent translocation of presequence-containing proteins, but not the ADP/ATP carrier, proceeds independently of external ATP. Because depletion of cytosolic Hsp70 led to a decrease in the import competence of mitochondrial precursor proteins, external ATP is likely utilized by cytosolic Hsp70. In contrast, the ADP/ATP carrier requires external ATP for efficient import into mitochondria even after binding to mitochondria, a situation that is only partly attributed to cytosolic Hsp70.
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Affiliation(s)
- Takeyoshi Asai
- Department of Chemistry, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
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40
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Wiedemann N, Kozjak V, Chacinska A, Schönfisch B, Rospert S, Ryan MT, Pfanner N, Meisinger C. Machinery for protein sorting and assembly in the mitochondrial outer membrane. Nature 2003; 424:565-71. [PMID: 12891361 DOI: 10.1038/nature01753] [Citation(s) in RCA: 300] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2003] [Accepted: 05/07/2003] [Indexed: 11/09/2022]
Abstract
Mitochondria contain translocases for the transport of precursor proteins across their outer and inner membranes. It has been assumed that the translocases also mediate the sorting of proteins to their submitochondrial destination. Here we show that the mitochondrial outer membrane contains a separate sorting and assembly machinery (SAM) that operates after the translocase of the outer membrane (TOM). Mas37 forms a constituent of the SAM complex. The central role of the SAM complex in the sorting and assembly pathway of outer membrane proteins explains the various pleiotropic functions that have been ascribed to Mas37 (refs 4, 11-15). These results suggest that the TOM complex, which can transport all kinds of mitochondrial precursor proteins, is not sufficient for the correct integration of outer membrane proteins with a complicated topology, and instead transfers precursor proteins to the SAM complex.
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Affiliation(s)
- Nils Wiedemann
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Str. 7, D-79104 Freiburg, Germany
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41
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Bauer MF, Hofmann S, Neupert W. Import of mitochondrial proteins. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2003; 53:57-90. [PMID: 12512337 DOI: 10.1016/s0074-7742(02)53004-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Matthias F Bauer
- Institute of Clinical Chemistry, Molecular Diagnostics and Mitochondrial Genetics and Diabetes Research Group, Academic Hospital Munich-Schwabing Kölner Platz, D-80804 München, Germany
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42
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Rehling P, Pfanner N, Meisinger C. Insertion of hydrophobic membrane proteins into the inner mitochondrial membrane--a guided tour. J Mol Biol 2003; 326:639-57. [PMID: 12581629 DOI: 10.1016/s0022-2836(02)01440-7] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Only a few mitochondrial proteins are encoded by the organellar genome. The majority of mitochondrial proteins are nuclear encoded and thus have to be transported into the organelle from the cytosol. Within the mitochondrion proteins have to be sorted into one of the four sub-compartments: the outer or inner membranes, the intermembrane space or the matrix. These processes are mediated by complex protein machineries within the different compartments that act alone or in concert with each other. The translocation machinery of the outer membrane is formed by a multi-subunit protein complex (TOM complex), that is built up by signal receptors and the general import pore (GIP). The inner membrane houses two multi-subunit protein complexes that each handles special subsets of mitochondrial proteins on their way to their final destination. According to their primary function these two complexes have been termed the pre-sequence translocase (or TIM23 complex) and the protein insertion complex (or TIM22 complex). The identification of components of these complexes and the analysis of the molecular mechanisms underlying their function are currently an exciting and fast developing field of molecular cell biology.
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Affiliation(s)
- Peter Rehling
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Str. 7, D-79104 Freiburg, Germany.
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43
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Vothknecht UC, Soll J. Chloroplast quest: a journey from the cytosol into the chloroplast and beyond. Rev Physiol Biochem Pharmacol 2002; 145:181-222. [PMID: 12224527 DOI: 10.1007/bfb0116432] [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: 02/26/2023]
Abstract
Chloroplasts are characteristic organelles of plants and algae and the site of oxygenic photosynthesis. They are surrounded by a double membrane and possess an internal membrane system, the thylakoids, on which the photosynthetic machinery is located. They originated more than 1.2 billion years ago from an endosymbiotic event between an already photosynthetic ancestor of present day cyanobacteria and a mitochondriate host cell. During the transformation of the internalized cyanobacterium into a cell organelle most of the genetic information of the endosymbiot got lost or was transferred into the nucleus of the host. Chloroplast proteins encoded by nuclear genes are synthesized on cytoplasmic ribosomes and have to be relocated into the organelle. This is achieved by a proteinaceous import machinery in the outer and inner envelope of the chloroplasts. Proteins destined for the thylakoid membrane and the thylakoid lumen are further translocated by several different pathways into or across this membrane. The subject of this review is the quest of nuclear encoded chloroplast proteins into the organelle and to their final suborganellar location.
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Affiliation(s)
- Ute C Vothknecht
- Botanisches Institut, Ludwig-Maximilian-Universität München, Menzinger Str. 67, D-80638 München, Germany
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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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Beddoe T, Lithgow T. Delivery of nascent polypeptides to the mitochondrial surface. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1592:35-9. [PMID: 12191766 DOI: 10.1016/s0167-4889(02)00262-8] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Thousands of polypeptides with diverse biochemical properties, some of which are extremely hydrophobic, are targeted from cytoplasmic ribosomes to the surface of mitochondria. Localised synthesis, as well as transient interactions with a wide array of molecular chaperones and other cytoplasmic factors, can promote productive interaction of mitochondrial proteins with the TOM complex to initiate protein import into mitochondria.
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Affiliation(s)
- Travis Beddoe
- Russell Grimwade School of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria 3010, Australia
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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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Affiliation(s)
- M T Ryan
- Department of Biochemistry, La Trobe University, 3086 Melbourne, Australia
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48
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Abstract
The vast majority of chloroplast proteins are synthesized in precursor form on cytosolic ribosomes. Chloroplast precursor proteins have cleavable, N-terminal targeting signals called transit peptides. Transit peptides direct precursor proteins to the chloroplast in an organelle-specific way. They can be phosphorylated by a cytosolic protein kinase, and this leads to the formation of a cytosolic guidance complex. The guidance complex--comprising precursor, hsp70 and 14-3-3 proteins, as well as several unidentified components--docks at the outer envelope membrane. Translocation of precursor proteins across the envelope is achieved by the joint action of molecular machines called Toc (translocon at the outer envelope membrane of chloroplasts) and Tic (translocon at the inner envelope membrane of chloroplasts), respectively. The action of the Toc/Tic apparatus requires the hydrolysis of ATP and GTP at different levels, indicating energetic requirements and regulatory properties of the import process. The main subunits of the Toc and Tic complexes have been identified and characterized in vivo, in organello and in vitro. Phylogenetic evidence suggests that several translocon subunits are of cyanobacterial origin, indicating that today's import machinery was built around a prokaryotic core.
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Affiliation(s)
- Paul Jarvis
- Department of Biology, University of Leicester, UK.
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49
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Suzuki H, Maeda M, Mihara K. Characterization of rat TOM70 as a receptor of the preprotein translocase of the mitochondrial outer membrane. J Cell Sci 2002; 115:1895-905. [PMID: 11956321 DOI: 10.1242/jcs.115.9.1895] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We cloned a ∼70 kDa rat mitochondrial outer membrane protein (OM70)with a sequence identity of 28.1% and 20.1% with N. crassa and S. cerevisiae Tom70, respectively. Even with this low sequence identity,however, the proteins share a remarkable structural similarity: they have 7-10 tetratricopeptide repeat motifs and are anchored to the outer membrane through the N-terminal transmembrane domain with the bulk portion located in the cytosol. Antibodies against OM70 inhibited import of preproteins, such as the ADP/ATP carrier and rTOM40, that use internal targeting signals but not the import of cleavable presequence-containing preproteins. Blue native gel electrophoresis and immunoprecipitation of digitoninsolubilized mitochondrial outer membranes revealed that OM70 was loosely associated with the ∼400 kDa translocase complex of the mitochondrial outer membrane, which contains rTOM22 and rTOM40. A yeast two-hybrid system demonstrated that OM70 interacted with rTOM20 and rTOM22 through the cytoplasmic domains. Thus, OM70 is a functional homologue of fungal Tom70 and functions as a receptor of the preprotein import machinery of the rat mitochondrial outer membrane. Furthermore, the N-terminal 66 residue region of OM70, which comprises a hydrophilic 41 residue N-terminal domain, a 22 residue transmembrane domain and three arginine residues, is sufficient to act as a mitochondria-targeting signal, and the arginine cluster is crucial for this function.
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MESH Headings
- Adenosine Triphosphatases/metabolism
- Animals
- Bacterial Proteins
- Cell Compartmentation/physiology
- DNA, Complementary/genetics
- DNA, Complementary/isolation & purification
- Escherichia coli Proteins/metabolism
- Eukaryotic Cells/cytology
- Eukaryotic Cells/enzymology
- Fungal Proteins/antagonists & inhibitors
- Fungal Proteins/genetics
- Fungal Proteins/isolation & purification
- Intracellular Membranes/enzymology
- Intracellular Membranes/ultrastructure
- Macromolecular Substances
- Membrane Proteins/antagonists & inhibitors
- Membrane Proteins/genetics
- Membrane Proteins/isolation & purification
- Membrane Proteins/metabolism
- Membrane Transport Proteins/metabolism
- Mitochondria, Liver/enzymology
- Mitochondria, Liver/ultrastructure
- Mitochondrial Precursor Protein Import Complex Proteins
- Mitochondrial Proteins/genetics
- Mitochondrial Proteins/isolation & purification
- Molecular Sequence Data
- Protein Structure, Tertiary/physiology
- Protein Transport/physiology
- Rats
- Receptors, Cell Surface
- Receptors, Cytoplasmic and Nuclear/genetics
- Receptors, Cytoplasmic and Nuclear/isolation & purification
- SEC Translocation Channels
- SecA Proteins
- Sequence Homology, Amino Acid
- Sequence Homology, Nucleic Acid
- Subcellular Fractions/enzymology
- Subcellular Fractions/ultrastructure
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Affiliation(s)
- Hiroyuki Suzuki
- Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Fukuoka 812-8582, Japan
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50
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Abstract
The vast majority of chloroplast proteins are synthesized in precursor form on cytosolic ribosomes. Chloroplast precursor proteins have cleavable, N-terminal targeting signals called transit peptides. Transit peptides direct precursor proteins to the chloroplast in an organelle-specific way. They can be phosphorylated by a cytosolic protein kinase, and this leads to the formation of a cytosolic guidance complex. The guidance complex--comprising precursor, hsp70 and 14-3-3 proteins, as well as several unidentified components--docks at the outer envelope membrane. Translocation of precursor proteins across the envelope is achieved by the joint action of molecular machines called Toc (translocon at the outer envelope membrane of chloroplasts) and Tic (translocon at the inner envelope membrane of chloroplasts), respectively. The action of the Toc/Tic apparatus requires the hydrolysis of ATP and GTP at different levels, indicating energetic requirements and regulatory properties of the import process. The main subunits of the Toc and Tic complexes have been identified and characterized in vivo, in organello and in vitro. Phylogenetic evidence suggests that several translocon subunits are of cyanobacterial origin, indicating that today's import machinery was built around a prokaryotic core.
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Affiliation(s)
- P Jarvis
- Department of Biology, University of Leicester, UK.
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