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Zegallai HM, Abu-El-Rub E, Cole LK, Field J, Mejia EM, Gordon JW, Marshall AJ, Hatch GM. Tafazzin deficiency impairs mitochondrial metabolism and function of lipopolysaccharide activated B lymphocytes in mice. FASEB J 2021; 35:e22023. [PMID: 34767647 DOI: 10.1096/fj.202100811rr] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2021] [Revised: 10/05/2021] [Accepted: 10/19/2021] [Indexed: 01/21/2023]
Abstract
B lymphocytes are responsible for humoral immunity and play a key role in the immune response. Optimal mitochondrial function is required to support B cell activity during activation. We examined how deficiency of tafazzin, a cardiolipin remodeling enzyme required for mitochondrial function, alters the metabolic activity of B cells and their response to activation by lipopolysaccharide in mice. B cells were isolated from 3-month-old wild type or tafazzin knockdown mice and incubated for up to 72 h with lipopolysaccharide and cell proliferation, expression of cell surface markers, secretion of antibodies and chemokines, proteasome and immunoproteasome activities, and metabolic function determined. In addition, proteomic analysis was performed to identify altered levels of proteins involved in survival, immunogenic, proteasomal and mitochondrial processes. Compared to wild type lipopolysaccharide activated B cells, lipopolysaccharide activated tafazzin knockdown B cells exhibited significantly reduced proliferation, lowered expression of cluster of differentiation 86 and cluster of differentiation 69 surface markers, reduced secretion of immunoglobulin M antibody, reduced secretion of keratinocytes-derived chemokine and macrophage-inflammatory protein-2, reduced proteasome and immunoproteasome activities, and reduced mitochondrial respiration and glycolysis. Proteomic analysis revealed significant alterations in key protein targets that regulate cell survival, immunogenicity, proteasomal processing and mitochondrial function consistent with the findings of the above functional studies. The results indicate that the cardiolipin transacylase enzyme tafazzin plays a key role in regulating mouse B cell function and metabolic activity during activation through modulation of mitochondrial function.
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Affiliation(s)
- Hana M Zegallai
- Diabetes Research Envisioned and Accomplished in Manitoba (DREAM) Theme, Children's Hospital Research Institute of Manitoba, Winnipeg, Manitoba, Canada.,Department of Pharmacology & Therapeutics, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Ejlal Abu-El-Rub
- Department of Physiology and Pathophysiology, Yarmouk University, Irbid, Jordan.,Department of Basic Medical Sciences, Faculty of Medicine, Yarmouk University, Irbid, Jordan.,Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, Manitoba, Canada.,Department of Regenerative Medicine, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Laura K Cole
- Diabetes Research Envisioned and Accomplished in Manitoba (DREAM) Theme, Children's Hospital Research Institute of Manitoba, Winnipeg, Manitoba, Canada.,Department of Pharmacology & Therapeutics, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Jared Field
- Diabetes Research Envisioned and Accomplished in Manitoba (DREAM) Theme, Children's Hospital Research Institute of Manitoba, Winnipeg, Manitoba, Canada.,Department of Human Anatomy and Cell Science, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Edgard M Mejia
- Department of Immunology, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Joseph W Gordon
- Diabetes Research Envisioned and Accomplished in Manitoba (DREAM) Theme, Children's Hospital Research Institute of Manitoba, Winnipeg, Manitoba, Canada.,Department of Human Anatomy and Cell Science, University of Manitoba, Winnipeg, Manitoba, Canada.,College of Nursing, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Aaron J Marshall
- Department of Immunology, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Grant M Hatch
- Diabetes Research Envisioned and Accomplished in Manitoba (DREAM) Theme, Children's Hospital Research Institute of Manitoba, Winnipeg, Manitoba, Canada.,Department of Pharmacology & Therapeutics, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
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2
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Tamadaddi C, Sagar V, Verma AK, Afsal F, Sahi C. Expansion of the evolutionarily conserved network of J-domain proteins in the Arabidopsis mitochondrial import complex. PLANT MOLECULAR BIOLOGY 2021; 105:385-403. [PMID: 33206359 DOI: 10.1007/s11103-020-01095-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2020] [Accepted: 11/07/2020] [Indexed: 06/11/2023]
Abstract
We report that discriminate interaction between the expanded mitochondrial chaperone network and variability in their expression might determine their functional specificities and impart robustness to mitochondrial import processes in plants. Mitochondrial Hsp70 (mtHsp70), the central component of the pre-sequence associated motor (PAM) complex, is crucial for the import of proteins to the mitochondrial matrix. Activity of mtHsp70 is regulated by a heterodimeric complex of two J-domain proteins (JDPs), Pam18 and Pam16. Compared to other eukaryotes, plants harbor multiple copies of these JDPs, which posit that plants have an increasingly complex mtHsp70: JDP network in their mitochondrial matrix. Here, we show that although highly similar in sequence, some of the plant JDPs are functionally different. Protein: protein interaction studies including yeast two-hybrid and Bimolecular Fluorescence Complementation revealed that while all the AtPam18s interacted with AtPam16s, the strengths of these promiscuous interactions are variable. Further, down-regulation of AtPAM16L affected seed germination, even in the presence of its seemingly identical paralog, AtPAM16. Knockdown of AtPAM16L caused reduction in mitochondrial number and deregulation of several mitochondrial genes, suggesting towards a specific role of AtPam16L in maintaining mitochondrial homeostasis, especially under stress conditions. Our findings suggest that variations in the spatio-temporal expression, accompanied by discriminate interactions between the JDPs, might be defining the functional specificity of the mtHsp70 co-chaperone machinery and providing resilience to mitochondrial import processes in plants, especially under stress conditions.
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Affiliation(s)
- Chetana Tamadaddi
- Department of Biological Sciences, Indian Institute of Science Education and Research Bhopal, Room Number 117 AB3, IISER Bhopal, Bhopal Bypass Road, Bhopal, MP, 462066, India
| | - Vinay Sagar
- Department of Biological Sciences, Indian Institute of Science Education and Research Bhopal, Room Number 117 AB3, IISER Bhopal, Bhopal Bypass Road, Bhopal, MP, 462066, India
- National Center for Biological Sciences, Rajiv Gandhi Nagar, Kodigehalli, Bengaluru, Karnataka, India
| | - Amit K Verma
- Department of Biological Sciences, Indian Institute of Science Education and Research Bhopal, Room Number 117 AB3, IISER Bhopal, Bhopal Bypass Road, Bhopal, MP, 462066, India
- Department of Biochemistry, University of Wisconsin-Madison, Madison, USA
| | - Fathima Afsal
- Department of Biological Sciences, Indian Institute of Science Education and Research Bhopal, Room Number 117 AB3, IISER Bhopal, Bhopal Bypass Road, Bhopal, MP, 462066, India
| | - Chandan Sahi
- Department of Biological Sciences, Indian Institute of Science Education and Research Bhopal, Room Number 117 AB3, IISER Bhopal, Bhopal Bypass Road, Bhopal, MP, 462066, India.
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Schulz C, Schendzielorz A, Rehling P. Unlocking the presequence import pathway. Trends Cell Biol 2015; 25:265-75. [DOI: 10.1016/j.tcb.2014.12.001] [Citation(s) in RCA: 103] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2014] [Revised: 11/26/2014] [Accepted: 12/01/2014] [Indexed: 10/24/2022]
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Duncan EJ, Cheetham ME, Chapple JP, van der Spuy J. The role of HSP70 and its co-chaperones in protein misfolding, aggregation and disease. Subcell Biochem 2015; 78:243-73. [PMID: 25487025 DOI: 10.1007/978-3-319-11731-7_12] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Molecular chaperones and their associated co-chaperones are essential in health and disease as they are key facilitators of protein folding, quality control and function. In particular, the HSP70 molecular chaperone networks have been associated with neurodegenerative diseases caused by aberrant protein folding. The pathogenesis of these disorders usually includes the formation of deposits of misfolded, aggregated protein. HSP70 and its co-chaperones have been recognised as potent modulators of inclusion formation and cell survival in cellular and animal models of neurodegenerative disease. In has become evident that the HSP70 chaperone machine functions not only in folding, but also in proteasome mediated degradation of neurodegenerative disease proteins. Thus, there has been a great deal of interest in the potential manipulation of molecular chaperones as a therapeutic approach for many neurodegenerations. Furthermore, mutations in several HSP70 co-chaperones and putative co-chaperones have been identified as causing inherited neurodegenerative and cardiac disorders, directly linking the HSP70 chaperone system to human disease.
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Affiliation(s)
- Emma J Duncan
- Molecular Endocrinology Centre, William Harvey Research Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, Charter House Square, EC1M 6BQ, London, UK,
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Regev-Rudzki N, Gabriel K, Bursać D. The evolution and function of co-chaperones in mitochondria. Subcell Biochem 2015; 78:201-217. [PMID: 25487023 DOI: 10.1007/978-3-319-11731-7_10] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Mitochondrial chaperones mediate and affect critical organellar processes, essential for cellular function. These chaperone systems have both prokaryotic and eukaryotic features. While some of the mitochondrial co-chaperones have clear homologues in prokaryotes, some are unique to eukaryotes and have no homologues in the chaperone machinery of other cellular compartments. The mitochondrial co-chaperones are required for protein import into the organelle and in enforcing the structure of the main chaperones. In addition to novel types of interaction with their senior partners, unexpected and essential interactions between the co-chaperones themselves have recently been described.
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Affiliation(s)
- Neta Regev-Rudzki
- Department of Biological Chemistry, The Weizmann Institute of Science, Rehovolt, Israel,
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Nisemblat S, Parnas A, Yaniv O, Azem A, Frolow F. Crystallization and structure determination of a symmetrical 'football' complex of the mammalian mitochondrial Hsp60-Hsp10 chaperonins. Acta Crystallogr F Struct Biol Commun 2014; 70:116-9. [PMID: 24419632 PMCID: PMC3943094 DOI: 10.1107/s2053230x1303389x] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2013] [Accepted: 12/15/2013] [Indexed: 11/10/2022] Open
Abstract
The mitochondrial Hsp60-Hsp10 complex assists the folding of various proteins impelled by ATP hydrolysis, similar to the bacterial chaperonins GroEL and GroES. The near-atomic structural details of the mitochondrial chaperonins are not known, despite the fact that almost two decades have passed since the structures of the bacterial chaperonins became available. Here, the crystallization procedure, diffraction experiments and structure determination by molecular replacement of the mammalian mitochondrial chaperonin HSP60 (E321K mutant) and its co-chaperonin Hsp10 are reported.
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Affiliation(s)
- Shahar Nisemblat
- Department of Biochemistry and Molecular Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
- The Daniella Rich Institute for Structural Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
| | - Avital Parnas
- Department of Biochemistry and Molecular Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
- The Daniella Rich Institute for Structural Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
| | - Oren Yaniv
- The Daniella Rich Institute for Structural Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
- Department of Molecular Microbiology and Biotechnology, George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
| | - Abdussalam Azem
- Department of Biochemistry and Molecular Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
- The Daniella Rich Institute for Structural Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
| | - Felix Frolow
- The Daniella Rich Institute for Structural Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
- Department of Molecular Microbiology and Biotechnology, George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
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Marom M, Azem A, Mokranjac D. Understanding the molecular mechanism of protein translocation across the mitochondrial inner membrane: still a long way to go. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1808:990-1001. [PMID: 20646995 DOI: 10.1016/j.bbamem.2010.07.011] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2010] [Revised: 07/08/2010] [Accepted: 07/10/2010] [Indexed: 11/18/2022]
Abstract
In order to reach the final place of their function, approximately half of the proteins in any eukaryotic cell have to be transported across or into one of the membranes in the cell. In this article, we present an overview of our current knowledge concerning the structural properties of the TIM23 complex and their relationship with the molecular mechanism of protein transport across the mitochondrial inner membrane. This article is part of a Special Issue entitled Protein translocation across or insertion into membranes.
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Affiliation(s)
- Milit Marom
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel
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Sinha D, Joshi N, Chittoor B, Samji P, D'Silva P. Role of Magmas in protein transport and human mitochondria biogenesis. Hum Mol Genet 2010; 19:1248-62. [PMID: 20053669 PMCID: PMC2838536 DOI: 10.1093/hmg/ddq002] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
Magmas, a conserved mammalian protein essential for eukaryotic development, is overexpressed in prostate carcinomas and cells exposed to granulocyte-macrophage colony-stimulating factor (GM-CSF). Reduced Magmas expression resulted in decreased proliferative rates in cultured cells. However, the cellular function of Magmas is still elusive. In this report, we have showed that human Magmas is an ortholog of Saccharomyces cerevisiae Pam16 having similar functions and is critical for protein translocation across mitochondrial inner membrane. Human Magmas shows a complete growth complementation of Δpam16 yeast cells at all temperatures. On the basis of our analysis, we report that Magmas localizes into mitochondria and is peripherally associated with inner mitochondrial membrane in yeast and humans. Magmas forms a stable subcomplex with J-protein Pam18 or DnaJC19 through its C-terminal region and is tethered to TIM23 complex of yeast and humans. Importantly, amino acid alterations in Magmas leads to reduced stability of the subcomplex with Pam18 that results in temperature sensitivity and in vivo protein translocation defects in yeast cells. These observations highlight the central role of Magmas in protein import and mitochondria biogenesis. In humans, absence of a functional DnaJC19 leads to dilated cardiac myophathic syndrome (DCM), a genetic disorder with characteristic features of cardiac myophathy and neurodegeneration. We propose that the mutations resulting in decreased stability of functional Magmas:DnaJC19 subcomplex at human TIM23 channel leads to impaired protein import and cellular respiration in DCM patients. Together, we propose a model showing how Magmas:DnaJC19 subcomplex is associated with TIM23 complex and thus regulates mitochondrial import process.
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Affiliation(s)
- Devanjan Sinha
- Department of Biochemistry, Indian Institute of Science, Bangalore, Karnataka, India
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9
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Parnas A, Nadler M, Nisemblat S, Horovitz A, Mandel H, Azem A. The MitCHAP-60 disease is due to entropic destabilization of the human mitochondrial Hsp60 oligomer. J Biol Chem 2009; 284:28198-28203. [PMID: 19706612 DOI: 10.1074/jbc.m109.031997] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The 60-kDa heat shock protein (mHsp60) is a vital cellular complex that mediates the folding of many of the mitochondrial proteins. Its function is executed in cooperation with the co-chaperonin, mHsp10, and requires ATP. Recently, the discovery of a new mHsp60-associated neurodegenerative disorder, MitCHAP-60 disease, has been reported. The disease is caused by a point mutation at position 3 (D3G) of the mature mitochondrial Hsp60 protein, which renders it unable to complement the deletion of the homologous bacterial protein in Escherichia coli (Magen, D., Georgopoulos, C., Bross, P., Ang, D., Segev, Y., Goldsher, D., Nemirovski, A., Shahar, E., Ravid, S., Luder, A., Heno, B., Gershoni-Baruch, R., Skorecki, K., and Mandel, H. (2008) Am. J. Hum. Genet. 83, 30-42). The molecular basis of the MitCHAP-60 disease is still unknown. In this study, we present an in vitro structural and functional analysis of the purified wild-type human mHsp60 and the MitCHAP-60 mutant. We show that the D3G mutation leads to destabilization of the mHsp60 oligomer and causes its disassembly at low protein concentrations. We also show that the mutant protein has impaired protein folding and ATPase activities. An additional mutant that lacks the first three amino acids (N-del), including Asp-3, is similarly impaired in refolding activity. Surprisingly, however, this mutant exhibits profound stabilization of its oligomeric structure. These results suggest that the D3G mutation leads to entropic destabilization of the mHsp60 oligomer, which severely impairs its chaperone function, thereby causing the disease.
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Affiliation(s)
- Avital Parnas
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, 69778 Tel Aviv
| | - Michal Nadler
- Department of Structural Biology, Weizmann Institute of Science, Rehovot 76100
| | - Shahar Nisemblat
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, 69778 Tel Aviv
| | - Amnon Horovitz
- Department of Structural Biology, Weizmann Institute of Science, Rehovot 76100.
| | - Hanna Mandel
- Rappaport Faculty of Medicine and Research Institute, Technion-Israel Institute of Technology and Metabolic Disease Unit, Rambam Health Care Campus, Haifa 31096, Israel
| | - Abdussalam Azem
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, 69778 Tel Aviv.
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Tamura Y, Endo T, Iijima M, Sesaki H. Ups1p and Ups2p antagonistically regulate cardiolipin metabolism in mitochondria. ACTA ACUST UNITED AC 2009; 185:1029-45. [PMID: 19506038 PMCID: PMC2711612 DOI: 10.1083/jcb.200812018] [Citation(s) in RCA: 131] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cardiolipin, a unique phospholipid composed of four fatty acid chains, is located mainly in the mitochondrial inner membrane (IM). Cardiolipin is required for the integrity of several protein complexes in the IM, including the TIM23 translocase, a dynamic complex which mediates protein import into the mitochondria through interactions with the import motor presequence translocase–associated motor (PAM). In this study, we report that two homologous intermembrane space proteins, Ups1p and Ups2p, control cardiolipin metabolism and affect the assembly state of TIM23 and its association with PAM in an opposing manner. In ups1Δ mitochondria, cardiolipin levels were decreased, and the TIM23 translocase showed altered conformation and decreased association with PAM, leading to defects in mitochondrial protein import. Strikingly, loss of Ups2p restored normal cardiolipin levels and rescued TIM23 defects in ups1Δ mitochondria. Furthermore, we observed synthetic growth defects in ups mutants in combination with loss of Pam17p, which controls the integrity of PAM. Our findings provide a novel molecular mechanism for the regulation of cardiolipin metabolism.
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Affiliation(s)
- Yasushi Tamura
- Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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Elsner S, Simian D, Iosefson O, Marom M, Azem A. The mitochondrial protein translocation motor: structural conservation between the human and yeast Tim14/Pam18-Tim16/Pam16 co-chaperones. Int J Mol Sci 2009; 10:2041-2053. [PMID: 19564938 PMCID: PMC2695266 DOI: 10.3390/ijms10052041] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2009] [Revised: 04/11/2009] [Accepted: 04/14/2009] [Indexed: 01/23/2023] Open
Abstract
Most of our knowledge regarding the process of protein import into mitochondria has come from research employing Saccharomyces cerevisiae as a model system. Recently, several mammalian homologues of the mitochondrial motor proteins were identified. Of particular interest for us is the human Tim14/Pam18-Tim16/Pam16 complex. We chose a structural approach in order to examine the evolutionary conservation between yeast Tim14/Pam18-Tim16/Pam16 proteins and their human homologues. For this purpose, we examined the structural properties of the purified human proteins and their interaction with their yeast homologues, in vitro. Our results show that the soluble domains of the human Tim14/Pam18 and Tim16/Pam16 proteins interact with their yeast counterparts, forming heterodimeric complexes and that these complexes interact with yeast mtHsp70.
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Affiliation(s)
| | | | | | | | - Abdussalam Azem
- Author to whom correspondence should be addressed; E-mail:
(A.A.); Tel. + 972 3 6409007; Fax: + 972 3 6406834
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Slutsky-Leiderman O, Marom M, Iosefson O, Levy R, Maoz S, Azem A. The interplay between components of the mitochondrial protein translocation motor studied using purified components. J Biol Chem 2007; 282:33935-42. [PMID: 17881357 DOI: 10.1074/jbc.m704435200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The final step of protein translocation across the mitochondrial inner membrane is mediated by a translocation motor composed of 1) the matrix-localized, ATP-hydrolyzing, 70-kDa heat shock protein mHsp70; 2) its anchor to the import channel, Tim44; 3) the nucleotide exchange factor Mge1; and 4) a J-domain-containing complex of co-chaperones, Tim14/Pam18-Tim16/Pam16. Despite its essential role in the biogenesis of mitochondria, the mechanism by which the translocation motor functions is still largely unknown. The goal of this work was to carry out a structure-function analysis of the mitochondrial translocation motor utilizing purified components, with an emphasis on the formation of the Tim44-mHsp70 complex. To this end, we purified Tim44 and monitored its interaction with other components of the motor using cross-linking with bifunctional reagents. The effects of nucleotides, the J-domain-containing components, and the P5 peptide (CALLSAPRR, representing part of the mitochondrial targeting signal of aspartate aminotransferase) on the formation of the translocation motor were examined. Our results show that only the peptide and nucleotides, but not J-domain-containing proteins, affect the Tim44-mHsp70 interaction. Additionally, binding of Tim44 to mHsp70 prevents the formation of a complex between the latter and Tim14/Pam18-Tim16/Pam16. Thus, mutually exclusive interactions between various components of the motor with mHsp70 regulate its functional cycle. The results are discussed in light of known models for the function of the mitochondrial translocation motor.
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Affiliation(s)
- Olga Slutsky-Leiderman
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69778, Israel
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