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Davletshin AI, Matveeva AA, Poletaeva II, Evgen'ev MB, Garbuz DG. The role of molecular chaperones in the mechanisms of epileptogenesis. Cell Stress Chaperones 2023; 28:599-619. [PMID: 37755620 PMCID: PMC10746656 DOI: 10.1007/s12192-023-01378-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2023] [Revised: 08/30/2023] [Accepted: 09/08/2023] [Indexed: 09/28/2023] Open
Abstract
Epilepsy is a group of neurological diseases which requires significant economic costs for the treatment and care of patients. The central point of epileptogenesis stems from the failure of synaptic signal transmission mechanisms, leading to excessive synchronous excitation of neurons and characteristic epileptic electroencephalogram activity, in typical cases being manifested as seizures and loss of consciousness. The causes of epilepsy are extremely diverse, which is one of the reasons for the complexity of selecting a treatment regimen for each individual case and the high frequency of pharmacoresistant cases. Therefore, the search for new drugs and methods of epilepsy treatment requires an advanced study of the molecular mechanisms of epileptogenesis. In this regard, the investigation of molecular chaperones as potential mediators of epileptogenesis seems promising because the chaperones are involved in the processing and regulation of the activity of many key proteins directly responsible for the generation of abnormal neuronal excitation in epilepsy. In this review, we try to systematize current data on the role of molecular chaperones in epileptogenesis and discuss the prospects for the use of chemical modulators of various chaperone groups' activity as promising antiepileptic drugs.
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Affiliation(s)
| | - Anna A Matveeva
- Engelhardt Institute of Molecular Biology RAS, 119991, Moscow, Russia
- Moscow Institute of Physics and Technology, 141700, Dolgoprudny, Moscow Region, Russia
| | - Inga I Poletaeva
- Biology Department, Lomonosov Moscow State University, 119991, Moscow, Russia
| | | | - David G Garbuz
- Engelhardt Institute of Molecular Biology RAS, 119991, Moscow, Russia
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2
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Sučec I, Bersch B, Schanda P. How do Chaperones Bind (Partly) Unfolded Client Proteins? Front Mol Biosci 2021; 8:762005. [PMID: 34760928 PMCID: PMC8573040 DOI: 10.3389/fmolb.2021.762005] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2021] [Accepted: 10/06/2021] [Indexed: 01/03/2023] Open
Abstract
Molecular chaperones are central to cellular protein homeostasis. Dynamic disorder is a key feature of the complexes of molecular chaperones and their client proteins, and it facilitates the client release towards a folded state or the handover to downstream components. The dynamic nature also implies that a given chaperone can interact with many different client proteins, based on physico-chemical sequence properties rather than on structural complementarity of their (folded) 3D structure. Yet, the balance between this promiscuity and some degree of client specificity is poorly understood. Here, we review recent atomic-level descriptions of chaperones with client proteins, including chaperones in complex with intrinsically disordered proteins, with membrane-protein precursors, or partially folded client proteins. We focus hereby on chaperone-client interactions that are independent of ATP. The picture emerging from these studies highlights the importance of dynamics in these complexes, whereby several interaction types, not only hydrophobic ones, contribute to the complex formation. We discuss these features of chaperone-client complexes and possible factors that may contribute to this balance of promiscuity and specificity.
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Affiliation(s)
- Iva Sučec
- CEA, CNRS, Institut de Biologie Structurale (IBS), Univ. Grenoble Alpes, Grenoble, France
| | - Beate Bersch
- CEA, CNRS, Institut de Biologie Structurale (IBS), Univ. Grenoble Alpes, Grenoble, France
| | - Paul Schanda
- CEA, CNRS, Institut de Biologie Structurale (IBS), Univ. Grenoble Alpes, Grenoble, France.,Institute of Science and Technology Austria, Klosterneuburg, Austria
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3
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Abstract
Efficient movement of proteins across membranes is required for cell health. The translocation process is particularly challenging when the channel in the membrane through which proteins must pass is narrow—such as those in the membranes of the endoplasmic reticulum and mitochondria. Hsp70 molecular chaperones play roles on both sides of these membranes, ensuring efficient translocation of proteins synthesized on cytosolic ribosomes into the interior of these organelles. The “import motor” in the mitochondrial matrix, which is essential for driving the movement of proteins across the mitochondrial inner membrane, is arguably the most complex Hsp70-based system in the cell.
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Affiliation(s)
- Elizabeth A Craig
- Department of Biochemistry, University of Wisconsin - Madison, 433 Babcock Drive, Madison, WI, 53706, USA.
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4
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Afolayan AJ, Alexander M, Holme RL, Michalkiewicz T, Rana U, Teng RJ, Zemanovic S, Sahoo D, Pritchard KA, Konduri GG. Domain Mapping of Heat Shock Protein 70 Reveals That Glutamic Acid 446 and Arginine 447 Are Critical for Regulating Superoxide Dismutase 2 Function. J Biol Chem 2016; 292:2369-2378. [PMID: 28028182 DOI: 10.1074/jbc.m116.756122] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2016] [Revised: 12/19/2016] [Indexed: 12/15/2022] Open
Abstract
Stress-inducible heat shock protein 70 (hsp70) interacts with superoxide dismutase 2 (SOD2) in the cytosol after synthesis to transfer the enzyme to the mitochondria for subsequent activation. However, the structural basis for this interaction remains to be defined. To map the SOD2-binding site in hsp70, mutants of hsp70 were made and tested for their ability to bind SOD2. These studies showed that SOD2 binds in the amino acid 393-537 region of the chaperone. To map the hsp70-binding site in SOD2, we used a series of pulldown assays and showed that hsp70 binds to the amino-terminal domain of SOD2. To better define the binding site, we used a series of decoy peptides derived from the primary amino acid sequence in the SOD2-binding site in hsp70. This study shows that SOD2 specifically binds to hsp70 at 445GERAMT450 Small peptides containing GERAMT inhibited the transfer of SOD2 to the mitochondria and decreased SOD2 activity in vitro and in vivo To determine the amino acid residues in hsp70 that are critical for SOD2 interactions, we substituted each amino acid residue for alanine or more conservative residues, glutamine or asparagine, in the GERAMT-binding site. Substitutions of E446A/Q and R447A/Q inhibited the ability of the GERAMT peptide to bind SOD2 and preserved SOD2 function more than other substitutions. Together, these findings indicate that the GERAMT sequence is critical for hsp70-mediated regulation of SOD2 and that Glu446 and Arg447 cooperate with other amino acid residues in the GERAMT-binding site for proper chaperone-dependent regulation of SOD2 antioxidant function.
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Affiliation(s)
- Adeleye J Afolayan
- From the Department of Pediatrics, Cardiovascular Research Center, .,Children's Research Institute
| | - Maxwell Alexander
- From the Department of Pediatrics, Cardiovascular Research Center.,Children's Research Institute
| | - Rebecca L Holme
- Children's Research Institute.,Department of Medicine, Medical College of Wisconsin, Milwaukee, Wisconsin 53226
| | - Teresa Michalkiewicz
- From the Department of Pediatrics, Cardiovascular Research Center.,Children's Research Institute
| | - Ujala Rana
- From the Department of Pediatrics, Cardiovascular Research Center.,Children's Research Institute
| | - Ru-Jeng Teng
- From the Department of Pediatrics, Cardiovascular Research Center.,Children's Research Institute
| | - Sara Zemanovic
- From the Department of Pediatrics, Cardiovascular Research Center.,Children's Research Institute
| | - Daisy Sahoo
- Children's Research Institute.,Department of Medicine, Medical College of Wisconsin, Milwaukee, Wisconsin 53226
| | - Kirkwood A Pritchard
- Children's Research Institute.,Department of Surgery, Division of Pediatric Surgery, and
| | - Girija G Konduri
- From the Department of Pediatrics, Cardiovascular Research Center.,Children's Research Institute
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5
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DsbA-DsbAmut fusion chaperon improved soluble expression of human trypsinogen-1 in Escherichia coli. Front Chem Sci Eng 2015. [DOI: 10.1007/s11705-015-1519-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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6
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Samaddar M, Goswami AV, Purushotham J, Hegde P, D'Silva P. Role of the loop L4,5 in allosteric regulation in mtHsp70s: in vivo significance of domain communication and its implications in protein translocation. Mol Biol Cell 2014; 25:2129-42. [PMID: 24829379 PMCID: PMC4091826 DOI: 10.1091/mbc.e14-03-0821] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The SBD loop L4,5 in mtHsp70s functions synergistically with the linker region to maintain the interdomain interface governing protein translocation and mitochondrial biogenesis. Intragenic suppressors of a communication-impaired L4,5 mutant reveal molecular insights into the allosteric regulation of mtHsp70s at the in vivo level. Mitochondrial Hsp70 (mtHsp70) is essential for a vast repertoire of functions, including protein import, and requires effective interdomain communication for efficient partner-protein interactions. However, the in vivo functional significance of allosteric regulation in eukaryotes is poorly defined. Using integrated biochemical and yeast genetic approaches, we provide compelling evidence that a conserved substrate-binding domain (SBD) loop, L4,5, plays a critical role in allosteric communication governing mtHsp70 chaperone functions across species. In yeast, a temperature-sensitive L4,5 mutation (E467A) disrupts bidirectional domain communication, leading to compromised protein import and mitochondrial function. Loop L4,5 functions synergistically with the linker in modulating the allosteric interface and conformational transitions between SBD and the nucleotide-binding domain (NBD), thus regulating interdomain communication. Second-site intragenic suppressors of E467A isolated within the SBD suppress domain communication defects by conformationally altering the allosteric interface, thereby restoring import and growth phenotypes. Strikingly, the suppressor mutations highlight that restoration of communication from NBD to SBD alone is the minimum essential requirement for effective in vivo function when primed at higher basal ATPase activity, mimicking the J-protein–bound state. Together these findings provide the first mechanistic insights into critical regions within the SBD of mtHsp70s regulating interdomain communication, thus highlighting its importance in protein translocation and mitochondrial biogenesis.
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Affiliation(s)
- Madhuja Samaddar
- Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India
| | | | - Jaya Purushotham
- Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India
| | - Pushpa Hegde
- Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India
| | - Patrick D'Silva
- Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India
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7
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Abstract
The secretory pathway is responsible for the synthesis, folding, and delivery of a diverse array of cellular proteins. Secretory protein synthesis begins in the endoplasmic reticulum (ER), which is charged with the tasks of correctly integrating nascent proteins and ensuring correct post-translational modification and folding. Once ready for forward traffic, proteins are captured into ER-derived transport vesicles that form through the action of the COPII coat. COPII-coated vesicles are delivered to the early Golgi via distinct tethering and fusion machineries. Escaped ER residents and other cycling transport machinery components are returned to the ER via COPI-coated vesicles, which undergo similar tethering and fusion reactions. Ultimately, organelle structure, function, and cell homeostasis are maintained by modulating protein and lipid flux through the early secretory pathway. In the last decade, structural and mechanistic studies have added greatly to the strong foundation of yeast genetics on which this field was built. Here we discuss the key players that mediate secretory protein biogenesis and trafficking, highlighting recent advances that have deepened our understanding of the complexity of this conserved and essential process.
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8
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Abstract
Proteins need to be unfolded when translocated through the pores in mitochondrial and other cellular membranes. Knotted proteins, however, might get stuck during this process since the diameter of the pore is smaller than the size of maximally tightened knot. In the present article, I briefly review the experimental and numerical studies of tight knots in proteins, with a particular emphasis on the estimates of the size of these knots. Next, I discuss the process of protein translocation through the mitochondrial pores and report the results of molecular dynamics simulations of knotted protein translocation, which show how the knot can indeed block the pore.
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9
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Goswami AV, Chittoor B, D'Silva P. Understanding the functional interplay between mammalian mitochondrial Hsp70 chaperone machine components. J Biol Chem 2010; 285:19472-82. [PMID: 20392697 PMCID: PMC2885226 DOI: 10.1074/jbc.m110.105957] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mitochondria biogenesis requires the import of several precursor proteins that are synthesized in the cytosol. The mitochondrial heat shock protein 70 (mtHsp70) machinery components are highly conserved among eukaryotes, including humans. However, the functional properties of human mtHsp70 machinery components have not been characterized among all eukaryotic families. To study the functional interactions, we have reconstituted the components of the mtHsp70 chaperone machine (Hsp70/J-protein/GrpE/Hep) and systematically analyzed in vitro conditions for biochemical functions. We observed that the sequence-specific interaction of human mtHsp70 toward mitochondrial client proteins differs significantly from its yeast counterpart Ssc1. Interestingly, the helical lid of human mtHsp70 was found dispensable to the binding of P5 peptide as compared with the other Hsp70s. We observed that the two human mitochondrial matrix J-protein splice variants differentially regulate the mtHsp70 chaperone cycle. Strikingly, our results demonstrated that human Hsp70 escort protein (Hep) possesses a unique ability to stimulate the ATPase activity of mtHsp70 as well as to prevent the aggregation of unfolded client proteins similar to J-proteins. We observed that Hep binds with the C terminus of mtHsp70 in a full-length context and this interaction is distinctly different from unfolded client-specific or J-protein binding. In addition, we found that the interaction of Hep at the C terminus of mtHsp70 is regulated by the helical lid region. However, the interaction of Hep at the ATPase domain of the human mtHsp70 is mutually exclusive with J-proteins, thus promoting a similar conformational change that leads to ATPase stimulation. Additionally, we highlight the biochemical defects of the mtHsp70 mutant (G489E) associated with a myelodysplastic syndrome.
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Affiliation(s)
- Arvind Vittal Goswami
- Department of Biochemistry, Indian Institute of Science, Bangalore 560012, Karnataka, India
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10
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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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11
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Hoffmann F, Maser E. Carbonyl Reductases and Pluripotent Hydroxysteroid Dehydrogenases of the Short-chain Dehydrogenase/reductase Superfamily. Drug Metab Rev 2008; 39:87-144. [PMID: 17364882 DOI: 10.1080/03602530600969440] [Citation(s) in RCA: 147] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Carbonyl reduction of aldehydes, ketones, and quinones to their corresponding hydroxy derivatives plays an important role in the phase I metabolism of many endogenous (biogenic aldehydes, steroids, prostaglandins, reactive lipid peroxidation products) and xenobiotic (pharmacologic drugs, carcinogens, toxicants) compounds. Carbonyl-reducing enzymes are grouped into two large protein superfamilies: the aldo-keto reductases (AKR) and the short-chain dehydrogenases/reductases (SDR). Whereas aldehyde reductase and aldose reductase are AKRs, several forms of carbonyl reductase belong to the SDRs. In addition, there exist a variety of pluripotent hydroxysteroid dehydrogenases (HSDs) of both superfamilies that specifically catalyze the oxidoreduction at different positions of the steroid nucleus and also catalyze, rather nonspecifically, the reductive metabolism of a great number of nonsteroidal carbonyl compounds. The present review summarizes recent findings on carbonyl reductases and pluripotent HSDs of the SDR protein superfamily.
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Affiliation(s)
- Frank Hoffmann
- Institute of Toxicology and Pharmacology for Natural Scientists, University Medical School Schleswig-Holstein, Campus Kiel, Brunswiker Strasse, Kiel, 10, 24105, Germany
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12
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Lu HM, Liang J. A model study of protein nascent chain and cotranslational folding using hydrophobic-polar residues. Proteins 2008; 70:442-9. [PMID: 17680696 DOI: 10.1002/prot.21575] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
To study protein nascent chain folding during biosynthesis, we investigate the folding behavior of models of hydrophobic and polar (HP) chains at growing length using both two-dimensional square lattice model and an optimized three-dimensional 4-state discrete off-lattice model. After enumerating all possible sequences and conformations of HP heteropolymers up to length N = 18 and N = 15 in two and three-dimensional space, respectively, we examine changes in adopted structure, stability, and tolerance to single point mutation as the nascent chain grows. In both models, we find that stable model proteins have fewer folded nascent chains during growth, and often will only fold after reaching full length. For the few occasions where partial chains of stable proteins fold, these partial conformations on average are very similar to the corresponding parts of the final conformations at full length. Conversely, we find that sequences with fewer stable nascent chains and sequences with native-like folded nascent chains are more stable. In addition, these stable sequences in general can have many more point mutations and still fold into the same conformation as the wild type sequence. Our results suggest that stable proteins are less likely to be trapped in metastable conformations during biosynthesis, and are more resistant to point-mutations. Our results also imply that less stable proteins will require the assistance of chaperone and other factors during nascent chain folding. Taken together with other reported studies, it seems that cotranslational folding may not be a general mechanism of in vivo protein folding for small proteins, and in vitro folding studies are still relevant for understanding how proteins fold biologically.
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Affiliation(s)
- Hsiao-Mei Lu
- Department of Bioengineering, MC-063 University of Illinois at Chicago, Chicago, Illinois 60607, USA
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13
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Amemiya H, Matsuzaka K, Kokubu E, Ohta S, Inoue T. Cellular responses of rat periodontal ligament cells under hypoxia and re-oxygenation conditions in vitro. J Periodontal Res 2007; 43:322-7. [PMID: 18086167 DOI: 10.1111/j.1600-0765.2007.01032.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
BACKGROUND AND OBJECTIVE The aim of this study was to investigate the responses of periodontal ligament cells under hypoxia and re-oxygenation conditions in vitro. MATERIAL AND METHODS Periodontal ligament fibroblasts were isolated from rat incisors. In the hypoxia group, cells were incubated in 2% O(2) for 1-3 d. In the re-oxygenation group, cells were first incubated under the same conditions as the hypoxia group for 24 h and then were returned to normoxic conditions and cultured for 1-2 additional days. RESULTS Proliferation ratios increased in all groups in a time-dependent manner. Proliferation ratios in both the hypoxia and re-oxygenation groups were significantly higher than in the control group on days 2 and 3. Alkaline phosphatase activity was significantly higher in the hypoxia group than in the control and the re-oxygenation groups. The expression of bone sialoprotein mRNA was significantly higher in the hypoxia group than in the control group on days 1 and 2. The expression of vascular endothelial growth factor mRNA was significantly higher in the hypoxia group than in the control group on days 1 and 2. In the re-oxygenation group, the level of expression of bone sialoprotein mRNA and vascular endothelial growth factor mRNA were similar to those of the control group. The expression of heat shock protein 70 mRNA in the hypoxia group was similar to that in the control group, whereas in the re-oxygenation group it was statistically higher than in the other groups. CONCLUSION These results suggest that periodontal ligament cells maintain their osteogenic ability in hypoxia and re-oxygenation conditions in vitro.
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Affiliation(s)
- H Amemiya
- Department of Clinical Pathophysiology, Tokyo Dental College, Chiba, Japan
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14
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Abstract
About 10% to 15% of the nuclear genes of eukaryotic organisms encode mitochondrial proteins. These proteins are synthesized in the cytosol and recognized by receptors on the surface of mitochondria. Translocases in the outer and inner membrane of mitochondria mediate the import and intramitochondrial sorting of these proteins; ATP and the membrane potential are used as energy sources. Chaperones and auxiliary factors assist in the folding and assembly of mitochondrial proteins into their native, three-dimensional structures. This review summarizes the present knowledge on the import and sorting of mitochondrial precursor proteins, with a special emphasis on unresolved questions and topics of current research.
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Affiliation(s)
- Walter Neupert
- Institut für Physiologische Chemie, Universität München, 81377 München, Germany.
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15
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Martínez JA, Tavárez JJ, Oliveira CM, Banerjee DK. Potentiation of angiogenic switch in capillary endothelial cells by cAMP: A cross-talk between up-regulated LLO biosynthesis and the HSP-70 expression. Glycoconj J 2007; 23:209-20. [PMID: 16691504 DOI: 10.1007/s10719-006-7926-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
During tumor growth and invasion, the endothelial cells from a relatively quiescent endothelium start proliferating. The exact mechanism of switching to a new angiogenic phenotype is currently unknown. We have examined the role of intracellular cAMP in this process. When a non-transformed capillary endothelial cell line was treated with 2 mM 8Br-cAMP, cell proliferation was enhanced by approximately 70%. Cellular morphology indicated enhanced mitosis after 32-40 h with almost one-half of the cell population in the S phase. Bcl-2 expression and caspase-3, -8, and -9 activity remained unaffected. A significant increase in the Glc(3)Man(9)GlcNAc(2)-PP-Dol biosynthesis and turnover, Factor VIIIC N-glycosylation, and cell surface expression of N-glycans was observed in cells treated with 8Br-cAMP. Dol-P-Man synthase activity in the endoplasmic reticulum membranes also increased. A 1.4-1.6-fold increase in HSP-70 and HSP-90 expression was also observed in 8Br-cAMP treated cells. On the other hand, the expression of GRP-78/Bip was 2.3-fold higher compared to that of GRP-94 in control cells, but after 8Br-cAMP treatment for 32 h, it was reduced by 3-fold. GRP-78/Bip expression in untreated cells was 1.2-1.5-fold higher when compared with HSP-70 and HSP-90, whereas that of the GRP-94 was 1.5-1.8-fold lower. After 8Br-cAMP treatment, GRP-78/Bip expression was reduced 4.5-4.8-fold, but the GRP-94 was reduced by 1.5-1.6-fold only. Upon comparison, a 2.9-fold down-regulation of GRP-78/Bip was observed compared to GRP-94. We, therefore, conclude that a high level of Glc(3)Man(9)GlcNAc(2)-PP-Dol, resulting from 8Br-cAMP stimulation up-regulated HSP-70 expression and down-regulated that of the GRP-78/Bip, maintained adequate protein folding, and reduced endoplasmic reticulum stress. As a result capillary endothelial cell proliferation was induced.
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Affiliation(s)
- Juan A Martínez
- Department of Biochemistry, School of Medicine, University of Puerto Rico, Medical Sciences Campus, San Juan, PR 00936-5067, USA
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16
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Kameyama Y, Filion F, Yoo JG, Smith LC. Characterization of mitochondrial replication and transcription control during rat early development in vivo and in vitro. Reproduction 2007; 133:423-32. [PMID: 17307910 DOI: 10.1530/rep-06-0263] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
In vitroculture (IVC), used in assisted reproductive technologies, is a major environmental stress on the embryo. To evaluate the effect of IVC on mitochondrial transcription and the control of mtDNA replication, we measured the mtDNA copy number and relative amount of mRNA for mitochondrial-related genes in individual rat oocytes, zygotes and embryos using real-time PCR. The average mtDNA copy number was 147 600 (±3000) in metaphase II oocytes. The mtDNA copy number was stable throughoutin vivoearly development and IVC induced an increase in mtDNA copy number from the 8-cell stage onwards.GapdmRNA levels vary during early development and IVC did not change the patterns of these housekeeping gene transcripts.PolrmtmRNA levels did not vary during early development up to the morula stage but increased at the blastocyst stage. IVC induced the up-regulation ofPolrmtmRNA, one of the key genes regulating mtDNA transcription and replication, at the blastocyst stage. An increase inmt-Nd4mRNA preceded the blastocyst-related event observed in nuclear-encodedGapdandPolrmt, suggesting that the expression of mitochondrial encoded genes is controlled differently from nuclear encoded genes. We conclude that the IVC system can perturb mitochondrial transcription and the control of mtDNA replication in rat embryos. This perturbation of mtDNA regulation may be responsible for the abnormal physiology, metabolism and viability ofin vitro-derived embryos.
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Affiliation(s)
- Yuichi Kameyama
- Faculté de Médecine Vétérinaire, Centre de Recherche en Reproduction Animale, Université de Montréal, Saint-Hyacinthe, Québec, Canada J2S7C6 and Faculty of Bioindustry, Tokyo University of Agriculture, Abashiri, Hokkaido 099-2493, Japan
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17
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Rassow J, Pfanner N. Molecular chaperones and intracellular protein translocation. Rev Physiol Biochem Pharmacol 2006; 126:199-264. [PMID: 7886379 DOI: 10.1007/bfb0049777] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- J Rassow
- Biochemisches Institut, Universität Freiburg, Germany
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18
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Zullo SJ, Parks WT, Chloupkova M, Wei B, Weiner H, Fenton WA, Eisenstadt JM, Merril CR. Stable Transformation of CHO Cells and Human NARP Cybrids Confers Oligomycin Resistance (olir) Following Transfer of a Mitochondrial DNA–Encoded olirATPase6 Gene to the Nuclear Genome: A Model System for mtDNA Gene Therapy. Rejuvenation Res 2005; 8:18-28. [PMID: 15798371 DOI: 10.1089/rej.2005.8.18] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Point and deletion mutations and a general depletion of mammalian mitochondrial DNA (mtDNA) give rise to a wide variety of medical syndromes that are refractory to treatment, possibly including aging itself. While gene therapy directed at correcting such deficits in the mitochondrial genome may offer some therapeutic benefits, there are inherent problems associated with a direct approach. These problems are primarily due to the high mitochondrial genome copy number in each cell and the mitochondrial genome being "protected" inside the double-membrane mitochondrial organelle. In an alternative approach there is evidence that genes normally present in the mitochondrial genome can be incorporated into the nuclear genome. To extend such studies, we modified the Chinese Hamster Ovary (CHO) mtDNA-located ATPase6 gene (possessing a mutation which confers oligomycin resistance- oli(r)) by altering the mtDNA code to the universal code (U-code) to permit the correct translation of its mRNA in the cytoplasm. The U-code construct was inserted into the nuclear genome (nucDNA) of a wild type CHO cell. The expressed transgene products enabled the transformed CHO cell lines to grow in up to 1000 ng mL(-1) oligomycin, while untransformed sensitive CHO cells were eliminated in 1 ng mL(-1) oligomycin. This approach, termed allotopic expression, provides a model that may make possible the transfer of all 13 mtDNA mammalian protein-encoding genes to the nucDNA, for treatments of mtDNA disorders. The CHO mtATPase6 protein is 85% identical to both the mouse and human mtATPase6 protein; these proteins are highly conserved in the region of the oligomycin resistance mutation. They are also well conserved in the regions of the oligomycin resistance mutation of the mouse, and in the region of a mutation found in Leigh's syndrome (T8993G), also called NARP (neurogenic weakness, ataxia, retinitis pigmentosum). It is likely that the CHO oli(r) mtATPase6 Ucode construct could impart oligomycin-resistance in human and mouse cells, as well as function in place of the mutant ATPase subunit in a NARP cell line. Preliminary experiments on human cybrids homoplasmic for the NARP mutation (kindly supplied by D.C. Wallace), transformed with our construct, display an increased oligomycin resistance that supports these suppositions.
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Affiliation(s)
- S J Zullo
- Laboratory of Biochemical Genetics, NIMH, NIH, Bethesda, Maryland, USA.
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19
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Rial DV, Ottado J, Ceccarelli EA. Precursors with altered affinity for Hsp70 in their transit peptides are efficiently imported into chloroplasts. J Biol Chem 2003; 278:46473-81. [PMID: 12970339 DOI: 10.1074/jbc.m306684200] [Citation(s) in RCA: 22] [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 chloroplasts is postulated to occur with the involvement of molecular chaperones. We have determined that the transit peptide of ferredoxin-NADP(H) reductase precursor binds preferentially to an Hsp70 from chloroplast stroma. To investigate the role of Hsp70 molecular chaperones in chloroplast protein import, we analyzed the import into pea chloroplasts of preproteins with decreased Hsp70 binding affinity in their transit peptides. Our results indicate that the precursor with the lowest affinity for Hsp70 molecular chaperones in its transit peptide was imported to chloroplasts with similar apparent Km as the wild type precursor and a 2-fold increase in Vmax. Thus, a strong interaction between chloroplast stromal Hsp70 and the transit peptide seems not to be essential for protein import. These results indicate that in chloroplasts the main unfolding force during protein import may be applied by molecular chaperones other than Hsp70s. Although stromal Hsp70s undoubtedly participate in chloroplast biogenesis, the role of these molecular chaperones in chloroplast protein translocation differs from the one proposed in the mechanisms postulated up to date.
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Affiliation(s)
- Daniela V Rial
- Molecular Biology Division, Rosario Institute of Molecular & Cellular Biology, Faculty of Biochemical and Pharmaceutical Sciences, National University of Rosario, Suipacha 531, S2002LRK Rosario, Argentina
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20
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Rial DV, Lombardo VA, Ceccarelli EA, Ottado J. The import of ferredoxin-NADP+ reductase precursor into chloroplasts is modulated by the region between the transit peptide and the mature core of the protein. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:5431-9. [PMID: 12423341 DOI: 10.1046/j.1432-1033.2002.03233.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Protein transport across organelles' membranes requires that precursor proteins adopt an unfolded structure in order to be translocated by the import machinery. Ferredoxin-NADP+ reductase precursor, as well as many others, acquires a tightly folded structure that needs to be unfolded before or during its import. Several steps of chloroplast protein import are not fully understood. In particular, the role of different regions of the precursor protein has not been completely elucidated. In this work, we have studied the import into chloroplasts of precursor proteins with inclusions of amino acid spacers between the transit peptide and the mature protein, and with deletions in the N-terminal region of the mature enzyme. We measured the import rate constants for these precursors and the results indicate that the distance between the transit peptide and the core of the mature protein determines the import kinetics. The longer precursors were imported into the organelle faster than the wild type form. Precursors with deletions in the N-terminal region of the mature protein also showed increased import rates compared to the wild type. Homology studies amongst all family members reveal that only chloroplastic proteins possess this region. We suggest that even if the first amino acids of the mature protein do not contribute to its overall structural stability, they condition the kinetic parameters of the import reaction. Besides, the distance between the transit peptide and the mature protein core may be modulating the import rate at which the chloroplast incorporates this protein from the cytosol.
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Affiliation(s)
- Daniela V Rial
- Molecular Biology Division, IBR (Instituto de Biología Molecular y Celular de, Rosario), CONICET, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Rosario, Argentina
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21
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Abstract
Proteins that are destined for the matrix of mitochondria are transported into this organelle by two translocases: the TOM complex, which transports proteins across the outer mitochondrial membrane; and the TIM23 complex, which gets them through the inner mitochondrial membrane. Two models have been proposed to explain how this protein-import machinery works -- a targeted Brownian ratchet, in which random motion is translated into vectorial motion, or a 'power stroke', which is exerted by a component of the import machinery. Here, we review the data for and against each model.
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Affiliation(s)
- Walter Neupert
- Institut für Physiologische Chemie, Universität München, Butenandtstrabetae 5, Gebäude B, D-81377 Munich, Germany.
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22
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Affiliation(s)
- T Krimmer
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, 79104 Freiburg, Germany
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23
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24
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Meisinger C, Ryan MT, Hill K, Model K, Lim JH, Sickmann A, Müller H, Meyer HE, Wagner R, Pfanner N. Protein import channel of the outer mitochondrial membrane: a highly stable Tom40-Tom22 core structure differentially interacts with preproteins, small tom proteins, and import receptors. Mol Cell Biol 2001; 21:2337-48. [PMID: 11259583 PMCID: PMC86867 DOI: 10.1128/mcb.21.7.2337-2348.2001] [Citation(s) in RCA: 135] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The preprotein translocase of the yeast mitochondrial outer membrane (TOM) consists of the initial import receptors Tom70 and Tom20 and a approximately 400-kDa (400 K) general import pore (GIP) complex that includes the central receptor Tom22, the channel Tom40, and the three small Tom proteins Tom7, Tom6, and Tom5. We report that the GIP complex is a highly stable complex with an unusual resistance to urea and alkaline pH. Under mild conditions for mitochondrial lysis, the receptor Tom20, but not Tom70, is quantitatively associated with the GIP complex, forming a 500K to 600K TOM complex. A preprotein, stably arrested in the GIP complex, is released by urea but not high salt, indicating that ionic interactions are not essential for keeping the preprotein in the GIP complex. Under more stringent detergent conditions, however, Tom20 and all three small Tom proteins are released, while the preprotein remains in the GIP complex. Moreover, purified outer membrane vesicles devoid of translocase components of the intermembrane space and inner membrane efficiently accumulate the preprotein in the GIP complex. Together, Tom40 and Tom22 thus represent the functional core unit that stably holds accumulated preproteins. The GIP complex isolated from outer membranes exhibits characteristic TOM channel activity with two coupled conductance states, each corresponding to the activity of purified Tom40, suggesting that the complex contains two simultaneously active and coupled channel pores.
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Affiliation(s)
- C Meisinger
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Germany
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25
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Lim JH, Martin F, Guiard B, Pfanner N, Voos W. The mitochondrial Hsp70-dependent import system actively unfolds preproteins and shortens the lag phase of translocation. EMBO J 2001; 20:941-50. [PMID: 11230118 PMCID: PMC145481 DOI: 10.1093/emboj/20.5.941] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Unfolding is an essential process during translocation of preproteins into mitochondria; however, controversy exists as to whether mitochondria play an active role in unfolding. We have established an in vitro system with a kinetic saturation of the mitochondrial import machinery, yielding translocation rates comparable to in vivo import rates. Preproteins with short N-terminal segments in front of a folded domain show a characteristic delay of the onset of translocation (lag phase) although the maximal import rate is similar to that of longer preproteins. The lag phase is shortened by extending the N-terminal segment to improve the accessibility to matrix heat shock protein 70 and abolished by unfolding of the preprotein. A mutant mtHsp70 defective in binding to the inner membrane prolongs the lag phase and reduces the translocation activity. A direct comparison of the rate of spontaneous unfolding in solution with that during translocation demonstrates that unfolding by mitochondria is significantly faster, proving an active unfolding process. We conclude that access of mtHsp70 to N-terminal preprotein segments is critical for active unfolding and initiation of translocation.
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Affiliation(s)
- Joo Hyun Lim
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Fakultät für Biologie, Universität Freiburg, Schänzlestrasse 1, D-79104 Freiburg, Germany and Centre de Génétique Moléculaire, Laboratoire propre du CNRS associeté à l’Université Pierre et Marie Curie, 91190 Gif-sur-Yvette, France Present address: Department of Chemical Physics, The Weizmann Institute of Science, Rehovot 76100, Israel Corresponding author e-mail:
| | - Falk Martin
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Fakultät für Biologie, Universität Freiburg, Schänzlestrasse 1, D-79104 Freiburg, Germany and Centre de Génétique Moléculaire, Laboratoire propre du CNRS associeté à l’Université Pierre et Marie Curie, 91190 Gif-sur-Yvette, France Present address: Department of Chemical Physics, The Weizmann Institute of Science, Rehovot 76100, Israel Corresponding author e-mail:
| | - Bernard Guiard
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Fakultät für Biologie, Universität Freiburg, Schänzlestrasse 1, D-79104 Freiburg, Germany and Centre de Génétique Moléculaire, Laboratoire propre du CNRS associeté à l’Université Pierre et Marie Curie, 91190 Gif-sur-Yvette, France Present address: Department of Chemical Physics, The Weizmann Institute of Science, Rehovot 76100, Israel Corresponding author e-mail:
| | - Nikolaus Pfanner
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Fakultät für Biologie, Universität Freiburg, Schänzlestrasse 1, D-79104 Freiburg, Germany and Centre de Génétique Moléculaire, Laboratoire propre du CNRS associeté à l’Université Pierre et Marie Curie, 91190 Gif-sur-Yvette, France Present address: Department of Chemical Physics, The Weizmann Institute of Science, Rehovot 76100, Israel Corresponding author e-mail:
| | - Wolfgang Voos
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Fakultät für Biologie, Universität Freiburg, Schänzlestrasse 1, D-79104 Freiburg, Germany and Centre de Génétique Moléculaire, Laboratoire propre du CNRS associeté à l’Université Pierre et Marie Curie, 91190 Gif-sur-Yvette, France Present address: Department of Chemical Physics, The Weizmann Institute of Science, Rehovot 76100, Israel Corresponding author e-mail:
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26
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Abstract
Protein unfolding is a key step in the import of some proteins into mitochondria and chloroplasts and in the degradation of regulatory proteins by ATP-dependent proteases. In contrast to protein folding, the reverse process has remained largely uninvestigated until now. This review discusses recent discoveries on the mechanism of protein unfolding during translocation into mitochondria. The mitochondria can actively unfold preproteins by unraveling them from the N-terminus. The central component of the mitochondrial import motor, the matrix heat shock protein 70, functions by both pulling and holding the preproteins.
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Affiliation(s)
- A Matouschek
- Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, IL 60208-3500, USA.
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27
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De Jongh HH. The helix nucleation site and propensity of the synthetic mitochondrial presequence of ornithine carbamoyltransferase. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:5796-804. [PMID: 10971591 DOI: 10.1046/j.1432-1327.2000.01654.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
This study describes the helix nucleation site and helix propagation of the amphiphilic helical structure of the mitochondrial presequence of rat ornithine carbamoyltransferase. We investigated this property of the 32-residue synthetic presequence using CD and 2D-HR NMR techniques by determining the structure as a function of the concentration of trifluoroethanol. It was found that the hydrophobic cluster Ile7-Leu8-Leu9 forms the helix nucleation site, expanding to include residues Asn4 to Lys16 when the concentration of trifluoroethanol is increased from 10 to 30%. At higher trifluoroethanol concentrations an increased 'stiffening' of the polypeptide backbone (to Arg26) is observed. In addition, by recording CD spectra at different trifluoroethanol concentrations as a function of temperature, it was found that the equilibrium constant between helix and random coil formation for this peptide exhibits a strong temperature dependence with maximum values between 20 and 30 degrees C. Comparison of these equilibrium constants with those of homopolymers stressed the unique character of the mitochondrial presequence. The findings are discussed in relation to the molecular recognition events at different stages of the transport process of this protein into mitochondria.
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Affiliation(s)
- H H De Jongh
- Wageningen Centre for Food Sciences and Centre for Protein Technology, Wageningen University, the Netherlands.
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28
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Kurokawa Y, Yanagi H, Yura T. Overexpression of protein disulfide isomerase DsbC stabilizes multiple-disulfide-bonded recombinant protein produced and transported to the periplasm in Escherichia coli. Appl Environ Microbiol 2000; 66:3960-5. [PMID: 10966415 PMCID: PMC92245 DOI: 10.1128/aem.66.9.3960-3965.2000] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Dsb proteins (DsbA, DsbB, DsbC, and DsbD) catalyze formation and isomerization of protein disulfide bonds in the periplasm of Escherichia coli. By using a set of Dsb coexpression plasmids constructed recently, we analyzed the effects of Dsb overexpression on production of horseradish peroxidase (HRP) isozyme C that contains complex disulfide bonds and tends to aggregate when produced in E. coli. When transported to the periplasm, HRP was unstable but was markedly stabilized upon simultaneous overexpression of the set of Dsb proteins (DsbABCD). Whereas total HRP production increased severalfold upon overexpression of at least disulfide-bonded isomerase DsbC, maximum transport of HRP to the periplasm seemed to require overexpression of all DsbABCD proteins, suggesting that excess Dsb proteins exert synergistic effects in assisting folding and transport of HRP. Periplasmic production of HRP also increased when calcium, thought to play an essential role in folding of nascent HRP polypeptide, was added to the medium with or without Dsb overexpression. These results suggest that Dsb proteins and calcium play distinct roles in periplasmic production of HRP, presumably through facilitating correct folding. The present Dsb expression plasmids should be useful in assessing and dissecting periplasmic production of proteins that contain multiple disulfide bonds in E. coli.
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Affiliation(s)
- Y Kurokawa
- HSP Research Institute, Kyoto Research Park, Kyoto 600-8813, Japan
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29
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Lan L, Isenmann S, Wattenberg BW. Targeting and insertion of C-terminally anchored proteins to the mitochondrial outer membrane is specific and saturable but does not strictly require ATP or molecular chaperones. Biochem J 2000; 349:611-21. [PMID: 10880361 PMCID: PMC1221185 DOI: 10.1042/0264-6021:3490611] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
A distinct class of proteins contain a C-terminal membrane anchor and a cytoplasmic functional domain. A subset of these proteins is targeted to the mitochondrial outer membrane. Here, to probe for the involvement of a saturable targeting mechanism for this class of proteins, and to elucidate the roles of chaperone proteins and ATP, we have utilized an in vitro targeting system consisting of in vitro-synthesized proteins and isolated mitochondria. To establish the specificity of targeting we have used a closely related protein pair. VAMP-1A and VAMP-1B are splice variants of the vesicle-associated membrane protein/synaptobrevin-1 (VAMP-1) gene. In intact cells VAMP-1B is targeted to mitochondria whereas VAMP-1A is targeted to membranes of the secretory pathway, yet these isoforms differ by only five amino acids at the extreme C-terminus. Here we demonstrate that, in vitro, VAMP-1B is imported into both intact mitochondria and mitochondrial outer-membrane vesicles with a 15-fold greater efficiency than VAMP-1A. We generated and purified bacterially expressed fusion proteins consisting of the C-terminal two-thirds of VAMP-1A or -1B proteins fused to glutathione S-transferase (GST). Using these fusion proteins we demonstrate that protein targeting and insertion is saturable and specific for the VAMP-1B membrane anchor. To elucidate the role of cytosolic chaperones on VAMP-1B targeting, we also used the purified, Escherichia coli-derived fusion proteins. (33)P-Labelled GST-VAMP-1B(61-116), but not GST-VAMP-1A(61-118), was efficiently targeted to mitochondria in a chaperone-free system. Thus the information required for targeting is contained within the targeted protein itself and not the chaperone or a chaperone-protein complex, although chaperones may be required to maintain a transport-competent conformation. Moreover, ATP was required for transport only in the presence of cytosolic chaperone proteins. Therefore the ATP requirement of transport appears to reflect the participation of chaperones and not any other ATP-dependent step. These data demonstrate that targeting of C-terminally anchored proteins to mitochondria is sequence specific and mediated by a saturable mechanism. Neither ATP nor chaperone proteins are strictly required for either specific targeting or membrane insertion.
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Affiliation(s)
- L Lan
- Division of Human Immunology, Hanson Centre for Cancer Research, Institute of Medical and Veterinary Sciences, Adelaide, South Australia 5000, Australia
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30
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Esaki M, Kanamori T, Nishikawa SI, Endo T. Two distinct mechanisms drive protein translocation across the mitochondrial outer membrane in the late step of the cytochrome b(2) import pathway. Proc Natl Acad Sci U S A 1999; 96:11770-5. [PMID: 10518525 PMCID: PMC18361 DOI: 10.1073/pnas.96.21.11770] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The import of cytochrome b(2) into mitochondria consists of two steps. The translocation of the first part of the presequence across the inner membrane is coupled with the translocation of the tightly folded heme-binding domain across the outer membrane and requires a membrane potential DeltaPsi and the functions of mitochondrial Hsp70 (mHsp70) in the matrix. Once the heme-binding domain has passed the outer membrane, the translocation of the rest of the polypeptide chain across the outer membrane becomes independent of DeltaPsi and mHsp70. Here we analyzed the late DeltaPsi- and mHsp70-independent step in the transport of cytochrome b(2) fusion proteins into the intermembrane space (IMS). The import of the cytochrome b(2) fusion proteins containing two protein domains linked by a spacer segment into mitochondria was arrested at a stage at which one domain folded on each side of the outer membrane, along the pathway that is consistent with the stop-transfer model. The mature-size form of the translocation intermediate could move across the outer membrane in both directions, and the stabilization of the protein domain in the IMS promoted the forward translocation. On the other hand, the intermediate-size form of the translocation intermediate, which retains the anchorage to the inner membrane, was transported into the IMS independently of the stability of the protein domain in the IMS. These results suggest that two distinct mechanisms, the Brownian ratchet and the anchor diffusion mechanisms, can operate for the transmembrane movement of the mature-size form and the intermediate-size form, respectively, of cytochrome b(2) species.
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Affiliation(s)
- M Esaki
- Department of Chemistry, Faculty of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
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31
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Zámocký M, Koller F. Understanding the structure and function of catalases: clues from molecular evolution and in vitro mutagenesis. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 1999; 72:19-66. [PMID: 10446501 DOI: 10.1016/s0079-6107(98)00058-3] [Citation(s) in RCA: 213] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
This review gives an overview about the structural organisation of different evolutionary lines of all enzymes capable of efficient dismutation of hydrogen peroxide. Major potential applications in biotechnology and clinical medicine justify further investigations. According to structural and functional similarities catalases can be divided in three subgroups. Typical catalases are homotetrameric haem proteins. The three-dimensional structure of six representatives has been resolved to atomic resolution. The central core of each subunit reveals a characteristic "catalase fold", extremely well conserved among this group. In the native tetramer structure pairs of subunits tightly interact via exchange of their N-terminal arms. This pseudo-knot structures implies a highly ordered assembly pathway. A minor subgroup ("large catalases") possesses an extra flavodoxin-like C-terminal domain. A > or = 25 A long channel leads from the enzyme surface to the deeply buried active site. It enables rapid and selective diffusion of the substrates to the active center. In several catalases NADPH is tightly bound close to the surface. This cofactor may prevent and reverse the formation of compound II, an inactive reaction intermediate. Bifunctional catalase-peroxidase are haem proteins which probably arose via gene duplication of an ancestral peroxidase gene. No detailed structural information is currently available. Even less is know about manganese catalases. Their di-manganese reaction centers may be evolutionary.
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Affiliation(s)
- M Zámocký
- Institut für Biochemie and Molekulare Zellbiologie, Vienna, Austria.
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32
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Gaume B, Klaus C, Ungermann C, Guiard B, Neupert W, Brunner M. Unfolding of preproteins upon import into mitochondria. EMBO J 1998; 17:6497-507. [PMID: 9822595 PMCID: PMC1170997 DOI: 10.1093/emboj/17.22.6497] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Unfolding of preproteins and translocation across the mitochondrial membranes requires their interaction with mt-Hsp70 and Tim44 at the inner face of the inner membrane and ATP as an energy source. We measured the temperature dependence of the rates of unfolding and import into the matrix of two folded passenger domains, the tightly folded heme-binding domain (HBD) of cytochrome b2 and the loosely folded mouse dihydrofolate reductase (DHFR). Despite the stability of the HBD, its rates of thermal breathing were fast and the preprotein was imported rapidly at all temperatures. In contrast, rates of unfolding and import of DHFR were strongly temperature dependent and import was significantly slower than unfolding. In addition, import rates of DHFR were strongly dependent on the length of the presequence. We propose that the mitochondrial import motor does not exert a constant pulling force. Rather, mt-Hsp70 appears to release a translocating polypeptide chain such that the precursor can then slide back and refold on the surface of the mitochondria. Refolding competes with translocation, and passengers may undergo several rounds of unfolding and refolding prior to their import.
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Affiliation(s)
- B Gaume
- Institut für Physiologische Chemie der Universität München, Goethestrasse 33, 80336 München, Germany
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33
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Sciacco M, Gasparo-Rippa P, Vu TH, Tanji K, Shanske S, Mendell JR, Schon EA, DiMauro S, Bonilla E. Study of mitochondrial DNA depletion in muscle by single-fiber polymerase chain reaction. Muscle Nerve 1998; 21:1374-81. [PMID: 9771659 DOI: 10.1002/(sici)1097-4598(199811)21:11<1374::aid-mus3>3.0.co;2-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
We studied muscle biopsies from 3 children with a mitochondrial myopathy characterized histochemically by the presence of ragged-red fibers (RRF) and various numbers of cytochrome c oxidase (COX)-negative fibers. We quantitated the absolute amounts of total mitochondrial DNA (mtDNA) in isolated normal COX-positive muscle fibers and in COX-negative RRF. There was severe mtDNA depletion in all fibers from the two most severe cases. In the third case mtDNA depletion could not be established with conventional diagnostic tools, but it was documented in single COX-negative fibers; COX-positive fibers showed the same amounts of mtDNA as fibers from aged-matched controls. Our observations indicate that mtDNA single-fiber PCR quantitation is a highly sensitive and specific method for diagnosing cases with focal mtDNA depletion. This method also allows one to correlate amounts of mtDNA with histochemical phenotypes in individual fibers from patients and age-matched controls, thereby providing important information about the functional role of residual mtDNA.
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Affiliation(s)
- M Sciacco
- Department of Neurology, College of Physicians and Surgeons of Columbia University, New York, New York 10032, USA
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34
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Lu Z, Cyr DM. Protein folding activity of Hsp70 is modified differentially by the hsp40 co-chaperones Sis1 and Ydj1. J Biol Chem 1998; 273:27824-30. [PMID: 9774392 DOI: 10.1074/jbc.273.43.27824] [Citation(s) in RCA: 180] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Specification of Hsp70 action in cellular protein metabolism may occur through the formation of specialized Hsp70:Hsp40 pairs. To test this model, we compared the ability of purified Sis1 and Ydj1 to regulate the ATPase and protein-folding activity of Hsp70 Ssa1 and Ssb1/2 proteins. Ydj1 and Sis1 could both functionally interact with Ssa1, but not the Ssb1/2 proteins, to refold luciferase. Interestingly, Ydj1:Ssa1 could promote up to four times more luciferase folding than Sis1:Ssa1. This functional difference was explored and could not be accounted for by differences in the ability of Sis1 and Ydj1 to regulate Ssa1 ATPase activity. Instead, differences in the chaperone function of Ydj1 and Sis1 were observed. Ydj1 was dramatically more effective than Sis1 at suppressing the thermally induced aggregation of luciferase. Paradoxically, Sis1 and Ydj1 could bind similar quantities of chemically denatured luciferase. The polypeptide binding domain of Sis1 was found to lie between residues 171-352 and correspond to its conserved carboxyl terminus. The conserved carboxyl terminus of Ydj1 is also known to participate in the binding of nonnative polypeptides. Thus, Ydj1 appears more efficient at assisting Ssa1 in folding luciferase because its contains a zinc finger-like region that is absent from Sis1. Ydj1 and Sis1 are structurally and functionally distinct Hsp40 proteins that can specify Ssa1 action by generating Hsp70:Hsp40 pairs that exhibit different chaperone activities.
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Affiliation(s)
- Z Lu
- Department of Cell Biology, School of Medicine, University of Alabama Medical Center, Birmingham, Alabama 35294-0005, USA
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35
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Sepuri NB, Gordon DM, Pain D. A GTP-dependent "push" is generally required for efficient protein translocation across the mitochondrial inner membrane into the matrix. J Biol Chem 1998; 273:20941-50. [PMID: 9694843 DOI: 10.1074/jbc.273.33.20941] [Citation(s) in RCA: 25] [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
Mitochondrial biogenesis requires translocation of numerous preproteins across both outer and inner membranes into the matrix of the organelle. This translocation process requires a membrane potential (DeltaPsi) and ATP. We have recently demonstrated that the efficient import of a urea-denatured preprotein into the matrix requires GTP hydrolysis (Sepuri, N. B. V., Schülke, N., and Pain, D. (1998) J. Biol. Chem. 273, 1420-1424). We now demonstrate that GTP is generally required for efficient import of various preproteins, both native and urea-denatured. The GTP participation is localized to a particular stage in the protein import process. In the presence of DeltaPsi but no added nucleoside triphosphates, the transmembrane movement of preproteins proceeds only to a point early in their translocation across the inner membrane. The completion of translocation into the matrix is independent of DeltaPsi but is dependent on a GTP-mediated "push." This push is likely mediated by a membrane-bound GTPase on the cis side of the inner membrane. This conclusion is based on two observations: (i) GTP does not readily cross the inner membrane barrier and hence, primarily acts outside the inner membrane to stimulate import, and (ii) the GTP-dependent stage of import does not require soluble constituents of the intermembrane space and can be observed in isolated mitoplasts. Efficient import into the matrix, however, is achieved only through the coordinated action of a cis GTP-dependent push and a trans ATP-dependent "pull."
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Affiliation(s)
- N B Sepuri
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
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36
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Casari G, De Fusco M, Ciarmatori S, Zeviani M, Mora M, Fernandez P, De Michele G, Filla A, Cocozza S, Marconi R, Dürr A, Fontaine B, Ballabio A. Spastic paraplegia and OXPHOS impairment caused by mutations in paraplegin, a nuclear-encoded mitochondrial metalloprotease. Cell 1998; 93:973-83. [PMID: 9635427 DOI: 10.1016/s0092-8674(00)81203-9] [Citation(s) in RCA: 540] [Impact Index Per Article: 20.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Hereditary spastic paraplegia (HSP) is characterized by progressive weakness and spasticity of the lower limbs due to degeneration of corticospinal axons. We found that patients from a chromosome 16q24.3-linked HSP family are homozygous for a 9.5 kb deletion involving a gene encoding a novel protein, named Paraplegin. Two additional Paraplegin mutations, both resulting in a frameshift, were found in a complicated and in a pure form of HSP. Paraplegin is highly homologous to the yeast mitochondrial ATPases, AFG3, RCA1, and YME1, which have both proteolytic and chaperon-like activities at the inner mitochondrial membrane. Immunofluorescence analysis and import experiments showed that Paraplegin localizes to mitochondria. Analysis of muscle biopsies from two patients carrying Paraplegin mutations showed typical signs of mitochondrial OXPHOS defects, thus suggesting a mechanism for neurodegeneration in HSP-type disorders.
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MESH Headings
- ATPases Associated with Diverse Cellular Activities
- Adult
- Amino Acid Sequence
- Cell Nucleus/genetics
- Chromosome Deletion
- Chromosomes, Human, Pair 16/genetics
- Cloning, Molecular
- DNA, Complementary/genetics
- Female
- Fetus
- Frameshift Mutation/genetics
- Humans
- Italy
- Male
- Metalloendopeptidases/genetics
- Mitochondria/enzymology
- Molecular Sequence Data
- Muscle, Skeletal/pathology
- Oxidative Phosphorylation
- Pedigree
- RNA, Messenger/analysis
- Sequence Analysis, DNA
- Sequence Homology, Amino Acid
- Spastic Paraplegia, Hereditary/enzymology
- Spastic Paraplegia, Hereditary/genetics
- Spastic Paraplegia, Hereditary/pathology
- Yeasts/enzymology
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Affiliation(s)
- G Casari
- Telethon Institute of Genetics and Medicine, Milan, Italy
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37
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Kumarevel TS, Gromiha MM, Ponnuswamy MN. Solvent accessibility analysis on the mutants of Hsc70 ATPase fragment. Biophys Chem 1998; 71:99-111. [PMID: 9750050 DOI: 10.1016/s0301-4622(97)00137-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Molecular chaperones are the cellular proteins which mediate the correct folding of other polypeptides. The concept of 'solvent accessibility' is one of the most powerful tools to understand the structure and stability of protein molecules. The hydrophobic variation of amino acid residues due to point mutations at many active sites of chaperone protein Hsc70 using solvent accessibility analysis is carried out. The numerical indices for several properties of amino acid residues, such as, reduction in accessibility, preference of amino acid residues in interior and surface parts, transfer free energy and the preference of amino acid residues to change their positions (buried/exposed) due to amino acid substitutions for Hsc70 and its mutants were set up. The accessibility of amino acid residues varies much between native and mutant proteins whereas there is no major changes on their conformations. The conformational stability for Hsc70 and its mutants were established and the computed hydrophobic free energy change is around 10 kcal/mol due to single amino acid substitution.
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Affiliation(s)
- T S Kumarevel
- Department of Crystallography and Biophysics, University of Madras, Guindy Campus, Chennai 600025, India
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38
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Rapaport D, Mayer A, Neupert W, Lill R. cis and trans sites of the TOM complex of mitochondria in unfolding and initial translocation of preproteins. J Biol Chem 1998; 273:8806-13. [PMID: 9535859 DOI: 10.1074/jbc.273.15.8806] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Translocation of preproteins across the mitochondrial outer membrane is mediated by the TOM complex. Our previous studies led to the concept of two preprotein binding sites acting in series, the surface-exposed cis site and the trans site exposed to the intermembrane space. We report here that preproteins are bound to the cis site in a labile fashion even at low ionic strength, whereas intermediates arrested at the trans site remained firmly bound at higher salt concentration. The stability of the trans site intermediate results from interactions of both the presequence and unfolded parts of the mature part of the preprotein with the TOM complex. Binding to the trans site proceeded at rates comparable with those of unfolding of the mature domain and appeared to be kinetically limited by the unfolding reaction. Efficient binding to the trans site and unfolding were observed with both outer membrane vesicles and intact mitochondria whose membrane potential, DeltaPsi, was dissipated. Upon re-establishing DeltaPsi, trans site-bound preprotein resumed translocation into the matrix. The rates of unfolding and binding to the trans site were the same as those for translocation into intact energized mitochondria. We conclude that preprotein unfolding in intact mitochondria can take place without the involvement of the translocation machinery of the inner membrane and, in particular, the matrix Hsp70 chaperone. Further, preprotein unfolding at the outer membrane can be a rate-limiting step for formation of the trans site intermediate and for the entire translocation reaction.
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Affiliation(s)
- D Rapaport
- Institut für Physiologische Chemie, Physikalische Biochemie und Zellbiologie der Universität München, Goethestrabetae 33, 80336 München, Federal Republic of Germany
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39
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Chauwin JF, Oster G, Glick BS. Strong precursor-pore interactions constrain models for mitochondrial protein import. Biophys J 1998; 74:1732-43. [PMID: 9545036 PMCID: PMC1299518 DOI: 10.1016/s0006-3495(98)77884-1] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Mitochondrial precursor proteins are imported from the cytosol into the matrix compartment through a proteinaceous translocation pore. Import is driven by mitochondrial Hsp70 (mHsp70), a matrix-localized ATPase. There are currently two postulated mechanisms for this function of mHsp70: 1) The "Brownian ratchet" model proposes that the precursor chain diffuses within the pore, and that binding of mHsp70 to the lumenal portion of the chain biases this diffusion. 2) The "power stroke" model proposes that mHsp70 undergoes a conformational change that actively pulls the precursor chain through the pore. Here we formulate these two models quantitatively, and compare their performance in light of recent experimental evidence that precursor chains interact strongly with the walls of the translocation pore. Under these conditions the simulated Brownian ratchet is inefficient, whereas the power stroke mechanism seems to be a plausible description of the import process.
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Affiliation(s)
- J F Chauwin
- Department of Molecular and Cellular Biology, University of California, Berkeley 94720-3112, USA
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40
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Joly JC, Leung WS, Swartz JR. Overexpression of Escherichia coli oxidoreductases increases recombinant insulin-like growth factor-I accumulation. Proc Natl Acad Sci U S A 1998; 95:2773-7. [PMID: 9501165 PMCID: PMC19644 DOI: 10.1073/pnas.95.6.2773] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Transient overexpression of either DsbA or DsbC can double the yield of periplasmic insulin-like growth factor (IGF)-I in Escherichia coli to 8.5 g/liter. Strikingly, most of the overexpressed DsbA or DsbC is found in the reduced form, implying that enhanced disulfide isomerization is responsible for the substantial increase in IGF-I yield. All of the accumulated IGF-I has had the signal sequence removed, underscoring the secretion capacity of this organism as well as its utility for efficient production of polypeptide with the correct amino terminus. The overexpressed IGF-I constitutes approximately 30% of the total cell protein. Overproduction of active site mutants of DsbA instead of the wild-type gene do not produce this increase in yield. With wild-type levels of DsbA and DsbC, most of the secreted IGF-I is found in disulfide-linked aggregates, although 10% is soluble and about 5% is correctly folded. Contrary to expectations, overexpression of the disulfide oxidoreductases decreased the soluble fraction. Because the aggregated protein can be efficiently solubilized and refolded, the increased yield is a significant benefit for the production of IGF-I.
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Affiliation(s)
- J C Joly
- Department of Cell Culture and Fermentation, Research and Development, Genentech, Inc., South San Francisco, CA 94080, USA.
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41
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Abstract
Mitochondria import most of their proteins from the cytosol. Dynamic protein complexes in the mitochondrial outer and inner membranes are responsible for the specific recognition and membrane translocation of preproteins. The preprotein translocase of the outer mitochondrial membrane contains several import receptors and a general import pore. The preprotein translocase of the inner membrane consists of a channel interacting with preproteins in transit and an import motor that includes the matrix heat shock protein Hsp70. Acidic patches of import components are thought to guide the import of positively charged signal sequences (acid chain hypothesis). Energy input is derived from the inner membrane potential and ATP. Proteins in the mitochondrial matrix are required for proteolytic processing and folding of imported proteins. The dynamic nature of the membrane translocase permits sorting of preproteins at distinct stages of the import pathway.
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Affiliation(s)
- N Pfanner
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Germany.
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42
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Sepuri NB, Schülke N, Pain D. GTP hydrolysis is essential for protein import into the mitochondrial matrix. J Biol Chem 1998; 273:1420-4. [PMID: 9430677 DOI: 10.1074/jbc.273.3.1420] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Protein import into the innermost compartment of mitochondria (the matrix) requires a membrane potential (delta psi) across the inner membrane, as well as ATP-dependent interactions with chaperones in the matrix and cytosol. The role of nucleoside triphosphates other than ATP during import into the matrix, however, remains to be determined. Import of urea-denatured precursors does not require cytosolic chaperones. We have therefore used a purified and urea-denatured preprotein in our import assays to bypass the requirement of external ATP. Using this modified system, we demonstrate that GTP stimulates protein import into the matrix; the stimulatory effect is directly mediated by GTP hydrolysis and does not result from conversion of GTP to ATP. Both external GTP and matrix ATP are necessary; neither one can substitute for the other if efficient import is to be achieved. These results suggest a "push-pull" mechanism of import, which may be common to other post-translational translocation pathways.
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Affiliation(s)
- N B Sepuri
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia 19104-6085, USA
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43
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Schneider G, Sjöling S, Wallin E, Wrede P, Glaser E, von Heijne G. Feature-extraction from endopeptidase cleavage sites in mitochondrial targeting peptides. Proteins 1998. [DOI: 10.1002/(sici)1097-0134(19980101)30:1<49::aid-prot5>3.0.co;2-f] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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44
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Gruhler A, Arnold I, Seytter T, Guiard B, Schwarz E, Neupert W, Stuart RA. N-terminal hydrophobic sorting signals of preproteins confer mitochondrial hsp70 independence for import into mitochondria. J Biol Chem 1997; 272:17410-5. [PMID: 9211883 DOI: 10.1074/jbc.272.28.17410] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The requirement of mitochondrial hsp70 (mt-hsp70) for the import of a series of preproteins containing hydrophobic sorting signals into isolated yeast mitochondria was investigated. Here we demonstrate that the presence of such a sorting signal in proximity to the N-terminal matrix-targeting sequence of a preprotein can secure a translocating polypeptide chain in the import channel in a manner that does not require mt-hsp70 activity. Trapping the translocating chain in this fashion leads to efficient processing by the mitochondrial processing peptidase and to complete translocation across the outer mitochondrial membrane into the intermembrane space. These mt-hsp70-independent effects appear to be exerted at the level of the inner membrane through an interaction of the hydrophobic core of the sorting signal with component(s) of the translocase of the inner membrane. Hydrophobic sorting signals of inner membrane proteins inserted into the membrane from the matrix, as well as those of intermembrane space proteins, are capable of causing this mt-hsp70-independent stabilization, demonstrating that this phenomenon is not unique to those preproteins normally sorted to the intermembrane space.
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Affiliation(s)
- A Gruhler
- Institut für Physiologische Chemie, Universität München, Goethestrasse 33, 80336 München, Federal Republic of Germany
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45
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Artigues A, Iriarte A, Martinez-Carrion M. Refolding intermediates of acid-unfolded mitochondrial aspartate aminotransferase bind to hsp70. J Biol Chem 1997; 272:16852-61. [PMID: 9201992 DOI: 10.1074/jbc.272.27.16852] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The cytosolic (cAAT) and mitochondrial (mAAT) isozymes of eukaryotic aspartate aminotransferase share a high degree of sequence identity and almost identical three-dimensional structure. The rat liver proteins can be refolded and reassembled into active dimers after unfolding at low pH. However, refolding of the mitochondrial form after unfolding at pH 2.0 is arrested in the presence of hsp70, whereas this chaperone does not affect the refolding of the cytosolic isozyme unfolded under similar conditions. To elucidate the nature of the differential interaction between hsp70 and the two transaminase forms, we have characterized their refolding from their acid-unfolded states. The recovery of activity of the cytosolic enzyme is monophasic and can be adequately described by a single first-order reaction. By contrast, two sequential first-order rate-limiting steps can be detected for the refolding and reactivation of the mitochondrial protein. The overall refolding pathway of mAAT includes a very fast collapse to an intermediate with 80% of the secondary structure of the active dimer. This is followed by a slow isomerization to form assembly-competent monomers that rapidly associate to form an inactive dimer and a final structural rearrangement of the dimer to the native conformation. Analysis of the interaction of hsp70 with intermediates along the folding pathway of mAAT shows that the polypeptide loses its ability to bind to the chaperone after it has proceeded through the first isomerization/fast dimerization steps. Thus it appears that only the first collapsed intermediate states in the folding of mAAT bind hsp70. By contrast a faster refolding of cAAT from this collapsed state could explain, at least in part, the inability of hsp70 to bind this isozyme.
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Affiliation(s)
- A Artigues
- Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri-Kansas City, Kansas City, Missouri 64110-2499, USA
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46
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Haynes RL, Zheng T, Nicchitta CV. Structure and folding of nascent polypeptide chains during protein translocation in the endoplasmic reticulum. J Biol Chem 1997; 272:17126-33. [PMID: 9202031 DOI: 10.1074/jbc.272.27.17126] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
To investigate the role of protein folding and chaperone-nascent chain interactions in translocation across the endoplasmic reticulum membrane, the translocation of wild type and mutant forms of preprolactin were studied in vivo and in vitro. The preprolactin mutant studied contains an 18-amino acid substitution at the amino terminus of the mature protein, eliminating a disulfide-bonded loop domain. In COS-7 cells, mutant prolactin accumulated in the endoplasmic reticulum as stable protein-protein and disulfide-bonded aggregates, whereas wild type prolactin was efficiently secreted. In vitro, wild type and mutant preprolactin translocated with equal efficiency although both translation products were recovered as heterogeneous aggregates. Studies with translocation intermediates indicated that aggregation occurred co-translationally. To evaluate the contribution of lumenal chaperones to translocation and folding, in vitro studies were performed with native and reconstituted, chaperone-deficient membranes. The absence of lumenal chaperones was associated with a decrease in translocation efficiency and pronounced aggregation of the translation products. These studies suggest that chaperone-nascent chain interactions significantly enhance translocation and indicate that in the absence of such interactions, aggregation can serve as the predominant in vitro protein folding end point. The ramifications of these observations on investigations into the mechanism of translocation are discussed.
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Affiliation(s)
- R L Haynes
- Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA
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47
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Horst M, Oppliger W, Rospert S, Schönfeld HJ, Schatz G, Azem A. Sequential action of two hsp70 complexes during protein import into mitochondria. EMBO J 1997; 16:1842-9. [PMID: 9155010 PMCID: PMC1169787 DOI: 10.1093/emboj/16.8.1842] [Citation(s) in RCA: 119] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The mitochondrial chaperone mhsp70 mediates protein transport across the inner membrane and protein folding in the matrix. These two reactions are effected by two different mhsp70 complexes. The ADP conformation of mhsp70 favors formation of a complex on the inner membrane; this 'import complex' contains mhsp70, its membrane anchor Tim44 and the nucleotide exchange factor mGrpE. The ATP conformation of mhsp70 favors formation of a complex in the matrix; this 'folding complex' contains mhsp70, the mitochondrial DnaJ homolog Mdj1 and mGrpE. A precursor protein entering the matrix interacts first with the import complex and then with the folding complex. A chaperone can thus function as part of two different complexes within the same organelle.
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Affiliation(s)
- M Horst
- Biozentrum, Universität Basel, Switzerland
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48
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Protein transport into and across the thylakoid membrane. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 1997. [DOI: 10.1016/s1011-1344(96)07408-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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49
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Suh Y, Benedik MJ. Secretion of nuclease across the outer membrane of Serratia marcescens and its energy requirements. J Bacteriol 1997; 179:677-83. [PMID: 9006020 PMCID: PMC178747 DOI: 10.1128/jb.179.3.677-683.1997] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Extracellular secretion of Serratia marcescens nuclease occurs as a two-step process via a periplasmic intermediate. Unlike other extracellular proteins secreted by gram-negative bacteria by the general secretory pathway, nuclease accumulates in the periplasm in its active form for an unusually long time before its export into the growth medium. The energy requirements for extracellular secretion of nuclease from the periplasm were investigated. Our results suggest that the second step of secretion across the outer membrane is dependent upon the external pH; acidic pH effectively but reversibly blocks extracellular secretion. However, electrochemical proton gradient, and possibly ATP hydrolysis, are not required for this step. We suggest that nuclease uses a novel mechanism for the second step of secretion in S. marcescens.
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Affiliation(s)
- Y Suh
- Department of Biochemical and Biophysical Sciences, University of Houston, Texas 77204-5934, USA
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50
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Cyr DM. Coupling chemical energy by the hsp70/tim44 complex to drive protein translocation into mitochondria. J Bioenerg Biomembr 1997; 29:29-34. [PMID: 9067799 DOI: 10.1023/a:1022455621111] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
A dynamic complex between the mitochondrial cognate of hsp70 (mthsp70) and the inner membrane protein tim44 couples energy derived from ATP hydrolysis to drive multiple steps in the mitochondrial protein import pathway: (1) The delta psi dependent import step and the mthsp70/tim44 complex cooperate to facilitate the unidirectional transfer of the mitochondrial targeting signal across the inner membrane. (2) The mthsp70/tim44 complex helps to unfold domains on precursors proteins that arrive at the import apparatus in a folded conformation on the cis side of the outer membrane. (3) Completion of import is then driven by the mthsp70/ tim44 complex in a manner that is independent of delta psi. Mechanisms proposed to explain how the mthsp70/tim44 complex harvests chemical energy to drive these aspects of the import process are discussed.
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Affiliation(s)
- D M Cyr
- Department of Cell Biology, School of Medicine, University of Alabama at Birmingham 35294-0005, USA
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