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Bersch K, Lobos Matthei I, Thoms S. Multiple Localization by Functional Translational Readthrough. Subcell Biochem 2018; 89:201-219. [PMID: 30378024 DOI: 10.1007/978-981-13-2233-4_8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
In a compartmentalized cell, correct protein localization is crucial for function of virtually all cellular processes. From the cytoplasm as a starting point, proteins are imported into organelles by specific targeting signals. Many proteins, however, act in more than one cellular compartment. In this chapter, we discuss mechanisms by which proteins can be targeted to multiple organelles with a focus on a novel gene regulatory mechanism, functional translational readthrough, that permits multiple targeting of proteins to the peroxisome and other organelles. In mammals, lactate and malate dehydrogenase are the best-characterized enzymes whose targeting is controlled by functional translational readthrough.
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Affiliation(s)
- Kristina Bersch
- Department of Child and Adolescent Health, University Medical Center Göttingen, University of Göttingen, Robert-Koch-Str. 40, 37075, Göttingen, Germany
| | - Ignacio Lobos Matthei
- Department of Child and Adolescent Health, University Medical Center Göttingen, University of Göttingen, Robert-Koch-Str. 40, 37075, Göttingen, Germany
| | - Sven Thoms
- Department of Child and Adolescent Health, University Medical Center Göttingen, University of Göttingen, Robert-Koch-Str. 40, 37075, Göttingen, Germany.
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2
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Mechanisms and physiological impact of the dual localization of mitochondrial intermembrane space proteins. Biochem Soc Trans 2015; 42:952-8. [PMID: 25109985 DOI: 10.1042/bst20140104] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Eukaryotic cells developed diverse mechanisms to guide proteins to more than one destination within the cell. Recently, the proteome of the IMS (intermembrane space) of mitochondria of yeast cells was identified showing that approximately 20% of all soluble IMS proteins are dually localized to the IMS, as well as to other cellular compartments. Half of these dually localized proteins are important for oxidative stress defence and the other half are involved in energy homoeostasis. In the present review, we discuss the mechanisms leading to the dual localization of IMS proteins and the implications for mitochondrial function.
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Kalderon B, Pines O. Protein folding as a driving force for dual protein targeting in eukaryotes. Front Mol Biosci 2014; 1:23. [PMID: 25988164 PMCID: PMC4428415 DOI: 10.3389/fmolb.2014.00023] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2014] [Accepted: 10/28/2014] [Indexed: 01/19/2023] Open
Abstract
It is well documented that in eukaryotic cells molecules of one protein can be located in several subcellular locations, a phenomenon termed dual targeting, dual localization, or dual distribution. The differently localized identical or nearly identical proteins are termed “echoforms.” Our conventional definition of dual targeted proteins refers to situations in which one of the echoforms is translocated through/into a membrane. Thus, dual targeted proteins are recognized by at least one organelle's receptors and translocation machineries within the lipid bilayer. In this review we attempt to evaluate mechanisms and situations in which protein folding is the major determinant of dual targeting and of the relative distribution levels of echoforms in the subcellular compartments of the eukaryotic cell. We show that the decisive folding step can occur prior, during or after translocation through the bilayer of a biological membrane. This phenomenon involves folding catalysts in the cell such as chaperones, proteases and modification enzymes, and targeting processes such as signal recognition, translocation through membranes, trapping, retrotranslocation and reverse translocation.
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Affiliation(s)
- Bella Kalderon
- Department of Microbiology and Molecular Genetics, Faculty of Medicine, Institute for Medical Research Israel-Canada, Hebrew University of Jerusalem Jerusalem, Israel
| | - Ophry Pines
- Department of Microbiology and Molecular Genetics, Faculty of Medicine, Institute for Medical Research Israel-Canada, Hebrew University of Jerusalem Jerusalem, Israel ; CREATE-NUS-HUJ Cellular and Molecular Mechanisms of Inflammation Program, National University of Singapore Singapore, Singapore
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4
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Liang P, Zhang F, Chen W, Hu X, Huang Y, Li S, Ren M, He L, Li R, Li X, Xu J, Wu Z, Lu G, Yu X. Identification and biochemical characterization of adenylate kinase 1 from Clonorchis sinensis. Parasitol Res 2013; 112:1719-27. [PMID: 23455935 DOI: 10.1007/s00436-013-3330-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2012] [Accepted: 01/29/2013] [Indexed: 11/27/2022]
Abstract
Adenylate kinase 1 is responsible for the conversion of AMP into ADP involved in purine metabolism. In the present study, adenylate kinase 1 gene (CsADK1) was isolated from an adult cDNA library of Clonorchis sinensis, and the recombinant protein was expressed in Escherichia coli. Bioinformatics analysis implied that the putative protein contained 197 amino acids, and some residues in conservative binding sites of CsADK1 were substituted. The structure modeling analysis showed that CsADK1 was composed of a core domain, an NMP-binding domain, and a LID domain, which was just a small loop. It demonstrated that CsADK1 was a short isoform of ADKs. Moreover, CsADK1 was identified as an excretory/secretory product by western blot analysis. Real-time quantitative PCR showed that expression level of CsADK1 at the stage of excysted metacercaria was higher than those of adult worm (18.8-folds, P<0.01), metacercariae (1.5-folds, P<0.01), and eggs (5.6-folds, P<0.01). In addition, histochemistry analysis showed that CsADK1 was extensively distributed in metacercariae and in the vitellaria and eggs of adult worms. The Km and Vmax value for substrate ADP were 2.2 mM and 0.9 mM/min, respectively. The optimal temperature and pH value were 37 °C and from 7.5 to 8.0, respectively. The enzyme activity was highly dependent on Mg2+, and the optimal concentration of Mg2+ was 2 mM. However, the enzyme activity was slightly activated by Ca2+, and Mn2+ has no effect on activity. For monovalent ions, activity was highly activated by K+ and NH4+, but slightly by Li+. Taken together, CsADK1 was a metal ion-dependent enzyme involved in purine metabolism, which was important for development and reproduction, and might be a potential candidate for drug target for clonorchiasis.
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Affiliation(s)
- Pei Liang
- Department of Parasitology, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, 510080, China
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5
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Sangar MC, Bansal S, Avadhani NG. Bimodal targeting of microsomal cytochrome P450s to mitochondria: implications in drug metabolism and toxicity. Expert Opin Drug Metab Toxicol 2010; 6:1231-51. [PMID: 20629582 PMCID: PMC2940958 DOI: 10.1517/17425255.2010.503955] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
IMPORTANCE OF THE FIELD Microsomal CYPs are critical for drug metabolism and toxicity. Recent studies show that these CYPs are also present in the mitochondrial compartment of human and rodent tissues. Mitochondrial CYP1A1 and 2E1 show both overlapping and distinct metabolic activities compared to microsomal forms. Mitochondrial CYP2E1 also induces oxidative stress. The mechanisms of mitochondria targeting of CYPs and their role in drug metabolism and toxicity are important factors to consider while determining the drug dose and in drug development. AREAS COVERED IN THIS REVIEW This review highlights the mechanisms of bimodal targeting of CYP1A1, 2B1, 2E1 and 2D6 to mitochondria and microsomes. The review also discusses differences in structure and function of mitochondrial CYPs. WHAT THE READERS WILL GAIN A comprehensive review of the literature on drug metabolism in the mitochondrial compartment and their potential for inducing mitochondrial dysfunction. TAKE HOME MESSAGE Studies on the biochemistry, pharmacology and pharmacogenetic analysis of CYPs are mostly focused on the molecular forms associated with the microsomal membrane. However, the mitochondrial CYPs in some individuals can represent a substantial part of the tissue pool and contribute in a significant way to drug metabolism, clearance and toxicity.
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Affiliation(s)
- Michelle C Sangar
- University of Pennsylvania, School of Veterinary Medicine, Department of Animal Biology and the Mari Lowe Center for Comparative Oncology, Philadelphia, PA 19104, USA
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Yogev O, Pines O. Dual targeting of mitochondrial proteins: mechanism, regulation and function. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1808:1012-20. [PMID: 20637721 DOI: 10.1016/j.bbamem.2010.07.004] [Citation(s) in RCA: 142] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2010] [Revised: 07/04/2010] [Accepted: 07/07/2010] [Indexed: 01/25/2023]
Abstract
One solution found in evolution to increase the number of cellular functions, without increasing the number of genes, is distribution of single gene products to more than one cellular compartment. It is well documented that in eukaryotic cells, molecules of one protein can be located in several subcellular locations, a phenomenon termed dual targeting, dual localization, or dual distribution. The differently localized proteins are coined in this review "echoforms" indicating repetitious forms of the same protein (echo in Greek denotes repetition) distinctly placed in the cell. This term replaces the term to "isoproteins" or "isoenzymes" which are reserved for proteins with the same activity but different amino acid sequences. Echoforms are identical or nearly identical, even though, as referred to in this review may, in some cases, surprisingly have a totally different function in the different compartments. With regard to mitochondria, our operational definition of dual targeted proteins refers to situations in which one of the echoforms is translocated through/into a mitochondrial membrane. In this review we ask how, when and why mitochondrial proteins are dual localized in the cell. We describe mechanisms of dual targeting of proteins between mitochondria and other compartments of the eukaryotic cell. In particular, we have paid attention to situations in which dual localization is regulated in time, location or function. In addition, we have attempted to provide a broader view concerning the phenomenon of dual localization of proteins by looking at mechanisms that are beyond our simple definition of dual targeting. This article is part of a Special Issue entitled Protein translocation across or insertion into membranes.
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Affiliation(s)
- Ohad Yogev
- Department of Microbiology and Molecular Genetics, IMRIC, Faculty of Medicine, Hebrew University, Jerusalem 91120, Israel
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McKinnon DJ, Brzezowski P, Wilson KE, Gray GR. Mitochondrial and chloroplastic targeting signals of NADP+-dependent isocitrate dehydrogenase. Biochem Cell Biol 2009; 87:963-74. [PMID: 19935882 DOI: 10.1139/o09-066] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2023] Open
Abstract
Many mitochondrial and chloroplast proteins are encoded in the nucleus and subsequently imported into the organelles via active protein transport systems. While usually highly specific, some proteins are dual-targeted to both organelles. In tobacco (Nicotiana tabacum L.), the cDNA encoding the mitochondrial isoform of NADP+-dependent isocitrate dehydrogenase (NADP+-ICDH) contains two translational ATG start sites, suggesting the possibility of tandem targeting signals. In this work, the putative mitochondrial and chloroplastic targeting signals from NADP+-ICDH were fused to a yellow fluorescent protein (YFP) reporter to generate a series of constructs and introduced into tobacco leaves by Agrobacterium-mediated transient transformation. The subsequent sub-cellular locations of the ICDH:YFP fusion proteins were then examined using confocal microscopy. Constructs predicted to be targeted to the chloroplast all localized to the chloroplast. However, this was not the case for all of the constructs that were predicted to be mitochondrial targeted. Although some constructs localized to mitochondria as expected, others appeared to be chloroplast localized. This was attributed to an additional 50 amino acid residues of the mature NADP+-ICDH protein that were present in those constructs, generated from either 'Xanthi' or 'Petit Havana' cultivars of tobacco. The results of this study raise interesting questions regarding the targeting and processing of organellar isoforms of NADP+-ICDH.
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Affiliation(s)
- David J McKinnon
- Department of Plant Sciences, University of Saskatchewan, Saskatoon, SK S7N 5A8, Canada
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Martí MC, Olmos E, Calvete JJ, Díaz I, Barranco-Medina S, Whelan J, Lázaro JJ, Sevilla F, Jiménez A. Mitochondrial and nuclear localization of a novel pea thioredoxin: identification of its mitochondrial target proteins. PLANT PHYSIOLOGY 2009; 150:646-57. [PMID: 19363090 PMCID: PMC2689981 DOI: 10.1104/pp.109.138073] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2009] [Accepted: 04/06/2009] [Indexed: 05/15/2023]
Abstract
Plants contain several genes encoding thioredoxins (Trxs), small proteins involved in the regulation of the activity of many enzymes through dithiol-disulfide exchange. In addition to chloroplastic and cytoplasmic Trx systems, plant mitochondria contain a reduced nicotinamide adenine dinucleotide phosphate-dependent Trx reductase and a specific Trx o, and to date, there have been no reports of a gene encoding a plant nuclear Trx. We report here the presence in pea (Pisum sativum) mitochondria and nuclei of a Trx isoform (PsTrxo1) that seems to belong to the Trx o group, although it differs from this Trx type by its absence of introns in the genomic sequence. Western-blot analysis with isolated mitochondria and nuclei, immunogold labeling, and green fluorescent protein fusion constructs all indicated that PsTrxo1 is present in both cell compartments. Moreover, the identification by tandem mass spectrometry of the native mitochondrial Trx after gel filtration using the fast-protein liquid chromatography system of highly purified mitochondria and the in vitro uptake assay into isolated mitochondria also corroborated a mitochondrial location for this protein. The recombinant PsTrxo1 protein has been shown to be reduced more effectively by the Saccharomyces cerevisiae mitochondrial Trx reductase Trr2 than by the wheat (Triticum aestivum) cytoplasmic reduced nicotinamide adenine dinucleotide phosphate-dependent Trx reductase. PsTrxo1 was able to activate alternative oxidase, and it was shown to interact with a number of mitochondrial proteins, including peroxiredoxin and enzymes mainly involved in the photorespiratory process.
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Affiliation(s)
- María C Martí
- Department of Stress Biology and Plant Pathology, Centro de Edafología y Biología Aplicada del Segura, Consejo Superior de Investigaciones Científicas, E-30100 Murcia, Spain
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Dinur-Mills M, Tal M, Pines O. Dual targeted mitochondrial proteins are characterized by lower MTS parameters and total net charge. PLoS One 2008; 3:e2161. [PMID: 18478128 PMCID: PMC2367453 DOI: 10.1371/journal.pone.0002161] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2008] [Accepted: 03/20/2008] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND In eukaryotic cells, identical proteins can be located in different subcellular compartments (termed dual-targeted proteins). METHODOLOGY/PRINCIPAL FINDINGS We divided a reference set of mitochondrial proteins (published single gene studies) into two groups: i) Dual targeted mitochondrial proteins and ii) Exclusive mitochondrial proteins. Mitochondrial proteins were considered dual-targeted if they were also found or predicted to be localized to the cytosol, the nucleus, the endoplasmic reticulum (ER) or the peroxisome. We found that dual localized mitochondrial proteins have i) A weaker mitochondrial targeting sequence (MitoProtII score, hydrophobic moment and number of basic residues) and ii) a lower whole-protein net charge, when compared to exclusive mitochondrial proteins. We have also generated an annotation list of dual-targeted proteins within the predicted yeast mitochondrial proteome. This considerably large group of dual-localized proteins comprises approximately one quarter of the predicted mitochondrial proteome. We supported this prediction by experimental verification of a subgroup of the predicted dual targeted proteins. CONCLUSIONS/SIGNIFICANCE Taken together, these results establish dual targeting as a widely abundant phenomenon that should affect our concepts of gene expression and protein function. Possible relationships between the MTS/mature sequence traits and protein dual targeting are discussed.
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Affiliation(s)
- Maya Dinur-Mills
- Department of Molecular Biology, Hebrew University Medical School, Jerusalem, Israel
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Regev-Rudzki N, Pines O. Eclipsed distribution: A phenomenon of dual targeting of protein and its significance. Bioessays 2007; 29:772-82. [PMID: 17621655 DOI: 10.1002/bies.20609] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
One of the surprises from genome sequencing projects is the apparently small number of predicted genes in different eukaryotic cells, particularly human. One possible reason for this 'shortage' of genes is multiple distribution of proteins; a single protein is targeted to more than one subcellular compartment and consequently participates in different biochemical pathways and might have completely different functions. Indeed, in recent years, there have been reports on proteins that were found to be localized in cellular compartments other than those initially attributed to them. Furthermore, the phenomenon of highly uneven isoprotein distribution was recently observed and termed 'eclipsed distribution'. In these cases, the amount of one of the isoproteins, in one of the locations, is significantly minute and its detection by standard biochemical and visualization methods is masked by the presence of the dominant isoprotein. In fact, the minute amounts of eclipsed proteins can be essential. Since detecting eclipsed distribution is difficult, we assume that this phenomenon is probably more common than currently recorded. Hence, developing methods for localization and functional detection of eclipsed proteins is a challenge in cell biology research. Finally, eclipsed distribution may lead to cellular pathologies as has been suggested to occur in human disorders such as Prion diseases and Alzheimer. This review provides a short description of the eclipsed distribution phenomenon followed by an overview of protein distribution mechanisms, examples of eclipsed distribution and experimental approaches for revealing these elusive proteins.
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Affiliation(s)
- Neta Regev-Rudzki
- Molecular Biology, Medical School, Hebrew University of Jerusalem, Jerusalem, Israel
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11
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Karniely S, Pines O. Single translation--dual destination: mechanisms of dual protein targeting in eukaryotes. EMBO Rep 2005; 6:420-5. [PMID: 15864293 PMCID: PMC1299304 DOI: 10.1038/sj.embor.7400394] [Citation(s) in RCA: 140] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2005] [Accepted: 02/23/2005] [Indexed: 11/09/2022] Open
Abstract
It is well documented that single eukaryotic genes can give rise to proteins that are localized to several subcellular locations. This is achieved at the level of transcription, splicing and translation, and results in two or more translation products that either harbour or lack specific targeting signals. Nevertheless, the possibility of dual targeting of a single translation product has recently emerged. Here, we review cases of such dual targeting with emphasis on the mechanisms through which these phenomena occur. Proteins that harbour one signal, two separate signals or an overlapping ambiguous signal may follow dual distribution in the cell. The mechanism of dual targeting is driven by the competition or promiscuity of various molecular events. Protein folding, post-translational modification and protein-protein interaction are key players in this phenomenon.
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Affiliation(s)
- Sharon Karniely
- Department of Molecular Biology, Hebrew University Medical School, Jerusalem 91120, Israel
| | - Ophry Pines
- Department of Molecular Biology, Hebrew University Medical School, Jerusalem 91120, Israel
- Tel: +972 2 675 7203; Fax: +972 2 675 7260;
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12
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Biswas TK, Getz GS. Requirement of different mitochondrial targeting sequences of the yeast mitochondrial transcription factor Mtf1p when synthesized in alternative translation systems. Biochem J 2005; 383:383-91. [PMID: 15257659 PMCID: PMC1134080 DOI: 10.1042/bj20040691] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Mitochondrial (mt) translocation of the nuclearly encoded mt transcription factor Mtf1p appears to occur independent of a cleavable presequence, mt receptor, mt membrane potential or ATP [Biswas and Getz (2002) J. Biol. Chem. 277, 45704-45714]. To understand further the import strategy of Mtf1p, we investigated the import of the wild-type and N-terminal-truncated Mtf1p mutants synthesized in two different in vitro translation systems. These Mtf1p derivatives were generated either in the RRL (rabbit reticulocyte lysate) or in the WGE (wheat germ extract) translation system. Under the in vitro import conditions, the RRL-synthesized full-length Mtf1p but not the N-terminal-truncated Mtf1p product was efficiently imported into mitochondria, suggesting that the N-terminal sequence is important for its import. On the other hand, when these Mtf1p products were generated in the WGE system, surprisingly, the N-terminal-truncated products, but not the full-length protein, were effectively translocated into mitochondria. Despite these differences between the translation systems, in both cases, import occurs at a low temperature and has no requirement for a trypsin-sensitive mt receptor, mt membrane potential or ATP hydrolysis. Together, these observations suggest that, in the presence of certain cytoplasmic factors (derived from either RRL or WGE), Mtf1p is capable of using alternative import signals present in different regions of the protein. This appears to be the first example of usage of different targeting sequences for the transport of a single mt protein into the mt matrix.
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Affiliation(s)
- Tapan K Biswas
- Department of Pathology, University of Chicago, 5841 South Maryland Avenue, Chicago, IL 60637, USA.
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Gu Y, Gordon DM, Amutha B, Pain D. A GTP:AMP phosphotransferase, Adk2p, in Saccharomyces cerevisiae. Role of the C terminus in protein folding/stabilization, thermal tolerance, and enzymatic activity. J Biol Chem 2005; 280:18604-9. [PMID: 15753074 DOI: 10.1074/jbc.m500847200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Adenylate kinases participate in maintaining the homeostasis of cellular nucleotides. Depending on the yeast strains, the GTP:AMP phosphotransferase is encoded by the nuclear gene ADK2 with or without a single base pair deletion/insertion near the 3' end of the open reading frame, and the corresponding protein exists as either Adk2p (short) or Adk2p (long) in the mitochondrial matrix. These two forms are identical except that the three C-terminal residues of Adk2p (short) are changed in Adk2p (long), and the latter contains an additional nine amino acids at the C terminus of the protein. The short form of Adk2p has so far been considered to be inactive (Schricker, R., Magdolen, V., Strobel, G., Bogengruber, E., Breitenbach, M., and Bandlow, W. (1995) J. Biol. Chem. 270, 31103-31110). Using purified proteins, we show that at the physiological temperature for yeast growth (30 degrees C), both short and long forms of Adk2p are enzymatically active. However, in contrast to the short form, Adk2p (long) is quite resistant to thermal inactivation, urea denaturation, and degradation by trypsin. Unfolding of the long form by high concentrations of urea greatly stimulated its import into isolated mitochondria. Using an integration-based gene-swapping approach, we found that regardless of the yeast strains used, the steady state levels of endogenous Adk2p (long) in mitochondria were 5-10-fold lower compared with those of Adk2p (short). Together, these results suggest that the modified C-terminal domain in Adk2p (long) is not essential for enzyme activity, but it contributes to and strengthens protein folding and/or stability and is particularly important for maintaining enzyme activity under stress conditions.
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Affiliation(s)
- Yajuan Gu
- Department of Pharmacology and Physiology, UMDNJ-New Jersey Medical School, Newark, New Jersey 07103-1709, USA
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14
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Villa H, Pérez-Pertejo Y, García-Estrada C, Reguera RM, Requena JM, Tekwani BL, Balaña-Fouce R, Ordóñez D. Molecular and functional characterization of adenylate kinase 2 gene from Leishmania donovani. ACTA ACUST UNITED AC 2003; 270:4339-47. [PMID: 14622299 DOI: 10.1046/j.1432-1033.2003.03826.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
ATP-regenerating enzymes may have an important role in maintaining ATP levels in mitochondria-like kinetoplast organelle and glycosomes in parasitic protozoa. Adenylate kinase (AK) (ATP:AMP phosphotransferase) catalyses the reversible transfer of the gamma-phosphate group from ATP to AMP, releasing two molecules of ADP. This study describes cloning and functional characterization of the gene encoding AK2 from a genomic library of Leishmania donovani and also its expression in leishmania promastigote cultures. AK2 was localized on an approximately 1.9-Mb chromosomal band as a single copy gene. L. donovani AK2 gene is expressed as a single 1.9-kb mRNA transcript that is developmentally regulated and accumulated during the early log phase. The overexpression of L. donovani AKgene in Escherichia coli yielded a 26-kDa polypeptide that could be refolded to a functional protein with AK activity. The recombinant protein was purified to apparent homogeneity. Kinetic analysis of purified L. donovani AK showed hyperbolic behaviour for both ATP and AMP, with Km values of 104 and 74 microM, respectively. The maximum enzyme activity (Vmax) was 0.18 micromol.min(-1).mg(-1) protein. P1,P5-(bis adenosine)-5'-pentaphosphate (Ap5A), the specific inhibitor of AK, competitively inhibited activity of the recombinant enzymes with estimated Ki values of 190 nM and 160 nM for ATP and AMP, respectively. Ap5A also inhibited the growth of L. donovani promastigotes in vitro which could be only partially reversed by the addition of ADP. Thus, presence of a highly regulated AK2, which may have role in maintenance of ADP/ATP levels in L. donovani, has been demonstrated.
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Affiliation(s)
- Héctor Villa
- Departamento de Farmacología y Toxicología (INTOXCAL), Facultad de Veterinaria, Universidad de León, Spain
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15
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Biswas TK, Getz GS. Import of yeast mitochondrial transcription factor (Mtf1p) via a nonconventional pathway. J Biol Chem 2002; 277:45704-14. [PMID: 12270918 DOI: 10.1074/jbc.m202565200] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The yeast mitochondrial (mt) transcription factor Mtf1p is imported into the mitochondria from the cytoplasm without a conventional mt-targeting presequence. To understand its import the mt translocation of wild type and mutant Mtf1p constructs was investigated in vitro under various assay conditions. We report here that Mtf1p, unlike most mt matrix proteins hitherto studied, is translocated into the mitochondria independent of membrane potential, ATP hydrolysis, and membrane receptor. This unusual import of Mtf1p was also observed on ice (3 degrees C). Sub-mitochondrial fractionation demonstrated that Mtf1p was translocated in vitro to one or more of the same mt sites as the endogenous protein that includes the matrix. To identify the mt-targeting sequence of Mtf1p, various N-terminal, C-terminal, or internally deleted Mtf1p derivatives were generated. The full-length and C-terminal deletions but not the N-terminal truncated Mtf1p were imported into mitochondria, indicating the importance of its N-terminal sequence for mt targeting. However, the internal deletion of Mtf1p revealed that the first 150-amino acid N-terminal sequence alone was not sufficient for mt targeting of Mtf1p, suggesting that an extended rather than a short N-terminal sequence is required for import. We favor a model in which Mtf1p adopts an import-competent conformation during translation. Consistent with this model are three findings: most of the protein sequence appears to be required for optimal import, urea denaturation eliminates its import competence, and the import-competent form of the protein is more resistant to tryptic hydrolysis than is the denatured protein. This represents a novel mechanism for mitochondrial protein import.
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Affiliation(s)
- Tapan K Biswas
- Department of Pathology, University of Chicago, Chicago, Illinois 60637, USA.
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16
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Schricker R, Angermayr M, Strobel G, Klinke S, Korber D, Bandlow W. Redundant mitochondrial targeting signals in yeast adenylate kinase. J Biol Chem 2002; 277:28757-64. [PMID: 12045196 DOI: 10.1074/jbc.m201561200] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Yeast adenylate kinase (Aky2p, Adk1p) occurs simultaneously in cytoplasm and mitochondrial intermembrane space. It has no cleavable mitochondrial targeting sequence, and the signal for mitochondrial import and submitochondrial sorting is largely unknown. The extreme N terminus of Aky2p is able to direct cytoplasmic passengers to mitochondria. However, an Aky2 mutant lacking this sequence is imported with about the same efficiency as the wild type. To identify possible import-relevant information in the interior, parts of Aky2p were exchanged by homologous in vitro recombination for the respective segments of the purely cytoplasmic isozyme, Ura6p. Import studies revealed an internal region of about 40 amino acids, which was sufficient to direct the chimera to mitochondria but not for correct submitochondrial sorting. The respective Ura6p hybrid was arrested in the mitochondrial membrane at a position where it was inaccessible to protease but was released by alkaline extraction, suggesting that it had entered an import channel and passed the initial steps of recognition and uptake. Site-specific mutations within the presumptive address-specifying segment identified the amphipathic helix 5. A Ura6 mutant protein in which helix 5 had been replaced with the respective sequence from Aky2p was imported, and this address sequence cooperates with the N terminus in the respective double mutant in a synergistic fashion.
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Affiliation(s)
- Roland Schricker
- Department Biologie I, Bereich Genetik, Ludwig Maximilians Universität München, Maria-Ward-Strasse 1a, D-80638 Munich, Germany
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17
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Strobel G, Zollner A, Angermayr M, Bandlow W. Competition of spontaneous protein folding and mitochondrial import causes dual subcellular location of major adenylate kinase. Mol Biol Cell 2002; 13:1439-48. [PMID: 12006643 PMCID: PMC111117 DOI: 10.1091/mbc.01-08-0396] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Sorting of cytoplasmically synthesized proteins to their target compartments usually is highly efficient so that cytoplasmic precursor pools are negligible and a particular gene product occurs at one subcellular location only. Yeast major adenylate kinase (Adk1p/Aky2p) is one prominent exception to this rule. In contrast to most mitochondrial proteins, only a minor fraction (6-8%) is taken up into the mitochondrial intermembrane space, whereas the bulk of the protein remains in the cytosol in sequence-identical form. We demonstrate that Adk1p/Aky2p uses a novel mechanism for subcellular partitioning between cytoplasm and mitochondria, which is based on competition between spontaneous protein folding and mitochondrial targeting and import. Folding is spontaneous and rapid and can dispense with molecular chaperons. After denaturation, enzymatic activity of Adk1p/Aky2p returns within a few minutes and, once folded, the protein is thermally and proteolytically very stable. In an uncoupled cell-free organellar import system, uptake of Adk1p/Aky2p is negligible, but can be improved by previous chaotropic denaturation. Import ensues independently of Hsp70 or membrane potential. Thus, nascent Adk1p/Aky2p has two options: either it is synthesized to completion and folds into an enzymatically active import-incompetent conformation that remains in the cytosol; or, during synthesis and before commencement of significant tertiary structure formation, it reaches a mitochondrial surface receptor and is internalized.
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Affiliation(s)
- Gertrud Strobel
- Institut für Genetik und Mikrobiologie der Universität München, D-80638 Munich, Germany
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18
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Emanuelsson O, von Heijne G, Schneider G. Analysis and prediction of mitochondrial targeting peptides. Methods Cell Biol 2002; 65:175-87. [PMID: 11381593 DOI: 10.1016/s0091-679x(01)65011-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- O Emanuelsson
- Stockholm Bioinformatics Center, Stockholm University, S-10691 Stockholm, Sweden
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19
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Krokan HE, Otterlei M, Nilsen H, Kavli B, Skorpen F, Andersen S, Skjelbred C, Akbari M, Aas PA, Slupphaug G. Properties and functions of human uracil-DNA glycosylase from the UNG gene. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 2002; 68:365-86. [PMID: 11554311 DOI: 10.1016/s0079-6603(01)68112-1] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The human UNG-gene at position 12q24.1 encodes nuclear (UNG2) and mitochondrial (UNG1) forms of uracil-DNA glycosylase using differentially regulated promoters, PA and PB, and alternative splicing to produce two proteins with unique N-terminal sorting sequences. PCNA and RPA co-localize with UNG2 in replication foci and interact with N-terminal sequences in UNG2. Mitochondrial UNG1 is processed to shorter forms by mitochondrial processing peptidase (MPP) and an unidentified mitochondrial protease. The common core catalytic domain in UNG1 and UNG2 contains a conserved DNA binding groove and a tight-fitting uracil-binding pocket that binds uracil only when the uracil-containing nucleotide is flipped out. Certain single amino acid substitutions in the active site of the enzyme generate DNA glycosylases that remove either thymine or cytosine. These enzymes induce cytotoxic and mutagenic abasic (AP) sites in the E. coli chromosome and were used to examine biological consequences of AP sites. It has been assumed that a major role of the UNG gene product(s) is to repair mutagenic U:G mispairs caused by cytosine deamination. However, one major role of UNG2 is to remove misincorporated dUMP residues. Thus, knockout mice deficient in Ung activity (Ung-/- mice) have only small increases in GC-->AT transition mutations, but Ung-/- cells are deficient in removal of misincorporated dUMP and accumulate approximately 2000 uracil residues per cell. We propose that BER is important both in the prevention of cancer and for preserving the integrity of germ cell DNA during evolution.
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Affiliation(s)
- H E Krokan
- Institute of Cancer Research and Molecular Biology, Norwegian University of Science and Technology, N-7489 Trondheim, Norway
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20
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Angermayr M, Strobel G, Zollner A, Korber D, Bandlow W. Two parameters improve efficiency of mitochondrial uptake of adenylate kinase: decreased folding velocity and increased propensity of N-terminal alpha-helix formation. FEBS Lett 2001; 508:427-32. [PMID: 11728466 DOI: 10.1016/s0014-5793(01)03122-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The long isoform of eukaryotic adenylate kinase has a dual subcellular location in the cytoplasm and in the mitochondrial intermembrane space. Protein sequences and modifications are identical in both locations. In yeast, the bulk of the major form of adenylate kinase (Aky2p) is in the cytoplasm and, in the steady state, only 5-8% is sorted to the mitochondrial intermembrane space. Since the reasons for exclusion from mitochondrial import are unclear, we have constructed aky2 mutants with elevated mitochondrial uptake efficiency of Aky2p in vivo and in vitro. We have analyzed the effect of the mutations on secondary structure prediction in silico and have tested folding velocity and folding stability. One type of mutants displayed decreased proteolytic stability and retarded renaturation kinetics after chaotropic denaturation implying that deterioration of folding leads to prolonged presentation of target information to mitochondrial import receptors, thereby effecting improved uptake. In a second type of mutants, increased import efficiency was correlated with an increased probability of formation of an alpha-helix with increased amphipathic moment at the N-terminus suggesting that targeting interactions with mitochondrial import receptors had been improved at the level of binding affinity.
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Affiliation(s)
- M Angermayr
- Institut für Genetik und Mikrobiologie der Universität München, Maria-Ward-Strasse 1a, D-80638, Munich, Germany
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21
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Knox C, Sass E, Neupert W, Pines O. Import into mitochondria, folding and retrograde movement of fumarase in yeast. J Biol Chem 1998; 273:25587-93. [PMID: 9748223 DOI: 10.1074/jbc.273.40.25587] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A single translation product of the FUM1 gene encoding fumarase is distributed between the cytosol and mitochondria of Saccharomyces cerevisiae. All fumarase translation products are targeted and processed in mitochondria before distribution. Here we show that targeting of fumarase is coupled to translation and initially involves insertion of the protein across the mitochondrial membranes and processing by the matrix protease. Rapid folding of fumarase may determine its requirement for coupling of its translocation with translation and unique route of distribution. The amino termini of most fumarase molecules are translocated across the mitochondrial membranes and processed. Unlike the in vivo situation where these molecules are released into the cytosol, in vitro they remain externally attached to the mitochondria, thereby positioned for release from the organelle. Our model suggests that fumarase displays a unique mechanism of targeting and distribution, which occurs cotranslationally and involves folding and retrograde movement of the processed protein back through the translocation pore.
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Affiliation(s)
- C Knox
- Department of Molecular Biology, Hebrew University Medical School, Jerusalem 91120, Israel
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