1
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Kizmaz B, Nutz A, Egeler A, Herrmann JM. Protein insertion into the inner membrane of mitochondria: routes and mechanisms. FEBS Open Bio 2024; 14:1627-1639. [PMID: 38664330 PMCID: PMC11452304 DOI: 10.1002/2211-5463.13806] [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: 02/23/2024] [Revised: 03/28/2024] [Accepted: 04/11/2024] [Indexed: 10/06/2024] Open
Abstract
The inner membrane of mitochondria contains hundreds of different integral membrane proteins. These proteins transport molecules into and out of the matrix, they carry out multifold catalytic reactions and they promote the biogenesis or degradation of mitochondrial constituents. Most inner membrane proteins are encoded by nuclear genes and synthesized in the cytosol from where they are imported into mitochondria by translocases in the outer and inner membrane. Three different import routes direct proteins into the inner membrane and allow them to acquire their appropriate membrane topology. First, mitochondrial import intermediates can be arrested at the level of the TIM23 inner membrane translocase by a stop-transfer sequence to reach the inner membrane by lateral insertion. Second, proteins can be fully translocated through the TIM23 complex into the matrix from where they insert into the inner membrane in an export-like reaction. Carriers and other polytopic membrane proteins embark on a third insertion pathway: these hydrophobic proteins employ the specialized TIM22 translocase to insert from the intermembrane space (IMS) into the inner membrane. This review article describes these three targeting routes and provides an overview of the machinery that promotes the topogenesis of mitochondrial inner membrane proteins.
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Affiliation(s)
- Büsra Kizmaz
- Cell BiologyUniversity of Kaiserslautern, RPTUGermany
| | - Annika Nutz
- Cell BiologyUniversity of Kaiserslautern, RPTUGermany
| | - Annika Egeler
- Cell BiologyUniversity of Kaiserslautern, RPTUGermany
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2
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Amberg KL, Hao L, Cranz-Mileva S, Zaratiegui M. Proteasome regulation of petite-negativity in fission yeast. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.09.593392. [PMID: 38798546 PMCID: PMC11118472 DOI: 10.1101/2024.05.09.593392] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2024]
Abstract
Mitochondria carry out essential functions in eukaryotic cells. The mitochondrial genome encodes factors critical to support oxidative phosphorylation and mitochondrial protein import necessary for these functions. However, organisms like budding yeast can readily lose their mitochondrial genome, yielding respiration-deficient petite mutants. The fission yeast Schizosaccharomyces pombe is petite-negative, but some nuclear mutations enable the loss of its mitochondrial genome. Here, we characterize the classical petite-positive mutation ptp1-1 as a loss of function allele of the proteasome 19S regulatory subunit component mts4/rpn1, involved in the Ubiquitin-dependent degradation pathway. The mutation results in an altered oxidative stress response, with increased levels of oxidized glutathione, and increased levels of mitochondrial and cytoplasmic chaperones. We propose that Ubiquitin-proteasome regulation of chaperones involved in the Unfolded Protein Response and mitochondrial protein import underlies petite-negativity in fission yeast.
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Affiliation(s)
- Katie Lin Amberg
- Department of Molecular Biology and Biochemistry, Division of Life Sciences Rutgers, the State University of new Jersey
| | - Lyrica Hao
- Department of Molecular Biology and Biochemistry, Division of Life Sciences Rutgers, the State University of new Jersey
| | - Susanne Cranz-Mileva
- Department of Molecular Biology and Biochemistry, Division of Life Sciences Rutgers, the State University of new Jersey
| | - Mikel Zaratiegui
- Department of Molecular Biology and Biochemistry, Division of Life Sciences Rutgers, the State University of new Jersey
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3
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Panessa GM, Tassoni-Tsuchida E, Pires MR, Felix RR, Jekabson R, de Souza-Pinto NC, da Cunha FM, Brandman O, Cussiol JRR. Opi1-mediated transcriptional modulation orchestrates genotoxic stress response in budding yeast. Genetics 2023; 225:iyad130. [PMID: 37440469 PMCID: PMC10691878 DOI: 10.1093/genetics/iyad130] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2023] [Revised: 06/28/2023] [Accepted: 07/03/2023] [Indexed: 07/15/2023] Open
Abstract
In budding yeast, the transcriptional repressor Opi1 regulates phospholipid biosynthesis by repressing expression of genes containing inositol-sensitive upstream activation sequences. Upon genotoxic stress, cells activate the DNA damage response to coordinate a complex network of signaling pathways aimed at preserving genomic integrity. Here, we reveal that Opi1 is important to modulate transcription in response to genotoxic stress. We find that cells lacking Opi1 exhibit hypersensitivity to genotoxins, along with a delayed G1-to-S-phase transition and decreased gamma-H2A levels. Transcriptome analysis using RNA sequencing reveals that Opi1 plays a central role in modulating essential biological processes during methyl methanesulfonate (MMS)-associated stress, including repression of phospholipid biosynthesis and transduction of mating signaling. Moreover, Opi1 induces sulfate assimilation and amino acid metabolic processes, such as arginine and histidine biosynthesis and glycine catabolism. Furthermore, we observe increased mitochondrial DNA instability in opi1Δ cells upon MMS treatment. Notably, we show that constitutive activation of the transcription factor Ino2-Ino4 is responsible for genotoxin sensitivity in Opi1-deficient cells, and the production of inositol pyrophosphates by Kcs1 counteracts Opi1 function specifically during MMS-induced stress. Overall, our findings highlight Opi1 as a critical sensor of genotoxic stress in budding yeast, orchestrating gene expression to facilitate appropriate stress responses.
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Affiliation(s)
- Giovanna Marques Panessa
- Departamento de Bioquímica, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, SP 04023-900, Brazil
| | - Eduardo Tassoni-Tsuchida
- Department of Biology, Stanford University, Stanford, CA 94305, USA
- Department of Biochemistry, Stanford University, Stanford, CA 94305, USA
| | - Marina Rodrigues Pires
- Departamento de Bioquímica, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, SP 04023-900, Brazil
| | - Rodrigo Rodrigues Felix
- Departamento de Bioquímica, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, SP 04023-900, Brazil
| | - Rafaella Jekabson
- Departamento de Bioquímica, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, SP 04023-900, Brazil
| | | | - Fernanda Marques da Cunha
- Departamento de Bioquímica, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, SP 04023-900, Brazil
| | - Onn Brandman
- Department of Biochemistry, Stanford University, Stanford, CA 94305, USA
| | - José Renato Rosa Cussiol
- Departamento de Bioquímica, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, SP 04023-900, Brazil
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4
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Taubenschmid-Stowers J, Orthofer M, Laemmerer A, Krauditsch C, Rózsová M, Studer C, Lötsch D, Gojo J, Gabler L, Dyczynski M, Efferth T, Hagelkruys A, Widhalm G, Peyrl A, Spiegl-Kreinecker S, Hoepfner D, Bian S, Berger W, Knoblich JA, Elling U, Horn M, Penninger JM. A whole-genome scan for Artemisinin cytotoxicity reveals a novel therapy for human brain tumors. EMBO Mol Med 2023; 15:e16959. [PMID: 36740985 DOI: 10.15252/emmm.202216959] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Revised: 12/14/2022] [Accepted: 12/22/2022] [Indexed: 02/07/2023] Open
Abstract
The natural compound Artemisinin is the most widely used antimalarial drug worldwide. Based on its cytotoxicity, it is also used for anticancer therapy. Artemisinin and its derivates are endoperoxides that damage proteins in eukaryotic cells; their definite mechanism of action and host cell targets, however, have remained largely elusive. Using yeast and haploid stem cell screening, we demonstrate that a single cellular pathway, namely porphyrin (heme) biosynthesis, is required for the cytotoxicity of Artemisinins. Genetic or pharmacological modulation of porphyrin production is sufficient to alter its cytotoxicity in eukaryotic cells. Using multiple model systems of human brain tumor development, such as cerebral glioblastoma organoids, and patient-derived tumor spheroids, we sensitize cancer cells to dihydroartemisinin using the clinically approved porphyrin enhancer and surgical fluorescence marker 5-aminolevulinic acid, 5-ALA. A combination treatment of Artemisinins and 5-ALA markedly and specifically killed brain tumor cells in all model systems tested, including orthotopic patient-derived xenografts in vivo. These data uncover the critical molecular pathway for Artemisinin cytotoxicity and a sensitization strategy to treat different brain tumors, including drug-resistant human glioblastomas.
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Affiliation(s)
- Jasmin Taubenschmid-Stowers
- IMBA, Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna Biocenter, Vienna, Austria
| | | | - Anna Laemmerer
- Center for Cancer Research and Comprehensive Cancer Center-Central Nervous System Tumor Unit, Medical University of Vienna, Vienna, Austria
- Department of Pediatrics and Adolescent Medicine and Comprehensive Center for Pediatrics, Medical University of Vienna, Vienna, Austria
| | - Christian Krauditsch
- IMBA, Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna Biocenter, Vienna, Austria
| | | | | | - Daniela Lötsch
- Center for Cancer Research and Comprehensive Cancer Center-Central Nervous System Tumor Unit, Medical University of Vienna, Vienna, Austria
- Department of Neurosurgery, Medical University Vienna, Vienna, Austria
| | - Johannes Gojo
- Department of Pediatrics and Adolescent Medicine and Comprehensive Center for Pediatrics, Medical University of Vienna, Vienna, Austria
| | - Lisa Gabler
- Center for Cancer Research and Comprehensive Cancer Center-Central Nervous System Tumor Unit, Medical University of Vienna, Vienna, Austria
- Department of Pediatric Oncology, Dana-Farber Boston Children's Cancer and Blood Disorders Center, Boston, MA, USA
- Broad Institute of Harvard and MIT, Cambridge, MA, USA
| | | | - Thomas Efferth
- Department of Pharmaceutical Biology, Institute of Pharmaceutical and Biomedical Sciences, Johannes Gutenberg University, Mainz, Germany
| | - Astrid Hagelkruys
- IMBA, Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna Biocenter, Vienna, Austria
| | - Georg Widhalm
- Department of Neurosurgery, Medical University Vienna, Vienna, Austria
| | - Andreas Peyrl
- Department of Pediatrics and Adolescent Medicine and Comprehensive Center for Pediatrics, Medical University of Vienna, Vienna, Austria
| | - Sabine Spiegl-Kreinecker
- Department of Neurosurgery, Kepler University Hospital GmbH, Johannes Kepler University Linz, Linz, Austria
| | | | - Shan Bian
- IMBA, Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna Biocenter, Vienna, Austria
- Institute for Regenerative Medicine, Shanghai East Hospital, School of Life Sciences and Technology, Tongji University, Shanghai, China
- Frontier Science Center for Stem Cell Research, Tongji University, Shanghai, China
| | - Walter Berger
- Center for Cancer Research and Comprehensive Cancer Center-Central Nervous System Tumor Unit, Medical University of Vienna, Vienna, Austria
| | - Juergen A Knoblich
- IMBA, Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna Biocenter, Vienna, Austria
| | - Ulrich Elling
- IMBA, Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna Biocenter, Vienna, Austria
| | | | - Josef M Penninger
- IMBA, Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna Biocenter, Vienna, Austria
- Department of Medical Genetics, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada
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5
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Song J, Steidle L, Steymans I, Singh J, Sanner A, Böttinger L, Winter D, Becker T. The mitochondrial Hsp70 controls the assembly of the F 1F O-ATP synthase. Nat Commun 2023; 14:39. [PMID: 36596815 PMCID: PMC9810599 DOI: 10.1038/s41467-022-35720-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2022] [Accepted: 12/20/2022] [Indexed: 01/04/2023] Open
Abstract
The mitochondrial F1FO-ATP synthase produces the bulk of cellular ATP. The soluble F1 domain contains the catalytic head that is linked via the central stalk and the peripheral stalk to the membrane embedded rotor of the FO domain. The assembly of the F1 domain and its linkage to the peripheral stalk is poorly understood. Here we show a dual function of the mitochondrial Hsp70 (mtHsp70) in the formation of the ATP synthase. First, it cooperates with the assembly factors Atp11 and Atp12 to form the F1 domain of the ATP synthase. Second, the chaperone transfers Atp5 into the assembly line to link the catalytic head with the peripheral stalk. Inactivation of mtHsp70 leads to integration of assembly-defective Atp5 variants into the mature complex, reflecting a quality control function of the chaperone. Thus, mtHsp70 acts as an assembly and quality control factor in the biogenesis of the F1FO-ATP synthase.
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Affiliation(s)
- Jiyao Song
- Institute for Biochemistry and Molecular Biology, Faculty of Medicine, University of Bonn, Bonn, Germany.,Institute for Biochemistry and Molecular Biology, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Liesa Steidle
- Institute for Biochemistry and Molecular Biology, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Isabelle Steymans
- Institute for Biochemistry and Molecular Biology, Faculty of Medicine, University of Bonn, Bonn, Germany
| | - Jasjot Singh
- Institute for Biochemistry and Molecular Biology, Faculty of Medicine, University of Bonn, Bonn, Germany
| | - Anne Sanner
- Institute for Biochemistry and Molecular Biology, Faculty of Medicine, University of Bonn, Bonn, Germany
| | - Lena Böttinger
- Institute for Biochemistry and Molecular Biology, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Dominic Winter
- Institute for Biochemistry and Molecular Biology, Faculty of Medicine, University of Bonn, Bonn, Germany
| | - Thomas Becker
- Institute for Biochemistry and Molecular Biology, Faculty of Medicine, University of Bonn, Bonn, Germany.
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6
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Chen P, Michel AH, Zhang J. Transposon insertional mutagenesis of diverse yeast strains suggests coordinated gene essentiality polymorphisms. Nat Commun 2022; 13:1490. [PMID: 35314699 PMCID: PMC8938418 DOI: 10.1038/s41467-022-29228-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Accepted: 03/01/2022] [Indexed: 12/18/2022] Open
Abstract
Due to epistasis, the same mutation can have drastically different phenotypic consequences in different individuals. This phenomenon is pertinent to precision medicine as well as antimicrobial drug development, but its general characteristics are largely unknown. We approach this question by genome-wide assessment of gene essentiality polymorphism in 16 Saccharomyces cerevisiae strains using transposon insertional mutagenesis. Essentiality polymorphism is observed for 9.8% of genes, most of which have had repeated essentiality switches in evolution. Genes exhibiting essentiality polymorphism lean toward having intermediate numbers of genetic and protein interactions. Gene essentiality changes tend to occur concordantly among components of the same protein complex or metabolic pathway and among a group of over 100 mitochondrial proteins, revealing molecular machines or functional modules as units of gene essentiality variation. Most essential genes tolerate transposon insertions consistently among strains in one or more coding segments, delineating nonessential regions within essential genes.
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Affiliation(s)
- Piaopiao Chen
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Agnès H Michel
- Department of Biochemistry, University of Oxford, Oxford, OX1 3QU, UK
| | - Jianzhi Zhang
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, 48109, USA.
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7
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Whole-Genome Transformation of Yeast Promotes Rare Host Mutations with a Single Causative SNP Enhancing Acetic Acid Tolerance. Mol Cell Biol 2022; 42:e0056021. [PMID: 35311587 PMCID: PMC9022575 DOI: 10.1128/mcb.00560-21] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Whole-genome (WG) transformation (WGT) with DNA from the same or another species has been used to obtain strains with superior traits. Very few examples have been reported in eukaryotes—most apparently involving integration of large fragments of foreign DNA into the host genome. We show that WGT of a haploid acetic acid-sensitive Saccharomyces cerevisiae strain with DNA from a tolerant strain, but not from nontolerant strains, generated many tolerant transformants, some of which were stable upon subculturing under nonselective conditions. The most tolerant stable transformant contained no foreign DNA but only seven nonsynonymous single nucleotide polymorphisms (SNPs), of which none was present in the donor genome. The SNF4 mutation c.[805G→T], generating Snf4E269*, was the main causative SNP. Allele exchange of SNF4E269* or snf4Δ in industrial strains with unrelated genetic backgrounds enhanced acetic acid tolerance during fermentation under industrially relevant conditions. Our work reveals a surprisingly small number of mutations introduced by WGT, which do not bear any sequence relatedness to the genomic DNA (gDNA) of the donor organism, including the causative mutation. Spontaneous mutagenesis under protection of a transient donor gDNA fragment, maintained as extrachromosomal circular DNA (eccDNA), might provide an explanation. Support for this mechanism was obtained by transformation with genomic DNA of a yeast strain containing NatMX and selection on medium with nourseothricin. Seven transformants were obtained that gradually lost their nourseothricin resistance upon subculturing in nonselective medium. Our work shows that WGT is an efficient strategy for rapidly generating and identifying superior alleles capable of improving selectable traits of interest in industrial yeast strains.
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8
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Stenger M, Le DT, Klecker T, Westermann B. Systematic analysis of nuclear gene function in respiratory growth and expression of the mitochondrial genome in S. cerevisiae. MICROBIAL CELL 2020; 7:234-249. [PMID: 32904421 PMCID: PMC7453639 DOI: 10.15698/mic2020.09.729] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The production of metabolic energy in form of ATP by oxidative phosphorylation depends on the coordinated action of hundreds of nuclear-encoded mitochondrial proteins and a handful of proteins encoded by the mitochondrial genome (mtDNA). We used the yeast Saccharomyces cerevisiae as a model system to systematically identify the genes contributing to this process. Integration of genome-wide high-throughput growth assays with previously published large data sets allowed us to define with high confidence a set of 254 nuclear genes that are indispensable for respiratory growth. Next, we induced loss of mtDNA in the yeast deletion collection by growth on ethidium bromide-containing medium and identified twelve genes that are essential for viability in the absence of mtDNA (i.e. petite-negative). Replenishment of mtDNA by cytoduction showed that respiratory-deficient phenotypes are highly variable in many yeast mutants. Using a mitochondrial genome carrying a selectable marker, ARG8m, we screened for mutants that are specifically defective in maintenance of mtDNA and mitochondrial protein synthesis. We found that up to 176 nuclear genes are required for expression of mitochondria-encoded proteins during fermentative growth. Taken together, our data provide a comprehensive picture of the molecular processes that are required for respiratory metabolism in a simple eukaryotic cell.
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Affiliation(s)
- Maria Stenger
- Zellbiologie, Universität Bayreuth, 95440 Bayreuth, Germany
| | - Duc Tung Le
- Zellbiologie, Universität Bayreuth, 95440 Bayreuth, Germany
| | - Till Klecker
- Zellbiologie, Universität Bayreuth, 95440 Bayreuth, Germany
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9
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AIF meets the CHCHD4/Mia40-dependent mitochondrial import pathway. Biochim Biophys Acta Mol Basis Dis 2020; 1866:165746. [PMID: 32105825 DOI: 10.1016/j.bbadis.2020.165746] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2019] [Revised: 02/19/2020] [Accepted: 02/20/2020] [Indexed: 02/06/2023]
Abstract
In the mitochondria of healthy cells, Apoptosis-Inducing factor (AIF) is required for the optimal functioning of the respiratory chain machinery, mitochondrial integrity, cell survival, and proliferation. In all analysed species, it was revealed that the downregulation or depletion of AIF provokes mainly the post-transcriptional loss of respiratory chain Complex I protein subunits. Recent progress in the field has revealed that AIF fulfils its mitochondrial pro-survival function by interacting physically and functionally with CHCHD4, the evolutionarily-conserved human homolog of yeast Mia40. The redox-regulated CHCHD4/Mia40-dependent import machinery operates in the intermembrane space of the mitochondrion and controls the import of a set of nuclear-encoded cysteine-motif carrying protein substrates. In addition to their participation in the biogenesis of specific respiratory chain protein subunits, CHCHD4/Mia40 substrates are also implicated in the control of redox regulation, antioxidant response, translation, lipid homeostasis and mitochondrial ultrastructure and dynamics. Here, we discuss recent insights on the AIF/CHCHD4-dependent protein import pathway and review current data concerning the CHCHD4/Mia40 protein substrates in metazoan. Recent findings and the identification of disease-associated mutations in AIF or in specific CHCHD4/Mia40 substrates have highlighted these proteins as potential therapeutic targets in a variety of human disorders.
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10
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Kumar A, Matta SK, D'Silva P. Role of conserved regions of Tim22 in the structural organization of the carrier translocase. J Cell Sci 2020; 133:jcs.244632. [DOI: 10.1242/jcs.244632] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Accepted: 06/15/2020] [Indexed: 11/20/2022] Open
Abstract
Mitochondrial biogenesis requires efficient sorting of various proteins into different mitochondrial sub-compartments mediated by dedicated protein machinery present in the outer and inner membrane. Among them, the TIM22 complex enables the integration of complex membrane proteins with internal targeting signals into the inner membrane. Although the Tim22 forms the core of the complex, the dynamic recruitment of subunits to the channel is still enigmatic. The present study first-time highlights that IMS and TM4 regions of Tim22 are critically required for the interaction of the membrane-embedded subunits including, Tim54, Tim18, and Sdh3, thereby maintain the functional architecture of TIM22 translocase. On the other hand, TM1 and TM2 regions of Tim22 are important for the Tim18 association, while TM3 is exclusively required for the Sdh3 interaction. Moreover, the impairment in TIM22 complex assembly influences its translocase activity, mitochondrial network, and the viability of cells lacking mitochondrial DNA. Overall our findings provide compelling evidence to highlight the significance of conserved regions of Tim22 that are important for the maintenance of the TIM22 complex and mitochondrial integrity.
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Affiliation(s)
- Abhishek Kumar
- Department of Biochemistry, New Biological Sciences Building, Indian Institute of Science, C V Raman Avenue, Bangalore-560012, India
| | - Srujan Kumar Matta
- Department of Biochemistry, New Biological Sciences Building, Indian Institute of Science, C V Raman Avenue, Bangalore-560012, India
| | - Patrick D'Silva
- Department of Biochemistry, New Biological Sciences Building, Indian Institute of Science, C V Raman Avenue, Bangalore-560012, India
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11
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Garcia EJ, de Jonge JJ, Liao PC, Stivison E, Sing CN, Higuchi-Sanabria R, Boldogh IR, Pon LA. Reciprocal interactions between mtDNA and lifespan control in budding yeast. Mol Biol Cell 2019; 30:2943-2952. [PMID: 31599702 PMCID: PMC6857569 DOI: 10.1091/mbc.e18-06-0356] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2018] [Revised: 09/25/2019] [Accepted: 10/01/2019] [Indexed: 01/01/2023] Open
Abstract
Loss of mitochondrial DNA (mtDNA) results in loss of mitochondrial respiratory activity, checkpoint-regulated inhibition of cell cycle progression, defects in growth, and nuclear genome instability. However, after several generations, yeast cells can adapt to the loss of mtDNA. During this adaptation, rho0 cells, which have no mtDNA, exhibit increased growth rates and nuclear genome stabilization. Here, we report that an immediate response to loss of mtDNA is a decrease in replicative lifespan (RLS). Moreover, we find that adapted rho0 cells bypass the mtDNA inheritance checkpoint, exhibit increased mitochondrial function, and undergo an increase in RLS as they adapt to the loss of mtDNA. Transcriptome analysis reveals that metabolic reprogramming to compensate for defects in mitochondrial function is an early event during adaptation and that up-regulation of stress response genes occurs later in the adaptation process. We also find that specific subtelomeric genes are silenced during adaptation to loss of mtDNA. Moreover, we find that deletion of SIR3, a subtelomeric gene silencing protein, inhibits silencing of subtelomeric genes associated with adaptation to loss of mtDNA, as well as adaptation-associated increases in mitochondrial function and RLS extension.
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Affiliation(s)
- Enrique J. Garcia
- Department of Pathology and Cell Biology and Institute of Human Nutrition, College of Physicians and Surgeons, Columbia University, New York, NY 10032
| | - Janeska J. de Jonge
- Department of Pathology and Cell Biology and Institute of Human Nutrition, College of Physicians and Surgeons, Columbia University, New York, NY 10032
| | - Pin-Chao Liao
- Department of Pathology and Cell Biology and Institute of Human Nutrition, College of Physicians and Surgeons, Columbia University, New York, NY 10032
| | - Elizabeth Stivison
- Department of Pathology and Cell Biology and Institute of Human Nutrition, College of Physicians and Surgeons, Columbia University, New York, NY 10032
| | - Cierra N. Sing
- Department of Pathology and Cell Biology and Institute of Human Nutrition, College of Physicians and Surgeons, Columbia University, New York, NY 10032
| | - Ryo Higuchi-Sanabria
- Department of Pathology and Cell Biology and Institute of Human Nutrition, College of Physicians and Surgeons, Columbia University, New York, NY 10032
| | - Istvan R. Boldogh
- Department of Pathology and Cell Biology and Institute of Human Nutrition, College of Physicians and Surgeons, Columbia University, New York, NY 10032
| | - Liza A. Pon
- Department of Pathology and Cell Biology and Institute of Human Nutrition, College of Physicians and Surgeons, Columbia University, New York, NY 10032
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12
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Mirzalieva O, Jeon S, Damri K, Hartke R, Drwesh L, Demishtein-Zohary K, Azem A, Dunn CD, Peixoto PM. Deletion of Mgr2p Affects the Gating Behavior of the TIM23 Complex. Front Physiol 2019; 9:1960. [PMID: 30697167 PMCID: PMC6340964 DOI: 10.3389/fphys.2018.01960] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Accepted: 12/28/2018] [Indexed: 11/13/2022] Open
Abstract
The TIM23 complex is a hub for translocation of preproteins into or across the mitochondrial inner membrane. This dual sorting mechanism is currently being investigated, and in yeast appears to be regulated by a recently discovered subunit, the Mgr2 protein. Deletion of Mgr2p has been found to delay protein translocation into the matrix and accumulation in the inner membrane. This result and other findings suggested that Mgr2p controls the lateral release of inner membrane proteins harboring a stop-transfer signal that follows an N-terminal amino acid signal. However, the mechanism of lateral release is unknown. Here, we used patch clamp electrophysiology to investigate the role of Mgr2p on the channel activity of TIM23. Deletion of Mgr2p decreased normal channel frequency and increased occurrence of a residual TIM23 activity. The residual channel lacked gating transitions but remained sensitive to synthetic import signal peptides. Similarly, a G145L mutation in Tim23p displaced Mgr2p from the import complex leading to gating impairment. These results suggest that Mgr2p regulates the gating behavior of the TIM23 channel.
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Affiliation(s)
- Oygul Mirzalieva
- Department of Natural Sciences, Baruch College, The City University of New York, New York City, NY, United States
| | - Shinhye Jeon
- Department of Natural Sciences, Baruch College, The City University of New York, New York City, NY, United States
| | - Kevin Damri
- Department of Natural Sciences, Baruch College, The City University of New York, New York City, NY, United States
| | - Ruth Hartke
- Department of Natural Sciences, Baruch College, The City University of New York, New York City, NY, United States
| | - Layla Drwesh
- Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Keren Demishtein-Zohary
- Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Abdussalam Azem
- Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Cory D Dunn
- Institute of Biotechnology, Helsinki Institute of Life Science, University of Helsinki, Helsinki, Finland.,Department of Molecular Biology and Genetics, Koç University, Istanbul, Turkey
| | - Pablo M Peixoto
- Department of Natural Sciences, Baruch College, The City University of New York, New York City, NY, United States.,MCD Program, The Graduate Center, The City University of New York, New York City, NY, United States
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13
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Li S, Giardina DM, Siegal ML. Control of nongenetic heterogeneity in growth rate and stress tolerance of Saccharomyces cerevisiae by cyclic AMP-regulated transcription factors. PLoS Genet 2018; 14:e1007744. [PMID: 30388117 PMCID: PMC6241136 DOI: 10.1371/journal.pgen.1007744] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2018] [Revised: 11/14/2018] [Accepted: 10/05/2018] [Indexed: 01/01/2023] Open
Abstract
Genetically identical cells exhibit extensive phenotypic variation even under constant and benign conditions. This so-called nongenetic heterogeneity has important clinical implications: within tumors and microbial infections, cells show nongenetic heterogeneity in growth rate and in susceptibility to drugs or stress. The budding yeast, Saccharomyces cerevisiae, shows a similar form of nongenetic heterogeneity in which growth rate correlates positively with susceptibility to acute heat stress at the single-cell level. Using genetic and chemical perturbations, combined with high-throughput single-cell assays of yeast growth and gene expression, we show here that heterogeneity in intracellular cyclic AMP (cAMP) levels acting through the conserved Ras/cAMP/protein kinase A (PKA) pathway and its target transcription factors, Msn2 and Msn4, underlies this nongenetic heterogeneity. Lower levels of cAMP correspond to slower growth, as shown by direct comparison of cAMP concentration in subpopulations enriched for slower vs. faster growing cells. Concordantly, an endogenous reporter of this pathway’s activity correlates with growth in individual cells. The paralogs Msn2 and Msn4 differ in their roles in nongenetic heterogeneity in a way that demonstrates slow growth and stress tolerance are not inevitably linked. Heterogeneity in growth rate requires each, whereas only Msn2 is required for heterogeneity in expression of Tsl1, a subunit of trehalose synthase that contributes to acute-stress tolerance. Perturbing nongenetic heterogeneity by mutating genes in this pathway, or by culturing wild-type cells with the cell-permeable cAMP analog 8-bromo-cAMP or the PKA inhibitor H89, significantly impacts survival of acute heat stress. Perturbations that increase intracellular cAMP levels reduce the slower-growing subpopulation and increase susceptibility to acute heat stress, whereas PKA inhibition slows growth and decreases susceptibility to acute heat stress. Loss of Msn2 reduces, but does not completely eliminate, the correlation in individual cells between growth rate and acute-stress survival, suggesting a major role for the Msn2 pathway in nongenetic heterogeneity but also a residual benefit of slow growth. Our results shed light on the genetic control of nongenetic heterogeneity and suggest a possible means of defeating bet-hedging pathogens or tumor cells by making them more uniformly susceptible to treatment. Nongenetic heterogeneity exists when a trait differs among individuals that have identical genotypes and environments. A clonal population can maximize its long-term success in an uncertain environment by diversifying its phenotypes via nongenetic heterogeneity: the currently unfavored ones may become the favored ones when conditions change. Nongenetic heterogeneity has clinical relevance. For example, populations of tumor cells or infectious microbes show cell-to-cell differences in growth and in drug or stress tolerance. This heterogeneity hampers efficient treatment and can potentiate harmful evolution of a tumor or pathogen. We show that in budding yeast, heterogeneity in intracellular cyclic AMP levels acting through the conserved Ras/cAMP/protein kinase A (PKA) pathway and its target transcription factors, Msn2 and Msn4, underlies the nongenetic heterogeneity of both single-cell growth rate and acute heat-stress tolerance. Perturbations of this pathway significantly affect population survival upon acute heat stress. These results illuminate a mechanism of nongenetic heterogeneity and suggest the potential value of antitumor or antifungal treatment strategies that target nongenetic heterogeneity to render the tumor or pathogen population more uniformly susceptible to a second drug that aims to kill.
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Affiliation(s)
- Shuang Li
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, New York, United States of America
| | - Daniella M. Giardina
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, New York, United States of America
| | - Mark L. Siegal
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, New York, United States of America
- * E-mail:
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14
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Vargas Möller-Hergt B, Carlström A, Suhm T, Ott M. Insertion Defects of Mitochondrially Encoded Proteins Burden the Mitochondrial Quality Control System. Cells 2018; 7:cells7100172. [PMID: 30336542 PMCID: PMC6211022 DOI: 10.3390/cells7100172] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2018] [Revised: 10/07/2018] [Accepted: 10/16/2018] [Indexed: 12/31/2022] Open
Abstract
The mitochondrial proteome contains proteins from two different genetic systems. Proteins are either synthesized in the cytosol and imported into the different compartments of the organelle or directly produced in the mitochondrial matrix. To ensure proteostasis, proteins are monitored by the mitochondrial quality control system, which will degrade non-native polypeptides. Defective mitochondrial membrane proteins are degraded by membrane-bound AAA-proteases. These proteases are regulated by factors promoting protein turnover or preventing their degradation. Here we determined genetic interactions between the mitoribosome receptors Mrx15 and Mba1 with the quality control system. We show that simultaneous absence of Mrx15 and the regulators of the i-AAA protease Mgr1 and Mgr3 provokes respiratory deficiency. Surprisingly, mutants lacking Mrx15 were more tolerant against proteotoxic stress. Furthermore, yeast cells became hypersensitive against proteotoxic stress upon deletion of MBA1. Contrary to Mrx15, Mba1 cooperates with the regulators of the m-AAA and i-AAA proteases. Taken together, these results suggest that membrane protein insertion and mitochondrial AAA-proteases are functionally coupled, possibly reflecting an early quality control step during mitochondrial protein synthesis.
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Affiliation(s)
| | - Andreas Carlström
- Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden.
| | - Tamara Suhm
- Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden.
| | - Martin Ott
- Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden.
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15
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AAA Proteases: Guardians of Mitochondrial Function and Homeostasis. Cells 2018; 7:cells7100163. [PMID: 30314276 PMCID: PMC6210556 DOI: 10.3390/cells7100163] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2018] [Revised: 10/04/2018] [Accepted: 10/09/2018] [Indexed: 12/30/2022] Open
Abstract
Mitochondria are dynamic, semi-autonomous organelles that execute numerous life-sustaining tasks in eukaryotic cells. Functioning of mitochondria depends on the adequate action of versatile proteinaceous machineries. Fine-tuning of mitochondrial activity in response to cellular needs involves continuous remodeling of organellar proteome. This process not only includes modulation of various biogenetic pathways, but also the removal of superfluous proteins by adenosine triphosphate (ATP)-driven proteolytic machineries. Accordingly, all mitochondrial sub-compartments are under persistent surveillance of ATP-dependent proteases. Particularly important are highly conserved two inner mitochondrial membrane-bound metalloproteases known as m-AAA and i-AAA (ATPases associated with diverse cellular activities), whose mis-functioning may lead to impaired organellar function and consequently to development of severe diseases. Herein, we discuss the current knowledge of yeast, mammalian, and plant AAA proteases and their implications in mitochondrial function and homeostasis maintenance.
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16
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Coyne LP, Chen XJ. mPOS is a novel mitochondrial trigger of cell death - implications for neurodegeneration. FEBS Lett 2017; 592:759-775. [PMID: 29090463 DOI: 10.1002/1873-3468.12894] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2017] [Revised: 10/14/2017] [Accepted: 10/26/2017] [Indexed: 12/14/2022]
Abstract
In addition to its central role in energy metabolism, the mitochondrion has many other functions essential for cell survival. When stressed, the multifunctional mitochondria are expected to engender multifaceted cell stress with complex physiological consequences. Potential extra-mitochondrial proteostatic burdens imposed by inefficient protein import have been largely overlooked. Accumulating evidence suggests that a diverse range of pathogenic mitochondrial stressors, which do not directly target the core protein import machinery, can reduce cell fitness by disrupting the proteostatic network in the cytosol. The resulting stress, named mitochondrial precursor overaccumulation stress (mPOS), is characterized by the toxic accumulation of unimported mitochondrial proteins in the cytosol. Here, we review our current understanding of how mitochondrial dysfunction can impact the cytosolic proteome and proteostatic signaling. We also discuss the intriguing possibility that the mPOS model may help untangle the cause-effect relationship between mitochondrial dysfunction and cytosolic protein aggregation, which are probably the two most prominent molecular hallmarks of neurodegenerative disease.
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Affiliation(s)
- Liam P Coyne
- Department of Biochemistry and Molecular Biology, State University of New York Upstate Medical University, Syracuse, NY, USA
| | - Xin Jie Chen
- Department of Biochemistry and Molecular Biology, State University of New York Upstate Medical University, Syracuse, NY, USA.,Department of Neuroscience and Physiology, State University of New York Upstate Medical University, Syracuse, NY, USA
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17
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Wu X, Li L, Jiang H. Mitochondrial inner-membrane protease Yme1 degrades outer-membrane proteins Tom22 and Om45. J Cell Biol 2017; 217:139-149. [PMID: 29138251 PMCID: PMC5748973 DOI: 10.1083/jcb.201702125] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2017] [Revised: 09/03/2017] [Accepted: 10/18/2017] [Indexed: 01/26/2023] Open
Abstract
The turnover of mitochondrial outer-membrane proteins is known to be mediated by the cytoplasmic ubiquitin–proteasome pathway. Wu et al. report the unexpected finding that two outer-membrane proteins Tom22 and Om45 are inwardly translocated into mitochondria and degraded by the inner-membrane protease Yme1. Mitochondria are double-membraned organelles playing essential metabolic and signaling functions. The mitochondrial proteome is under surveillance by two proteolysis systems: the ubiquitin–proteasome system degrades mitochondrial outer-membrane (MOM) proteins, and the AAA proteases maintain the proteostasis of intramitochondrial compartments. We previously identified a Doa1–Cdc48-Ufd1-Npl4 complex that retrogradely translocates ubiquitinated MOM proteins to the cytoplasm for degradation. In this study, we report the unexpected identification of MOM proteins whose degradation requires the Yme1-Mgr1-Mgr3i-AAA protease complex in mitochondrial inner membrane. Through immunoprecipitation and in vivo site-specific photo–cross-linking experiments, we show that both Yme1 adapters Mgr1 and Mgr3 recognize the intermembrane space (IMS) domains of the MOM substrates and facilitate their recruitment to Yme1 for proteolysis. We also provide evidence that the cytoplasmic domain of substrate can be dislocated into IMS by the ATPase activity of Yme1. Our findings indicate a proteolysis pathway monitoring MOM proteins from the IMS side and suggest that the MOM proteome is surveilled by mitochondrial and cytoplasmic quality control machineries in parallel.
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Affiliation(s)
- Xi Wu
- School of Life Sciences, Peking University, Beijing, China .,National Institute of Biological Sciences, Beijing, China
| | - Lanlan Li
- College of Life Sciences, Beijing Normal University, Beijing, China
| | - Hui Jiang
- National Institute of Biological Sciences, Beijing, China
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18
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Gaspar ML, Chang YF, Jesch SA, Aregullin M, Henry SA. Interaction between repressor Opi1p and ER membrane protein Scs2p facilitates transit of phosphatidic acid from the ER to mitochondria and is essential for INO1 gene expression in the presence of choline. J Biol Chem 2017; 292:18713-18728. [PMID: 28924045 DOI: 10.1074/jbc.m117.809970] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Revised: 09/08/2017] [Indexed: 12/20/2022] Open
Abstract
In the yeast Saccharomyces cerevisiae, the Opi1p repressor controls the expression of INO1 via the Opi1p/Ino2p-Ino4p regulatory circuit. Inositol depletion favors Opi1p interaction with both Scs2p and phosphatidic acid at the endoplasmic reticulum (ER) membrane. Inositol supplementation, however, favors the translocation of Opi1p from the ER into the nucleus, where it interacts with the Ino2p-Ino4p complex, attenuating transcription of INO1 A strain devoid of Scs2p (scs2Δ) and a mutant, OPI1FFAT, lacking the ability to interact with Scs2p were utilized to examine the specific role(s) of the Opi1p-Scs2p interaction in the regulation of INO1 expression and overall lipid metabolism. Loss of the Opi1p-Scs2p interaction reduced INO1 expression and conferred inositol auxotrophy. Moreover, inositol depletion in strains lacking this interaction resulted in Opi1p being localized to sites of lipid droplet formation, coincident with increased synthesis of triacylglycerol. Supplementation of choline to inositol-depleted growth medium led to decreased TAG synthesis in all three strains. However, in strains lacking the Opi1p-Scs2p interaction, Opi1p remained in the nucleus, preventing expression of INO1 These data support the conclusion that a specific pool of phosphatidic acid, associated with lipid droplet formation in the perinuclear ER, is responsible for the initial rapid exit of Opi1p from the nucleus to the ER and is required for INO1 expression in the presence of choline. Moreover, the mitochondria-specific phospholipid, cardiolipin, was significantly reduced in both strains compromised for Opi1p-Scs2p interaction, indicating that this interaction is required for the transfer of phosphatidic acid from the ER to the mitochondria for cardiolipin synthesis.
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Affiliation(s)
- Maria L Gaspar
- From the Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853
| | - Yu-Fang Chang
- From the Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853
| | - Stephen A Jesch
- From the Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853
| | - Manuel Aregullin
- From the Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853
| | - Susan A Henry
- From the Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853
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19
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Mitochondrial Cochaperone Mge1 Is Involved in Regulating Susceptibility to Fluconazole in Saccharomyces cerevisiae and Candida Species. mBio 2017; 8:mBio.00201-17. [PMID: 28720726 PMCID: PMC5516249 DOI: 10.1128/mbio.00201-17] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
MGE1 encodes a yeast chaperone involved in Fe-S cluster metabolism and protein import into the mitochondria. In this study, we identified MGE1 as a multicopy suppressor of susceptibility to the antifungal fluconazole in the model yeast Saccharomyces cerevisiae. We demonstrate that this phenomenon is not exclusively dependent on the integrity of the mitochondrial DNA or on the presence of the drug efflux pump Pdr5. Instead, we show that the increased dosage of Mge1 plays a protective role by retaining increased amounts of ergosterol upon fluconazole treatment. Iron metabolism and, more particularly, Fe-S cluster formation are involved in regulating this process, since the responsible Hsp70 chaperone, Ssq1, is required. Additionally, we show the necessity but, by itself, insufficiency of activating the iron regulon in establishing the Mge1-related effect on drug susceptibility. Finally, we confirm a similar role for Mge1 in fluconazole susceptibility in the pathogenic fungi Candida glabrata and Candida albicans. Although they are mostly neglected compared to bacterial infections, fungal infections pose a serious threat to the human population. While some of them remain relatively harmless, infections that reach the bloodstream often become lethal. Only a few therapies are available, and resistance of the pathogen to these drugs is a frequently encountered problem. It is thus essential that more research is performed on how these pathogens cope with the treatment and cause recurrent infections. Baker’s yeast is often used as a model to study pathogenic fungi. We show here, by using this model, that iron metabolism and the formation of the important iron-sulfur clusters are involved in regulating susceptibility to fluconazole, the most commonly used antifungal drug. We show that the same process likely also occurs in two of the most regularly isolated pathogenic fungi, Candida glabrata and Candida albicans.
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20
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Glynn SE. Multifunctional Mitochondrial AAA Proteases. Front Mol Biosci 2017; 4:34. [PMID: 28589125 PMCID: PMC5438985 DOI: 10.3389/fmolb.2017.00034] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Accepted: 05/08/2017] [Indexed: 11/28/2022] Open
Abstract
Mitochondria perform numerous functions necessary for the survival of eukaryotic cells. These activities are coordinated by a diverse complement of proteins encoded in both the nuclear and mitochondrial genomes that must be properly organized and maintained. Misregulation of mitochondrial proteostasis impairs organellar function and can result in the development of severe human diseases. ATP-driven AAA+ proteins play crucial roles in preserving mitochondrial activity by removing and remodeling protein molecules in accordance with the needs of the cell. Two mitochondrial AAA proteases, i-AAA and m-AAA, are anchored to either face of the mitochondrial inner membrane, where they engage and process an array of substrates to impact protein biogenesis, quality control, and the regulation of key metabolic pathways. The functionality of these proteases is extended through multiple substrate-dependent modes of action, including complete degradation, partial processing, or dislocation from the membrane without proteolysis. This review discusses recent advances made toward elucidating the mechanisms of substrate recognition, handling, and degradation that allow these versatile proteases to control diverse activities in this multifunctional organelle.
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Affiliation(s)
- Steven E Glynn
- Department of Biochemistry and Cell Biology, Stony Brook UniversityStony Brook, NY, United States
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21
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Eisenberg-Bord M, Schuldiner M. Mitochatting - If only we could be a fly on the cell wall. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2017; 1864:1469-1480. [PMID: 28433686 DOI: 10.1016/j.bbamcr.2017.04.012] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 01/07/2017] [Revised: 04/12/2017] [Accepted: 04/18/2017] [Indexed: 12/24/2022]
Abstract
Mitochondria, cellular metabolic hubs, perform many essential processes and are required for the production of metabolites such as ATP, iron-sulfur clusters, heme, amino acids and nucleotides. To fulfill their multiple roles, mitochondria must communicate with all other organelles to exchange small molecules, ions and lipids. Since mitochondria are largely excluded from vesicular trafficking routes, they heavily rely on membrane contact sites. Contact sites are areas of close proximity between organelles that allow efficient transfer of molecules, saving the need for slow and untargeted diffusion through the cytosol. More globally, multiple metabolic pathways require coordination between mitochondria and additional organelles and mitochondrial activity affects all other cellular entities and vice versa. Therefore, uncovering the different means of mitochondrial communication will allow us a better understanding of mitochondria and may illuminate disease processes that occur in the absence of proper cross-talk. In this review we focus on how mitochondria interact with all other organelles and emphasize how this communication is essential for mitochondrial and cellular homeostasis. This article is part of a Special Issue entitled: Membrane Contact Sites edited by Christian Ungermann and Benoit Kornmann.
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Affiliation(s)
- Michal Eisenberg-Bord
- Department of Molecular Genetics, Weizmann Institute of Science, 7610001 Rehovot, Israel
| | - Maya Schuldiner
- Department of Molecular Genetics, Weizmann Institute of Science, 7610001 Rehovot, Israel.
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22
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Akdoğan E, Tardu M, Garipler G, Baytek G, Kavakli İH, Dunn CD. Reduced Glucose Sensation Can Increase the Fitness of Saccharomyces cerevisiae Lacking Mitochondrial DNA. PLoS One 2016; 11:e0146511. [PMID: 26751567 PMCID: PMC4709096 DOI: 10.1371/journal.pone.0146511] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Accepted: 12/19/2015] [Indexed: 12/12/2022] Open
Abstract
Damage to the mitochondrial genome (mtDNA) can lead to diseases for which there are no clearly effective treatments. Since mitochondrial function and biogenesis are controlled by the nutrient environment of the cell, it is possible that perturbation of conserved, nutrient-sensing pathways may successfully treat mitochondrial disease. We found that restricting glucose or otherwise reducing the activity of the protein kinase A (PKA) pathway can lead to improved proliferation of Saccharomyces cerevisiae cells lacking mtDNA and that the transcriptional response to mtDNA loss is reduced in cells with diminished PKA activity. We have excluded many pathways and proteins from being individually responsible for the benefits provided to cells lacking mtDNA by PKA inhibition, and we found that robust import of mitochondrial polytopic membrane proteins may be required in order for cells without mtDNA to receive the full benefits of PKA reduction. Finally, we have discovered that the transcription of genes involved in arginine biosynthesis and aromatic amino acid catabolism is altered after mtDNA damage. Our results highlight the potential importance of nutrient detection and availability on the outcome of mitochondrial dysfunction.
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Affiliation(s)
- Emel Akdoğan
- Department of Molecular Biology and Genetics, Koç University, Sarıyer, İstanbul, 34450, Turkey
| | - Mehmet Tardu
- Department of Chemical and Biological Engineering, Koç University, Sarıyer, İstanbul, 34450, Turkey
| | - Görkem Garipler
- Department of Molecular Biology and Genetics, Koç University, Sarıyer, İstanbul, 34450, Turkey
| | - Gülkız Baytek
- Department of Molecular Biology and Genetics, Koç University, Sarıyer, İstanbul, 34450, Turkey
| | - İ. Halil Kavakli
- Department of Molecular Biology and Genetics, Koç University, Sarıyer, İstanbul, 34450, Turkey
- Department of Chemical and Biological Engineering, Koç University, Sarıyer, İstanbul, 34450, Turkey
| | - Cory D. Dunn
- Department of Molecular Biology and Genetics, Koç University, Sarıyer, İstanbul, 34450, Turkey
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23
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Proteasome Impairment Induces Recovery of Mitochondrial Membrane Potential and an Alternative Pathway of Mitochondrial Fusion. Mol Cell Biol 2015; 36:347-62. [PMID: 26552703 DOI: 10.1128/mcb.00920-15] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2015] [Accepted: 11/04/2015] [Indexed: 12/18/2022] Open
Abstract
Mitochondria are vital and highly dynamic organelles that continuously fuse and divide to maintain mitochondrial quality. Mitochondrial dysfunction impairs cellular integrity and is known to be associated with various human diseases. However, the mechanism by which the quality of mitochondria is maintained remains largely unexplored. Here we show that impaired proteasome function recovers the growth of yeast cells lacking Fzo1, a pivotal protein for mitochondrial fusion. Decreased proteasome activity increased the mitochondrial oxidoreductase protein Mia40 and the ratio of the short isoform of mitochondrial intermembrane protein Mgm1 (s-Mgm1) to the long isoform (l-Mgm1). The increase in Mia40 restored mitochondrial membrane potential, while the increase in the s-Mgm1/l-Mgm1 ratio promoted mitochondrial fusion in an Fzo1-independent manner. Our findings demonstrate a new pathway for mitochondrial quality control that is induced by proteasome impairment.
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24
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Bohovych I, Chan SS, Khalimonchuk O. Mitochondrial protein quality control: the mechanisms guarding mitochondrial health. Antioxid Redox Signal 2015; 22:977-94. [PMID: 25546710 PMCID: PMC4390190 DOI: 10.1089/ars.2014.6199] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/26/2014] [Accepted: 12/20/2014] [Indexed: 12/20/2022]
Abstract
SIGNIFICANCE Mitochondria are complex dynamic organelles pivotal for cellular physiology and human health. Failure to maintain mitochondrial health leads to numerous maladies that include late-onset neurodegenerative diseases and cardiovascular disorders. Furthermore, a decline in mitochondrial health is prevalent with aging. A set of evolutionary conserved mechanisms known as mitochondrial quality control (MQC) is involved in recognition and correction of the mitochondrial proteome. RECENT ADVANCES Here, we review current knowledge and latest developments in MQC. We particularly focus on the proteolytic aspect of MQC and its impact on health and aging. CRITICAL ISSUES While our knowledge about MQC is steadily growing, critical gaps remain in the mechanistic understanding of how MQC modules sense damage and preserve mitochondrial welfare, particularly in higher organisms. FUTURE DIRECTIONS Delineating how coordinated action of the MQC modules orchestrates physiological responses on both organellar and cellular levels will further elucidate the current picture of MQC's role and function in health, cellular stress, and degenerative diseases.
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Affiliation(s)
- Iryna Bohovych
- Department of Biochemistry, University of Nebraska-Lincoln, Lincoln, Nebraska
- Nebraska Redox Biology Center, University of Nebraska-Lincoln, Lincoln, Nebraska
| | - Sherine S.L. Chan
- Department of Drug Discovery and Biomedical Sciences, Medical University of South Carolina, Charleston, South Carolina
| | - Oleh Khalimonchuk
- Department of Biochemistry, University of Nebraska-Lincoln, Lincoln, Nebraska
- Nebraska Redox Biology Center, University of Nebraska-Lincoln, Lincoln, Nebraska
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25
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Steffen J, Koehler CM. The great escape: Mgr2 of the mitochondrial TIM23 translocon is a gatekeeper Tasked with releasing membrane proteins. Mol Cell 2015; 56:613-4. [PMID: 25479635 DOI: 10.1016/j.molcel.2014.11.022] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
By using a combination of biochemistry and genetics, in this issue of Molecular CellIeva et al. (2014) uncover an unexpected role for Mgr2 of the mitochondrial TIM23 translocon as a gatekeeper in the release of membrane proteins from the translocon.
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Affiliation(s)
- Janos Steffen
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Carla M Koehler
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095, USA; Molecular Biology Institute, University of California, Los Angeles, Los Angeles, CA 90095, USA; Jonsson Comprehensive Cancer Center, University of California, Los Angeles, Los Angeles, CA 90095, USA.
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26
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Rainbolt TK, Saunders JM, Wiseman RL. YME1L degradation reduces mitochondrial proteolytic capacity during oxidative stress. EMBO Rep 2014; 16:97-106. [PMID: 25433032 DOI: 10.15252/embr.201438976] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Mitochondrial proteostasis is maintained by a network of ATP-dependent quality control proteases including the inner membrane protease YME1L. Here, we show that YME1L is a stress-sensitive mitochondrial protease that is rapidly degraded in response to acute oxidative stress. This degradation requires reductions in cellular ATP and involves the activity of the ATP-independent protease OMA1. Oxidative stress-dependent reductions in YME1L inhibit protective YME1L-dependent functions and increase cellular sensitivity to oxidative insult. Collectively, our results identify stress-induced YME1L degradation as a biologic process that attenuates protective regulation of mitochondrial proteostasis and promotes cellular death in response to oxidative stress.
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Affiliation(s)
- T Kelly Rainbolt
- Department of Molecular & Experimental Medicine, Department of Chemical Physiology, The Scripps Research Institute, La Jolla, CA, USA
| | - Jaclyn M Saunders
- Department of Molecular & Experimental Medicine, Department of Chemical Physiology, The Scripps Research Institute, La Jolla, CA, USA
| | - R Luke Wiseman
- Department of Molecular & Experimental Medicine, Department of Chemical Physiology, The Scripps Research Institute, La Jolla, CA, USA
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27
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Martínez C, Contreras A, Aguilera O, Ganga A, García V. The ICY1 gene from Saccharomyces cerevisiae affects nitrogen consumption during alcoholic fermentation. ELECTRON J BIOTECHN 2014. [DOI: 10.1016/j.ejbt.2014.04.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
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28
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Metabolic and environmental conditions determine nuclear genomic instability in budding yeast lacking mitochondrial DNA. G3-GENES GENOMES GENETICS 2014; 4:411-23. [PMID: 24374640 PMCID: PMC3962481 DOI: 10.1534/g3.113.010108] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Mitochondrial dysfunctions are an internal cause of nuclear genome instability. Because mitochondria are key regulators of cellular metabolism, we have investigated a potential link between external growth conditions and nuclear chromosome instability in cells with mitochondrial defects. Using Saccharomyces cerevisiae, we found that cells lacking mitochondrial DNA (rho0 cells) have a unique feature, with nuclear chromosome instability that occurs in nondividing cells and strongly fluctuates depending on the cellular environment. Calorie restriction, lower growth temperatures, growth at alkaline pH, antioxidants (NAC, Tiron), or presence of nearby wild-type cells all efficiently stabilize nuclear genomes of rho0 cells, whereas high glucose and ethanol boost instability. In contrast, other respiratory mutants that still possess mitochondrial DNA (RHO(+)) keep fairly constant instability rates under the same growth conditions, like wild-type or other RHO(+) controls. Our data identify mitochondrial defects as an important driver of nuclear genome instability influenced by environmental factors.
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Rainbolt TK, Atanassova N, Genereux JC, Wiseman RL. Stress-regulated translational attenuation adapts mitochondrial protein import through Tim17A degradation. Cell Metab 2013; 18:908-19. [PMID: 24315374 PMCID: PMC3904643 DOI: 10.1016/j.cmet.2013.11.006] [Citation(s) in RCA: 153] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/31/2013] [Revised: 08/08/2013] [Accepted: 11/06/2013] [Indexed: 12/28/2022]
Abstract
Stress-regulated signaling pathways protect mitochondrial proteostasis and function from pathologic insults. Despite the importance of stress-regulated signaling pathways in mitochondrial proteome maintenance, the molecular mechanisms by which these pathways maintain mitochondrial proteostasis remain largely unknown. We identify Tim17A as a stress-regulated subunit of the translocase of the inner membrane 23 (TIM23) mitochondrial protein import complex. We show that Tim17A protein levels are decreased downstream of stress-regulated translational attenuation induced by eukaryotic initiation factor 2α (eIF2α) phosphorylation through a mechanism dependent on the mitochondrial protease YME1L. Furthermore, we demonstrate that decreasing Tim17A attenuates TIM23-dependent protein import, promotes the induction of mitochondrial unfolded protein response (UPR)-associated proteostasis genes, and confers stress resistance in C. elegans and mammalian cells. Thus, our results indicate that Tim17A degradation is a stress-responsive mechanism by which cells adapt mitochondrial protein import efficiency and promote mitochondrial proteostasis in response to the numerous pathologic insults that induce stress-regulated translation attenuation.
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Affiliation(s)
- T Kelly Rainbolt
- Department of Molecular & Experimental Medicine, Department of Chemical Physiology, The Scripps Research Institute, La Jolla, CA 92037, USA
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30
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Ieva R, Heißwolf AK, Gebert M, Vögtle FN, Wollweber F, Mehnert CS, Oeljeklaus S, Warscheid B, Meisinger C, van der Laan M, Pfanner N. Mitochondrial inner membrane protease promotes assembly of presequence translocase by removing a carboxy-terminal targeting sequence. Nat Commun 2013; 4:2853. [DOI: 10.1038/ncomms3853] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2013] [Accepted: 11/01/2013] [Indexed: 01/04/2023] Open
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31
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Luévano-Martínez LA, Appolinario P, Miyamoto S, Uribe-Carvajal S, Kowaltowski AJ. Deletion of the transcriptional regulator opi1p decreases cardiolipin content and disrupts mitochondrial metabolism in Saccharomyces cerevisiae. Fungal Genet Biol 2013; 60:150-8. [DOI: 10.1016/j.fgb.2013.03.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Revised: 03/01/2013] [Accepted: 03/26/2013] [Indexed: 12/24/2022]
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Defects associated with mitochondrial DNA damage can be mitigated by increased vacuolar pH in Saccharomyces cerevisiae. Genetics 2013; 194:285-90. [PMID: 23502676 DOI: 10.1534/genetics.113.149708] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
While searching for mutations that alleviate detrimental effects of mitochondrial DNA (mtDNA) damage, we found that disrupting vacuolar biogenesis permitted survival of a sensitized yeast background after mitochondrial genome loss. Furthermore, elevating vacuolar pH increases proliferation after mtDNA deletion and reverses the protein import defect of mitochondria lacking DNA.
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Aun A, Tamm T, Sedman J. Dysfunctional mitochondria modulate cAMP-PKA signaling and filamentous and invasive growth of Saccharomyces cerevisiae. Genetics 2013; 193:467-81. [PMID: 23172851 PMCID: PMC3567737 DOI: 10.1534/genetics.112.147389] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2012] [Accepted: 11/05/2012] [Indexed: 01/04/2023] Open
Abstract
Mitochondrial metabolism is targeted by conserved signaling pathways that mediate external information to the cell. However, less is known about whether mitochondrial dysfunction interferes with signaling and thereby modulates the cellular response to environmental changes. In this study, we analyzed defective filamentous and invasive growth of the yeast Saccharomyces cerevisiae strains that have a dysfunctional mitochondrial genome (rho mutants). We found that the morphogenetic defect of rho mutants was caused by specific downregulation of FLO11, the adhesin essential for invasive and filamentous growth, and did not result from general metabolic changes brought about by interorganellar retrograde signaling. Transcription of FLO11 is known to be regulated by several signaling pathways, including the filamentous-growth-specific MAPK and cAMP-activated protein kinase A (cAMP-PKA) pathways. Our analysis showed that the filamentous-growth-specific MAPK pathway retained functionality in respiratory-deficient yeast cells. In contrast, the cAMP-PKA pathway was downregulated, explaining also various phenotypic traits observed in rho mutants. Thus, our results indicate that dysfunctional mitochondria modulate the output of the conserved cAMP-PKA signaling pathway.
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Affiliation(s)
| | | | - Juhan Sedman
- Department of Biochemistry, Institute of Molecular and Cell Biology, University of Tartu, Tartu 51010, Estonia
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34
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Voos W, Ward LA, Truscott KN. The role of AAA+ proteases in mitochondrial protein biogenesis, homeostasis and activity control. Subcell Biochem 2013; 66:223-263. [PMID: 23479443 DOI: 10.1007/978-94-007-5940-4_9] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Mitochondria are specialised organelles that are structurally and functionally integrated into cells in the vast majority of eukaryotes. They are the site of numerous enzymatic reactions, some of which are essential for life. The double lipid membrane of the mitochondrion, that spatially defines the organelle and is necessary for some functions, also creates a physical but semi-permeable barrier to the rest of the cell. Thus to ensure the biogenesis, regulation and maintenance of a functional population of proteins, an autonomous protein handling network within mitochondria is required. This includes resident mitochondrial protein translocation machinery, processing peptidases, molecular chaperones and proteases. This review highlights the contribution of proteases of the AAA+ superfamily to protein quality and activity control within the mitochondrion. Here they are responsible for the degradation of unfolded, unassembled and oxidatively damaged proteins as well as the activity control of some enzymes. Since most knowledge about these proteases has been gained from studies in the eukaryotic microorganism Saccharomyces cerevisiae, much of the discussion here centres on their role in this organism. However, reference is made to mitochondrial AAA+ proteases in other organisms, particularly in cases where they play a unique role such as the mitochondrial unfolded protein response. As these proteases influence mitochondrial function in both health and disease in humans, an understanding of their regulation and diverse activities is necessary.
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Affiliation(s)
- Wolfgang Voos
- Institut für Biochemie und Molekularbiologie (IBMB), Universität Bonn, Nussallee 11, 53115, Bonn, Germany,
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Kulawiak B, Höpker J, Gebert M, Guiard B, Wiedemann N, Gebert N. The mitochondrial protein import machinery has multiple connections to the respiratory chain. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2012; 1827:612-26. [PMID: 23274250 DOI: 10.1016/j.bbabio.2012.12.004] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2012] [Revised: 12/12/2012] [Accepted: 12/17/2012] [Indexed: 01/09/2023]
Abstract
The mitochondrial inner membrane harbors the complexes of the respiratory chain and protein translocases required for the import of mitochondrial precursor proteins. These complexes are functionally interdependent, as the import of respiratory chain precursor proteins across and into the inner membrane requires the membrane potential. Vice versa the membrane potential is generated by the proton pumping complexes of the respiratory chain. Besides this basic codependency four different systems for protein import, processing and assembly show further connections to the respiratory chain. The mitochondrial intermembrane space import and assembly machinery oxidizes cysteine residues within the imported precursor proteins and is able to donate the liberated electrons to the respiratory chain. The presequence translocase of the inner membrane physically interacts with the respiratory chain. The mitochondrial processing peptidase is homologous to respiratory chain subunits and the carrier translocase of the inner membrane even shares a subunit with the respiratory chain. In this review we will summarize the import of mitochondrial precursor proteins and highlight these special links between the mitochondrial protein import machinery and the respiratory chain. This article is part of a Special Issue entitled: Respiratory complex II: Role in cellular physiology and disease.
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Affiliation(s)
- Bogusz Kulawiak
- Institut für Biochemie und Molekularbiologie, ZBMZ, Universität Freiburg, Freiburg, Germany
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36
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Schreiner B, Westerburg H, Forné I, Imhof A, Neupert W, Mokranjac D. Role of the AAA protease Yme1 in folding of proteins in the intermembrane space of mitochondria. Mol Biol Cell 2012; 23:4335-46. [PMID: 22993211 PMCID: PMC3496608 DOI: 10.1091/mbc.e12-05-0420] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
We show here that the i-AAA protease Yme1 has a role in folding of proteins in the intermembrane space of mitochondria and identify a number of endogenous proteins that aggregate in its absence. Thus the function of Yme1 in mitochondrial proteostasis extends beyond its role in proteolytic removal of misfolded and nonassembled inner membrane proteins. The vast majority of mitochondrial proteins are synthesized in the cytosol and transported into the organelle in a largely, if not completely, unfolded state. The proper function of mitochondria thus depends on folding of several hundreds of proteins in the various subcompartments of the organelle. Whereas folding of proteins in the mitochondrial matrix is supported by members of several chaperone families, very little is known about folding of proteins in the intermembrane space (IMS). We targeted dihydrofolate reductase (DHFR) as a model substrate to the IMS of yeast mitochondria and analyzed its folding. DHFR can fold in this compartment, and its aggregation upon heat shock can be prevented in an ATP-dependent manner. Yme1, an AAA (ATPases associated with diverse cellular activities) protease of the IMS, prevented aggregation of DHFR. Analysis of protein aggregates in mitochondria lacking Yme1 revealed the presence of a number of proteins involved in the establishment of mitochondrial ultrastructure, lipid metabolism, protein import, and respiratory growth. These findings explain the pleiotropic effects of deletion of YME1 and suggest an important role for Yme1 as a folding assistant, in addition to its proteolytic function, in the protein homeostasis of mitochondria
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Affiliation(s)
- Bernadette Schreiner
- Adolf Butenandt Institute, Physiological Chemistry, University of Munich, 81377 Munich, Germany
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37
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Short MK, Hallett JP, Tar K, Dange T, Schmidt M, Moir R, Willis IM, Jubinsky PT. The yeast magmas ortholog pam16 has an essential function in fermentative growth that involves sphingolipid metabolism. PLoS One 2012; 7:e39428. [PMID: 22808036 PMCID: PMC3393719 DOI: 10.1371/journal.pone.0039428] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2011] [Accepted: 05/22/2012] [Indexed: 01/06/2023] Open
Abstract
Magmas is a growth factor responsive gene encoding an essential mitochondrial protein in mammalian cells. Pam16, the Magmas ortholog in Saccharomyces cerevisiae, is a component of the presequence translocase-associated motor. A temperature-sensitive allele (pam16-I61N) was used to query an array of non-essential gene-deletion strains for synthetic genetic interactions. The pam16-I61N mutation at ambient temperature caused synthetic lethal or sick phenotypes with genes involved in lipid metabolism, perixosome synthesis, histone deacetylation and mitochondrial protein import. The gene deletion array was also screened for suppressors of the pam16-I61N growth defect to identify compensatory pathways. Five suppressor genes were identified (SUR4, ISC1, IPT1, SKN1, and FEN1) and all are involved in sphingolipid metabolism. pam16-I61N cells cultured in glucose at non-permissive temperatures resulted in rapid growth inhibition and G1 cell cycle arrest, but cell viability was maintained. Altered mitochondria morphology, reduced peroxisome induction in glycerol/ethanol and oleate, and changes in the levels of several sphingolipids including C18 alpha-hydroxy-phytoceramide, were also observed in the temperature sensitive strain. Deletion of SUR4, the strongest suppressor, reversed the temperature sensitive fermentative growth defect, the morphological changes and the elevated levels of C18 alpha-hydroxy phytoceramide in pam16-I61N. Deletion of the other four suppressor genes had similar effects on C18 alpha-hydroxy-phytoceramide levels and restored proliferation to the pam16-I61N strain. In addition, pam16-I61N inhibited respiratory growth, likely by reducing cardiolipin, which is essential for mitochondrial function. Our results suggest that the pleiotropic effects caused by impaired Pam16/Magmas function are mediated in part by changes in lipid metabolism.
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Affiliation(s)
- Mary K. Short
- Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - Joshua P. Hallett
- Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - Krisztina Tar
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - Thomas Dange
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - Marion Schmidt
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - Robyn Moir
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - Ian M. Willis
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
- Department of Systems and Computational Biology, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - Paul T. Jubinsky
- Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, New York, United States of America
- Department of Pediatrics, Section of Hematology/Oncology, Yale University School of Medicine, New Haven, Connecticut, United States of America
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38
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Gebert M, Schrempp SG, Mehnert CS, Heißwolf AK, Oeljeklaus S, Ieva R, Bohnert M, von der Malsburg K, Wiese S, Kleinschroth T, Hunte C, Meyer HE, Haferkamp I, Guiard B, Warscheid B, Pfanner N, van der Laan M. Mgr2 promotes coupling of the mitochondrial presequence translocase to partner complexes. ACTA ACUST UNITED AC 2012; 197:595-604. [PMID: 22613836 PMCID: PMC3365495 DOI: 10.1083/jcb.201110047] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Many mitochondrial proteins are synthesized with N-terminal presequences in the cytosol. The presequence translocase of the inner mitochondrial membrane (TIM23) translocates preproteins into and across the membrane and associates with the matrix-localized import motor. The TIM23 complex consists of three core components and Tim21, which interacts with the translocase of the outer membrane (TOM) and the respiratory chain. We have identified a new subunit of the TIM23 complex, the inner membrane protein Mgr2. Mitochondria lacking Mgr2 were deficient in the Tim21-containing sorting form of the TIM23 complex. Mgr2 was required for binding of Tim21 to TIM23(CORE), revealing a binding chain of TIM23(CORE)-Mgr2/Tim21-respiratory chain. Mgr2-deficient yeast cells were defective in growth at elevated temperature, and the mitochondria were impaired in TOM-TIM23 coupling and the import of presequence-carrying preproteins. We conclude that Mgr2 is a coupling factor of the presequence translocase crucial for cell growth at elevated temperature and for efficient protein import.
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Affiliation(s)
- Michael Gebert
- Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Fakultät für Biologie, Funktionelle Proteomik, Universität Freiburg, 79104 Freiburg, Germany
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39
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Levy SF, Ziv N, Siegal ML. Bet hedging in yeast by heterogeneous, age-correlated expression of a stress protectant. PLoS Biol 2012; 10:e1001325. [PMID: 22589700 PMCID: PMC3348152 DOI: 10.1371/journal.pbio.1001325] [Citation(s) in RCA: 261] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2011] [Accepted: 03/26/2012] [Indexed: 01/06/2023] Open
Abstract
A new experimental approach reveals a bet-hedging strategy in unstressed, clonal yeast cells, whereby they adopt a range of growth states that correlate with expression of a trehalose-synthesis regulator and predict resistance to future stress. Genetically identical cells grown in the same culture display striking cell-to-cell heterogeneity in gene expression and other traits. A crucial challenge is to understand how much of this heterogeneity reflects the noise tolerance of a robust system and how much serves a biological function. In bacteria, stochastic gene expression results in cell-to-cell heterogeneity that might serve as a bet-hedging mechanism, allowing a few cells to survive through an antimicrobial treatment while others perish. Despite its clinical importance, the molecular mechanisms underlying bet hedging remain unclear. Here, we investigate the mechanisms of bet hedging in Saccharomyces cerevisiae using a new high-throughput microscopy assay that monitors variable protein expression, morphology, growth rate, and survival outcomes of tens of thousands of yeast microcolonies simultaneously. We find that clonal populations display broad distributions of growth rates and that slow growth predicts resistance to heat killing in a probabalistic manner. We identify several gene products that are likely to play a role in bet hedging and confirm that Tsl1, a trehalose-synthesis regulator, is an important component of this resistance. Tsl1 abundance correlates with growth rate and replicative age and predicts survival. Our results suggest that yeast bet hedging results from multiple epigenetic growth states determined by a combination of stochastic and deterministic factors. Genetically identical cells grown in the same environment can display heterogeneity in their morphology, behavior, and composition of their cellular components. In some microorganisms, such cellular heterogeneity can underlie a phenomenon known as bet hedging because it enables some cells to survive in harsh environments, hence increasing the overall population fitness when environmental shifts are unpredictable. Bet hedging is likely to be an important strategy by which microbes infect humans and evade antimicrobial treatments, yet little is known of how cellular heterogeneity contributes to microbial survival. Here, we study the mechanisms underlying bet hedging in yeast. We find that populations of genetically identical yeast contain a broad distribution of growth rates and that slow growth predicts resistance to heat killing in a graded fashion. We identify several gene products that are likely to play a role in this bet-hedging strategy and confirm that Tsl1, a regulator of the production of the disaccharide trehalose, is an important component of acute stress resistance. Finally, we find that old age in cells correlates with a Tsl1-abundant, stress-resistant cell state. Our results suggest that trehalose synthesis is part of a complex and multifactorial mechanism that underlies bet hedging in yeast.
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Affiliation(s)
- Sasha F. Levy
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, New York, United States of America
- * E-mail: (SFL); (MLS)
| | - Naomi Ziv
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, New York, United States of America
| | - Mark L. Siegal
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, New York, United States of America
- * E-mail: (SFL); (MLS)
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40
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Stiburek L, Cesnekova J, Kostkova O, Fornuskova D, Vinsova K, Wenchich L, Houstek J, Zeman J. YME1L controls the accumulation of respiratory chain subunits and is required for apoptotic resistance, cristae morphogenesis, and cell proliferation. Mol Biol Cell 2012; 23:1010-23. [PMID: 22262461 PMCID: PMC3302729 DOI: 10.1091/mbc.e11-08-0674] [Citation(s) in RCA: 129] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Loss-of-function studies show that the human mitochondrial YME1L protease ensures cell proliferation, maintains normal cristae morphology and complex I activity, acts in an antiapoptotic manner, protects mitochondria from accumulation of oxidatively damaged membrane proteins, and is involved in proteolytic regulation of respiratory chain biogenesis. Mitochondrial ATPases associated with diverse cellular activities (AAA) proteases are involved in the quality control and processing of inner-membrane proteins. Here we investigate the cellular activities of YME1L, the human orthologue of the Yme1 subunit of the yeast i‑AAA complex, using stable short hairpin RNA knockdown and expression experiments. Human YME1L is shown to be an integral membrane protein that exposes its carboxy-terminus to the intermembrane space and exists in several complexes of 600–1100 kDa. The stable knockdown of YME1L in human embryonic kidney 293 cells led to impaired cell proliferation and apoptotic resistance, altered cristae morphology, diminished rotenone-sensitive respiration, and increased susceptibility to mitochondrial membrane protein carbonylation. Depletion of YME1L led to excessive accumulation of nonassembled respiratory chain subunits (Ndufb6, ND1, and Cox4) in the inner membrane. This was due to a lack of YME1L proteolytic activity, since the excessive accumulation of subunits was reversed by overexpression of wild-type YME1L but not a proteolytically inactive YME1L variant. Similarly, the expression of wild-type YME1L restored the lamellar cristae morphology of YME1L-deficient mitochondria. Our results demonstrate the importance of mitochondrial inner-membrane proteostasis to both mitochondrial and cellular function and integrity and reveal a novel role for YME1L in the proteolytic regulation of respiratory chain biogenesis.
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Affiliation(s)
- Lukas Stiburek
- Department of Pediatrics and Adolescent Medicine, Charles University in Prague and General University Hospital in Prague, 12808 Prague 2, Czech Republic
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41
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Gebert N, Gebert M, Oeljeklaus S, von der Malsburg K, Stroud D, Kulawiak B, Wirth C, Zahedi R, Dolezal P, Wiese S, Simon O, Schulze-Specking A, Truscott K, Sickmann A, Rehling P, Guiard B, Hunte C, Warscheid B, van der Laan M, Pfanner N, Wiedemann N. Dual Function of Sdh3 in the Respiratory Chain and TIM22 Protein Translocase of the Mitochondrial Inner Membrane. Mol Cell 2011; 44:811-8. [DOI: 10.1016/j.molcel.2011.09.025] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2011] [Revised: 08/18/2011] [Accepted: 09/20/2011] [Indexed: 10/14/2022]
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Multiple roles of the Cox20 chaperone in assembly of Saccharomyces cerevisiae cytochrome c oxidase. Genetics 2011; 190:559-67. [PMID: 22095077 DOI: 10.1534/genetics.111.135665] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The Cox2 subunit of Saccharomyces cerevisiae cytochrome c oxidase is synthesized in the mitochondrial matrix as a precursor whose leader peptide is rapidly processed by the inner membrane protease following translocation to the intermembrane space. Processing is chaperoned by Cox20, an integral inner membrane protein whose hydrophilic domains are located in the intermembrane space, and Cox20 remains associated with mature, unassembled Cox2. The Cox2 C-tail domain is exported post-translationally by the highly conserved translocase Cox18 and associated proteins. We have found that Cox20 is required for efficient export of the Cox2 C-tail. Furthermore, Cox20 interacts by co-immune precipitation with Cox18, and this interaction requires the presence of Cox2. We therefore propose that Cox20 binding to Cox2 on the trans side of the inner membrane accelerates dissociation of newly exported Cox2 from the Cox18 translocase, promoting efficient cycling of the translocase. The requirement for Cox20 in cytochrome c oxidase assembly and respiratory growth is partially bypassed by yme1, mgr1 or mgr3 mutations, each of which reduce i-AAA protease activity in the intermembrane space. Thus, Cox20 also appears to stabilize unassembled Cox2 against degradation by the i-AAA protease. Pre-Cox2 leader peptide processing by Imp1 occurs in the absence of Cox20 and i-AAA protease activity, but is greatly reduced in efficiency. Under these conditions some mature Cox2 is assembled into cytochrome c oxidase allowing weak respiratory growth. Thus, the Cox20 chaperone has important roles in leader peptide processing, C-tail export, and stabilization of Cox2.
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43
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Gerdes F, Tatsuta T, Langer T. Mitochondrial AAA proteases--towards a molecular understanding of membrane-bound proteolytic machines. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2011; 1823:49-55. [PMID: 22001671 DOI: 10.1016/j.bbamcr.2011.09.015] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2011] [Revised: 09/13/2011] [Accepted: 09/15/2011] [Indexed: 10/16/2022]
Abstract
Mitochondrial AAA proteases play an important role in the maintenance of mitochondrial proteostasis. They regulate and promote biogenesis of mitochondrial proteins by acting as processing enzymes and ensuring the selective turnover of misfolded proteins. Impairment of AAA proteases causes pleiotropic defects in various organisms including neurodegeneration in humans. AAA proteases comprise ring-like hexameric complexes in the mitochondrial inner membrane and are functionally conserved from yeast to man, but variations are evident in the subunit composition of orthologous enzymes. Recent structural and biochemical studies revealed how AAA proteases degrade their substrates in an ATP dependent manner. Intersubunit coordination of the ATP hydrolysis leads to an ordered ATP hydrolysis within the AAA ring, which ensures efficient substrate dislocation from the membrane and translocation to the proteolytic chamber. In this review, we summarize recent findings on the molecular mechanisms underlying the versatile functions of mitochondrial AAA proteases and their relevance to those of the other AAA+ machines.
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Affiliation(s)
- Florian Gerdes
- Institute for Genetics, Centre for Molecular Medicine (CMMC), Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), University of Cologne, Zülpicher Str. 47a, 50674 Cologne, Germany.
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44
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Dunn CD. Running on empty: does mitochondrial DNA mutation limit replicative lifespan in yeast?: Mutations that increase the division rate of cells lacking mitochondrial DNA also extend replicative lifespan in Saccharomyces cerevisiae. Bioessays 2011; 33:742-8. [PMID: 21826691 DOI: 10.1002/bies.201100050] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Mitochondrial DNA (mtDNA) mutations escalate with increasing age in higher organisms. However, it has so far been difficult to experimentally determine whether mtDNA mutation merely correlates with age or directly limits lifespan. A recent study shows that budding yeast can also lose functional mtDNA late in life. Interestingly, independent studies of replicative lifespan (RLS) and of mtDNA-deficient cells show that the same mutations can increase both RLS and the division rate of yeast lacking the mitochondrial genome. These exciting, parallel findings imply a potential causal relationship between mtDNA mutation and replicative senescence. Furthermore, these results suggest more efficient methods for discovering genes that determine lifespan.
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Affiliation(s)
- Cory D Dunn
- Department of Molecular Biology and Genetics, Koç University, Istanbul, Turkey.
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45
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Claypool SM, Whited K, Srijumnong S, Han X, Koehler CM. Barth syndrome mutations that cause tafazzin complex lability. ACTA ACUST UNITED AC 2011; 192:447-62. [PMID: 21300850 PMCID: PMC3101092 DOI: 10.1083/jcb.201008177] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Deficits in mitochondrial function result in many human diseases. The X-linked disease Barth syndrome (BTHS) is caused by mutations in the tafazzin gene TAZ1. Its product, Taz1p, participates in the metabolism of cardiolipin, the signature phospholipid of mitochondria. In this paper, a yeast BTHS mutant tafazzin panel is established, and 18 of the 21 tested BTHS missense mutations cannot functionally replace endogenous tafazzin. Four BTHS mutant tafazzins expressed at low levels are degraded by the intermembrane space AAA (i-AAA) protease, suggesting misfolding of the mutant polypeptides. Paradoxically, each of these mutant tafazzins assembles in normal protein complexes. Furthermore, in the absence of the i-AAA protease, increased expression and assembly of two of the BTHS mutants improve their function. However, the BTHS mutant complexes are extremely unstable and accumulate as insoluble aggregates when disassembled in the absence of the i-AAA protease. Thus, the loss of function for these BTHS mutants results from the inherent instability of the mutant tafazzin complexes.
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Affiliation(s)
- Steven M Claypool
- Department of Physiology, Johns Hopkins School of Medicine, Baltimore, MD 21205, USA.
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Francis BR, Thorsness PE. Hsp90 and mitochondrial proteases Yme1 and Yta10/12 participate in ATP synthase assembly in Saccharomyces cerevisiae. Mitochondrion 2011; 11:587-600. [PMID: 21439406 DOI: 10.1016/j.mito.2011.03.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2010] [Revised: 02/22/2011] [Accepted: 03/15/2011] [Indexed: 10/18/2022]
Abstract
Hsc82 and Hsp82, the Hsp90 family proteins of yeast, are both required for fermentative growth at 37°C. Inactivation of either of the mitochondrial AAA proteases, Yme1 or Yta10/12, allows fermentative growth of hsc82∆ or hsp82∆ strains at 37°C. Genetic evidence indicates interaction of Hsc82/Hsp82 with the Yme1 and Yta10/Yta12 complexes in promoting F(1)F(o)-ATPase activity, with Hsc82 specifically required for F(1)-ATPase assembly. A previously reported mutation in Rpt3, one of the six ATPases of the proteasome, suppresses yme1∆ phenotypes and increases transcription of HSC82 but not HSP82. These genetic interactions describe a functional role for Hsp90 proteins in mitochondrial biogenesis.
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Affiliation(s)
- Brian R Francis
- Department of Molecular Biology, University of Wyoming, Laramie, WY 82071, USA
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Kochmak SA, Knorre DA, Sokolov SS, Severin FF. Physiological scenarios of programmed loss of mitochondrial DNA function and death of yeast. BIOCHEMISTRY (MOSCOW) 2011; 76:167-71. [DOI: 10.1134/s0006297911020015] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Truscott KN, Lowth BR, Strack PR, Dougan DA. Diverse functions of mitochondrial AAA+ proteins: protein activation, disaggregation, and degradation. Biochem Cell Biol 2010; 88:97-108. [PMID: 20130683 DOI: 10.1139/o09-167] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
In eukaryotes, mitochondria are required for the proper function of the cell and as such the maintenance of proteins within this organelle is crucial. One class of proteins, collectively known as the AAA+ (ATPases associated with various cellular activities) superfamily, make a number of important contributions to mitochondrial protein homeostasis. In this organelle, they contribute to the maturation and activation of proteins, general protein quality control, respiratory chain complex assembly, and mitochondrial DNA maintenance and integrity. To achieve such diverse functions this group of ATP-dependent unfoldases utilize the energy from ATP hydrolysis to modulate the structure of proteins via unique domains and (or) associated functional components. In this review, we describe the current status of knowledge regarding the known mitochondrial AAA+ proteins and their role in this organelle.
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Affiliation(s)
- Kaye N Truscott
- La Trobe University, Science Dr., Melbourne, Victoria 3086, Australia
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Fungal homoserine kinase (thr1Delta) mutants are attenuated in virulence and die rapidly upon threonine starvation and serum incubation. EUKARYOTIC CELL 2010; 9:729-37. [PMID: 20305003 DOI: 10.1128/ec.00045-10] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The fungally conserved subset of amino acid biosynthetic enzymes not present in humans offer exciting potential as an unexploited class of antifungal drug targets. Since threonine biosynthesis is essential in Cryptococcus neoformans, we further explored the potential of threonine biosynthetic enzymes as antifungal drug targets by determining the survival in mice of Saccharomyces cerevisiae homoserine kinase (thr1Delta) and threonine synthase (thr4Delta) mutants. In striking contrast to aspartate kinase (hom3Delta) mutants, S. cerevisiae thr1Delta and thr4Delta mutants were severely depleted after only 4 h in vivo. Similarly, Candida albicans thr1Delta mutants, but not hom3Delta mutants, were significantly attenuated in virulence. Consistent with the in vivo phenotypes, S. cerevisiae thr1Delta and thr4Delta mutants as well as C. albicans thr1Delta mutants were extremely serum sensitive. In both species, serum sensitivity was suppressed by the addition of threonine, a feedback inhibitor of Hom3p. Because mutation of the HOM3 and HOM6 genes, required for the production of the toxic pathway intermediate homoserine, also suppressed serum sensitivity, we hypothesize that serum sensitivity is a consequence of homoserine accumulation. Serum survival is critical for dissemination, an important virulence determinant: thus, together with the essential nature of C. neoformans threonine synthesis, the cross-species serum sensitivity of thr1Delta mutants makes the fungus-specific Thr1p, and likely Thr4p, ideal antifungal drug targets.
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Homoserine toxicity in Saccharomyces cerevisiae and Candida albicans homoserine kinase (thr1Delta) mutants. EUKARYOTIC CELL 2010; 9:717-28. [PMID: 20305002 DOI: 10.1128/ec.00044-10] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
In addition to threonine auxotrophy, mutation of the Saccharomyces cerevisiae threonine biosynthetic genes THR1 (encoding homoserine kinase) and THR4 (encoding threonine synthase) results in a plethora of other phenotypes. We investigated the basis for these other phenotypes and found that they are dependent on the toxic biosynthetic intermediate homoserine. Moreover, homoserine is also toxic for Candida albicans thr1Delta mutants. Since increasing levels of threonine, but not other amino acids, overcome the homoserine toxicity of thr1Delta mutants, homoserine may act as a toxic threonine analog. Homoserine-mediated lethality of thr1Delta mutants is blocked by cycloheximide, consistent with a role for protein synthesis in this lethality. We identified various proteasome and ubiquitin pathway components that either when mutated or present in high copy numbers suppressed the thr1Delta mutant homoserine toxicity. Since the doa4Delta and proteasome mutants identified have reduced ubiquitin- and/or proteasome-mediated proteolysis, the degradation of a particular protein or subset of proteins likely contributes to homoserine toxicity.
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