301
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Abstract
The twin-arginine translocation (Tat) pathway is responsible for the export of folded proteins across the cytoplasmic membrane of bacteria. Substrates for the Tat pathway include redox enzymes requiring cofactor insertion in the cytoplasm, multimeric proteins that have to assemble into a complex prior to export, certain membrane proteins, and proteins whose folding is incompatible with Sec export. These proteins are involved in a diverse range of cellular activities including anaerobic metabolism, cell envelope biogenesis, metal acquisition and detoxification, and virulence. The Escherichia coli translocase consists of the TatA, TatB, and TatC proteins, but little is known about the precise sequence of events that leads to protein translocation, the energetic requirements, or the mechanism that prevents the export of misfolded proteins. Owing to the unique characteristics of the pathway, it holds promise for biotechnological applications.
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Affiliation(s)
- Philip A Lee
- Institute for Cellular and Molecular Biology, Department of Chemical Engineering, University of Texas, Austin, Texas 78712-0231, USA.
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302
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Kang SW, Rane NS, Kim SJ, Garrison JL, Taunton J, Hegde RS. Substrate-specific translocational attenuation during ER stress defines a pre-emptive quality control pathway. Cell 2006; 127:999-1013. [PMID: 17129784 PMCID: PMC3656606 DOI: 10.1016/j.cell.2006.10.032] [Citation(s) in RCA: 220] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2006] [Revised: 08/30/2006] [Accepted: 10/04/2006] [Indexed: 10/23/2022]
Abstract
Eukaryotic proteins entering the secretory pathway are translocated into the ER by signal sequences that vary widely in primary structure. We now provide a functional rationale for this long-observed sequence diversity by demonstrating that differences among signals facilitate substrate-selective modulation of protein translocation. We find that during acute ER stress, translocation of secretory and membrane proteins is rapidly and transiently attenuated in a signal sequence-selective manner. Their cotranslational rerouting to the cytosol for degradation reduces the burden of misfolded substrates entering the ER and represents a pathway for pre-emptive quality control (pQC). Bypassing the pQC pathway for the prion protein increases its rate of aggregation in the ER lumen during prolonged stress and renders cells less capable of viable recovery. Conversely, pharmacologically augmenting pQC during ER stress proved protective. Thus, protein translocation is a physiologically regulated process that is utilized for pQC as part of the ER stress response.
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Affiliation(s)
- Sang-Wook Kang
- Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, 18 Library Drive, Building 18T, Room 101, Bethesda, MD, 20892, USA
| | - Neena S. Rane
- Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, 18 Library Drive, Building 18T, Room 101, Bethesda, MD, 20892, USA
| | - Soo Jung Kim
- Functional Genomic Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, 305-333, Korea
| | - Jennifer L. Garrison
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, CA, 94107, USA
| | - Jack Taunton
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, CA, 94107, USA
| | - Ramanujan S. Hegde
- Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, 18 Library Drive, Building 18T, Room 101, Bethesda, MD, 20892, USA
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303
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Fujiki Y, Okumoto K, Kinoshita N, Ghaedi K. Lessons from peroxisome-deficient Chinese hamster ovary (CHO) cell mutants. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2006; 1763:1374-81. [PMID: 17045664 DOI: 10.1016/j.bbamcr.2006.09.012] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2006] [Revised: 09/05/2006] [Accepted: 09/06/2006] [Indexed: 10/24/2022]
Abstract
Cells with a genetic defect affecting a biological activity and/or a cell phenotype are generally called "cell mutants" and are a highly useful tool in genetic, biochemical, as well as cell biological research. To investigate peroxisome biogenesis and human peroxisome biogenesis disorders, more than a dozen complementation groups of Chinese hamster ovary (CHO) cell mutants defective in peroxisome assembly have been successfully isolated and established as a model system. Moreover, successful PEX gene cloning studies by taking advantage of rapid functional complementation assay of CHO cell mutants invaluably contributed to the accomplishment of isolation of pathogenic genes responsible for peroxisome biogenesis diseases. Molecular mechanisms of peroxisome assembly are currently investigated by making use of such mammalian cell mutants.
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Affiliation(s)
- Yukio Fujiki
- Department of Biology, Faculty of Sciences, Kyushu University Graduate School, 6-10-1 Hakozaki, Fukuoka 812-8581, Japan.
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304
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Abstract
The characteristic structural organization of mitochondria is the product of synthesis of macromolecules within the mitochondria together with the import of proteins and lipids synthesized outside the organelle. Synthetic and import processes are required for mitochondrial proliferation and might also facilitate the growth of pre-existing mitochondria. Recent evidence indicates that these events are regulated in a complex way by several agonists and environmental conditions, through activation of specific signaling pathways and transcription factors. A newly discovered role of this organelle in retrograde intracellular signaling back to the nucleus has also emerged. This is likely to have far-reaching implications in development, aging, disease and environmental adaptation. Generation of nitric oxide (NO) appears to be an important player in these processes, possibly acting as a unifying molecular switch to trigger the whole mitochondrial biogenesis process. High levels of NO acutely inhibit cell respiration by binding to cytochrome c oxidase. Conversely, chronic, smaller increases in NO levels stimulate mitochondrial biogenesis in diverse cell types. NO-induced mitochondrial biogenesis seems to be linked to proliferation and differentiation of normal and tumor cells, as well as in aging.
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Affiliation(s)
- Enzo Nisoli
- Department of Pharmacology, Chemotherapy and Medical Toxicology, School of Medicine, Milan University, via Vanvitelli 32, 20129 Milan, Italy.
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305
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Sibbald MJJB, Ziebandt AK, Engelmann S, Hecker M, de Jong A, Harmsen HJM, Raangs GC, Stokroos I, Arends JP, Dubois JYF, van Dijl JM. Mapping the pathways to staphylococcal pathogenesis by comparative secretomics. Microbiol Mol Biol Rev 2006; 70:755-88. [PMID: 16959968 PMCID: PMC1594592 DOI: 10.1128/mmbr.00008-06] [Citation(s) in RCA: 204] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
The gram-positive bacterium Staphylococcus aureus is a frequent component of the human microbial flora that can turn into a dangerous pathogen. As such, this organism is capable of infecting almost every tissue and organ system in the human body. It does so by actively exporting a variety of virulence factors to the cell surface and extracellular milieu. Upon reaching their respective destinations, these virulence factors have pivotal roles in the colonization and subversion of the human host. It is therefore of major importance to obtain a clear understanding of the protein transport pathways that are active in S. aureus. The present review aims to provide a state-of-the-art roadmap of staphylococcal secretomes, which include both protein transport pathways and the extracytoplasmic proteins of these organisms. Specifically, an overview is presented of the exported virulence factors, pathways for protein transport, signals for cellular protein retention or secretion, and the exoproteomes of different S. aureus isolates. The focus is on S. aureus, but comparisons with Staphylococcus epidermidis and other gram-positive bacteria, such as Bacillus subtilis, are included where appropriate. Importantly, the results of genomic and proteomic studies on S. aureus secretomes are integrated through a comparative "secretomics" approach, resulting in the first definition of the core and variant secretomes of this bacterium. While the core secretome seems to be largely employed for general housekeeping functions which are necessary to thrive in particular niches provided by the human host, the variant secretome seems to contain the "gadgets" that S. aureus needs to conquer these well-protected niches.
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Affiliation(s)
- M J J B Sibbald
- Department of Medical Microbiology, University Medical Centre Groningen, Groningen, The Netherlands
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306
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Champion PAD, Stanley SA, Champion MM, Brown EJ, Cox JS. C-Terminal Signal Sequence Promotes Virulence Factor Secretion in Mycobacterium tuberculosis. Science 2006; 313:1632-6. [PMID: 16973880 DOI: 10.1126/science.1131167] [Citation(s) in RCA: 157] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Mycobacterium tuberculosis uses the ESX-1/Snm system [early secreted antigen 6 kilodaltons (ESAT-6) system 1/secretion in mycobacteria] to deliver virulence factors into host macrophages during infection. Despite its essential role in virulence, the mechanism of ESX-1 secretion is unclear. We found that the unstructured C terminus of the CFP-10 substrate was recognized by Rv3871, a cytosolic component of the ESX-1 system that itself interacts with the membrane protein Rv3870. Point mutations in the signal that abolished binding of CFP-10 to Rv3871 prevented secretion of the CFP-10 (culture filtrate protein, 10 kilodaltons)/ESAT-6 virulence factor complex. Attachment of the signal to yeast ubiquitin was sufficient for secretion from M. tuberculosis cells, demonstrating that this ESX-1 signal is portable.
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Affiliation(s)
- Patricia A Digiuseppe Champion
- Department of Microbiology and Immunology, University of California, San Francisco, 600 16th Street, Campus Box 2200, San Francisco, CA 94143-2200, USA
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307
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Fisher A, Montal M. Characterization of Clostridial botulinum neurotoxin channels in neuroblastoma cells. Neurotox Res 2006; 9:93-100. [PMID: 16785104 DOI: 10.1007/bf03033926] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
The channel and chaperone activities of Clostridial botulinum neurotoxin (BoNT) A were investigated in Neuro 2a neuroblastoma cells under conditions that closely emulate those prevalent at the endosome. Channel activity occurs in bursts interspersed between periods of little or no activity. The channels are voltage dependent, opening only at negative voltages. Within bursts, the channel resides preferentially in the open state. The channels open to a main conductance of 105 +/- 5 pS or 65 +/- 4 pS in 200 mM CsCl or NaCl, respectively. The BoNT channels display a conspicuous subconductance of 10 +/- 2 pS. The neuroblastoma cell line appears, therefore, to be a suitable system to characterize the BoNT channel and to pursue evaluation of plausible strategies for targeted drug delivery thereby minimizing the requirement for in vivo animal testing.
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Affiliation(s)
- A Fisher
- Section of Neurobiology, Division of Biological Sciences, University of California San Diego, La Jolla, 92093-0366, USA
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308
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Wagner S, Bader ML, Drew D, de Gier JW. Rationalizing membrane protein overexpression. Trends Biotechnol 2006; 24:364-71. [PMID: 16820235 DOI: 10.1016/j.tibtech.2006.06.008] [Citation(s) in RCA: 199] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2006] [Revised: 04/20/2006] [Accepted: 06/16/2006] [Indexed: 11/27/2022]
Abstract
Functional and structural studies of membrane proteins usually require overexpression of the proteins in question. Often, however, the 'trial and error' approaches that are mainly used to produce membrane proteins are not successful. Our rapidly increasing understanding of membrane protein insertion, folding and degradation means that membrane protein overexpression can be more rationalized, both at the level of the overexpression host and the overexpressed membrane protein. This change of mindset is likely to have a significant impact on membrane protein research.
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Affiliation(s)
- Samuel Wagner
- Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden
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309
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Holm PJ, Bhakat P, Jegerschöld C, Gyobu N, Mitsuoka K, Fujiyoshi Y, Morgenstern R, Hebert H. Structural Basis for Detoxification and Oxidative Stress Protection in Membranes. J Mol Biol 2006; 360:934-45. [PMID: 16806268 DOI: 10.1016/j.jmb.2006.05.056] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2006] [Revised: 05/17/2006] [Accepted: 05/19/2006] [Indexed: 11/25/2022]
Abstract
Synthesis of mediators of fever, pain and inflammation as well as protection against reactive molecules and oxidative stress is a hallmark of the MAPEG superfamily (membrane associated proteins in eicosanoid and glutathione metabolism). The structure of a MAPEG member, rat microsomal glutathione transferase 1, at 3.2 A resolution, solved here in complex with glutathione by electron crystallography, defines the active site location and a cytosolic domain involved in enzyme activation. The glutathione binding site is found to be different from that of the canonical soluble glutathione transferases. The architecture of the homotrimer supports a catalytic mechanism involving subunit interactions and reveals both cytosolic and membraneous substrate entry sites, providing a rationale for the membrane location of the enzyme.
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Affiliation(s)
- Peter J Holm
- Department of Biosciences and Nutrition, Karolinska Institutet and School of Technology and Health, Royal Institute of Technology, SE-14157 Huddinge, Sweden
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310
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Meinecke M, Wagner R, Kovermann P, Guiard B, Mick DU, Hutu DP, Voos W, Truscott KN, Chacinska A, Pfanner N, Rehling P. Tim50 Maintains the Permeability Barrier of the Mitochondrial Inner Membrane. Science 2006; 312:1523-6. [PMID: 16763150 DOI: 10.1126/science.1127628] [Citation(s) in RCA: 153] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Transport of metabolites across the mitochondrial inner membrane is highly selective, thereby maintaining the electrochemical proton gradient that functions as the main driving force for cellular adenosine triphosphate synthesis. Mitochondria import many preproteins via the presequence translocase of the inner membrane. However, the reconstituted Tim23 protein constitutes a pore remaining mainly in its open form, a state that would be deleterious in organello. We found that the intermembrane space domain of Tim50 induced the Tim23 channel to close. Presequences overcame this effect and activated the channel for translocation. Thus, the hydrophilic cis domain of Tim50 maintains the permeability barrier of mitochondria by closing the translocation pore in a presequence-regulated manner.
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Affiliation(s)
- Michael Meinecke
- Biophysik, Universität Osnabrück, FB Biologie/Chemie, D-49034 Osnabrück, Germany
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