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Joy Ogbechi, Belinda S Hall, Thomas Sbarrato, Jack Taunton, Anne E Willis, Ronald C Wek, Rachel E Simmonds
Mycolactone is the exotoxin virulence factor of Mycobacterium ulcerans that causes the neglected tropical disease Buruli ulcer. We recently showed it to be a broad spectrum inhibitor of Sec61-dependent co-translational translocation of proteins into the endoplasmic reticulum (ER). An outstanding question is the molecular pathway linking this to its known cytotoxicity. We have now used translational profiling to better understand the reprogramming that occurs in cells exposed to mycolactone. Gene ontology identified enrichment in genes involved in cellular response to stress, and apoptosis signalling among those showing enhanced translation...
March 14, 2018: Cell Death & Disease
Katharina Braunger, Stefan Pfeffer, Shiteshu Shrimal, Reid Gilmore, Otto Berninghausen, Elisabet C Mandon, Thomas Becker, Friedrich Förster, Roland Beckmann
Protein synthesis, transport and N-glycosylation are coupled at the mammalian endoplasmic reticulum (ER) by complex formation between the ribosome, the Sec61 protein-conducting channel and the oligosaccharyltransferase (OST). Here, we used different cryo-electron microscopy approaches to determine structures of native and solubilized ribosome-Sec61-OST complexes. A molecular model for the catalytic OST subunit revealed how STT3A is integrated into the OST and how STT3 paralog specificity for translocon-associated OST is achieved...
March 8, 2018: Science
Xuemei Wan, Jeffrey D Serrill, Ian R Humphreys, Michelle Tan, Kerry L McPhail, Ian G Ganley, Jane E Ishmael
Our understanding of autophagy and lysosomal function has been greatly enhanced by the discovery of natural product structures that can serve as chemical probes to reveal new patterns of signal transduction in cells. Coibamide A is a cytotoxic marine natural product that induces mTOR-independent autophagy as an adaptive stress response that precedes cell death. Autophagy-related (ATG) protein 5 (ATG5) is required for coibamide-induced autophagy but not required for coibamide-induced apoptosis. Using wild-type and autophagy-deficient mouse embryonic fibroblasts (MEFs) we demonstrate that coibamide-induced toxicity is delayed in ATG5-/- cells relative to ATG5+/+ cells...
March 1, 2018: Marine Drugs
David Cruz-Garcia, Vivek Malhotra, Amy J Curwin
It is usually assumed that eukaryotic cells secrete only proteins that contain a signal sequence for Sec61 mediated translocation into the lumen of endoplasmic reticulum (ER). Surprisingly however, many proteins, such as superoxide dismutase (SOD)1, acyl-CoA binding protein (Acb1), interleukin 1β, fibroblast growth factor 2 and the adipokine Unpaired2, to name a few, are secreted even though they lack a signal sequence. The discovery that these proteins are secreted has presented a new challenge and we describe here a common pathway by which SOD1 and Acb1 are specifically secreted upon nutrient starvation...
February 24, 2018: Seminars in Cell & Developmental Biology
Lin Bai, Tong Wang, Gongpu Zhao, Amanda Kovach, Huilin Li
N-glycosylation is a ubiquitous modification of eukaryotic secretory and membrane-bound proteins; about 90% of glycoproteins are N-glycosylated. The reaction is catalysed by an eight-protein oligosaccharyltransferase complex, OST, embedded in the ER membrane. Our understanding of eukaryotic protein N-glycosylation has been limited owing to the lack of high-resolution structures. Here we report a 3.5-Å resolution cryo-EM structure of the Saccharomyces cerevisiae OST, revealing the structures of Ost1-5, Stt3, Wbp1, and Swp1...
January 22, 2018: Nature
Sebastian Jung, Jörg Tatzelt
Impaired transport of intrinsically disordered proteins through the Sec61 and SecY translocon; implications for prion diseases.
February 1, 2018: Prion
Bruna Figueiredo Costa, Patrizia Cassella, Sara Francesca Colombo, Nica Borgese
Tail-anchored (TA) proteins insert into their target organelles by incompletely elucidated post-translational pathways. Some TA proteins spontaneously insert into protein-free liposomes, yet target a specific organelle in vivo. Two spontaneously inserting cytochrome b5 forms, b5-ER and b5-RR, which differ only in the charge of the C-terminal region, target the ER or the mitochondrial outer membrane (MOM), respectively. To bridge the gap between the cell-free and in cellula results, we analyzed targeting in digitonin-permeabilized adherent HeLa cells...
January 23, 2018: Traffic
Sang Mi Shim, Ha Rim Choi, Ki Woon Sung, Yoon Jee Lee, Sung Tae Kim, Daeho Kim, Su Ran Mun, Joonsung Hwang, Hyunjoo Cha-Molstad, Aaron Ciechanover, Bo Yeon Kim, Yong Tae Kwon
BiP and other endoplasmic reticulum (ER)-resident proteins are thought to be metabolically stable and to function primarily in the ER lumen. We sought to assess how the abundance of these proteins dynamically fluctuates in response to various stresses and how their subpopulations are relocated to non-ER compartments such as the cytosol. We showed that the molecular chaperone BiP (also known as GRP78) was short-lived under basal conditions and ER stress. The turnover of BiP was in part driven by its amino-terminal arginylation (Nt-arginylation) by the arginyltransferase ATE1, which generated an autophagic N-degron of the N-end rule pathway...
January 2, 2018: Science Signaling
Yi Qian, Qing-Hua Han, Dan Liu, Peng-Fei Tu, Ke-Wu Zeng, Hong Liang
Dried stem bark from Albizia julibrissin(AJ) is a common traditional Chinese herb with several therapy effects including insomnia, anxiety and anti-tumor. Recently, the anti-tumor effect and mechanism studies of AJ have drawn much attention; however, there are still some troubles in chemical composition separation, which leads to the difficulties in pharmacological research of AJ. In this study, we firstly confirmed the proliferation inhibitory effect of total saponins from AJ(TSAJ)on human hepatocarcinoma(HepG2) cells, and also tested the apoptosis induction effect of TSAJ...
October 2017: Zhongguo Zhong Yao za Zhi, Zhongguo Zhongyao Zazhi, China Journal of Chinese Materia Medica
Yimeng Zhu, Gangming Zhang, Shaoyu Lin, Juanming Shi, Hong Zhang, Junjie Hu
Sec61β, a subunit of the Sec61 translocon complex, is not essential in yeast and commonly used as a marker of endoplasmic reticulum (ER). In higher eukaryotes, such as Drosophila, deletion of Sec61β causes lethality, but its physiological role is unclear. Here, we show that Sec61β interacts directly with microtubules. Overexpression of Sec61β containing small epitope tags, but not a RFP tag, induces dramatic bundling of the ER and microtubule. A basic region in the cytosolic domain of Sec61β is critical for microtubule association...
November 22, 2017: Protein & Cell
Sven Lang, Stefan Pfeffer, Po-Hsien Lee, Adolfo Cavalié, Volkhard Helms, Friedrich Förster, Richard Zimmermann
The membrane of the endoplasmic reticulum (ER) of nucleated human cells harbors the protein translocon, which facilitates membrane integration or translocation of almost every newly synthesized polypeptide targeted to organelles of the endo- and exocytotic pathway. The translocon comprises the polypeptide-conducting Sec61 channel and several additional proteins and complexes that are permanently or transiently associated with the heterotrimeric Sec61 complex. This ensemble of proteins facilitates ER targeting of precursor polypeptides, modification of precursor polypeptides in transit through the Sec61 complex, and Sec61 channel gating, i...
2017: Frontiers in Physiology
Caroline Isaac, Annie Mauborgne, Alfonso Grimaldi, Kemy Ade, Michel Pohl, Cristina Limatola, Yves Boucher, Caroline Demangel, Laure Guenin-Macé
BACKGROUND: Mycolactone is a macrolide produced by the skin pathogen Mycobacterium ulcerans, with cytotoxic, analgesic and immunomodulatory properties. The latter were recently shown to result from mycolactone blocking the Sec61-dependent production of pro-inflammatory mediators by immune cells. Here we investigated whether mycolactone similarly affects the inflammatory responses of the nervous cell subsets involved in pain perception, transmission and maintenance. We also investigated the effects of mycolactone on the neuroinflammation that is associated with chronic pain in vivo...
November 2017: PLoS Neglected Tropical Diseases
Alise J Ponsero, Aeid Igbaria, Maxwell A Darch, Samia Miled, Caryn E Outten, Jakob R Winther, Gael Palais, Benoit D'Autréaux, Agnès Delaunay-Moisan, Michel B Toledano
In the endoplasmic reticulum (ER), Ero1 catalyzes disulfide bond formation and promotes glutathione (GSH) oxidation to GSSG. Since GSSG cannot be reduced in the ER, maintenance of the ER glutathione redox state and levels likely depends on ER glutathione import and GSSG export. We used quantitative GSH and GSSG biosensors to monitor glutathione import into the ER of yeast cells. We found that glutathione enters the ER by facilitated diffusion through the Sec61 protein-conducting channel, while oxidized Bip (Kar2) inhibits transport...
September 21, 2017: Molecular Cell
Shiteshu Shrimal, Natalia A Cherepanova, Reid Gilmore
In metazoan organisms, the STT3A isoform of the oligosaccharyltransferase is localized adjacent to the protein translocation channel to catalyze co-translational N-linked glycosylation of proteins in the endoplasmic reticulum. The mechanism responsible for the interaction between the STT3A complex and the translocation channel has not been addressed. Using genetically modified human cells that are deficient in DC2 or KCP2 proteins, we show that loss of DC2 causes a defect in co-translational N-glycosylation of proteins that mimics an STT3A-/- phenotype...
November 6, 2017: Journal of Cell Biology
Viridiana Gracida-Jiménez, Ricardo Mondragón-González, Griselda Vélez-Aguilera, Alejandra Vásquez-Limeta, Marco S Laredo-Cisneros, Juan de Dios Gómez-López, Luis Vaca, Sarah C Gourlay, Laura A Jacobs, Steve J Winder, Bulmaro Cisneros
β-Dystroglycan (β-DG) is a transmembrane protein with critical roles in cell adhesion, cytoskeleton remodeling and nuclear architecture. This functional diversity is attributed to the ability of β-DG to target to, and conform specific protein assemblies at the plasma membrane (PM) and nuclear envelope (NE). Although a classical NLS and importin α/β mediated nuclear import pathway has already been described for β-DG, the intracellular trafficking route by which β-DG reaches the nucleus is unknown. In this study, we demonstrated that β-DG undergoes retrograde intracellular trafficking from the PM to the nucleus via the endosome-ER network...
August 29, 2017: Scientific Reports
Brock Roberts, Amanda Haupt, Andrew Tucker, Tanya Grancharova, Joy Arakaki, Margaret A Fuqua, Angelique Nelson, Caroline Hookway, Susan A Ludmann, Irina A Mueller, Ruian Yang, Rick Horwitz, Susanne M Rafelski, Ruwanthi N Gunawardane
We present a CRISPR/Cas9 genome-editing strategy to systematically tag endogenous proteins with fluorescent tags in human induced pluripotent stem cells (hiPSC). To date, we have generated multiple hiPSC lines with monoallelic green fluorescent protein tags labeling 10 proteins representing major cellular structures. The tagged proteins include alpha tubulin, beta actin, desmoplakin, fibrillarin, nuclear lamin B1, nonmuscle myosin heavy chain IIB, paxillin, Sec61 beta, tight junction protein ZO1, and Tom20...
October 15, 2017: Molecular Biology of the Cell
L F M van de Laarschot, J P H Drenth
Polycystic liver disease (PLD) is a heterogeneous genetic condition. PKD1 and PKD2 germline mutations are found in patients with autosomal dominant polycystic kidney disease (ADPKD). Autosomal dominant polycystic liver disease (ADPLD) is associated with germline mutations in PRKCSH, SEC63, LRP5, and recently ALG8, and SEC61. GANAB mutations are found in both patient groups. Loss of heterozygosity of PLD-genes in cyst epithelium contributes to the development of hepatic cysts. A genetic interaction network is implied in hepatic cystogenesis that connects the endoplasmic glycoprotein control mechanisms and polycystin expression and localization...
August 4, 2017: Biochimica et Biophysica Acta
Desirée Schubert, Marie-Christine Klein, Sarah Hassdenteufel, Andrés Caballero-Oteyza, Linlin Yang, Michele Proietti, Alla Bulashevska, Janine Kemming, Johannes Kühn, Sandra Winzer, Stephan Rusch, Manfred Fliegauf, Alejandro A Schäffer, Stefan Pfeffer, Roger Geiger, Adolfo Cavalié, Hongzhi Cao, Fang Yang, Yong Li, Marta Rizzi, Hermann Eibel, Robin Kobbe, Amy L Marks, Brian P Peppers, Robert W Hostoffer, Jennifer M Puck, Richard Zimmermann, Bodo Grimbacher
BACKGROUND: Primary antibody deficiencies (PADs) are the most frequent primary immunodeficiencies in human subjects. The genetic causes of PADs are largely unknown. Sec61 translocon alpha 1 subunit (SEC61A1) is the major subunit of the Sec61 complex, which is the main polypeptide-conducting channel in the endoplasmic reticulum membrane. SEC61A1 is a target gene of spliced X-box binding protein 1 and strongly induced during plasma cell (PC) differentiation. OBJECTIVE: We identified a novel genetic defect and studied its pathologic mechanism in 11 patients from 2 unrelated families with PADs...
August 4, 2017: Journal of Allergy and Clinical Immunology
Jeff E Grotzke, Patrycja Kozik, Jean-David Morel, Francis Impens, Natalia Pietrosemoli, Peter Cresswell, Sebastian Amigorena, Caroline Demangel
Although antigen cross-presentation in dendritic cells (DCs) is critical to the initiation of most cytotoxic immune responses, the intracellular mechanisms and traffic pathways involved are still unclear. One of the most critical steps in this process, the export of internalized antigen to the cytosol, has been suggested to be mediated by Sec61. Sec61 is the channel that translocates signal peptide-bearing nascent polypeptides into the endoplasmic reticulum (ER), and it was also proposed to mediate protein retrotranslocation during ER-associated degradation (a process called ERAD)...
July 18, 2017: Proceedings of the National Academy of Sciences of the United States of America
Tom A Rapoport, Long Li, Eunyong Park
Many proteins are translocated across the endoplasmic reticulum (ER) membrane in eukaryotes or the plasma membrane in prokaryotes. These proteins use hydrophobic signal sequences or transmembrane (TM) segments to trigger their translocation through the protein-conducting Sec61/SecY channel. Substrates are first directed to the channel by cytosolic targeting factors, which use hydrophobic pockets to bind diverse signal and TM sequences. Subsequently, these hydrophobic sequences insert into the channel, docking into a groove on the outside of the lateral gate of the channel, where they also interact with lipids...
October 6, 2017: Annual Review of Cell and Developmental Biology
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