26 research outputs found

    Anthrax toxin requires ZDHHC5-mediated palmitoylation of its surface-processing host enzymes

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    The protein acyl transferase ZDHHC5 was recently proposed to regulate trafficking in the endocytic pathway. Therefore, we explored the function of this enzyme in controlling the action of bacterial toxins. We found that ZDHHC5 activity is required for two very different toxins: the anthrax lethal toxin and the pore-forming toxin aerolysin. Both of these toxins have precursor forms, the protoxins, which can use the proprotein convertases Furin and PC7 for activation. We show that ZDHHC5 indeed affects the processing of the protoxins to their active forms. We found that Furin and PC7 can both be S-palmitoylated and are substrates of ZDHHC5. The impact of ZDHHC5 on Furin/PC7-mediated anthrax toxin cleavage is dual, having an indirect and a direct component. First, ZDHHC5 affects the homeostasis and trafficking of a subset of cellular proteins, including Furin and PC7, presumably by affecting the endocytic/recycling pathway. Second, while not inhibiting the protease activity per se, ZDHHC5-mediated Furin/PC7 palmitoylation is required for the cleavage of the anthrax toxin. Finally, we show that palmitoylation of Furin and PC7 promotes their association with plasma membrane microdomains. Both the receptor-bound toxin and the convertases are of very low abundance at the cell surface. Their encounter is unlikely on reasonable time scales. This work indicates that palmitoylation drives their encounter in specific domains, allowing processing and thereby intoxication of the cell

    S-acylation controls SARS-CoV-2 membrane lipid organization and enhances infectivity

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    SARS-CoV-2 virions are surrounded by a lipid bilayer that contains membrane proteins such as spike, responsible for target-cell binding and virus fusion. We found that during SARS-CoV-2 infection, spike becomes lipid modified, through the sequential action of the S-acyltransferases ZDHHC20 and 9. Particularly striking is the rapid acylation of spike on 10 cytosolic cysteines within the ER and Golgi. Using a combination of computational, lipidomics, and biochemical approaches, we show that this massive lipidation controls spike biogenesis and degradation, and drives the formation of localized ordered cholesterol and sphingolipid-rich lipid nanodomains in the early Golgi, where viral budding occurs. Finally, S-acylation of spike allows the formation of viruses with enhanced fusion capacity. Our study points toward S-acylating enzymes an

    Geographical and temporal distribution of SARS-CoV-2 clades in the WHO European Region, January to June 2020

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    We show the distribution of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) genetic clades over time and between countries and outline potential genomic surveillance objectives. We applied three genomic nomenclature systems to all sequence data from the World Health Organization European Region available until 10 July 2020. We highlight the importance of real-time sequencing and data dissemination in a pandemic situation, compare the nomenclatures and lay a foundation for future European genomic surveillance of SARS-CoV-2

    Assembly and substrate recognition properties of human CCT subunits of the TRiC chaperonin

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    Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biology, 2014.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis. "September 2014." Vita. Page 214 blank.Includes bibliographical references (pages 162-181).Group II chaperonins are large multi-subunit complexes that fold cytosolic proteins to their native structures. They are composed of two back-to-back rings of 7-9 subunits. The eukaryotic cytosolic type II chaperonin Tailless Complex Polypeptide-1 (TCP-1) Ring Complex (TRiC) consists of eight different subunits identified as Chaperonin Containing TCP-1 (CCT) [alpha] (1) - [theta] (8). TRiC is necessary for folding about 10% of newly synthesized proteins and is essential for folding actin and tubulin. Most of the research on TRiC in the last 20 years has focused on yeast and bovine TRiC. However, recently, there has been inquiry into TRiC as a target for disease therapy for Huntington's disease, cataract, and some cancers. Consequently, to understand human TRiC, we purified endogenous TRiC from HeLa cells for characterization. These complexes contained all eight of the CCT subunits as determined by immunoblot. The structures were well organized as double-rings of eight subunits each, using negative stain electron microscopy (EM). Human TRiC was active in suppressing aggregation and refolding two different substrates: luciferase (a model substrate) and human [gamma]D-crystallin (H[gamma]D-Crys; a physiological substrate found in the eye lens). To further understand human TRiC, we expressed all of the human CCT subunits, one at a time in E. coli. This was done so that the subunit specificities of the CCT subunits could be studied and so we could have a system where these proteins could be genetically manipulated. Theoretically, all eight subunits in the mature TRiC-complex are needed to successfully recognize all substrates that need to be folded in the cell. We found that two CCT subunits, CCT4 and CCT5, but not the others, formed TRiC-like homo-oligomeric rings in the absence of the other CCT subunits. Purification of these complexes and subsequent structural assays by negative stain and cryo-EM showed that they formed double rings of eight subunits per ring. Biochemically, we found that CCT4 and CCT5 hydrolyzed ATP at the same rate as human TRiC, could refold luciferase to the same level as human TRiC, and suppressed aggregation of H[gamma]D-Crys. The homo-oligomeric complexes also assisted the refolding of H[gamma]D-Crys, a property not observed in the lens specific [alpha]-crystallin chaperone. On the substrates studied, CCT4 and CCT5 homo-oligomers worked as efficiently as hetero-oligomeric TRiC. More stringent substrates such as actin and tubulin need to be studied to further understand CCT specificity. Two mutations, one in CCT4 (C450Y) and one in CCT5 (H147R), have been implicated in hereditary sensory neuropathy. In order to study the defective mutant proteins, we introduced these mutations into the CCT4 and CCT5 constructs. We found that for CCT4, the newly translated mutant polypeptide chains aggregated much more than wild-type (WT) CCT4. While the mutant formed some rings in the E. coli lysate, as assayed by sucrose ultracentrifugation gradients and negative stain EM, they were not stable throughout the purification and the final purified sample contained few homo-oligomers. The mutant CCT5 polypeptide chains were properly folded and assembled in homo-oligomers. H147R CCT5 was able to hydrolyze ATP at a similar rate as WT CCT5. However, in the H[gamma]D-Crys aggregation suppression and refolding assay, mutant huntingtin aggregation suppression assay, and actin refolding assay, mutant CCT5 was not as efficient in suppression or refolding as WT CCT5. Therefore, the H147R mutation in CCT5 led to a chaperoning defect while the C450Y mutation in CCT4 led to a folding/stability defect. In order to understand features of partially folded intermediates that group II chaperonins recognize in a substrate, we investigated whether the archaeal group II chaperonin from Methanococcus maripaludis (Mm-Cpn) could recognize a variety of H[gamma]D-Crys mutants. These mutations were in regions of the protein that could act as recognition signals of substrate - unpaired aromatics, domain interface, and buried core residues. We found that Mm-Cpn was able to recognize all of these mutants, better than it recognized WT H[gamma]D-Crys. In addition, Mm-Cpn could refold most of the mutants to levels higher than WT H[gamma]D-Crys. Therefore, we concluded that Mm-Cpn doesn't recognize any of the proposed recognition signals but recognizes some [beta]-sheet interface exposed in these mutants. These studies further our knowledge of group II chaperonins and specifically human TRiC, and open up some new avenues for the investigation of the folding, assembly and function of this eukaryotic protein essential for the reproduction of all cells.by Oksana A. Sergeeva.Ph. D

    A Hoard from the Uvek Fortified Site: an Accidental Find of 1994

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    A hoard of pottery, metal lamps, mirrors and a lampad, accidentally discovered on the Uvek settlement site in 1994 is made public. The pottery items are represented by three Qashan pottery bowls with underglaze painting and a red-clay jug. The two bronze lamps demonstrate the nearest analogy to those found on the Tsarev fortified settlement site and belong to the type that was spread in the Golden Horde cities. The copper lampad is a product of Byzantine circle, also common in Russia. The two bronze mirrors were imported from China or were made according to Chinese tradition. The objects bear traces of a fire. The authors have concluded that the assemblage had belonged to a wealthy who resided in the Russian Christian quarter. The items were probably concealed in the 1360s as a result of the tragic events associated with the start of the "Great troubles" in the Golden Horde

    Kicking Out Pathogens in Exosomes

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    Host-pathogen interactions involve a series of attacks and counter-attacks. Miao et al. show that, although some invading bacteria can take shelter in lysosomes by neutralizing their pH, this respite is temporary, as host cells can expel them in exosomes

    Co-expression of CCT subunits hints at TRiC assembly

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    The eukaryotic cytosolic chaperonin, t-complex polypeptide 1 (TCP-1) ring complex or TRiC, is responsible for folding a tenth of the proteins in the cell. TRiC is a double-ringed barrel with each ring composed of eight different CCT (chaperonin containing TCP-1) subunits. In order for the subunits to assemble together into mature TRiC, which is believed to contain one and only one of each of these subunits per ring, they must be translated from different chromosomes, correctly folded and assembled. When expressed alone in Escherichia coli, the subunits CCT4 and CCT5, interestingly, form TRiC-like homo-oligomeric rings. To explore potential subunit-subunit interactions, we co-expressed these homo-oligomerizing CCT4 and CCT5 subunits or the archaeal chaperonin Mm-Cpn (Methanococcus maripaludis chaperonin) with CCT1-8, one at a time. We found that CCT5 shifted all of the CCT subunits, with the exception of CCT6, into double-barrel TRiC-like complexes, while CCT4 only interacted with CCT5 and CCT8 to form chaperonin rings. We hypothesize that these specific interactions may be due to the formation of hetero-oligomers in E. coli, although more work is needed for validation. We also observed the interaction of CCT5 and Mm-Cpn with smaller fragments of the CCT subunits, confirming their intrinsic chaperone activity. Based on this hetero-oligomer data, we propose that TRiC assembly relies on subunit exchange with some stable homo-oligomers, possibly CCT5, as base assembly units. Eventually, analysis of CCT arrangement in various tissues and at different developmental times is anticipated to provide additional insight on TRiC assembly and CCT subunit composition

    Core features of the hormonal status in in vitro grown potato plants

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    Some time ago, potato transformants expressing Agrobacterium-derived auxin synthesis gene tms1 were generated. These tms1-transgenic plants, showing enhanced productivity, were studied for their hormonal status, turnover and responses in comparison with control plants. For this purpose, contents of phytohormones belonging to six different classes (auxins, cytokinins, gibberellins, abscisic, jasmonic and salicylic acids) were determined by a sensitive UPLC-MS/MS method in tubers and shoots of in vitro grown plants. To date, this study represents the most comprehensive analysis of the potato hormonal system. On the basis of obtained results, several new generalizations concerning potato hormonal status were drawn. Overall, these data can serve as a framework for forthcoming integrative studies of the hormonal system in potato plants
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