Project description:Eukaryotic cells have evolved extensive protein quality control mechanisms to remove faulty translation products. Here we show that yeast cells continually produce faulty mitochondrial polypeptides that stall on the ribosome during translation but are imported into the mitochondria. The cytosolic protein Vms1, together with the E3 ligase Ltn1, protects against the mitochondrial toxicity of these proteins and maintains cell viability under respiratory conditions. In the absence of these factors, stalled polypeptides aggregate after import and sequester critical mitochondrial chaperone and translation machinery. Aggregation depends on C-terminal alanyl/threonyl sequences (CAT-tails) that are attached to stalled polypeptides on 60S ribosomes by Rqc2. Vms1 binds to 60S ribosomes at the mitochondrial surface and antagonizes Rqc2, thereby facilitating import, impeding aggregation and directing aberrant polypeptides to intra-mitochondrial quality control. Vms1 is a key component of a rescue pathway for ribosome-stalled mitochondrial polypeptides that are inaccessible to ubiquitylation, due to coupling of translation and translocation.
Project description:Protein aggregation is associated with neurodegeneration and various other pathologies. How specific cellular environments modulate the aggregation of disease proteins is not well understood. Here we investigated how the endoplasmic reticulum (ER) quality control system handles β-sheet proteins that were designed de novo to form amyloid-like fibrils. While these proteins undergo toxic aggregation in the cytosol, we find that targeting them to the ER (ER-β) strongly reduces their toxicity. ER-β is retained within the ER in a soluble polymeric state, despite reaching very high concentrations exceeding those of ER-resident molecular chaperones. ER-β is not removed by ER-associated degradation (ERAD) but interferes with ERAD of other proteins. These findings demonstrate a remarkable capacity of the ER to prevent the formation of insoluble β-aggregates and the secretion of potentially toxic protein species. Our results also suggest a generic mechanism by which proteins with exposed β-sheet structure in the ER interfere with proteostasis.
Project description:The tau protein aggregates in several neurodegenerative disorders, referred to as tauopathies. The type of tau isoforms (4R/3R) observed in brain aggregates is used to classify tauopathies. However, distinguishing tauopathies in cerebrospinal fluid remains challenging. Here, we demonstrated that the difference in tau isoforms between tauopathies is only observed in aggregates, not in soluble brain extracts. We therefore used untargeted mass spectrometry to characterize all post-translational modifications of both the aggregated and the soluble tau protein obtained from human brain tissue of patients with Alzheimer’s disease, cortico-basal degeneration, Pick’s disease, and fronto-temporal lobe degeneration. We found specific soluble signatures predictive of each tauopathy and its peculiar type of aggregated tau isoforms. These findings provide potential targets for developing cerebrospinal fluid assays able to distinguish between tauopathies in vivo. The comparison between soluble and aggregated tau features indicates potential mechanisms of tau aggregation, providing novel therapeutic leads for these diseases
Project description:Mucus has an important protective function and forms a barrier that minimizes the bacterial contact with the colonic epithelium. It is organized as a complex network with several specific proteins of which most are still poorly understood. Abundant proteins in intestinal mucus, in addition to the mucin MUC2, are CLCA1 and FCGBP. FCGBP is expressed in all intestinal goblet cells and secreted into the mucus. It is comprised of repeated von Willebrand Factor D (vWD) domain assemblies, of which most have a GDPH amino acid sequence. This sequence can be autocatalytically cleaved, as previously found in MUC2 and MUC5AC. We show that all vWD with a GDPH sequence are cleaved, and that these cleavages occur early during biosynthesis in the endoplasmic reticulum. All cleaved fragments remained connected by a disulfide bond within each vWD domain. The cleavage can generate a C-terminal reactive Asp-anhydride that could react with other molecules, such as MUC2, but this was not observed. Quantitative analyses by mass spectrometry showed that, in chaotropic solutions, FCGBP was mainly soluble whereas MUC2 was insoluble, and most of the secreted FCGBP was not covalently bound to MUC2. As its name indicates, FCGBP has been suggested to bind IgG, something that was not possible to reproduce in vitro using purified proteins. The function of FCGBP is still unknown, but our results suggest that the Asp-anhydrides do not contribute to covalent crosslinking in the mucin framework nor does FCGBP incorporate IgG in mucus.
Project description:The aim of the project was to quantify protein aggregation and disaggregation in human cells after transient non-lethal heat shock and during recovery. In addition, the non-aggregating proteins were analyzed by two-dimensional proteome profiling to detect changes in thermal stability upon heat shock. For aggregation/disaggregation study, K562 cells were grown in light SILAC medium which was changed to heavy medium 90 minutes before heat treatment (10 minutes at 44C). After heat shock, cells were let to recover at 37C. Samples were collected before and after the heat shock as well as on multiple time points during recovery (one, two, three and five hours). Protein intensities from soluble fraction (extracted with mild detergent - NP40) was compared to a control samples that on parallel were treated with mock shock (10 minutes at +37C). Samples were labelled with TMT labels and pooled. The medium switch prior to heat shock also allowed to monitor changes in protein synthesis caused by the heat shock. For control, an analysis of total protein amount (extracted with strong detergent - SDS) was conducted. For two-dimensional proteome profiling, aliquots of heat shocked and mock shocked samples were exposed to a temperature gradient (from 37.0C to 66.3C). Samples from two adjacent temperatures were labelled with TMT and pooled. Proteins from soluble fractions were quantified and heat shock-induced changes in thermal stability were analyzed.
Project description:Huntington’s disease is caused by a polyglutamine repeat expansion at the N-terminus of the huntingtin protein which affects the function and folding of the protein, and results in intracellular protein aggregates. Here, we examined whether this mutation leads to altered ubiquitination of huntingtin and other proteins in both soluble and insoluble fractions of brain lysates of the Q175 knock-in Huntington disease mouse model and the Q20 wild-type mouse model. Ubiquitination sites are detected by identification of Gly-Gly (diGly) remnant motifs that remain on modified lysine residues after digestion. We identified K6, K9, K132, K804 and K837 as endogenous ubiquitination sites of soluble huntingtin, with wild-type huntingtin being mainly ubiquitinated at K132, K804 and K837. Mutant huntingtin protein levels were strongly reduced in the soluble fraction while K6 and K9 were mainly ubiquitinated. In the insoluble fraction increased levels of huntingtin K6 and K9 diGly sites were observed for mutant huntingtin as compared to wild type. Besides huntingtin, proteins with various roles, including membrane organization, transport, mRNA processing, gene transcription, translation, catabolic processes and oxidative phosphorylation, were differently expressed or ubiquitinated in wild-type and mutant huntingtin brain tissues. Correlating protein and diGly site fold-changes in the soluble fraction revealed that diGly site abundances of the majority of the proteins were not related to protein fold-changes, indicating that these proteins were differentially ubiquitinated in the Q175 mice. In contrast, both the fold-change of the protein level and diGly site level were increased for several proteins in the insoluble fraction, including ubiquitin, ubiquilin-2, sequestosome-1/p62 and myo5a. Our data sheds light on putative novel proteins involved in different cellular processes as well as their ubiquitination status in Huntington’s disease, which forms the basis for further mechanistic studies to understand the role of differential ubiquitination of huntingtin as well as ubiquitin-regulated processes in Huntington’s disease.
Project description:Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant disease caused by an alanine tract expansion mutation in Poly(A)-binding protein nuclear 1 (expPABPN1). To model OPMD in a myogenic and physiological context, we generated mouse myoblast cell clones stably expressing either human wild type (WT) or expPABPN1 at low levels. The transgene expression is induced upon myotube differentiation and results in formation of insoluble nuclear PABPN1 aggregates that are similar to the in vivo aggregates. Quantitative analysis of PABPN1 protein in myotube cultures revealed that expPABPN1 accumulation and aggregation is greater than that of the WT protein. In a comparative study we found that aggregation of expPABPN1 is more affected by inhibition of proteasome activity, as compared with the WT PABPN1 aggregation. Consistent with this, in myotubes cultures expressing expPABPN1 deregulation of the proteasome was identified as the most significantly deregulated pathway. Differences in the accumulation of soluble WT and expPABPN1 were consistent with differences in ubiquitination and protein turnover. This study indicates, for the first time, that in myotubes the ratio of soluble to insoluble expPABPN1 is significantly lower compared to that of the WT protein. We suggest that this difference can contribute to muscle weakness in OPMD. Clones on IM2 mouse myotubes that stably express Ala10-PABPN1-FLAG (WTA, WTD) or Ala17-PABPN1-FLAG (D7E). The transgene expression level in D7E and WTA are similar. WTA and WTD reflects differences in expression levels. RNA was extracted from myotubes of WTA, WTD and D7E in triplicates. cDNA synthesis and lebeling was preformed with the Illumina cDNA labeling kit.
Project description:We describe an in vivo chromatin purification system for genome-wide epigenetic profiling in C. elegans. In this system, we coexpressed the E. coli biotin ligase enzyme (BirA), together with the C. elegans H3.3 gene fused to BioTag, a 23-amino acid peptide serving as a biotinylation substrate for BirA, in vivo in worms. We developed methods to isolate chromatin under different salt extraction conditions, followed by affinity purification of biotinylated chromatin with streptavidin and genome-wide profiling with microarrays. For data usage terms and conditions, please refer to http://www.genome.gov/27528022 and http://www.genome.gov/Pages/Research/ENCODE/ENCODEDataReleasePolicyFinal2008.pdf All experiments were done using two channels per chip, comparing DNAs extracted from either salt-extracted or insoluble chromatin to whole nuclear chromatin, whole nuclear chromatin to randomly fragmented genomic DNA, streptavidin-bound biotin-tagged histone-variant-containing chromatin to salt-extracted chromatin, gel-purified mononucleosomes to whole EDTA-extracted soluble chromatin, or streptavidin-bound biotin-tagged histone-variant-containing chromatin to whole EDTA-extracted soluble chromatin to randomly fragmented DNA from embryo nuceli.
Project description:Whole-genome DNA microarray analysis of Geobacter sulfurreducens cells grown on Fe(III)-oxide or Mn(IV)-oxide versus cells grown on soluble Fe(III) citrate indicated that there were significant differences in transcription patterns during growth on the insoluble metal oxides compared to growth on soluble Fe(III). Many of the genes that appeared to be up-regulated during growth on the metal hydroxides were involved in electron transport. The most highly up-regulated genes for both conditions were omcS and omcT, which encode co-transcribed c-type cytochromes exposed on the outer surface of the cell that are known to be required for Fe(III) and Mn(IV)-oxide reduction. Other electron transport genes that were up-regulated on both insoluble metals included the gene coding for the outer membrane c-type cytochrome, OmcG, genes for the outer membrane proteins, OmpB and OmpC, and the gene that codes for the structural protein of electrically conductive pili, PilA. Genes that were up-regulated in cells grown on Fe(III)-oxide but not Mn(IV)-oxide, included outer membrane c-type cytochromes including OmcE, a putative DMSO reductase protein, and proteins from the cytochrome bc1 complex. Electron transport genes that were only up-regulated in Mn(IV)-oxide grown cells included the genes that code for the outer membrane c-type cytochromes, OmcZ and OmcB, the periplasmic c-type cytochrome, MacA, and fumarate reductase. Genetic studies indicated that the c-type cytochrome proteins, PpcH, OmcJ, OmcM, OmcV, MacA, OmcF, OmcI, and OmcQ, and the iron sulfur subunit of the cytochrome b/b6 complex, QcrA, are important for reduction of insoluble Fe(III)-oxides but do not appear to be important for Mn(IV) reduction. These results demonstrate that the physiology of Fe(III) reducing bacteria differ significantly during growth on insoluble electron and soluble electron acceptors and emphasizes the importance of c-type cytochromes in extracellular electron transfer in G. sulfurreducens. Geobacter sulfurreducens cells were grown with acetate (5 mM) provided as the electron donor and either Fe(III) oxide or Fe(III) citrate provided as the electron acceptor. Cells were harvested at mid-log and total RNA was extracted. Total RNA (0.5 M-NM-<g) was amplified using the MessageAmp II-Bacteria Kit (Ambion, Foster City, CA) according to the manufacturers instructions. Ten micrograms of amplified RNA (aRNA) was chemically labeled with Cy3 (for the control or soluble electron acceptor condition) or Cy5 (for the experimental or insoluble electron acceptor condition) dye using the MicroMax ASAP RNA Labeling Kit (Perkin Elmer, Wellesley, MA) according to the manufacturerM-bM-^@M-^Ys instructions. RNA samples from three biological replicates were hybridized in duplicate on 12K Combimatrix antisense-detecting arrays. The experimental condition (DL1 grown with Mn(IV) oxide as acceptor) was labeled with cy5, the control condition (DL1 grown with Fe(III) citrate as acceptor) was labeled with cy3
Project description:Whole-genome DNA microarray analysis of Geobacter sulfurreducens cells grown on Fe(III)-oxide or Mn(IV)-oxide versus cells grown on soluble Fe(III) citrate indicated that there were significant differences in transcription patterns during growth on the insoluble metal oxides compared to growth on soluble Fe(III). Many of the genes that appeared to be up-regulated during growth on the metal hydroxides were involved in electron transport. The most highly up-regulated genes for both conditions were omcS and omcT, which encode co-transcribed c-type cytochromes exposed on the outer surface of the cell that are known to be required for Fe(III) and Mn(IV)-oxide reduction. Other electron transport genes that were up-regulated on both insoluble metals included the gene coding for the outer membrane c-type cytochrome, OmcG, genes for the outer membrane proteins, OmpB and OmpC, and the gene that codes for the structural protein of electrically conductive pili, PilA. Genes that were up-regulated in cells grown on Fe(III)-oxide but not Mn(IV)-oxide, included outer membrane c-type cytochromes including OmcE, a putative DMSO reductase protein, and proteins from the cytochrome bc1 complex. Electron transport genes that were only up-regulated in Mn(IV)-oxide grown cells included the genes that code for the outer membrane c-type cytochromes, OmcZ and OmcB, the periplasmic c-type cytochrome, MacA, and fumarate reductase. Genetic studies indicated that the c-type cytochrome proteins, PpcH, OmcJ, OmcM, OmcV, MacA, OmcF, OmcI, and OmcQ, and the iron sulfur subunit of the cytochrome b/b6 complex, QcrA, are important for reduction of insoluble Fe(III)-oxides but do not appear to be important for Mn(IV) reduction. These results demonstrate that the physiology of Fe(III) reducing bacteria differ significantly during growth on insoluble electron and soluble electron acceptors and emphasizes the importance of c-type cytochromes in extracellular electron transfer in G. sulfurreducens. Geobacter sulfurreducens cells were grown with acetate (5 mM) provided as the electron donor and either Fe(III) oxide or Fe(III) citrate provided as the electron acceptor. Cells were harvested at mid-log and total RNA was extracted. Total RNA (0.5 M-NM-<g) was amplified using the MessageAmp II-Bacteria Kit (Ambion, Foster City, CA) according to the manufacturers instructions. Ten micrograms of amplified RNA (aRNA) was chemically labeled with Cy3 (for the control or soluble electron acceptor condition) or Cy5 (for the experimental or insoluble electron acceptor condition) dye using the MicroMax ASAP RNA Labeling Kit (Perkin Elmer, Wellesley, MA) according to the manufacturerM-bM-^@M-^Ys instructions. RNA samples from three biological replicates were hybridized in duplicate on 12K Combimatrix antisense-detecting arrays. The experimental condition (DL1 grown with Fe(III) oxide as acceptor) was labeled with cy5, the control condition (DL1 grown with Fe(III) citrate as acceptor) was labeled with cy3