Project description:Crucial metabolic functions of peroxisomes rely on a variety of peroxisomal membrane proteins (PMPs). While mRNA transcripts of PMPs were shown to be colocalized with peroxisomes, the process by which PMPs efficiently couple translation with targeting to the peroxisomal membrane remained elusive. Here, we combine quantitative electron microscopy with proximity-specific ribosome profiling and reveal that translation of specific PMPs occurs on the surface of peroxisomes in the yeast Saccharomyces cerevisiae. This places peroxisomes alongside chloroplasts, mitochondria, and the endoplasmic reticulum as organelles that use localized translation for ensuring correct insertion of hydrophobic proteins into their membranes. Moreover, the correct targeting of these transcripts to peroxisomes is crucial for peroxisomal and cellular function, emphasizing the importance of localized translation for cellular physiology.
Project description:The cytosol-facing organelle outer membrane (OM) is a layer that separates from but also communicates with cellular compartments for the import and exchange of proteins, metabolites and signaling molecules. OM resident proteins are also the targets of cellular surveillance systems by which the cell controls organelle homeostasis for promoting cell survival under stress. However, discovery of OM proteins and their dynamically interacting partners by traditional approaches can be very challenging. In this study, we developed an outer membrane proximity labeling system (OMPL) using biotin ligase mediated proximity biotinylation to map the proximity proteome of the cytosol-facing mitochondria, chloroplast and peroxisome outer membranes in living Arabidopsis cells. The power of this optimized system is highlighted by the discovery of the cytosolic factors and OM receptor candidates that are potentially involved in protein local translation and translocation, membrane contact sites and organelle quality control. Moreover, this OMPL plants generated in this study can be used for rapid and specific isolation of intact mitochondria and peroxisome. Our findings provide ample ground for further investigations on important questions in organelle biology.
Project description:The mechanisms that govern organelle remodeling remain poorly defined. Lysosomes degrade cargo from various routes including endocytosis, phagocytosis and autophagy. For phagocytes, lysosomes are a kingpin organelle since they are essential to kill pathogens and process and present antigens. During phagocyte activation, lysosomes undergo a striking reorganization, changing from dozens of globular structures to a tubular network, in a process that requires the phosphatidylinositol-3-kinase-AKT-mTOR signalling pathway. Here, we show that lysosomes undergo a remarkable expansion in volume and holding capacity during phagocyte activation within 2 h of LPS stimulation. Lysosome expansion was paralleled by an increase in lysosomal protein levels, but this was unexpectedly independent of TFEB and TFE3 transcription factors, known to scale up lysosome biogenesis. Instead, we demonstrate a hitherto unappreciated mechanism of acute organelle expansion via mTORC1-dependent increase in translation of mRNAs encoding key lysosomal proteins. Importantly, mTORC1-dependent increase in translation activity was necessary for efficient and rapid antigen presentation by dendritic cells. Collectively, we identified a previously unknown and functionally relevant mechanism for lysosome expansion that relies on mTORC1-dependent enhanced translation of mRNAs to boost protein synthesis and lysosome biogenesis in response to an infection signal.
Project description:Peroxisomes are primarily metabolic organelles with important functions in lipid metabolism, such as fatty acid oxidation and ether phospholipid synthesis (e.g. plasmalogens). Certain viruses, such as human cytomegalovirus (HCMV), hijack organelle functions to facilitate their replication and spread. However, the role of peroxisomes in herpesvirus replication remains elusive. Following a discovery that peroxisome proteins are upregulated upon HCMV infection, we quantified the production of plasmalogens, lipids that require peroxisome functions. In agreement with the increase in peroxisome protein abundance, plasmalogen production was increased by HCMV infection.
Project description:Peroxisomes are primarily metabolic organelles with important functions in lipid metabolism, such as fatty acid oxidation and ether phospholipid synthesis (e.g., plasmalogens). Certain viruses, such as human cytomegalovirus (HCMV), hijack organelle functions to facilitate their replication and spread. However, the role of peroxisomes in herpesvirus replication remains elusive. Therefore, we used targeted mass spectrometry to quantify 60 peroxisome proteins through the HCMV infection cycle. We provide two proteomic experiments. The first experiment (raw files labeled as 20180123) is of samples in biological triplicate from uninfected human fibroblasts and infected human fibroblasts at 6, 24, 48, 72, and 120 hours post infection. The second experiment (raw files labeled as 201806) is from uninfected/infected fibroblasts during phosphonoformate (PFA) treatment and fibroblasts infected with UV-treated HCMV.
Project description:The compartmentalisation of distinct organelles within eukaryotic cells is essential for their diverse functions, however, how their structures and functions depend on each other has not been systematically explored. We combined a fluorescent reporter of mitochondrial stress with genome-wide CRISPR knockout screening and identified networks of genes involved in the biogenesis and metabolism of diverse organelles. Targeted organelle gene knockouts identified that defects in peroxisomes, Golgi, and ER cause mitochondrial fragmentation and dysfunction. Correlative light and electron microscopy analysed using artificial intelligence-directed voxel extraction revealed in unprecedented detail how impaired mitochondrial interactions with diverse organelles caused cell-wide defects in their morphology and biogenesis. Multi-omics analyses identified a unified proteome stress response and global shifts in lipid and glycoprotein homeostasis that are elicited when organelle biogenesis is compromised. Our comprehensive resource has defined metabolic and morphological interactions between organelles that can be mined to understand how changes in organelle components drive diverse cellular pathologies.
Project description:Eukaryotic cells contain several membrane-separated organelles to compartmentalize distinct metabolic reactions. However, it has remained unclear how these organelle systems are coordinated, when cells adapt metabolic pathways to support their development, survival or effector functions. Here we present OrgaPlexing, a multispectral organelle imaging approach for the comprehensive mapping of six key metabolic organelles and their interactions. We use this analysis on macrophages, immune cells that undergo rapid metabolic switches upon sensing bacterial and inflammatory stimuli. Our results identify lipid droplets (LDs) as primary inflammatory responder organelle, which forms three- and four-way interactions with other organelles. While clusters with endoplasmic reticulum (ER) and mitochondria (M-ER-LD unit) help supply fatty acids for LD growth, the additional recruitment of peroxisomes (M-ER-P-LD unit) supports fatty acid efflux from LDs. Interference with individual components of these units has direct functional consequences for inflammatory lipid synthesis. Together, we show that macrophages form functional multi-organellar units (MOUs) to support metabolic adaptation, and provide an experimental strategy to identify organelle-metabolic signaling hubs.
Project description:The molecular causes of deteriorating oocyte quality during aging are poorly defined. Since oocyte developmental competence relies on post-transcriptional regulations, we tested whether defective mRNA translation contributes to this decline in quality. Disruption in ribosome loading on maternal transcripts is present in old oocytes. Using a candidate approach, we detect altered translation of 3’-UTR-reporters and altered poly(A) length of the endogenous mRNAs. mRNA polyadenylation depends on the cytoplasmic polyadenylation binding protein 1 (CPEB1). Cpeb1 mRNA translation and protein levels are decreased in old oocytes. This decrease causes de-repression of Ccnb1 translation in quiescent oocytes, premature CDK1 activation, and accelerated reentry into meiosis. De-repression of Ccnb1 is corrected by Cpeb1 mRNA injection in old oocytes. Oocyte-specific Cpeb1 haploinsufficiency in young oocytes recapitulates all the translation phenotypes of old oocytes. These findings demonstrate that a dysfunction in the oocyte translation program is associated with the decline in oocyte quality during aging.
Project description:Firczuk2013 - Eukaryotic mRNA translation machinery
This is a model of Saccharomyces cerevisiae
mRNA translation which includes the initiation, elongation and termination phases. The model is for 20 condon mRNAs. The building of a multi-factor complex in initiation and also the different processes in elongation and termination are modelled in detail. The model takes into account that ribosomes cover more than one codon of mRNA so that the movement of ribosomes are effectively blocked by other ribosomes several codons downstream. It is assumed that 15 codons are occupied by each ribosome. This blocking effect is considered in reaction R18 in initiation and also reaction R26, the reaction where translocation of ribosomes takes place in elongation. The kinetic functions of these two reactions are based on MacDonald et al. 1968 and Heinrich & Rapaport 1980. All other kinetic functions follow mass-action kinetics. The concentrations of transfer RNA species (Met-tRNA, aa-tRNA and tRNA in the model) are kept constant, while the other species' concentrations can change in the course of the simulation. The model describes the translation of a short mRNA with 20 codons. Therefore, all reactions in the elongation cycle (R22, R23, R25, R26, R28 and R29) and the corresponding species are replicated accordingly to model the species with ribosomes bound at different positions. In summary, the model contains 165 different species and 141 reactions.
The value of the 56 rate constant parameters were estimated by fitting the model against a series of experimental data consisting of modulation of the various translation factors (Figures 2, 3 and S3). Overall the parameter estimation was carried out over 212 different data points (steady states).
This model is described in the article:
An in vivo control map for the eukaryotic mRNA translation machinery
Helena Firczuk, Shichina Kannambath, Jürgen Pahle, Amy Claydon, Robert Beynon, John Duncan, Hans Westerhoff, Pedro Mendes and John EG McCarthy
Molecular Systems Biology. 9:635
Abstract:
Rate control analysis defines the in vivo control map governing yeast protein synthesis and generates an extensively parameterized digital model of the translation pathway. Among other non-intuitive outcomes, translation demonstrates a high degree of functional modularity and comprises a non-stoichiometric combination of proteins manifesting functional convergence on a shared maximal translation rate. In exponentially growing cells, polypeptide elongation (eEF1A, eEF2, and eEF3) exerts the strongest control. The two other strong control points are recruitment of mRNA and tRNAi to the 40S ribosomal subunit (eIF4F and eIF2) and termination (eRF1; Dbp5). In contrast, factors that are found to promote mRNA scanning efficiency on a longer than-average 5′untranslated region (eIF1, eIF1A, Ded1, eIF2B, eIF3, and eIF5) exceed the levels required for maximal control. This is expected to allow the cell to minimize scanning transition times, particularly for longer 5′UTRs. The analysis reveals these and other collective adaptations of control shared across the factors, as well as features that reflect functional modularity and system robustness. Remarkably, gene duplication is implicated in the fine control of cellular protein synthesis.
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