Showing papers on "Cellular compartment published in 2013"
TL;DR: It is the hypothesis that mitochondria and chloroplasts are the original sites of melatonin synthesis in the early stage of endosymbiotic organisms; this synthetic capacity was carried into host eukaryotes by the above‐mentioned bacteria and preserved during evolution.
Abstract: Mitochondria and chloroplasts are major sources of free radical generation in living organisms. Because of this, these organelles require strong protection from free radicals and associated oxidative stress. Melatonin is a potent free radical scavenger and antioxidant. It meets the criteria as a mitochondrial and chloroplast antioxidant. Evidence has emerged to show that both mitochondria and chloroplasts may have the capacity to synthesize and metabolize melatonin. The activity of arylalkylamine N-acetyltransferase (AANAT), the reported rate-limiting enzyme in melatonin synthesis, has been identified in mitochondria, and high levels of melatonin have also been found in this organelle. From an evolutionary point of view, the precursor of mitochondria probably is the purple nonsulfur bacterium, particularly, Rhodospirillum rubrum, and chloroplasts are probably the descendents of cyanobacteria. These bacterial species were endosymbionts of host proto-eukaryotes and gradually transformed into cellular organelles, that is, mitochondria and chloroplasts, respectively, thereby giving rise to eukaryotic cells. Of special importance, both purple nonsulfur bacteria (R. rubrum) and cyanobacteria synthesize melatonin. The enzyme activities required for melatonin synthesis have also been detected in these primitive species. It is our hypothesis that mitochondria and chloroplasts are the original sites of melatonin synthesis in the early stage of endosymbiotic organisms; this synthetic capacity was carried into host eukaryotes by the above-mentioned bacteria. Moreover, their melatonin biosynthetic capacities have been preserved during evolution. In most, if not in all cells, mitochondria and chloroplasts may continue to be the primary sites of melatonin generation. Melatonin production in other cellular compartments may have derived from mitochondria and chloroplasts. On the basis of this hypothesis, it is also possible to explain why plants typically have higher melatonin levels than do animals. In plants, both chloroplasts and mitochondria likely synthesize melatonin, while animal cells contain only mitochondria. The high levels of melatonin produced by mitochondria and chloroplasts are used to protect these important cellular organelles against oxidative stress and preserve their physiological functions. The superior beneficial effects of melatonin in both mitochondria and chloroplasts have been frequently reported.
432 citations
TL;DR: This review will focus on the common organizing principles underlying the many MCSs found between the ER and virtually all compartments of the cell, and on how the ER establishes a network of M CSs for the trafficking of vital metabolites and information.
388 citations
TL;DR: The synthesis, regulation, and intracellular distribution of SMs are discussed, and the many direct roles played by membrane SM in various cellular functions and processes will also be discussed.
247 citations
TL;DR: Different aspects of phospholipid domain formation in bacterial membranes, mainly in Gram-negative Escherichia coli and Gram-positive Bacillus subtilis are summarized.
Abstract: Membranes are vital structures for cellular life forms. As thin, hydrophobic films, they provide a physical barrier separating the aqueous cytoplasm from the outside world or from the interiors of other cellular compartments. They maintain a selective permeability for the import and export of water-soluble compounds, enabling the living cell to maintain a stable chemical environment for biological processes. Cell membranes are primarily composed of two crucial substances, lipids and proteins. Bacterial membranes can sense environmental changes or communication signals from other cells and they support different cell processes, including cell division, differentiation, protein secretion and supplementary protein functions. The original fluid mosaic model of membrane structure has been recently revised because it has become apparent that domains of different lipid composition are present in both eukaryotic and prokaryotic cell membranes. In this review, we summarize different aspects of phospholipid domain formation in bacterial membranes, mainly in Gram-negative Escherichia coli and Gram-positive Bacillus subtilis. We describe the role of these lipid domains in membrane dynamics and the localization of specific proteins and protein complexes in relation to the regulation of cellular function.
122 citations
TL;DR: This review aimed to summarize the experimental data concerning all aspects of the HS response in mammalian cells, such as HS-induced structural and functional alterations of cell membranes, the cytoskeleton and cellular organelles; the associated pathways that result in different modes of cell death and cell cycle arrest; and the effects of HS on transcription, splicing, translation, DNA repair, and replication.
Abstract: Heat shock (HS) is one of the best-studied exogenous cellular stresses. The cellular response to HS utilizes ancient molecular networks that are based primarily on the action of stress-induced heat shock proteins and HS factors. However, in one way or another, all cellular compartments and metabolic processes are involved in such a response. In this review, we aimed to summarize the experimental data concerning all aspects of the HS response in mammalian cells, such as HS-induced structural and functional alterations of cell membranes, the cytoskeleton and cellular organelles; the associated pathways that result in different modes of cell death and cell cycle arrest; and the effects of HS on transcription, splicing, translation, DNA repair, and replication.
116 citations
TL;DR: It was shown that lysosomal proteases are not only able to initiate apoptotic signaling but can also amplify the apoptotic pathways initiated in other cellular compartments and the therapeutic potential of intervention in lysOSomal membrane permeabilization will be discussed.
Abstract: The endocytic pathway is a system specialized for the uptake of compounds from the cell microenvironment for their degradation. It contains an arsenal of hydrolases, including proteases, which are normally enclosed in membrane-bound organelles, but if released to the cytosol can initiate apoptosis signaling pathways. Endogenous and exogenous compounds have been identified that can mediate destabilization of lysosomal membranes, and it was shown that lysosomal proteases are not only able to initiate apoptotic signaling but can also amplify the apoptotic pathways initiated in other cellular compartments. The endocytic pathway also receives cargo destined for degradation via the autophagic pathway. By recycling energy and biosynthetic substrates, and by degrading damaged organelles and molecules, the endocytic system assists the autophagic system in resisting apoptotic stimuli. Steps leading to lysosomal membrane permeabilization and subsequent triggering of cell death as well as the therapeutic potential of intervention in lysosomal membrane permeabilization will be discussed.
108 citations
TL;DR: The data suggest an evolutionarily conserved role of cytosolic monothiol multidomain Grxs in cellular iron metabolism pathways.
Abstract: The mechanisms by which eukaryotic cells handle and distribute the essential micronutrient iron within the cytosol and other cellular compartments are only beginning to emerge. The yeast monothiol multidomain glutaredoxins (Grx) 3 and 4 are essential for both transcriptional iron regulation and intracellular iron distribution. Despite the fact that the mechanisms of iron metabolism differ drastically in fungi and higher eukaryotes, the glutaredoxins are conserved, yet their precise function in vertebrates has remained elusive. Here we demonstrate a crucial role of the vertebrate-specific monothiol multidomain Grx3 (PICOT) in cellular iron homeostasis. During zebrafish embryonic development, depletion of Grx3 severely impairs the maturation of hemoglobin, the major iron-consuming process. Silencing of human Grx3 expression in HeLa cells decreases the activities of several cytosolic Fe/S proteins, for example, iron-regulatory protein 1, a major component of posttranscriptional iron regulation. As a consequence, Grx3-depleted cells show decreased levels of ferritin and increased levels of transferrin receptor, features characteristic of cellular iron starvation. Apparently, Grx3-deficient cells are unable to efficiently use iron, despite unimpaired cellular iron uptake. These data suggest an evolutionarily conserved role of cytosolic monothiol multidomain glutaredoxins in cellular iron metabolism pathways, including the biogenesis of Fe/S proteins and hemoglobin maturation.
95 citations
TL;DR: The results reveal that the liver of rats with adjuvant-induced arthritis presents a pronounced oxidative stress and that, in consequence, injury to lipids and proteins is highly significant.
81 citations
TL;DR: This review discusses various modeling attempts that have been performed to understand both long-distance shuttling and short-distance targeting of organelles and shows how the combination of mechanical and mathematical modeling with cell biological approaches has contributed to the understanding of intracellular transport logistics.
79 citations
TL;DR: This chapter will review the key mechanisms regulating cellular Mg (2+) homeostasis and their impairments under the most common diseases associated with Mg(2+) loss or deficiency.
Abstract: Mammalian cells tightly regulate cellular Mg2+ content through a variety of transport and buffering mechanisms under the control of various hormones and cellular second messengers. The effect of these hormones and agents results in dynamic changes in the total content of Mg2+ being transported across the cell membrane and redistributed within cellular compartments. The importance of maintaining proper cellular Mg2+ content optimal for the activity of various cellular enzymes and metabolic cycles is underscored by the evidence that several diseases are characterized by a loss of Mg2+ within specific tissues as a result of defective transport, hormonal stimulation, or metabolic impairment. This chapter will review the key mechanisms regulating cellular Mg2+ homeostasis and their impairments under the most common diseases associated with Mg2+ loss or deficiency.
72 citations
TL;DR: It is speculated that the metabolic capacity of peroxisomes might be larger than previously assumed, and dual targeting of proteins to both the cytoplasm and the peroxISome might be more widespread.
Abstract: Cellular compartmentalization into organelles serves to separate biological processes within the environment of a single cell. While some metabolic reactions are specific to a single organelle, others occur in more than one cellular compartment. Specific targeting of proteins to compartments inside of eukaryotic cells is mediated by defined sequence motifs. To achieve multiple targeting to different compartments cells use a variety of strategies. Here, we focus on mechanisms leading to dual targeting of peroxisomal proteins. In many instances, isoforms of peroxisomal proteins with distinct intracellular localization are encoded by separate genes. But also single genes can give rise to differentially localized proteins. Different isoforms can be generated by use of alternative transcriptional start sites, by differential splicing or ribosomal read-through of stop codons. In all these cases different peptide variants are produced, of which only one carries a peroxisomal targeting signal. Alternatively, peroxisomal proteins contain additional signals that compete for intracellular targeting. Dual localization of proteins residing in both the cytoplasm and in peroxisomes may also result from use of inefficient targeting signals. The recent observation that some bona fide cytoplasmic enzymes were also found in peroxisomes indicates that dual targeting of proteins to both the cytoplasm and the peroxisome might be more widespread. Although current knowledge of proteins exhibiting only partial peroxisomal targeting is far from being complete, we speculate that the metabolic capacity of peroxisomes might be larger than previously assumed.
TL;DR: First applications include protein targeting to cytoskeleton, to the plasma membrane, to lysosomes, the initiation of the PI3K/mTOR pathway, and multiplexed protein complex formation in combination with the rapamycin dimerization system.
TL;DR: The present review emphasizes the beneficial interactions among photosynthesis, dark respiration and photorespiration, in relation to metabolism of C, N and S, and the patterns of minimization of ROS production and scavenging of excess ROS in intracellular compartments are highlighted.
Abstract: The bioenergetic processes of photosynthesis and respiration are mutually beneficial. Their interaction extends to photorespiration, which is linked to optimize photosynthesis. The interplay of these three pathways is facilitated by two major phenomena: sharing of energy/metabolite resources and maintenance of optimal levels of reactive oxygen species (ROS). The resource sharing among different compartments of plant cells is based on the production/utilization of reducing equivalents (NADPH, NADH) and ATP as well as on the metabolite exchange. The responsibility of generating the cellular requirements of ATP and NAD(P)H is mostly by the chloroplasts and mitochondria. In turn, besides the chloroplasts, the mitochondria, cytosol and peroxisomes are common sinks for reduced equivalents. Transporters located in membranes ensure the coordinated movement of metabolites across the cellular compartments. The present review emphasizes the beneficial interactions among photosynthesis, dark respiration and photorespiration, in relation to metabolism of C, N and S. Since the bioenergetic reactions tend to generate ROS, the cells modulate chloroplast and mitochondrial reactions, so as to ensure that the ROS levels do not rise to toxic levels. The patterns of minimization of ROS production and scavenging of excess ROS in intracellular compartments are highlighted. Some of the emerging developments are pointed out, such as model plants, orientation/movement of organelles and metabolomics.
TL;DR: Current understanding of the intracellular localization of P-gp is highlighted, the traffic and cycling pathways among the cellular compartments as well as between these compartments and the plasma membrane; and the cellular factors regulating P-GP traffic and Cycling are highlighted.
Abstract: P-glycoprotein (P-gp), an ATP-binding cassette, is able to transport structurally and chemically unrelated substrates. Over-expression of P-gp in cancer cells significantly decreases the intercellular amount of anticancer drugs, and results in multidrug resistance in cancer cells, a major obstacle in cancer chemotherapy. P-gp is mainly localized on the plasma membrane and functions as a drug efflux pump; however, P-gp is also localized in many intracellular compartments, such as endoplasmic reticulum, Golgi, endosomes, and lysosomes. P-gp moves between the intracellular compartments and the plasma membrane in a microtubule-actin dependent manner. This review highlights our current understanding of (1) the intracellular localization of P-gp; (2) the traffic and cycling pathways among the cellular compartments as well as between these compartments and the plasma membrane; and (3) the cellular factors regulating P-gp traffic and cycling. This review also presents a potential implication in overcoming P-gp-mediated multidrug resistance by targeting P-gp traffic and cycling pathways and impairing P-gp localization on the plasma membrane.
TL;DR: Data demonstrate the utility of SCH to predict quantitatively total tissue accumulation and elucidate mechanisms of hepatocellular drug accumulation such as active uptake versus binding/sequestration.
Abstract: Prediction of clinical efficacy, toxicity, and drug-drug interactions may be improved by accounting for the intracellular unbound drug concentration (Cunbound) in vitro and in vivo. Furthermore, subcellular drug distribution may aid in predicting efficacy, toxicity, and risk assessment. The present study was designed to quantify the intracellular Cunbound and subcellular localization of drugs in rat sandwich-cultured hepatocytes (SCH) compared with rat isolated perfused liver (IPL) tissue. Probe drugs with distinct mechanisms of hepatocellular uptake and accumulation were selected for investigation. Following drug treatment, SCH and IPL tissues were homogenized and fractionated by differential centrifugation to enrich for subcellular compartments. Binding in crude lysate and cytosol was determined by equilibrium dialysis; the Cunbound and intracellular-to-extracellular Cunbound ratio (Kpu,u) were used to describe accumulation of unbound drug. Total accumulation (Kpobserved) in whole tissue was well predicted by the SCH model (within 2- to 3-fold) for the selected drugs. Ritonavir (Kpu,u ∼1) was evenly distributed among cellular compartments, but highly bound, which explained the observed accumulation within liver tissue. Rosuvastatin was recovered primarily in the cytosolic fraction, but did not exhibit extensive binding, resulting in a Kpu,u >1 in liver tissue and SCH, consistent with efficient hepatic uptake. Despite extensive binding and sequestration of furamidine within liver tissue, a significant portion of cellular accumulation was attributed to unbound drug (Kpu,u >16), as expected for a charged, hepatically derived metabolite. Data demonstrate the utility of SCH to predict quantitatively total tissue accumulation and elucidate mechanisms of hepatocellular drug accumulation such as active uptake versus binding/sequestration.
TL;DR: Investigation of effects of glucotoxic conditions on the catalytic activation of caspase 3 and the associated degradation of one of its substrate proteins, namely lamin-B results in the degradation of native lamin B, which may be due to increased ER stress under these conditions.
TL;DR: This study reveals a novel mechanism of dual targeting to either the ER or mitochondria that is mediated by structural features within the nascent chain.
Abstract: Protein targeting to specified cellular compartments is essential to maintain cell function and homeostasis. In eukaryotic cells, two major pathways rely on N-terminal signal peptides to target proteins to either the endoplasmic reticulum (ER) or mitochondria. In this study, we show that the ER signal peptides of the prion protein-like protein shadoo, the neuropeptide hormone somatostatin and the amyloid precursor protein have the property to mediate alternative targeting to mitochondria. Remarkably, the targeting direction of these signal peptides is determined by structural elements within the nascent chain. Each of the identified signal peptides promotes efficient ER import of nascent chains containing α-helical domains, but targets unstructured polypeptides to mitochondria. Moreover, we observed that mitochondrial targeting by the ER signal peptides correlates inversely with ER import efficiency. When ER import is compromised, targeting to mitochondria is enhanced, whereas improving ER import efficiency decreases mitochondrial targeting. In conclusion, our study reveals a novel mechanism of dual targeting to either the ER or mitochondria that is mediated by structural features within the nascent chain.
TL;DR: Assessing perturbations in activation or inhibition of ER stress and UPR signaling pathways are likely to be informative parameters to measure when analyzing mechanisms of action of xenobiotic-induced toxicity.
Abstract: The proper folding, assembly, and maintenance of cellular proteins is a highly regulated process and is critical for cellular homeostasis. Multiple cellular compartments have adapted their own systems to ensure proper protein folding, and quality control mechanisms are in place to manage stress due to the accumulation of unfolded proteins. When the accumulation of unfolded proteins exceeds the capacity to restore homeostasis, these systems can result in a cell death response. Unfolded protein accumulation in the endoplasmic reticulum (ER) leads to ER stress with activation of the unfolded protein response (UPR) governed by the activating transcription factor 6 (ATF6), inositol requiring enzyme-1 (IRE1), and PKR-like endoplasmic reticulum kinase (PERK) signaling pathways. Many xenobiotics have been shown to influence ER stress and UPR signaling with either pro-survival or pro-death features. The ultimate outcome is dependent on many factors including the mechanism of action of the xenobiotic, concentration of xenobiotic, duration of exposure (acute vs. chronic), cell type affected, nutrient levels, oxidative stress, state of differentiation, and others. Assessing perturbations in activation or inhibition of ER stress and UPR signaling pathways are likely to be informative parameters to measure when analyzing mechanisms of action of xenobiotic-induced toxicity.
TL;DR: Interestingly, Elp3 in the parasites of this phylum, including Toxoplasma gondii (TgElp3), possesses a unique C-terminal transmembrane domain (TMD) that localizes the protein to the mitochondrion, supporting the idea that ElP3 performs novel functions across eukaryotes that are independent of transcriptional elongation.
TL;DR: Once considered inconspicuous, recent new insights in the formation and function of peroxisomes have revealed a much more subtle interplay between organelles that warrant a re-evaluation of the historical assignment of perxisomes as being either autonomous or ER-derived.
TL;DR: Recent advances are discussed in the understanding of phosphoinositide organization during platelet activation, which provides an additional layer of complexity to the temporo-spatial organization of intracellular signaling events.
TL;DR: Results indicate that in SH-SY5Y neuroblastoma cells intracellular Aβ is not preferentially localized to any particular organelle and, to a large extent, is secreted from the cells.
Abstract: Amyloid-β peptide (Aβ), the main component of Alzheimer's disease (AD) senile plaques, has been found to accumulate within the lysosomal compartment of AD neurons. We have previously shown that in differentiated SH-SY5Y neuroblastoma cells cultured under normal conditions, the majority of Aβ is localized extralysosomally, while oxidative stress significantly increases intralysosomal Aβ content through activation of macroautophagy. It is, however, not clear which cellular compartments contain extralysosomal Aβ in intact SH-SY5Y cells, and how oxidative stress influences the distribution of extralysosomal Aβ. Using confocal laser scanning microscopy and immunoelectron microscopy, we showed that in differentiated neuroblastoma cells cultured under normal conditions Aβ (Aβ40, Aβ42, and Aβ oligomers) is colocalized with both membrane-bound organelles (endoplasmic reticulum, Golgi complexes, multivesicular bodies/late endosomes, lysosomes, exocytotic vesicles and mitochondria) and non-membrane-bound cytosolic structures. Neuroblastoma cells stably transfected with AβPP Swedish KM670/671NL double mutation showed enlarged amount of Aβ colocalized with membrane compartments. Suppression of exocytosis by 5 nM tetanus toxin resulted in a significant increase of the amount of cytosolic Aβ as well as Aβ colocalized with exocytotic vesicles, endoplasmic reticulum, Golgi complexes, and lysosomes. Hyperoxia increased Aβ localization in the endoplasmic reticulum, Golgi apparatus, mitochondria, and lysosomes, but not in the secretory vesicles. These results indicate that in SH-SY5Y neuroblastoma cells intracellular Aβ is not preferentially localized to any particular organelle and, to a large extent, is secreted from the cells. Challenging cells to hyperoxia, exocytosis inhibition, or Aβ overproduction increased intracellular Aβ levels but did not dramatically changed its localization pattern.
TL;DR: The solute transport processes required to connect peroxisomes with other cell compartments are described and the known and yet-to-be-defined transport proteins that mediate these metabolic exchanges across theperoxisomal bilayer are discussed.
Abstract: Tremendous progress in plant peroxisome research has revealed unexpected metabolic functions for plant peroxisomes. Besides photorespiration and lipid metabolism, plant peroxisomes play a key role in many metabolic and signaling pathways, such as biosynthesis of phytohormones, pathogen defense, senescence-associated processes, biosynthesis of biotin and isoprenoids, and metabolism of urate, polyamines, sulfite, phylloquinone, volatile benzenoids, and branched chain amino acids. These peroxisomal pathways require an interplay with other cellular compartments, including plastids, mitochondria, and the cytosol. Consequently, a considerable number of substrates, intermediates, end products, and cofactors have to shuttle across peroxisome membranes. However, our knowledge of their membrane passage is still quite limited. This review describes the solute transport processes required to connect peroxisomes with other cell compartments. Furthermore, we discuss the known and yet-to-be-defined transport proteins that mediate these metabolic exchanges across the peroxisomal bilayer.
TL;DR: Rational engineering of plant primary metabolism requires a detailed and molecular understanding of the membrane transporters, which still lags behind that of soluble enzymes.
TL;DR: Fractionation improves the sensitivity of the method when compared to the classical affinity purification procedure using soluble WCE while keeping a very high specificity and leads to the discovery of novel interactions of RNAP II carboxyl-terminal domain (CTD) interacting domain (CID) proteins with POLR2A.
Abstract: Affinity purification combined with tandem mass spectrometry (AP-MS/MS) is a well-established method used to discover interaction partners for a given protein of interest. Because most AP-MS/MS approaches are performed using the soluble fraction of whole cell extracts (WCE), information about the cellular compartments where the interactions occur is lost. More importantly, classical AP-MS/MS often fails to identify interactions that take place in the nonsoluble fraction of the cell, for example, on the chromatin or membranes; consequently, protein complexes that are less soluble are underrepresented. In this paper, we introduce a method called multiple cell compartment AP-MS/MS (MCC-AP-MS/MS), which identifies the interactions of a protein independently in three fractions of the cell: the cytoplasm, the nucleoplasm, and the chromatin. We show that this fractionation improves the sensitivity of the method when compared to the classical affinity purification procedure using soluble WCE while keeping a very high specificity. Using three proteins known to localize in various cell compartments as baits, the CDK9 subunit of transcription elongation factor P-TEFb, the RNA polymerase II (RNAP II)-associated protein 4 (RPAP4), and the largest subunit of RNAP II, POLR2A, we show that MCC-AP-MS/MS reproducibly yields fraction-specific interactions. Finally, we demonstrate that this improvement in sensitivity leads to the discovery of novel interactions of RNAP II carboxyl-terminal domain (CTD) interacting domain (CID) proteins with POLR2A.
TL;DR: It seems that extranuclear fractions of nuclear hormone receptors commonly serve this function, and a direct interaction of small-molecule hormones with membrane phospholipids and with mRNA is also postulated, in which the reaction to hormonal stimulus appears within seconds or minutes.
Abstract: Small-molecule hormones play crucial roles in the development and in the maintenance of an adult mammalian organism. On the molecular level, they regulate a plethora of biological pathways. Part of their actions depends on their transcription-regulating properties, exerted by highly specific nuclear receptors which are hormone-dependent transcription factors. Nuclear hormone receptors interact with coactivators, corepressors, basal transcription factors, and other transcription factors in order to modulate the activity of target genes in a manner that is dependent on tissue, age and developmental and pathophysiological states. The biological effect of this mechanism becomes apparent not earlier than 30–60 minutes after hormonal stimulus. In addition, small-molecule hormones modify the function of the cell by a number of nongenomic mechanisms, involving interaction with proteins localized in the plasma membrane, in the cytoplasm, as well as with proteins localized in other cellular membranes and in nonnuclear cellular compartments. The identity of such proteins is still under investigation; however, it seems that extranuclear fractions of nuclear hormone receptors commonly serve this function. A direct interaction of small-molecule hormones with membrane phospholipids and with mRNA is also postulated. In these mechanisms, the reaction to hormonal stimulus appears within seconds or minutes.
TL;DR: ToF‐SIMS analysis proved the uptake of the particles into the cell body, provided images of their distribution around the cell nucleus and indications that the cell membranes are undulated by the µm‐sized particles beneath the membrane.
Abstract: Label-free characterization of cellular compartments and molecular structures in single cells has become possible by means of ToF-SIMS 3D analysis [1, 2]. Major molecular building blocks, such as amino acid fragments and phophatidylcholine fragments could be detected successfully. A correlation between the distribution of these components and the intracellular architecture (golgi, nucleus, nucleoli) was possible and the respective results were in line with the expectations derived from cell biology textbooks.
TL;DR: Given the role of GM1 as a cell-surface receptor for the cholera toxin and that levels of both GM1 and cholesterol in the TGN-endosomal compartment are upregulated in some inherited diseases, this protocol can potentially be applied to the analysis of disease-associated changes to GM1-enriched intracellular membranes.
Abstract: This article describes a procedure to prepare a raft-like intracellular membrane fraction enriched for the trans-Golgi network (TGN) and endosomal compartments. The initial step in this technique involves cell disruption by homogenization, followed by clearance of the plasma membrane, late endosomes, mitochondria and the endoplasmic reticulum by differential sedimentation. Carbonate treatment, sonication and sucrose density-gradient ultracentrifugation are subsequently used to isolate the target membranes. The isolated subcellular fraction contains less than 1% of the total cellular proteins, but it is highly enriched for syntaxin-6 and Rab11. Typically, 40-60% of the cellular pool of GM1 glycosphingolipid and 10-20% of the total cellular cholesterol cofractionate with this buoyant membrane fraction. Given the role of GM1 as a cell-surface receptor for the cholera toxin and that levels of both GM1 and cholesterol in the TGN-endosomal compartment are upregulated in some inherited diseases, this protocol can potentially be applied to the analysis of disease-associated changes to GM1-enriched intracellular membranes. The isolated membranes are very well separated from caveolin-rich domains of the plasma membrane, the TGN and recycling endosomes. The entire protocol can be completed in as little as 1 d.
TL;DR: A discussion on the commercially‐available reagents that have shown the most promise for each organelle of interest, including endoplasmic reticulum/nuclear membrane, Golgi apparatus, mitochondria, nucleoli, and nuclei, with an emphasis on localization of these structures for microscopy.
Abstract: A wide range of fluorescent dyes and reagents exist for labeling organelles in live and fixed cells. Choosing between them can sometimes be confusing, and optimization for many of them can be challenging. Presented here is a discussion on the commercially-available reagents that have shown the most promise for each organelle of interest, including endoplasmic reticulum/nuclear membrane, Golgi apparatus, mitochondria, nucleoli, and nuclei, with an emphasis on localization of these structures for microscopy. Included is a featured reagent for each structure with a recommended protocol, troubleshooting guide, and example image.
TL;DR: It is shown that alteration of tRNA-NT stability influences its intracellular distribution due to variations in organelle import capacities, which suggests the fate of the protein is determined not only by the transit peptide sequence, but also by the physicochemical properties of the mature protein.
Abstract: tRNA-NTs (tRNA nucleotidyltransferases) are required for the maturation or repair of tRNAs by ensuring that they have an intact cytidine-cytidine-adenosine sequence at their 3′-termini. Therefore this enzymatic activity is found in all cellular compartments, namely the nucleus, cytoplasm, plastids and mitochondria, in which tRNA synthesis or translation occurs. A single gene codes for tRNA-NT in plants, suggesting a complex targeting mechanism. Consistent with this, distinct signals have been proposed for plastidic, mitochondrial and nuclear targeting. Our previous research has shown that in addition to N-terminal targeting information, the mature domain of the protein itself modifies targeting to mitochondria and plastids. This suggests the existence of an as yet unknown determinate for the distribution of dual-targeted proteins between these two organelles. In the present study, we explore the enzymatic and physicochemical properties of tRNA-NT variants to correlate the properties of the enzyme with the intracellular distribution of the protein. We show that alteration of tRNA-NT stability influences its intracellular distribution due to variations in organelle import capacities. Hence the fate of the protein is determined not only by the transit peptide sequence, but also by the physicochemical properties of the mature protein.