Browse
Submit Data
Databases
API
Help

Dataset Information

0 Views

0 Connections

0 Citations

0 Reanalyses

0 Downloads

Omics score: 0

Identification of a lysosomal protein causing lipid transfer, using a fluorescence assay designed to monitor membrane fusion between rat liver endosomes and lysosomes.

ABSTRACT: In the present and previous studies [Mullock, Perez, Kuwana, Gray and Luzio (1994) J. Cell Biol. 126, 1173-1182], we have attempted to investigate endosome-lysosome fusion using an assay based on the dilution of the self-quenching fluorescent lipid probe octadecylrhodamine. Although some characteristics of fluorescence dequenching were consistent with those observed in other cell-free assays, we have now demonstrated that increased fluorescence was due to leakage of an intralysosomal lipid-transfer protein. This protein was purified and found to be a 22 kDa molecule with sequence, immunological and functional characteristics strongly suggesting that it is the rat homologue of human GM2-activator protein. Both the 22 kDa protein and recombinant human GM2-activator protein caused fluorescence dequenching either when mixed with octadecylrhodamine-loaded endosomes and lysosomal membranes or in a liposome system. The data were consistent with GM2-activator protein acting as an octadecylrhodamine-transfer protein. Antibodies to the 22 kDa protein added to cell-free endosome-lysosome content-mixing assays had no effect, although they could inhibit fluorescence dequenching caused by the protein. Thus this protein is not required in any fusion event involved in delivery of ligands from endosomes to lysosomes. The existence within an intracellular organelle of a protein capable of acting as an octadecylrhodamine-transfer protein suggests the need for caution in the interpretation of fluorescence-dequenching assays using mammalian subcellular fractions.

SUBMITTER: Kuwana T

PROVIDER: S-EPMC1136814 | biostudies-other | 1995 Jun

REPOSITORIES: biostudies-other

ACCESS DATA

Json Xml

Similar Datasets

Resolving vesicle fusion from lysis to monitor calcium-triggered lysosomal exocytosis in astrocytes.

Project description:Optical imaging of individual vesicle exocytosis is providing new insights into the mechanism and regulation of secretion by cells. To study calcium-triggered secretion from astrocytes, we used acridine orange (AO) to label vesicles. Although AO is often used for imaging exocytosis, we found that imaging vesicles labeled with AO can result in their photolysis. Here, we define experimental and analytical approaches that permit us to distinguish unambiguously between fusion, leakage, and lysis of individual vesicles. We have used this approach to demonstrate that lysosomes undergo calcium-triggered exocytosis in astrocytes.

| S-EPMC1955787 | biostudies-literature

G protein-coupled receptor sorting to endosomes and lysosomes.

Project description:The heptahelical G protein-coupled receptors (GPCRs) belong to the largest family of cell surface signaling receptors encoded in the human genome. GPCRs signal to diverse extracellular stimuli and control a vast number of physiological responses, making this receptor class the target of nearly half the drugs currently in use. In addition to rapid desensitization, receptor trafficking is crucial for the temporal and spatial control of GPCR signaling. Sorting signals present in the intracytosolic domains of GPCRs regulate trafficking through the endosomal-lysosomal system. GPCR internalization is mediated by serine and threonine phosphorylation and arrestin binding. Short, linear peptide sequences including tyrosine- and dileucine-based motifs, and PDZ ligands that are recognized by distinct endocytic adaptor proteins also mediate internalization and endosomal sorting of GPCRs. We present new data from bioinformatic searches that reveal the presence of these types of sorting signals in the cytoplasmic tails of many known GPCRs. Several recent studies also indicate that the covalent modification of GPCRs with ubiquitin serves as a signal for internalization and lysosomal sorting, expanding the diversity of mechanisms that control trafficking of mammalian GPCRs.

| S-EPMC2869288 | biostudies-literature

Unconventional secretion of FABP4 by endosomes and secretory lysosomes.

Project description:An appreciation of the functional properties of the cytoplasmic fatty acid binding protein 4 (FABP4) has advanced with the recent demonstration that an extracellular form secreted by adipocytes regulates a wide range of physiological functions. Little, however, is known about the mechanisms that mediate the unconventional secretion of FABP4. Here, we demonstrate that FABP4 secretion is mediated by a membrane-bounded compartment, independent of the conventional endoplasmic reticulum-Golgi secretory pathway. We show that FABP4 secretion is also independent of GRASP proteins, autophagy, and multivesicular bodies but involves enclosure within endosomes and secretory lysosomes. We highlight the physiological significance of this pathway with the demonstration that an increase in plasma levels of FABP4 is inhibited by chloroquine treatment of mice. These findings chart the pathway of FABP4 secretion and provide a potential therapeutic means to control metabolic disorders associated with its dysregulated secretion.

| S-EPMC5800802 | biostudies-literature

Fusion of lysosomes with secretory organelles leads to uncontrolled exocytosis in the lysosomal storage disease mucolipidosis type IV.

Project description:Mutations in TRPML1 cause the lysosomal storage disease mucolipidosis type IV (MLIV). The role of TRPML1 in cell function and how the mutations cause the disease are not well understood. Most studies focus on the role of TRPML1 in constitutive membrane trafficking to and from the lysosomes. However, this cannot explain impaired neuromuscular and secretory cells' functions that mediate regulated exocytosis. Here, we analyzed several forms of regulated exocytosis in a mouse model of MLIV and, opposite to expectations, we found enhanced exocytosis in secretory glands due to enlargement of secretory granules in part due to fusion with lysosomes. Preliminary exploration of synaptic vesicle size, spontaneous mEPSCs, and glutamate secretion in neurons provided further evidence for enhanced exocytosis that was rescued by re-expression of TRPML1 in neurons. These features were not observed in Niemann-Pick type C1. These findings suggest that TRPML1 may guard against pathological fusion of lysosomes with secretory organelles and suggest a new approach toward developing treatment for MLIV.

| S-EPMC5290820 | biostudies-literature

A voltage-gated calcium channel regulates lysosomal fusion with endosomes and autophagosomes and is required for neuronal homeostasis.

Project description:Autophagy helps deliver sequestered intracellular cargo to lysosomes for proteolytic degradation and thereby maintains cellular homeostasis by preventing accumulation of toxic substances in cells. In a forward mosaic screen in Drosophila designed to identify genes required for neuronal function and maintenance, we identified multiple cacophony (cac) mutant alleles. They exhibit an age-dependent accumulation of autophagic vacuoles (AVs) in photoreceptor terminals and eventually a degeneration of the terminals and surrounding glia. cac encodes an ?1 subunit of a Drosophila voltage-gated calcium channel (VGCC) that is required for synaptic vesicle fusion with the plasma membrane and neurotransmitter release. Here, we show that cac mutant photoreceptor terminals accumulate AV-lysosomal fusion intermediates, suggesting that Cac is necessary for the fusion of AVs with lysosomes, a poorly defined process. Loss of another subunit of the VGCC, ?2? or straightjacket (stj), causes phenotypes very similar to those caused by the loss of cac, indicating that the VGCC is required for AV-lysosomal fusion. The role of VGCC in AV-lysosomal fusion is evolutionarily conserved, as the loss of the mouse homologues, Cacna1a and Cacna2d2, also leads to autophagic defects in mice. Moreover, we find that CACNA1A is localized to the lysosomes and that loss of lysosomal Cacna1a in cerebellar cultured neurons leads to a failure of lysosomes to fuse with endosomes and autophagosomes. Finally, we show that the lysosomal CACNA1A but not the plasma-membrane resident CACNA1A is required for lysosomal fusion. In summary, we present a model in which the VGCC plays a role in autophagy by regulating the fusion of AVs with lysosomes through its calcium channel activity and hence functions in maintaining neuronal homeostasis.

| S-EPMC4374850 | biostudies-literature

FORTIS: a live-cell assay to monitor AMPA receptors using pH-sensitive fluorescence tags.

Project description:The real-time live fluorescent monitoring of surface AMPA receptors (AMPARs) could open new opportunities for drug discovery and phenotypic screening concerning neuropsychiatric disorders. We have developed FORTIS, a tool based on pH sensitivity capable of detecting subtle changes in surface AMPARs at a neuronal population level. The expression of SEP-GluA1 or pHuji-GluA1 recombinant AMPAR subunits in mammalian neurons cultured in 96-well plates enables surface AMPARs to be monitored with a microplate reader. Thus, FORTIS can register rapid changes in surface AMPARs induced by drugs or genetic modifications without having to rely on conventional electrophysiology or imaging. By combining FORTIS with pharmacological manipulations, basal surface AMPARs, and plasticity-like changes can be monitored. We expect that employing FORTIS to screen for changes in surface AMPARs will accelerate both neuroscience research and drug discovery.

| S-EPMC8160262 | biostudies-literature

A mechanism-based fluorescence transfer assay for examining ketosynthase selectivity.

Project description:Since their discovery, polyketide synthases have received massive attention from researchers hoping to harness their potential as a platform for generating new and improved therapeutics. Despite significant strides toward this end, inherent specificities within the enzymes responsible for polyketide production have severely limited these efforts. We have developed a mechanism-based, fluorescence transfer assay for a key enzyme component of all polyketide synthases, the ketosynthase domain. As demonstrated, this method can be used with both ketosynthase-containing didomains and full modules. As proof of principle, the ketosynthase domain from module 6 of the 6-deoxyerythronolide synthase is examined for its ability to accept a variety of simple thioester substrates. Consistent with its natural hexaketide substrate, we find that this ketosynthase prefers longer, α-branched thioesters and its ability to distinguish these structural features is quite remarkable. Substrate electronics are also tested via a variety of p-substituted aromatic groups. In all, we expect this technique to find considerable use in the field of polyketide biosynthesis and engineering due to its extraordinary simplicity and very distinct visible readout.

| S-EPMC4232300 | biostudies-literature

A designed protein binding-pocket to control excited-state intramolecular proton transfer fluorescence.

Project description:Excited-state intramolecular proton transfer involves a photochemical isomerization and creates the opportunity for the emission of two distinct wavelengths of light from a single fluorophore. The selectivity between these two wavelengths of emission is dependent on the environment around the fluorophore and suggests the possibility for ratiometric monitoring of protein microenvironments. Unfortunately, nonspecific binding of ESIPT fluorophores does not often lead to dramatic changes in the ratio between the two wavelengths of emission. A protein binding pocket was designed to selectively discriminate between the two channels of emission available to an ESIPT fluorophore. This work is significant because it demonstrates that specific interactions between the protein and the fluorophore are essential to realize strong ratiometric differences between the two possible wavelengths of emission. The design strategies proposed here lead to an ESIPT fluorophore that can discern subtle differences in the interface between two proteins.

| S-EPMC6549506 | biostudies-literature

Huntingtin coordinates the dynein-mediated dynamic positioning of endosomes and lysosomes.

Project description:Huntingtin (Htt) is a membrane-associated scaffolding protein that interacts with microtubule motors as well as actin-associated adaptor molecules. We examined a role for Htt in the dynein-mediated intracellular trafficking of endosomes and lysosomes. In HeLa cells depleted of either Htt or dynein, early, recycling, and late endosomes (LE)/lysosomes all become dispersed. Despite altered organelle localization, kinetic assays indicate only minor defects in intracellular trafficking. Expression of full-length Htt is required to restore organelle localization in Htt-depleted cells, supporting a role for Htt as a scaffold that promotes functional interactions along its length. In dynein-depleted cells, LE/lysosomes accumulate in tight patches near the cortex, apparently enmeshed by cortactin-positive actin filaments; Latrunculin B-treatment disperses these patches. Peripheral LE/lysosomes in dynein-depleted cells no longer colocalize with microtubules. Htt may be required for this off-loading, as the loss of microtubule association is not seen in Htt-depleted cells or in cells depleted of both dynein and Htt. Inhibition of kinesin-1 relocalizes peripheral LE/lysosomes induced by Htt depletion but not by dynein depletion, consistent with their detachment from microtubules upon dynein knockdown. Together, these data support a model of Htt as a facilitator of dynein-mediated trafficking that may regulate the cytoskeletal association of dynamic organelles.

| S-EPMC3038646 | biostudies-literature

Phosphorylation-Assisted Luciferase Complementation Assay Designed to Monitor Kinase Activity and Kinase-Domain-Mediated Protein-Protein Binding.

Project description:Protein kinases are key regulators of cell signaling and have been important therapeutic targets for three decades. ATP-competitive drugs directly inhibit the activity of kinases but these enzymes work as part of complex protein networks in which protein-protein interactions (often referred to as kinase docking) may govern a more complex activation pattern. Kinase docking is indispensable for many signaling disease-relevant Ser/Thr kinases and it is mediated by a dedicated surface groove on the kinase domain which is distinct from the substrate-binding pocket. Thus, interfering with kinase docking provides an alternative strategy to control kinases. We describe activity sensors developed for p90 ribosomal S6 kinase (RSK) and mitogen-activated protein kinases (MAPKs: ERK, p38, and JNK) whose substrate phosphorylation is known to depend on kinase-docking-groove-mediated protein-protein binding. The in vitro assays were based on fragment complementation of the NanoBit luciferase, which is facilitated upon substrate motif phosphorylation. The new phosphorylation-assisted luciferase complementation (PhALC) sensors are highly selective and the PhALC assay is a useful tool for the quantitative analysis of kinase activity or kinase docking, and even for high-throughput screening of academic compound collections.

| S-EPMC10573712 | biostudies-literature

OmicsDI is part of the ELIXIR infrastructure

OmicsDI is an Elixir interoperability service. Learn more ›

Tweets

OmicsDI Databases

PRIDE
PeptideAtlas
MassIVE
JPOST Repository
Physiome Model Repository

EGA
EVA
ENA
LINCS
PAXDB
Cell Collective

MetaboLights
Metabolomics Workbench
MetabolomeExpress
GNPS
BioModels
FAIRDOMHub

ArrayExpress
dbGaP
ExpressionAtlas
GEO
NODE

Information

Databases
Help
API
Contact us
Code on GitHub
Terms of use
Submit Data