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PubMed1991

Distinct biochemical requirements for the budding, targeting, and fusion of ER-derived transport vesicles.

The transport of pro-alpha-factor from the ER to the Golgi apparatus in gently lysed yeast spheroplasts is mediated by diffusible vesicles. These transport vesicles contain core-glycosylated pro-alpha-factor and are physically separable from donor ER and target Golgi compartments. The formation of diffusible vesicles from the ER requires ATP, Sec12p, Sec23p, and GTP hydrolysis. The vesicles produced are functionally distinct from the ER: they transfer pro-alpha-factor to the Golgi apparatus faster and more efficiently than the ER, they do not require Sec12p or Sec23p to complete transfer, and transfer is resistant to GTP gamma S. Targeting of vesicles to the Golgi apparatus requires Ypt1p and Sec18p. Fusion of vesicles that have targeted requires calcium and ATP.

Adenosine Triphosphate↗

PubMed2001

Novel members of the human oxysterol-binding protein family bind phospholipids and regulate vesicle transport.

Oxysterol-binding proteins (OSBPs) are a family of eukaryotic intracellular lipid receptors. Mammalian OSBP1 binds oxygenated derivatives of cholesterol and mediates sterol and phospholipid synthesis through as yet poorly undefined mechanisms. The precise cellular roles for the remaining members of the oxysterol-binding protein family remain to be elucidated. In yeast, a family of OSBPs has been identified based on primary sequence similarity to the ligand binding domain of mammalian OSBP1. Yeast Kes1p, an oxysterol-binding protein family member that consists of only the ligand binding domain, has been demonstrated to regulate the Sec14p pathway for Golgi-derived vesicle transport. Specifically, inactivation of the KES1 gene resulted in the ability of yeast to survive in the absence of Sec14p, a phosphatidylinositol/phosphatidylcholine transfer protein that is normally required for cell viability due to its essential requirement in transporting vesicles from the Golgi. We cloned the two human members of the OSBP family, ORP1 and ORP2, with the highest degree of similarity to yeast Kes1p. We expressed ORP1 and ORP2 in yeast lacking Sec14p and Kes1p function and found that ORP1 complemented Kes1p function with respect to cell growth and Golgi vesicle transport, whereas ORP2 was unable to do so. Phenotypes associated with overexpression of ORP2 in yeast were a dramatic decrease in cell growth and a block in Golgi-derived vesicle transport distinct from that of ORP1. Purification of ORP1 and ORP2 for ligand binding studies demonstrated ORP1 and ORP2 did not bind 25-hydroxycholesterol but instead bound phospholipids with both proteins exhibiting strong binding to phosphatidic acid and weak binding to phosphatidylinositol 3-phosphate. In Chinese hamster ovary cells, ORP1 localized to a cytosolic location, whereas ORP2 was associated with the Golgi apparatus, consistent with our vesicle transport studies that indicated ORP1 and ORP2 function at different steps in the regulation of vesicle transport.

Amino Acid Sequence↗

PubMed1994

Toxic neurofilamentous axonopathies and fast axonal transport. V. Reduced bidirectional vesicle transport in cultured neurons by acrylamide and glycidamide.

Fast axonal transport deficiencies as mechanisms of action of acrylamide in producing axonal degeneration are under evaluation. The current study determines the effects of acrylamide and several analogues on the number of vesicles moving within the neurite processes of cultured rat embryonic neurons. Acrylamide produced severe, concentration-dependent (0.25-1.0 mM) and time-dependent (0-60 min) reduction in the quantity of vesicles translocated in both the anterograde and retrograde directions. Glycidamide, a potential neurotoxic metabolite of acrylamide, produced a time-dependent but not a concentration-dependent (in the 0.25-1.0 mM range) reduction in bidirectional transport. Based on inhibition at 60 min, glycidamide was estimated to be 4 times more potent than acrylamide in altering transport. Propionamide, a C1-C2 saturated nonneurotoxic acrylamide analogue, had no effect on axonal transport. While a tendency for methylene bisacrylamide (MbACR) to reduce vesicle transport was noted, at the concentration used no statistically significant differences from control were observed. The data support the correlation between toxicant-induced fast anterograde and retrograde axonal transport reductions and axonal degeneration produced by acrylamide and its analogues.

Acrylamide↗

PubMed2001

A vesicle transport system inside chloroplasts.

Intracellular transport via membrane vesicle traffic is a well known feature of eukaryotic cells. Yet, no vesicle transport system has been described for prokaryotes or organelles of prokaryotic origin, such as chloroplasts and mitochondria. Here we show that chloroplasts possess a vesicle transport system with features similar to vesicle traffic in homotypic membrane fusion. Vesicle formation and fusion is affected by specific inhibitors, e.g. nucleotide analogues, protein phosphatase inhibitors and Ca2+ antagonists. This vesicle transfer is an ongoing process in mature chloroplasts indicating that it represents an important new pathway in the formation and maintenance of the thylakoid membranes.

Biological Transport↗

PubMed1999

Specific interaction of the yeast cis-Golgi syntaxin Sed5p and the coat protein complex II component Sec24p of endoplasmic reticulum-derived transport vesicles.

The generation of transport vesicles at the endoplasmic reticulum (ER) depends on cytosolic proteins, which, in the form of subcomplexes (Sec23p/Sec24p; Sec13p/Sec31p) are recruited to the ER membrane by GTP-bound Sar1p and form the coat protein complex II (COPII). Using affinity chromatography and two-hybrid analyses, we found that the essential COPII component Sec24p, but not Sec23p, binds to the cis-Golgi syntaxin Sed5p. Sec24p/Sed5p interaction in vitro was not dependent on the presence of [Sar1p.GTP]. The binding of Sec24p to Sed5p is specific; none of the other seven yeast syntaxins bound to this COPII component. Whereas the interaction site of Sec23p is within the N-terminal half of the 926-aa-long Sec24p (amino acid residues 56-549), Sed5p binds to the N- and C-terminal halves of the protein. Destruction by mutagenesis of a potential zinc finger within the N-terminal half of Sec24p led to a nonfunctional protein that was still able to bind Sec23p and Sed5p. Sec24p/Sed5p binding might be relevant for cargo selection during transport-vesicle formation and/or for vesicle targeting to the cis-Golgi.

Binding Sites↗

PubMed1998

Effect of ethanol on intracellular vesicular transport from Golgi to the apical cell membrane: role of phosphatidylinositol 3-kinase and phospholipase A2 in Golgi transport vesicles association and fusion with the apical membrane.

The study of ethanol effects on intracellular transport and membrane biogenesis in rat hepatocytes revealed that, during synthesis of transport vesicles, the cytosolic phosphatidylinositol 3-kinase incorporated into the membrane of Golgi transport vesicles and a portion of the vesicular phosphatidylinositol was phosphorylated to phosphatidylinositol 3-phosphate. Association of the enzyme with Golgi transport vesicles and the transport to the apical portion of the cell membrane was not affected by 0 to 120 mM ethanol, but was dependent on the presence of the p85 subunit of the phosphatidylinositol 3-kinase. In the presence of ATP-enriched cytosol and calcium ions, association of Golgi transport vesicles with the apical membrane was followed by phospholipase A2-specific hydrolysis of phosphatidylinositol 3-phosphate and incorporation of the transport vesicle membrane into the apical membrane. Association of Golgi transport vesicles with apical membranes was not affected by preincubation of the cell membrane or Golgi transport vesicles with 0 to 120 mM ethanol, but was inhibited when the p85 phosphatidylinositol 3-kinase was incorporated into the membrane before incubation with Golgi transport vesicles. The fusion of Golgi transport vesicles with the apical membrane and generation of lysophosphatidylinositol 3-phosphate and arachidonate was inhibited with EGTA or after depletion of ATP from cytosol. Results of these studies provide evidence that phosphatidylinositol 3-kinase and phospholipase A2 activities are crucial for the final step of exocytotic transport. The process consists of two stages. First, the p85 subunit of phosphatidylinositol 3-kinase is involved in the specific association of the vesicle with membrane receptor, and that is followed by phospholipase A2-specific lysophospholipid generation, perturbation of the membranes, and fusion of the transport vesicle membrane with the apical membrane. Addition of ethanol to the in vitro transport system decreased production of Golgi transport vesicles, but had no effect on their association with apical membrane or fusion with the membrane.

Animals↗

PubMed1998

Microtubule-dependent vesicle transport: modulation of channel and transporter activity in liver and kidney.

Microtubule-based vesicle transport driven by kinesin and cytoplasmic dynein motor proteins facilitates several membrane-trafficking steps including elements of endocytosis and exocytosis in many different cell types. Most early studies on the role of microtubule-dependent vesicle transport in membrane trafficking focused either on neurons or on simple cell lines. More recently, other work has considered the role of microtubule-based vesicle transport in other physiological systems, including kidney and liver. Investigation of the role of microtubule-based vesicle transport in membrane trafficking in cells of the kidney and liver suggests a major role for microtubule-based vesicle transport in the rapid and directed movement of ion channels and transporters to and from the apical plasma membranes, events essential for kidney and liver function and homeostasis. This review discusses the evidence supporting a role for microtubule-based vesicle transport and the motor proteins, kinesin and cytoplasmic dynein, in different aspects of membrane trafficking in cells of the kidney and liver, with emphasis on those functions such as maintenance of ion channel and transporter composition in apical membranes that are specialized functions of these organs. Evidence that defects in microtubule-based transport contribute to diseases of the kidney and liver is also discussed.

Animals↗

PubMed1999

Vesicle transport: the role of actin filaments and myosin motors.

The transport of vesicles and the retention of organelles at specific locations are fundamental processes in cells. Actin filaments and myosin motors have been shown to be required for both of these tasks. Most of the organelles in cells associate with actin filaments and some of the myosin motors required for movement on actin filaments have been identified. Myosin V has been shown to transport endoplasmic reticulum (ER) vesicles in neurons, pigment granules in melanocytes, and the vacuole in yeast. Myosin I has been shown to be involved in the transport of Golgi-derived vesicles in epithelial cells. Myosin VI has been shown to be associated with Golgi-derived vesicles, and cytoplasmic vesicles in living Drosophila embryos. Myosin II may be a vesicle motor but its role in vesicle transport has not been resolved. Secretory vesicles, endosomes and mitochondria appear to be transported on actin filaments but the myosin motors on these organelles have not been identified. Mitochondria in yeast may be transported by the dynamic assembly of an actin "tail." The model that has unified all of these findings is the concept that long-range movement of vesicles occurs on microtubules and short-range movement on actin filaments. The details of how the microtubule-dependent and the actin-dependent motors are coordinated are important questions in the field. There is now strong evidence that two molecular motors, kinesin and myosin V, interact with each other and perhaps function as a complex on vesicles. An understanding of the interrelationship of microtubules and actin filaments and the motors that move cargo on them will ultimately establish how vesicles and organelles are transported to their specific locations in cells.

Actins↗

PubMed1990

The molecular control of transport vesicle fusion.

The fusion of transport vesicles with the appropriate target membrane in constitutive transport is a complex and well-controlled process. Many of the molecular details of the reactions that result in this control are being revealed through the use of cell-free assays of protein transport as well as by the study of the molecular genetics of secretion in yeast. Kinetic analyses have indicated that several structural intermediates are formed after transport vesicles attach to their destination, but before they fuse with the appropriate membrane. Proteins that mediate the formation and processing of these intermediates have been identified. Included among these are small molecular weight GTP-binding proteins. This intricate set of reactions may ensure the fidelity of transport and guard the integrity of the organelles along the transport pathway.

Animals↗

PubMed2002

Myelin biogenesis: vesicle transport in oligodendrocytes.

Intracellular trafficking of membranes plays an essential role in the biogenesis and maintenance of myelin. The requisite proteins and lipids are transported from their sites of synthesis to myelin via vesicles. Vesicle transport is tightly coordinated with synthesis of lipids and proteins. To maintain the structural and functional organization of oligodendrocytes it is essential synchronize the various pathways of vesicle transport and to coordinate vesicle transport with reorganization of cytoskeleton. The systems that regulate the targeting of protein to myelin by vesicle transport are now being described. Here we review the current knowledge of these systems including those involved in (a) protein folding, (b) protein sorting and formation of carrier vesicles, (c) vesicle transport along elements of the cytoskeleton, and (d) vesicle targeting/fusion.

Animals↗

PubMed2001

Role of Erv29p in collecting soluble secretory proteins into ER-derived transport vesicles.

Proteins are transported from the endoplasmic reticulum (ER) in vesicles formed by coat protein complex II (COPII). Soluble secretory proteins are thought to leave the ER in these vesicles by "bulk flow" or through recognition by hypothetical shuttling receptors. We found that Erv29p, a conserved transmembrane protein, was directly required for packaging glycosylated pro-alpha-factor (gpalphaf) into COPII vesicles in Saccharomyces cerevisiae. Further, an Erv29p-gpalphaf complex was isolated from ER-derived transport vesicles. In vivo, export of gpalphaf from the ER was saturable and depended on the expression level of Erv29p. These results indicate that membrane receptors can link soluble cargo proteins to the COPII coat.

COP-Coated Vesicles↗

PubMed1992

Immuno-isolation of Sec7p-coated transport vesicles from the yeast secretory pathway.

The transport of proteins destined for post-endoplasmic reticulum locations in the secretory pathway is mediated by small vesicular carriers. Transport vesicles have been generated in cell-free assays from the yeast Saccharomyces cerevisiae, and mammalian systems. Yeast genes encoding cytosolic components that participate in vesicular traffic were first identified from the collection of conditional-lethal sec-(secretory) mutants. Mutations in the yeast SEC7 gene disrupt protein transport in the secretory pathway at the nonpermissive temperature. The SEC7 gene product is a phosphoprotein of relative molecular mass 230,000 that functions from the cytoplasmic aspect of intracellular membranes. We report that in a yeast cell-free transport assay, the introduction of antibodies to Sec7 protein (Sec7p) results in the accumulation of transport vesicles. These vesicles are retrieved with Sec7p-specific antibodies by immuno-isolation for biochemical and electron microscopic characterization. Sec7p on the surface of the accumulated transport vesicles, in combination with previous genetic and biochemical studies, implicate Sec7p as part of a (non-clathrin) vesicle coat. This Sec7p-containing coat structure is proposed to be essential for vesicle budding at multiple stages in the yeast secretory pathway.

Biological Transport↗

PubMed1992

Biogenesis of endoplasmic reticulum transport vesicles transferring gastric apomucin from ER to Golgi.

Rough endoplasmic reticulum (RER) transport vesicles were generated from gastric mucous cell RER microsomes in the presence of labeled precursors of phospholipids. The vesicles contained 7-10% of their proteins in the form of apomucin (cargo), and 80% of de novo synthesized phosphatidylcholine (PC) was incorporated into the vesicular membrane. In the absence of choline and ethanolamine precursors or in the presence of 3 mM N-ethylmaleimide (NEM), an inhibitor of CTP:phosphocholine cytidylyltransferase, formation of the transport vesicles, their enrichment in the newly synthesized PC, and the total synthesis of PC decreased by 86%, whereas in the presence of 3 mM Zn2+, complete blockage of vesicle formation and PC synthesis was observed. Analysis of the mucin-transporting vesicles indicated that the CTP:phosphocholine cytidylyltransferase and 1,2-diacyl-sn-glycerol:CDP-choline phosphotransferase remained associated with transport vesicles released from ER. The enzymes and other proteins separated from the vesicle surface prior to vesicle fusion with Golgi and the process was induced by phosphorylation. Based on the results of this study, it is proposed that the formation of the ER transport vesicles of gastric mucosal cells is in concert with synthesis of phospholipids and thus in part is regulated by phospholipid-synthesizing enzymes that reside on the membrane during its biogenesis and dissociate from its surface once the task is completed.

Animals↗

PubMed2004

The lipid binding pleckstrin homology domain in UNC-104 kinesin is necessary for synaptic vesicle transport in Caenorhabditis elegans.

UNC-104 (KIF1A) is a kinesin motor that transports synaptic vesicles from the neuronal cell body to the terminal. Previous in vitro studies have shown that a Dictyostelium relative of UNC-104 transports liposomes containing acidic phospholipids, but whether this interaction is needed for the recognition and transport of synaptic vesicles in metazoans remains unexplored. Here, we have introduced mutations in the nonmotor domain of UNC-104 and examined whether these mutant motors can rescue an unc-104 Caenorhabditis elegans strain. We show that a pleckstrin homology (PH) domain in UNC-104 is essential for membrane transport in living C. elegans, that this PH domain binds specifically to phosphatidylinositol-4,5-bisphosphate (PI(4,5)P(2)), and that point mutants in the PH domain that interfere with PI(4,5)P(2) binding in vitro also interfere with UNC-104 function in vivo. Several other lipid-binding modules could not effectively substitute for the UNC-104 PH domain in this in vivo assay. Real time imaging also revealed that a lipid-binding point mutation in the PH domain reduced movement velocity and processivity of individual UNC-104::GFP punctae in neurites. These results reveal a critical role for PI(4,5)P(2) binding in UNC-104-mediated axonal transport and shows that the cargo-binding properties of the distal PH domain can affect motor output.

Amino Acid Sequence↗

PubMed2001

The molecular mechanism of targeted vesicle transport in cytokinesis.

Recent studies have demonstrated that vesicle transport to cleavage furrow is indispensable for cytokinesis. Some animal and plant cells form distinct structures during cell division known as central spindle and phragmoplast, respectively. Several essential factors involved in the vesicle transport have been isolated so far. SNARE proteins and molecular motors play a central role in this process. For future research of cytokinesis, it is important to investigate these factors as well as cytoskeletal components of the contractile ring in detail. This review focuses on the molecular mechanism of targeted vesicle transport in cytokinesis.

Animals↗

PubMed2006

Dense core vesicles resemble active-zone transport vesicles and are diminished following synaptogenesis in mature hippocampal slices.

Large dense core vesicles (approximately 100 nm) contain neuroactive peptides and other co-transmitters. Smaller dense core vesicles (approximately 80 nm) are known to contain components of the presynaptic active zone and thought to transport and deliver these components during developmental synaptogenesis. It is not known whether excitatory axons in area CA1 contain such dense core vesicles, and whether they contribute to synaptic plasticity of mature hippocampus. Serial section electron microscopy was used to identify dense core vesicles in presynaptic axons in s. radiatum of area CA1 in adult rat hippocampus. Comparisons were made among perfusion-fixed hippocampus and hippocampal slices that undergo synaptogenesis during recovery in vitro. Dense core vesicles occurred in 26.1+/-3.6% of axonal boutons in perfusion fixed hippocampus, and in only 17.6+/-4.5% of axonal boutons in hippocampal slices (P<0.01). Most of the dense core vesicle positive boutons contained only one dense core vesicle, and no reconstructed axonal bouton had more than a total of 10 dense core vesicles in either condition. Overall the dense core vesicles had average diameters of 79+/-11 nm. These small dense core vesicles were usually located near nonsynaptic membranes and rarely occurred near the edge of a presynaptic active zone. Their size, low frequency, locations, and decrease following recuperative synaptogenesis in slices are novel findings that merit further study with respect to small dense core vesicle content and possible contributions to synapse assembly and plasticity in the mature hippocampus.

Animals↗

PubMed2004

Visualization of vesicle transport along and between distinct pathways in neurites of living cells.

Trafficking of secretory vesicles along neurites of PC12 cells was visualized by 2D and 3D real-time imaging using fluorescence microscopy. Vesicle motion along distinct pathways was directly seen. From an overlay of individual pathways, the underlying cytoskeletal filament could be imaged at a subwavelength resolution. Continuous vesicle transport was interrupted by periods of diffusive motion with concomitant pathway changes. Statistical analysis shows that such interruptions were distributed stochastically along the filament, indicating a limited processivity of motor proteins also in a cellular context. Periods of diffusive motion facilitated the interaction with actively transported vesicles. Frequent associations and dissociations of vesicles have been observed consistently, pointing to a functional relevance of vesicle cotransport.

Animals↗

PubMed1996

Transport vesicle docking: SNAREs and associates.

Proteins that function in transport vesicle docking are being identified at a rapid rate. So-called v- and t-SNAREs form the core of a vesicle docking complex. Additional accessory proteins are required to protect SNAREs from promiscuous binding and to deprotect SNAREs under conditions in which transport vesicle docking should occur. Because access to SNAREs must be regulated, other proteins must also contain specificity determinants to accomplish delivery of transport vesicles to their distinct and specific membrane targets.

Animals↗