The Experts below are selected from a list of 258 Experts worldwide ranked by ideXlab platform
Todd R. Graham - One of the best experts on this subject based on the ideXlab platform.
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Requirement for Neo1p in Retrograde Transport from the Golgi Complex to the Endoplasmic Reticulum
Molecular biology of the cell, 2003Co-Authors: Zhaolin Hua, Todd R. GrahamAbstract:Neo1p from Saccharomyces cerevisiae is an essential P-type ATPase and potential aminophospholipid translocase (flippase) in the Drs2p family. We have previously implicated Drs2p in protein transport steps in the late secretory pathway requiring ADP-ribosylation factor (ARF) and clathrin. Here, we present evidence that epitope-tagged Neo1p localizes to the endoplasmic reticulum (ER) and Golgi Complex and is required for a retrograde transport pathway between these organelles. Using conditional alleles of NEO1, we find that loss of Neo1p function causes cargo-specific defects in anterograde protein transport early in the secretory pathway and perturbs glycosylation in the Golgi Complex. Rer1-GFP, a protein that cycles between the ER and Golgi Complex in COPI and COPII vesicles, is mislocalized to the vacuole in neo1-ts at the nonpermissive temperature. These phenotypes suggest that the anterograde protein transport defect is a secondary consequence of a defect in a COPI-dependent retrograde pathway. We propose that loss of lipid asymmetry in the cis Golgi perturbs retrograde protein transport to the ER.
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Organization of the Yeast Golgi Complex into at Least Four Funtionally Distinct Compartments
Molecular biology of the cell, 2000Co-Authors: William T. Brigance, Charles Barlowe, Todd R. GrahamAbstract:Pro-alpha-factor (pro-alphaf) is posttranslationally modified in the yeast Golgi Complex by the addition of alpha1,6-, alpha1,2-, and alpha1,3-linked mannose to N-linked oligosaccharides and by a Kex2p-initiated proteolytic processing event. Previous work has indicated that the alpha1,6- and alpha1,3-mannosylation and Kex2p-dependent processing of pro-alphaf are initiated in three distinct compartments of the Golgi Complex. Here, we present evidence that alpha1,2-mannosylation of pro-alphaf is also initiated in a distinct Golgi compartment. Linkage-specific antisera and an endo-alpha1,6-D-mannanase (endoM) were used to quantitate the amount of each pro-alphaf intermediate during transport through the Golgi Complex. We found that alpha1,6-, alpha1,2-, and alpha1,3-mannose were sequentially added to pro-alphaf in a temporally ordered manner, and that the intercompartmental transport factor Sec18p/N-ethylmaleimide-sensitive factor was required for each step. The Sec18p dependence implies that a transport event was required between each modification event. In addition, most of the Golgi-modified pro-alphaf that accumulated in brefeldin A-treated cells received only alpha1,6-mannosylation as did approximately 50% of pro-alphaf transported to the Golgi in vitro. This further supports the presence of an early Golgi compartment that houses an alpha1,6-mannosyltransferase but lacks alpha1,2-mannosyltransferase activity in vivo. We propose that the alpha1,6-, alpha1,2-, and alpha1,3-mannosylation and Kex2p-dependent processing events mark the cis, medial, trans, and trans-Golgi network of the yeast Golgi Complex, respectively.
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The Golgi Complex of Saccharomyces cerevisiae
Botany, 1995Co-Authors: Vladimir Krasnov, Todd R. GrahamAbstract:The Golgi Complex of Saccharomyces cerevisiae is required for protein transport, posttranslational modification, and sorting within the secretory pathway. Only in the last few years has it become clear that these events are functionally organized into distinct Golgi compartments analagous to the cis–trans compartments of the plant and animal Golgi Complex. The mechanisms by which the Golgi Complex maintains its own organization and complement of intrinsic enzymes against the flow of lipid and protein through the secretory pathway are still poorly understood. However, studies using Saccharomyces cerevisiae as a model system are providing insights into mechanisms of Golgi protein localization that appear to be conserved between yeast and mammalian cells. This review describes the structure and organization of the yeast Golgi Complex and recent work towards defining localization signals within intrinsic enzymes of this organelle. Key words: Golgi Complex, protein sorting, Saccharomyces cerevisiae, α-1,3-mann...
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The Golgi Complex of Saccharomyces cerevisiae
Canadian Journal of Botany, 1995Co-Authors: Vladimir Krasnov, Todd R. GrahamAbstract:The Golgi Complex of Saccharomyces cerevisiae is required for protein transport, posttranslational modification, and sorting within the secretory pathway. Only in the last few years has it become clear that these events are functionally organized into distinct Golgi compartments analagous to the cis–trans compartments of the plant and animal Golgi Complex. The mechanisms by which the Golgi Complex maintains its own organization and complement of intrinsic enzymes against the flow of lipid and protein through the secretory pathway are still poorly understood. However, studies using Saccharomyces cerevisiae as a model system are providing insights into mechanisms of Golgi protein localization that appear to be conserved between yeast and mammalian cells. This review describes the structure and organization of the yeast Golgi Complex and recent work towards defining localization signals within intrinsic enzymes of this organelle. Key words: Golgi Complex, protein sorting, Saccharomyces cerevisiae, α-1,3-mannosyltransferase.
William J Brown - One of the best experts on this subject based on the ideXlab platform.
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regulation of the Golgi Complex by phospholipid remodeling enzymes
Biochimica et Biophysica Acta, 2012Co-Authors: Benjamin A Clarke, William J BrownAbstract:The mammalian Golgi Complex is a highly dynamic organelle consisting of stacks of flattened cisternae with associated coated vesicles and membrane tubules that contribute to cargo import and export, intra-cisternal trafficking, and overall Golgi architecture. At the morphological level, all of these structures are continuously remodeled to carry out these trafficking functions. Recent advances have shown that continual phospholipid remodeling by phospholipase A (PLA) and lysophospholipid acyltransferase (LPAT) enzymes, which deacylate and reacylate Golgi phospholipids, respectively, contributes to this morphological remodeling. Here we review the identification and characterization of four cytoplasmic PLA enzymes and one integral membrane LPAT that participate in the dynamic functional organization of the Golgi Complex, and how some of these enzymes are integrated to determine the relative abundance of COPI vesicle and membrane tubule formation.
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Regulation of the Golgi Complex by phospholipid remodeling enzymes.
Biochimica et biophysica acta, 2012Co-Authors: Benjamin A Clarke, William J BrownAbstract:The mammalian Golgi Complex is a highly dynamic organelle consisting of stacks of flattened cisternae with associated coated vesicles and membrane tubules that contribute to cargo import and export, intra-cisternal trafficking, and overall Golgi architecture. At the morphological level, all of these structures are continuously remodeled to carry out these trafficking functions. Recent advances have shown that continual phospholipid remodeling by phospholipase A (PLA) and lysophospholipid acyltransferase (LPAT) enzymes, which deacylate and reacylate Golgi phospholipids, respectively, contributes to this morphological remodeling. Here we review the identification and characterization of four cytoplasmic PLA enzymes and one integral membrane LPAT that participate in the dynamic functional organization of the Golgi Complex, and how some of these enzymes are integrated to determine the relative abundance of COPI vesicle and membrane tubule formation. This article is part of a Special Issue entitled Lipids and Vesicular Transport.
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The phospholipase Complex PAFAH Ib regulates the functional organization of the Golgi Complex
The Journal of cell biology, 2010Co-Authors: Marie E. Bechler, Anne M. Doody, Esther L. Racoosin, Lin Lin, Kelvin H. Lee, William J BrownAbstract:We report that platelet-activating factor acetylhydrolase (PAFAH) Ib, comprised of two phospholipase A(2) (PLA(2)) subunits, alpha1 and alpha2, and a third subunit, the dynein regulator lissencephaly 1 (LIS1), mediates the structure and function of the Golgi Complex. Both alpha1 and alpha2 partially localize on Golgi membranes, and purified catalytically active, but not inactive alpha1 and alpha2 induce Golgi membrane tubule formation in a reconstitution system. Overexpression of wild-type or mutant alpha1 or alpha2 revealed that both PLA(2) activity and LIS1 are important for maintaining Golgi structure. Knockdown of PAFAH Ib subunits fragments the Golgi Complex, inhibits tubule-mediated reassembly of intact Golgi ribbons, and slows secretion of cargo. Our results demonstrate a cooperative interplay between the PLA(2) activity of alpha1 and alpha2 with LIS1 to facilitate the functional organization of the Golgi Complex, thereby suggesting a model that links phospholipid remodeling and membrane tubulation to dynein-dependent transport.
Vytas A Bankaitis - One of the best experts on this subject based on the ideXlab platform.
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Analysis of oxysterol binding protein homologue Kes1p function in regulation of Sec14p-dependent protein transport from the yeast Golgi Complex
Journal of Cell Biology, 2002Co-Authors: Xinmin Li, Marcos P. Rivas, Jennifer Marchena, Bharat Mehrotra, Anu Chaudhary, Li Feng, Min Fang, Vytas A BankaitisAbstract:Oxysterol binding proteins (OSBPs) comprise a large conserved family of proteins in eukaryotes. Their ubiquity notwithstanding, the functional activities of these proteins remain unknown. Kes1p, one of seven members of the yeast OSBP family, negatively regulates Golgi Complex secretory functions that are dependent on the action of the major yeast phosphatidylinositol/phosphatidylcholine Sec14p. We now demonstrate that Kes1p is a peripheral membrane protein of the yeast Golgi Complex, that localization to the Golgi Complex is required for Kes1p function in vivo, and that targeting of Kes1p to the Golgi Complex requires binding to a phosphoinositide pool generated via the action of the Pik1p, but not the Stt4p, PtdIns 4-kinase. Localization of Kes1p to yeast Golgi region also requires function of a conserved motif found in all members of the OSBP family. Finally, we present evidence to suggest that Kes1p may regulate adenosine diphosphate-ribosylation factor (ARF) function in yeast, and that it may be through altered regulation of ARF that Kes1p interfaces with Sec14p in controlling Golgi region secretory function.
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The contribution of lipids and lipid metabolism to cellular functions of the Golgi Complex.
Biochimica et biophysica acta, 1998Co-Authors: Min Fang, Marcos P. Rivas, Vytas A BankaitisAbstract:The history of the Golgi Complex now reaches its 100 year anniversary. Over the past several decades, tremendous effort has gone into cataloguing Golgi resident proteins, measuring the lipid compositions of Golgi membranes, and in elucidating the pathways by which proteins and lipids traffic through this unique organelle. Only in the past 8 years or so has experimental scrutiny extended to the investigation of how lipids and proteins cooperate to endow the Golgi with its various capabilities regarding protein/lipid transport and sorting. In this chapter we review some of the most recent advances in deciphering the functional interfaces between lipids and proteins of the Golgi Complex.
Maria Antonietta De Matteis - One of the best experts on this subject based on the ideXlab platform.
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The Golgi Complex in disease and therapy.
Current opinion in cell biology, 2018Co-Authors: Francesca Zappa, Mario Failli, Maria Antonietta De MatteisAbstract:The Golgi Complex occupies a strategic position in the endomembrane system and acts not only as a key trafficking and sorting station and a vital biosynthetic center for glycoproteins and lipids, but also as an active signaling hub. As such, the Golgi Complex participates in the establishment and maintenance of cell compartmentalization and in general, cell processes such as cell growth and apoptosis. The different functions of the Golgi Complex are executed by composite molecular machineries that have been exhaustively dissected over the last three decades. These machineries can become dysfunctional as a result of mutations in the respective encoding genes or may be hijacked by infectious agents or misregulated in the course of multifactorial diseases such as neurodegeneration and cancer. Small molecules targeting components of these machineries have been instrumental in dissecting their functions in in vitro studies and some of them have been developed or are currently under development for clinical use.
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Phosphoinositides in Golgi Complex function.
Sub-cellular biochemistry, 2012Co-Authors: Giovanni D'angelo, Mariella Vicinanza, Cathal Wilson, Maria Antonietta De MatteisAbstract:The Golgi Complex is a ribbon-like organelle composed of stacks of flat cisternae interconnected by tubular junctions. It occupies a central position in the endomembrane system as proteins and lipids that are synthesized in the endoplasmic reticulum (ER) pass through the Golgi Complex to undergo biosynthetic modification (mainly glycosylation) and to be sorted to their final destinations. In addition the Golgi Complex possesses a number of activities, apparently not directly connected with its main role in trafficking and sorting, which have been recently reviewed in Wilson et al. 2011. In spite of the constant massive flux of material the Golgi Complex maintains its identity and phosphoinositides (PIs), among other factors, play a central role in this process. The active metabolism of PIs at the Golgi is necessary for the proper functioning of the organelle both in terms of membrane trafficking/sorting and its manifold metabolic and signalling activities. Phosphatidylinositol 4-phosphate (PtdIns4P), in particular, is responsible for the recruitment of numerous cytosolic proteins that recognise and bind PtdIns4P via specific lipid-binding domains. In this chapter we will summarize the findings that have contributed to our current understanding of the role of PIs in the biology of the Golgi Complex in terms of the regulation of PI metabolism and the functional roles and regulation of PtdIns4P effectors.
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The Golgi Complex
FEBS letters, 2009Co-Authors: Maria Antonietta De Matteis, Daniela Corda, Alberto LuiniAbstract:The ultrastructural arrangement of membranes of the Golgi Complex has been characterized in Golgi fractions isolated from rat liver. Procedures for isolation of these fractions have been modified to provide a good yield of Golgi membranes (60 to 70%) with greater than 50-fold purification of sialyl transferase, an enzyme specific for the Golgi Complex. The isolated membranes appear well preserved and both the dimensions and appearance of the Golgi Complex observed by negative staining and in sections of the isolated membranes correlate well with that in liver sections.
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The role of the phosphoinositides at the Golgi Complex.
Biochemical Society symposium, 2007Co-Authors: Maria Antonietta De Matteis, Giovanni D'angeloAbstract:Eukaryotic cells are organized into a Complex system of subcompartments, each with its distinct protein and lipid composition. A continuous flux of membranes crosses these compartments, and in some cases direct connections exist between the different organelles. It is thus surprising that they can maintain their individual identities. Small GTPases and the phosphoinositides have emerged as the key regulators in the maintenance of the identity of the Golgi Complex. This property is due to their ability to act either alone or, more often, in combination, as cues directing and controlling the recruitment of proteins that possess phosphoinositide-binding domains. Among these many proteins there are the lipid transfer proteins, which can transfer ceramide, oxysterol, cholesterol and possibly glucosylceramide. By regulating these lipid transfer proteins in this way, this binomial combination of the small GTPases and the phosphoinositides acquires a further important role: control of the synthesis and/or distribution of other important integral constituents of cell organelles, such as the sphingolipids and cholesterol. This role is particularly relevant at the level of the Golgi Complex, a key organelle in the biosynthesis, transport and sorting of both lipids and proteins that is located at the intersection of the secretory and endocytic pathways.
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Phosphoinositides and the Golgi Complex.
Current opinion in cell biology, 2002Co-Authors: Maria Antonietta De Matteis, Anna Godi, Daniela CordaAbstract:Phosphoinositides act as precursors of second messengers and membrane ligands for protein modules. Specific lipid kinases and phosphatases are located and differentially regulated in cell organelles, generating a non-uniform distribution of phosphoinositides. Although it is not clear whether and how the phosphoinositide pools are integrated, it is certain that they locally control fundamental processes, including membrane trafficking. This applies to the Golgi Complex, where a direct, central role of the phosphatidylinositol 4,5-bisphosphate precursor phosphatidylinositol 4-phosphate has recently been reported.
Anne K Kenworthy - One of the best experts on this subject based on the ideXlab platform.
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depalmitoylated ras traffics to and from the Golgi Complex via a nonvesicular pathway
Journal of Cell Biology, 2005Co-Authors: Shawn J Goodwin, Kimberly R Drake, Carl Rogers, Latasha Wright, Jennifer Lippincottschwartz, Mark R Philips, Anne K KenworthyAbstract:Palmitoylation is postulated to regulate Ras signaling by modulating its intracellular trafficking and membrane microenvironment. The mechanisms by which palmitoylation contributes to these events are poorly understood. Here, we show that dynamic turnover of palmitate regulates the intracellular trafficking of HRas and NRas to and from the Golgi Complex by shifting the protein between vesicular and nonvesicular modes of transport. A combination of time-lapse microscopy and photobleaching techniques reveal that in the absence of palmitoylation, GFP-tagged HRas and NRas undergo rapid exchange between the cytosol and ER/Golgi membranes, and that wild-type GFP-HRas and GFP-NRas are recycled to the Golgi Complex by a nonvesicular mechanism. Our findings support a model where palmitoylation kinetically traps Ras on membranes, enabling the protein to undergo vesicular transport. We propose that a cycle of depalmitoylation and repalmitoylation regulates the time course and sites of Ras signaling by allowing the protein to be released from the cell surface and rapidly redistributed to intracellular membranes.