51
|
Abstract
P4 ATPases (subfamily IV P-type ATPases) form a specialized subfamily of P-type ATPases and have been implicated in phospholipid translocation from the exoplasmic to the cytoplasmic leaflet of biological membranes. Pivotal roles of P4 ATPases have been demonstrated in eukaryotes, ranging from yeast, fungi and plants to mice and humans. P4 ATPases might exert their cellular functions by combining enzymatic phospholipid translocation activity with an enzyme-independent action. The latter could be involved in the timely recruitment of proteins involved in cellular signalling, vesicle coat assembly and cytoskeleton regulation. In the present review, we outline the current knowledge of the biochemical and cellular functions of P4 ATPases in the eukaryotic membrane.
Collapse
|
52
|
Graham TR, Kozlov MM. Interplay of proteins and lipids in generating membrane curvature. Curr Opin Cell Biol 2010; 22:430-6. [PMID: 20605711 DOI: 10.1016/j.ceb.2010.05.002] [Citation(s) in RCA: 158] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2010] [Revised: 04/09/2010] [Accepted: 05/03/2010] [Indexed: 01/14/2023]
Abstract
The majority of intracellular membranes have strongly bent shapes with radii of curvature ranging from 20 to 50 nm. Many different proteins provide the substantial energy needed to generate and sustain this curvature. One of the most effective mechanisms of curvature creation is based on asymmetry of membrane monolayers. Proteins generate this asymmetry by flipping phospholipid across the membrane, modifying lipid molecules, or embedding their hydrophobic domains into the membrane matrix. We review the physical principles of these mechanisms of membrane bending and highlight the action of specific proteins driving vesicle-mediated transport. A model of clathrin-mediated vesicle budding from the trans-Golgi network is described to illustrate the interplay and mutual reinforcement of different mechanisms for generating membrane curvature.
Collapse
Affiliation(s)
- Todd R Graham
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235, USA.
| | | |
Collapse
|
53
|
Barbosa S, Pratte D, Schwarz H, Pipkorn R, Singer-Krüger B. Oligomeric Dop1p is Part of the Endosomal Neo1p-Ysl2p-Arl1p Membrane Remodeling Complex. Traffic 2010; 11:1092-106. [DOI: 10.1111/j.1600-0854.2010.01079.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
54
|
Paulusma CC, Oude Elferink RP. P4 ATPases - The physiological relevance of lipid flipping transporters. FEBS Lett 2010; 584:2708-16. [DOI: 10.1016/j.febslet.2010.04.071] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2010] [Revised: 04/28/2010] [Accepted: 04/28/2010] [Indexed: 11/27/2022]
|
55
|
Merkulova M, Bakulina A, Thaker YR, Grüber G, Marshansky V. Specific motifs of the V-ATPase a2-subunit isoform interact with catalytic and regulatory domains of ARNO. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2010; 1797:1398-409. [PMID: 20153292 DOI: 10.1016/j.bbabio.2010.02.009] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2009] [Revised: 01/11/2010] [Accepted: 02/08/2010] [Indexed: 11/19/2022]
Abstract
We have previously shown that the V-ATPase a2-subunit isoform interacts specifically, and in an intra-endosomal acidification-dependent manner, with the Arf-GEF ARNO. In the present study, we examined the molecular mechanism of this interaction using synthetic peptides and purified recombinant proteins in protein-association assays. In these experiments, we revealed the involvement of multiple sites on the N-terminus of the V-ATPase a2-subunit (a2N) in the association with ARNO. While six a2N-derived peptides interact with wild-type ARNO, only two of them (named a2N-01 and a2N-03) bind to its catalytic Sec7-domain. However, of these, only the a2N-01 peptide (MGSLFRSESMCLAQLFL) showed specificity towards the Sec7-domain compared to other domains of the ARNO protein. Surface plasmon resonance kinetic analysis revealed a very strong binding affinity between this a2N-01 peptide and the Sec7-domain of ARNO, with dissociation constant KD=3.44x10(-7) M, similar to the KD=3.13x10(-7) M binding affinity between wild-type a2N and the full-length ARNO protein. In further pull-down experiments, we also revealed the involvement of multiple sites on ARNO itself in the association with a2N. However, while its catalytic Sec7-domain has the strongest interaction, the PH-, and PB-domains show much weaker binding to a2N. Interestingly, an interaction of the a2N to a peptide corresponding to ARNO's PB-domain was abolished by phosphorylation of ARNO residue Ser392. The 3D-structures of the non-phosphorylated and phosphorylated peptides were resolved by NMR spectroscopy, and we have identified rearrangements resulting from Ser392 phosphorylation. Homology modeling suggests that these alterations may modulate the access of the a2N to its interaction pocket on ARNO that is formed by the Sec7 and PB-domains. Overall, our data indicate that the interaction between the a2-subunit of V-ATPase and ARNO is a complex process involving various binding sites on both proteins. Importantly, the binding affinity between the a2-subunit and ARNO is in the same range as those previously reported for the intramolecular association of subunits within V-ATPase complex itself, indicating an important cell biological role for the interaction between the V-ATPase and small GTPase regulatory proteins.
Collapse
Affiliation(s)
- Maria Merkulova
- Center for Systems Biology, Program in Membrane Biology and Division of Nephrology, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
| | | | | | | | | |
Collapse
|
56
|
López-Marqués RL, Poulsen LR, Hanisch S, Meffert K, Buch-Pedersen MJ, Jakobsen MK, Pomorski TG, Palmgren MG. Intracellular targeting signals and lipid specificity determinants of the ALA/ALIS P4-ATPase complex reside in the catalytic ALA alpha-subunit. Mol Biol Cell 2010; 21:791-801. [PMID: 20053675 PMCID: PMC2828965 DOI: 10.1091/mbc.e09-08-0656] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Phospholipid flipping across cellular membranes contributes to vesicle biogenesis in eukaryotes and involves flippases (P4-ATPases). However, the minimal composition of the flippase machinery remains to be determined. We demonstrate that cellular targeting and lipid specificity of P4-ATPases require the α-subunit but are independent of the β-subunit. Members of the P4 subfamily of P-type ATPases are believed to catalyze flipping of phospholipids across cellular membranes, in this way contributing to vesicle biogenesis in the secretory and endocytic pathways. P4-ATPases form heteromeric complexes with Cdc50-like proteins, and it has been suggested that these act as β-subunits in the P4-ATPase transport machinery. In this work, we investigated the role of Cdc50-like β-subunits of P4-ATPases for targeting and function of P4-ATPase catalytic α-subunits. We show that the Arabidopsis P4-ATPases ALA2 and ALA3 gain functionality when coexpressed with any of three different ALIS Cdc50-like β-subunits. However, the final cellular destination of P4-ATPases as well as their lipid substrate specificity are independent of the nature of the ALIS β-subunit they were allowed to interact with.
Collapse
Affiliation(s)
- Rosa L López-Marqués
- Center for Membrane Pumps in Cells and Disease, PUMPKIN, Danish National Research Foundation, Department of Plant Biology and Biotechnology, Faculty of Life Sciences, University of Copenhagen, Frederiksberg C, Denmark.
| | | | | | | | | | | | | | | |
Collapse
|
57
|
Puts CF, Lenoir G, Krijgsveld J, Williamson P, Holthuis JCM. A P4-ATPase Protein Interaction Network Reveals a Link between Aminophospholipid Transport and Phosphoinositide Metabolism. J Proteome Res 2009; 9:833-42. [DOI: 10.1021/pr900743b] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Catheleyne F. Puts
- Membrane Enzymology, Bijvoet Center and Institute of Biomembranes, and Biomolecular Mass Spectometry and Proteomics Group, Bijvoet Center and Netherlands Proteomics Center, Utrecht University, 3584 CH Utrecht, The Netherlands and Department of Biology, Amherst College, Amherst, Massachusetts 01002
| | - Guillaume Lenoir
- Membrane Enzymology, Bijvoet Center and Institute of Biomembranes, and Biomolecular Mass Spectometry and Proteomics Group, Bijvoet Center and Netherlands Proteomics Center, Utrecht University, 3584 CH Utrecht, The Netherlands and Department of Biology, Amherst College, Amherst, Massachusetts 01002
| | - Jeroen Krijgsveld
- Membrane Enzymology, Bijvoet Center and Institute of Biomembranes, and Biomolecular Mass Spectometry and Proteomics Group, Bijvoet Center and Netherlands Proteomics Center, Utrecht University, 3584 CH Utrecht, The Netherlands and Department of Biology, Amherst College, Amherst, Massachusetts 01002
| | - Patrick Williamson
- Membrane Enzymology, Bijvoet Center and Institute of Biomembranes, and Biomolecular Mass Spectometry and Proteomics Group, Bijvoet Center and Netherlands Proteomics Center, Utrecht University, 3584 CH Utrecht, The Netherlands and Department of Biology, Amherst College, Amherst, Massachusetts 01002
| | - Joost C. M. Holthuis
- Membrane Enzymology, Bijvoet Center and Institute of Biomembranes, and Biomolecular Mass Spectometry and Proteomics Group, Bijvoet Center and Netherlands Proteomics Center, Utrecht University, 3584 CH Utrecht, The Netherlands and Department of Biology, Amherst College, Amherst, Massachusetts 01002
| |
Collapse
|
58
|
|
59
|
Regulation of a Golgi flippase by phosphoinositides and an ArfGEF. Nat Cell Biol 2009; 11:1421-6. [PMID: 19898464 PMCID: PMC2787759 DOI: 10.1038/ncb1989] [Citation(s) in RCA: 105] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2009] [Accepted: 09/09/2009] [Indexed: 12/22/2022]
Abstract
The essential role for phosphatidylinositol 4-phosphate (PtdIns[4]P) in vesicle-mediated protein transport from the trans-Golgi network (TGN) was first described in budding yeast1–3. However, the identity of downstream effectors of PtdIns[4]P in this system has been elusive. Here, we show that Drs2p, a type IV P-type ATPase required for phospholipid translocase (flippase) activity and transport vesicle budding from the TGN4–8, is an effector of PtdIns[4]P. Drs2p-dependent flip of a fluorescent phosphatidylserine analogue across purified TGN membranes requires synthesis of PtdIns[4]P by the PtdIns 4-kinase Pik1p. PtdIns[4]P binds to a regulatory domain in the C-terminal tail of Drs2p that has homology to a split PH domain and is required for Drs2p activity. In addition, basic residues required for phosphoinositide binding overlap a binding site for the ArfGEF Gea2p that was previously mapped9. ArfGEF binding to this C-terminal domain also stimulates flippase activity in TGN membrane preparations. These interactions imply the presence of a novel coincidence detection system used to activate phospholipid translocation at sites of vesicle formation.
Collapse
|
60
|
Bui QT, Golinelli-Cohen MP, Jackson CL. Large Arf1 guanine nucleotide exchange factors: evolution, domain structure, and roles in membrane trafficking and human disease. Mol Genet Genomics 2009; 282:329-50. [PMID: 19669794 PMCID: PMC7088145 DOI: 10.1007/s00438-009-0473-3] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2009] [Accepted: 07/19/2009] [Indexed: 12/16/2022]
Abstract
The Sec7 domain ADP-ribosylation factor (Arf) guanine nucleotide exchange factors (GEFs) are found in all eukaryotes, and are involved in membrane remodeling processes throughout the cell. This review is focused on members of the GBF/Gea and BIG/Sec7 subfamilies of Arf GEFs, all of which use the class I Arf proteins (Arf1-3) as substrates, and play a fundamental role in trafficking in the endoplasmic reticulum (ER)—Golgi and endosomal membrane systems. Members of the GBF/Gea and BIG/Sec7 subfamilies are large proteins on the order of 200 kDa, and they possess multiple homology domains. Phylogenetic analyses indicate that both of these subfamilies of Arf GEFs have members in at least five out of the six eukaryotic supergroups, and hence were likely present very early in eukaryotic evolution. The homology domains of the large Arf1 GEFs play important functional roles, and are involved in interactions with numerous protein partners. The large Arf1 GEFs have been implicated in several human diseases. They are crucial host factors for the replication of several viral pathogens, including poliovirus, coxsackievirus, mouse hepatitis coronavirus, and hepatitis C virus. Mutations in the BIG2 Arf1 GEF have been linked to autosomal recessive periventricular heterotopia, a disorder of neuronal migration that leads to severe malformation of the cerebral cortex. Understanding the roles of the Arf1 GEFs in membrane dynamics is crucial to a full understanding of trafficking in the secretory and endosomal pathways, which in turn will provide essential insights into human diseases that arise from misregulation of these pathways.
Collapse
Affiliation(s)
- Quynh Trang Bui
- Laboratoire d'Enzymologie et Biochimie Structurales, Bat 34, CNRS, 1, Avenue de la Terrasse, 91198 Gif-sur-Yvette, France
| | | | | |
Collapse
|
61
|
Muthusamy BP, Natarajan P, Zhou X, Graham TR. Linking phospholipid flippases to vesicle-mediated protein transport. Biochim Biophys Acta Mol Cell Biol Lipids 2009; 1791:612-9. [PMID: 19286470 DOI: 10.1016/j.bbalip.2009.03.004] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2009] [Revised: 03/03/2009] [Accepted: 03/04/2009] [Indexed: 11/16/2022]
Abstract
Type IV P-type ATPases (P4-ATPases) are a large family of putative phospholipid translocases (flippases) implicated in the generation of phospholipid asymmetry in biological membranes. P4-ATPases are typically the largest P-type ATPase subgroup found in eukaryotic cells, with five members in Saccharomyces cerevisiae, six members in Caenorhabditis elegans, 12 members in Arabidopsis thaliana and 14 members in humans. In addition, many of the P4-ATPases require interaction with a noncatalytic subunit from the CDC50 gene family for their transport out of the endoplasmic reticulum (ER). Deficiency of a P4-ATPase (Atp8b1) causes liver disease in humans, and studies in a variety of model systems indicate that P4-ATPases play diverse and essential roles in membrane biogenesis. In addition to their proposed role in establishing and maintaining plasma membrane asymmetry, P4-ATPases are linked to vesicle-mediated protein transport in the exocytic and endocytic pathways. Recent studies have also suggested a role for P4-ATPases in the nonvesicular intracellular trafficking of sterols. Here, we discuss the physiological requirements for yeast P4-ATPases in phospholipid translocase activity, transport vesicle budding and ergosterol metabolism, with an emphasis on Drs2p and its noncatalytic subunit, Cdc50p.
Collapse
|
62
|
Folmer DE, Elferink RPJO, Paulusma CC. P4 ATPases - lipid flippases and their role in disease. Biochim Biophys Acta Mol Cell Biol Lipids 2009; 1791:628-35. [PMID: 19254779 DOI: 10.1016/j.bbalip.2009.02.008] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2009] [Revised: 02/12/2009] [Accepted: 02/12/2009] [Indexed: 12/11/2022]
Abstract
P4 ATPases (type 4 P-type ATPases) are multispan transmembrane proteins that have been implicated in phospholipid translocation from the exoplasmic to the cytoplasmic leaflet of biological membranes. Studies in Saccharomyces cerevisiae have indicated that P4 ATPases are important in vesicle biogenesis and are required for vesicular trafficking along several intracellular vesicular transport routes. Although little is known about mammalian P4 ATPases, some members of this subfamily appear to be associated with human disease or mouse pathophysiology. ATP8B1, a phosphatidylserine translocase, is the most extensively studied mammalian P4 ATPase. This protein is important for maintaining the detergent resistant properties of the apical membrane of the hepatocyte. Mutations in ATP8B1 give rise to severe liver disease. Furthermore, a role for Atp8b3 in mouse sperm cell capacitation has been suggested, whereas deficiency of Atp10a and Atp10d leads to insulin resistance and obesity in mice. Here we review the present status on the pathophysiological consequences of P4 ATPase deficiency.
Collapse
Affiliation(s)
- Dineke E Folmer
- AMC Liver Center, Academic Medical Center, University of Amsterdam, Meibergdreef 69-71, 1105BK Amsterdam, The Netherlands
| | | | | |
Collapse
|
63
|
Puts CF, Holthuis JCM. Mechanism and significance of P4 ATPase-catalyzed lipid transport: lessons from a Na+/K+-pump. Biochim Biophys Acta Mol Cell Biol Lipids 2009; 1791:603-11. [PMID: 19233312 DOI: 10.1016/j.bbalip.2009.02.005] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2008] [Revised: 02/07/2009] [Accepted: 02/10/2009] [Indexed: 11/19/2022]
Abstract
Members of the P(4) subfamily of P-type ATPases are believed to catalyze phospholipid transport across membrane bilayers, a process influencing a host of cellular functions. Atomic structures and functional analysis of P-type ATPases that pump small cations and metal ions revealed a transport mechanism that appears to be conserved throughout the family. A challenging problem is to understand how this mechanism is adapted in P(4) ATPases to flip phospholipids. P(4) ATPases form oligomeric complexes with members of the CDC50 protein family. While formation of these complexes is required for P(4) ATPase export from the endoplasmic reticulum, little is known about the functional role of the CDC50 subunits. The Na(+)/K(+)-ATPase and closely-related H(+)/K(+)-ATPase are the only other P-type pumps that are oligomeric, comprising mandatory beta-subunits that are strikingly reminiscent of CDC50 proteins. Besides serving a role in the functional maturation of the catalytic alpha-subunit, the beta-subunit also contributes specifically to intrinsic transport properties of the Na(+)/K(+) pump. As beta-subunits and CDC50 proteins likely adopted similar structures to accomplish analogous tasks, current knowledge of the Na(+)/K(+)-ATPase provides a useful guide for understanding the inner workings of the P(4) ATPase class of lipid pumps.
Collapse
Affiliation(s)
- Catheleyne F Puts
- Membrane Enzymology, Bijvoet Center and Institute of Biomembranes, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | | |
Collapse
|
64
|
Liu K, Surendhran K, Nothwehr SF, Graham TR. P4-ATPase requirement for AP-1/clathrin function in protein transport from the trans-Golgi network and early endosomes. Mol Biol Cell 2008; 19:3526-35. [PMID: 18508916 DOI: 10.1091/mbc.e08-01-0025] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Drs2p is a resident type 4 P-type ATPase (P4-ATPase) and potential phospholipid translocase of the trans-Golgi network (TGN) where it has been implicated in clathrin function. However, precise protein transport pathways requiring Drs2p and how it contributes to clathrin-coated vesicle budding remain unclear. Here we show a functional codependence between Drs2p and the AP-1 clathrin adaptor in protein sorting at the TGN and early endosomes of Saccharomyces cerevisiae. Genetic criteria indicate that Drs2p and AP-1 operate in the same pathway and that AP-1 requires Drs2p for function. In addition, we show that loss of AP-1 markedly increases Drs2p trafficking to the plasma membrane, but does not perturb retrieval of Drs2p from the early endosome back to the TGN. Thus AP-1 is required at the TGN to sort Drs2p out of the exocytic pathway, presumably for delivery to the early endosome. Moreover, a conditional allele that inactivates Drs2p phospholipid translocase (flippase) activity disrupts its own transport in this AP-1 pathway. Drs2p physically interacts with AP-1; however, AP-1 and clathrin are both recruited normally to the TGN in drs2Delta cells. These results imply that Drs2p acts independently of coat recruitment to facilitate AP-1/clathrin-coated vesicle budding from the TGN.
Collapse
Affiliation(s)
- Ke Liu
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235-1634, USA
| | | | | | | |
Collapse
|
65
|
Yeast and human Ysl2p/hMon2 interact with Gga adaptors and mediate their subcellular distribution. EMBO J 2008; 27:1423-35. [PMID: 18418388 DOI: 10.1038/emboj.2008.75] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2007] [Accepted: 03/19/2008] [Indexed: 11/09/2022] Open
Abstract
The Gga proteins represent a family of ubiquitously expressed clathrin adaptors engaged in vesicle budding at the tubular endosomal network/trans Golgi network. Their membrane recruitment is commonly thought to involve interactions with Arf and signals in cargo through the so-called VHS domain. For yeast Gga proteins, however, partners binding to its VHS domain have remained elusive and Gga localization does not absolutely depend on Arf. Here, we demonstrate that yeast Gga recruitment relies on a network of interactions between the scaffold Ysl2p/Mon2p, the small GTPase Arl1p, and the flippase Neo1p. Deletion of either YSL2 or ARL1 causes mislocalization of Gga2p, whereas a neo1-69 mutant accumulates Gga2p on aberrant structures. Remarkably, Ysl2p directly interacts with human and yeast Ggas through the VHS domain, and binding to Gga proteins is also found for the human Ysl2p orthologue hMon2. Thus, Ysl2p represents an essential, evolutionarily conserved member of a network controlling direct binding and membrane docking of Ggas. Because activated Arl1p is part of the network that binds Gga2p, Arf and Arf-like GTPases may interact in a regulatory cascade.
Collapse
|
66
|
Szul T, Grabski R, Lyons S, Morohashi Y, Shestopal S, Lowe M, Sztul E. Dissecting the role of the ARF guanine nucleotide exchange factor GBF1 in Golgi biogenesis and protein trafficking. J Cell Sci 2007; 120:3929-40. [PMID: 17956946 DOI: 10.1242/jcs.010769] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
COPI recruitment to membranes appears to be essential for the biogenesis of the Golgi and for secretory trafficking. Preventing COPI recruitment by expressing inactive forms of the ADP-ribosylation factor (ARF) or the ARF-activating guanine nucleotide exchange factor GBF1, or by treating cells with brefeldin A (BFA), causes the collapse of the Golgi into the endoplasmic reticulum (ER) and arrests trafficking of soluble and transmembrane proteins at the ER. Here, we assess COPI function in Golgi biogenesis and protein trafficking by preventing COPI recruitment to membranes by removing GBF1. We report that siRNA-mediated depletion of GBF1 causes COPI dispersal but does not lead to collapse of the Golgi. Instead, it causes extensive tubulation of the cis-Golgi. The Golgi-derived tubules target to peripheral ER-Golgi intermediate compartment (ERGIC) sites and create dynamic continuities between the ERGIC and the cis-Golgi compartment. COPI dispersal in GBF1-depleted cells causes dramatic inhibition of the trafficking of transmembrane proteins. Unexpectedly, soluble proteins continue to be secreted from GBF1-depleted cells. Our findings suggest that a secretory pathway capable of trafficking soluble proteins can be maintained in cells in which COPI recruitment is compromised by GBF1 depletion. However, the trafficking of transmembrane proteins through the existing pathway requires GBF1-mediated ARF activation and COPI recruitment.
Collapse
Affiliation(s)
- Tomasz Szul
- Department of Cell Biology, University of Alabama at Birmingham, 1918 University Blvd, Birmingham, AL 35924, USA
| | - Robert Grabski
- Department of Cell Biology, University of Alabama at Birmingham, 1918 University Blvd, Birmingham, AL 35924, USA
| | - Susan Lyons
- Department of Cell Biology, University of Alabama at Birmingham, 1918 University Blvd, Birmingham, AL 35924, USA
| | - Yuichi Morohashi
- University of Manchester, Faculty of Life Sciences, Manchester M13 9PT, UK
| | - Svetlana Shestopal
- Department of Cell Biology, University of Alabama at Birmingham, 1918 University Blvd, Birmingham, AL 35924, USA
| | - Martin Lowe
- University of Manchester, Faculty of Life Sciences, Manchester M13 9PT, UK
| | - Elizabeth Sztul
- Department of Cell Biology, University of Alabama at Birmingham, 1918 University Blvd, Birmingham, AL 35924, USA
| |
Collapse
|
67
|
Eimer S, Gottschalk A, Hengartner M, Horvitz HR, Richmond J, Schafer WR, Bessereau JL. Regulation of nicotinic receptor trafficking by the transmembrane Golgi protein UNC-50. EMBO J 2007; 26:4313-23. [PMID: 17853888 PMCID: PMC2034668 DOI: 10.1038/sj.emboj.7601858] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2007] [Accepted: 08/22/2007] [Indexed: 01/21/2023] Open
Abstract
Nicotinic acetylcholine receptors (AChRs) are pentameric ligand-gated ion channels that mediate fast synaptic transmission at the neuromuscular junction (NMJ). After assembly in the endoplasmic reticulum (ER), AChRs must be transported to the plasma membrane through the secretory apparatus. Little is known about specific molecules that mediate this transport. Here we identify a gene that is required for subtype-specific trafficking of assembled nicotinic AChRs in Caenorhabditis elegans. unc-50 encodes an evolutionarily conserved integral membrane protein that localizes to the Golgi apparatus. In the absence of UNC-50, a subset of AChRs present in body-wall muscle are sorted to the lysosomal system and degraded. However, the trafficking of a second AChR type and of GABA ionotropic receptors expressed in the same muscle cells is not affected in unc-50 mutants. These results suggest that, in addition to ER quality control, assembled AChRs are sorted within the Golgi system by a mechanism that controls the amount of cell-surface AChRs in a subtype-specific way.
Collapse
Affiliation(s)
- Stefan Eimer
- Ecole Normale Supérieure, Biology Department, Paris, France
- INSERM, U789, Biologie cellulaire de la synapse, Paris, France
| | - Alexander Gottschalk
- Division of Biological Sciences, University of California, San Diego, La Jolla, CA, USA
| | - Michael Hengartner
- Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - H Robert Horvitz
- Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Janet Richmond
- Department of Biology, University of Illinois, Chicago, IL, USA
| | - William R Schafer
- Division of Biological Sciences, University of California, San Diego, La Jolla, CA, USA
| | - Jean-Louis Bessereau
- Ecole Normale Supérieure, Biology Department, Paris, France
- INSERM, U789, Biologie cellulaire de la synapse, Paris, France
- Ecole Normale Supérieure, INSERM, U789, Biologie cellulaire de la synapse, 46 Rue d'Ulm, Paris 75005, France. Tel.: +33 1 44 32 23 05; Fax: +33 1 44 32 36 54; E-mail:
| |
Collapse
|
68
|
Liu K, Hua Z, Nepute JA, Graham TR. Yeast P4-ATPases Drs2p and Dnf1p are essential cargos of the NPFXD/Sla1p endocytic pathway. Mol Biol Cell 2006; 18:487-500. [PMID: 17122361 PMCID: PMC1783782 DOI: 10.1091/mbc.e06-07-0592] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Drs2p family P-type ATPases (P4-ATPases) are required in multiple vesicle-mediated protein transport steps and are proposed to be phospholipid translocases (flippases). The P4-ATPases Drs2p and Dnf1p cycle between the exocytic and endocytic pathways, and here we define endocytosis signals required by these proteins to maintain a steady-state localization to internal organelles. Internalization of Dnf1p from the plasma membrane uses an NPFXD endocytosis signal and its recognition by Sla1p, part of an endocytic coat/adaptor complex with clathrin, Pan1p, Sla2p/End4p, and End3p. Drs2p has multiple endocytosis signals, including two NPFXDs near the C terminus and PEST-like sequences near the N terminus that may mediate ubiquitin (Ub)-dependent endocytosis. Drs2p localizes to the trans-Golgi network in wild-type cells and accumulates on the plasma membrane when both the Ub- and NPFXD-dependent endocytic mechanisms are inactivated. Surprisingly, the pan1-20 temperature-sensitive mutant is constitutively defective for Ub-dependent endocytosis but is not defective for NPFXD-dependent endocytosis at the permissive growth temperature. To sustain viability of pan1-20, Drs2p must be endocytosed through the NPFXD/Sla1p pathway. Thus, Drs2p is an essential endocytic cargo in cells compromised for Ub-dependent endocytosis. These results demonstrate an essential role for endocytosis in retrieving proteins back to the Golgi, and they define critical cargos of the NPFXD/Sla1p system.
Collapse
Affiliation(s)
- Ke Liu
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235-1634
| | - Zhaolin Hua
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235-1634
| | - Joshua A. Nepute
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235-1634
| | - Todd R. Graham
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235-1634
| |
Collapse
|
69
|
Noji T, Yamamoto T, Saito K, Fujimura-Kamada K, Kondo S, Tanaka K. Mutational analysis of the Lem3p-Dnf1p putative phospholipid-translocating P-type ATPase reveals novel regulatory roles for Lem3p and a carboxyl-terminal region of Dnf1p independent of the phospholipid-translocating activity of Dnf1p in yeast. Biochem Biophys Res Commun 2006; 344:323-31. [PMID: 16600184 DOI: 10.1016/j.bbrc.2006.03.095] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2006] [Accepted: 03/16/2006] [Indexed: 11/16/2022]
Abstract
Lem3p-Dnf1p is a putative aminophospholipid translocase (APLT) complex that is localized to the plasma membrane; Lem3p is required for Dnf1p localization to the plasma membrane. We have identified lem3 mutations, which did not affect formation or localization of the Lem3p-Dnf1p complex, but caused a synthetic growth defect with the null mutation of CDC50, a structurally and functionally redundant homologue of LEM3. Interestingly, these lem3 mutants exhibited nearly normal levels of NBD-labeled phospholipid internalization across the plasma membrane, suggesting that Lem3p may have other functions in addition to regulation of the putative APLT activity of Dnf1p at the plasma membrane. Similarly, deletion of the COOH-terminal cytoplasmic region of Dnf1p affected neither the localization nor the APLT activity of Dnf1p at the plasma membrane, but caused a growth defect in the cdc50Delta background. Our results suggest that the Lem3p-Dnf1p complex may play a role distinct from its plasma membrane APLT activity when it substitutes for the Cdc50p-Drs2p complex, its redundant partner in the endosomal/trans-Golgi network compartments.
Collapse
Affiliation(s)
- Takehiro Noji
- Division of Molecular Interaction, Institute for Genetic Medicine, Hokkaido University, Sapporo 060-0815, Japan
| | | | | | | | | | | |
Collapse
|
70
|
Sakane H, Yamamoto T, Tanaka K. The Functional Relationship between the Cdc50p-Drs2p Putative Aminophospholipid Translocase and the Arf GAP Gcs1p in Vesicle Formation in the Retrieval Pathway from Yeast Early Endosomes to the TGN. Cell Struct Funct 2006; 31:87-108. [PMID: 17062999 DOI: 10.1247/csf.06021] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Drs2p, the catalytic subunit of the Cdc50p-Drs2p putative aminophospholipid translocase, has been implicated in conjunction with the Arf1 signaling pathway in the formation of clathrin-coated vesicles (CCVs) from the TGN. Herein, we searched for Arf regulator genes whose mutations were synthetically lethal with cdc50Delta, and identified the Arf GAP gene GCS1. Most of the examined transport pathways in the Cdc50p-depleted gcs1Delta mutant were nearly normal, including endocytic transport to vacuoles, carboxypeptidase Y sorting, and the processing and secretion of invertase. In contrast, this mutant exhibited severe defects in the early endosome-to-TGN transport pathway; proteins that are transported via this pathway, such as the v-SNARE Snc1p, the t-SNARE Tlg1p, and the chitin synthase III subunit Chs3p, accumulated in TGN-independent aberrant membrane structures. We extended our analyses to clathrin adaptors, and found that Gga1p/Gga2p and AP-1 were also involved in this pathway. The Cdc50p-depleted gga1Delta gga2Delta mutant and the gcs1Delta apl2Delta (the beta1 subunit of AP-1) mutant exhibited growth defects and intracellular Snc1p-containing membranes accumulated in these cells. These results suggest that Cdc50p-Drs2p plays an important role in the Arf1p-mediated formation of CCVs for the retrieval pathway from early endosomes to the TGN.
Collapse
Affiliation(s)
- Hiroshi Sakane
- Division of Molecular Interaction, Institute for Genetic Medicine, Hokkaido University Graduate School of Medicine, Kita-ku, Sapporo 060-0815, Japan
| | | | | |
Collapse
|
71
|
Yamaji-Hasegawa A, Tsujimoto M. Asymmetric Distribution of Phospholipids in Biomembranes. Biol Pharm Bull 2006; 29:1547-53. [PMID: 16880602 DOI: 10.1248/bpb.29.1547] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In eukaryotic cells, the biological membrane is characterized by a non-uniform distribution of membrane lipids, vertically as well as laterally. The paradigm for the vertical non-random distribution is the plasma membrane, where phosphatidylcholine (PC), sphingomyelin (SM), and glycosphingolipids are primarily located on the exoplasmic leaflet, while aminophospholipids, including phosphatidylserine (PS) and phosphatidylethanolamine (PE), are generally enriched in the cytoplasmic leaflet. Other minor phospholipids, such as phosphatidic acid and phosphatidylinositol (PI), are also enriched on the cytoplasmic face. Such asymmetrical distribution is related to each lipid regulating various biological events through interaction with other molecules. The clarification of the regulatory mechanism of the distribution and movement of membrane lipids is crucial to understanding the physiological roles of lipids. Here we focus on PS, which has been reported to be involved in apoptosis, blood coagulation and other biological phenomena, and summarize the present understanding of the dynamics of this phospholipid, including biosynthesis, metabolism, transport, and transbilayer movement. We also refer to diseases that have been reported to be related to phospholipid asymmetry.
Collapse
|
72
|
Abstract
Eukaryotic cells have systems of internal organelles to synthesize lipids and membrane proteins, to release secreted proteins, to take up nutrients and to degrade membrane-bound and internalized molecules. Proteins and lipids move from organelle to organelle using transport vesicles. The accuracy of this traffic depends upon organelles being correctly recognized. In general, organelles are identified by the activated GTPases and specific lipid species that they display. These short-lived determinants provide organelles with an identity that is both unique and flexible. Recent studies have helped to establish how cells maintain and restrict these determinants and explain how this system is exploited by invading pathogens.
Collapse
Affiliation(s)
- Rudy Behnia
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK
| | | |
Collapse
|
73
|
Gillingham AK, Whyte JRC, Panic B, Munro S. Mon2, a relative of large Arf exchange factors, recruits Dop1 to the Golgi apparatus. J Biol Chem 2005; 281:2273-80. [PMID: 16301316 DOI: 10.1074/jbc.m510176200] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The protein Mon2 is distantly related to the guanine nucleotide exchange factors (GEFs) that activate Arf1 on Golgi membranes. However, unlike these "large" Arf GEFs, Mon2 lacks the Sec7 domain that catalyzes nucleotide exchange on Arf1. Here we report that yeast Mon2 shares extensive homology with the noncatalytic parts of both the BIG and Golgi brefeldin A resistance factor subfamilies of Arf GEFs and is located to the trans-Golgi. Moreover, we find that Mon2 forms a complex with Dop1, a large cytoplasmic protein conserved in evolution from humans to protozoa. Deletion of Mon2 results in mislocalization of Dop1 from the Golgi and defects in cycling between endosomes and the Golgi. However, unlike Mon2, Dop1 is essential for yeast viability. A conditional allele of Dop1 shows that loss of Dop1 activity not only affects endosome to Golgi transport but also causes a severe perturbation of the organization of the endoplasmic reticulum. Thus, it appears that Dop1 plays a widespread role in membrane organization, and Mon2 acts as a scaffold to recruit the Golgi-localized pool of Dop1.
Collapse
Affiliation(s)
- Alison K Gillingham
- Medical Research Council Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, United Kingdom
| | | | | | | |
Collapse
|
74
|
Luini A, Ragnini-Wilson A, Polishchuck RS, De Matteis MA. Large pleiomorphic traffic intermediates in the secretory pathway. Curr Opin Cell Biol 2005; 17:353-61. [PMID: 15993575 DOI: 10.1016/j.ceb.2005.06.012] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2005] [Accepted: 06/08/2005] [Indexed: 01/07/2023]
Abstract
There are two main classes of traffic intermediates that operate in intracellular trafficking pathways: small round vesicles, and large pleiomorphic carriers (LPCs). While both are essential, the LPCs appear to be responsible for moving the bulk of the secretory traffic between distant compartments. LPCs are much larger and more variable in shape than vesicles, and they have evident interconnected tubular and saccular/cisternal components. They appear to form by en bloc extrusion and cleavage of large membrane areas of the donor organelle. Although many proteins and lipids that are involved in LPC formation have been identified, the intrinsic complexity of these carriers and current technical limitations mean that a coherent picture of the process of of LPC formation is only just beginning to emerge.
Collapse
Affiliation(s)
- Alberto Luini
- Department of Cell Biology and Oncology, Consorzio Mario Negri Sud, 66030 Santa Maria Imbaro, Chieti, Italy.
| | | | | | | |
Collapse
|
75
|
Szul T, Garcia-Mata R, Brandon E, Shestopal S, Alvarez C, Sztul E. Dissection of membrane dynamics of the ARF-guanine nucleotide exchange factor GBF1. Traffic 2005; 6:374-85. [PMID: 15813748 DOI: 10.1111/j.1600-0854.2005.00282.x] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
ADP-ribosylation factor (ARF)-facilitated recruitment of COP I to membranes is required for secretory traffic. The guanine nucleotide exchange factor GBF1 activates ARF and regulates ARF/COP I dynamics at the endoplasmic reticulum (ER)-Golgi interface. Like ARF and coatomer, GBF1 peripherally associates with membranes. ADP-ribosylation factor and coatomer have been shown to rapidly cycle between membranes and cytosol, but the membrane dynamics of GBF1 are unknown. Here, we used fluorescence recovery after photobleaching to characterize the behavior of GFP-tagged GBF1. We report that GBF1 rapidly cycles between membranes and the cytosol (t1/2 is approximately 17 +/- 1 seconds). GBF1 cycles faster than GFP-tagged ARF, suggesting that in each round of association/dissociation, GBF1 catalyzes a single event of ARF activation, and that the activated ARF remains on membrane after GBF1 dissociation. Using three different approaches [expression of an inactive (E794K) GBF1 mutant, expression of the ARF1 (T31N) mutant with decreased affinity for GTP and Brefeldin A treatment], we show that GBF1 is stabilized on membranes when in a complex with ARF-GDP. GBF1 dissociation from ARF and membranes is triggered by its catalytic activity, i.e. the displacement of GDP and the subsequent binding of GTP to ARF. Our findings imply that continuous cycles of recruitment and dissociation of GBF1 to membranes are required for sustained ARF activation and COP I recruitment that underlies ER-Golgi traffic.
Collapse
Affiliation(s)
- Tomasz Szul
- Department of Cell Biology, University of Alabama at Birmingham, Birmingham, AL 35924, USA
| | | | | | | | | | | |
Collapse
|
76
|
Munro S. The Golgi apparatus: defining the identity of Golgi membranes. Curr Opin Cell Biol 2005; 17:395-401. [PMID: 15975778 DOI: 10.1016/j.ceb.2005.06.013] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2005] [Accepted: 06/07/2005] [Indexed: 02/01/2023]
Abstract
The Golgi apparatus is a stack of compartments that serves as a central junction for membrane traffic, with carriers moving through the stack as well as arriving from, and departing toward, many other destinations in the cell. This requires that the different compartments in the Golgi recruit from the cytosol a distinct set of proteins to mediate accurate membrane traffic. This recruitment appears to reflect recognition of small GTPases of the Rab and Arf family, or of lipid species such as PtdIns(4)P and diacylglycerol, which provide a unique "identity" for each compartment. Recent work is starting to reveal the mechanisms by which these labile landmarks are generated in a spatially restricted manner on specific parts of the Golgi.
Collapse
Affiliation(s)
- Sean Munro
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK.
| |
Collapse
|
77
|
Paulusma CC, Oude Elferink RPJ. The type 4 subfamily of P-type ATPases, putative aminophospholipid translocases with a role in human disease. Biochim Biophys Acta Mol Basis Dis 2005; 1741:11-24. [PMID: 15919184 DOI: 10.1016/j.bbadis.2005.04.006] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2005] [Revised: 04/21/2005] [Accepted: 04/25/2005] [Indexed: 11/22/2022]
Abstract
The maintenance of phospholipid asymmetry in membrane bilayers is a paradigm in cell biology. However, the mechanisms and proteins involved in phospholipid translocation are still poorly understood. Members of the type 4 subfamily of P-type ATPases have been implicated in the translocation of phospholipids from the outer to the inner leaflet of membrane bilayers. In humans, several inherited disorders have been identified which are associated with loci harboring type 4 P-type ATPase genes. Up to now, one inherited disorder, Byler disease or progressive familial intrahepatic cholestasis type 1 (PFIC1), has been directly linked to mutations in a type 4 P-type ATPase gene. How the absence of an aminophospholipid translocase activity relates to this severe disease is, however, still unclear. Studies in the yeast Saccharomyces cerevisiae have recently identified important roles for type 4 P-type ATPases in intracellular membrane- and protein-trafficking events. These processes require an (amino)phospholipid translocase activity to initiate budding or fusion of membrane vesicles from or with other membranes. The studies in yeast have greatly contributed to our cell biological insight in membrane dynamics and intracellular-trafficking events; if this knowledge can be translated to mammalian cells and organs, it will help to elucidate the molecular mechanisms which underlie severe inherited human diseases such as Byler disease.
Collapse
Affiliation(s)
- C C Paulusma
- Department of Experimental Hepatology, Academic Medical Center/AMC Liver Center, Meibergdreef 69-71, 1105 BK Amsterdam, The Netherlands.
| | | |
Collapse
|
78
|
Donaldson JG, Honda A, Weigert R. Multiple activities for Arf1 at the Golgi complex. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2005; 1744:364-73. [PMID: 15979507 DOI: 10.1016/j.bbamcr.2005.03.001] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Received: 12/23/2004] [Revised: 02/28/2005] [Accepted: 03/01/2005] [Indexed: 10/25/2022]
Abstract
The Arf family of GTPases regulates membrane traffic and organelle structure. At the Golgi complex, Arf proteins facilitate membrane recruitment of many cytoplasmic coat proteins to allow sorting of membrane proteins for transport, stimulate the activity of enzymes that modulate the lipid composition of the Golgi, and assemble a cytoskeletal scaffold on the Golgi. Arf1 is the Arf family member most closely studied for its function at the Golgi complex. A number of regulators that activate and inactivate Arf1 on the Golgi have been described that localize to different regions of the organelle. This spatial distribution of Arf regulators may facilitate the recruitment of the coat proteins and other Arf effectors to different regions of the Golgi complex.
Collapse
Affiliation(s)
- Julie G Donaldson
- Laboratory of Cell Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Building 50, Room 2503, Bethesda, MD 20892, USA.
| | | | | |
Collapse
|
79
|
Mouratou B, Biou V, Joubert A, Cohen J, Shields DJ, Geldner N, Jürgens G, Melançon P, Cherfils J. The domain architecture of large guanine nucleotide exchange factors for the small GTP-binding protein Arf. BMC Genomics 2005; 6:20. [PMID: 15717927 PMCID: PMC553965 DOI: 10.1186/1471-2164-6-20] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2004] [Accepted: 02/17/2005] [Indexed: 11/24/2022] Open
Abstract
Background Small G proteins, which are essential regulators of multiple cellular functions, are activated by guanine nucleotide exchange factors (GEFs) that stimulate the exchange of the tightly bound GDP nucleotide by GTP. The catalytic domain responsible for nucleotide exchange is in general associated with non-catalytic domains that define the spatio-temporal conditions of activation. In the case of small G proteins of the Arf subfamily, which are major regulators of membrane trafficking, GEFs form a heterogeneous family whose only common characteristic is the well-characterized Sec7 catalytic domain. In contrast, the function of non-catalytic domains and how they regulate/cooperate with the catalytic domain is essentially unknown. Results Based on Sec7-containing sequences from fully-annotated eukaryotic genomes, including our annotation of these sequences from Paramecium, we have investigated the domain architecture of large ArfGEFs of the BIG and GBF subfamilies, which are involved in Golgi traffic. Multiple sequence alignments combined with the analysis of predicted secondary structures, non-structured regions and splicing patterns, identifies five novel non-catalytic structural domains which are common to both subfamilies, revealing that they share a conserved modular organization. We also report a novel ArfGEF subfamily with a domain organization so far unique to alveolates, which we name TBS (TBC-Sec7). Conclusion Our analysis unifies the BIG and GBF subfamilies into a higher order subfamily, which, together with their being the only subfamilies common to all eukaryotes, suggests that they descend from a common ancestor from which species-specific ArfGEFs have subsequently evolved. Our identification of a conserved modular architecture provides a background for future functional investigation of non-catalytic domains.
Collapse
Affiliation(s)
- Barbara Mouratou
- Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, avenue de la Terrasse, 91198 Gif sur Yvette cedex, France
| | - Valerie Biou
- Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, avenue de la Terrasse, 91198 Gif sur Yvette cedex, France
| | - Alexandra Joubert
- Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, avenue de la Terrasse, 91198 Gif sur Yvette cedex, France
| | - Jean Cohen
- Centre de Génétique Moléculaire, CNRS, Gif-sur-Yvette, France
| | - David J Shields
- Department of Cell Biology, University of Alberta, Edmonton, Canada
| | - Niko Geldner
- Center of Plant Molecular Biology, Universitaet Tuebingen, Tuebingen, Germany
- Plant Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, USA
| | - Gerd Jürgens
- Center of Plant Molecular Biology, Universitaet Tuebingen, Tuebingen, Germany
| | - Paul Melançon
- Department of Cell Biology, University of Alberta, Edmonton, Canada
| | - Jacqueline Cherfils
- Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, avenue de la Terrasse, 91198 Gif sur Yvette cedex, France
| |
Collapse
|
80
|
Abstract
The best-understood mechanisms for generating transport vesicles in the secretory and endocytic pathways involve the localized assembly of cytosolic coat proteins such as clathrin, coat protein complex (COP)I and COPII onto membranes. These coat proteins can deform membranes by themselves, but accessory proteins might help to generate the tight curvature needed to form a vesicle. Enzymes that pump phospholipid from one leaflet of the bilayer to the other (flippases) can deform membranes by creating an imbalance in the phospholipid number between the two leaflets. Recent studies describe a requirement for the yeast Drs2p family of P-type ATPases in both phospholipid translocation and protein transport in the secretory and endocytic pathways. This indicates that flippases work with coat proteins to form vesicles.
Collapse
Affiliation(s)
- Todd R Graham
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235-1634, USA.
| |
Collapse
|
81
|
Futai E, Hamamoto S, Orci L, Schekman R. GTP/GDP exchange by Sec12p enables COPII vesicle bud formation on synthetic liposomes. EMBO J 2004; 23:4146-55. [PMID: 15457212 PMCID: PMC524392 DOI: 10.1038/sj.emboj.7600428] [Citation(s) in RCA: 108] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2004] [Accepted: 09/06/2004] [Indexed: 11/08/2022] Open
Abstract
The generation of COPII vesicles from synthetic liposome membranes requires the minimum coat components Sar1p, Sec23/24p, Sec13/31p, and a nonhydrolyzable GTP analog such as GMP-PNP. However, in the presence of GTP and the full complement of coat subunits, nucleotide hydrolysis by Sar1p renders the coat insufficiently stable to sustain vesicle budding. In order to recapitulate a more authentic, GTP-dependent budding event, we introduced the Sar1p nucleotide exchange catalyst, Sec12p, and evaluated the dynamics of coat assembly and disassembly by light scattering and tryptophan fluorescence measurements. The catalytic, cytoplasmic domain of Sec12p (Sec12DeltaCp) activated Sar1p with a turnover 10-fold higher than the GAP activity of Sec23p stimulated by the full coat. COPII assembly was stabilized on liposomes incubated with Sec12DeltaCp and GTP. Numerous COPII budding profiles were visualized on membranes, whereas a parallel reaction conducted in the absence of Sec12DeltaCp produced no such profiles. We suggest that Sec12p participates actively in the growth of COPII vesicles by charging new Sar1p-GTP molecules that insert at the boundary between a bud and the surrounding endoplasmic reticulum membrane.
Collapse
Affiliation(s)
- Eugene Futai
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, USA
| | - Susan Hamamoto
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, USA
- Howard Hughes Medical Institute, University of California, Berkeley, CA, USA
| | - Lelio Orci
- Department of Cellular Physiology and Metabolism, University of Geneva Medical School, Geneva, Switzerland
| | - Randy Schekman
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, USA
- Howard Hughes Medical Institute, University of California, Berkeley, CA, USA
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3202, USA. Tel.: +1 510 642 5686; Fax: +1 510 642 7846; E-mail:
| |
Collapse
|
82
|
Wicky S, Schwarz H, Singer-Krüger B. Molecular interactions of yeast Neo1p, an essential member of the Drs2 family of aminophospholipid translocases, and its role in membrane trafficking within the endomembrane system. Mol Cell Biol 2004; 24:7402-18. [PMID: 15314152 PMCID: PMC507011 DOI: 10.1128/mcb.24.17.7402-7418.2004] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Neo1p is an essential yeast member of the highly conserved Drs2 family of P-type ATPases with proposed aminophospholipid translocase activity. Here we present evidence that Neo1p localizes to endosomes and Golgi elements. In agreement with that finding, the temperature-sensitive neo1-37 and neo1-69 mutants exhibit defects in receptor-mediated endocytosis, vacuole biogenesis, and vacuolar protein sorting. Furthermore, neo1 mutants accumulate aberrantly shaped membranous structures most likely derived from vacuoles and the endosomal/Golgi system. At permissive temperatures, HA-Neo1-69p, like wild-type Neo1p, is stable and associates with endosomes. In contrast, HA-Neo1-37p is rapidly degraded and is predominantly retained within the endoplasmic reticulum (ER). Thus, the two neo1 alleles affect the stability and localization of the mutant polypeptides in different ways. A C-terminally truncated and a C-terminally epitope-tagged version of Neo1p are nonfunctional and also mislocalize to the ER. In agreement with a role within the endomembrane system, Neo1p exhibits genetic and physical interactions with Ysl2p, a potential guanine nucleotide exchange factor for Arl1p. Interestingly, deletion of ARL1 rescues the temperature sensitivity of neo1-37 and neo1-69. We demonstrate that Arl1p in its myristoylated and GTP-bound form is responsible for the inhibitory effect. Thus, Neo1p, Ysl2p, and Arl1p represent three proteins that collaborate in membrane trafficking within the endosomal/Golgi system.
Collapse
Affiliation(s)
- Sidonie Wicky
- Institute for Biochemistry, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
| | | | | |
Collapse
|
83
|
Natarajan P, Wang J, Hua Z, Graham TR. Drs2p-coupled aminophospholipid translocase activity in yeast Golgi membranes and relationship to in vivo function. Proc Natl Acad Sci U S A 2004; 101:10614-9. [PMID: 15249668 PMCID: PMC489982 DOI: 10.1073/pnas.0404146101] [Citation(s) in RCA: 152] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Aminophospholipid translocases (APLTs) are defined primarily by their ability to flip fluorescent or spin-labeled derivatives of phosphatidylserine (PS) and phosphatidylethanolamine (PE) from the external leaflet of a membrane bilayer to the cytosolic leaflet and are thought to establish phospholipid asymmetry in biological membranes. The identities of APLTs remain unknown, although candidate proteins include the Drs2p/ATPase II subfamily of P-type ATPases. Drs2p from budding yeast localizes to the trans-Golgi network (TGN), and here we show that this membrane contains an ATP-dependent APLT that flips 7-nitro-2-1,3-benzoxadiazol-4-yl (NBD) PS and PE derivatives from the luminal to the cytosolic leaflet. To assess the contribution of Drs2p to this activity, TGN membranes were prepared from strains harboring WT or temperature-sensitive alleles of DRS2 and null alleles of three other potential APLT genes (DNF1, DNF2, and DNF3). Assay of these membranes indicated that Drs2p was required for the ATP-dependent translocation of NBD-PS, whereas no active translocation of NBD-PE or NBD-phosphatidylcholine was detected. The specificity of Drs2p for NBD-PS suggested that translocation of PS would be required for the function of Drs2p in protein transport from the TGN. However, cho1 yeast strains that are unable to synthesize PS do not phenocopy drs2 but instead transport proteins normally via the secretory pathway. In addition, a drs2 cho1 double mutant retains drs2 transport defects. Therefore, whereas NBD-PS is a preferred substrate for Drs2p in vitro, endogenous PS is not an obligatory substrate in vivo for the role Drs2p plays in protein transport.
Collapse
Affiliation(s)
- Paramasivam Natarajan
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235-1634, USA
| | | | | | | |
Collapse
|
84
|
Hua Z, Graham TR. Requirement for neo1p in retrograde transport from the Golgi complex to the endoplasmic reticulum. Mol Biol Cell 2003; 14:4971-83. [PMID: 12960419 PMCID: PMC284799 DOI: 10.1091/mbc.e03-07-0463] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
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.
Collapse
Affiliation(s)
- Zhaolin Hua
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37235-1634, USA
| | | |
Collapse
|