1
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Highland CM, Fromme JC. Arf1 directly recruits the Pik1-Frq1 PI4K complex to regulate the final stages of Golgi maturation. Mol Biol Cell 2021; 32:1064-1080. [PMID: 33788598 PMCID: PMC8101487 DOI: 10.1091/mbc.e21-02-0069] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Proper Golgi complex function depends on the activity of Arf1, a GTPase whose effectors assemble and transport outgoing vesicles. Phosphatidylinositol 4-phosphate (PI4P) generated at the Golgi by the conserved PI 4-kinase Pik1 (PI4KIIIβ) is also essential for Golgi function, although its precise roles in vesicle formation are less clear. Arf1 has been reported to regulate PI4P production, but whether Pik1 is a direct Arf1 effector is not established. Using a combination of live-cell time-lapse imaging analyses, acute PI4P depletion experiments, and in vitro protein–protein interaction assays on Golgi-mimetic membranes, we present evidence for a model in which Arf1 initiates the final stages of Golgi maturation by tightly controlling PI4P production through direct recruitment of the Pik1-Frq1 PI4-kinase complex. This PI4P serves as a critical signal for AP-1 and secretory vesicle formation, the final events at maturing Golgi compartments. This work therefore establishes the regulatory and temporal context surrounding Golgi PI4P production and its precise roles in Golgi maturation.
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Affiliation(s)
- Carolyn M Highland
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853
| | - J Christopher Fromme
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853
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2
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Schoppe J, Mari M, Yavavli E, Auffarth K, Cabrera M, Walter S, Fröhlich F, Ungermann C. AP-3 vesicle uncoating occurs after HOPS-dependent vacuole tethering. EMBO J 2020; 39:e105117. [PMID: 32840906 PMCID: PMC7560216 DOI: 10.15252/embj.2020105117] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2020] [Revised: 07/16/2020] [Accepted: 07/22/2020] [Indexed: 11/09/2022] Open
Abstract
Heterotetrameric adapter (AP) complexes cooperate with the small GTPase Arf1 or lipids in cargo selection, vesicle formation, and budding at endomembranes in eukaryotic cells. While most AP complexes also require clathrin as the outer vesicle shell, formation of AP-3-coated vesicles involved in Golgi-to-vacuole transport in yeast has been postulated to depend on Vps41, a subunit of the vacuolar HOPS tethering complex. HOPS has also been identified as the tether of AP-3 vesicles on vacuoles. To unravel this conundrum of a dual Vps41 function, we anchored Vps41 stably to the mitochondrial outer membrane. By monitoring AP-3 recruitment, we now show that Vps41 can tether AP-3 vesicles to mitochondria, yet AP-3 vesicles can form in the absence of Vps41 or clathrin. By proximity labeling and mass spectrometry, we identify the Arf1 GTPase-activating protein (GAP) Age2 at the AP-3 coat and show that tethering, but not fusion at the vacuole can occur without complete uncoating. We conclude that AP-3 vesicles retain their coat after budding and that their complete uncoating occurs only after tethering at the vacuole.
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Affiliation(s)
- Jannis Schoppe
- Department of Biology/Chemistry, Biochemistry Section, University of Osnabrück, Osnabrück, Germany
| | - Muriel Mari
- Department of Biomedical Sciences of Cells and Systems, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
| | - Erdal Yavavli
- Department of Biology/Chemistry, Biochemistry Section, University of Osnabrück, Osnabrück, Germany
| | - Kathrin Auffarth
- Department of Biology/Chemistry, Biochemistry Section, University of Osnabrück, Osnabrück, Germany
| | - Margarita Cabrera
- Departament de Ciències Experimentals i de la Salut, Universitat Pompeu Farba, Barcelona, Spain
| | - Stefan Walter
- Center of Cellular Nanoanalytic Osnabrück (CellNanOs), University of Osnabrück, Osnabrück, Germany
| | - Florian Fröhlich
- Center of Cellular Nanoanalytic Osnabrück (CellNanOs), University of Osnabrück, Osnabrück, Germany.,Department of Biology/Chemistry, Molecular Membrane Biology Section, University of Osnabrück, Osnabrück, Germany
| | - Christian Ungermann
- Department of Biology/Chemistry, Biochemistry Section, University of Osnabrück, Osnabrück, Germany.,Center of Cellular Nanoanalytic Osnabrück (CellNanOs), University of Osnabrück, Osnabrück, Germany
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3
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Ganesan S, Tavassoli M, Shabits BN, Zaremberg V. Tubular ER Associates With Diacylglycerol-Rich Structures During Lipid Droplet Consumption. Front Cell Dev Biol 2020; 8:700. [PMID: 32850820 PMCID: PMC7403446 DOI: 10.3389/fcell.2020.00700] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2020] [Accepted: 07/09/2020] [Indexed: 11/13/2022] Open
Abstract
Growth resumption from stationary phase in Saccharomyces cerevisiae, is characterized by lipid droplet (LD) consumption and channeling of lipid precursors toward synthesis of membranes. We have previously determined that triacylglycerol lipolysis contributes to a pool of diacylglycerol (DAG) associated with the yeast vacuole that is enriched in structures that are in close proximity to LDs. In this study we have monitored these structures using a DAG sensor fused to GFP during isolation of LDs. A unique fraction containing the DAG sensor, with low presence of LDs, was identified. Membranes enriched in the DAG probe were obtained by immunoaffinity purification using a GFP nanobody, and the associated proteome was investigated by mass spectrometry. It was determined this LD-associated fraction was enriched in proteins known to shape the tubular endoplasmic reticulum (ER) like Yop1, Sey1, Rtn1, and Rtn2. Consistently, cells lacking three of these proteins (rtn1Δ rtn2Δ yop1Δ) exhibited delayed LD consumption, larger LDs and abnormal LD distribution. In addition, the triple mutant displayed aberrant localization of the DAG sensor after 5 h of growth resumption from stationary phase. Manipulation of DAG levels by overexpression of the DAG kinase Dgk1, impacted localization of the DAG probe and affected fitness of the triple mutant. Altogether these results link LD consumption to tubular ER expansion as a gateway of lipid precursors that otherwise accumulate in vacuolar associated membranes or other internal compartments. Furthermore, conversion of DAG to phosphatidic acid (PA) in the absence of a functional tubular ER was toxic to cells, suggesting the ratio of PA to DAG is critical to allow growth progression.
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Affiliation(s)
| | - Marjan Tavassoli
- Department of Biological Sciences, University of Calgary, Calgary, AB, Canada
| | - Brittney N Shabits
- Department of Biological Sciences, University of Calgary, Calgary, AB, Canada
| | - Vanina Zaremberg
- Department of Biological Sciences, University of Calgary, Calgary, AB, Canada
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4
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Hertle AP, García-Cerdán JG, Armbruster U, Shih R, Lee JJ, Wong W, Niyogi KK. A Sec14 domain protein is required for photoautotrophic growth and chloroplast vesicle formation in Arabidopsis thaliana. Proc Natl Acad Sci U S A 2020; 117:9101-9111. [PMID: 32245810 PMCID: PMC7183190 DOI: 10.1073/pnas.1916946117] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
In eukaryotic photosynthetic organisms, the conversion of solar into chemical energy occurs in thylakoid membranes in the chloroplast. How thylakoid membranes are formed and maintained is poorly understood. However, previous observations of vesicles adjacent to the stromal side of the inner envelope membrane of the chloroplast suggest a possible role of membrane transport via vesicle trafficking from the inner envelope to the thylakoids. Here we show that the model plant Arabidopsis thaliana has a chloroplast-localized Sec14-like protein (CPSFL1) that is necessary for photoautotrophic growth and vesicle formation at the inner envelope membrane of the chloroplast. The cpsfl1 mutants are seedling lethal, show a defect in thylakoid structure, and lack chloroplast vesicles. Sec14 domain proteins are found only in eukaryotes and have been well characterized in yeast, where they regulate vesicle budding at the trans-Golgi network. Like the yeast Sec14p, CPSFL1 binds phosphatidylinositol phosphates (PIPs) and phosphatidic acid (PA) and acts as a phosphatidylinositol transfer protein in vitro, and expression of Arabidopsis CPSFL1 can complement the yeast sec14 mutation. CPSFL1 can transfer PIP into PA-rich membrane bilayers in vitro, suggesting that CPSFL1 potentially facilitates vesicle formation by trafficking PA and/or PIP, known regulators of membrane trafficking between organellar subcompartments. These results underscore the role of vesicles in thylakoid biogenesis and/or maintenance. CPSFL1 appears to be an example of a eukaryotic cytosolic protein that has been coopted for a function in the chloroplast, an organelle derived from endosymbiosis of a cyanobacterium.
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Affiliation(s)
- Alexander P Hertle
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720;
| | - José G García-Cerdán
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3102
- Howard Hughes Medical Institute, University of California, Berkeley, CA 94720
| | - Ute Armbruster
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3102
| | - Robert Shih
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
| | - Jimmy J Lee
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3102
| | - Winnie Wong
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
| | - Krishna K Niyogi
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720;
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3102
- Howard Hughes Medical Institute, University of California, Berkeley, CA 94720
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5
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Arakel EC, Huranova M, Estrada AF, Rau EM, Spang A, Schwappach B. Dissection of GTPase-activating proteins reveals functional asymmetry in the COPI coat of budding yeast. J Cell Sci 2019; 132:jcs.232124. [PMID: 31331965 PMCID: PMC6737914 DOI: 10.1242/jcs.232124] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2019] [Accepted: 07/12/2019] [Indexed: 12/11/2022] Open
Abstract
The Arf GTPase controls formation of the COPI vesicle coat. Recent structural models of COPI revealed the positioning of two Arf1 molecules in contrasting molecular environments. Each of these pockets for Arf1 is expected to also accommodate an Arf GTPase-activating protein (ArfGAP). Structural evidence and protein interactions observed between isolated domains indirectly suggest that each niche preferentially recruits one of the two ArfGAPs known to affect COPI, i.e. Gcs1/ArfGAP1 and Glo3/ArfGAP2/3, although only partial structures are available. The functional role of the unique non-catalytic domain of either ArfGAP has not been integrated into the current COPI structural model. Here, we delineate key differences in the consequences of triggering GTP hydrolysis through the activity of one versus the other ArfGAP. We demonstrate that Glo3/ArfGAP2/3 specifically triggers Arf1 GTP hydrolysis impinging on the stability of the COPI coat. We show that the Snf1 kinase complex, the yeast homologue of AMP-activated protein kinase (AMPK), phosphorylates the region of Glo3 that is crucial for this effect and, thereby, regulates its function in the COPI-vesicle cycle. Our results revise the model of ArfGAP function in the molecular context of COPI. This article has an associated First Person interview with the first author of the paper. Highlighted Article: The regulatory domain of the COPI-associated ArfGAP Glo3 can stabilize the COPI coat. GTP hydrolysis is necessary to resolve the stabilised state. This mechanism is regulated by phosphorylation.
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Affiliation(s)
- Eric C Arakel
- Department of Molecular Biology, Universitätsmedizin Göttingen, Humboldtallee 23, 37073 Göttingen, Germany
| | - Martina Huranova
- Growth and Development, Biozentrum, University of Basel, Klingelbergstrasse 50/70, 4056 Basel, Switzerland.,Laboratory of Adaptive Immunity, Institute of Molecular Genetics of the Czech Academy of Sciences, Videnska 1083, 142 20 Prague 4, Czech Republic
| | - Alejandro F Estrada
- Growth and Development, Biozentrum, University of Basel, Klingelbergstrasse 50/70, 4056 Basel, Switzerland
| | - E-Ming Rau
- Growth and Development, Biozentrum, University of Basel, Klingelbergstrasse 50/70, 4056 Basel, Switzerland
| | - Anne Spang
- Growth and Development, Biozentrum, University of Basel, Klingelbergstrasse 50/70, 4056 Basel, Switzerland
| | - Blanche Schwappach
- Department of Molecular Biology, Universitätsmedizin Göttingen, Humboldtallee 23, 37073 Göttingen, Germany .,Max-Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
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6
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Lipid transfer proteins and the tuning of compartmental identity in the Golgi apparatus. Chem Phys Lipids 2016; 200:42-61. [DOI: 10.1016/j.chemphyslip.2016.06.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2016] [Revised: 06/21/2016] [Accepted: 06/22/2016] [Indexed: 11/23/2022]
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7
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Huang J, Ghosh R, Tripathi A, Lönnfors M, Somerharju P, Bankaitis VA. Two-ligand priming mechanism for potentiated phosphoinositide synthesis is an evolutionarily conserved feature of Sec14-like phosphatidylinositol and phosphatidylcholine exchange proteins. Mol Biol Cell 2016; 27:2317-30. [PMID: 27193303 PMCID: PMC4945147 DOI: 10.1091/mbc.e16-04-0221] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Accepted: 05/12/2016] [Indexed: 12/21/2022] Open
Abstract
The two-ligand priming mechanism for stimulated phosphoinositide synthesis described for Saccharomyces Sec14 is also a conserved feature of Sec14-like phosphatidylinositol- and phosphatidylcholine-transfer proteins of the most evolutionarily advanced plants. Lipid signaling, particularly phosphoinositide signaling, plays a key role in regulating the extreme polarized membrane growth that drives root hair development in plants. The Arabidopsis AtSFH1 gene encodes a two-domain protein with an amino-terminal Sec14-like phosphatidylinositol transfer protein (PITP) domain linked to a carboxy-terminal nodulin domain. AtSfh1 is critical for promoting the spatially highly organized phosphatidylinositol-4,5-bisphosphate signaling program required for establishment and maintenance of polarized root hair growth. Here we demonstrate that, like the yeast Sec14, the AtSfh1 PITP domain requires both its phosphatidylinositol (PtdIns)- and phosphatidylcholine (PtdCho)-binding properties to stimulate PtdIns-4-phosphate [PtdIns(4)P] synthesis. Moreover, we show that both phospholipid-binding activities are essential for AtSfh1 activity in supporting polarized root hair growth. Finally, we report genetic and biochemical evidence that the two-ligand mechanism for potentiation of PtdIns 4-OH kinase activity is a broadly conserved feature of plant Sec14-nodulin proteins, and that this strategy appeared only late in plant evolution. Taken together, the data indicate that the PtdIns/PtdCho-exchange mechanism for stimulated PtdIns(4)P synthesis either arose independently during evolution in yeast and in higher plants, or a suitable genetic module was introduced to higher plants from a fungal source and subsequently exploited by them.
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Affiliation(s)
- Jin Huang
- Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M Health Sciences Center, College Station, TX 77843-1114
| | - Ratna Ghosh
- Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M Health Sciences Center, College Station, TX 77843-1114
| | - Ashutosh Tripathi
- Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M Health Sciences Center, College Station, TX 77843-1114
| | - Max Lönnfors
- Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M Health Sciences Center, College Station, TX 77843-1114
| | - Pentti Somerharju
- Faculty of Medicine, Department of Biochemistry and Developmental Biology, University of Helsinki, 00290 Helsinki, Finland
| | - Vytas A Bankaitis
- Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M Health Sciences Center, College Station, TX 77843-1114 Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843-2128 Department of Chemistry, Texas A&M University, College Station, TX 77840
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8
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Johansen J, Ramanathan V, Beh CT. Vesicle trafficking from a lipid perspective: Lipid regulation of exocytosis in Saccharomyces cerevisiae. CELLULAR LOGISTICS 2014. [PMID: 23181198 PMCID: PMC3498074 DOI: 10.4161/cl.20490] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The protein cargo transported by specific types of vesicles largely defines the different secretory trafficking pathways operating within cells. However, mole per mole the most abundant cargo contained within transport vesicles is not protein, but lipid. Taking a "lipid-centric" point-of-view, we examine the importance of lipid signaling, membrane lipid organization and lipid metabolism for vesicle transport during exocytosis in budding yeast. In fact, the essential requirement for some exocytosis regulatory proteins can be bypassed by making simple manipulations of the lipids involved. During polarized exocytosis the sequential steps required to generate post-Golgi vesicles and target them to the plasma membrane (PM) involves the interplay of several types of lipids that are coordinately linked through PI4P metabolism and signaling. In turn, PI4P levels are regulated by PI4P kinases, the Sac1p PI4P phosphatase and the yeast Osh proteins, which are homologs of mammalian oxysterol-binding protein (OSBP). Together these regulators integrate the transitional steps required for vesicle maturation directly through changes in lipid composition and organization.
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Affiliation(s)
- Jesper Johansen
- Department of Molecular Biology and Biochemistry; Simon Fraser University; Burnaby, BC Canada
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9
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Abstract
The striking morphology of the Golgi complex has fascinated cell biologists since its discovery over 100 years ago. Yet, despite intense efforts to understand how membrane flow relates to Golgi form and function, this organelle continues to baffle cell biologists and biochemists alike. Fundamental questions regarding Golgi function, while hotly debated, remain unresolved. Historically, Golgi function has been described from a protein-centric point of view, but we now appreciate that conceptual frameworks for how lipid metabolism is integrated with Golgi biogenesis and function are essential for a mechanistic understanding of this fascinating organelle. It is from a lipid-centric perspective that we discuss the larger question of Golgi dynamics and membrane trafficking. We review the growing body of evidence for how lipid metabolism is integrally written into the engineering of the Golgi system and highlight questions for future study.
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Affiliation(s)
- Vytas A Bankaitis
- Department of Cell and Developmental Biology, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7090, USA.
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10
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Devising Powerful Genetics, Biochemical and Structural Tools in the Functional Analysis of Phosphatidylinositol Transfer Proteins (PITPs) Across Diverse Species. Methods Cell Biol 2012; 108:249-302. [DOI: 10.1016/b978-0-12-386487-1.00013-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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11
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Mousley CJ, Davison JM, Bankaitis VA. Sec14 like PITPs couple lipid metabolism with phosphoinositide synthesis to regulate Golgi functionality. Subcell Biochem 2012; 59:271-87. [PMID: 22374094 DOI: 10.1007/978-94-007-3015-1_9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
An interface coordinating lipid metabolism with proteins that regulate membrane trafficking is necessary to regulate Golgi morphology and dynamics. Such an interface facilitates the membrane deformations required for vesicularization, forms platforms for protein recruitment and assembly on appropriate sites on a membrane surface and provides lipid co-factors for optimal protein activity in the proper spatio-temporally regulated manner. Importantly, Sec14 and Sec14-like proteins are a unique superfamily of proteins that sense specific aspects of lipid metabolism, employing this information to potentiate phosphoinositide production. Therefore, Sec14 and Sec14 like proteins form central conduits to integrate multiple aspects of lipid metabolism with productive phosphoinositide signaling.
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Affiliation(s)
- Carl J Mousley
- Department of Cell & Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, 27599-7090, Chapel Hill, NC, USA,
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12
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Abstract
Bacteria and eukaryotic cells contain geometry-sensing tools in their cytosol: protein motifs or domains that recognize the curvature, concave or convex, deep or shallow, of lipid membranes. These sensors contrast with classical lipid-binding domains by their extended structure and, sometimes, counterintuitive chemistry. Among the sensors are long amphipathic helices, such as the ALPS motif and the N-terminal region of α-synuclein, whose apparent "design defects" translate into a remarkable ability to specifically adsorb to the surface of small vesicles. Fundamental differences in the lipid composition of membranes of the early and late secretory pathways probably explain why some sensors use mostly electrostatics whereas others take advantage of the hydrophobic effect. Membrane curvature sensors help to organize very diverse reactions, such as lipid transfer between membranes, the tethering of vesicles at the Golgi apparatus, and the assembly-disassembly cycle of protein coats.
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Affiliation(s)
- Bruno Antonny
- Université de Nice-Sophia Antipolis and Centre National de la Recheche Scientifique, Institut de Pharmacologie Moléculaire et Cellulaire, 06560 Valbonne, France.
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13
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Ren J, Schaaf G, Bankaitis VA, Ortlund EA, Pathak MC. Crystallization and preliminary X-ray diffraction analysis of Sfh3, a member of the Sec14 protein superfamily. Acta Crystallogr Sect F Struct Biol Cryst Commun 2011; 67:1239-43. [PMID: 22102037 PMCID: PMC3212372 DOI: 10.1107/s1744309111027096] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2011] [Accepted: 07/06/2011] [Indexed: 11/10/2022]
Abstract
Sec14 is the major phosphatidylinositol (PtdIns)/phosphatidylcholine (PtdCho) transfer protein in the yeast Saccharomyces cerevisiae and is the founding member of the Sec14 protein superfamily. Recent functional data suggest that Sec14 functions as a nanoreactor for PtdCho-regulated presentation of PtdIns to PtdIns kinase to affect membrane trafficking. Extrapolation of this concept to other members of the Sec14 superfamily suggests a mechanism by which a comprehensive cohort of Sec14-like nanoreactors sense correspondingly diverse pools of lipid metabolites. In turn, metabolic information is translated to signaling circuits driven by phosphoinositide metabolism. Sfh3, one of five Sec14 homologs in yeast, exhibits several interesting functional features, including its unique localization to lipid particles and microsomes. This localization forecasts novel regulatory interfaces between neutral lipid metabolism and phosphoinositide signaling. To launch a detailed structural and functional characterization of Sfh3, the recombinant protein was purified to homogeneity, diffraction-quality crystals were produced and a native X-ray data set was collected to 2.2 Å resolution. To aid in phasing, SAD X-ray diffraction data were collected to 1.93 Å resolution from an SeMet-labeled crystal at the Southeast Regional Collaborative Access Team at the Advanced Photon Source. Here, the cloning and purification of Sfh3 and the preliminary diffraction of Sfh3 crystals are reported, enabling structural analyses that are expected to reveal novel principles governing ligand binding and functional specificity for Sec14-superfamily proteins.
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Affiliation(s)
- Jihui Ren
- Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7090, USA
| | - Gabriel Schaaf
- Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7090, USA
| | - Vytas A. Bankaitis
- Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7090, USA
| | - Eric A. Ortlund
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Manish C. Pathak
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322, USA
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14
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Ghosh R, Bankaitis VA. Phosphatidylinositol transfer proteins: negotiating the regulatory interface between lipid metabolism and lipid signaling in diverse cellular processes. Biofactors 2011; 37:290-308. [PMID: 21915936 DOI: 10.1002/biof.180] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Phosphoinositides represent only a small percentage of the total cellular lipid pool. Yet, these molecules play crucial roles in diverse intracellular processes such as signal transduction at membrane-cytosol interface, regulation of membrane trafficking, cytoskeleton organization, nuclear events, and the permeability and transport functions of the membrane. A central principle in such lipid-mediated signaling is the appropriate coordination of these events. Such an intricate coordination demands fine spatial and temporal control of lipid metabolism and organization, and consistent mechanisms for specifically coupling these parameters to dedicated physiological processes. In that regard, recent studies have identified Sec14-like phosphatidylcholine transfer protein (PITPs) as "coincidence detectors," which spatially and temporally link the diverse aspects of the cellular lipid metabolome with phosphoinositide signaling. The integral role of PITPs in eukaryotic signal transduction design is amply demonstrated by the mammalian diseases associated with the derangements in the function of these proteins, to stress response and developmental regulation in plants, to fungal dimorphism and pathogenicity, to membrane trafficking in yeast, and higher eukaryotes. This review updates the recent advances made in the understanding of how these proteins, specifically PITPs of the Sec14-protein superfamily, operate at the molecular level and further describes how this knowledge has advanced our perception on the diverse biological functions of PITPs.
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Affiliation(s)
- Ratna Ghosh
- Lineberger Comprehensive Cancer Center, Department of Cell and Developmental Biology, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27526-7090, USA.
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15
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Schaaf G, Dynowski M, Mousley CJ, Shah SD, Yuan P, Winklbauer EM, de Campos MKF, Trettin K, Quinones MC, Smirnova TI, Yanagisawa LL, Ortlund EA, Bankaitis VA. Resurrection of a functional phosphatidylinositol transfer protein from a pseudo-Sec14 scaffold by directed evolution. Mol Biol Cell 2011; 22:892-905. [PMID: 21248202 PMCID: PMC3057712 DOI: 10.1091/mbc.e10-11-0903] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Sec14-superfamily proteins integrate the lipid metabolome with phosphoinositide synthesis and signaling via primed presentation of phosphatidylinositol (PtdIns) to PtdIns kinases. Sec14 action as a PtdIns-presentation scaffold requires heterotypic exchange of phosphatidylcholine (PtdCho) for PtdIns, or vice versa, in a poorly understood progression of regulated conformational transitions. We identify mutations that confer Sec14-like activities to a functionally inert pseudo-Sec14 (Sfh1), which seemingly conserves all of the structural requirements for Sec14 function. Unexpectedly, the "activation" phenotype results from alteration of residues conserved between Sfh1 and Sec14. Using biochemical and biophysical, structural, and computational approaches, we find the activation mechanism reconfigures atomic interactions between amino acid side chains and internal water in an unusual hydrophilic microenvironment within the hydrophobic Sfh1 ligand-binding cavity. These altered dynamics reconstitute a functional "gating module" that propagates conformational energy from within the hydrophobic pocket to the helical unit that gates pocket access. The net effect is enhanced rates of phospholipid-cycling into and out of the Sfh1* hydrophobic pocket. Taken together, the directed evolution approach reveals an unexpectedly flexible functional engineering of a Sec14-like PtdIns transfer protein-an engineering invisible to standard bioinformatic, crystallographic, and rational mutagenesis approaches.
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Affiliation(s)
- Gabriel Schaaf
- Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, NC 27599, USA.
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16
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Graham TR, Burd CG. Coordination of Golgi functions by phosphatidylinositol 4-kinases. Trends Cell Biol 2010; 21:113-21. [PMID: 21282087 DOI: 10.1016/j.tcb.2010.10.002] [Citation(s) in RCA: 137] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2010] [Revised: 10/04/2010] [Accepted: 10/05/2010] [Indexed: 12/14/2022]
Abstract
Phosphatidylinositol 4-kinases (PI4Ks) regulate vesicle-mediated export from the Golgi apparatus via phosphatidylinositol 4-phosphate (PtdIns4P) binding effector proteins that control vesicle budding reactions and regulate membrane dynamics. Evidence has emerged from the characterization of Golgi PI4K effectors that vesicle budding and lipid dynamics are tightly coupled via a regulatory network that ensures that the appropriate membrane composition is established before a transport vesicle buds from the Golgi. An important hub of this network is protein kinase D, which regulates the activity of PI4K and several PtdIns4P effectors that control sphingolipid and sterol content of Golgi membranes. Other newly identified PtdIns4P effectors include Vps74/GOLPH3, a phospholipid flippase called Drs2 and Sec2, a Rab guanine nucleotide exchange factor (GEF). These effectors orchestrate membrane transformation events facilitating vesicle formation and targeting. In this review, we discuss how PtdIns4P signaling is integrated with membrane biosynthetic and vesicle budding machineries to potentially coordinate these crucial functions of the Golgi apparatus.
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Affiliation(s)
- Todd R Graham
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235, USA.
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Lettner T, Zeidler U, Gimona M, Hauser M, Breitenbach M, Bito A. Candida albicans AGE3, the ortholog of the S. cerevisiae ARF-GAP-encoding gene GCS1, is required for hyphal growth and drug resistance. PLoS One 2010; 5:e11993. [PMID: 20700541 PMCID: PMC2916835 DOI: 10.1371/journal.pone.0011993] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2010] [Accepted: 07/12/2010] [Indexed: 01/05/2023] Open
Abstract
BACKGROUND Hyphal growth and multidrug resistance of C. albicans are important features for virulence and antifungal therapy of this pathogenic fungus. METHODOLOGY/PRINCIPAL FINDINGS Here we show by phenotypic complementation analysis that the C. albicans gene AGE3 is the functional ortholog of the yeast ARF-GAP-encoding gene GCS1. The finding that the gene is required for efficient endocytosis points to an important functional role of Age3p in endosomal compartments. Most C. albicans age3Delta mutant cells which grew as cell clusters under yeast growth conditions showed defects in filamentation under different hyphal growth conditions and were almost completely disabled for invasive filamentous growth. Under hyphal growth conditions only a fraction of age3Delta cells shows a wild-type-like polarization pattern of the actin cytoskeleton and lipid rafts. Moreover, age3Delta cells were highly susceptible to several unrelated toxic compounds including antifungal azole drugs. Irrespective of the AGE3 genotype, C-terminal fusions of GFP to the drug efflux pumps Cdr1p and Mdr1p were predominantly localized in the plasma membrane. Moreover, the plasma membranes of wild-type and age3Delta mutant cells contained similar amounts of Cdr1p, Cdr2p and Mdr1p. CONCLUSIONS/SIGNIFICANCE The results indicate that the defect in sustaining filament elongation is probably caused by the failure of age3Delta cells to polarize the actin cytoskeleton and possibly of inefficient endocytosis. The high susceptibility of age3Delta cells to azoles is not caused by inefficient transport of efflux pumps to the cell membrane. A possible role of a vacuolar defect of age3Delta cells in drug susceptibility is proposed and discussed. In conclusion, our study shows that the ARF-GAP Age3p is required for hyphal growth which is an important virulence factor of C. albicans and essential for detoxification of azole drugs which are routinely used for antifungal therapy. Thus, it represents a promising antifungal drug target.
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Affiliation(s)
- Thomas Lettner
- Department of Cell Biology, University of Salzburg, Salzburg, Austria
| | - Ute Zeidler
- Institut Pasteur, Unité Biologie et Pathogénicité Fongiques, Paris, France
| | - Mario Gimona
- Department of Cell Biology, University of Salzburg, Salzburg, Austria
| | - Michael Hauser
- Department of Molecular Biology, University of Salzburg, Salzburg, Austria
| | | | - Arnold Bito
- Department of Cell Biology, University of Salzburg, Salzburg, Austria
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Sphingolipid metabolism in trans-golgi/endosomal membranes and the regulation of intracellular homeostatic processes in eukaryotic cells. ACTA ACUST UNITED AC 2010; 50:339-48. [DOI: 10.1016/j.advenzreg.2009.12.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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19
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Bankaitis VA, Mousley CJ, Schaaf G. The Sec14 superfamily and mechanisms for crosstalk between lipid metabolism and lipid signaling. Trends Biochem Sci 2009; 35:150-60. [PMID: 19926291 DOI: 10.1016/j.tibs.2009.10.008] [Citation(s) in RCA: 137] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2009] [Revised: 10/26/2009] [Accepted: 10/27/2009] [Indexed: 01/03/2023]
Abstract
Lipid signaling pathways define central mechanisms for cellular regulation. Productive lipid signaling requires an orchestrated coupling between lipid metabolism, lipid organization and the action of protein machines that execute appropriate downstream reactions. Using membrane trafficking control as primary context, we explore the idea that the Sec14-protein superfamily defines a set of modules engineered for the sensing of specific aspects of lipid metabolism and subsequent transduction of 'sensing' information to a phosphoinositide-driven 'execution phase'. In this manner, the Sec14 superfamily connects diverse territories of the lipid metabolome with phosphoinositide signaling in a productive 'crosstalk' between these two systems. Mechanisms of crosstalk, by which non-enzymatic proteins integrate metabolic cues with the action of interfacial enzymes, represent unappreciated regulatory themes in lipid signaling.
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Affiliation(s)
- Vytas A Bankaitis
- Department of Cell & Developmental Biology, Lineberger Comprehensive Cancer Center, School of Medicine, University of North Carolina at Chapel Hill. Chapel Hill, North Carolina 27599-7090, USA
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20
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Phillips SE, Vincent P, Rizzieri KE, Schaaf G, Bankaitis VA, Gaucher EA. The Diverse Biological Functions of Phosphatidylinositol Transfer Proteins in Eukaryotes. Crit Rev Biochem Mol Biol 2008; 41:21-49. [PMID: 16455519 DOI: 10.1080/10409230500519573] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Phosphatidylinositol/phosphatidylcholine transfer proteins (PITPs) remain largely functionally uncharacterized, despite the fact that they are highly conserved and are found in all eukaryotic cells thus far examined by biochemical or sequence analysis approaches. The available data indicate a role for PITPs in regulating specific interfaces between lipid-signaling and cellular function. In this regard, a role for PITPs in controlling specific membrane trafficking events is emerging as a common functional theme. However, the mechanisms by which PITPs regulate lipid-signaling and membrane-trafficking functions remain unresolved. Specific PITP dysfunctions are now linked to neurodegenerative and intestinal malabsorption diseases in mammals, to stress response and developmental regulation in higher plants, and to previously uncharacterized pathways for regulating membrane trafficking in yeast and higher eukaryotes, making it clear that PITPs are integral parts of a highly conserved signal transduction strategy in eukaryotes. Herein, we review recent progress in deciphering the biological functions of PITPs, and discuss some of the open questions that remain.
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Affiliation(s)
- Scott E Phillips
- Department of Cell and Developmental Biology, School of Medicine, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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21
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Mousley CJ, Tyeryar K, Ile KE, Schaaf G, Brost RL, Boone C, Guan X, Wenk MR, Bankaitis VA. Trans-Golgi network and endosome dynamics connect ceramide homeostasis with regulation of the unfolded protein response and TOR signaling in yeast. Mol Biol Cell 2008; 19:4785-803. [PMID: 18753406 DOI: 10.1091/mbc.e08-04-0426] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Synthetic genetic array analyses identify powerful genetic interactions between a thermosensitive allele (sec14-1(ts)) of the structural gene for the major yeast phosphatidylinositol transfer protein (SEC14) and a structural gene deletion allele (tlg2Delta) for the Tlg2 target membrane-soluble N-ethylmaleimide-sensitive factor attachment protein receptor. The data further demonstrate Sec14 is required for proper trans-Golgi network (TGN)/endosomal dynamics in yeast. Paradoxically, combinatorial depletion of Sec14 and Tlg2 activities elicits trafficking defects from the endoplasmic reticulum, and these defects are accompanied by compromise of the unfolded protein response (UPR). UPR failure occurs downstream of Hac1 mRNA splicing, and it is further accompanied by defects in TOR signaling. The data link TGN/endosomal dynamics with ceramide homeostasis, UPR activity, and TOR signaling in yeast, and they identify the Sit4 protein phosphatase as a primary conduit through which ceramides link to the UPR. We suggest combinatorial Sec14/Tlg2 dysfunction evokes inappropriate turnover of complex sphingolipids in endosomes. One result of this turnover is potentiation of ceramide-activated phosphatase-mediated down-regulation of the UPR. These results provide new insight into Sec14 function, and they emphasize the TGN/endosomal system as a central hub for homeostatic regulation in eukaryotes.
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Affiliation(s)
- Carl J Mousley
- Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7090, USA
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Curwin AJ, McMaster CR. Structure and function of the enigmatic Sec14 domain-containing proteins and the etiology of human disease. ACTA ACUST UNITED AC 2008. [DOI: 10.2217/17460875.3.4.399] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
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23
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Schaaf G, Ortlund EA, Tyeryar KR, Mousley CJ, Ile KE, Garrett TA, Ren J, Woolls MJ, Raetz CR, Redinbo MR, Bankaitis VA. Functional anatomy of phospholipid binding and regulation of phosphoinositide homeostasis by proteins of the sec14 superfamily. Mol Cell 2008; 29:191-206. [PMID: 18243114 PMCID: PMC7808562 DOI: 10.1016/j.molcel.2007.11.026] [Citation(s) in RCA: 197] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2007] [Revised: 09/27/2007] [Accepted: 11/14/2007] [Indexed: 11/28/2022]
Abstract
Sec14, the major yeast phosphatidylinositol (PtdIns)/phosphatidylcholine (PtdCho) transfer protein, regulates essential interfaces between lipid metabolism and membrane trafficking from the trans-Golgi network (TGN). How Sec14 does so remains unclear. We report that Sec14 binds PtdIns and PtdCho at distinct (but overlapping) sites, and both PtdIns- and PtdCho-binding activities are essential Sec14 activities. We further show both activities must reside within the same molecule to reconstitute a functional Sec14 and for effective Sec14-mediated regulation of phosphoinositide homeostasis in vivo. This regulation is uncoupled from PtdIns-transfer activity and argues for an interfacial presentation mode for Sec14-mediated potentiation of PtdIns kinases. Such a regulatory role for Sec14 is a primary counter to action of the Kes1 sterol-binding protein that antagonizes PtdIns 4-OH kinase activity in vivo. Collectively, these findings outline functional mechanisms for the Sec14 superfamily and reveal additional layers of complexity for regulating phosphoinositide homeostasis in eukaryotes.
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Affiliation(s)
- Gabriel Schaaf
- Department of Cell and Developmental Biology, School of Medicine, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7090, USA
- These authors contributed equally to this work
| | - Eric A. Ortlund
- Department of Chemistry, School of Medicine, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7090, USA
- Department of Biochemistry and Biophysics, School of Medicine, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7090, USA
- These authors contributed equally to this work
| | - Kimberly R. Tyeryar
- Department of Cell and Developmental Biology, School of Medicine, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7090, USA
| | - Carl J. Mousley
- Department of Cell and Developmental Biology, School of Medicine, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7090, USA
| | - Kristina E. Ile
- Department of Cell and Developmental Biology, School of Medicine, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7090, USA
| | - Teresa A. Garrett
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA
| | - Jihui Ren
- Department of Cell and Developmental Biology, School of Medicine, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7090, USA
| | - Melissa J. Woolls
- Department of Cell and Developmental Biology, School of Medicine, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7090, USA
| | - Christian R.H. Raetz
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA
| | - Matthew R. Redinbo
- Department of Chemistry, School of Medicine, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7090, USA
- Department of Biochemistry and Biophysics, School of Medicine, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7090, USA
| | - Vytas A. Bankaitis
- Department of Cell and Developmental Biology, School of Medicine, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7090, USA
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DeRegis CJ, Rahl PB, Hoffman GR, Cerione RA, Collins RN. Mutational analysis of betaCOP (Sec26p) identifies an appendage domain critical for function. BMC Cell Biol 2008; 9:3. [PMID: 18211691 PMCID: PMC2262067 DOI: 10.1186/1471-2121-9-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2007] [Accepted: 01/22/2008] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The appendage domain of the gammaCOP subunit of the COPI vesicle coat bears a striking structural resemblance to adaptin-family appendages despite limited primary sequence homology. Both the gammaCOP appendage domain and an equivalent region on betaCOP contain the FxxxW motif; the conservation of this motif suggested the existence of a functional appendage domain in betaCOP. RESULTS Sequence comparisons in combination with structural prediction tools show that the fold of the COOH-terminus of Sec26p is strongly predicted to closely mimic that of adaptin-family appendages. Deletion of the appendage domain of Sec26p results in inviability in yeast, over-expression of the deletion construct is dominant negative and mutagenesis of this region identifies residues critical for function. The ArfGAP Glo3p was identified via suppression screening as a potential downstream modulator of Sec26p in a manner that is independent of the GAP activity of Glo3p but requires the presence of the COOH-terminal ISS motifs. CONCLUSION Together, these results indicate an essential function for the predicted betaCOP appendage and suggest that both COPI appendages perform a biologically active regulatory role with a structure related to adaptin-family appendage domains.
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Affiliation(s)
- Carol J DeRegis
- Graduate Program in Comparative Biomedical Sciences, Cornell University, Ithaca NY 14853, USA
| | - Peter B Rahl
- Graduate Program in Pharmacology, Cornell University, Ithaca, NY 14853, USA
| | - Gregory R Hoffman
- Graduate Program in Biophysics, Cornell University, Ithaca, NY 14853, USA
| | - Richard A Cerione
- Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
| | - Ruth N Collins
- Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA
- Department of Molecular Medicine, Cornell University, C4-109 Veterinary Medical Center, Ithaca, NY 14853, USA
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25
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Yan D, Olkkonen VM. Characteristics of oxysterol binding proteins. INTERNATIONAL REVIEW OF CYTOLOGY 2008; 265:253-85. [PMID: 18275891 DOI: 10.1016/s0074-7696(07)65007-4] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Protein families characterized by a ligand binding domain related to that of oxysterol binding protein (OSBP) have been identified in eukaryotic species from yeast to humans. These proteins, designated OSBP-related (ORP) or OSBP-like (OSBPL) proteins, have been implicated in various cellular functions. However, the detailed mechanisms of their action have remained elusive. Data from our and other laboratories suggest that binding of sterol ligands may be a unifying theme. Work with Saccharomyces cerevisiae ORPs suggests a function of these proteins in the nonvesicular intracellular transport of sterols, in secretory vesicle transport from the Golgi complex, and in the establishment of cell polarity. Mammals have more ORP genes, and differential splicing substantially increases the complexity of the encoded protein family. Functional studies on mammalian ORPs point in different directions: integration of sterol and sphingomyelin metabolism, sterol transport, regulation of neutral lipid metabolism, control of the microtubule-dependent motility of endosomes/lysosomes, and regulation of signaling cascades. We envision that during evolution, the functions of ORPs have diverged from an ancestral one in sterol transport, to meet the increasing demand of the regulatory potential in multicellular organisms. Our working hypothesis is that mammalian ORPs mainly act as sterol sensors that relay information to a spectrum of different cellular processes.
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Affiliation(s)
- Daoguang Yan
- Department of Molecular Medicine, National Public Health Institute, Biomedicum, FI-00290 Helsinki, Finland
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26
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Ryan MM, Temple BR, Phillips SE, Bankaitis VA. Conformational dynamics of the major yeast phosphatidylinositol transfer protein sec14p: insight into the mechanisms of phospholipid exchange and diseases of sec14p-like protein deficiencies. Mol Biol Cell 2007; 18:1928-42. [PMID: 17344474 PMCID: PMC1855008 DOI: 10.1091/mbc.e06-11-1024] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2006] [Revised: 01/30/2007] [Accepted: 02/27/2007] [Indexed: 11/11/2022] Open
Abstract
Molecular dynamics simulations coupled with functional analyses of the major yeast phosphatidylinositol/phosphatidylcholine transfer protein Sec14p identify structural elements involved in regulating the ability of Sec14p to execute phospholipid exchange. The molecular dynamics simulations suggest large rigid body motions within the Sec14p molecule accompany closing and opening of an A(10)/T(4)/A(11) helical gate, and that "state-of-closure" of this helical gate determines access to the Sec14p phospholipid binding cavity. The data also project that conformational dynamics of the helical gate are controlled by a hinge unit (residues F(212), Y(213), K(239), I(240), and I(242)) that links to the N- and C-terminal ends of the helical gate, and by a novel gating module (composed of the B(1)LB(2) and A(12)LT(5) substructures) through which conformational information is transduced to the hinge. The (114)TDKDGR(119) motif of B(1)LB(2) plays an important role in that transduction process. These simulations offer new mechanistic possibilities for an important half-reaction of the Sec14p phospholipid exchange cycle that occurs on membrane surfaces after Sec14p has ejected bound ligand, and is reloading with another phospholipid molecule. These conformational transitions further suggest structural rationales for known disease missense mutations that functionally compromise mammalian members of the Sec14-protein superfamily.
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Affiliation(s)
- Margaret M. Ryan
- *Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Research Center; and
| | - Brenda R.S. Temple
- R. L. Juliano Structural Bioinformatics Core Facility, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7090
| | - Scott E. Phillips
- *Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Research Center; and
| | - Vytas A. Bankaitis
- *Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Research Center; and
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27
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Bankaitis VA, Vincent P, Merkulova M, Tyeryar K, Liu Y. Phosphatidylinositol transfer proteins and functional specification of lipid signaling pools. ACTA ACUST UNITED AC 2007; 47:27-40. [PMID: 17335879 PMCID: PMC2080876 DOI: 10.1016/j.advenzreg.2006.12.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- Vytas A Bankaitis
- Department of Cell & Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7090, USA.
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28
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Antonny B. Membrane deformation by protein coats. Curr Opin Cell Biol 2006; 18:386-94. [PMID: 16782321 DOI: 10.1016/j.ceb.2006.06.003] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2006] [Accepted: 06/05/2006] [Indexed: 12/14/2022]
Abstract
Protein coats deform lipid membranes into spherical buds, which undergo fission at the neck to become vesicles. To induce membrane curvature, protein coats use basic tools including amphipathic helices and concave protein surfaces, and take advantage of the bulk properties of cellular membranes, such as loose lipid packing in the endoplasmic reticulum and cis-Golgi and the abundance of anionic lipids in the cytosolic leaflet of the plasma membrane. Protein scaffolds, sensors of membrane curvature and finely tuned reactions such as GTP hydrolysis permit the spatial and temporal organization of these tools, making protein coats self-organized molecular machines. Because biological membranes generally adhere to a cytoskeleton, the functioning of protein coats is coupled to other large remodeling events at the membrane interface.
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Affiliation(s)
- Bruno Antonny
- CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Université de Nice Sophia-Antipolis, 06560 Valbonne, France.
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29
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Preuss ML, Schmitz AJ, Thole JM, Bonner HKS, Otegui MS, Nielsen E. A role for the RabA4b effector protein PI-4Kbeta1 in polarized expansion of root hair cells in Arabidopsis thaliana. ACTA ACUST UNITED AC 2006; 172:991-8. [PMID: 16567499 PMCID: PMC2063757 DOI: 10.1083/jcb.200508116] [Citation(s) in RCA: 217] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
The RabA4b GTPase labels a novel, trans-Golgi network compartment displaying a developmentally regulated polar distribution in growing Arabidopsis thaliana root hair cells. GTP bound RabA4b selectively recruits the plant phosphatidylinositol 4-OH kinase, PI-4Kβ1, but not members of other PI-4K families. PI-4Kβ1 colocalizes with RabA4b on tip-localized membranes in growing root hairs, and mutant plants in which both the PI-4Kβ1 and -4Kβ2 genes are disrupted display aberrant root hair morphologies. PI-4Kβ1 interacts with RabA4b through a novel homology domain, specific to eukaryotic type IIIβ PI-4Ks, and PI-4Kβ1 also interacts with a Ca2+ sensor, AtCBL1, through its NH2 terminus. We propose that RabA4b recruitment of PI-4Kβ1 results in Ca2+-dependent generation of PI-4P on this compartment, providing a link between Ca2+ and PI-4,5P2–dependent signals during the polarized secretion of cell wall components in tip-growing root hair cells.
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Affiliation(s)
- Mary L Preuss
- Donald Danforth Plant Science Center, St. Louis, MO 63132, USA
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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: 33] [Impact Index Per Article: 1.8] [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.
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Affiliation(s)
- Hiroshi Sakane
- Division of Molecular Interaction, Institute for Genetic Medicine, Hokkaido University Graduate School of Medicine, Kita-ku, Sapporo 060-0815, Japan
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31
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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.
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Affiliation(s)
- Alberto Luini
- Department of Cell Biology and Oncology, Consorzio Mario Negri Sud, 66030 Santa Maria Imbaro, Chieti, Italy.
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32
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Wong TA, Fairn GD, Poon PP, Shmulevitz M, McMaster CR, Singer RA, Johnston GC. Membrane metabolism mediated by Sec14 family members influences Arf GTPase activating protein activity for transport from the trans-Golgi. Proc Natl Acad Sci U S A 2005; 102:12777-82. [PMID: 16126894 PMCID: PMC1200303 DOI: 10.1073/pnas.0506156102] [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] [Indexed: 11/18/2022] Open
Abstract
The budding yeast Saccharomyces cerevisiae contains a family of Arf (ADP-ribosylation factor) GTPase activating protein (GAP) proteins with the Gcs1 + Age2 ArfGAP pair providing essential overlapping function for the movement of transport vesicles from the trans-Golgi network. We have generated a temperature-sensitive but stable version of the Gcs1 protein that is impaired only for trans-Golgi transport and find that deleterious effects of this enfeebled Gcs1-4 mutant protein are relieved by increased gene dosage of the gcs1-4 mutant gene itself or by the SFH2 gene (also called CSR1), encoding a phosphatidylinositol transfer protein (PITP). This effect was not seen for the SEC14 gene, encoding the founding member of the yeast PITP protein family, even though the Gcs1 and Age2 ArfGAPs are known to be downstream effectors of Sec14-mediated activity for trans-Golgi transport. Sfh2-mediated suppression of inadequate Gcs1-4 function depended on phospholipase D, whereas inadequate Gcs1-4 activity was relieved by increasing levels of diacylglycerol (DAG). Recombinant Gcs1 protein was found to bind certain phospholipids but not DAG. Our findings favor a model of Gcs1 localization through binding to specific phospholipids and activation of ArfGAP activity by DAG-mediated membrane curvature as the transport vesicle is formed. Thus, ArfGAPs are subject to both temporal and spatial regulation that is facilitated by Sfh2-mediated modulation of the lipid environment.
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Affiliation(s)
- Tania A Wong
- Department of Microbiology and Immunology, Faculty of Medicine, Dalhousie University, Halifax, NS, Canada B3H 1X5
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Bankaitis VA, Phillips S, Yanagisawa L, Li X, Routt S, Xie Z. Phosphatidylinositol transfer protein function in the yeast Saccharomyces cerevisiae. ACTA ACUST UNITED AC 2005; 45:155-70. [PMID: 16118014 DOI: 10.1016/j.advenzreg.2005.02.014] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
PITPs regulate the interface between lipid metabolism and cellular functions, but the fundamental nature of this regulation is not understood. Yeast and mouse studies demonstrate strict coupling of individual PITPs to specific cellular activities, but the invisibility of these specificities in in vitro models for PITP activity is remarkable. In our opinion, delineation of PITP functions requires the continued application of genetic approaches such as those summarized here. Future studies dedicated to enhancing our understanding of the mechanisms of action of Sec14p-like and metazoan PITPs are worthy goals for three reasons. First, it is becoming abundantly clear that PITPs act at important biological interfaces that involve lipid and protein trafficking, phospholipid biosynthesis and polarized membrane growth. Because these interfaces are critical not only to cellular functions, but also to developmental processes, the function of PITPs in development of multicellular organisms is a particularly attractive area of research that remains essentially untapped. Second, the yeast studies indicate functional linkages between Sec14p-like PITPs and members of ubiquitous but entirely uncharacterized eukaryotic proteins such as OSBP family members. Finally, the link of PITPs to disease is already clear since PITP deficiencies lie at the foundation of novel mechanisms of neurodegenerative, glucose homeostatic and gastrointestinal disorders in mammals. Given that the contribution of Sec14p-like proteins to the PITP complement of mammalian cells is completely uninvestigated, and that the mammalian genome encodes many proteins of this class, we anticipate such advances will directly and positively impact our understanding of the molecular basis of such diseases.
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Affiliation(s)
- Vytas A Bankaitis
- Department of Cell and Developmental Biology, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7090, USA.
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Zhuang X, Xu Y, Chong K, Lan L, Xue Y, Xu Z. OsAGAP, an ARF-GAP from rice, regulates root development mediated by auxin in Arabidopsis. PLANT, CELL & ENVIRONMENT 2005; 28:147-56. [PMID: 16010732 DOI: 10.1111/j.1365-3040.2004.01253.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Arf (ADP-ribosylation factor) proteins, which mediate vesicular transport, have little or no intrinsic GTPase activity. They rely on the action of GTPase-activating proteins (GAPs) and guanine nucleotide exchange factors (GEFs) for their function. In the present study the OsAGAP gene in rice, which encoded a protein with predicted structure similar to ArfGAP, was identified. The purified OsAGAP-GST fusion protein was able to stimulate the GTPase activity of rice Arf. Furthermore, OsAGAP can rescue the defect of vesicular transport in the yeast gcs1 delta glo3 delta double-mutant cells. Transgenic Arabidopsis with OsAGAP constitutively expression showed reduced apical dominance, shorter primary roots, increasing number of longer adventitious roots. Many of the phenotypes can be phenocopied by treatment of exogenous indoleacetic acid level (IAA) in wild-type plants. Determination of whole-plant IAA level showed that there is a sharp increase of free IAA in OsAGAP transgenic Arabidopsis seedlings. In addition, removal of the 4-day-old shoot apex could inhibit the adventitious root formation in the transgenic seedlings. These results suggest OsAGAP, an ARF-GAP of rice, maybe involved in the mediation of plant root development by regulating auxin level.
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Affiliation(s)
- X Zhuang
- Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, CAS, Beijing, China
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De Matteis MA, Godi A. Protein–lipid interactions in membrane trafficking at the Golgi complex. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2004; 1666:264-74. [PMID: 15519320 DOI: 10.1016/j.bbamem.2004.07.002] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2004] [Accepted: 07/09/2004] [Indexed: 11/16/2022]
Abstract
The integrated interplay between proteins and lipids drives many key cellular processes, such as signal transduction, cytoskeleton remodelling and membrane trafficking. The last of these, membrane trafficking, has the Golgi complex as its central station. Not only does this organelle orchestrates the biosynthesis, transport and intracellular distribution of many proteins and lipids, but also its own function and structure is dictated by intimate functional and physical relationships between protein-based and lipid-based machineries. These machineries are involved in the control of the fundamental events that govern membrane traffic, such as in the budding, fission and fusion of transport intermediates, in the regulation of the shape and geometry of the Golgi membranes themselves, and, finally, in the generation of "signals" that can have local actions in the secretory system, or that may affect other cellular systems. Lipid-protein interactions rely on the abilities of certain protein domains to recognize specific lipids. These interactions are mediated, in particular, through the headgroups of the phospholipids, although a few of these protein domains are able to specifically interact with the phospholipid acyl chains. Recent evidence also indicates that some proteins and/or protein domains are more sensitive to the physical environment of the membrane bilayer (such as its curvature) than to its chemical composition.
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Affiliation(s)
- M A De Matteis
- Department of Cell Biology and Oncology, Consorzio Mario Negri Sud, Via Nazionale, 66030 Santa Maria Imbaro (Chieti), Italy.
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Peterman TK, Ohol YM, McReynolds LJ, Luna EJ. Patellin1, a novel Sec14-like protein, localizes to the cell plate and binds phosphoinositides. PLANT PHYSIOLOGY 2004; 136:3080-94; discussion 3001-2. [PMID: 15466235 PMCID: PMC523369 DOI: 10.1104/pp.104.045369] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2004] [Revised: 07/23/2004] [Accepted: 07/23/2004] [Indexed: 05/19/2023]
Abstract
Membrane trafficking is central to construction of the cell plate during plant cytokinesis. Consequently, a detailed understanding of the process depends on the characterization of molecules that function in the formation, transport, targeting, and fusion of membrane vesicles to the developing plate, as well as those that participate in its consolidation and maturation into a fully functional partition. Here we report the initial biochemical and functional characterization of patellin1 (PATL1), a novel cell-plate-associated protein that is related in sequence to proteins involved in membrane trafficking in other eukaryotes. Analysis of the Arabidopsis genome indicated that PATL1 is one of a small family of Arabidopsis proteins, characterized by a variable N-terminal domain followed by two domains found in other membrane-trafficking proteins (Sec14 and Golgi dynamics domains). Results from immunolocalization and biochemical fractionation studies suggested that PATL1 is recruited from the cytoplasm to the expanding and maturing cell plate. In vesicle-binding assays, PATL1 bound to specific phosphoinositides, important regulators of membrane trafficking, with a preference for phosphatidylinositol(5)P, phosphatidylinositol(4,5)P(2), and phosphatidylinositol(3)P. Taken together, these findings suggest a role for PATL1 in membrane-trafficking events associated with cell-plate expansion or maturation and point to the involvement of phosphoinositides in cell-plate biogenesis.
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Affiliation(s)
- T Kaye Peterman
- Department of Biological Sciences, Wellesley College, Wellesley, Massachusetts 02481, USA.
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Lewis SM, Poon PP, Singer RA, Johnston GC, Spang A. The ArfGAP Glo3 is required for the generation of COPI vesicles. Mol Biol Cell 2004; 15:4064-72. [PMID: 15254269 PMCID: PMC515341 DOI: 10.1091/mbc.e04-04-0316] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2004] [Revised: 06/25/2004] [Accepted: 07/01/2004] [Indexed: 11/11/2022] Open
Abstract
The small GTPase Arf and coatomer (COPI) are required for the generation of retrograde transport vesicles. Arf activity is regulated by guanine exchange factors (ArfGEF) and GTPase-activating proteins (ArfGAPs). The ArfGAPs Gcs1 and Glo3 provide essential overlapping function for retrograde vesicular transport from the Golgi to the endoplasmic reticulum. We have identified Glo3 as a component of COPI vesicles. Furthermore, we find that a mutant version of the Glo3 protein exerts a negative effect on retrograde transport, even in the presence of the ArfGAP Gcs1. Finally, we present evidence supporting a role for ArfGAP protein in the generation of COPI retrograde transport vesicles.
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Affiliation(s)
- Stephen M Lewis
- Departments of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 1X5
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Shemesh T, Luini A, Malhotra V, Burger KNJ, Kozlov MM. Prefission constriction of Golgi tubular carriers driven by local lipid metabolism: a theoretical model. Biophys J 2004; 85:3813-27. [PMID: 14645071 PMCID: PMC1303683 DOI: 10.1016/s0006-3495(03)74796-1] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Membrane transport within mammalian cells is mediated by small vesicular as well as large pleiomorphic transport carriers (TCs). A major step in the formation of TCs is the creation and subsequent narrowing of a membrane neck connecting the emerging carrier with the initial membrane. In the case of small vesicular TCs, neck formation may be directly induced by the coat proteins that cover the emerging vesicle. However, the mechanism underlying the creation and narrowing of a membrane neck in the generation of large TCs remains unknown. We present a theoretical model for neck formation based on the elastic model of membranes. Our calculations suggest a lipid-driven mechanism with a central role for diacylglycerol (DAG). The model is applied to a well-characterized in vitro system that reconstitutes TC formation from the Golgi complex, namely the pearling and fission of Golgi tubules induced by CtBP/BARS, a protein that catalyzes the conversion of lysophosphatidic acid into phosphatidic acid. In view of the importance of a PA-DAG cycle in the formation of Golgi TCs, we assume that the newly formed phosphatidic acid undergoes rapid dephosphorylation into DAG. DAG possesses a unique molecular shape characterized by an extremely large negative spontaneous curvature, and it redistributes rapidly between the membrane monolayers and along the membrane surface. Coupling between local membrane curvature and local lipid composition results, by mutual enhancement, in constrictions of the tubule into membrane necks, and a related inhomogeneous lateral partitioning of DAG. Our theoretical model predicts the exact dimensions of the constrictions observed in the pearling Golgi tubules. Moreover, the model is able to explain membrane neck formation by physiologically relevant mole fractions of DAG.
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Affiliation(s)
- Tom Shemesh
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
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Gray JV, Petsko GA, Johnston GC, Ringe D, Singer RA, Werner-Washburne M. "Sleeping beauty": quiescence in Saccharomyces cerevisiae. Microbiol Mol Biol Rev 2004; 68:187-206. [PMID: 15187181 PMCID: PMC419917 DOI: 10.1128/mmbr.68.2.187-206.2004] [Citation(s) in RCA: 436] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
Abstract
The cells of organisms as diverse as bacteria and humans can enter stable, nonproliferating quiescent states. Quiescent cells of eukaryotic and prokaryotic microorganisms can survive for long periods without nutrients. This alternative state of cells is still poorly understood, yet much benefit is to be gained by understanding it both scientifically and with reference to human health. Here, we review our knowledge of one "model" quiescent cell population, in cultures of yeast grown to stationary phase in rich media. We outline the importance of understanding quiescence, summarize the properties of quiescent yeast cells, and clarify some definitions of the state. We propose that the processes by which a cell enters into, maintains viability in, and exits from quiescence are best viewed as an environmentally triggered cycle: the cell quiescence cycle. We synthesize what is known about the mechanisms by which yeast cells enter into quiescence, including the possible roles of the protein kinase A, TOR, protein kinase C, and Snf1p pathways. We also discuss selected mechanisms by which quiescent cells maintain viability, including metabolism, protein modification, and redox homeostasis. Finally, we outline what is known about the process by which cells exit from quiescence when nutrients again become available.
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Affiliation(s)
- Joseph V Gray
- Division of Molecular Genetics, Faculty of Biomedical and Life Sciences, University of Glasgow, Anderson College, 56 Dumbarton Rd., Glasgow G11 6NU, United Kingdom.
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Bankaitis VA, Cortese J, Phillips SE, Alb JG. Phosphatidylinositol transfer protein function in the mouse. ACTA ACUST UNITED AC 2004; 44:201-18. [PMID: 15581491 DOI: 10.1016/j.advenzreg.2003.11.014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- Vytas A Bankaitis
- Department of Cell and Developmental Biology, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7090, USA.
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Rudge SA, Sciorra VA, Iwamoto M, Zhou C, Strahl T, Morris AJ, Thorner J, Engebrecht J. Roles of phosphoinositides and of Spo14p (phospholipase D)-generated phosphatidic acid during yeast sporulation. Mol Biol Cell 2003; 15:207-18. [PMID: 14528019 PMCID: PMC307541 DOI: 10.1091/mbc.e03-04-0245] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
During yeast sporulation, internal membrane synthesis ensures that each haploid nucleus is packaged into a spore. Prospore membrane formation requires Spo14p, a phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2]-stimulated phospholipase D (PLD), which hydrolyzes phosphatidylcholine (PtdCho) to phosphatidic acid (PtdOH) and choline. We found that both meiosis and spore formation also require the phosphatidylinositol (PtdIns)/PtdCho transport protein Sec14p. Specific ablation of the PtdIns transport activity of Sec14p was sufficient to impair spore formation but not meiosis. Overexpression of Pik1p, a PtdIns 4-kinase, suppressed the sec14-1 meiosis and spore formation defects; conversely, pik1-ts diploids failed to undergo meiosis and spore formation. The PtdIns(4)P 5-kinase, Mss4p, also is essential for spore formation. Use of phosphoinositide-specific GFP-PH domain reporters confirmed that PtdIns(4,5)P2 is enriched in prospore membranes. sec14, pik1, and mss4 mutants displayed decreased Spo14p PLD activity, whereas absence of Spo14p did not affect phosphoinositide levels in vivo, suggesting that formation of PtdIns(4,5)P2 is important for Spo14p activity. Spo14p-generated PtdOH appears to have an essential role in sporulation, because treatment of cells with 1-butanol, which supports Spo14p-catalyzed PtdCho breakdown but leads to production of Cho and Ptd-butanol, blocks spore formation at concentrations where the inert isomer, 2-butanol, has little effect. Thus, rather than a role for PtdOH in stimulating PtdIns(4,5)P2 formation, our findings indicate that during sporulation, Spo14p-mediated PtdOH production functions downstream of Sec14p-, Pik1p-, and Mss4p-dependent PtdIns(4,5)P2 synthesis.
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Affiliation(s)
- Simon A Rudge
- Department of Cellular and Molecular Medicine, School of Medicine, and Howard Hughes Medical Institute, University of California, San Diego, La Jolla, California 92093-0668, USA
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Alb JG, Cortese JD, Phillips SE, Albin RL, Nagy TR, Hamilton BA, Bankaitis VA. Mice lacking phosphatidylinositol transfer protein-alpha exhibit spinocerebellar degeneration, intestinal and hepatic steatosis, and hypoglycemia. J Biol Chem 2003; 278:33501-18. [PMID: 12788952 PMCID: PMC7798478 DOI: 10.1074/jbc.m303591200] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
Phosphatidylinositol transfer proteins (PITPs) regulate the interface between lipid metabolism and cellular functions. We now report that ablation of PITP alpha function leads to aponecrotic spinocerebellar disease, hypoglycemia, and intestinal and hepatic steatosis in mice. The data indicate that hypoglycemia is in part associated with reduced proglucagon gene expression and glycogenolysis that result from pancreatic islet cell defects. The intestinal and hepatic steatosis results from the intracellular accumulation of neutral lipid and free fatty acid mass in these organs and suggests defective trafficking of triglycerides and diacylglycerols from the endoplasmic reticulum. We propose that deranged intestinal and hepatic lipid metabolism and defective proglucagon gene expression contribute to hypoglycemia in PITP alpha-/- mice, and that hypoglycemia is a significant contributing factor in the onset of spinocerebellar disease. Taken together, the data suggest an unanticipated role for PITP alpha in with glucose homeostasis and in mammalian endoplasmic reticulum functions that interface with transport of specific luminal lipid cargoes.
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Affiliation(s)
- James G. Alb
- Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599-7090
| | - Jorge D. Cortese
- Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599-7090
| | - Scott E. Phillips
- Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599-7090
| | - Roger L. Albin
- Department of Neurology, University of Michigan School of Medicine, Ann Arbor Veterans Affairs Medical Center GRECC, Ann Arbor, Michigan 48104-0520
| | - Tim R. Nagy
- Department of Nutrition, University of Alabama at Birmingham, Birmingham, Alabama 35294
| | - Bruce A. Hamilton
- University of California School of Medicine, San Diego, La Jolla, California 92093-0644
| | - Vytas A. Bankaitis
- Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599-7090
- To whom correspondence should be addressed. Tel.: 919-962-9870; Fax: 919-966-1856;
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Abstract
The molecular machines that drive protein transport through the secretory pathway function exert their activities on the surfaces of membrane bilayers. It is now clear that the various lipid components of these bilayers play direct and versatile roles in modulating the activity of proteins that either themselves constitute core components of the membrane trafficking machinery, or represent proteins that regulate such core components.
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Affiliation(s)
- Vytas A Bankaitis
- Department of Cell and Developmental Biology, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7090, USA.
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Current Awareness on Yeast. Yeast 2003. [DOI: 10.1002/yea.940] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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