301
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Yuan H, Takeuchi E, Salant DJ. Podocyte slit-diaphragm protein nephrin is linked to the actin cytoskeleton. Am J Physiol Renal Physiol 2002; 282:F585-91. [PMID: 11880318 DOI: 10.1152/ajprenal.00290.2001] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Nephrin is an Ig-like transmembrane protein. It is a major component of the podocyte slit diaphragm and is essential for maintaining normal glomerular permeability. CD2-associated protein (CD2AP) is also necessary for normal glomerular permeability and is a putative nephrin adapter molecule. Here, we document that nephrin and CD2AP are linked to the actin cytoskeleton. As detected by Western blot analysis, nephrin and CD2AP were both insoluble when cell membranes from normal rat glomeruli were extracted with 0.5% Triton X-100 (TX-100) at 4 degrees C in the presence of divalent cations, but they were solubilized when the extraction included potassium iodide (KI) to depolymerize F-actin. In addition, a small fraction of the solubilized nephrin and CD2AP was recovered in the low-density fractions of OptiPrep flotation gradients, which indicates that a portion of nephrin, possibly associated with CD2AP, resides in a cholesterol- or sphingolipid-rich region of the plasma membrane. Immunofluorescent staining of unfixed sections of normal rat kidney for nephrin, CD2AP, and F-actin was unaltered by treatment with TX-100 but was greatly diminished by addition of KI. Nephrin staining was slightly reduced by cholesterol depletion with methyl-beta-cyclodextrin in the presence of TX-100 but was nearly absent after addition of KI. These results document that nephrin anchors the slit diaphragm to the actin cytoskeleton, possibly by linkage to CD2AP, and that nephrin traverses a relatively cholesterol-poor region of the podocyte plasma membrane. In addition, a small pool of actin-associated nephrin and CD2AP resides in lipid rafts, possibly in the cholesterol-rich apical region of the podocyte-foot processes.
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Affiliation(s)
- Huaiping Yuan
- Evans Biomedical Research Center, Department of Medicine, Boston University Medical Center, Boston, Massachusetts 02118, USA
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302
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Ahn A, Gibbons DL, Kielian M. The fusion peptide of Semliki Forest virus associates with sterol-rich membrane domains. J Virol 2002; 76:3267-75. [PMID: 11884551 PMCID: PMC136022 DOI: 10.1128/jvi.76.7.3267-3275.2002] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Semliki Forest virus (SFV) is an enveloped alphavirus whose membrane fusion is triggered by low pH and promoted by cholesterol and sphingolipid in the target membrane. Fusion is mediated by E1, a viral membrane protein containing the putative fusion peptide. Virus mutant studies indicate that SFV's cholesterol dependence is controlled by regions of E1 outside of the fusion peptide. Both E1 and E1*, a soluble ectodomain form of E1, interact with membranes in a reaction dependent on low pH, cholesterol, and sphingolipid and form highly stable homotrimers. Here we have used detergent extraction and gradient floatation experiments to demonstrate that E1* associated selectively with detergent-resistant membrane domains (DRMs or rafts). In contrast, reconstituted full-length E1 protein or influenza virus fusion peptide was not associated with DRMs. Methyl beta-cyclodextrin quantitatively extracted both cholesterol and E1* from membranes in the absence of detergent, suggesting a strong association of E1* with sterol. Monoclonal antibody studies demonstrated that raft association was mediated by the proposed E1 fusion peptide. Thus, although other regions of E1 are implicated in the control of virus cholesterol dependence, once the SFV fusion peptide inserts in the target membrane it has a high affinity for membrane domains enriched in cholesterol and sphingolipid.
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Affiliation(s)
- Anna Ahn
- Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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303
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Bavari S, Bosio CM, Wiegand E, Ruthel G, Will AB, Geisbert TW, Hevey M, Schmaljohn C, Schmaljohn A, Aman MJ. Lipid raft microdomains: a gateway for compartmentalized trafficking of Ebola and Marburg viruses. J Exp Med 2002; 195:593-602. [PMID: 11877482 PMCID: PMC2193767 DOI: 10.1084/jem.20011500] [Citation(s) in RCA: 368] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
Spatiotemporal aspects of filovirus entry and release are poorly understood. Lipid rafts act as functional platforms for multiple cellular signaling and trafficking processes. Here, we report the compartmentalization of Ebola and Marburg viral proteins within lipid rafts during viral assembly and budding. Filoviruses released from infected cells incorporated raft-associated molecules, suggesting that viral exit occurs at the rafts. Ectopic expression of Ebola matrix protein and glycoprotein supported raft-dependent release of filamentous, virus-like particles (VLPs), strikingly similar to live virus as revealed by electron microscopy. Our findings also revealed that the entry of filoviruses requires functional rafts, identifying rafts as the site of virus attack. The identification of rafts as the gateway for the entry and exit of filoviruses and raft-dependent generation of VLPs have important implications for development of therapeutics and vaccination strategies against infections with Ebola and Marburg viruses.
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Affiliation(s)
- Sina Bavari
- Dept. of Cell Biology and Biochemistry, U.S. Army Medical Research Institute of Infectious Diseases, Frederick, MD 21702-5011, USA.
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304
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Risco C, Rodríguez JR, López-Iglesias C, Carrascosa JL, Esteban M, Rodríguez D. Endoplasmic reticulum-Golgi intermediate compartment membranes and vimentin filaments participate in vaccinia virus assembly. J Virol 2002; 76:1839-55. [PMID: 11799179 PMCID: PMC135913 DOI: 10.1128/jvi.76.4.1839-1855.2002] [Citation(s) in RCA: 154] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2001] [Accepted: 11/12/2001] [Indexed: 01/31/2023] Open
Abstract
Vaccinia virus (VV) has a complex morphogenetic pathway whose first steps are poorly characterized. We have studied the early phase of VV assembly, when viral factories and spherical immature viruses (IVs) form in the cytoplasm of the infected cell. After freeze-substitution numerous cellular elements are detected around assembling viruses: membranes, ribosomes, microtubules, filaments, and unidentified structures. A double membrane is clearly resolved in the VV envelope for the first time, and freeze fracture reveals groups of tubules interacting laterally on the surface of the viroplasm foci. These data strongly support the hypothesis of a cellular tubulovesicular compartment, related to the endoplasmic reticulum-Golgi intermediate compartment (ERGIC), as the origin of the first VV envelope. Moreover, the cytoskeletal vimentin intermediate filaments are found around viral factories and inside the viroplasm foci, where vimentin and the VV core protein p39 colocalize in the areas where crescents protrude. Confocal microscopy showed that ERGIC elements and vimentin filaments concentrate in the viral factories. We propose that modified cellular ERGIC membranes and vimentin intermediate filaments act coordinately in the construction of viral factories and the first VV form through a unique mechanism of viral morphogenesis from cellular elements.
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Affiliation(s)
- Cristina Risco
- Department of Macromolecular Structure, Centro Nacional de Biotecnología Consejo Superior de Investigaciones Científicas, Campus Universidad Autónoma, Madrid 28049, Spain.
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305
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Kozak SL, Heard JM, Kabat D. Segregation of CD4 and CXCR4 into distinct lipid microdomains in T lymphocytes suggests a mechanism for membrane destabilization by human immunodeficiency virus. J Virol 2002; 76:1802-15. [PMID: 11799176 PMCID: PMC135872 DOI: 10.1128/jvi.76.4.1802-1815.2002] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Recent evidence has suggested that plasma membrane sphingolipids and cholesterol spontaneously coalesce into raft-like microdomains and that specific proteins, including CD4 and some other T-cell signaling molecules, sequester into these rafts. In agreement with these results, we found that CD4 and the associated Lck tyrosine kinase of peripheral blood mononuclear cells and H9 leukemic T cells were selectively and highly enriched in a low-density lipid fraction that was resistant at 0 degrees C to the neutral detergent Triton X-100 but was disrupted by extraction of cholesterol with filipin or methyl-beta-cyclodextrin. In contrast, the CXCR4 chemokine receptor, a coreceptor for X4 strains of human immunodeficiency virus type 1 (HIV-1), was almost completely excluded from the detergent-resistant raft fraction. Accordingly, as determined by immunofluorescence with confocal microscopy, CD4 and CXCR4 did not coaggregate into antibody-induced cell surface patches or into patches of CXCR4 that formed naturally at the ruffled edges of adherent cells. The CXCR4 fluorescent patches were extracted with cold 1% Triton X-100, whereas the CD4 patches were resistant. In stringent support of these data, CD4 colocalized with patches of cholera toxin bound to the raft-associated sphingoglycolipid GM1, whereas CXCR4 did not. Addition of the CXCR4-activating chemokine SDF-1 alpha did not induce CXCR4 movement into rafts. Moreover, binding of purified monomeric gp120 envelope glycoproteins from strains of HIV-1 that use this coreceptor did not stimulate detectable redistributions of CD4 or CXCR4 between their separate membrane domains. However, adsorption of multivalent gp120-containing HIV-1 virion particles appeared to destabilize the local CD4-containing rafts. Indeed, adsorbed HIV-1 virions were detected by immunofluorescence microscopy and were almost all situated in nonraft regions of the cell surface. We conclude that HIV-1 initially binds to CD4 in a raft domain and that its secondary associations with CXCR4 require shifts of proteins and associated lipids away from their preferred lipid microenvironments. Our evidence suggests that these changes in protein-lipid interactions destabilize the plasma membrane microenvironment underlying the virus by at least several kilocalories per mole, and we propose that this makes an important contribution to fusion of the viral and cellular membranes during infection. Thus, binding of HIV-1 may be favored by the presence of CD4 in rafts, but the rafts may then disperse prior to the membrane fusion reaction.
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Affiliation(s)
- Susan L Kozak
- Department of Biochemistry and Molecular Biology, Oregon Health Sciences University, Portland, Oregon 97201-3098, USA
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306
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Influenza virus replication. ACTA ACUST UNITED AC 2002. [DOI: 10.1016/s0168-7069(02)07002-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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307
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Blom TS, Koivusalo M, Kuismanen E, Kostiainen R, Somerharju P, Ikonen E. Mass spectrometric analysis reveals an increase in plasma membrane polyunsaturated phospholipid species upon cellular cholesterol loading. Biochemistry 2001; 40:14635-44. [PMID: 11724577 DOI: 10.1021/bi0156714] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Here we used electrospray ionization mass spectrometry for quantitative determination of lipid molecular species in human fibroblasts and their plasma membrane incorporated into enveloped viruses. Both influenza virus selecting ordered domains and vesicular stomatitis virus (VSV) depleted of such domains [Scheiffele, P., et al. (1999) J. Biol. Chem. 274, 2038-2044] were analyzed. The major difference between influenza and VSV was found to be a marked enrichment of glycosphingolipids in the former. The effect of chronic cholesterol loading on viral lipid composition was studied in Niemann-Pick type C (NPC) fibroblasts. Both NPC-derived influenza and VSV virions contained increased amounts of cholesterol. Furthermore, polyunsaturated phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine were enriched in NPC-derived virions at the expense of the monounsaturated ones. When normal fibroblasts were acutely loaded with cholesterol using cyclodextrin complexes, an adjustment toward increasingly unsaturated phospholipid species was observed, most clearly for phosphatidylcholine and sphingomyelin. Our results provide evidence that (1) glycosphingolipids are enriched in domains through which influenza virus buds, (2) chronic cholesterol accumulation increases the cholesterol content of both glycosphingolipid-enriched and intervening plasma membrane domains, and (3) an increase in membrane cholesterol content is accompanied by an increased level of polyunsaturated species of the major membrane phospholipids. We suggest that remodeling of phospholipids toward higher unsaturation may serve as both an acute and a long-term adaptive mechanism in human cellular membranes against cholesterol excess.
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Affiliation(s)
- T S Blom
- Department of Molecular Medicine, National Public Health Institute, Viikki Drug Discovery Technology Center, University of Helsinki, Helsinki, Finland
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308
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Li X, Galli T, Leu S, Wade JB, Weinman EJ, Leung G, Cheong A, Louvard D, Donowitz M. Na+-H+ exchanger 3 (NHE3) is present in lipid rafts in the rabbit ileal brush border: a role for rafts in trafficking and rapid stimulation of NHE3. J Physiol 2001; 537:537-52. [PMID: 11731584 PMCID: PMC2278967 DOI: 10.1111/j.1469-7793.2001.00537.x] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2001] [Accepted: 08/03/2001] [Indexed: 11/29/2022] Open
Abstract
1. Rabbit ileal Na+-absorbing cell Na+-H+ exchanger 3 (NHE3) was shown to exist in three pools in the brush border (BB), including a population in lipid rafts. Approximately 50% of BB NHE3 was associated with Triton X-100-soluble fractions and the other approximately 50% with Triton X-100-insoluble fractions; approximately 33% of the detergent-insoluble NHE3 was present in cholesterol-enriched lipid microdomains (rafts). 2. The raft pool of NHE3 was involved in the stimulation of BB NHE3 activity with epidermal growth factor (EGF). Both EGF and clonidine treatments were associated with a rapid increase in the total amount of BB NHE3. This EGF- and clonidine-induced increase of BB NHE3 was associated with an increase in the raft pool of NHE3 and to a smaller extent with an increase in the total detergent-insoluble fraction, but there was no change in the detergent-soluble pool. In agreement with the rapid increase in the amount of NHE3 in the BB, EGF also caused a rapid stimulation of BB Na+-H+ exchange activity. 3. Disrupting rafts by removal of cholesterol with methyl-beta-cyclodextrin (MbetaCD) or destabilizing the actin cytoskeleton with cytochalasin D decreased the amount of NHE3 in early endosomes isolated by OptiPrep gradient fractionation. Specifically, NHE3 was shown to associate with endosomal vesicles immunoisolated by anti-EEA1 (early endosomal autoantigen 1) antibody-coated magnetic beads and the endosome-associated NHE3 was decreased by cytochalasin D and MbetaCD treatment. 4. We conclude that: (i) a pool of ileal BB NHE3 exists in lipid rafts; (ii) EGF and clonidine increase the amount of BB NHE3; (iii) lipid rafts and to a lesser extent, the cytoskeleton, but not the detergent-soluble NHE3 pool, are involved in the EGF- and clonidine-induced acute increase in amount of BB NHE3; (iv) lipid rafts and the actin cytoskeleton play important roles in the basal endocytosis of BB NHE3.
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Affiliation(s)
- X Li
- Department of Medicine, GI Division, Johns Hopkins University School of Medicine, Baltimore, MD 21205-2195, USA
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309
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Abstract
Influenza viruses bud from the plasma membrane of virus-infected cells. Although budding is a critical step in virus replication, little is known about the requirements of the budding process. In this report, we have investigated the role of ATP in influenza virus budding by treating influenza virus infected Madin-Darby canine kidney (MDCK) cells with a number of metabolic inhibitors. When WSN virus-infected MDCK cells were exposed to antimycin A, carbonyl cyanide m-chlorophenylhydrazone, carbonyl cyanide p-trifluoromethoxy-phenylhydrazone, or oligomycin for a short time (15 min or 1 h) late in the infectious cycle, the rate of virus budding decreased. This inhibitory effect was reversible upon removal of the inhibitors. The role of ATP hydrolysis was analyzed by treating lysophosphatidylcholine (LPC)-permeabilized live filter-grown virus-infected MDCK cells with nonpermeable ATP analogues from the basal side and assaying virus budding from the apical side. In LPC-permeabilized cells, membrane-impermeable ATP analogues such as adenosine 5'-O-(3-thiotriphosphate) or 5'-adenylylimidodiphosphate caused reduction of virus budding which could be partially restored by adding excess ATP. These data demonstrated that ATP hydrolysis and not just ATP binding was required for virus budding. However, inhibitors of ion channel (ATPases) and protein ubiquitinylation, which also required the ATP as energy source, did not affect influenza virus budding, suggesting that neither ion channel nor protein ubiquitinylation activity was involved in influenza virus budding. On the other hand, treatment with dimethyl sulfoxide (DMSO), which decreases membrane viscosity, reduced the rate of virus budding, demonstrating that the physical state of membrane viscosity and membrane fluidity had an important effect on virus budding. Data presented in the report indicate that influenza virus budding is an active ATP-dependent process and suggest that reduced virus budding by ATP depletion and DMSO treatment may be partly due to decreased membrane viscosity.
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Affiliation(s)
- E K Hui
- Department of Microbiology, Immunology, and Molecular Genetics, UCLA School of Medicine, Los Angeles, California 90095-1747, USA
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310
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Ono A, Freed EO. Plasma membrane rafts play a critical role in HIV-1 assembly and release. Proc Natl Acad Sci U S A 2001; 98:13925-30. [PMID: 11717449 PMCID: PMC61143 DOI: 10.1073/pnas.241320298] [Citation(s) in RCA: 524] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
HIV-1 particle production occurs in a series of steps promoted by the viral Gag protein. Although it is well established that assembly and release take place at the plasma membrane, the nature of membrane assembly sites remains poorly understood. We show here that Gag specifically associates with cholesterol-enriched microdomains ("rafts") at the plasma membrane. Kinetic studies demonstrate that raft association follows membrane binding, and the analysis of Gag mutants reveals that, whereas the N terminus of Gag mediates raft binding, this association is greatly enhanced by Gag-Gag interaction domains. We observe that depletion of cellular cholesterol markedly and specifically reduces HIV-1 particle production. Furthermore, treatment of virus-producing cells or virus particles with raft-disrupting agents significantly impairs virus infectivity. These results identify the association of Gag with plasma membrane rafts as an important step in HIV-1 replication. These findings may lead to novel strategies for suppressing HIV-1 replication in vivo.
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Affiliation(s)
- A Ono
- Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Building 4, Room 307, 9000 Rockville Pike, Bethesda, MD 20892-0460, USA
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311
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Korte T, Epand RF, Epand RM, Blumenthal R. Role of the Glu residues of the influenza hemagglutinin fusion peptide in the pH dependence of fusion activity. Virology 2001; 289:353-61. [PMID: 11689057 DOI: 10.1006/viro.2001.1108] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To elucidate the role of the fusion peptide in influenza hemagglutinin (HA)-mediated fusion, we compared pH-dependent conformational changes and fusion mediated by wild-type and a mutant HA in which Glu residues at positions 11 and 15 of the fusion peptide are substituted for valine. The pH dependence of conformational changes and kinetics of fusion with erythrocytes was the same for both forms of HA. The time for commitment and the temperature dependence of HA-mediated fusion were also the same. However, striking differences were observed between wild-type and mutant fusion peptides in their interactions with lipid membranes at neutral and acidic pH. Since elimination of the negatively charged residues allows the exposed fusion peptide to penetrate the bilayer at pH values closer to neutral, but does not affect conformational changes and fusion activity in intact HA, we conclude that conformational changes are tightly coupled to fusion peptide insertion in the overall HA-mediated fusion cascade.
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Affiliation(s)
- T Korte
- Laboratory of Experimental and Computational Biology, National Institutes of Health, Frederick, Maryland 21702, USA
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312
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Abstract
BACKGROUND Lipid rafts are currently an intensely investigated topic of cell biology. In addition to a demonstrated role in signal transduction of the host cell, lipid rafts serve as entry and exit sites for microbial pathogens and toxins, such as FimH-expressing enterobacteria, influenza virus, measles virus and cholera toxin. Furthermore, caveolae, a specialised form of lipid raft, are required for the conversion of the non-pathogenic prion protein to the pathogenic scrapie isoform. OBJECTIVES A number of reports have shown, directly or indirectly, that lipid rafts are important at various stages of the human immunodeficiency virus type-1 (HIV-1) replication cycle. The purpose of this paper is to provide a brief overview of the role of membrane-associated lipid rafts in cell biology, and to evaluate how HIV-1 has hijacked this cellular component to support HIV-1 replication. Special sections are devoted to discussing the role of lipid rafts in (1) the entry of HIV-1, (2) signal transduction regulation in HIV-1-infected cells, (3) the trafficking of HIV-1 proteins via lipid rafts during HIV-1 assembly; and a further section discusses the role of cholesterol in mature HIV-1. SUMMARY Like a number of other pathogens, HIV-1 has evolved to rely on the host cell lipid rafts to support its propagation during multiple stages of the HIV-1 replication cycle. This review has highlighted the importance of lipid rafts in HIV-1 replication.
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Affiliation(s)
- S M Campbell
- AIDS Pathogenesis Research Unit, Macfarlane Burnet Centre for Medical Research, Fairfield, Victoria 3078, Australia
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313
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Xu X, Bittman R, Duportail G, Heissler D, Vilcheze C, London E. Effect of the structure of natural sterols and sphingolipids on the formation of ordered sphingolipid/sterol domains (rafts). Comparison of cholesterol to plant, fungal, and disease-associated sterols and comparison of sphingomyelin, cerebrosides, and ceramide. J Biol Chem 2001; 276:33540-6. [PMID: 11432870 DOI: 10.1074/jbc.m104776200] [Citation(s) in RCA: 424] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ordered lipid domains enriched in sphingolipids and cholesterol (lipid rafts) have been implicated in numerous functions in biological membranes. We recently found that lipid domain/raft formation is dependent on the sterol component having a structure that allows tight packing with lipids having saturated acyl chains (Xu, X., and London, E. (2000) Biochemistry 39, 844-849). In this study, the domain-promoting activities of various natural sterols were compared with that of cholesterol using both fluorescence quenching and detergent insolubility methods. Using model membranes, it was shown that, like cholesterol, both plant and fungal sterols promote the formation of tightly packed, ordered lipid domains by lipids with saturated acyl chains. Surprisingly ergosterol, a fungal sterol, and 7-dehydrocholesterol, a sterol present in elevated levels in Smith-Lemli-Opitz syndrome, were both significantly more strongly domain-promoting than cholesterol. Domain formation was also affected by the structure of the sphingolipid (or that of an equivalent "saturated" phospholipid) component. Sterols had pronounced effects on domain formation by sphingomyelin and dipalmitoylphosphatidylcholine but only a weak influence on the ability of cerebrosides to form domains. Strikingly it was found that a small amount of ceramide (3 mol %) significantly stabilized domain/raft formation. The molecular basis for, and the implications of, the effects of different sterols and sphingolipids (especially ceramide) on the behavior and biological function of rafts are discussed.
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Affiliation(s)
- X Xu
- Department of Biochemistry and Cell Biology, State University of New York at Stony Brook, Stony Brook, New York 11794-5215, USA
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314
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Lindwasser OW, Resh MD. Multimerization of human immunodeficiency virus type 1 Gag promotes its localization to barges, raft-like membrane microdomains. J Virol 2001; 75:7913-24. [PMID: 11483736 PMCID: PMC115035 DOI: 10.1128/jvi.75.17.7913-7924.2001] [Citation(s) in RCA: 206] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Gag polyprotein of human immunodeficiency virus type 1 (HIV-1) organizes the assembly of nascent virions at the plasma membrane of infected cells. Here we demonstrate that a population of Gag is present in distinct raft-like membrane microdomains that we have termed "barges." Barges have a higher density than standard rafts, most likely due to the presence of oligomeric Gag-Gag assembly complexes. The regions of the Gag protein responsible for barge targeting were mapped by examining the flotation behavior of wild-type and mutant proteins on Optiprep density gradients. N-myristoylation of Gag was necessary for association with barges. Removal of the NC and p6 domains shifted much of the Gag from barges into typical raft fractions. These data are consistent with a model in which multimerization of myristoylated Gag proteins drives association of Gag oligomers into raft-like barges. The functional significance of barge association was revealed by several lines of evidence. First, Gag isolated from virus-like particles was almost entirely localized in barges. Moreover, a comparison of wild-type Gag with Fyn(10)Gag, a chimeric protein containing the N-terminal sequence of Fyn, revealed that Fyn(10)Gag exhibited increased affinity for barges and a two- to fourfold increase in particle production. These results imply that association of Gag with raft-like barge membrane microdomains plays an important role in the HIV-1 assembly process.
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Affiliation(s)
- O W Lindwasser
- Cell Biology Program, Memorial Sloan-Kettering Cancer Center, and Graduate Program in Cell Biology and Genetics, Weill Graduate School of Medical Sciences of Cornell University, New York, New York 10021, USA
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315
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Abstract
Cholesterol-sphingolipid microdomains (lipid rafts) are part of the machinery ensuring correct intracellular trafficking of proteins and lipids. The most apparent roles of rafts are in sorting and vesicle formation, although their roles in vesicle movement and cytoskeletal connections as well as in vesicle docking and fusion are coming into focus. New evidence suggests that compositionally distinct lipid microdomains are assembled and may coexist within a given membrane. Important clues have also been uncovered about the mechanisms coupling raft-dependent signaling and endocytic uptake.
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Affiliation(s)
- E Ikonen
- Department of Molecular Medicine, National Public Health Institute, Biomedicum Helsinki, PO Box 104, Haartmaninkatu 8, 00251, Helsinki, Finland.
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316
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Abstract
Specific interactions between envelope and core proteins govern the membrane assembly of most enveloped viruses. Despite this, mixed infections lead to pseudotyping, the association of the viral cores of one virus with the envelopes of another. How does this occur? We show here that the detergent-insoluble lipid rafts of the plasma membrane function as a natural meeting point for the transmembrane and core components of a phylogenetically diverse collection of enveloped viruses. As a result, viral particles preferentially incorporate both the envelope components of other viruses as well as the extra- and intracellular constituents of host cell lipid rafts, including gangliosides, glycosyl phosphatidylinositol-anchored surface proteins, and intracellular signal transduction molecules. Pharmacological disruption of lipid rafts interferes with virus production.
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Affiliation(s)
- W F Pickl
- Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
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317
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Niyogi K, Hildreth JE. Characterization of new syncytium-inhibiting monoclonal antibodies implicates lipid rafts in human T-cell leukemia virus type 1 syncytium formation. J Virol 2001; 75:7351-61. [PMID: 11462007 PMCID: PMC114970 DOI: 10.1128/jvi.75.16.7351-7361.2001] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
We have previously shown that erythroleukemia cells (K562) transfected with vascular adhesion molecule 1 (VCAM-1) are susceptible to human T-cell leukemia virus type 1 (HTLV-1)-induced syncytium formation. Since expression of VCAM-1 alone is not sufficient to render cells susceptible to HTLV-1 fusion, K562 cells appear to express a second molecule critical for HTLV-induced syncytium formation. By immunizing mice with K562 cells, we have isolated four monoclonal antibodies (MAbs), K5.M1, K5.M2, K5.M3, and K5.M4, that inhibit HTLV-induced syncytium formation between infected MT2 cells and susceptible K562/VCAM1 cells. These MAbs recognize distinct proteins on the surface of cells as determined by cell phenotyping, immunoprecipitation, and Western blot analysis. Since three of the proteins recognized by the MAbs appear to be GPI linked, we isolated lipid rafts and determined by immunoblot analysis that all four MAbs recognize proteins that sort entirely or in large part to lipid rafts. Dispersion of lipid rafts on the cells by cholesterol depletion with beta-cyclodextrin resulted in inhibition of syncytium formation, and this effect was not seen when the beta-cyclodextrin was preloaded with cholesterol before treating the cells. The results of these studies suggest that lipid rafts may play an important role in HTLV-1 syncytium formation.
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Affiliation(s)
- K Niyogi
- The Leukocyte Immunochemistry Laboratory, Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 212056, USA
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318
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Liao Z, Cimakasky LM, Hampton R, Nguyen DH, Hildreth JE. Lipid rafts and HIV pathogenesis: host membrane cholesterol is required for infection by HIV type 1. AIDS Res Hum Retroviruses 2001; 17:1009-19. [PMID: 11485618 DOI: 10.1089/088922201300343690] [Citation(s) in RCA: 272] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In a previous study we showed that budding of HIV-1 particles occurs at highly specialized membrane microdomains known as lipid rafts. These microdomains are characterized by a distinct lipid composition that includes high concentrations of cholesterol, sphingolipids, and glycolipids. Since cholesterol is known to play a key role in the entry of some other viruses, our observation of HIV budding from lipid rafts led us to investigate the role in HIV-1 entry of cholesterol and lipid rafts in the plasma membrane of susceptible cells. We have used 2-OH-propyl-beta-cyclodextrin (beta-cyclodextrin) to deplete cellular cholesterol and disperse lipid rafts. Our results show that removal of cellular cholesterol rendered primary cells and cell lines highly resistant to HIV-1-mediated syncytium formation and to infection by both CXCR4- and CCR5-specific viruses. beta-Cyclodextrin treatment of cells partially reduced HIV-1 binding, while rendering chemokine receptors highly sensitive to antibody-mediated internalization. There was no effect on CD4 expression. All of the above-described effects were readily reversed by incubating cholesterol-depleted cells with low concentrations of cholesterol-loaded beta-cyclodextrin to restore cholesterol levels. Cholesterol depletion made cells resistant to SDF-1-induced binding to ICAM-1 through LFA-1. Since LFA-1 contributes significantly to cell binding by HIV-1, this latter effect may have contributed to the observed reduction in HIV-1 binding to cells after treatment with beta-cyclodextrin. Our results indicate that cholesterol may be critical to the HIV-1 coreceptor function of chemokine receptors and is required for infection of cells by HIV-1.
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Affiliation(s)
- Z Liao
- Immunochemistry Laboratory, Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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319
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Puertollano R, Martínez-Menárguez JA, Batista A, Ballesta J, Alonso MA. An intact dilysine-like motif in the carboxyl terminus of MAL is required for normal apical transport of the influenza virus hemagglutinin cargo protein in epithelial Madin-Darby canine kidney cells. Mol Biol Cell 2001; 12:1869-83. [PMID: 11408592 PMCID: PMC37348 DOI: 10.1091/mbc.12.6.1869] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2000] [Revised: 02/27/2001] [Accepted: 04/02/2001] [Indexed: 01/12/2023] Open
Abstract
The MAL proteolipid, a component of the integral protein sorting machinery, has been demonstrated as being necessary for normal apical transport of the influenza virus hemagglutinin (HA) and the overall apical membrane proteins in Madin-Darby canine kidney (MDCK) cells. The MAL carboxy terminus ends with the sequence Arg-Trp-Lys-Ser-Ser (RWKSS), which resembles dilysine-based motifs involved in protein sorting. To investigate whether the RWKSS pentapeptide plays a role in modulating the distribution of MAL and/or its function in apical transport, we have expressed MAL proteins with distinct carboxy terminus in MDCK cells whose apical transport was impaired by depletion of endogenous MAL. Apical transport of HA was restored to normal levels by expression of MAL with an intact but not with modified carboxyl terminal sequences bearing mutations that impair the functioning of dilysine-based sorting signals, although all the MAL proteins analyzed incorporated efficiently into lipid rafts. Ultrastructural analysis indicated that compared with MAL bearing an intact RWKSS sequence, a mutant with lysine -3 substituted by serine showed a twofold increased presence in clathrin-coated cytoplasmic structures and a reduced expression on the plasma membrane. These results indicate that the carboxyl-terminal RWKSS sequence modulates the distribution of MAL in clathrin-coated elements and is necessary for HA transport to the apical surface.
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Affiliation(s)
- R Puertollano
- Centro de Biología Molecular "Severo Ochoa," Universidad Autónoma de Madrid, Spain
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320
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Morikawa Y, Kinoshita A, Goto T, Tomoda H, Sano K. Membrane relocation but not tight binding of human immunodeficiency virus type 1 Gag particles myristoylated in Escherichia coli. Virology 2001; 283:343-52. [PMID: 11336559 DOI: 10.1006/viro.2001.0886] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Expression of human immunodeficiency virus Gag protein and the N-terminal matrix (MA) domain in Escherichia coli yielded spherical structures in the cytoplasm. When human N-myristoyltransferase was coexpressed, both Gag and MA were fully myristoylated and spherical structures were relocated in close proximity to the cytoplasmic membrane. However, neither myristoylated Gag nor MA exhibited tight binding to E. coli membrane, suggesting that myristoylation in E. coli did not confer membrane affinity on Gag despite the relocation. Our data also suggest that the morphogenetic pathway of Gag particles in prokaryotic cells differs from that in eukaryotic cells despite biochemical similarities of in the form of Gag expressed.
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Affiliation(s)
- Y Morikawa
- The Kitasato Institute, Shirokane 5-9-1, Minato-ku, Tokyo 108-8642, Japan.
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321
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Gower TL, Graham BS. Antiviral activity of lovastatin against respiratory syncytial virus in vivo and in vitro. Antimicrob Agents Chemother 2001; 45:1231-7. [PMID: 11257039 PMCID: PMC90448 DOI: 10.1128/aac.45.4.1231-1237.2001] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Respiratory syncytial virus (RSV) is an important human pathogen that can cause severe and life-threatening respiratory infections in infants and immunocompromised adults. We have recently shown that the RSV F glycoprotein, which mediates viral fusion, binds to RhoA. One of the steps in RhoA activation involves isoprenylation at the carboxy terminus of the protein by geranylgeranyltransferase. This modification allows RhoA to be attached to phosphatidyl serine on the inner leaflet of the plasma membrane. Treatment of mice with lovastatin, a drug that inhibits prenylation pathways in the cell by directly inhibiting hydroxymethylglutaryl coenzyme A reductase, diminishes RSV but not vaccinia virus replication when administered up to 24 h after RSV infection and decreases virus-induced weight loss and illness in mice. The inhibition of replication is not likely due to the inhibition of cholesterol biosynthesis, since gemfibrozil, another cholesterol-lowering agent, did not affect virus replication and serum cholesterol levels were not significantly lowered by lovastatin within the time frame of the experiment. Lovastatin also reduces cell-to-cell fusion in cell culture and eliminates RSV replication in HEp-2 cells. These data indicate that lovastatin, more specific isoprenylation inhibitors, or other pharmacological approaches for preventing RhoA membrane localization should be considered for evaluation as a preventive antiviral therapy for selected groups of patients at high risk for severe RSV disease, such as the institutionalized elderly and bone marrow or lung transplant recipients.
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Affiliation(s)
- T L Gower
- Department of Microbiology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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322
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van der Goot FG, Harder T. Raft membrane domains: from a liquid-ordered membrane phase to a site of pathogen attack. Semin Immunol 2001; 13:89-97. [PMID: 11308292 DOI: 10.1006/smim.2000.0300] [Citation(s) in RCA: 197] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
While the existence of cholesterol/sphingolipid (raft) membrane domains in the plasma membrane is now supported by strong experimental evidence, the structure of these domains, their size, their dynamics, and their molecular composition remain to be understood. Raft domains are thought to represent a specific physical state of lipid bilayers, the liquid-ordered phase. Recent observations suggest that in the mammalian plasma membrane small raft domains in ordered lipid phases are in a dynamic equilibrium with a less ordered membrane environment. Rafts may be enlarged and/or stabilized by protein-mediated cross-linking of raft-associated components. These changes of plasma membrane structure are perceived by the cells as signals, most likely an important element of immunoreceptor signalling. Pathogens abuse raft domains on the host cell plasma membrane as concentration devices, as signalling platforms and/or entry sites into the cell. Elucidation of these interactions requires a detailed understanding raft structure and dynamics.
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Affiliation(s)
- F G van der Goot
- Department of Biochemistry, University of Geneva, 1211 Geneva, 30 quai E. Ansermet, Switzerland.
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323
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Kawasaki K, Yin JJ, Subczynski WK, Hyde JS, Kusumi A. Pulse EPR detection of lipid exchange between protein-rich raft and bulk domains in the membrane: methodology development and its application to studies of influenza viral membrane. Biophys J 2001; 80:738-48. [PMID: 11159441 PMCID: PMC1301272 DOI: 10.1016/s0006-3495(01)76053-5] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
A pulse saturation-recovery electron paramagnetic resonance (EPR) method has been developed that allows estimation of the exchange rates of a spin-labeled lipid between the bulk domain and the protein-rich membrane domain, in which the rate of collision between the spin label and molecular oxygen is reduced (slow-oxygen transport domain, or SLOT domain). It is based on the measurements of saturation-recovery signals of a lipid spin label as a function of concentrations of both molecular oxygen and the spin label. Influenza viral membrane, one of the simplest paradigms for the study of biomembranes, showed the presence of two membrane domains with slow and fast collision rates with oxygen (a 16-fold difference) at 30 degrees C. The outbound rate from and the inbound rate into the SLOT domain (or possibly the rate of the domain disintegration and formation) were estimated to be 7.7 x 10(4) and 4.6 x 10(4) s(-1), (15 micros residency time), respectively, indicating that the SLOT domain is highly dynamic and that the entire SLOT domain represents about one-third of the membrane area. Because the oxygen transport rate in the SLOT domain is a factor of two smaller than that in purple membrane, where bacteriorhodopsin is aggregated, we propose that the SLOT domain in the viral membrane is the cholesterol-rich raft domain stabilized by the trimers of hemagglutinin and/or the tetramers of neuraminidase.
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Affiliation(s)
- K Kawasaki
- National Institute of Bioscience and Human Technology, Tsukuba 305-8566, Japan
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324
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Flood EA, McKenzie MO, Lyles DS. Role of M protein aggregation in defective assembly of temperature-sensitive M protein mutants of vesicular stomatitis virus. Virology 2000; 278:520-33. [PMID: 11118374 DOI: 10.1006/viro.2000.0675] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The goal of these experiments was to determine the steps in virus assembly that are defective at the nonpermissive temperature in temperature-sensitive (ts) matrix (M) protein mutants of vesicular stomatitis virus. It has been proposed that mutations in M protein either reduce the binding affinity for nucleocapsids or lead to aggregation, reducing the amount of M protein available for virus assembly. Cytosolic or membrane-derived M proteins from wild-type VSV and two ts M protein mutant viruses, tsM301 and tsO23, as well as a revertant of tsO23 virus, O23R1, were analyzed for binding to nucleocapsid-M protein (NCM) complexes and for M protein aggregation. The experiments presented here showed that ts M proteins synthesized at the nonpermissive temperature were capable of binding to nucleocapsids and that aggregation of ts M proteins did not reduce the amount of soluble M protein below the amount required for assembly of the O23R1 virus. Instead, the most pronounced defect in ts M proteins was in the ability of membrane-derived M proteins to be solubilized in the presence of the detergent Triton X-100. It is proposed that this detergent-insoluble form of M protein interferes with a step necessary to initiate assembly of NCM complexes. A similar detergent, Triton X-114, caused aggregation of membrane-derived wild-type M protein, disproving an earlier proposal that membrane-derived M protein behaves like an integral membrane protein in the presence of Triton X-114. Aggregation of wild-type M protein in the presence of Triton X-100 could be induced by incubation at 37 degrees C with a high-molecular-weight fraction isolated from uninfected cells by sucrose gradient centrifugation. These results implicate host components in inducing M protein aggregation.
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Affiliation(s)
- E A Flood
- Molecular Genetics Program, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157-1064, USA
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325
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Scianimanico S, Schoehn G, Timmins J, Ruigrok RH, Klenk HD, Weissenhorn W. Membrane association induces a conformational change in the Ebola virus matrix protein. EMBO J 2000; 19:6732-41. [PMID: 11118208 PMCID: PMC305896 DOI: 10.1093/emboj/19.24.6732] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The matrix protein VP40 from Ebola virus is targeted to the plasma membrane, where it is thought to induce assembly and budding of virions through its association with the lipid bilayer. Ebola virus VP40 is expressed as a monomeric molecule in solution, consisting of two loosely associated domains. Here we show that a C-terminal truncation of seven residues destabilizes the monomeric closed conformation and induces spontaneous hexamerization in solution, as indicated by chemical cross-linking and electron microscopy. Three-dimensional reconstruction of electron microscopy images shows ring-like structures consisting of the N-terminal domain along with evidence for flexibly attached C-terminal domains. In vitro destabilization of the monomer by urea treatment results in similar hexameric molecules in solution. In addition, we demonstrate that membrane association of wild-type VP40 also induces the conformational switch from monomeric to hexameric molecules that may form the building blocks for initiation of virus assembly and budding. Such a conformational change induced by bilayer targeting may be a common feature of many viral matrix proteins and its potential inhibition may result in new anti-viral therapies.
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Affiliation(s)
- S Scianimanico
- European Molecular Biology Laboratory (EMBL) Grenoble Outstation, 6 rue Jules Horowitz, 38000 Grenoble, France
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326
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Abstract
Cholesterol plays an indispensable role in regulating the properties of cell membranes in mammalian cells. Recent advances suggest that cholesterol exerts many of its actions mainly by maintaining sphingolipid rafts in a functional state. How rafts contribute to cholesterol metabolism and transport in the cell is still an open issue. It has long been known that cellular cholesterol levels are precisely controlled by biosynthesis, efflux from cells, and influx of lipoprotein cholesterol into cells. The regulation of cholesterol homeostasis is now receiving a new focus, and this changed perspective may throw light on diseases caused by cholesterol excess, the prime example being atherosclerosis.
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Affiliation(s)
- K Simons
- Max Planck Institute for Molecular Cell Biology and Genetics, Pfotenhauerstrasse, 01307 Dresden, Germany.
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327
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Abstract
The route of initial entry influences how host cells respond to intracellular pathogens. Recent studies have demonstrated that a wide variety of pathogens target lipid microdomains in host cell membranes, known as lipid rafts, to enter host cells as an infectious strategy.
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Affiliation(s)
- C M Rosenberger
- Biotechnology Laboratory and Department of Microbiology and Immunology, University of British Columbia, British Columbia V6T 1Z3, Vancouver, Canada
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328
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Lu X, Silver J. Ecotropic murine leukemia virus receptor is physically associated with caveolin and membrane rafts. Virology 2000; 276:251-8. [PMID: 11040117 DOI: 10.1006/viro.2000.0555] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We used a Sindbis virus expression system to stably express a chimeric ecotropic murine leukemia virus (MLV) receptor gene, CAT1, fused to green fluorescent protein (gfp) in BHK cells. The chimeric gene was expressed on the cell surface and functioned as an MLV receptor. Using gfp as an epitope tag, we found that CAT1 cross-immunoprecipitated with caveolin, a cellular protein associated non-clathrin-coated endocytic vesicles. Biochemical studies showed that CAT1 copurified with caveolin in a detergent-insoluble membrane fraction that forms cholesterol-rich "rafts" on the cell surface. Disruption of rafts by methyl-beta-cyclodextrin, a drug that extracts cholesterol, reduced susceptibility to MLV without decreasing surface CAT1. The results indicate that association of the MLV receptor with cholesterol-rich rafts is important for an early step in virus infection.
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Affiliation(s)
- X Lu
- Laboratory of Molecular Microbiology, National Institutes of Health, Bethesda, Maryland, 20892, USA
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329
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Simons M, Krämer EM, Thiele C, Stoffel W, Trotter J. Assembly of myelin by association of proteolipid protein with cholesterol- and galactosylceramide-rich membrane domains. J Cell Biol 2000; 151:143-54. [PMID: 11018060 PMCID: PMC2189802 DOI: 10.1083/jcb.151.1.143] [Citation(s) in RCA: 216] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Myelin is a specialized membrane enriched in glycosphingolipids and cholesterol that contains a limited spectrum of proteins. We investigated the assembly of myelin components by oligodendrocytes and analyzed the role of lipid-protein interactions in this process. Proteolipid protein (PLP), the major myelin protein, was recovered from cultured oligodendrocytes from a low-density CHAPS-insoluble membrane fraction (CIMF) enriched in myelin lipids. PLP associated with the CIMF after leaving the endoplasmic reticulum but before exiting the Golgi apparatus, suggesting that myelin lipid and protein components assemble in the Golgi complex. The specific association of PLP with myelin lipids in CIMF was supported by the finding that it was efficiently cross-linked to photoactivable cholesterol, but not to phosphatidylcholine, which is underrepresented in both myelin and CIMF. Furthermore, depletion of cholesterol or inhibition of sphingolipid synthesis in oligodendrocytes abolished the association of PLP with CIMF. Thus, PLP may be recruited to myelin rafts, represented by CIMF, via lipid-protein interactions. In contrast to oligodendrocytes, after transfection in BHK cells, PLP is absent from isolated CIMF, suggesting that PLP requires specific lipids for raft association. In mice deficient in the enzyme ceramide galactosyl transferase, which cannot synthesize the main myelin glycosphingolipids, a large fraction of PLP no longer associates with rafts. Formation of a cholesterol- and galactosylceramide-rich membrane domain (myelin rafts) may be critical for the sorting of PLP and assembly of myelin in oligodendrocytes.
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Affiliation(s)
- M Simons
- Department of Neurobiology, University of Heidelberg, 69120 Heidelberg, Germany
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330
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Abstract
All enveloped viruses must bud through a cellular membrane in order to acquire their lipid bilayer, but little is known about this important stage in virus biogenesis. We have developed a quantitative biochemical assay to monitor the budding of Semliki Forest virus (SFV), an enveloped alphavirus that buds from the plasma membrane in a reaction requiring both viral spike proteins and nucleocapsid. The assay was based on cell surface biotinylation of newly synthesized virus spike proteins and retrieval of biotinylated virions using streptavidin-conjugated magnetic particles. Budding of biotin-tagged SFV was continuous for at least 2 h, independent of microfilaments and microtubules, strongly temperature dependent, and relatively independent of continued exocytic transport. Studies of cell surface spike proteins at early times of infection showed that these spikes did not efficiently bud into virus particles and were rapidly degraded. In contrast, at later times of infection, spike protein degradation was markedly reduced and efficient budding was then observed. The previously described cholesterol requirement in SFV exit was shown to be due to a block in budding in the absence of cholesterol and correlated with the continued degradation of spike proteins at all times of virus infection in sterol-deficient cells.
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Affiliation(s)
- Y E Lu
- Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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331
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Dessen A, Volchkov V, Dolnik O, Klenk HD, Weissenhorn W. Crystal structure of the matrix protein VP40 from Ebola virus. EMBO J 2000; 19:4228-36. [PMID: 10944105 PMCID: PMC302032 DOI: 10.1093/emboj/19.16.4228] [Citation(s) in RCA: 135] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Ebola virus maturation occurs at the plasma membrane of infected cells and involves the clustering of the viral matrix protein VP40 at the assembly site as well as its interaction with the lipid bilayer. Here we report the X-ray crystal structure of VP40 from Ebola virus at 2.0 A resolution. The crystal structure reveals that Ebola virus VP40 is topologically distinct from all other known viral matrix proteins, consisting of two domains with unique folds, connected by a flexible linker. The C-terminal domain, which is absolutely required for membrane binding, contains large hydrophobic patches that may be involved in the interaction with lipid bilayers. Likewise, a highly basic region is shared between the two domains. The crystal structure reveals how the molecule may be able to switch from a monomeric conformation to a hexameric form, as observed in vitro. Its implications for the assembly process are discussed.
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Affiliation(s)
- A Dessen
- European Molecular Biology Laboratory Grenoble Outstation, 6 rue Jules Horowitz, 38000 Grenoble, France
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332
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Ruigrok RW, Schoehn G, Dessen A, Forest E, Volchkov V, Dolnik O, Klenk HD, Weissenhorn W. Structural characterization and membrane binding properties of the matrix protein VP40 of Ebola virus. J Mol Biol 2000; 300:103-12. [PMID: 10864502 DOI: 10.1006/jmbi.2000.3822] [Citation(s) in RCA: 119] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The matrix protein VP40 of Ebola virus is believed to play a central role in viral assembly as it targets the plasma membrane of infected cells and subsequently forms a tightly packed layer on the inner side of the viral envelope. Expression of VP40 in Escherichia coli and subsequent proteolysis yielded two structural variants differing by a C-terminal truncation 114 amino acid residues long. As indicated by chemical cross-linking studies and electron microscopy, the larger polypeptide was present in a monomeric form, whereas the truncated one formed hexamers. When analyzed for their in vitro binding properties, both constructs showed that only monomeric VP40 efficiently associated with membranes containing negatively charged lipids. Membrane association of truncated, hexameric VP40 was inefficient, indicating a membrane-recognition role for the C-terminal part. Based on these observations we propose that assembly of Ebola virus involves the formation of VP40 hexamers that is mediated by the N-terminal part of the polypeptide.
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Affiliation(s)
- R W Ruigrok
- Grenoble Outstation, European Molecular Biology Laboratory (EMBL), 6 rue Jules Horowitz, Grenoble, 38000, France
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333
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Shevchenko A, Loboda A, Shevchenko A, Ens W, Standing KG. MALDI quadrupole time-of-flight mass spectrometry: a powerful tool for proteomic research. Anal Chem 2000; 72:2132-41. [PMID: 10815976 DOI: 10.1021/ac9913659] [Citation(s) in RCA: 230] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A MALDI QqTOF mass spectrometer has been used to identify proteins separated by one-dimensional or two-dimensional gel electrophoresis at the femtomole level. The high mass resolution and the high mass accuracy of this instrument in both MS and MS/MS modes allow identification of a protein either by peptide mass fingerprinting of the protein digest or from tandem mass spectra acquired by collision-induced dissociation of individual peptide precursors. A peptide mass map of the digest and tandem mass spectra of multiple peptide precursor ions can be acquired from the same sample in the course of a single experiment. Database searching and acquisition of MS and MS/MS spectra can be combined in an interactive fashion, increasing the information value of the analytical data. The approach has demonstrated its usefulness in the comprehensive characterization of protein in-gel digests, in the dissection of complex protein mixtures, and in sequencing of a low molecular weight integral membrane protein. Proteins can be identified in all types of sequence databases, including an EST database. Thus, MALDI QqTOF mass spectrometry promises to have remarkable potential for advancing proteomic research.
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Affiliation(s)
- A Shevchenko
- European Molecular Biology Laboratory (EMBL), Heidelberg, Germany.
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334
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Zhang J, Pekosz A, Lamb RA. Influenza virus assembly and lipid raft microdomains: a role for the cytoplasmic tails of the spike glycoproteins. J Virol 2000; 74:4634-44. [PMID: 10775599 PMCID: PMC111983 DOI: 10.1128/jvi.74.10.4634-4644.2000] [Citation(s) in RCA: 294] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2000] [Accepted: 02/16/2000] [Indexed: 12/20/2022] Open
Abstract
Influenza viruses encoding hemagglutinin (HA) and neuraminidase (NA) glycoproteins with deletions in one or both cytoplasmic tails (HAt- or NAt-) have a reduced association with detergent-insoluble glycolipids (DIGs). Mutations which eliminated various combinations of the three palmitoylation sites in HA exhibited reduced amounts of DIG-associated HA in virus-infected cells. The influenza virus matrix (M(1)) protein was also found to be associated with DIGs, but this association was decreased in cells infected with HAt- or NAt- virus. Regardless of the amount of DIG-associated protein, the HA and NA glycoproteins were targeted primarily to the apical surface of virus-infected, polarized cells. The uncoupling of DIG association and apical transport was augmented by the observation that the influenza A virus M(2) protein as well as the influenza C virus HA-esterase-fusion glycoprotein were not associated with DIGs but were apically targeted. The reduced DIG association of HAt- and NAt- is an intrinsic property of the glycoproteins, as similar reductions in DIG association were observed when the proteins were expressed from cDNA. Examination of purified virions indicated reduced amounts of DIG-associated lipids in the envelope of HAt- and NAt- viruses. The data indicate that deletion of both the HA and NA cytoplasmic tails results in reduced DIG association and changes in both virus polypeptide and lipid composition.
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Affiliation(s)
- J Zhang
- Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, Illinois 60208-3500, USA
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335
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Lockwich TP, Liu X, Singh BB, Jadlowiec J, Weiland S, Ambudkar IS. Assembly of Trp1 in a signaling complex associated with caveolin-scaffolding lipid raft domains. J Biol Chem 2000; 275:11934-42. [PMID: 10766822 DOI: 10.1074/jbc.275.16.11934] [Citation(s) in RCA: 338] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Trp1 has been proposed as a component of the store-operated Ca(2+) entry (SOC) channel. However, neither the molecular mechanism of SOC nor the role of Trp in this process is yet understood. We have examined possible molecular interactions involved in the regulation of SOC and Trp1 and report here for the first time that Trp1 is assembled in signaling complex associated with caveolin-scaffolding lipid raft domains. Endogenous hTrp1 and caveolin-1 were present in low density fractions of Triton X-100-extracted human submandibular gland cell membranes. Depletion of plasma membrane cholesterol increased Triton X-100 solubility of Trp1 and inhibited carbachol-stimulated Ca(2+) signaling. Importantly, thapsigargin stimulated Ca(2+) influx, but not internal Ca(2+) release, and inositol 1,4,5-triphosphate (IP(3))-stimulated I(soc) were also attenuated. Furthermore, both anti-Trp1 and anti-caveolin-1 antibodies co-immunoprecipitated hTrp1, caveolin-1, Galpha(q/11), and IP(3) receptor-type 3 (IP(3)R3). These results demonstrate that caveolar microdomains provide a scaffold for (i) assembly of key Ca(2+) signaling proteins into a complex and (ii) coordination of the molecular interactions leading to the activation of SOC. Importantly, we have shown that Trp1 is also localized in this microdomain where it interacts with one or more components of this complex, including IP(3)R3. This finding is potentially important in elucidating the physiological function of Trp.
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Affiliation(s)
- T P Lockwich
- Secretory Physiology Section, Gene Therapy and Therapeutics Branch, NIDCR, National Institutes of Health, Bethesda, Maryland 20892, USA
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336
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Nguyen DH, Hildreth JE. Evidence for budding of human immunodeficiency virus type 1 selectively from glycolipid-enriched membrane lipid rafts. J Virol 2000; 74:3264-72. [PMID: 10708443 PMCID: PMC111827 DOI: 10.1128/jvi.74.7.3264-3272.2000] [Citation(s) in RCA: 614] [Impact Index Per Article: 25.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A number of recent studies have demonstrated the significance of detergent-insoluble, glycolipid-enriched membrane domains or lipid rafts, especially in regard to activation and signaling in T lymphocytes. These domains can be viewed as floating rafts composed of sphingolipids and cholesterol which sequester glycosylphosphatidylinositol (GPI)-linked proteins, such as Thy-1 and CD59. CD45, a 200-kDa transmembrane phosphatase protein, is excluded from these domains. We have found that human immunodeficiency virus type 1 (HIV-1) particles produced by infected T-cell lines acquire the GPI-linked proteins Thy-1 and CD59, as well as the ganglioside GM1, which is known to partition preferentially into lipid rafts. In contrast, despite its high expression on the cell surface, CD45 was poorly incorporated into virus particles. Confocal fluorescence microscopy revealed that HIV-1 proteins colocalized with Thy-1, CD59, GM1, and a lipid raft-specific fluorescent lipid, DiIC(16)(3), in uropods of infected Jurkat cells. CD45 did not colocalize with HIV-1 proteins and was excluded from uropods. Dot immunoassay of Triton X-100-extracted membrane fractions revealed that HIV-1 p17 matrix protein and gp41 were present in the detergent-resistant fractions and that [(3)H]myristic acid-labeled HIV Gag showed a nine-to-one enrichment in lipid rafts. We propose a model for the budding of HIV virions through lipid rafts whereby host cell cholesterol, sphingolipids, and GPI-linked proteins within these domains are incorporated into the viral envelope, perhaps as a result of preferential sorting of HIV Gag to lipid rafts.
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Affiliation(s)
- D H Nguyen
- Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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337
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Bagnat M, Keränen S, Shevchenko A, Shevchenko A, Simons K. Lipid rafts function in biosynthetic delivery of proteins to the cell surface in yeast. Proc Natl Acad Sci U S A 2000; 97:3254-9. [PMID: 10716729 PMCID: PMC16225 DOI: 10.1073/pnas.97.7.3254] [Citation(s) in RCA: 403] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Lipid rafts, formed by lateral association of sphingolipids and cholesterol, have been implicated in membrane traffic and cell signaling in mammalian cells. Sphingolipids also have been shown to play a role in protein sorting in yeast. Therefore, we wanted to investigate whether lipid rafts exist in yeast and whether these membrane microdomains have an analogous function to their mammalian counterparts. We first developed a protocol for isolating detergent-insoluble glycolipid-enriched complexes (DIGs) from yeast cells. Sequencing of the major protein components of the isolated DIGs by mass spectrometry allowed us to identify, among others, Gas1p, Pma1p, and Nce2p. Using lipid biosynthetic mutants we could demonstrate that conditions that impair the synthesis of sphingolipids and ergosterol also disrupt raft association of Gas1p and Pma1p but not the secretion of acid phosphatase. That endoplasmic reticulum (ER)-to-Golgi transport of Gas1p is blocked in the sphingolipid mutant lcb1-100 raised the question of whether proteins associate with lipid rafts in the ER or later as shown in mammalian cells. Using the sec18-1 mutant we found that DIGs are present already in the ER. Taken together, our results suggest that lipid rafts are involved in the biosynthetic delivery of proteins to the yeast plasma membrane.
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Affiliation(s)
- M Bagnat
- Cell Biology Program and European Molecular Biology Laboratory, 69012 Heidelberg, Germany
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338
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Lipid rafts function in biosynthetic delivery of proteins to the cell surface in yeast. Proc Natl Acad Sci U S A 2000; 97. [PMID: 10716729 PMCID: PMC16225 DOI: 10.1073/pnas.060034697] [Citation(s) in RCA: 266] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Lipid rafts, formed by lateral association of sphingolipids and cholesterol, have been implicated in membrane traffic and cell signaling in mammalian cells. Sphingolipids also have been shown to play a role in protein sorting in yeast. Therefore, we wanted to investigate whether lipid rafts exist in yeast and whether these membrane microdomains have an analogous function to their mammalian counterparts. We first developed a protocol for isolating detergent-insoluble glycolipid-enriched complexes (DIGs) from yeast cells. Sequencing of the major protein components of the isolated DIGs by mass spectrometry allowed us to identify, among others, Gas1p, Pma1p, and Nce2p. Using lipid biosynthetic mutants we could demonstrate that conditions that impair the synthesis of sphingolipids and ergosterol also disrupt raft association of Gas1p and Pma1p but not the secretion of acid phosphatase. That endoplasmic reticulum (ER)-to-Golgi transport of Gas1p is blocked in the sphingolipid mutant lcb1-100 raised the question of whether proteins associate with lipid rafts in the ER or later as shown in mammalian cells. Using the sec18-1 mutant we found that DIGs are present already in the ER. Taken together, our results suggest that lipid rafts are involved in the biosynthetic delivery of proteins to the yeast plasma membrane.
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339
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McCarthy PK, Huang CH, Levin IW. Raman spectroscopic study of polycrystalline mono- and polyunsaturated 1-eicosanoyl-d(39)-2-eicosenoyl-sn-glycero-3-phosphocholines: bilayer lipid clustering and acyl chain order and disorder characteristics. Biopolymers 2000; 57:2-10. [PMID: 10679634 DOI: 10.1002/(sici)1097-0282(2000)57:1<2::aid-bip2>3.0.co;2-g] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Polycrystalline lipid samples of a series of mono- and polyunsaturated, double bond positional isomers of 1-eicosanoyl-d(39)-2-eicosenoyl-sn-glycero-3-phosphocholines [C(20-d(39)):C(20:1 Delta(j))PC, with j = 5, 8, 11, or 13; C(20-d(39)):C(20:2 Delta(11,14))PC; and C(20-d(39)):C(20:3 Delta(11, 14,17))PC] were investigated using vibrational Raman spectroscopy to assess the acyl chain packing order-disorder characteristics and putative bilayer cluster formation of the isotopically differentiated acyl chains. Perdeuteration of specifically the saturated sn-1 acyl chains for these bilayer systems enables each chain's intra- and intermolecular conformational and organizational properties to be evaluated separately. Various saturated chain methylene CD(2) and carbon-carbon (C&bond;C) stretching mode peak height intensity ratios and line width parameters for the polycrystalline samples demonstrate a high degree of sn-1 chain order that is unaffected by either the double bond placement or number of unsaturated bonds within the sn-2 chain. In contrast, the unsaturated sn-2 chain spectral signatures reflect increasing acyl chain conformational disorder as either the cis double bond is generally repositioned toward the chain terminus or the number of double bonds increases from one to three. The lipid bilayer chain packing differences observed between the sn-1 and sn-2 chains of this series of monounsaturated and polyunsaturated 20 carbon chain lipids suggest the existence of laterally distributed microdomains predicated on the formation of highly ordered, saturated sn-1 chain clusters.
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Affiliation(s)
- P K McCarthy
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0510, USA
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340
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Baumann NA, Vidugiriene J, Machamer CE, Menon AK. Cell surface display and intracellular trafficking of free glycosylphosphatidylinositols in mammalian cells. J Biol Chem 2000; 275:7378-89. [PMID: 10702311 DOI: 10.1074/jbc.275.10.7378] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
In addition to serving as membrane anchors for cell surface proteins, glycosylphosphatidylinositols (GPIs) can be found abundantly as free glycolipids in mammalian cells. In this study we analyze the subcellular distribution and intracellular transport of metabolically radiolabeled GPIs in three different cell lines. We use a variety of membrane isolation techniques (subcellular fractionation, plasma membrane vesiculation to isolate pure plasma membrane fractions, and enveloped viruses to sample cellular membranes) to provide direct evidence that free GPIs are not confined to their site of synthesis, the endoplasmic reticulum, but can redistribute to populate other subcellular organelles. Over short labeling periods (2.5 h), radiolabeled GPIs were found at similar concentration in all subcellular fractions with the exception of a mitochondria-enriched fraction where GPI concentration was low. Pulse-chase experiments over extended chase periods showed that although the total amount of cellular radiolabeled GPIs decreased, the plasma membrane complement of labeled GPIs increased. GPIs at the plasma membrane were found to populate primarily the exoplasmic leaflet as detected using periodate oxidation of the cell surface. Transport of GPIs to the cell surface was inhibited by Brefeldin A and blocked at 15 degrees C, suggesting that GPIs are transported to the plasma membrane via a vesicular mechanism. The rate of transport of radiolabeled GPIs to the cell surface was found to be comparable with the rate of secretion of newly synthesized soluble proteins destined for the extracellular space.
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Affiliation(s)
- N A Baumann
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
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341
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Robison CS, Whitt MA. The membrane-proximal stem region of vesicular stomatitis virus G protein confers efficient virus assembly. J Virol 2000; 74:2239-46. [PMID: 10666254 PMCID: PMC111705 DOI: 10.1128/jvi.74.5.2239-2246.2000] [Citation(s) in RCA: 106] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In this report, we show that the glycoprotein of vesicular stomatitis virus (VSV G) contains within its extracellular membrane-proximal stem (GS) a domain that is required for efficient VSV budding. To determine a minimal sequence in GS that provides for high-level virus assembly, we have generated a series of recombinant DeltaG-VSVs which express chimeric glycoproteins having truncated stem sequences. The recombinant viruses having chimeras with 12 or more membrane-proximal residues of the G stem, and including the G protein transmembrane-cytoplasmic tail domains, produced near-wild-type levels of particles. In contrast, viruses encoding chimeras with shorter or no G-stem sequences produced approximately 10- to 20-fold less. This budding domain when present in chimeric glycoproteins also promoted their incorporation into the VSV envelope. We suggest that the G-stem budding domain promotes virus release by inducing membrane curvature at sites where virus budding occurs or by recruiting condensed nucleocapsids to sites on the plasma membrane which are competent for efficient virus budding.
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Affiliation(s)
- C S Robison
- Department of Microbiology and Immunology, University of Tennessee-Memphis, Memphis, Tennessee 38163, USA
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342
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Günther-Ausborn S, Schoen P, Bartoldus I, Wilschut J, Stegmann T. Role of hemagglutinin surface density in the initial stages of influenza virus fusion: lack of evidence for cooperativity. J Virol 2000; 74:2714-20. [PMID: 10684287 PMCID: PMC111761 DOI: 10.1128/jvi.74.6.2714-2720.2000] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Membrane fusion mediated by influenza virus hemagglutinin (HA) is believed to proceed via the cooperative action of multiple HA trimers. To determine the minimal number of HA trimers required to trigger fusion, and to assess the importance of cooperativity between these HA trimers, we have generated virosomes containing coreconstituted HAs derived from two strains of virus with different pH dependencies for fusion, X-47 (optimal fusion at pH 5.1; threshold at pH 5.6) and A/Shangdong (optimal fusion at pH 5.6; threshold at pH 6.0), and measured fusion of these virosomes with erythrocyte ghosts by a fluorescence lipid mixing assay. Virosomes with different X-47-to-A/Shangdong HA ratios, at a constant HA-to-lipid ratio, showed comparable ghost-binding activities, and the low-pH-induced conformational change of A/Shangdong HA did not affect the fusion activity of X-47 HA. The initial rate of fusion of these virosomes at pH 5.7 increased directly proportional to the surface density of A/Shangdong HA, and a single A/Shangdong trimer per virosome appeared to suffice to induce fusion. The reciprocal of the lag time before the onset of fusion was directly proportional to the surface density of fusion-competent HA. These results support the notion that there is no cooperativity between HA trimers during influenza virus fusion.
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Affiliation(s)
- S Günther-Ausborn
- Department of Biophysical Chemistry, Biozentrum of the University of Basel, CH 4056 Basel, Switzerland.
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343
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Xu X, London E. The effect of sterol structure on membrane lipid domains reveals how cholesterol can induce lipid domain formation. Biochemistry 2000; 39:843-9. [PMID: 10653627 DOI: 10.1021/bi992543v] [Citation(s) in RCA: 393] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Detergent-insoluble membrane domains, enriched in saturated lipids and cholesterol, have been implicated in numerous biological functions. To understand how cholesterol promotes domain formation, the effect of various sterols and sterol derivatives on domain formation in mixtures of the saturated lipid dipalmitoylphosphatidylcholine (DPPC) and a fluorescence quenching analogue of an unsaturated lipid was compared. Quenching measurements demonstrated that several sterols (cholesterol, dihydrocholesterol, epicholesterol, and 25-hydroxycholesterol) promote formation of DPPC-enriched domains. Other sterols and sterol derivatives had little effect on domain formation (cholestane and lanosterol) or, surprisingly, strongly inhibit it (coprostanol, androstenol, cholesterol sulfate, and 4-cholestenone). The effect of sterols on domain formation was closely correlated with their effects on DPPC insolubility. Those sterols that promoted domain formation increased DPPC insolubility, whereas those sterols that inhibit domain formation decreased DPPC insolubility. The effects of sterols on the fluorescence polarization of diphenylhexatriene incorporated into DPPC-containing vesicles were also correlated with sterol structure. These experiments indicate that the effect of sterol on the ability of saturated lipids to form a tightly packed (i.e., tight in the sense that the lipids are closely packed with one another) and ordered state is the key to their effect on domain formation. Those sterols that promote tight packing of saturated lipids promote domain formation, while those sterols that inhibited tight packing of saturated lipids inhibited domain formation. The ability of some sterols to inhibit domain formation (i.e., act as "anti-cholesterols") should be a valuable tool for examining domain formation and properties in cells.
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Affiliation(s)
- X Xu
- Department of Biochemistry and Cell Biology and Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-5215, USA
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344
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Tatulian SA, Tamm LK. Secondary structure, orientation, oligomerization, and lipid interactions of the transmembrane domain of influenza hemagglutinin. Biochemistry 2000; 39:496-507. [PMID: 10642174 DOI: 10.1021/bi991594p] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Influenza virus hemagglutinin (HA), the viral envelope glycoprotein that mediates fusion between the viral and cellular membranes, is a homotrimer of three subunits, each containing two disulfide-linked polypeptide chains, HA(1) and HA(2). Each HA(2) chain spans the viral membrane with a single putative transmembrane alpha-helix near its C-terminus. Fusion experiments with recombinant HAs suggest that this sequence is required for a late step of membrane fusion, as a glycosylphosphatidylinositol-anchored analogue of HA only mediates "hemifusion" of membranes, i.e., the merging of the proximal, but not distal, leaflets of the two juxtaposed lipid bilayers [Kemble et al. (1994) Cell 76, 383-391]. To find a structural explanation for the function of the transmembrane domain of HA(2) in membrane fusion, we have studied the secondary structure, orientation, oligomerization, and lipid interactions of a synthetic peptide representing the transmembrane segment of X:31 HA (TMX31) by circular dichroism and attenuated total reflection Fourier transform infrared spectroscopy and by gel electrophoresis. The peptide was predominantly alpha-helical in detergent micelles and in phospholipid bilayers. The helicity was increased in lipid bilayers composed of acidic lipids compared to pure phosphatidylcholine bilayers. In planar lipid bilayers, the helices were oriented close to the membrane normal. TMX31 aggregated into small heat-resistant oligomers composed of two to five subunits in SDS micelles. Amide hydrogen exchange experiments indicated that a large fraction of the helical residues were accessible to water, suggesting the possibility that TMX31 forms pores in lipid bilayers. Finally, the peptide increased the acyl chain order in lipid bilayers, which may be related to the preferential association of HA with lipid "rafts" in the cell surface and which may be an important prerequisite for complete membrane fusion.
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Affiliation(s)
- S A Tatulian
- Department of Molecular Physiology and Biological Physics and Center for Structural Biology, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908-0736, USA
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345
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Kielian M, Chatterjee PK, Gibbons DL, Lu YE. Specific roles for lipids in virus fusion and exit. Examples from the alphaviruses. Subcell Biochem 2000; 34:409-55. [PMID: 10808340 DOI: 10.1007/0-306-46824-7_11] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/14/2023]
Affiliation(s)
- M Kielian
- Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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346
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Manié SN, de Breyne S, Debreyne S, Vincent S, Gerlier D. Measles virus structural components are enriched into lipid raft microdomains: a potential cellular location for virus assembly. J Virol 2000; 74:305-11. [PMID: 10590118 PMCID: PMC111540 DOI: 10.1128/jvi.74.1.305-311.2000] [Citation(s) in RCA: 185] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The process of measles virus (MV) assembly and subsequent budding is thought to occur in localized regions of the plasma membrane, to favor specific incorporation of viral components, and to facilitate the exclusion of host proteins. We demonstrate that during the course of virus replication, a significant proportion of MV structural proteins were selectively enriched in the detergent-resistant glycosphingolipids and cholesterol-rich membranes (rafts). Isolated rafts could infect the cell through a membrane fusion step and thus contained all of the components required to create a functional virion. However, they could be distinguished from the mature virions with regards to density and Triton X-100 resistance behavior. We further show that raft localization of the viral internal nucleoprotein and matrix protein was independent of the envelope glycoproteins, indicating that raft membranes could provide a platform for MV assembly. Finally, at least part of the raft MV components were included in the viral particle during the budding process. Taken together, these results strongly suggest a role for raft membranes in the processes of MV assembly and budding.
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Affiliation(s)
- S N Manié
- Immunité et Infections Virales, IVMC, CNRS-UCBL UMR5537, 69372 Lyon Cedex 08, France.
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347
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Vincent S, Spehner D, Manié S, Delorme R, Drillien R, Gerlier D. Inefficient measles virus budding in murine L.CD46 fibroblasts. Virology 1999; 265:185-95. [PMID: 10600591 DOI: 10.1006/viro.1999.0064] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Infection of mouse L.CD46 fibroblasts with measles virus resulted in a poor virus yield, although no defects in the steps of virus binding, entry or fusion, were detected. Two days post-infection, the level of expression of the viral F protein was found to be similar on the surface of infected L.CD46 and HeLa cells using a virus multiplicity enabling an equal number of cells to be infected. After immunofluorescence labelling and confocal microscopy, L.CD46 cells also displayed a significant increase in the co-localisation of the N protein with the cell surface H and F proteins. Immunogold labelling and transmission electron microscopy demonstrated the accumulation of numerous nucleocapsids near the plasma membrane of L. CD46 cells with little virus budding, in contrast to infected HeLa cells which displayed fewer cortical nucleocapsids and more enveloped viral particles. Purified virus particles from infected L. CD46 contained a reduced amount of H, F and M protein. Altogether, these data indicate that, in L.CD46 cells, the late stage of measles virus assembly is defective. This cellular model will be helpful for the identification of cellular factors controlling measles virus maturation.
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Affiliation(s)
- S Vincent
- Immunité Infections Virales, IVMC, CNRS-UCBL UMR 5537, Lyon Cedex 08, 69372, France
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348
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Mordue DG, Desai N, Dustin M, Sibley LD. Invasion by Toxoplasma gondii establishes a moving junction that selectively excludes host cell plasma membrane proteins on the basis of their membrane anchoring. J Exp Med 1999; 190:1783-92. [PMID: 10601353 PMCID: PMC2195726 DOI: 10.1084/jem.190.12.1783] [Citation(s) in RCA: 193] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/1999] [Accepted: 10/05/1999] [Indexed: 11/05/2022] Open
Abstract
The protozoan parasite Toxoplasma gondii actively penetrates its host cell by squeezing through a moving junction that forms between the host cell plasma membrane and the parasite. During invasion, this junction selectively controls internalization of host cell plasma membrane components into the parasite-containing vacuole. Membrane lipids flowed past the junction, as shown by the presence of the glycosphingolipid G(M1) and the cationic lipid label 1. 1'-dihexadecyl-3-3'-3-3'-tetramethylindocarbocyanine (DiIC(16)). Glycosylphosphatidylinositol (GPI)-anchored surface proteins, such as Sca-1 and CD55, were also readily incorporated into the parasitophorous vacuole (PV). In contrast, host cell transmembrane proteins, including CD44, Na(+)/K(+) ATPase, and beta1-integrin, were excluded from the vacuole. To eliminate potential differences in sorting due to the extracellular domains, parasite invasion was examined in host cells transfected with recombinant forms of intercellular adhesion molecule 1 (ICAM-1, CD54) that differed in their mechanism of membrane anchoring. Wild-type ICAM-1, which contains a transmembrane domain, was excluded from the PV, whereas both GPI-anchored ICAM-1 and a mutant of ICAM-1 missing the cytoplasmic tail (ICAM-1-Cyt(-)) were readily incorporated into the PV membrane. Our results demonstrate that during host cell invasion, Toxoplasma selectively excludes host cell transmembrane proteins at the moving junction by a mechanism that depends on their anchoring in the membrane, thereby creating a nonfusigenic compartment.
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Affiliation(s)
- Dana G. Mordue
- Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Naishadh Desai
- Department of Pathology and Center for Immunology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Michael Dustin
- Department of Pathology and Center for Immunology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - L. David Sibley
- Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri 63110
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349
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Füllekrug J, Scheiffele P, Simons K. VIP36 localisation to the early secretory pathway. J Cell Sci 1999; 112 ( Pt 17):2813-21. [PMID: 10444376 DOI: 10.1242/jcs.112.17.2813] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
VIP36, an integral membrane protein previously isolated from epithelial MDCK cells, is an intracellular lectin of the secretory pathway. Overexpressed VIP36 had been localised to the Golgi complex, plasma membrane and endocytic structures suggesting post-Golgi trafficking of this molecule (Fiedler et al., 1994). Here we provide evidence that endogenous VIP36 is localised to the Golgi apparatus and the early secretory pathway of MDCK and Vero cells and propose that retention is easily saturated. High resolution confocal microscopy shows partial overlap of VIP36 with Golgi marker proteins. Punctate cytoplasmic structures colocalise with coatomer and ERGIC-53, labeling ER-Golgi intermediate membrane structures. Cycling of VIP36 is suggested by colocalisation with anterograde cargo trapped in pre-Golgi structures and modification of its N-linked carbohydrate by glycosylation enzymes of medial Golgi cisternae. Furthermore, after brefeldin A treatment VIP36 is segregated from resident Golgi proteins and codistributes with ER-Golgi recycling proteins.
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Affiliation(s)
- J Füllekrug
- Cell Biology, European Molecular Biology Laboratory (EMBL), Meyerhofstr. 1, D-69117 Heidelberg, Germany
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