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  • 1
    Online Resource
    Online Resource
    New Method for Measuring the Anchoring Energy of Strongly-Bound Membrane-Associated Proteins
    Elsevier BV ; 2016
    In:  Biophysical Journal Vol. 110, No. 3 ( 2016-02), p. 578a-
    Details
    In: Biophysical Journal, Elsevier BV, Vol. 110, No. 3 ( 2016-02), p. 578a-
    Type of Medium: Online Resource
    ISSN: 0006-3495
    URL: Article
    DOI: 10.1016/j.bpj.2015.11.3091
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2016
    detail.hit.zdb_id: 1477214-0
    SSG: 12
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  • 2
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    Study of Insertion of Dengue E into Lipid Bilayers by Neutron Reflectivity and Molecular Dynamics Simulations
    Elsevier BV ; 2017
    In:  Biophysical Journal Vol. 112, No. 3 ( 2017-02), p. 35a-
    Details
    In: Biophysical Journal, Elsevier BV, Vol. 112, No. 3 ( 2017-02), p. 35a-
    Type of Medium: Online Resource
    ISSN: 0006-3495
    URL: Article
    DOI: 10.1016/j.bpj.2016.11.221
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2017
    detail.hit.zdb_id: 1477214-0
    SSG: 12
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  • 3
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    The Role Of Class Ii And Iii Viral Protein Transmembrane Domains (tmds) In Voltage-dependent Fusion
    Elsevier BV ; 2009
    In:  Biophysical Journal Vol. 96, No. 3 ( 2009-02), p. 360a-
    Details
    In: Biophysical Journal, Elsevier BV, Vol. 96, No. 3 ( 2009-02), p. 360a-
    Type of Medium: Online Resource
    ISSN: 0006-3495
    URL: Article
    DOI: 10.1016/j.bpj.2008.12.1817
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2009
    detail.hit.zdb_id: 1477214-0
    SSG: 12
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  • 4
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    An Epitope of the Semliki Forest Virus Fusion Protein Exposed during Virus-Membrane Fusion
    American Society for Microbiology ; 1999
    In:  Journal of Virology Vol. 73, No. 12 ( 1999-12), p. 10029-10039
    Details
    In: Journal of Virology, American Society for Microbiology, Vol. 73, No. 12 ( 1999-12), p. 10029-10039
    Abstract: Semliki Forest virus (SFV) is an enveloped alphavirus that infects cells via a membrane fusion reaction triggered by acidic pH in the endocytic pathway. Fusion is mediated by the spike protein E1 subunit, an integral membrane protein that contains the viral fusion peptide and forms a stable homotrimer during fusion. We have characterized four monoclonal antibodies (MAbs) specific for the acid conformation of E1. These MAbs did not inhibit fusion, suggesting that they bind to an E1 region different from the fusion peptide. Competition analyses demonstrated that all four MAbs bound to spatially related sites on acid-treated virions or isolated spike proteins. To map the binding site, we selected for virus mutants resistant to one of the MAbs, E1a-1. One virus isolate, SFV 4-2, showed reduced binding of three acid-specific MAbs including E1a-1, while its binding of one acid-specific MAb as well as non-acid-specific MAbs to E1 and E2 was unchanged. The SFV 4-2 mutant was fully infectious, formed the E1 homotrimer, and had the wild-type pH dependence of infection. Sequence analysis demonstrated that the relevant mutation in SFV 4-2 was a change of E1 glycine 157 to arginine (G157R). Decreased binding of MAb E1a-1 was observed under a wide range of assay conditions, strongly suggesting that the E1 G157R mutation directly affects the MAb binding site. These data thus localize an E1 region that is normally hidden in the neutral pH structure and becomes exposed as part of the reorganization of the spike protein to its fusion-active conformation.
    Type of Medium: Online Resource
    ISSN: 0022-538X , 1098-5514
    URL: Article
    DOI: 10.1128/JVI.73.12.10029-10039.1999
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 1999
    detail.hit.zdb_id: 1495529-5
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  • 5
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    E1 Mutants Identify a Critical Region in the Trimer Interface of the Semliki Forest Virus Fusion Protein
    American Society for Microbiology ; 2009
    In:  Journal of Virology Vol. 83, No. 21 ( 2009-11), p. 11298-11306
    Details
    In: Journal of Virology, American Society for Microbiology, Vol. 83, No. 21 ( 2009-11), p. 11298-11306
    Abstract: The alphavirus Semliki Forest virus (SFV) uses a membrane fusion reaction to infect host cells. Fusion of the virus and cell membranes is triggered by low pH in the endosome and is mediated by the viral membrane protein E1. During fusion, E1 inserts into the target membrane, trimerizes, and refolds into a hairpin conformation. Formation of the E1 homotrimer is critical to membrane fusion, but the mechanism of trimerization is not understood. The crystal structure of the postfusion E1 trimer shows that an aspartate residue, D188, is positioned in the central core trimer interface. D188 is conserved in all reported alphavirus E1 sequences. We tested the contribution of this amino acid to trimerization and fusion by replacing D188 with alanine (D188A) or lysine (D188K) in an SFV infectious clone. These mutations were predicted to disrupt specific interactions at this position and/or change their pH dependence. Our results indicated that the D188K mutation blocked SFV fusion and infection. At low pH, D188K E1 inserted into target membranes but was trapped as a target membrane-inserted monomer that did not efficiently form the stable core trimer. In contrast, the D188A mutant was infectious, although trimerization and fusion required a lower pH. While there are extensive contacts between E1 subunits in the homotrimer, the D188K mutant identifies an important “hot spot” for protein-protein interactions within the core trimer.
    Type of Medium: Online Resource
    ISSN: 0022-538X , 1098-5514
    URL: Article
    DOI: 10.1128/JVI.01147-09
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2009
    detail.hit.zdb_id: 1495529-5
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  • 6
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    Functions of the Stem Region of the Semliki Forest Virus Fusion Protein during Virus Fusion and Assembly
    American Society for Microbiology ; 2006
    In:  Journal of Virology Vol. 80, No. 22 ( 2006-11), p. 11362-11369
    Details
    In: Journal of Virology, American Society for Microbiology, Vol. 80, No. 22 ( 2006-11), p. 11362-11369
    Abstract: Membrane fusion of the alphaviruses is mediated by the E1 protein, a class II virus membrane fusion protein. During fusion, E1 dissociates from its heterodimer interaction with the E2 protein and forms a target membrane-inserted E1 homotrimer. The structure of the homotrimer is that of a trimeric hairpin in which E1 domain III and the stem region fold back toward the target membrane-inserted fusion peptide loop. The E1 stem region has a strictly conserved length and several highly conserved residues, suggesting the possibility of specific stem interactions along the trimer core and an important role in driving membrane fusion. Mutagenesis studies of the alphavirus Semliki Forest virus (SFV) here demonstrated that there was a strong requirement for the E1 stem in virus assembly and budding, probably reflecting its importance in lateral interactions of the envelope proteins. Surprisingly, however, neither the conserved length nor any specific residues of the stem were required for membrane fusion. Although the highest fusion activity was observed with wild-type E1, efficient fusion was mediated by stem mutants containing a variety of substitutions or deletions. A minimal stem length was required but could be conferred by a series of alanine residues. The lack of a specific stem sequence requirement during SFV fusion suggests that the interaction of domain III with the trimer core can provide sufficient driving force to mediate membrane merger.
    Type of Medium: Online Resource
    ISSN: 0022-538X , 1098-5514
    URL: Article
    DOI: 10.1128/JVI.01679-06
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2006
    detail.hit.zdb_id: 1495529-5
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  • 7
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    Novel Mutations That Control the Sphingolipid and Cholesterol Dependence of the Semliki Forest Virus Fusion Protein
    American Society for Microbiology ; 2002
    In:  Journal of Virology Vol. 76, No. 24 ( 2002-12-15), p. 12712-12722
    Details
    In: Journal of Virology, American Society for Microbiology, Vol. 76, No. 24 ( 2002-12-15), p. 12712-12722
    Abstract: The enveloped alphavirus Semliki Forest virus (SFV) infects cells via a membrane fusion reaction mediated by the E1 membrane protein. Efficient SFV-membrane fusion requires the presence of cholesterol and sphingolipid in the target membrane. Here we report on two mutants, srf-4 and srf-5 , selected for growth in cholesterol-depleted cells. Like the previously isolated srf-3 mutant (E1 proline 226 to serine), the phenotypes of the srf-4 and srf-5 mutants were conferred by single-amino-acid changes in the E1 protein: leucine 44 to phenylalanine and valine 178 to alanine, respectively. Like srf-3 , srf-4 and srf-5 show striking increases in the cholesterol independence of growth, infection, membrane fusion, and exit. Unexpectedly, and unlike srf-3 , srf-4 and srf-5 showed highly efficient fusion with sphingolipid-free membranes in both lipid- and content-mixing assays. Both srf-4 and srf-5 formed E1 homotrimers of decreased stability compared to the homotrimers of the wild type and the srf-3 mutant. All three srf mutations lie in the same domain of E1, but the srf-4 and srf-5 mutations are spatially separated from srf-3 . When expressed together, the three mutations could interact to produce increased sterol independence and to cause temperature-sensitive E1 transport. Thus, the srf-4 and srf-5 mutations identify novel regions of E1 that are distinct from the fusion peptide and srf-3 region and modulate the requirements for both sphingolipid and cholesterol in virus-membrane fusion.
    Type of Medium: Online Resource
    ISSN: 0022-538X , 1098-5514
    URL: Article
    DOI: 10.1128/JVI.76.24.12712-12722.2002
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2002
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  • 8
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    Multistep Regulation of Membrane Insertion of the Fusion Peptide of Semliki Forest Virus
    American Society for Microbiology ; 2004
    In:  Journal of Virology Vol. 78, No. 7 ( 2004-04), p. 3312-3318
    Details
    In: Journal of Virology, American Society for Microbiology, Vol. 78, No. 7 ( 2004-04), p. 3312-3318
    Abstract: A prevailing model for virus membrane fusion proteins has been that the hydrophobic fusion peptide is hidden in the prefusion conformation, becomes exposed once the fusion reaction is triggered, and then either inserts into target membranes or is rapidly inactivated. This model is in general agreement with the structure and mechanism of class I fusion proteins, such as the influenza virus hemagglutinin. We here describe studies of the class II fusion protein E1 from the alphavirus Semliki Forest virus (SFV). SFV fusion is triggered by low pH, which releases E1 from its heterodimeric interaction with the E2 protein and induces the formation of a stable E1 homotrimer. The exposure and target membrane interaction of the E1 fusion peptide (residues 83 to 100) were followed using a monoclonal antibody (MAb E1f) mapping to E1 residues 85 to 95. In agreement with the known structure of SFV and other alphaviruses, the fusion peptide was shielded in native SFV particles and exposed when E1-E2 dimer dissociation was triggered by acidic pH. In contrast, the fusion peptide on purified E1 ectodomains (E1 * ) was fully accessible at neutral pH. Functional assays showed that MAb E1f binding at neutral pH prevented subsequent low-pH-triggered E1 * interaction with target membranes and trimerization. E1 * was not inactivated by low pH when treated either in the absence of target membranes or in the presence of fusion-inactive cholesterol-deficient liposomes. Thus, the membrane insertion of the E1 fusion peptide is regulated by additional low-pH-dependent steps after exposure, perhaps involving an E1-cholesterol interaction.
    Type of Medium: Online Resource
    ISSN: 0022-538X , 1098-5514
    URL: Article
    DOI: 10.1128/JVI.78.7.3312-3318.2004
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2004
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  • 9
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    Mechanism of Tetherin Inhibition of Alphavirus Release
    American Society for Microbiology ; 2019
    In:  Journal of Virology Vol. 93, No. 7 ( 2019-04)
    Details
    In: Journal of Virology, American Society for Microbiology, Vol. 93, No. 7 ( 2019-04)
    Abstract: Tetherin is an interferon-inducible, antiviral host factor that broadly restricts enveloped virus release by tethering budded viral particles to the plasma membrane. In response, many viruses have evolved tetherin antagonists. The human tetherin gene can express two isoforms, long and short, due to alternative translation initiation sites in the N-terminal cytoplasmic tail. The long isoform (L-tetherin) contains 12 extra amino acids in its N terminus, including a dual tyrosine motif (YDYCRV) that is an internalization signal for clathrin-mediated endocytosis and a determinant of NF-κB activation. Tetherin restricts alphaviruses, which are highly organized enveloped RNA viruses that bud from the plasma membrane. L-tetherin is more efficient than S-tetherin in inhibiting alphavirus release in 293 cells. Here, we demonstrated that alphaviruses do not encode an antagonist for either of the tetherin isoforms. Instead, the isoform specificity reflected a requirement for tetherin endocytosis. The YXY motif in L-tetherin was necessary for alphavirus restriction in 293 cells but was not required for rhabdovirus restriction. L-tetherin’s inhibition of alphavirus release correlated with its internalization but did not involve NF-κB activation. In contrast, in U-2 OS cells, the YXY motif and the L-tetherin N-terminal domain were not required for either robust tetherin internalization or alphavirus inhibition. Tetherin forms that were negative for restriction accumulated at the surface of infected cells, while the levels of tetherin forms that restrict were decreased. Together, our results suggest that tetherin-mediated virus internalization plays an important role in the restriction of alphavirus release and that cell-type-specific cofactors may promote tetherin endocytosis. IMPORTANCE The mechanisms of tetherin’s antiviral activities and viral tetherin antagonism have been studied in detail for a number of different viruses. Although viral countermeasures against tetherin can differ significantly, overall, tetherin’s antiviral activity correlates with physical tethering of virus particles to prevent their release. While tetherin can mediate virus endocytic uptake and clearance, this has not been observed to be required for restriction. Here we show that efficient tetherin inhibition of alphavirus release requires efficient tetherin endocytosis. Our data suggest that this endocytic uptake can be mediated by tetherin itself or by a tetherin cofactor that promotes uptake of an endocytosis-deficient variant of tetherin.
    Type of Medium: Online Resource
    ISSN: 0022-538X , 1098-5514
    URL: Article
    DOI: 10.1128/JVI.02165-18
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2019
    detail.hit.zdb_id: 1495529-5
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  • 10
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    Online Resource
    fus-1 , a pH Shift Mutant of Semliki Forest Virus, Acts by Altering Spike Subunit Interactions via a Mutation in the E2 Subunit
    American Society for Microbiology ; 1998
    In:  Journal of Virology Vol. 72, No. 5 ( 1998-05), p. 4281-4287
    Details
    In: Journal of Virology, American Society for Microbiology, Vol. 72, No. 5 ( 1998-05), p. 4281-4287
    Abstract: Semliki Forest virus (SFV), an enveloped alphavirus, is a well-characterized paradigm for viruses that infect cells via endocytic uptake and low-pH-triggered fusion. The SFV spike protein is composed of a dimer of E1 and E2 transmembrane subunits, which dissociate upon exposure to low pH, liberating E2 and the fusogenic E1 subunit to undergo independent conformational changes. SFV fusion and infection are blocked by agents such as ammonium chloride, which act by raising the pH in the endosome and inhibiting the low-pH-induced conformational changes in the SFV spike protein. We have previously isolated an SFV mutant, fus-1 , that requires more acidic pH to trigger its fusion activity and is therefore more sensitive to inhibition by ammonium chloride. The acid shift in the fusion activity of fus-1 was here shown to be due to a more acidic pH threshold for the initial dissociation of the fus-1 spike dimer, thereby resulting in a more acidic pH requirement for the subsequent conformational changes in both fus-1 E1 and fus-1 E2. Sequence analysis demonstrated that the fus-1 phenotype was due to a mutation in the E2 spike subunit, threonine 12 to isoleucine. fus-1 revertants that have regained the parental fusion phenotype and ammonium chloride sensitivity were shown to have also regained E2 threonine 12. Our results identify a region of the SFV E2 spike protein subunit that regulates the pH dependence of E1-catalyzed fusion by controlling the dissociation of the E1/E2 dimer.
    Type of Medium: Online Resource
    ISSN: 0022-538X , 1098-5514
    URL: Article
    DOI: 10.1128/JVI.72.5.4281-4287.1998
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 1998
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