The Experts below are selected from a list of 49464 Experts worldwide ranked by ideXlab platform
John C Guatelli - One of the best experts on this subject based on the ideXlab platform.
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direct restriction of virus release and incorporation of the interferon induced protein bst 2 into hiv 1 particles
PLOS Pathogens, 2010Co-Authors: Kathleen Fitzpatrick, Mark Skasko, Thomas J Deerinck, John Crum, Mark H Ellisman, John C GuatelliAbstract:Investigation of the Vpu protein of HIV-1 recently uncovered a novel aspect of the mammalian innate response to enveloped viruses: retention of progeny Virions on the surface of infected cells by the interferon-induced, transmembrane and GPI-anchored protein BST-2 (CD317; tetherin). BST-2 inhibits diverse families of enveloped viruses, but how it restricts viral release is unclear. Here, immuno-electron microscopic data indicate that BST-2 is positioned to directly retain nascent HIV Virions on the plasma membrane of infected cells and is incorporated into Virions. Virion-incorporation was confirmed by capture of infectivity using antibody to the ectodomain of BST-2. Consistent with a direct tethering mechanism, we confirmed that proteolysis releases restricted Virions and further show that this removed the ectodomain of BST-2 from the cell surface. Unexpectedly, enzymatic cleavage of GPI anchors did not release restricted Virions, weighing against models in which individual BST-2 molecules span the Virion and host cell membranes. Although the exact molecular topology of restriction remains unsolved, we suggest that the incorporation of BST-2 into viral envelopes underlies its broad restrictive activity, whereas its relative exclusion from Virions and sites of viral assembly by proteins such as HIV-1 Vpu may provide viral antagonism of restriction.
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the interferon induced protein bst 2 restricts hiv 1 release and is downregulated from the cell surface by the viral vpu protein
Cell Host & Microbe, 2008Co-Authors: Nanette Van Damme, Chris Katsura, Rebecca L Jorgenson, Richard S Mitchell, Edward B Stephens, Marc C. Johnson, Daniel Goff, John C GuatelliAbstract:Summary The HIV-1 accessory protein Vpu counteracts a host factor that restricts Virion release from infected cells. Here we show that the interferon-induced cellular protein BST-2/HM1.24/CD317 is such a factor. BST-2 is downregulated from the cell surface by Vpu, and BST-2 is specifically expressed in cells that support the vpu phenotype. Exogenous expression of BST-2 inhibits HIV-1 Virion release, while suppression of BST-2 relieves the requirement for Vpu. Downregulation of BST-2 requires both the transmembrane/ion channel domain and conserved serines in the cytoplasmic domain of Vpu. Endogenous BST-2 colocalizes with the HIV-1 structural protein Gag in endosomes and at the plasma membrane, suggesting that BST-2 traps Virions within and on infected cells. The unusual structure of BST-2, which includes a transmembrane domain and a lumenal GPI anchor, may allow it to retain nascent enveloped Virions on cellular membranes, providing a mechanism of viral restriction counteracted by a specific viral accessory protein.
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producer cell modification of human immunodeficiency virus type 1 nef is a Virion protein
Journal of Virology, 1996Co-Authors: Mark W Pandori, Nicholas J S Fitch, Heather M Craig, Douglas D Richman, Celsa A Spina, John C GuatelliAbstract:Type 1 human immunodeficiency viruses encoding mutated nef reading frames are 10- to 30-fold less infectious than are isogenic viruses in which the nef gene is intact. This defect in infectivity causes nef-negative viruses to grow at an attenuated rate in vitro. To investigate the mechanism of Nef-mediated enhancement of viral growth rate and infectivity, a complementation analysis of nef mutant viruses was performed. To provide Nef in trans upon viral infection, a CEM derivative cell line (designated CLN) that expresses Nef under the control of the viral long terminal repeat was constructed. When nef-negative virus was grown in CLN cells, its growth rate was restored to wild-type levels. However, the output of nef-negative virus during the first 72 h after infection of CLN cells was not restored, suggesting that provision of Nef within the newly infected cell does not enhance the productivity of a nef-negative provirus. The genetically nef-negative Virions produced by the CLN cells, however, were restored to wild-type levels of infectivity as measured in a syncytium formation assay in which CD4-expressing HeLa cells were targets. These trans-complemented, genetically nef-negative Virions yielded wild-type levels of viral output following a single cycle of replication in primary CD4 T cells as well as in parental CEM cells. To define the determinants for producer cell modification of Virions by Nef, the role of myristoylation was investigated. Virus that encodes a myristoylation-negative nef was as impaired in infectivity as was virus encoding a deleted nef gene. Because myristoylation is required for both membrane association of Nef and optimal viral infectivity, the possibility that Nef protein is included in the Virion was investigated. Wild-type Virions were purified by filtration and exclusion chromatography. A Western blot (immunoblot) of the eluate fractions revealed a correlation between peak Nef signal and peak levels of p24 antigen. Although Virion-associated Nef was detected in part as the 27-kDa full-length protein, the majority of immunoreactive protein was detected as a 20-kDa isoform. nef-negative virus lacked both 27- and 20-kDa immunoreactive species. Production of wild-type Virions in the presence of a specific inhibitor of the human immunodeficiency virus type 1 protease resulted in Virions which contained only 27-kDa full-length Nef protein. These data indicate that Nef is a Virion protein which is processed by the viral protease into a 20-kDa isoform within the Virion particle.
Miklos S Z Kellermayer - One of the best experts on this subject based on the ideXlab platform.
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topography spike dynamics and nanomechanics of individual native sars cov 2 Virions
Nano Letters, 2021Co-Authors: Balint Kiss, Zoltan Kis, Bernadett Palyi, Miklos S Z KellermayerAbstract:SARS-CoV-2, the virus responsible for the current COVID-19 pandemic, displays a corona-shaped layer of spikes which play a fundamental role in the infection process. Recent structural data suggest that the spikes possess orientational freedom and the ribonucleoproteins segregate into basketlike structures. How these structural features regulate the dynamic and mechanical behavior of the native Virion are yet unknown. By imaging and mechanically manipulating individual, native SARS-CoV-2 Virions with atomic force microscopy, here, we show that their surface displays a dynamic brush owing to the flexibility and rapid motion of the spikes. The Virions are highly compliant and able to recover from drastic mechanical perturbations. Their global structure is remarkably temperature resistant, but the Virion surface becomes progressively denuded of spikes upon thermal exposure. The dynamics and the mechanics of SARS-CoV-2 are likely to affect its stability and interactions.
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topography spike dynamics and nanomechanics of individual native sars cov 2 Virions
bioRxiv, 2020Co-Authors: Balint Kiss, Zoltan Kis, Bernadett Palyi, Miklos S Z KellermayerAbstract:SARS-CoV-2, the virus responsible for the current COVID-19 pandemic, displays a corona-shaped layer of spikes which play fundamental role in the infection process. Recent structural data suggest that the spikes possess orientational freedom and the ribonucleoproteins segregate into basketlike structures. How these structural features regulate the dynamic and mechanical behavior of the native Virion, however, remain unknown. By imaging and mechanically manipulating individual, native SARS-CoV-2 Virions with atomic force microscopy, here we show that their surface displays a dynamic brush owing to the flexibility and rapid motion of the spikes. The Virions are highly compliant and able to recover from drastic mechanical perturbations. Their global structure is remarkably temperature resistant, but the Virion surface becomes progressively denuded of spikes upon thermal exposure. Thus, both the infectivity and thermal sensitivity of SARS-CoV-2 rely on the dynamics and the mechanics of the virus.
Nissin Moussatche - One of the best experts on this subject based on the ideXlab platform.
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the vaccinia virus e6 protein influences Virion protein localization during virus assembly
Virology, 2015Co-Authors: Richard C. Condit, Nissin MoussatcheAbstract:Vaccinia virus mutants in which expression of the Virion core protein gene E6R is repressed are defective in Virion morphogenesis. E6 deficient infections fail to properly package viroplasm into viral membranes, resulting in an accumulation of empty immature Virions and large aggregates of viroplasm. We have used immunogold electron microscopy and immunofluorescence confocal microscopy to assess the intracellular localization of several Virion structural proteins and enzymes during E6R mutant infections. We find that during E6R mutant infections Virion membrane proteins and Virion transcription enzymes maintain a normal localization within viral factories while several major core and lateral body proteins accumulate in aggregated virosomes. The results support a model in which vaccinia Virions are assembled from at least three substructures, the membrane, the viroplasm and a “pre-nucleocapsid”, and that the E6 protein is essential for maintaining proper localization of the seven-protein complex and the viroplasm during assembly.
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temperature sensitive mutant in the vaccinia virus e6 protein produce Virions that are transcriptionally inactive
Virology, 2010Co-Authors: Olga Boyd, Richard C. Condit, Audra L Strahl, Carson Rodeffer, Nissin MoussatcheAbstract:The vaccinia virus E6R gene encodes a late protein that is packaged into Virion cores. A temperature-sensitive mutant was used to study the role of this protein in viral replicative cycle. Cts52 has a P226L missense mutation in the E6R gene, shows a two-log reduction in plaque formation, but displays normal patterns of gene expression, late protein processing and DNA replication during infection. Mutant Virions produced at 40 °C were similar in their morphology to wt Virions grown at 40 °C. The particle to infectivity ratio was 50 times higher in purified Cts52 grown at 40 °C when compared to the mutant grown at permissive temperature. In vitro characterization of Cts-52 particles grown at 40 °C revealed no differences in protein composition or in DNA content and the mutant Virions could bind and enter cells. However, core particles prepared from Cts52 grown at 40 °C failed to transcribe in vitro. Our results show that E6 in the Virion has either a direct or an indirect role in viral transcription.
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in a nutshell structure and assembly of the vaccinia Virion
Advances in Virus Research, 2006Co-Authors: Richard C. Condit, Nissin Moussatche, Paula TraktmanAbstract:Poxviruses comprise a large family of viruses characterized by a large, linear dsDNA genome, a cytoplasmic site of replication and a complex Virion morphology. The most notorious member of the poxvirus family is variola, the causative agent of smallpox. The laboratory prototype virus used for the study of poxviruses is vaccinia, the virus that was used as a live, naturally attenuated vaccine for the eradication of smallpox. Both the morphogenesis and structure of poxvirus Virions are unique among viruses. Poxvirus Virions apparently lack any of the symmetry features common to other viruses such as helical or icosahedral capsids or nucleocapsids. Instead poxvirus Virions appear as "brick shaped" or "ovoid" membrane-bound particles with a complex internal structure featuring a walled, biconcave core flanked by "lateral bodies." The Virion assembly pathway involves a remarkable fabrication of membrane-containing crescents and immature Virions, which evolve into mature Virions in a process that is unparalleled in virology. As a result of significant advances in poxvirus genetics and molecular biology during the past 15 years, we can now positively identify over 70 specific gene products contained in poxvirus Virions, and we can describe the effects of mutations in over 50 specific genes on poxvirus assembly. This review summarizes these advances and attempts to assemble them into a comprehensible and thoughtful picture of poxvirus structure and assembly.
Balint Kiss - One of the best experts on this subject based on the ideXlab platform.
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topography spike dynamics and nanomechanics of individual native sars cov 2 Virions
Nano Letters, 2021Co-Authors: Balint Kiss, Zoltan Kis, Bernadett Palyi, Miklos S Z KellermayerAbstract:SARS-CoV-2, the virus responsible for the current COVID-19 pandemic, displays a corona-shaped layer of spikes which play a fundamental role in the infection process. Recent structural data suggest that the spikes possess orientational freedom and the ribonucleoproteins segregate into basketlike structures. How these structural features regulate the dynamic and mechanical behavior of the native Virion are yet unknown. By imaging and mechanically manipulating individual, native SARS-CoV-2 Virions with atomic force microscopy, here, we show that their surface displays a dynamic brush owing to the flexibility and rapid motion of the spikes. The Virions are highly compliant and able to recover from drastic mechanical perturbations. Their global structure is remarkably temperature resistant, but the Virion surface becomes progressively denuded of spikes upon thermal exposure. The dynamics and the mechanics of SARS-CoV-2 are likely to affect its stability and interactions.
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topography spike dynamics and nanomechanics of individual native sars cov 2 Virions
bioRxiv, 2020Co-Authors: Balint Kiss, Zoltan Kis, Bernadett Palyi, Miklos S Z KellermayerAbstract:SARS-CoV-2, the virus responsible for the current COVID-19 pandemic, displays a corona-shaped layer of spikes which play fundamental role in the infection process. Recent structural data suggest that the spikes possess orientational freedom and the ribonucleoproteins segregate into basketlike structures. How these structural features regulate the dynamic and mechanical behavior of the native Virion, however, remain unknown. By imaging and mechanically manipulating individual, native SARS-CoV-2 Virions with atomic force microscopy, here we show that their surface displays a dynamic brush owing to the flexibility and rapid motion of the spikes. The Virions are highly compliant and able to recover from drastic mechanical perturbations. Their global structure is remarkably temperature resistant, but the Virion surface becomes progressively denuded of spikes upon thermal exposure. Thus, both the infectivity and thermal sensitivity of SARS-CoV-2 rely on the dynamics and the mechanics of the virus.
Joel D Baines - One of the best experts on this subject based on the ideXlab platform.
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the herpes simplex virus type 1 ul20 protein modulates membrane fusion events during cytoplasmic Virion morphogenesis and virus induced cell fusion
Journal of Virology, 2004Co-Authors: Timothy P Foster, Joel D Baines, Jeffrey M Melancon, Konstantin G KousoulasAbstract:The herpes simplex virus type 1 (HSV-1) UL20 protein is an important determinant for Virion morphogenesis and virus-induced cell fusion. A precise deletion of the UL20 gene in the HSV-1 KOS strain was constructed without affecting the adjacent UL20.5 gene. The resultant KOS/UL20-null virus produced small plaques of 8 to 15 cells in Vero cells while it produced wild-type plaques on the complementing cell line G5. Electron microscopic examination of infected cells revealed that the KOS/UL20-null Virions predominantly accumulated capsids in the cytoplasm while a small percentage of Virions were found as enveloped Virions within cytoplasmic vacuoles. Recently, it was shown that UL20 expression was necessary and sufficient for cell surface expression of gK (T. P. Foster, X. Alvarez, and K. G. Kousoulas, J. Virol. 77:499-510, 2003). Therefore, we investigated the effect of UL20 on virus-induced cell fusion caused by syncytial mutations in gB and gK by constructing recombinant viruses containing the gBsyn3 or gKsyn1 mutations in a UL20-null genetic background. Both recombinant viruses failed to cause virus-induced cell fusion in Vero cells while they readily caused fusion of UL20-null complementing G5 cells. Ultrastructural examination of UL20-null viruses carrying the gBsyn3 or gKsyn1 mutation revealed a similar distribution of Virions as the KOS/UL20-null virus. However, cytoplasmic vacuoles contained aberrant Virions having multiple capsids within a single envelope. These multicapsid Virions may have been formed either by fusion of viral envelopes or by the concurrent reenvelopment of multiple capsids. These results suggest that the UL20 protein regulates membrane fusion phenomena involved in Virion morphogenesis and virus-induced cell fusion.
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ultrastructural localization of the herpes simplex virus type 1 ul31 ul34 and us3 proteins suggests specific roles in primary envelopment and egress of nucleocapsids
Journal of Virology, 2002Co-Authors: Ashley E Reynolds, Elizabeth Wills, Richard J Roller, Brent J Ryckman, Joel D BainesAbstract:The wild-type UL31, UL34, and US3 proteins localized on nuclear membranes and perinuclear Virions; the US3 protein was also on cytoplasmic membranes and extranuclear Virions. The UL31 and UL34 proteins were not detected in extracellular Virions. US3 deletion caused (i) Virion accumulation in nuclear membrane invaginations, (ii) delayed virus production onset, and (iii) reduced peak virus titers. These data support the herpes simplex virus type 1 deenvelopment-reenvelopment model of Virion egress and suggest that the US3 protein plays an important, but nonessential, role in the egress pathway.
