scholarly journals Expression of Major Capsid Protein VP-1 in the Absence of Viral Particles in Thymomas Induced by Murine Polyomavirus

2001 ◽  
Vol 75 (6) ◽  
pp. 2891-2899 ◽  
Author(s):  
Norberto Sanjuan ◽  
Analı́a Porrás ◽  
Javier Otero ◽  
Sofı́a Perazzo
Keyword(s):  
Electron Microscopy ◽  
Tumor Cells ◽  
Capsid Protein ◽  
Infectious Virus ◽  
Major Capsid Protein ◽  
Structural Protein ◽  
Induced Tumors ◽  
Viral Particles ◽  
Infected Cells ◽  
Murine Polyomavirus

ABSTRACT Thymomas induced by polyomavirus strain PTA in mice are known to express the major capsid protein VP-1. Since the expression of a late structural protein such as VP-1 is considered a sign of virus replication, the present work attempted to clarify the implication of the presence of this protein in tumor cells. Electron microscopy of tumors showed a striking absence of viral particles in the vast majority of the cells. However, immunoelectron microscopy of the same samples demonstrated intranuclear VP-1 in most cells despite the absence of viral particles. Very little infectious virus was recovered from tumors. A change in the electrophoretic mobility of VP-1 from thymomas was detected compared with VP-1 from productively infected cells. The data presented in this work prove that the expression of VP-1 in polyomavirus-induced tumors is not synonymous with the presence of infectious virus, suggesting a possible defect in viral encapsidation.

scholarly journals Small Capsid Protein pORF65 Is Essential for Assembly of Kaposi's Sarcoma-Associated Herpesvirus Capsids

2008 ◽  
Vol 82 (14) ◽  
pp. 7201-7211 ◽  
Author(s):  
Edward M. Perkins ◽  
Daniel Anacker ◽  
Aaron Davis ◽  
Vishwam Sankar ◽  
Richard F. Ambinder ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Capsid Protein ◽  
Insect Cells ◽  
Major Capsid Protein ◽  
Scaffold Protein ◽  
Velocity Sedimentation ◽  
Icosahedral Structure ◽  
Capsid Shell ◽  
Infected Cells ◽  
Hsv 1

ABSTRACT Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiologic agent for KS tumors, multicentric Castleman's disease, and primary effusion lymphomas. Like other herpesvirus capsids, the KSHV capsid is an icosahedral structure composed of six proteins. The capsid shell is made up of the major capsid protein, two triplex proteins, and the small capsid protein. The scaffold protein and the protease occupy the internal space. The assembly of KSHV capsids is thought to occur in a manner similar to that determined for herpes simplex virus type 1 (HSV-1). Our goal was to assemble KSHV capsids in insect cells using the baculovirus expression vector system. Six KSHV capsid open reading frames were cloned and the proteins expressed in Sf9 cells: pORF25 (major capsid protein), pORF62 (triplex 1), pORF26 (triplex 2), pORF17 (protease), pORF17.5 (scaffold protein), and also pORF65 (small capsid protein). When insect cells were coinfected with these baculoviruses, angular capsids that contained internal core structures were readily observed by conventional electron microscopy of the infected cells. Capsids were also readily isolated from infected cells by using rate velocity sedimentation. With immuno-electron microscopy methods, these capsids were seen to be reactive to antisera to pORF65 as well as to KSHV-positive human sera, indicating the correct conformation of pORF65 in these capsids. When either virus expressing the triplex proteins was omitted from the coinfection, capsids did not assemble; similar to observations made in HSV-1-infected cells. If the virus expressing the scaffold protein was excluded, large open shells that did not attain icosahedral structure were seen in the nuclei of infected cells. The presence of pORF65 was required for capsid assembly, in that capsids did not form if this protein was absent as judged by both by ultrastructural analysis of infected cells and rate velocity sedimentation experiments. Thus, a novel outcome of this study is the finding that the small capsid protein of KSHV, like the major capsid and triplex proteins, is essential for capsid shell assembly.

scholarly journals Ultrastructural analysis of SARS-CoV-2 interactions with the host cell via high resolution scanning electron microscopy

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Lucio Ayres Caldas ◽  
Fabiana Avila Carneiro ◽  
Luiza Mendonça Higa ◽  
Fábio Luiz Monteiro ◽  
Gustavo Peixoto da Silva ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
High Resolution ◽  
Vero Cells ◽  
Viral Interactions ◽  
Viral Particles ◽  
Direct Cell ◽  
Infected Cells ◽  
Scanning Electron ◽  
Intercellular Connections

Abstract SARS-CoV-2 is the cause of the ongoing COVID-19 pandemic. Here, we investigated the interaction of this new coronavirus with Vero cells using high resolution scanning electron microscopy. Surface morphology, the interior of infected cells and the distribution of viral particles in both environments were observed 2 and 48 h after infection. We showed areas of viral processing, details of vacuole contents, and viral interactions with the cell surface. Intercellular connections were also approached, and viral particles were adhered to these extensions suggesting direct cell-to-cell transmission of SARS-CoV-2.

scholarly journals The 4.4 Å structure of the giant Melbournevirus virion belonging to the Marseilleviridae family

2021 ◽  
Author(s):  
Raymond N Burton-Smith ◽  
Hemanth K N Reddy ◽  
Martin Svenda ◽  
Chantal Abergel ◽  
Kenta Okamoto ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Capsid Protein ◽  
Major Capsid Protein ◽  
Capsid Proteins ◽  
Atomic Model ◽  
Penton Base ◽  
Cryo Electron Microscopy ◽  
Internal Membrane ◽  
Structural Details ◽  
Giant Viruses

Members of Marseilleviridae, one family of icosahedral giant viruses classified in 2012 have been identified worldwide in all types of environments. The virion shows a characteristic internal membrane extrusion at the five-fold vertices of the capsid, but its structural details need to be elucidated. We now report the 4.4 Å cryo-electron microscopy structure of the Melbournevirus capsid. An atomic model of the major capsid protein (MCP) shows a unique cup structure on the trimer that accommodates additional proteins. A polyalanine model of the penton base protein shows internally extended N- and C-terminals, which indirectly connect to the internal membrane extrusion. The Marseilleviruses share the same orientational organisation of the MCPs as PBCV-1 and CroV, but do not appear to possess a protein akin to the ″tape measure″ of these viruses. Minor capsid proteins named PC-β, zipper, and scaffold are proposed to control the dimensions of the capsid during assembly.

scholarly journals Association of the Astrovirus Structural Protein VP90 with Membranes Plays a Role in Virus Morphogenesis

2007 ◽  
Vol 81 (19) ◽  
pp. 10649-10658 ◽  
Author(s):  
Ernesto Méndez ◽  
Gabriela Aguirre-Crespo ◽  
Guadalupe Zavala ◽  
Carlos F. Arias
Keyword(s):  
Virus Genome ◽  
Structural Protein ◽  
Nonstructural Proteins ◽  
Ultrastructural Studies ◽  
Protease Digestion ◽  
Viral Particles ◽  
Cell Release ◽  
Human Astrovirus ◽  
Infected Cells ◽  
Polyprotein Precursor

ABSTRACT VP90, the capsid polyprotein precursor of human astrovirus Yuc8, is assembled into viral particles, and its processing at the carboxy terminus by cellular caspases, to yield VP70, has been correlated with the cell release of the virus. Here, we characterized the effect of the VP90-VP70 processing on the properties of these proteins, as well as on their intracellular distribution. VP90 was found in membrane-enriched fractions (mVP90), as well as in fractions enriched in cytosolic proteins (cVP90), while VP70 was found exclusively in the latter fractions. Upon trypsin activation, infectivity was detected in all VP90-containing fractions, confirming that both mVP90 and cVP90 are able to assemble into particles; however, the two forms of VP90 showed differential sensitivities to trypsin, especially at their carboxy termini, which in the case of mVP90 was shown to remain membrane associated after protease digestion. Structural protein oligomers were detected in purified VP70-containing viruses, as well as in membrane-enriched fractions, but they were less evident in cytosolic fractions. Ultrastructural studies of infected cells revealed different types of viral particles, some of which appeared to be associated with membranes. By immunoelectron microscopy, structural proteins were shown to form virus particles in clusters and to associate with the edges of vesicles induced during infection, which also appear to contain subviral particles inside. Nonstructural proteins and viral RNA colocalized with mVP90, but not with cVP90, suggesting that mVP90 might represent the form of the protein that is initially assembled into particles, at the sites where the virus genome is being replicated.

scholarly journals Inside job: how the ESCRTs release HIV-1 from infected cells

2018 ◽  
Vol 46 (5) ◽  
pp. 1029-1036 ◽  
Author(s):  
James H. Hurley ◽  
A. King Cada
Keyword(s):  
Structural Protein ◽  
Endosomal Sorting ◽  
Cellular Processes ◽  
Self Assembling ◽  
Viral Particles ◽  
Immunodeficiency Virus ◽  
Infected Cells ◽  
Membrane Scission ◽  
Endosome Maturation ◽  
Hiv 1

Human immunodeficiency virus type 1 (HIV-1) hijacks the host endosomal sorting complex required for transport (ESCRT) proteins in order to release infectious viral particles from the cell. ESCRT recruitment is virtually essential for the production of infectious virus, despite that the main structural protein of HIV-1, Gag, is capable of self-assembling and eventually budding from membranes on its own. Recent data have reinforced the paradigm of ESCRT-dependent particle release while clarifying why this rapid release is so critical. The ESCRTs were originally discovered as integral players in endosome maturation and are now implicated in many important cellular processes beyond viral and endosomal budding. Nearly all of these roles have in common that membrane scission occurs from the inward face of the membrane neck, which we refer to as ‘reverse topology’ scission. A satisfactory mechanistic description of reverse-topology membrane scission by ESCRTs remains a major challenge both in general and in the context of HIV-1 release. New observations concerning the fundamental scission mechanism for ESCRTs in general, and the process of HIV-1 release specifically, have generated new insights in both directions, bringing us closer to a mechanistic understanding.

scholarly journals Mass Spectrometry-Based System for Identifying and Typing Norovirus Major Capsid Protein VP1

Viruses ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 2332
Author(s):  
Pei-Yu Chu ◽  
Hui-Wen Huang ◽  
Michittra Boonchan ◽  
Yu-Chang Tyan ◽  
Kevin Leroy Louis ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Capsid Protein ◽  
Major Capsid Protein ◽  
Ultra Performance Liquid Chromatography ◽  
Clinical Samples ◽  
Structural Protein ◽  
Promising Tool ◽  
Technological Advances ◽  
Primary Diagnostics ◽  
Capsid Protein Vp1

Norovirus-associated diseases are the most common foodborne illnesses worldwide. Polymerase chain reaction-based methods are the primary diagnostics for clinical samples; however, the high mutation rate of norovirus makes viral amplification and genotyping challenging. Technological advances in mass spectrometry (MS) make it a promising tool for identifying disease markers. Besides, the superior sensitivity of MS and proteomic approaches may enable the detection of all variants. Thus, this study aimed to establish an MS-based system for identifying and typing norovirus. We constructed three plasmids containing the major capsid protein VP1 of the norovirus GII.4 2006b, 2006a, and 2009a strains to produce virus-like particles for use as standards. Digested peptide signals were collected using a nano-flow ultra-performance liquid chromatography mass spectrometry (nano-UPLC/MSE) system, and analyzed by ProteinLynx Global SERVER and TREE-PUZZLE software. Results revealed that the LC/MSE system had an excellent coverage rate: the system detected more than 94% of amino acids of 3.61 femtomole norovirus VP1 structural protein. In the likelihood-mapping analysis, the proportions of unresolved quartets were 2.9% and 4.9% in the VP1 and S domains, respectively, which is superior to the 15.1% unresolved quartets in current PCR-based methodology. In summary, the use of LC/MSE may efficiently monitor genotypes, and sensitively detect structural and functional mutations of noroviruses.

scholarly journals The Amino-Conserved Domain of Human Cytomegalovirus UL80a Proteins Is Required for Key Interactions during Early Stages of Capsid Formation and Virus Production

2006 ◽  
Vol 81 (2) ◽  
pp. 620-628 ◽  
Author(s):  
Amy N. Loveland ◽  
Nang L. Nguyen ◽  
Edward J. Brignole ◽  
Wade Gibson
Keyword(s):  
Capsid Protein ◽  
Infectious Virus ◽  
Major Capsid Protein ◽  
Nuclear Translocation ◽  
Critical Role ◽  
Virus Production ◽  
Scaffolding Protein ◽  
Capsid Formation ◽  
Conserved Domain ◽  
Protease Precursor

ABSTRACT Assembly of many spherical virus capsids is guided by an internal scaffolding protein or group of proteins that are often cleaved and eliminated in connection with maturation and incorporation of the genome. In cytomegalovirus there are at least two proteins that contribute to this scaffolding function; one is the maturational protease precursor (pUL80a), and the other is the assembly protein precursor (pUL80.5) encoded by a shorter genetic element within UL80a. Yeast GAL4 two-hybrid assays established that both proteins contain a carboxyl-conserved domain that is required for their interaction with the major capsid protein (pUL86) and an amino-conserved domain (ACD) that is required for their self-interaction and for their interaction with each other. In the work reported here, we demonstrate that when the ACD is deleted (δACD) or disrupted by a point mutation (L47A), the bacterially expressed mutant protein sediments as a monomer during rate-velocity centrifugation, whereas the wild-type protein sediments mainly as oligomers. We also show that the L47A mutation reduces the production of infectious virus by at least 90%, results in the formation of irregular nuclear capsids, gives rise to tube-like structures in the nucleus that resemble the capsid core in cross-section and contain UL80 proteins, slows nuclear translocation of the major capsid protein, and may slow cleavage by the maturational protease. We provide physical corroboration that mutating the ACD disrupts self-interaction of the UL80 proteins and biological support for the proposal that the ACD has a critical role in capsid assembly and production of infectious virus.

scholarly journals Modification of Human Papillomavirus Minor Capsid Protein L2 by Sumoylation

2010 ◽  
Vol 84 (21) ◽  
pp. 11585-11589 ◽  
Author(s):  
Martina Bergant Marušič ◽  
Nina Mencin ◽  
Mia Ličen ◽  
Lawrence Banks ◽  
Helena Šterlinko Grm
Keyword(s):  
Human Papillomavirus ◽  
Infected Cell ◽  
Host Cell ◽  
Capsid Protein ◽  
Major Capsid Protein ◽  
Capsid Assembly ◽  
Complex Interplay ◽  
Hpv 16 ◽  
Minor Capsid Protein ◽  
Viral Particles

ABSTRACT The human papillomavirus (HPV) minor capsid protein L2 plays important roles in the generation of infectious viral particles and in the initial steps of infection. Here we show that HPV-16 L2 protein is sumoylated at lysine 35 and that sumoylation affects its stability. Interestingly, the sumoylated form of L2 cannot bind to the major capsid protein L1, suggesting a mechanism by which capsid assembly may be modulated in an infected cell. Additionally, L2 appears to modulate the overall sumoylation status of the host cell. These observations indicate a complex interplay between the HPV L2 protein and the host sumoylation machinery.

Sign in / Sign up

Export Citation Format

Share Document