scholarly journals Putative Autocleavage of Outer Capsid Protein μ1, Allowing Release of Myristoylated Peptide μ1N during Particle Uncoating, Is Critical for Cell Entry by Reovirus

2004 ◽  
Vol 78 (16) ◽  
pp. 8732-8745 ◽  
Author(s):  
Amy L. Odegard ◽  
Kartik Chandran ◽  
Xing Zhang ◽  
John S. L. Parker ◽  
Timothy S. Baker ◽  
...  
Keyword(s):  
Capsid Protein ◽  
Structural Changes ◽  
General Mechanism ◽  
Membrane Penetration ◽  
Outer Capsid Protein ◽  
Core Proteins ◽  
Peptide Release ◽  
Outer Capsid

ABSTRACT Several nonenveloped animal viruses possess an autolytic capsid protein that is cleaved as a maturation step during assembly to yield infectious virions. The 76-kDa major outer capsid protein μ1 of mammalian orthoreoviruses (reoviruses) is also thought to be autocatalytically cleaved, yielding the virion-associated fragments μ1N (4 kDa; myristoylated) and μ1C (72 kDa). In this study, we found that μ1 cleavage to yield μ1N and μ1C was not required for outer capsid assembly but contributed greatly to the infectivity of the assembled particles. Recoated particles containing mutant, cleavage-defective μ1 (asparagine → alanine substitution at amino acid 42) were competent for attachment; processing by exogenous proteases; structural changes in the outer capsid, including μ1 conformational change and σ1 release; and transcriptase activation but failed to mediate membrane permeabilization either in vitro (no hemolysis) or in vivo (no coentry of the ribonucleotoxin α-sarcin). In addition, after these particles were allowed to enter cells, the δ region of μ1 continued to colocalize with viral core proteins in punctate structures, indicating that both elements remained bound together in particles and/or trapped within the same subcellular compartments, consistent with a defect in membrane penetration. If membrane penetration activity was supplied in trans by a coinfecting genome-deficient particle, the recoated particles with cleavage-defective μ1 displayed much higher levels of infectivity. These findings led us to propose a new uncoating intermediate, at which particles are trapped in the absence of μ1N/μ1C cleavage. We additionally showed that this cleavage allowed the myristoylated, N-terminal μ1N fragment to be released from reovirus particles during entry-related uncoating, analogous to the myristoylated, N-terminal VP4 fragment of picornavirus capsid proteins. The results thus suggest that hydrophobic peptide release following capsid protein autocleavage is part of a general mechanism of membrane penetration shared by several diverse nonenveloped animal viruses.

scholarly journals Thermolabilizing Pseudoreversions in Reovirus Outer-Capsid Protein μ1 Rescue the Entry Defect Conferred by a Thermostabilizing Mutation

2007 ◽  
Vol 81 (14) ◽  
pp. 7400-7409 ◽  
Author(s):  
Melina A. Agosto ◽  
Jason K. Middleton ◽  
Elaine C. Freimont ◽  
John Yin ◽  
Max L. Nibert
Keyword(s):  
Capsid Protein ◽  
General Mechanism ◽  
Compensatory Mutation ◽  
Outer Capsid Protein ◽  
Viral Protein Synthesis ◽  
Animal Virus ◽  
Isolation And Characterization ◽  
Outer Capsid

ABSTRACT Heat-resistant mutants selected from infectious subvirion particles of mammalian reoviruses have determinative mutations in the major outer-capsid protein μ1. Here we report the isolation and characterization of intragenic pseudoreversions of one such thermostabilizing mutation. From a plaque that had survived heat selection, a number of viruses with one shared mutation but different second-site mutations were isolated. The effect of the shared mutation alone or in combination with second-site mutations was examined using recoating genetics. The shared mutation, D371A, was found to confer (i) substantial thermostability, (ii) an infectivity defect that followed attachment but preceded viral protein synthesis, and (iii) resistance to μ1 rearrangement in vitro, with an associated failure to lyse red blood cells. Three different second-site mutations were individually tested in combination with D371A and found to wholly or partially revert these phenotypes. Furthermore, when tested alone in recoated particles, each of these three second-site mutations conferred demonstrable thermolability. This and other evidence suggest that pseudoreversion of μ1-based thermostabilization can occur by a general mechanism of μ1-based thermolabilization, not requiring a specific compensatory mutation. The thermostabilizing mutation D371A as well as 9 of the 10 identified second-site mutations are located near contact regions between μ1 trimers in the reovirus outer capsid. The availability of both thermostabilizing and thermolabilizing mutations in μ1 should aid in defining the conformational rearrangements and mechanisms involved in membrane penetration during cell entry by this structurally complex nonenveloped animal virus.

scholarly journals Structural Protein VP2 of African Horse Sickness Virus Is Not Essential for Virus Replication In Vitro

2016 ◽  
Vol 91 (4) ◽  
Author(s):  
René G. P. van Gennip ◽  
Sandra G. P. van de Water ◽  
Christiaan A. Potgieter ◽  
Piet A. van Rijn
Keyword(s):  
Capsid Protein ◽  
Virus Replication ◽  
Hemorrhagic Disease ◽  
African Horse Sickness ◽  
Structural Protein ◽  
Outer Capsid Protein ◽  
African Horse Sickness Virus ◽  
Content Type ◽  
Outer Capsid

ABSTRACT The Reoviridae family consists of nonenveloped multilayered viruses with a double-stranded RNA genome consisting of 9 to 12 genome segments. The Orbivirus genus of the Reoviridae family contains African horse sickness virus (AHSV), bluetongue virus, and epizootic hemorrhagic disease virus, which cause notifiable diseases and are spread by biting Culicoides species. Here, we used reverse genetics for AHSV to study the role of outer capsid protein VP2, encoded by genome segment 2 (Seg-2). Expansion of a previously found deletion in Seg-2 indicates that structural protein VP2 of AHSV is not essential for virus replication in vitro. In addition, in-frame replacement of RNA sequences in Seg-2 by that of green fluorescence protein (GFP) resulted in AHSV expressing GFP, which further confirmed that VP2 is not essential for virus replication. In contrast to virus replication without VP2 expression in mammalian cells, virus replication in insect cells was strongly reduced, and virus release from insect cells was completely abolished. Further, the other outer capsid protein, VP5, was not copurified with virions for virus mutants without VP2 expression. AHSV without VP5 expression, however, could not be recovered, indicating that outer capsid protein VP5 is essential for virus replication in vitro. Our results demonstrate for the first time that a structural viral protein is not essential for orbivirus replication in vitro, which opens new possibilities for research on other members of the Reoviridae family. IMPORTANCE Members of the Reoviridae family cause major health problems worldwide, ranging from lethal diarrhea caused by rotavirus in humans to economic losses in livestock production caused by different orbiviruses. The Orbivirus genus contains many virus species, of which bluetongue virus, epizootic hemorrhagic disease virus, and African horse sickness virus (AHSV) cause notifiable diseases according to the World Organization of Animal Health. Recently, it has been shown that nonstructural proteins NS3/NS3a and NS4 are not essential for virus replication in vitro, whereas it is generally assumed that structural proteins VP1 to -7 of these nonenveloped, architecturally complex virus particles are essential. Here we demonstrate for the first time that structural protein VP2 of AHSV is not essential for virus replication in vitro. Our findings are very important for virologists working in the field of nonenveloped viruses, in particular reoviruses.

scholarly journals Selection of Single-Chain Antibodies against the VP8* Subunit of Rotavirus VP4 Outer Capsid Protein and Their Expression in Lactobacillus casei

2004 ◽  
Vol 70 (11) ◽  
pp. 6936-6939 ◽  
Author(s):  
Vicente Monedero ◽  
Jes�s Rodr�guez-D�az ◽  
Rosa Viana ◽  
Javier Buesa ◽  
Gaspar P�rez-Mart�nez
Keyword(s):  
Lactobacillus Casei ◽  
Probiotic Bacteria ◽  
Extracellular Expression ◽  
Outer Capsid Protein ◽  
Single Chain ◽  
Single Chain Antibodies ◽  
Outer Capsid ◽  
Selection Of

ABSTRACT Single-chain antibodies (scFv) recognizing the VP8* fraction of rotavirus outer capsid and blocking rotavirus infection in vitro were isolated by phage display. Vectors for the extracellular expression in Lactobacillus casei of one of the scFv were constructed. L. casei was able to secrete active scFv to the growth medium, showing the potential of probiotic bacteria to be engineered to express molecules suitable for in vivo antirotavirus therapies.

scholarly journals Protease Cleavage of Reovirus Capsid Protein μ1/μ1C Is Blocked by Alkyl Sulfate Detergents, Yielding a New Type of Infectious Subvirion Particle

1998 ◽  
Vol 72 (1) ◽  
pp. 467-475 ◽  
Author(s):  
Kartik Chandran ◽  
Max L. Nibert
Keyword(s):  
Virus Particle ◽  
Capsid Protein ◽  
Lipid Bilayers ◽  
Viral Entry ◽  
Mdck Cells ◽  
Alkyl Sulfate ◽  
Membrane Penetration ◽  
Reovirus Infection ◽  
Outer Capsid

ABSTRACT Mammalian reovirus virions undergo partial disassembly of the outer capsid upon exposure to proteases in vitro, producing infectious subvirion particles (ISVPs) that lack protein ς3 and contain protein μ1/μ1C as endoprotease-generated fragments μ1δ/δ and φ. ISVPs are thought to be required for two early steps in reovirus infection: membrane penetration and activation of the particle-bound viral transcriptase complexes. Genetic and biochemical evidence implicates outer-capsid protein μ1 in both these steps. To determine whether the cleavage of μ1/μ1C is relevant to the unique properties of ISVPs, we analyzed the properties of novel subvirion particles that lacked ς3 yet retained μ1/μ1C in an uncleaved but cleavable form. These detergent-plus-protease subvirion particles (dpSVPs) were produced by treating virions with chymotrypsin in the presence of micelle-forming concentrations of alkyl sulfate detergents. Infections with dpSVPs in murine L or canine MDCK cells provided evidence that the cleavage of μ1/μ1C during viral entry into these cells is dispensable for reovirus infection. Additionally, dpSVPs behaved like ISVPs in their capacity to permeabilize lipid bilayers and to undergo transcriptase activation in vitro, supporting the conclusion that cleavage of μ1/μ1C to μ1δ/δ and φ during viral entry is not required for either membrane penetration or transcriptase activation in cells. The capacity of alkyl sulfate detergents to inhibit the cleavage of μ1/μ1C in a reversible fashion suggests a specific association between virus particle and detergent micelles that may mimic virus particle-phospholipid membrane interactions during reovirus entry into cells.

scholarly journals Reovirus Virion-Like Particles Obtained by Recoating Infectious Subvirion Particles with Baculovirus-Expressed ς3 Protein: an Approach for Analyzing ς3 Functions during Virus Entry

1999 ◽  
Vol 73 (4) ◽  
pp. 2963-2973 ◽  
Author(s):  
Judit Jané-Valbuena ◽  
Max L. Nibert ◽  
Stephan M. Spencer ◽  
Stephen B. Walker ◽  
Timothy S. Baker ◽  
...  
Keyword(s):  
Capsid Protein ◽  
Virus Entry ◽  
Cysteine Proteinase ◽  
Reverse Genetic System ◽  
Lag Phase ◽  
Cysteine Proteinase Inhibitor ◽  
Outer Capsid Protein ◽  
Viral Mrnas ◽  
Outer Capsid

ABSTRACT Structure-function studies with mammalian reoviruses have been limited by the lack of a reverse-genetic system for engineering mutations into the viral genome. To circumvent this limitation in a partial way for the major outer-capsid protein ς3, we obtained in vitro assembly of large numbers of virion-like particles by binding baculovirus-expressed ς3 protein to infectious subvirion particles (ISVPs) that lack ς3. A level of ς3 binding approaching 100% of that in native virions was routinely achieved. The ς3 coat in these recoated ISVPs (rcISVPs) appeared very similar to that in virions by electron microscopy and three-dimensional image reconstruction. rcISVPs retained full infectivity in murine L cells, allowing their use to study ς3 functions in virus entry. Upon infection, rcISVPs behaved identically to virions in showing an extended lag phase prior to exponential growth and in being inhibited from entering cells by either the weak base NH4Cl or the cysteine proteinase inhibitor E-64. rcISVPs also mimicked virions in being incapable of in vitro activation to mediate lysis of erythrocytes and transcription of the viral mRNAs. Last, rcISVPs behaved like virions in showing minor loss of infectivity at 52°C. Since rcISVPs contain virion-like levels of ς3 but contain outer-capsid protein μ1/μ1C mostly cleaved at the δ-φ junction as in ISVPs, the fact that rcISVPs behaved like virions (and not ISVPs) in all of the assays that we performed suggests that ς3, and not the δ-φ cleavage of μ1/μ1C, determines the observed differences in behavior between virions and ISVPs. To demonstrate the applicability of rcISVPs for genetic studies of protein functions in reovirus entry (an approach that we call recoating genetics), we used chimeric ς3 proteins to localize the primary determinants of a strain-dependent difference in ς3 cleavage rate to a carboxy-terminal region of the ISVP-bound protein.

scholarly journals The VP7 Outer Capsid Protein of Rotavirus Induces Polyclonal B-Cell Activation

2004 ◽  
Vol 78 (13) ◽  
pp. 6974-6981 ◽  
Author(s):  
Sarah E. Blutt ◽  
Sue E. Crawford ◽  
Kelly L. Warfield ◽  
Dorothy E. Lewis ◽  
Mary K. Estes ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Capsid Protein ◽  
Cell Activation ◽  
B Cell Activation ◽  
Outer Capsid Protein ◽  
Rotavirus Infection ◽  
Virus Like Particles ◽  
Outer Capsid

ABSTRACT The early response to a homologous rotavirus infection in mice includes a T-cell-independent increase in the number of activated B lymphocytes in the Peyer's patches. The mechanism of this activation has not been previously determined. Since rotavirus has a repetitively arranged triple-layered capsid and repetitively arranged antigens can induce activation of B cells, one or more of the capsid proteins could be responsible for the initial activation of B cells during infection. To address this question, we assessed the ability of rotavirus and virus-like particles to induce B-cell activation in vivo and in vitro. Using infectious rotavirus, inactivated rotavirus, noninfectious but replication-competent virus, and virus-like particles, we determined that neither infectivity nor RNA was necessary for B-cell activation but the presence of the rotavirus outer capsid protein, VP7, was sufficient for murine B-cell activation. Preincubation of the virus with neutralizing VP7 antibodies inhibited B-cell activation. Polymyxin B treatment and boiling of the virus preparation were performed, which ruled out possible lipopolysaccharide contamination as the source of activation and confirmed that the structural conformation of VP7 is important for B-cell activation. These findings indicate that the structure and conformation of the outer capsid protein, VP7, initiate intestinal B-cell activation during rotavirus infection.

Development and efficacy of a grass carp reovirus (GCRV) outer capsid protein VP7 subunit vaccine

2012 ◽  
Vol 37 (6) ◽  
pp. 659-664 ◽  
Author(s):  
Shi-ying XU ◽  
Jing-hui LI ◽  
Yong ZOU ◽  
Lin LIU ◽  
Cheng-liang GONG ◽  
...  
Keyword(s):  
Capsid Protein ◽  
Grass Carp ◽  
Subunit Vaccine ◽  
Outer Capsid Protein ◽  
Grass Carp Reovirus ◽  
Outer Capsid

scholarly journals Structure of the Three N-Terminal Immunoglobulin Domains of the Highly Immunogenic Outer Capsid Protein from a T4-Like Bacteriophage

2011 ◽  
Vol 85 (16) ◽  
pp. 8141-8148 ◽  
Author(s):  
A. Fokine ◽  
M. Z. Islam ◽  
Z. Zhang ◽  
V. D. Bowman ◽  
V. B. Rao ◽  
...  
Keyword(s):  
Capsid Protein ◽  
Outer Capsid Protein ◽  
Outer Capsid

scholarly journals Interaction of Lactoferrin with Unsaturated Fatty Acids: In Vitro and In Vivo Study of Human Lactoferrin/Oleic Acid Complex Cytotoxicity

Materials ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1602
Author(s):  
Anna Elizarova ◽  
Alexey Sokolov ◽  
Valeria Kostevich ◽  
Ekaterina Kisseleva ◽  
Evgeny Zelenskiy ◽  
...  
Keyword(s):  
Oleic Acid ◽  
Structural Changes ◽  
Unsaturated Fatty Acids ◽  
Structural Features ◽  
Control Group ◽  
Acid Complex ◽  
Hepatoma 22A ◽  
Constitutive Parameters

As shown recently, oleic acid (OA) in complex with lactoferrin (LF) causes the death of cancer cells, but no mechanism(s) of that toxicity have been disclosed. In this study, constitutive parameters of the antitumor effect of LF/OA complex were explored. Complex LF/OA was prepared by titrating recombinant human LF with OA. Spectral analysis was used to assess possible structural changes of LF within its complex with OA. Structural features of apo-LF did not change within the complex LF:OA = 1:8, which was toxic for hepatoma 22a cells. Cytotoxicity of the complex LF:OA = 1:8 was tested in cultured hepatoma 22a cells and in fresh erythrocytes. Its anticancer activity was tested in mice carrying hepatoma 22a. In mice injected daily with LF-8OA, the same tumor grew significantly slower. In 20% of animals, the tumors completely resolved. LF alone was less efficient, i.e., the tumor growth index was 0.14 for LF-8OA and 0.63 for LF as compared with 1.0 in the control animals. The results of testing from 48 days after the tumor inoculation showed that the survival rate among LF-8OA-treated animals was 70%, contrary to 0% rate in the control group and among the LF-treated mice. Our data allow us to regard the complex of LF and OA as a promising tool for cancer treatment.

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