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1.
Front Cell Neurosci ; 15: 695106, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-34658789

RESUMO

Despite being perceived to be a relatively innocuous pathogen during its circulation in Africa in the 20th century, consequent outbreaks in French Polynesia and Latin America revealed the Zika virus (ZIKV) to be capable of causing severe neurological defects. Foetuses infected with the virus during pregnancy developed a range of pathologies including microcephaly, cerebral calcifications and macular scarring. These are now collectively known as Congenital Zika syndrome (CZS). It has been established that the neuropathogenesis of ZIKV results from infection of neural progenitor cells in the developing cerebral cortex. Following this, two main hypotheses have emerged: the virus causes either apoptosis or premature differentiation of neural progenitor cells, reducing the final number of mature neurons in the cerebral cortex. This review describes the cellular processes which could potentially cause virus induced apoptosis or premature differentiation, leading to speculation that a combination of the two may be responsible for the pathologies associated with ZIKV. The review also discusses which specific lineages of the ZIKV can employ these mechanisms. It has been unclear in the past whether the virus evolved its neurotropic capability following circulation in Africa, or if the virus has always caused microcephaly but public health surveillance in Africa had failed to detect it. Understanding the true neuropathogenesis of ZIKV is key to being prepared for further outbreaks in the future, and it will also provide insight into how neurotropic viruses can cause profound and life-long neurological defects.

2.
PLoS Pathog ; 17(6): e1009644, 2021 06.
Artigo em Inglês | MEDLINE | ID: mdl-34138976

RESUMO

Coronavirus infection induces the unfolded protein response (UPR), a cellular signalling pathway composed of three branches, triggered by unfolded proteins in the endoplasmic reticulum (ER) due to high ER load. We have used RNA sequencing and ribosome profiling to investigate holistically the transcriptional and translational response to cellular infection by murine hepatitis virus (MHV), often used as a model for the Betacoronavirus genus to which the recently emerged SARS-CoV-2 also belongs. We found the UPR to be amongst the most significantly up-regulated pathways in response to MHV infection. To confirm and extend these observations, we show experimentally the induction of all three branches of the UPR in both MHV- and SARS-CoV-2-infected cells. Over-expression of the SARS-CoV-2 ORF8 or S proteins alone is itself sufficient to induce the UPR. Remarkably, pharmacological inhibition of the UPR greatly reduced the replication of both MHV and SARS-CoV-2, revealing the importance of this pathway for successful coronavirus replication. This was particularly striking when both IRE1α and ATF6 branches of the UPR were inhibited, reducing SARS-CoV-2 virion release (~1,000-fold). Together, these data highlight the UPR as a promising antiviral target to combat coronavirus infection.


Assuntos
Antivirais/farmacologia , COVID-19/tratamento farmacológico , Vírus da Hepatite Murina/efeitos dos fármacos , Resposta a Proteínas não Dobradas/efeitos dos fármacos , Fator 6 Ativador da Transcrição/metabolismo , Animais , Antivirais/uso terapêutico , Linhagem Celular , Chlorocebus aethiops , Sistemas de Liberação de Medicamentos , Endorribonucleases/metabolismo , Células HEK293 , Humanos , Camundongos , Proteínas Serina-Treonina Quinases/metabolismo , RNA-Seq , Células Vero , Proteínas Virais/metabolismo , Replicação Viral/efeitos dos fármacos
3.
Nature ; 593(7860): 597-601, 2021 May.
Artigo em Inglês | MEDLINE | ID: mdl-33902106

RESUMO

N6-methyladenosine (m6A) is an abundant internal RNA modification1,2 that is catalysed predominantly by the METTL3-METTL14 methyltransferase complex3,4. The m6A methyltransferase METTL3 has been linked to the initiation and maintenance of acute myeloid leukaemia (AML), but the potential of therapeutic applications targeting this enzyme remains unknown5-7. Here we present the identification and characterization of STM2457, a highly potent and selective first-in-class catalytic inhibitor of METTL3, and a crystal structure of STM2457 in complex with METTL3-METTL14. Treatment of tumours with STM2457 leads to reduced AML growth and an increase in differentiation and apoptosis. These cellular effects are accompanied by selective reduction of m6A levels on known leukaemogenic mRNAs and a decrease in their expression consistent with a translational defect. We demonstrate that pharmacological inhibition of METTL3 in vivo leads to impaired engraftment and prolonged survival in various mouse models of AML, specifically targeting key stem cell subpopulations of AML. Collectively, these results reveal the inhibition of METTL3 as a potential therapeutic strategy against AML, and provide proof of concept that the targeting of RNA-modifying enzymes represents a promising avenue for anticancer therapy.

4.
J Virol ; 94(24)2020 11 23.
Artigo em Inglês | MEDLINE | ID: mdl-32938763

RESUMO

Despite their diversity, most double-stranded-RNA (dsRNA) viruses share a specialized T=1 capsid built from dimers of a single protein that provides a platform for genome transcription and replication. This ubiquitous capsid remains structurally undisturbed throughout the viral cycle, isolating the genome to avoid triggering host defense mechanisms. Human picobirnavirus (hPBV) is a dsRNA virus frequently associated with gastroenteritis, although its pathogenicity is yet undefined. Here, we report the cryo-electron microscopy (cryo-EM) structure of hPBV at 2.6-Å resolution. The capsid protein (CP) is arranged in a single-shelled, ∼380-Å-diameter T=1 capsid with a rough outer surface similar to that of dsRNA mycoviruses. The hPBV capsid is built of 60 quasisymmetric CP dimers (A and B) stabilized by domain swapping, and only the CP-A N-terminal basic region interacts with the packaged nucleic acids. hPBV CP has an α-helical domain with a fold similar to that of fungal partitivirus CP, with many domain insertions in its C-terminal half. In contrast to dsRNA mycoviruses, hPBV has an extracellular life cycle phase like complex reoviruses, which indicates that its own CP probably participates in cell entry. Using an in vitro reversible assembly/disassembly system of hPBV, we isolated tetramers as possible assembly intermediates. We used atomic force microscopy to characterize the biophysical properties of hPBV capsids with different cargos (host nucleic acids or proteins) and found that the CP N-terminal segment not only is involved in nucleic acid interaction/packaging but also modulates the mechanical behavior of the capsid in conjunction with the cargo.IMPORTANCE Despite intensive study, human virus sampling is still sparse, especially for viruses that cause mild or asymptomatic disease. Human picobirnavirus (hPBV) is a double-stranded-RNA virus, broadly dispersed in the human population, but its pathogenicity is uncertain. Here, we report the hPBV structure derived from cryo-electron microscopy (cryo-EM) and reconstruction methods using three capsid protein variants (of different lengths and N-terminal amino acid compositions) that assemble as virus-like particles with distinct properties. The hPBV near-atomic structure reveals a quasisymmetric dimer as the structural subunit and tetramers as possible assembly intermediates that coassemble with nucleic acids. Our structural studies and atomic force microscopy analyses indicate that hPBV capsids are potentially excellent nanocages for gene therapy and targeted drug delivery in humans.


Assuntos
Proteínas do Capsídeo/química , Capsídeo/ultraestrutura , Microscopia Crioeletrônica/métodos , Picobirnavirus/genética , Picobirnavirus/metabolismo , Capsídeo/metabolismo , Proteínas do Capsídeo/genética , Genoma Viral , Humanos , Modelos Moleculares , Conformação Proteica , Conformação Proteica em alfa-Hélice , Domínios Proteicos , RNA de Cadeia Dupla , Vírion/ultraestrutura , Montagem de Vírus
5.
Cell ; 181(7): 1502-1517.e23, 2020 06 25.
Artigo em Inglês | MEDLINE | ID: mdl-32559462

RESUMO

RNA viruses are a major human health threat. The life cycles of many highly pathogenic RNA viruses like influenza A virus (IAV) and Lassa virus depends on host mRNA, because viral polymerases cleave 5'-m7G-capped host transcripts to prime viral mRNA synthesis ("cap-snatching"). We hypothesized that start codons within cap-snatched host transcripts could generate chimeric human-viral mRNAs with coding potential. We report the existence of this mechanism of gene origination, which we named "start-snatching." Depending on the reading frame, start-snatching allows the translation of host and viral "untranslated regions" (UTRs) to create N-terminally extended viral proteins or entirely novel polypeptides by genetic overprinting. We show that both types of chimeric proteins are made in IAV-infected cells, generate T cell responses, and contribute to virulence. Our results indicate that during infection with IAV, and likely a multitude of other human, animal and plant viruses, a host-dependent mechanism allows the genesis of hybrid genes.


Assuntos
Capuzes de RNA/genética , Infecções por Vírus de RNA/genética , Proteínas Recombinantes de Fusão/genética , Regiões 5' não Traduzidas/genética , Animais , Bovinos , Linhagem Celular , Cricetinae , Cães , Humanos , Vírus da Influenza A/metabolismo , Camundongos , Proteínas Mutantes Quiméricas/genética , Proteínas Mutantes Quiméricas/metabolismo , Fases de Leitura Aberta/genética , Capuzes de RNA/metabolismo , Infecções por Vírus de RNA/metabolismo , Vírus de RNA/genética , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , RNA Viral/metabolismo , RNA Polimerase Dependente de RNA/genética , RNA Polimerase Dependente de RNA/metabolismo , Proteínas Recombinantes de Fusão/metabolismo , Transcrição Genética/genética , Proteínas Virais/metabolismo , Replicação Viral/genética
6.
Nat Microbiol ; 4(2): 280-292, 2019 02.
Artigo em Inglês | MEDLINE | ID: mdl-30478287

RESUMO

Enteroviruses comprise a large group of mammalian pathogens that includes poliovirus. Pathology in humans ranges from sub-clinical to acute flaccid paralysis, myocarditis and meningitis. Until now, all of the enteroviral proteins were thought to derive from the proteolytic processing of a polyprotein encoded in a single open reading frame. Here we report that many enterovirus genomes also harbour an upstream open reading frame (uORF) that is subject to strong purifying selection. Using echovirus 7 and poliovirus 1, we confirmed the expression of uORF protein in infected cells. Through ribosome profiling (a technique for the global footprinting of translating ribosomes), we also demonstrated translation of the uORF in representative members of the predominant human enterovirus species, namely Enterovirus A, B and C. In differentiated human intestinal organoids, uORF protein-knockout echoviruses are attenuated compared to the wild-type at late stages of infection where membrane-associated uORF protein facilitates virus release. Thus, we have identified a previously unknown enterovirus protein that facilitates virus growth in gut epithelial cells-the site of initial viral invasion into susceptible hosts. These findings overturn the 50-year-old dogma that enteroviruses use a single-polyprotein gene expression strategy and have important implications for the understanding of enterovirus pathogenesis.


Assuntos
Infecções por Enterovirus/virologia , Enterovirus/genética , Enterovirus/patogenicidade , Mucosa Intestinal/virologia , Fases de Leitura Aberta/fisiologia , Proteínas Virais/metabolismo , Linhagem Celular , Membrana Celular/metabolismo , Enterovirus/classificação , Expressão Gênica , Técnicas de Inativação de Genes , Genoma Viral/genética , Humanos , Mutação , Fases de Leitura Aberta/genética , Organoides/virologia , Filogenia , Biossíntese de Proteínas , RNA Viral/genética , RNA Viral/metabolismo , Seleção Genética , Proteínas Virais/genética , Liberação de Vírus
7.
J Virol ; 92(17)2018 09 01.
Artigo em Inglês | MEDLINE | ID: mdl-29950409

RESUMO

The genus Torovirus (subfamily Torovirinae, family Coronaviridae, order Nidovirales) encompasses a range of species that infect domestic ungulates, including cattle, sheep, goats, pigs, and horses, causing an acute self-limiting gastroenteritis. Using the prototype species equine torovirus (EToV), we performed parallel RNA sequencing (RNA-seq) and ribosome profiling (Ribo-seq) to analyze the relative expression levels of the known torovirus proteins and transcripts, chimeric sequences produced via discontinuous RNA synthesis (a characteristic of the nidovirus replication cycle), and changes in host transcription and translation as a result of EToV infection. RNA sequencing confirmed that EToV utilizes a unique combination of discontinuous and nondiscontinuous RNA synthesis to produce its subgenomic RNAs (sgRNAs); indeed, we identified transcripts arising from both mechanisms that would result in sgRNAs encoding the nucleocapsid. Our ribosome profiling analysis revealed that ribosomes efficiently translate two novel CUG-initiated open reading frames (ORFs), located within the so-called 5' untranslated region. We have termed the resulting proteins U1 and U2. Comparative genomic analysis confirmed that these ORFs are conserved across all available torovirus sequences, and the inferred amino acid sequences are subject to purifying selection, indicating that U1 and U2 are functionally relevant. This study provides the first high-resolution analysis of transcription and translation in this neglected group of livestock pathogens.IMPORTANCE Toroviruses infect cattle, goats, pigs, and horses worldwide and can cause gastrointestinal disease. There is no treatment or vaccine, and their ability to spill over into humans has not been assessed. These viruses are related to important human pathogens, including severe acute respiratory syndrome (SARS) coronavirus, and they share some common features; however, the mechanism that they use to produce sgRNA molecules differs. Here, we performed deep sequencing to determine how equine torovirus produces sgRNAs. In doing so, we also identified two previously unknown open reading frames "hidden" within the genome. Together these results highlight the similarities and differences between this domestic animal virus and related pathogens of humans and livestock.


Assuntos
Perfilação da Expressão Gênica , Biossíntese de Proteínas , Torovirus/crescimento & desenvolvimento , Torovirus/genética , Transcrição Genética , Proteínas Virais/biossíntese , Animais , Células Cultivadas , Cavalos , Interações Hospedeiro-Patógeno , Análise de Sequência de RNA , Proteínas Virais/genética , Cultura de Vírus
8.
Retrovirology ; 15(1): 10, 2018 01 22.
Artigo em Inglês | MEDLINE | ID: mdl-29357872

RESUMO

BACKGROUND: The retrovirus murine leukemia virus (MuLV) has an 8.3 kb RNA genome with a simple 5'-gag-pol-env-3' architecture. Translation of the pol gene is dependent upon readthrough of the gag UAG stop codon; whereas the env gene is translated from spliced mRNA transcripts. Here, we report the first high resolution analysis of retrovirus gene expression through tandem ribosome profiling (RiboSeq) and RNA sequencing (RNASeq) of MuLV-infected cells. RESULTS: Ribosome profiling of MuLV-infected cells was performed, using the translational inhibitors harringtonine and cycloheximide to distinguish initiating and elongating ribosomes, respectively. Meta-analyses of host cell gene expression demonstrated that the RiboSeq datasets specifically captured the footprints of translating ribosomes at high resolution. Direct measurement of ribosomal occupancy of the MuLV genomic RNA indicated that ~ 7% of ribosomes undergo gag stop codon readthrough to access the pol gene. Initiation of translation was found to occur at several additional sites within the 5' leaders of the gag and env transcripts, upstream of their respective annotated start codons. CONCLUSIONS: These experiments reveal the existence of a number of previously uncharacterised, ribosomally occupied open reading frames within the MuLV genome, with possible regulatory consequences. In addition, we provide the first direct measurements of stop codon readthrough efficiency during cellular infection.


Assuntos
Perfilação da Expressão Gênica/métodos , Regulação Viral da Expressão Gênica , Vírus da Leucemia Murina/genética , Ribossomos/metabolismo , Animais , Linhagem Celular , Células HEK293 , Humanos , Camundongos , Biossíntese de Proteínas/genética , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Ratos , Análise de Sequência de RNA , Fatores de Tempo , Transcrição Genética
9.
PLoS Pathog ; 12(2): e1005473, 2016 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-26919232

RESUMO

Members of the family Coronaviridae have the largest genomes of all RNA viruses, typically in the region of 30 kilobases. Several coronaviruses, such as Severe acute respiratory syndrome-related coronavirus (SARS-CoV) and Middle East respiratory syndrome-related coronavirus (MERS-CoV), are of medical importance, with high mortality rates and, in the case of SARS-CoV, significant pandemic potential. Other coronaviruses, such as Porcine epidemic diarrhea virus and Avian coronavirus, are important livestock pathogens. Ribosome profiling is a technique which exploits the capacity of the translating ribosome to protect around 30 nucleotides of mRNA from ribonuclease digestion. Ribosome-protected mRNA fragments are purified, subjected to deep sequencing and mapped back to the transcriptome to give a global "snap-shot" of translation. Parallel RNA sequencing allows normalization by transcript abundance. Here we apply ribosome profiling to cells infected with Murine coronavirus, mouse hepatitis virus, strain A59 (MHV-A59), a model coronavirus in the same genus as SARS-CoV and MERS-CoV. The data obtained allowed us to study the kinetics of virus transcription and translation with exquisite precision. We studied the timecourse of positive and negative-sense genomic and subgenomic viral RNA production and the relative translation efficiencies of the different virus ORFs. Virus mRNAs were not found to be translated more efficiently than host mRNAs; rather, virus translation dominates host translation at later time points due to high levels of virus transcripts. Triplet phasing of the profiling data allowed precise determination of translated reading frames and revealed several translated short open reading frames upstream of, or embedded within, known virus protein-coding regions. Ribosome pause sites were identified in the virus replicase polyprotein pp1a ORF and investigated experimentally. Contrary to expectations, ribosomes were not found to pause at the ribosomal frameshift site. To our knowledge this is the first application of ribosome profiling to an RNA virus.


Assuntos
Regulação Viral da Expressão Gênica , Vírus da Hepatite Murina/metabolismo , RNA Mensageiro/metabolismo , RNA Viral/metabolismo , Ribossomos/metabolismo , Proteínas Virais/metabolismo , Animais , Linhagem Celular , Mudança da Fase de Leitura do Gene Ribossômico , Perfilação da Expressão Gênica , Cinética , Mesocricetus , Camundongos , Vírus da Hepatite Murina/enzimologia , Fases de Leitura Aberta , Biossíntese de Proteínas , RNA Mensageiro/química , RNA Viral/química , Mapeamento por Restrição/métodos , Análise de Sequência de RNA , Transcrição Genética , Transcriptoma , Proteínas Virais/química , Proteínas Virais/genética , Fenômenos Fisiológicos Virais
10.
RNA ; 21(10): 1731-45, 2015 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-26286745

RESUMO

Ribosome profiling is a technique that permits genome-wide, quantitative analysis of translation and has found broad application in recent years. Here we describe a modified profiling protocol and software package designed to benefit more broadly the translation community in terms of simplicity and utility. The protocol, applicable to diverse organisms, including organelles, is based largely on previously published profiling methodologies, but uses duplex-specific nuclease (DSN) as a convenient, species-independent way to reduce rRNA contamination. We show that DSN-based depletion compares favorably with other commonly used rRNA depletion strategies and introduces little bias. The profiling protocol typically produces high levels of triplet periodicity, facilitating the detection of coding sequences, including upstream, downstream, and overlapping open reading frames (ORFs) and an alternative ribosome conformation evident during termination of protein synthesis. In addition, we provide a software package that presents a set of methods for parsing ribosomal profiling data from multiple samples, aligning reads to coding sequences, inferring alternative ORFs, and plotting average and transcript-specific aspects of the data. Methods are also provided for extracting the data in a form suitable for differential analysis of translation and translational efficiency.


Assuntos
Endonucleases/metabolismo , Ribossomos/metabolismo , Software , Chlamydomonas reinhardtii/genética , Biologia Computacional , Fases de Leitura Aberta
11.
J Virol ; 88(18): 10364-76, 2014 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-24991001

RESUMO

UNLABELLED: Translational readthrough--suppression of termination at a stop codon--is exploited in the replication cycles of several viruses and represents a potential target for antiviral intervention. In the gammaretroviruses, typified by Moloney murine leukemia virus (MuLV), gag and pol are in the same reading frame, separated by a UAG stop codon, and termination codon readthrough is required for expression of the viral Gag-Pol fusion protein. Here, we investigated the effect on MuLV replication of modulating readthrough efficiency. We began by manipulating the readthrough signal in the context of an infectious viral clone to generate a series of MuLV variants in which readthrough was stimulated or reduced. In carefully controlled infectivity assays, it was found that reducing the MuLV readthrough efficiency only 4-fold led to a marked defect and that a 10-fold reduction essentially abolished replication. However, up to an ∼ 8.5-fold stimulation of readthrough (up to 60% readthrough) was well tolerated by the virus. These high levels of readthrough were achieved using a two-plasmid system, with Gag and Gag-Pol expressed from separate infectious clones. We also modulated readthrough by silencing expression of eukaryotic release factors 1 and 3 (eRF1 and eRF3) or by introducing aminoglycosides into the cells. The data obtained indicate that gammaretroviruses tolerate a substantial excess of viral Gag-Pol synthesis but are very sensitive to a reduction in levels of this polyprotein. Thus, as is also the case for ribosomal frameshifting, antiviral therapies targeting readthrough with inhibitory agents are likely to be the most beneficial. IMPORTANCE: Many pathogenic RNA viruses and retroviruses use ribosomal frameshifting or stop codon readthrough to regulate expression of their replicase enzymes. These translational "recoding" processes are potential targets for antiviral intervention, but we have only a limited understanding of the consequences to virus replication of modulating the efficiency of recoding, particularly for those viruses employing readthrough. In this paper, we describe the first systematic analysis of the effect of increasing or decreasing readthrough efficiency on virus replication using the gammaretrovirus MuLV as a model system. We find unexpectedly that MuLV replication is only slightly inhibited by substantial increases in readthrough frequency, but as with other viruses that use recoding strategies, replication is quite sensitive to even modest reductions. These studies provide insights into both the readthrough process and MuLV replication and have implications for the selection of antivirals against gammaretroviruses.


Assuntos
Códon de Terminação/genética , Vírus da Leucemia Murina/genética , Biossíntese de Proteínas , Infecções por Retroviridae/veterinária , Replicação Viral , Animais , Proteínas de Fusão gag-pol/genética , Proteínas de Fusão gag-pol/metabolismo , Regulação Viral da Expressão Gênica , Vírus da Leucemia Murina/fisiologia , Camundongos , Infecções por Retroviridae/virologia , Doenças dos Roedores
12.
Biophys J ; 106(3): 687-95, 2014 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-24507609

RESUMO

Vaults are the largest ribonucleoprotein particles found in eukaryotic cells, with an unclear cellular function and promising applications as vehicles for drug delivery. In this article, we examine the local stiffness of individual vaults and probe their structural stability with atomic force microscopy under physiological conditions. Our data show that the barrel, the central part of the vault, governs both the stiffness and mechanical strength of these particles. In addition, we induce single-protein fractures in the barrel shell and monitor their temporal evolution. Our high-resolution atomic force microscopy topographies show that these fractures occur along the contacts between two major vault proteins and disappear over time. This unprecedented systematic self-healing mechanism, which enables these particles to reversibly adapt to certain geometric constraints, might help vaults safely pass through the nuclear pore complex and potentiate their role as self-reparable nanocontainers.


Assuntos
Elasticidade , Partículas de Ribonucleoproteínas em Forma de Abóbada/química , Estresse Mecânico
13.
J Virol ; 86(21): 11581-94, 2012 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-22896611

RESUMO

Programmed -1 ribosomal frameshifting is widely used in the expression of RNA virus replicases and represents a potential target for antiviral intervention. There is interest in determining the extent to which frameshifting efficiency can be modulated before virus replication is compromised, and we have addressed this question using the alpharetrovirus Rous sarcoma virus (RSV) as a model system. In RSV, frameshifting is essential in the production of the Gag-Pol polyprotein from the overlapping gag and pol coding sequences. The frameshift signal is composed of two elements, a heptanucleotide slippery sequence and, just downstream, a stimulatory RNA structure that has been proposed to be an RNA pseudoknot. Point mutations were introduced into the frameshift signal of an infectious RSV clone, and virus replication was monitored following transfection and subsequent infection of susceptible cells. The introduced mutations were designed to generate a range of frameshifting efficiencies, yet with minimal impact on encoded amino acids. Our results reveal that point mutations leading to a 3-fold decrease in frameshifting efficiency noticeably reduce virus replication and that further reduction is severely inhibitory. In contrast, a 3-fold stimulation of frameshifting is well tolerated. These observations suggest that small-molecule inhibitors of frameshifting are likely to have potential as agents for antiviral intervention. During the course of this work, we were able to confirm, for the first time in vivo, that the RSV stimulatory RNA is indeed an RNA pseudoknot but that the pseudoknot per se is not absolutely required for virus viability.


Assuntos
Mudança da Fase de Leitura do Gene Ribossômico , Vírus do Sarcoma de Rous/fisiologia , Replicação Viral , Sequência de Bases , Produtos do Gene gag/biossíntese , Produtos do Gene pol/biossíntese , Conformação de Ácido Nucleico , Mutação Puntual , RNA Viral/química , RNA Viral/genética , Vírus do Sarcoma de Rous/genética
14.
J Biol Chem ; 287(29): 24473-82, 2012 Jul 13.
Artigo em Inglês | MEDLINE | ID: mdl-22619177

RESUMO

In many viruses, a precursor particle, or procapsid, is assembled and undergoes massive chemical and physical modification to produce the infectious capsid. Capsid assembly and maturation are finely tuned processes in which viral and host factors participate. We show that the precursor of the VP2 capsid protein (pVP2) of the infectious bursal disease virus (IBDV), a double-stranded RNA virus, is processed at the C-terminal domain (CTD) by a host protease, the puromycin-sensitive aminopeptidase (PurSA). The pVP2 CTD (71 residues) has an important role in determining the various conformations of VP2 (441 residues) that build the T = 13 complex capsid. pVP2 CTD activity is controlled by co- and posttranslational proteolytic modifications of different targets by the VP4 viral protease and by VP2 itself to yield the mature VP2-441 species. Puromycin-sensitive aminopeptidase is responsible for the peptidase activity that cleaves the Arg-452-Arg-453 bond to generate the intermediate pVP2-452 polypeptide. A pVP2 R453A substitution abrogates PurSA activity. We used a baculovirus-based system to express the IBDV polyprotein in insect cells and found inefficient formation of virus-like particles similar to IBDV virions, which correlates with the absence of puromycin-sensitive aminopeptidase in these cells. Virus-like particle assembly was nonetheless rescued efficiently by coexpression of chicken PurSA or pVP2-452 protein. Silencing or pharmacological inhibition of puromycin-sensitive aminopeptidase activity in cell lines permissive for IBDV replication caused a major blockade in assembly and/or maturation of infectious IBDV particles, as virus yields were reduced markedly. PurSA activity is thus essential for IBDV replication.


Assuntos
Aminopeptidases/metabolismo , Proteínas do Capsídeo/metabolismo , Vírus da Doença Infecciosa da Bursa/fisiologia , Peptídeo Hidrolases/metabolismo , Vírus de RNA/fisiologia , Montagem de Vírus/fisiologia , Replicação Viral/fisiologia , Aminopeptidases/efeitos dos fármacos , Animais , Proteínas do Capsídeo/efeitos dos fármacos , Linhagem Celular , Cães , Vírus da Doença Infecciosa da Bursa/efeitos dos fármacos , Peptídeo Hidrolases/efeitos dos fármacos , Puromicina/farmacologia , Vírus de RNA/efeitos dos fármacos , RNA de Cadeia Dupla/genética , Montagem de Vírus/efeitos dos fármacos , Replicação Viral/efeitos dos fármacos
15.
J Biol Chem ; 285(6): 3643-3650, 2010 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-19933276

RESUMO

Capsid proteins that adopt distinct conformations constitute a paradigm of the structural polymorphism of macromolecular assemblies. We show the molecular basis of the flexibility mechanism of VP2, the capsid protein of the double-stranded RNA virus infectious bursal disease virus. The initial assembly, a procapsid-like structure, is built by the protein precursor pVP2 and requires VP3, the other infectious bursal disease virus major structural protein, which acts as a scaffold. The pVP2 C-terminal region, which is proteolyzed during virus maturation, contains an amphipathic alpha-helix that acts as a molecular switch. In the absence of VP3, efficient virus-like particle assembly occurs when the structural unit is a VP2-based chimeric protein with an N-terminal-fused His(6) tag. The His tag has a positively charged N terminus and a negatively charged C terminus, both important for virion-like structure assembly. The charge distributions of the VP3 C terminus and His tag are similar. We tested whether the His tag emulates the role of VP3 and found that the presence of a VP3 C-terminal peptide in VP2-based chimeric proteins resulted in the assembly of virus-like particles. We analyzed the electrostatic interactions between these two charged morphogenetic peptides, in which a single residue was mutated to impede the predicted interaction, followed by a compensatory double mutation to rescue electrostatic interactions. The effects of these mutations were monitored by following the virus-like and/or virus-related assemblies. Our results suggest that the basic face of the pVP2 amphipathic alpha-helix interacts with the acidic region of the VP3 C terminus and that this interaction is essential for VP2 acquisition of competent conformations for capsid assembly.


Assuntos
Proteínas do Capsídeo/metabolismo , Vírus da Doença Infecciosa da Bursa/fisiologia , Vírus de RNA/fisiologia , Proteínas Virais/metabolismo , Western Blotting , Capsídeo/metabolismo , Proteínas do Capsídeo/química , Proteínas do Capsídeo/genética , Eletroforese em Gel de Poliacrilamida , Vírus da Doença Infecciosa da Bursa/genética , Vírus da Doença Infecciosa da Bursa/ultraestrutura , Microscopia Eletrônica , Mutação , Vírus de RNA/genética , Vírus de RNA/ultraestrutura , Eletricidade Estática , Proteínas Virais/química , Proteínas Virais/genética , Vírion/metabolismo , Montagem de Vírus
16.
J Biol Chem ; 284(12): 8064-72, 2009 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-19144647

RESUMO

Viral capsids are envisioned as vehicles to deliver the viral genome to the host cell. They are nonetheless dynamic protective shells, as they participate in numerous processes of the virus cycle such as assembly, genome packaging, binding to receptors, and uncoating among others. In so doing, they undergo large scale conformational changes. Capsid proteins with essential enzymatic activities are being described more frequently. Here we show that the precursor (pVP2) of the capsid protein VP2 of the infectious bursal disease virus (IBDV), an avian double-stranded RNA virus, has autoproteolytic activity. The pVP2 C-terminal region is first processed by the viral protease VP4. VP2 Asp-431, lying in a flexible loop preceding the C-terminal most alpha-helix, is responsible for the endopeptidase activity that cleaves the Ala-441-Phe-442 bond to generate the mature VP2 polypeptide. The D431N substitution abrogates the endopeptidase activity without introducing a significant conformational change, as deduced from the three-dimensional structure of the mutant protein at 3.1 A resolution. Combinations of VP2 polypeptides containing mutations affecting either the cleavage or the catalytic site revealed that pVP2 proteolytic processing is the result of a monomolecular cis-cleavage reaction. The D431N mutation does not affect the assembly of the VP2 trimers that constitute the capsid building block. Although VP2 D431N trimers are capable of assembling both pentamers and hexamers, expression of a polyprotein gene harboring the D431N mutation does not result in the assembly of IBDV virus-like particles. Reverse genetics analyses demonstrate that pVP2 self-processing is essential for the assembly of an infectious IBDV progeny.


Assuntos
Proteínas do Capsídeo/química , Endopeptidases/química , Vírus da Doença Infecciosa da Bursa/enzimologia , Precursores de Proteínas/química , Proteínas Estruturais Virais/química , Substituição de Aminoácidos , Proteínas do Capsídeo/genética , Proteínas do Capsídeo/metabolismo , Cristalografia por Raios X , Endopeptidases/genética , Endopeptidases/metabolismo , Genoma Viral/fisiologia , Vírus da Doença Infecciosa da Bursa/genética , Mutação de Sentido Incorreto , Precursores de Proteínas/genética , Precursores de Proteínas/metabolismo , Estrutura Secundária de Proteína/fisiologia , Estrutura Terciária de Proteína/fisiologia , Proteínas Estruturais Virais/genética , Proteínas Estruturais Virais/metabolismo , Montagem de Vírus/fisiologia , Internalização do Vírus
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