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Frontiers in Microbiology 2023is one order of RNA virus, with the largest single-stranded positive sense RNA genome enwrapped with membrane envelope. It comprises four families () and has been... (Review)
Review
is one order of RNA virus, with the largest single-stranded positive sense RNA genome enwrapped with membrane envelope. It comprises four families () and has been circulating in humans and animals for almost one century, posing great threat to livestock and poultry,as well as to public health. shares similar life cycle: attachment to cell surface, entry, primary translation of replicases, viral RNA replication in cytoplasm, translation of viral proteins, virion assembly, budding, and release. The viral RNA synthesis is the critical step during infection, including genomic RNA (gRNA) replication and subgenomic mRNAs (sg mRNAs) transcription. gRNA replication requires the synthesis of a negative sense full-length RNA intermediate, while the sg mRNAs transcription involves the synthesis of a nested set of negative sense subgenomic intermediates by a discontinuous strategy. This RNA synthesis process is mediated by the viral replication/transcription complex (RTC), which consists of several enzymatic replicases derived from the polyprotein 1a and polyprotein 1ab and several cellular proteins. These replicases and host factors represent the optimal potential therapeutic targets. Hereby, we summarize the classification, associated diseases, "replication organelle," replication and transcription mechanisms, as well as related regulatory factors.
PubMed: 38328580
DOI: 10.3389/fmicb.2023.1291761 -
Emerging Microbes & Infections Dec 2023Viral envelope glycoproteins are crucial for viral infections. In the process of enveloped viruses budding and release from the producer cells, viral envelope... (Review)
Review
Viral envelope glycoproteins are crucial for viral infections. In the process of enveloped viruses budding and release from the producer cells, viral envelope glycoproteins are presented on the viral membrane surface as spikes, promoting the virus's next-round infection of target cells. However, the host cells evolve counteracting mechanisms in the long-term virus-host co-evolutionary processes. For instance, the host cell antiviral factors could potently suppress viral replication by targeting their envelope glycoproteins through multiple channels, including their intracellular synthesis, glycosylation modification, assembly into virions, and binding to target cell receptors. Recently, a group of studies discovered that some host antiviral proteins specifically recognized host proprotein convertase (PC) furin and blocked its cleavage of viral envelope glycoproteins, thus impairing viral infectivity. Here, in this review, we briefly summarize several such host antiviral factors and analyze their roles in reducing furin cleavage of viral envelope glycoproteins, aiming at providing insights for future antiviral studies.
Topics: Humans; Furin; Viral Envelope Proteins; SARS-CoV-2; Ebolavirus; HIV-1; Antiviral Agents; Hemorrhagic Fever, Ebola; COVID-19; Glycoproteins; Virus Diseases
PubMed: 36591809
DOI: 10.1080/22221751.2022.2164742 -
International Journal of Molecular... Sep 2023Porcine deltacoronavirus (PDCoV) is an emerging virus that poses a significant threat to the global swine industry. Its membrane (M) protein is crucial for virion...
Porcine deltacoronavirus (PDCoV) is an emerging virus that poses a significant threat to the global swine industry. Its membrane (M) protein is crucial for virion assembly and virus-host interactions. We selected the hydrophilic region of M protein for prokaryotic expression, purification, and recombinant protein production. Utilizing hybridoma technology, we prepared the monoclonal antibody (mAb) 24-A6 against M protein. The mAb 24-A6 was shown to be suitable for use in immunofluorescence assays, western blotting, and immunoprecipitation, with specificity for PDCoV and no cross-reactivity with other five porcine viruses. The M protein was observed to be expressed as early as 3 h after PDCoV infection, increasing its expression over the duration of infection. Notably, the antigenic epitope of the M protein identified as SPESRL recognized by mAb 24-A6 was found within a conserved structural domain (SWWSFNPETNNL) of the coronavirus M protein, indicating a crucial overlap between a functionally important viral assembly region and a region recognized by the immune system. Our findings provide valuable insights into mAb 24-A6 targeting the antigenic epitope of M protein and may contribute to the development of diagnostic tools for PDCoV infection and fundamental research into the function of PDCoV M protein.
Topics: Animals; Swine; Membrane Proteins; Antibodies, Monoclonal; Deltacoronavirus; Epitopes
PubMed: 37762237
DOI: 10.3390/ijms241813934 -
Gut and Liver Mar 2024Current treatment of chronic hepatitis B virus (HBV) infection, pegylated interferon-α (pegIFN-α) and nucleos(t)ide analogue (NA), can suppress HBV replication,... (Review)
Review
Current treatment of chronic hepatitis B virus (HBV) infection, pegylated interferon-α (pegIFN-α) and nucleos(t)ide analogue (NA), can suppress HBV replication, reverse liver inflammation and fibrosis, and decrease risks of cirrhosis and hepatocellular carcinoma, but hepatitis B surface antigen (HBsAg) loss is rare. Functional HBV cure is defined as undetectable HBsAg and unquantifiable serum HBV DNA for at least 24 weeks after a finite course of therapy. This requires suppression of HBV replication and viral protein production as well as restoration of immune response to HBV. Direct-acting antivirals targeting virus entry, capsid assembly, viral protein production and secretion are in clinical trials. In parallel, immune modulatory therapies to stimulate HBV-specific immune response and to remove immune blockade are being tested. Clinical trials of direct-acting antivirals alone or immune modulatory therapies alone have not been successful in achieving HBV cure. Recent combinations of direct-acting antivirals and immune modulatory therapies have shown promising results particularly with combinations that included pegIFN-α. These results need to be confirmed in larger studies with longer follow-up, and further work is needed to develop simpler regimens with fewer drugs that can be administered orally and safely. While there is a strong desire to develop finite therapies that can achieve HBV cure, safety is paramount and new therapies must provide incremental value compared to standard of care, which is predominantly long-term NA therapy.
PubMed: 38533651
DOI: 10.5009/gnl240023 -
Journal of Virology Oct 2023The influenza A virus genome consists of eight distinct viral RNAs (vRNAs) that are typically packaged into a single virion as an octameric complex. How this genome...
The influenza A virus genome consists of eight distinct viral RNAs (vRNAs) that are typically packaged into a single virion as an octameric complex. How this genome complex is assembled and incorporated into the virion is poorly understood, but previous research suggests a coordinative role for packaging signals present in all vRNAs. Here, we show that disruption of two packaging signals in a model H7N7 influenza A virus results in a mixture of virions with unusual vRNA content, including empty virions, virions with one to four vRNAs, and virions with octameric complexes composed of vRNA duplicates. Our results suggest that (i) the assembly of error-free octameric complexes proceeds through a series of defined vRNA sub-complexes and (ii) virions can bud without incorporating complete octameric complexes.
Topics: Genome, Viral; Influenza A virus; Influenza A Virus, H7N7 Subtype; RNA, Viral; Viral Genome Packaging; Virion; Virus Assembly
PubMed: 37811996
DOI: 10.1128/jvi.01076-23 -
Journal of Virology Aug 2023Proliferating cell nuclear antigen (PCNA) belongs to the DNA sliding clamp family. Via interacting with various partner proteins, PCNA plays critical roles in DNA...
Proliferating cell nuclear antigen (PCNA) belongs to the DNA sliding clamp family. Via interacting with various partner proteins, PCNA plays critical roles in DNA replication, DNA repair, chromatin assembly, epigenetic inheritance, chromatin remodeling, and many other fundamental biological processes. Although PCNA and PCNA-interacting partner networks are conserved across species, PCNA of a given species is rarely functional in heterologous systems, emphasizing the importance of more representative PCNA studies. Here, we report two crystal structures of PCNA from African swine fever virus (ASFV), which is the only member of the family. Compared to the eukaryotic and archaeal PCNAs and the sliding clamp structural homologs from other viruses, PCNA possesses unique sequences and/or conformations at several regions, such as the J-loop, interdomain-connecting loop (IDCL), P-loop, and C-tail, which are involved in partner recognition or modification of sliding clamps. In addition to double-stranded DNA binding, we also demonstrate that PCNA can modestly enhance the ligation activity of the LIG protein. The unique structural features of PCNA can serve as a potential target for the development of ASFV-specific inhibitors and help combat the deadly virus. IMPORTANCE Two high-resolution crystal structures of African swine fever virus proliferating cell nuclear antigen (PCNA) are presented here. Structural comparison revealed that PCNA is unique at several regions, such as the J-loop, the interdomain-connecting loop linker, and the P-loop, which may play important roles in ASFV-specific partner selection of PCNA. Unlike eukaryotic and archaeal PCNAs, PCNA possesses high double-stranded DNA-binding affinity. Besides DNA binding, PCNA can also modestly enhance the ligation activity of the LIG protein, which is essential for the replication and repair of ASFV genome. The unique structural features make PCNA a potential target for drug development, which will help combat the deadly virus.
Topics: Animals; African Swine Fever; African Swine Fever Virus; DNA; Molecular Conformation; Proliferating Cell Nuclear Antigen; Swine; Viral Proteins
PubMed: 37534905
DOI: 10.1128/jvi.00748-23 -
Acta Biochimica Et Biophysica Sinica Jul 2023Liquid-liquid phase separation (LLPS) has emerged as a crucial mechanism for cellular compartmentalization. One prominent example of this is the stress granule. Found in...
Liquid-liquid phase separation (LLPS) has emerged as a crucial mechanism for cellular compartmentalization. One prominent example of this is the stress granule. Found in various types of cells, stress granule is a biomolecular condensate formed through phase separation. It comprises numerous RNA and RNA-binding proteins. Over the past decades, substantial knowledge has been gained about the composition and dynamics of stress granules. SGs can regulate various signaling pathways and have been associated with numerous human diseases, such as neurodegenerative diseases, cancer, and infectious diseases. The threat of viral infections continues to loom over society. Both DNA and RNA viruses depend on host cells for replication. Intriguingly, many stages of the viral life cycle are closely tied to RNA metabolism in human cells. The field of biomolecular condensates has rapidly advanced in recent times. In this context, we aim to summarize research on stress granules and their link to viral infections. Notably, stress granules triggered by viral infections behave differently from the canonical stress granules triggered by sodium arsenite (SA) and heat shock. Studying stress granules in the context of viral infections could offer a valuable platform to link viral replication processes and host anti-viral responses. A deeper understanding of these biological processes could pave the way for innovative interventions and treatments for viral infectious diseases. They could potentially bridge the gap between basic biological processes and interactions between viruses and their hosts.
Topics: Humans; Cytoplasmic Granules; Stress Granules; RNA; Virus Diseases; Biological Phenomena; Virus Replication
PubMed: 37401177
DOI: 10.3724/abbs.2023117 -
PLoS Pathogens Oct 2023In the case of the Japanese encephalitis virus (JEV), the envelope protein (E), a major component of viral particles, contains a highly conserved N-linked glycosylation...
In the case of the Japanese encephalitis virus (JEV), the envelope protein (E), a major component of viral particles, contains a highly conserved N-linked glycosylation site (E: N154). Glycosylation of the E protein is thought to play an important role in the ability of the virus to attach to target cells during transmission; however, its role in viral particle formation and release remains poorly understood. In this study, we investigated the role of N-glycosylation of flaviviral structural proteins in viral particle formation and secretion by introducing mutations in viral structural proteins or cellular factors involved in glycoprotein transport and processing. The number of secreted subviral particles (SVPs) was significantly reduced in N154A, a glycosylation-null mutant, but increased in D67N, a mutant containing additional glycosylation sites, indicating that the amount of E glycosylation regulates the release of SVPs. SVP secretion was reduced in cells deficient in galactose, sialic acid, and N-acetylglucosamine modifications in the Golgi apparatus; however, these reductions were not significant, suggesting that glycosylation mainly plays a role in pre-Golgi transport. Fluorescent labeling of SVPs using a split green fluorescent protein (GFP) system and time-lapse imaging by retention using selective hooks (RUSH) system revealed that the glycosylation-deficient mutant was arrested before endoplasmic reticulum (ER)- Golgi transport. However, the absence of ERGIC-53 and ERGIC-L, ER-Golgi transport cargo receptors that recognize sugar chains on cargo proteins, does not impair SVP secretion. In contrast, the solubility of the N154A mutant of E or the N15A/T17A mutant of prM in cells was markedly lower than that of the wild type, and proteasome-mediated rapid degradation of these mutants was observed, indicating the significance of glycosylation of both prM and E in proper protein folding and assembly of viral particles in the ER.
Topics: Glycosylation; Flavivirus; Viral Envelope Proteins; Encephalitis Virus, Japanese; Virion
PubMed: 37819933
DOI: 10.1371/journal.ppat.1011681 -
Nature Communications Apr 2024Controlled assembly of a protein shell around a viral genome is a key step in the life cycle of many viruses. Here we report a strategy for regulating the co-assembly of...
Controlled assembly of a protein shell around a viral genome is a key step in the life cycle of many viruses. Here we report a strategy for regulating the co-assembly of nonviral proteins and nucleic acids into highly ordered nucleocapsids in vitro. By fusing maltose binding protein to the subunits of NC-4, an engineered protein cage that encapsulates its own encoding mRNA, we successfully blocked spontaneous capsid assembly, allowing isolation of the individual monomers in soluble form. To initiate RNA-templated nucleocapsid formation, the steric block can be simply removed by selective proteolysis. Analyses by transmission and cryo-electron microscopy confirmed that the resulting assemblies are structurally identical to their RNA-containing counterparts produced in vivo. Enzymatically triggered cage formation broadens the range of RNA molecules that can be encapsulated by NC-4, provides unique opportunities to study the co-assembly of capsid and cargo, and could be useful for studying other nonviral and viral assemblies.
Topics: Nucleocapsid; Cryoelectron Microscopy; Maltose-Binding Proteins; Virus Assembly; Capsid; RNA, Viral; Capsid Proteins; RNA, Messenger
PubMed: 38678040
DOI: 10.1038/s41467-024-47808-1 -
Current Opinion in Virology Aug 2023Cellular cryo-electron tomography (cryo-ET) offers 3D snapshots at molecular resolution capturing pivotal steps during viral infection. However, tomogram quality depends... (Review)
Review
Cellular cryo-electron tomography (cryo-ET) offers 3D snapshots at molecular resolution capturing pivotal steps during viral infection. However, tomogram quality depends on the vitrification level of the sample and its thickness. In addition, mandatory inactivation protocols to assure biosafety when handling highly pathogenic viruses during cryo-ET can compromise sample preservation. Here, we focus on different strategies applied in cryo-ET and discuss their advantages and limitations with reference to severe acute respiratory syndrome coronavirus 2 studies. We highlight the importance of virus-like particle (VLP) and replicon systems to study virus assembly and replication in a cellular context without inactivation protocols. We discuss the application of chemical fixation and different irradiation methods in cryo-ET sample preparation and acquisition workflows.
Topics: Humans; Electron Microscope Tomography; Containment of Biohazards; Cryoelectron Microscopy; COVID-19; Virus Diseases
PubMed: 37348443
DOI: 10.1016/j.coviro.2023.101338