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Han X, Xu H, Weng Y, Chen R, Xu J, Cao T, Sun R, Shan Y, He F, Fang W, Li X. N pro of classical swine fever virus enhances HMGB1 acetylation and its degradation by lysosomes to evade from HMGB1-mediated antiviral immunity. Virus Res 2024; 339:199280. [PMID: 37995963 PMCID: PMC10709370 DOI: 10.1016/j.virusres.2023.199280] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2023] [Revised: 11/17/2023] [Accepted: 11/18/2023] [Indexed: 11/25/2023]
Abstract
Classical swine fever virus (CSFV) can dampen the host innate immunity by destabilizing IRF3 upon its binding with viral Npro. High mobility group box 1 (HMGB1), a non-histone nuclear protein, has diverse functions, including inflammation, innate immunity, etc., which are closely related to its cellular localization. We investigated potential mutual interactions between CSFV and HMGB1 and their effects on virus replication. We found that HMGB1 at the protein level, but not at mRNA level, was markedly reduced in CSFV-infected or Npro-expressing IPEC-J2 cells. HMGB1 in the nuclear compartment is anti-CSFV by promoting IFN-mediated innate immune response, as evidenced by overexpression of nuclear or cytoplasmic dominant HMGB1 mutant in IPEC-J2 cells stimulated with poly(I:C). However, CSFV Npro upregulates HMGB1 acetylation, a modification that promotes HMGB1 translocation into the cytoplasmic compartment where it is degraded by lysosomes. Ethyl pyruvate could downregulate HMGB1 acetylation and prevent Npro-mediated HMGB1 reduction. Inhibition of deacetylase HDAC1 with MS275 or by RNA silencing could promote Npro-mediated HMGB1 degradation. Taken together, our study elucidates the mechanism with which HMGB1 in the nuclei initiates antiviral innate immune response to suppress CSFV replication and elaborates the pathway by which CSFV uses its Npro to evade from HMGB1-mediated antiviral immunity through upregulating HMGB1 acetylation with subsequent translocation into cytoplasm for lysosomal degradation.
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Affiliation(s)
- Xiao Han
- Zhejiang University Institute of Preventive Veterinary Medicine & Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Hangzhou, Zhejiang 310058, China
| | - Hankun Xu
- Zhejiang University Institute of Preventive Veterinary Medicine & Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Hangzhou, Zhejiang 310058, China
| | - Yifan Weng
- Zhejiang University Institute of Preventive Veterinary Medicine & Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Hangzhou, Zhejiang 310058, China
| | - Rong Chen
- Zhejiang University Institute of Preventive Veterinary Medicine & Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Hangzhou, Zhejiang 310058, China
| | - Jidong Xu
- Zhejiang University Institute of Preventive Veterinary Medicine & Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Hangzhou, Zhejiang 310058, China
| | - Tong Cao
- Zhejiang University Institute of Preventive Veterinary Medicine & Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Hangzhou, Zhejiang 310058, China
| | - Renjie Sun
- Zhejiang Provincial Center for Animal Disease Prevention & Control, Hangzhou, Zhejiang 311199, China
| | - Ying Shan
- Zhejiang University Institute of Preventive Veterinary Medicine & Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Hangzhou, Zhejiang 310058, China
| | - Fang He
- Zhejiang University Institute of Preventive Veterinary Medicine & Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Hangzhou, Zhejiang 310058, China
| | - Weihuan Fang
- Zhejiang University Institute of Preventive Veterinary Medicine & Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Hangzhou, Zhejiang 310058, China.
| | - Xiaoliang Li
- Zhejiang University Institute of Preventive Veterinary Medicine & Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Hangzhou, Zhejiang 310058, China.
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Wen S, Li X, Lv X, Liu K, Ren J, Zhai J, Song Y. Current progress on innate immune evasion mediated by Npro protein of pestiviruses. Front Immunol 2023; 14:1136051. [PMID: 37090696 PMCID: PMC10115221 DOI: 10.3389/fimmu.2023.1136051] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2023] [Accepted: 03/27/2023] [Indexed: 04/08/2023] Open
Abstract
Interferon (IFN), the most effective antiviral cytokine, is involved in innate and adaptive immune responses and is essential to the host defense against virus invasion. Once the host was infected by pathogens, the pathogen-associated molecular patterns (PAMPs) were recognized by the host pattern recognition receptors (PRRs), which activates interferon regulatory transcription factors (IRFs) and nuclear factor-kappa B (NF-κB) signal transduction pathway to induce IFN expression. Pathogens have acquired many strategies to escape the IFN-mediated antiviral immune response. Pestiviruses cause massive economic losses in the livestock industry worldwide every year. The immune escape strategies acquired by pestiviruses during evolution are among the major difficulties in its control. Previous experiments indicated that Erns, as an envelope glycoprotein unique to pestiviruses with RNase activity, could cleave viral ss- and dsRNAs, therefore inhibiting the host IFN production induced by viral ss- and dsRNAs. In contrast, Npro, the other envelope glycoprotein unique to pestiviruses, mainly stimulates the degradation of transcription factor IRF-3 to confront the IFN response. This review mainly summarized the current progress on mechanisms mediated by Npro of pestiviruses to antagonize IFN production.
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Affiliation(s)
- Shubo Wen
- Preventive Veterinary Laboratory, College of Animal Science and Technology, Inner Mongolia Minzu University, Tongliao, China
- Key Laboratory of Zoonose Prevention and Control, Universities of Inner Mongolia Autonomous Region, Tongliao, China
- Beef Cattle Disease Control and Engineering Technology Research Center, Inner Mongolia Autonomous Region, Tongliao, China
| | - Xintong Li
- State Key Laboratory of Membrane Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, China
| | - Xiangyu Lv
- Preventive Veterinary Laboratory, College of Animal Science and Technology, Inner Mongolia Minzu University, Tongliao, China
- Beef Cattle Disease Control and Engineering Technology Research Center, Inner Mongolia Autonomous Region, Tongliao, China
| | - Kai Liu
- Preventive Veterinary Laboratory, College of Animal Science and Technology, Inner Mongolia Minzu University, Tongliao, China
- Beef Cattle Disease Control and Engineering Technology Research Center, Inner Mongolia Autonomous Region, Tongliao, China
| | - Jingqiang Ren
- Wenzhou Key Laboratory for Virology and Immunology, Institute of Virology, Wenzhou University, Zhejiang, Wenzhou, China
- *Correspondence: Jingqiang Ren, ; Jingbo Zhai, ; Yang Song,
| | - Jingbo Zhai
- Preventive Veterinary Laboratory, College of Animal Science and Technology, Inner Mongolia Minzu University, Tongliao, China
- Key Laboratory of Zoonose Prevention and Control, Universities of Inner Mongolia Autonomous Region, Tongliao, China
- *Correspondence: Jingqiang Ren, ; Jingbo Zhai, ; Yang Song,
| | - Yang Song
- Preventive Veterinary Laboratory, College of Animal Science and Technology, Inner Mongolia Minzu University, Tongliao, China
- Key Laboratory of Zoonose Prevention and Control, Universities of Inner Mongolia Autonomous Region, Tongliao, China
- *Correspondence: Jingqiang Ren, ; Jingbo Zhai, ; Yang Song,
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A double deletion prevents replication of the pestivirus bovine viral diarrhea virus in the placenta of pregnant heifers. PLoS Pathog 2021; 17:e1010107. [PMID: 34879119 PMCID: PMC8654156 DOI: 10.1371/journal.ppat.1010107] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2021] [Accepted: 11/10/2021] [Indexed: 01/13/2023] Open
Abstract
In contrast to wild type bovine viral diarhea virus (BVDV) specific double deletion mutants are not able to establish persistent infection upon infection of a pregnant heifer. Our data shows that this finding results from a defect in transfer of the virus from the mother animal to the fetus. Pregnant heifers were inoculated with such a double deletion mutant or the parental wild type virus and slaughtered pairwise on days 6, 9, 10 and 13 post infection. Viral RNA was detected via qRT-PCR and RNAscope analyses in maternal tissues for both viruses from day 6 p.i. on. However, the double deletion mutant was not detected in placenta and was only found in samples from animals infected with the wild type virus. Similarly, high levels of wild type viral RNA were present in fetal tissues whereas the genome of the double deletion mutant was not detected supporting the hypothesis of a specific inhibition of mutant virus replication in the placenta. We compared the induction of gene expression upon infection of placenta derived cell lines with wild type and mutant virus via gene array analysis. Genes important for the innate immune response were strongly upregulated by the mutant virus compared to the wild type in caruncle epithelial cells that establish the cell layer on the maternal side at the maternal–fetal interface in the placenta. Also, trophoblasts which can be found on the fetal side of the interface showed significant induction of gene expression upon infection with the mutant virus although with lower complexity. Growth curves recorded in both cell lines revealed a general reduction of virus replication in caruncular epithelial cells compared to the trophoblasts. Compared to the wild type virus this effect was dramtic for the mutant virus that reached only a TCID50 of 1.0 at 72 hours post infection. Here we report on animal studies elucidating mechanisms preventing the transfer of a double deletion mutant of a pestivirus to the fetus in pregnant heifers. This mutant lacks both known factors engaged in blocking the innate immune response to pestiviral infection. As shown also in earlier studies, this mutant was not detected in the fetuses at any of the tested time points in contrast to the wild-type (wt) virus. However, similar to the wt the mutant was detected in a large variety of different maternal tissues. The only exception was the placenta where only wt but not mutant virus was detected. Using gene array analyses we showed that infection of two cell lines derived either from the maternal or the fetal site of the maternal-fetal interface with the mutant virus induces a significant antiviral gene expression response. The reaction of cells from the maternal side was more complex and virus replication in these cells was reduced, almost completly blocking the mutant virus. These results support the hypothesis that replication of the mutant virus is blocked in the placenta due to a highly active innate immune response and the prevention of replication also blocks transfer of the virus to the fetus.
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Kröß C, Engele P, Sprenger B, Fischer A, Lingg N, Baier M, Öhlknecht C, Lier B, Oostenbrink C, Cserjan-Puschmann M, Striedner G, Jungbauer A, Schneider R. PROFICS: A bacterial selection system for directed evolution of proteases. J Biol Chem 2021; 297:101095. [PMID: 34418435 PMCID: PMC8446807 DOI: 10.1016/j.jbc.2021.101095] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2021] [Revised: 08/10/2021] [Accepted: 08/16/2021] [Indexed: 12/31/2022] Open
Abstract
Proteases serve as important tools in biotechnology and as valuable drugs or drug targets. Efficient protein engineering methods to study and modulate protease properties are thus of great interest for a plethora of applications. We established PROFICS (PRotease Optimization via Fusion-Inhibited Carbamoyltransferase-based Selection), a bacterial selection system, which enables the optimization of proteases for biotechnology, therapeutics or diagnosis in a simple overnight process. During the PROFICS process, proteases are selected for their ability to specifically cut a tag from a reporter enzyme and leave a native N-terminus. Precise and efficient cleavage after the recognition sequence reverses the phenotype of an Escherichia coli knockout strain deficient in an essential enzyme of pyrimidine synthesis. A toolbox was generated to select for proteases with different preferences for P1' residues (the residue immediately following the cleavage site). The functionality of PROFICS is demonstrated with viral proteases and human caspase-2. PROFICS improved caspase-2 activity up to 25-fold after only one round of mutation and selection. Additionally, we found a significantly improved tolerance for all P1' residues caused by a mutation in a substrate interaction site. We showed that this improved activity enables cells containing the new variant to outgrow cells containing all other mutants, facilitating its straightforward selection. Apart from optimizing enzymatic activity and P1' tolerance, PROFICS can be used to reprogram specificities, erase off-target activity, optimize expression via tags/codon usage, or even to screen for potential drug-resistance-conferring mutations in therapeutic targets such as viral proteases in an unbiased manner.
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Affiliation(s)
- Christina Kröß
- acib GmbH, Graz, Austria; Institute of Biochemistry and Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria
| | - Petra Engele
- acib GmbH, Graz, Austria; Institute of Biochemistry and Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria
| | - Bernhard Sprenger
- acib GmbH, Graz, Austria; Institute of Biochemistry and Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria
| | - Andreas Fischer
- acib GmbH, Graz, Austria; Department of Biotechnology, University of Natural Resources and Life Sciences, Vienna, Austria
| | - Nico Lingg
- acib GmbH, Graz, Austria; Department of Biotechnology, University of Natural Resources and Life Sciences, Vienna, Austria
| | - Magdalena Baier
- Institute of Biochemistry and Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria
| | - Christoph Öhlknecht
- acib GmbH, Graz, Austria; Institute of Molecular Modeling and Simulation, University of Natural Resources and Life Sciences, Vienna, Austria
| | - Bettina Lier
- acib GmbH, Graz, Austria; Institute of Molecular Modeling and Simulation, University of Natural Resources and Life Sciences, Vienna, Austria
| | - Chris Oostenbrink
- acib GmbH, Graz, Austria; Institute of Molecular Modeling and Simulation, University of Natural Resources and Life Sciences, Vienna, Austria
| | - Monika Cserjan-Puschmann
- acib GmbH, Graz, Austria; Department of Biotechnology, University of Natural Resources and Life Sciences, Vienna, Austria
| | - Gerald Striedner
- acib GmbH, Graz, Austria; Department of Biotechnology, University of Natural Resources and Life Sciences, Vienna, Austria
| | - Alois Jungbauer
- acib GmbH, Graz, Austria; Department of Biotechnology, University of Natural Resources and Life Sciences, Vienna, Austria
| | - Rainer Schneider
- acib GmbH, Graz, Austria; Institute of Biochemistry and Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria.
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Regions of conformational flexibility in the proprotein convertase PCSK9 and design of antagonists for LDL cholesterol lowering. Biochem Soc Trans 2020; 48:1323-1336. [DOI: 10.1042/bst20190672] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2020] [Revised: 07/08/2020] [Accepted: 07/20/2020] [Indexed: 12/29/2022]
Abstract
The proprotein convertase subtilisin/kexin type 9 (PCSK9) regulates plasma LDL cholesterol levels by binding to the liver LDL receptor (LDLR) and promoting its degradation. Therefore, PCSK9 has become a compelling new therapeutic target for lipid lowering and the prevention of cardiovascular disease. PCSK9 contains two regions of conformational flexibility, the N-terminal regions of the prodomain and of the catalytic domain. The recognition that the latter region, the so-called P′ helix, is able to transition from an α-helical to a disordered state gave rise to new strategies to develop small molecule inhibitors of PCSK9 for lipid lowering. In the ordered state the P′ helix is buried in a groove of the PCSK9 catalytic domain located next to the main LDLR binding site. The transition to a disordered state leaves the groove site vacated and accessible for compounds to antagonize LDLR binding. By use of a groove-directed phage display strategy we were able to identify several groove-binding peptides. Based on structural information of PCSK9-peptide complexes, a minimized groove-binding peptide was generated and utilized as an anchor to extend towards the adjacent main LDLR binding site, either by use of a phage-displayed peptide extension library, or by appending organic moieties to yield organo-peptides. Both strategies led to antagonists with pharmacologic activities in cell-based assays. The intricate bipartite mechanism of the potent organo-peptide inhibitors was revealed by structural studies, showing that the core peptide occupies the N-terminal groove, while the organic moiety interacts with the LDLR binding site to create antagonism. These findings validate the PCSK9 groove as an attractive target site and should inspire the development of a new class of small molecule antagonists of PCSK9.
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Tucakov AK, Yavuz S, Schürmann EM, Mischler M, Klingebeil A, Meyers G. Restoration of glycoprotein E rns dimerization via pseudoreversion partially restores virulence of classical swine fever virus. J Gen Virol 2017; 99:86-96. [PMID: 29235980 DOI: 10.1099/jgv.0.000990] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The classical swine fever virus (CSFV) represents one of the most important pathogens of swine. The CSFV glycoprotein Erns is an essential structural protein and an important virulence factor. The latter is dependent on the RNase activity of this envelope protein and, most likely, its secretion from the infected cell. A further important feature with regard to its function as a virulence factor is the formation of disulfide-linked Erns homodimers that are found in virus-infected cells and virions. Mutant CSFV lacking cysteine (Cys) 171, the residue responsible for intermolecular disulfide bond formation, were found to be attenuated in pigs (Tews BA, Schürmann EM, Meyers G. J Virol 2009;83:4823-4834). In the course of an animal experiment with such a dimerization-negative CSFV mutant, viruses were reisolated from pigs that contained a mutation of serine (Ser) 209 to Cys. This mutation restored the ability to form disulphide-linked Erns homodimers. In transient expression studies Erns mutants carrying the S209C change were found to form homodimers with about wt efficiency. Also the secretion level of the mutated proteins was equivalent to that of wt Erns. Virus mutants containing the Cys171Ser/Ser209Cys configuration exhibited wt growth rates and increased virulence when compared with the Cys171Ser mutant. These results provide further support for the connection between CSFV virulence and Erns dimerization.
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Affiliation(s)
- Anna Katharina Tucakov
- Institut für Immunologie, Friedrich-Loeffler-Institut, D-17493 Greifswald-Insel Riems, Germany
| | - Sabine Yavuz
- Institut für Immunologie, Friedrich-Loeffler-Institut, D-17493 Greifswald-Insel Riems, Germany.,Present address: Fachdienst Verbraucherschutz und Veterinärangelegenheiten, Landratsamt Alb-Donau-Kreis, Ulm, Germany
| | - Eva-Maria Schürmann
- Institut für Immunologie, Friedrich-Loeffler-Institut, D-17493 Greifswald-Insel Riems, Germany.,Present address: Landesamt für Gesundheit und Lebensmittelsicherheit, Oberschleissheim, Germany
| | - Manjula Mischler
- Institut für Immunologie, Friedrich-Loeffler-Institut, D-17493 Greifswald-Insel Riems, Germany
| | - Anne Klingebeil
- Institut für Immunologie, Friedrich-Loeffler-Institut, D-17493 Greifswald-Insel Riems, Germany
| | - Gregor Meyers
- Institut für Immunologie, Friedrich-Loeffler-Institut, D-17493 Greifswald-Insel Riems, Germany
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Complex Virus-Host Interactions Involved in the Regulation of Classical Swine Fever Virus Replication: A Minireview. Viruses 2017; 9:v9070171. [PMID: 28678154 PMCID: PMC5537663 DOI: 10.3390/v9070171] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2017] [Revised: 06/15/2017] [Accepted: 06/27/2017] [Indexed: 02/06/2023] Open
Abstract
Classical swine fever (CSF), caused by classical swine fever virus (CSFV), is one of the most devastating epizootic diseases of pigs in many countries. Viruses are small intracellular parasites and thus rely on the cellular factors for replication. Fundamental aspects of CSFV-host interactions have been well described, such as factors contributing to viral attachment, modulation of genomic replication and translation, antagonism of innate immunity, and inhibition of cell apoptosis. However, those host factors that participate in the viral entry, assembly, and release largely remain to be elucidated. In this review, we summarize recent progress in the virus-host interactions involved in the life cycle of CSFV and analyze the potential mechanisms of viral entry, assembly, and release. We conclude with future perspectives and highlight areas that require further understanding.
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Pestivirus Npro Directly Interacts with Interferon Regulatory Factor 3 Monomer and Dimer. J Virol 2016; 90:7740-7. [PMID: 27334592 DOI: 10.1128/jvi.00318-16] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2016] [Accepted: 06/06/2016] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED Interferon regulatory factor 3 (IRF3) is a transcription factor involved in the activation of type I alpha/beta interferon (IFN-α/β) in response to viral infection. Upon viral infection, the IRF3 monomer is activated into a phosphorylated dimer, which induces the transcription of interferon genes in the nucleus. Viruses have evolved several ways to target IRF3 in order to subvert the innate immune response. Pestiviruses, such as classical swine fever virus (CSFV), target IRF3 for ubiquitination and subsequent proteasomal degradation. This is mediated by the viral protein N(pro) that interacts with IRF3, but the molecular details for this interaction are largely unknown. We used recombinant N(pro) and IRF3 proteins and show that N(pro) interacts with IRF3 directly without additional proteins and forms a soluble 1:1 complex. The full-length IRF3 but not merely either of the individual domains is required for this interaction. The interaction between N(pro) and IRF3 is not dependent on the activation state of IRF3, since N(pro) binds to a constitutively active form of IRF3 in the presence of its transcriptional coactivator, CREB-binding protein (CBP). The results indicate that the N(pro)-binding site on IRF3 encompasses a region that is unperturbed by the phosphorylation and subsequent activation of IRF3 and thus excludes the dimer interface and CBP-binding site. IMPORTANCE The pestivirus N-terminal protease, N(pro), is essential for evading the host's immune system by facilitating the degradation of interferon regulatory factor 3 (IRF3). However, the nature of the N(pro) interaction with IRF3, including the IRF3 species (inactive monomer versus activated dimer) that N(pro) targets for degradation, is largely unknown. We show that classical swine fever virus N(pro) and porcine IRF3 directly interact in solution and that full-length IRF3 is required for interaction with N(pro) Additionally, N(pro) interacts with a constitutively active form of IRF3 bound to its transcriptional cofactor, the CREB-binding protein. This is the first study to demonstrate that N(pro) is able to bind both inactive IRF3 monomer and activated IRF3 dimer and thus likely targets both IRF3 species for ubiquitination and proteasomal degradation.
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Npro fusion technology: On-column complementation to improve efficiency in biopharmaceutical production. Protein Expr Purif 2016; 120:42-50. [DOI: 10.1016/j.pep.2015.11.021] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2015] [Revised: 11/18/2015] [Accepted: 11/24/2015] [Indexed: 11/21/2022]
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Abstract
Pestiviruses are among the economically most important pathogens of livestock. The biology of these viruses is characterized by unique and interesting features that are both crucial for their success as pathogens and challenging from a scientific point of view. Elucidation of these features at the molecular level has made striking progress during recent years. The analyses revealed that major aspects of pestivirus biology show significant similarity to the biology of human hepatitis C virus (HCV). The detailed molecular analyses conducted for pestiviruses and HCV supported and complemented each other during the last three decades resulting in elucidation of the functions of viral proteins and RNA elements in replication and virus-host interaction. For pestiviruses, the analyses also helped to shed light on the molecular basis of persistent infection, a special strategy these viruses have evolved to be maintained within their host population. The results of these investigations are summarized in this chapter.
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Affiliation(s)
- Norbert Tautz
- Institute for Virology and Cell Biology, University of Lübeck, Lübeck, Germany
| | - Birke Andrea Tews
- Institut für Immunologie, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, Greifswald-Insel Riems, Germany
| | - Gregor Meyers
- Institut für Immunologie, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, Greifswald-Insel Riems, Germany.
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Mine J, Tamura T, Mitsuhashi K, Okamatsu M, Parchariyanon S, Pinyochon W, Ruggli N, Tratschin JD, Kida H, Sakoda Y. The N-terminal domain of Npro of classical swine fever virus determines its stability and regulates type I IFN production. J Gen Virol 2015; 96:1746-56. [PMID: 25809915 DOI: 10.1099/vir.0.000132] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The viral protein Npro is unique to the genus Pestivirus within the family Flaviviridae. After autocatalytic cleavage from the nascent polyprotein, Npro suppresses type I IFN (IFN-α/β) induction by mediating proteasomal degradation of IFN regulatory factor 3 (IRF-3). Previous studies found that the Npro-mediated IRF-3 degradation was dependent of a TRASH domain in the C-terminal half of Npro coordinating zinc by means of the amino acid residues C112, C134, D136 and C138. Interestingly, four classical swine fever virus (CSFV) isolates obtained from diseased pigs in Thailand in 1993 and 1998 did not suppress IFN-α/β induction despite the presence of an intact TRASH domain. Through systematic analyses, it was found that an amino acid mutation at position 40 or mutations at positions 17 and 61 in the N-terminal half of Npro of these four isolates were related to the lack of IRF-3-degrading activity. Restoring a histidine at position 40 or both a proline at position 17 and a lysine at position 61 based on the sequence of a functional Npro contributed to higher stability of the reconstructed Npro compared with the Npro from the Thai isolate. This led to enhanced interaction of Npro with IRF-3 along with its degradation by the proteasome. The results of the present study revealed that amino acid residues in the N-terminal domain of Npro are involved in the stability of Npro, in interaction of Npro with IRF-3 and subsequent degradation of IRF-3, leading to downregulation of IFN-α/β production.
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Affiliation(s)
- Junki Mine
- 1Laboratory of Microbiology, Department of Disease Control, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan
| | - Tomokazu Tamura
- 1Laboratory of Microbiology, Department of Disease Control, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan
| | - Kazuya Mitsuhashi
- 1Laboratory of Microbiology, Department of Disease Control, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan
| | - Masatoshi Okamatsu
- 1Laboratory of Microbiology, Department of Disease Control, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan
| | - Sujira Parchariyanon
- 2National Institute of Animal Health, Kaset Klang, Chatuchak, Bangkok 10900, Thailand
| | - Wasana Pinyochon
- 2National Institute of Animal Health, Kaset Klang, Chatuchak, Bangkok 10900, Thailand
| | - Nicolas Ruggli
- 3The Institute of Virology and Immunology IVI, Sensemattstrasse 293, 3147 Mittelhäusern, Switzerland
| | - Jon-Duri Tratschin
- 3The Institute of Virology and Immunology IVI, Sensemattstrasse 293, 3147 Mittelhäusern, Switzerland
| | - Hiroshi Kida
- 1Laboratory of Microbiology, Department of Disease Control, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan 4Research Center for Zoonosis Control, Hokkaido University, Sapporo 001-0020, Japan 5Global Station for Zoonosis Control, Global Institution for Collaborative Research and Education (GI-CoRE), Hokkaido University, Sapporo 001-0020, Japan
| | - Yoshihiro Sakoda
- 5Global Station for Zoonosis Control, Global Institution for Collaborative Research and Education (GI-CoRE), Hokkaido University, Sapporo 001-0020, Japan 1Laboratory of Microbiology, Department of Disease Control, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan
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12
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X-ray structure of the pestivirus NS3 helicase and its conformation in solution. J Virol 2015; 89:4356-71. [PMID: 25653438 DOI: 10.1128/jvi.03165-14] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
UNLABELLED Pestiviruses form a genus in the Flaviviridae family of small enveloped viruses with a positive-sense single-stranded RNA genome. Viral replication in this family requires the activity of a superfamily 2 RNA helicase contained in the C-terminal domain of nonstructural protein 3 (NS3). NS3 features two conserved RecA-like domains (D1 and D2) with ATPase activity, plus a third domain (D3) that is important for unwinding nucleic acid duplexes. We report here the X-ray structure of the pestivirus NS3 helicase domain (pNS3h) at a 2.5-Å resolution. The structure deviates significantly from that of NS3 of other genera in the Flaviviridae family in D3, as it contains two important insertions that result in a narrower nucleic acid binding groove. We also show that mutations in pNS3h that rescue viruses from which the core protein is deleted map to D3, suggesting that this domain may be involved in interactions that facilitate particle assembly. Finally, structural comparisons of the enzyme in different crystalline environments, together with the findings of small-angle X-ray-scattering studies in solution, show that D2 is mobile with respect to the rest of the enzyme, oscillating between closed and open conformations. Binding of a nonhydrolyzable ATP analog locks pNS3h in a conformation that is more compact than the closest apo-form in our crystals. Together, our results provide new insight and bring up new questions about pNS3h function during pestivirus replication. IMPORTANCE Although pestivirus infections impose an important toll on the livestock industry worldwide, little information is available about the nonstructural proteins essential for viral replication, such as the NS3 helicase. We provide here a comparative structural and functional analysis of pNS3h with respect to its orthologs in other viruses of the same family, the flaviviruses and hepatitis C virus. Our studies reveal differences in the nucleic acid binding groove that could have implications for understanding the unwinding specificity of pNS3h, which is active only on RNA duplexes. We also show that pNS3h has a highly dynamic behavior--a characteristic probably shared with NS3 helicases from all Flaviviridae members--that could be targeted for drug design by using recent algorithms to specifically block molecular motion. Compounds that lock the enzyme in a single conformation or limit its dynamic range of conformations are indeed likely to block its helicase function.
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Detection of zoonotic pathogens and characterization of novel viruses carried by commensal Rattus norvegicus in New York City. mBio 2014; 5:e01933-14. [PMID: 25316698 PMCID: PMC4205793 DOI: 10.1128/mbio.01933-14] [Citation(s) in RCA: 268] [Impact Index Per Article: 26.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Norway rats (Rattus norvegicus) are globally distributed and concentrate in urban environments, where they live and feed in closer proximity to human populations than most other mammals. Despite the potential role of rats as reservoirs of zoonotic diseases, the microbial diversity present in urban rat populations remains unexplored. In this study, we used targeted molecular assays to detect known bacterial, viral, and protozoan human pathogens and unbiased high-throughput sequencing to identify novel viruses related to agents of human disease in commensal Norway rats in New York City. We found that these rats are infected with bacterial pathogens known to cause acute or mild gastroenteritis in people, including atypical enteropathogenic Escherichia coli, Clostridium difficile, and Salmonella enterica, as well as infectious agents that have been associated with undifferentiated febrile illnesses, including Bartonella spp., Streptobacillus moniliformis, Leptospira interrogans, and Seoul hantavirus. We also identified a wide range of known and novel viruses from groups that contain important human pathogens, including sapoviruses, cardioviruses, kobuviruses, parechoviruses, rotaviruses, and hepaciviruses. The two novel hepaciviruses discovered in this study replicate in the liver of Norway rats and may have utility in establishing a small animal model of human hepatitis C virus infection. The results of this study demonstrate the diversity of microbes carried by commensal rodent species and highlight the need for improved pathogen surveillance and disease monitoring in urban environments. The observation that most emerging infectious diseases of humans originate in animal reservoirs has led to wide-scale microbial surveillance and discovery programs in wildlife, particularly in the developing world. Strikingly, less attention has been focused on commensal animals like rats, despite their abundance in urban centers and close proximity to human populations. To begin to explore the zoonotic disease risk posed by urban rat populations, we trapped and surveyed Norway rats collected in New York City over a 1-year period. This analysis revealed a striking diversity of known pathogens and novel viruses in our study population, including multiple agents associated with acute gastroenteritis or febrile illnesses in people. Our findings indicate that urban rats are reservoirs for a vast diversity of microbes that may affect human health and indicate a need for increased surveillance and awareness of the disease risks associated with urban rodent infestation.
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14
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Jefferson M, Donaszi-Ivanov A, Pollen S, Dalmay T, Saalbach G, Powell PP. Host factors that interact with the pestivirus N-terminal protease, Npro, are components of the ribonucleoprotein complex. J Virol 2014; 88:10340-53. [PMID: 24965446 PMCID: PMC4178888 DOI: 10.1128/jvi.00984-14] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2014] [Accepted: 06/18/2014] [Indexed: 12/22/2022] Open
Abstract
UNLABELLED The viral N-terminal protease N(pro) of pestiviruses counteracts cellular antiviral defenses through inhibition of IRF3. Here we used mass spectrometry to identify a new role for N(pro) through its interaction with over 55 associated proteins, mainly ribosomal proteins and ribonucleoproteins, including RNA helicase A (DHX9), Y-box binding protein (YBX1), DDX3, DDX5, eIF3, IGF2BP1, multiple myeloma tumor protein 2, interleukin enhancer binding factor 3 (IEBP3), guanine nucleotide binding protein 3, and polyadenylate-binding protein 1 (PABP-1). These are components of the translation machinery, ribonucleoprotein particles (RNPs), and stress granules. Significantly, we found that stress granule formation was inhibited in MDBK cells infected with a noncytopathic bovine viral diarrhea virus (BVDV) strain, Kyle. However, ribonucleoproteins binding to N(pro) did not inhibit these proteins from aggregating into stress granules. N(pro) interacted with YBX1 though its TRASH domain, since the mutant C112R protein with an inactive TRASH domain no longer redistributed to stress granules. Interestingly, RNA helicase A and La autoantigen relocated from a nuclear location to form cytoplasmic granules with N(pro). To address a proviral role for N(pro) in RNP granules, we investigated whether N(pro) affected RNA interference (RNAi), since interacting proteins are involved in RISC function during RNA silencing. Using glyceraldehyde-3-phosphate dehydrogenase (GAPDH) silencing with small interfering RNAs (siRNAs) followed by Northern blotting of GAPDH, expression of N(pro) had no effect on RNAi silencing activity, contrasting with other viral suppressors of interferon. We propose that N(pro) is involved with virus RNA translation in the cytoplasm for virus particle production, and when translation is inhibited following stress, it redistributes to the replication complex. IMPORTANCE Although the pestivirus N-terminal protease, N(pro), has been shown to have an important role in degrading IRF3 to prevent apoptosis and interferon production during infection, the function of this unique viral protease in the pestivirus life cycle remains to be elucidated. We used proteomic mass spectrometry to identify novel interacting proteins and have shown that N(pro) is present in ribosomal and ribonucleoprotein particles (RNPs), indicating a translational role in virus particle production. The virus itself can prevent stress granule assembly from these complexes, but this inhibition is not due to N(pro). A proviral role to subvert RNA silencing through binding of these host RNP proteins was not identified for this viral suppressor of interferon.
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Affiliation(s)
- Matthew Jefferson
- Biomedical Research Centre, Norwich Medical School, University of East Anglia, Norwich, Norfolk, United Kingdom
| | - Andras Donaszi-Ivanov
- Biomedical Research Centre, Norwich Medical School, University of East Anglia, Norwich, Norfolk, United Kingdom
| | - Sean Pollen
- Biological Sciences, University of East Anglia, Norwich, United Kingdom
| | - Tamas Dalmay
- Biological Sciences, University of East Anglia, Norwich, United Kingdom
| | - Gerhard Saalbach
- John Innes Centre, Norwich Research Park, Colney, Norwich, United Kingdom
| | - Penny P Powell
- Biomedical Research Centre, Norwich Medical School, University of East Anglia, Norwich, Norfolk, United Kingdom
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Walther C, Mayer S, Jungbauer A, Dürauer A. Getting ready for PAT: Scale up and inline monitoring of protein refolding of Npro fusion proteins. Process Biochem 2014. [DOI: 10.1016/j.procbio.2014.03.022] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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16
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Li Y, Shen L, Li C, Huang J, Zhao B, Sun Y, Li S, Luo Y, Qiu HJ. Visualization of the Npro protein in living cells using biarsenically labeling tetracysteine-tagged classical swine fever virus. Virus Res 2014; 189:67-74. [PMID: 24815879 DOI: 10.1016/j.virusres.2014.04.018] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2014] [Revised: 04/23/2014] [Accepted: 04/25/2014] [Indexed: 12/20/2022]
Abstract
Real-time fluorescence imaging of viral proteins in living cells is a valuable means to study virus-host interactions, and tetracysteine (TC)-biarsenical technology has been used in several viruses but not in classical swine fever virus (CSFV). Here, we generated CSFV mutants vSMTC385 or vSMTC412 bearing the small TC tag (CCPGCC) in the N-terminal region of the N(pro) protein. The mutants showed growth characteristics indistinguishable from that of the wild-type virus, and retained similar N(pro) subcellular localization to that of the parent virus. Furthermore, labeling with membrane-permeable biarsenical dye resulted in the fluorescent N(pro) protein in the context of virus infection. Finally, we showed that N(pro) was localized in the cytoplasm of CSFV-infected cells at 27 h post-infection (hpi) and present in the nucleus at 48 hpi, and the nuclear import and export was clearly observed from 36.5 to 37 hpi. Interestingly, our results demonstrated that N(pro) transported across the nuclear pores by passive diffusion, which might be prevented by exogenous interferon regulatory factor 3 interacting with N(pro). Taken together, biarsenical labeling allows real-time visualization of the nucleus import and export of the fluorescent N(pro) protein in CSFV-infected living cells.
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Affiliation(s)
- Yongfeng Li
- State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150001, PR China
| | - Liang Shen
- State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150001, PR China
| | - Chao Li
- State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150001, PR China
| | - Junhua Huang
- State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150001, PR China
| | - Bibo Zhao
- State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150001, PR China
| | - Yuan Sun
- State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150001, PR China
| | - Su Li
- State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150001, PR China
| | - Yuzi Luo
- State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150001, PR China
| | - Hua-Ji Qiu
- State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150001, PR China.
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Gottipati K, Acholi S, Ruggli N, Choi KH. Autocatalytic activity and substrate specificity of the pestivirus N-terminal protease Npro. Virology 2014; 452-453:303-9. [PMID: 24606708 DOI: 10.1016/j.virol.2014.01.026] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2013] [Revised: 11/27/2013] [Accepted: 01/27/2014] [Indexed: 10/25/2022]
Abstract
Pestivirus N(pro) is the first protein translated in the viral polypeptide, and cleaves itself off co-translationally generating the N-terminus of the core protein. Once released, N(pro) blocks the host׳s interferon response by inducing degradation of interferon regulatory factor-3. N(pro׳)s intracellular autocatalytic activity and lack of trans-activity have hampered in vitro cleavage studies to establish its substrate specificity and the roles of individual residues. We constructed N(pro)-GFP fusion proteins that carry the authentic cleavage site and determined the autoproteolytic activities of N(pro) proteins containing substitutions at the predicted catalytic sites Glu22 and Cys69, at Arg100 that forms a salt bridge with Glu22, and at the cleavage site Cys168. Contrary to previous reports, we show that N(pro׳)s catalytic activity does not involve Glu22, which may instead be involved in protein stability. Furthermore, N(pro) does not have specificity for Cys168 at the cleavage site even though this residue is conserved throughout the pestivirus genus.
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Affiliation(s)
- Keerthi Gottipati
- Department of Biochemistry & Molecular Biology, Sealy Center for Structural Biology and Molecular Biophysics, The University of Texas Medical Branch, Galveston, TX 77555-0647, USA
| | - Sudheer Acholi
- Department of Biochemistry & Molecular Biology, Sealy Center for Structural Biology and Molecular Biophysics, The University of Texas Medical Branch, Galveston, TX 77555-0647, USA
| | - Nicolas Ruggli
- Institute of Virology and Immunology, CH-3147 Mittelhäusern, Switzerland
| | - Kyung H Choi
- Department of Biochemistry & Molecular Biology, Sealy Center for Structural Biology and Molecular Biophysics, The University of Texas Medical Branch, Galveston, TX 77555-0647, USA.
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18
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N pro of Bungowannah virus exhibits the same antagonistic function in the IFN induction pathway than that of other classical pestiviruses. Vet Microbiol 2013; 168:340-7. [PMID: 24398226 DOI: 10.1016/j.vetmic.2013.11.038] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2013] [Revised: 11/22/2013] [Accepted: 11/25/2013] [Indexed: 01/01/2023]
Abstract
Bungowannah virus is the most divergent atypical pestivirus that had been detected up to now, and does not fit into any of the four approved species: Bovine viral diarrhea virus type 1 (BVDV-1) and type 2 (BVDV-2), Classical swine fever virus (CSFV) and Border disease virus (BDV). However, the presence of N(pro) and E(rns) coding regions, which are unique to pestiviruses, provides clear evidence of a pestivirus. Nevertheless, the amino acid identity of Bungowannah virus N(pro) and BVDV-1 N(pro) (strain CP7) is only 51.5%. By using a BVDV-1 backbone, a novel chimeric construct was generated, in which the genomic region encoding the non-structural protein N(pro) was replaced by that of Bungowannah virus (CP7_N(pro)-Bungo). In vitro studies of CP7_N(pro)-Bungo revealed autonomous replication with the same efficacy as the BVDV backbone CP7 and infectious high-titer virus could be collected. In order to compare the ability of interferon (IFN) suppression, two reporter gene assays, specific for type-I IFN, were carried out. In virus-infected cells, no significant difference in blocking of IFN expression between the parental virus CP7, Bungowannah virus and the chimeric construct CP7_N(pro)-Bungo could be detected. In contrast, an N(pro) deletion mutant showed an impaired replication in bovine cells and a marked type-I IFN response. Taken together, our findings reveal the compatibility of non-structural protein N(pro) of atypical Bungowannah virus with a BVDV type 1 backbone and its characteristic feature as an inhibitor of type-I IFN induction with an inhibitor-activity comparable to other pestiviruses.
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Gottipati K, Ruggli N, Gerber M, Tratschin JD, Benning M, Bellamy H, Choi KH. The structure of classical swine fever virus N(pro): a novel cysteine Autoprotease and zinc-binding protein involved in subversion of type I interferon induction. PLoS Pathog 2013; 9:e1003704. [PMID: 24146623 PMCID: PMC3798407 DOI: 10.1371/journal.ppat.1003704] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2013] [Accepted: 08/24/2013] [Indexed: 12/17/2022] Open
Abstract
Pestiviruses express their genome as a single polypeptide that is subsequently cleaved into individual proteins by host- and virus-encoded proteases. The pestivirus N-terminal protease (Npro) is a cysteine autoprotease that cleaves between its own C-terminus and the N-terminus of the core protein. Due to its unique sequence and catalytic site, it forms its own cysteine protease family C53. After self-cleavage, Npro is no longer active as a protease. The released Npro suppresses the induction of the host's type-I interferon-α/β (IFN-α/β) response. Npro binds interferon regulatory factor-3 (IRF3), the key transcriptional activator of IFN-α/β genes, and promotes degradation of IRF3 by the proteasome, thus preventing induction of the IFN-α/β response to pestivirus infection. Here we report the crystal structures of pestivirus Npro. Npro is structurally distinct from other known cysteine proteases and has a novel “clam shell” fold consisting of a protease domain and a zinc-binding domain. The unique fold of Npro allows auto-catalysis at its C-terminus and subsequently conceals the cleavage site in the active site of the protease. Although many viruses interfere with type I IFN induction by targeting the IRF3 pathway, little information is available regarding structure or mechanism of action of viral proteins that interact with IRF3. The distribution of amino acids on the surface of Npro involved in targeting IRF3 for proteasomal degradation provides insight into the nature of Npro's interaction with IRF3. The structures thus establish the mechanism of auto-catalysis and subsequent auto-inhibition of trans-activity of Npro, and its role in subversion of host immune response. Mammalian cells respond to viral infection by inducing an innate immune response involving interferon-α/β that mediates cellular antiviral defenses. Viruses, in turn, have evolved mechanisms to counter the host's innate immune response by inhibiting the interferon response. Pestiviruses use the virally encoded N-terminal protease (Npro) to suppress interferon-α/β induction. Npro first cleaves itself off from the viral polyprotein using its own cysteine protease activity. Released Npro then interacts with interferon regulatory factor-3 (IRF3), a transcriptional activator of interferon-β, and induces proteasome-mediated degradation of IRF3. We have determined the crystal structure of Npro from classical swine fever virus. Npro has a unique protease fold consisting of two domains. The N-terminal domain carries the protease active site and has the C-terminus, the auto-cleavage site, bound in the active site. Thus, following auto-cleavage at the C-terminus, Npro obstructs the catalytic site preventing further activity, making the protease active only once in its lifetime. The C-terminal domain carries a zinc-binding site that is required for interaction with IRF3. Surface mapping of the Npro residues essential for subversion of interferon induction provides insight into the interaction with IRF3 and its subsequent degradation. To our knowledge, this is the first structure of a direct IRF3 antagonist.
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Affiliation(s)
- Keerthi Gottipati
- Department of Biochemistry and Molecular Biology, Sealy Center for Structural Biology and Molecular Biophysics, The University of Texas Medical Branch at Galveston, Galveston, Texas, United States of America
| | - Nicolas Ruggli
- Institute of Virology and Immunology, Mittelhäusern, Switzerland
| | - Markus Gerber
- Institute of Virology and Immunology, Mittelhäusern, Switzerland
| | | | | | - Henry Bellamy
- Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, Louisiana, United States of America
| | - Kyung H. Choi
- Department of Biochemistry and Molecular Biology, Sealy Center for Structural Biology and Molecular Biophysics, The University of Texas Medical Branch at Galveston, Galveston, Texas, United States of America
- * E-mail:
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