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de Martin E, Schweizer M. Fifty Shades of Erns: Innate Immune Evasion by the Viral Endonucleases of All Pestivirus Species. Viruses 2022; 14:v14020265. [PMID: 35215858 PMCID: PMC8880635 DOI: 10.3390/v14020265] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Revised: 01/25/2022] [Accepted: 01/25/2022] [Indexed: 12/10/2022] Open
Abstract
The genus Pestivirus, family Flaviviridae, includes four historically accepted species, i.e., bovine viral diarrhea virus (BVDV)-1 and -2, classical swine fever virus (CSFV), and border disease virus (BDV). A large number of new pestivirus species were identified in recent years. A common feature of most members is the presence of two unique proteins, Npro and Erns, that pestiviruses evolved to regulate the host’s innate immune response. In addition to its function as a structural envelope glycoprotein, Erns is also released in the extracellular space, where it is endocytosed by neighboring cells. As an endoribonuclease, Erns is able to cleave viral ss- and dsRNAs, thus preventing the stimulation of the host’s interferon (IFN) response. Here, we characterize the basic features of soluble Erns of a large variety of classified and unassigned pestiviruses that have not yet been described. Its ability to form homodimers, its RNase activity, and the ability to inhibit dsRNA-induced IFN synthesis were investigated. Overall, we found large differences between the various Erns proteins that cannot be predicted solely based on their primary amino acid sequences, and that might be the consequence of different virus-host co-evolution histories. This provides valuable information to delineate the structure-function relationship of pestiviral endoribonucleases.
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Affiliation(s)
- Elena de Martin
- Institute of Virology and Immunology, Länggass-Str. 122, POB, CH-3001 Bern, Switzerland;
- Department of Infectious Diseases and Pathobiology, Vetsuisse Faculty, University of Bern, CH-3012 Bern, Switzerland
- Graduate School for Cellular and Biomedical Sciences, University of Bern, CH-3012 Bern, Switzerland
| | - Matthias Schweizer
- Institute of Virology and Immunology, Länggass-Str. 122, POB, CH-3001 Bern, Switzerland;
- Department of Infectious Diseases and Pathobiology, Vetsuisse Faculty, University of Bern, CH-3012 Bern, Switzerland
- Correspondence:
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The E rns Carboxyterminus: Much More Than a Membrane Anchor. Viruses 2021; 13:v13071203. [PMID: 34201636 PMCID: PMC8310223 DOI: 10.3390/v13071203] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Revised: 06/15/2021] [Accepted: 06/17/2021] [Indexed: 12/12/2022] Open
Abstract
Pestiviruses express the unique essential envelope protein Erns, which exhibits RNase activity, is attached to membranes by a long amphipathic helix, and is partially secreted from infected cells. The RNase activity of Erns is directly connected with pestivirus virulence. Formation of homodimers and secretion of the protein are hypothesized to be important for its role as a virulence factor, which impairs the host's innate immune response to pestivirus infection. The unusual membrane anchor of Erns raises questions with regard to proteolytic processing of the viral polyprotein at the Erns carboxy-terminus. Moreover, the membrane anchor is crucial for establishing the critical equilibrium between retention and secretion and ensures intracellular accumulation of the protein at the site of virus budding so that it is available to serve both as structural component of the virion and factor controlling host immune reactions. In the present manuscript, we summarize published as well as new data on the molecular features of Erns including aspects of its interplay with the other two envelope proteins with a special focus on the biochemistry of the Erns membrane anchor.
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Downstream Sequences Control the Processing of the Pestivirus E rns-E1 Precursor. J Virol 2020; 95:JVI.01905-20. [PMID: 33028718 DOI: 10.1128/jvi.01905-20] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Accepted: 09/30/2020] [Indexed: 02/06/2023] Open
Abstract
Like other enveloped viruses, pestiviruses employ cellular proteases for processing of their structural proteins. While typical signal peptidase cleavage motifs are present at the carboxy terminus of the signal sequence preceding Erns and the E1/E2 and E2/P7 sites, the Erns-E1 precursor is cleaved by signal peptidase at a highly unusual structure, in which the transmembrane sequence upstream of the cleavage site is replaced by an amphipathic helix. As shown before, the integrity of the amphipathic helix is crucial for efficient processing. The data presented here demonstrate that the E1 sequence downstream of this cleavage site is also important for the cleavage. Carboxy-terminal truncation of the E1 moiety as well as internal deletions in E1 reduced the cleavage efficiency to less than 30% of the wild-type (wt) level. Moreover, the C-terminal truncation by more than 30 amino acids resulted in strong secretion of the uncleaved fusion proteins. The reduced processing and increased secretion were even observed when 10 to 5 amino-terminal residues of E1 were left, whereas extensions by 1 or 3 E1 residues resulted in reduced processing but no significantly increased secretion. In contrast to the E1 sequences, a 10-amino-acid c-myc tag fused to the Erns C terminus had only marginal effect on secretion but was also not processed efficiently. Mutation of the von Heijne sequence upstream of E2 not only blocked the cleavage between E1 and E2 but also prevented the processing between Erns and E2. Thus, processing at the Erns-E1 site is a highly regulated process.IMPORTANCE Cellular signal peptidase (SPase) cleavage represents an important step in maturation of viral envelope proteins. Fine tuning of this system allows for establishment of concerted folding and processing processes in different enveloped viruses. We report here on SPase processing of the Erns-E1-E2 glycoprotein precursor of pestiviruses. Erns-E1 cleavage is delayed and only executed efficiently when the complete E1 sequence is present. C-terminal truncation of the Erns-E1 precursor impairs processing and leads to significant secretion of the protein. The latter is not detected when internal deletions preserving the E1 carboxy terminus are introduced, but also these constructs show impaired processing. Moreover, Erns-E1 is only processed after cleavage at the E1/E2 site. Thus, processing of the pestiviral glycoprotein precursor by SPase is done in an ordered way and depends on the integrity of the proteins for efficient cleavage. The functional importance of this processing scheme is discussed in the paper.
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Koethe S, König P, Wernike K, Pfaff F, Schulz J, Reimann I, Makoschey B, Beer M. A Synthetic Modified Live Chimeric Marker Vaccine against BVDV-1 and BVDV-2. Vaccines (Basel) 2020; 8:vaccines8040577. [PMID: 33023099 PMCID: PMC7712951 DOI: 10.3390/vaccines8040577] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Revised: 09/28/2020] [Accepted: 09/29/2020] [Indexed: 02/07/2023] Open
Abstract
Bovine viral diarrhea virus (BVDV), a pestivirus which exists in the two distinct species BVDV-1 (syn. Pestivirus A) and BVDV-2 (syn. Pestivirus B), is the causative agent of one of the most widespread and economically important virus infections in cattle. For economic as well as for animal health reasons, an increasing number of national BVDV control programs were recently implemented. The main focus lies on the detection and removal of persistently infected cattle. The application of efficient marker or DIVA (differentiation of infected from vaccinated animals) vaccines would be beneficial for the eradication success in regions with a high BVDV prevalence to prevent fetal infection and it would allow serological monitoring of the BVDV status also in vaccinated farms. Therefore, a marker vaccine based on the cytopathic (cp) BVDV-1b strain CP7 was constructed as a synthetic backbone (BVDV-1b_synCP7). For serological discrimination of vaccinated from infected animals, the viral protein Erns was substituted by the heterologous Erns of Bungowannah virus (BuPV, species Pestivirus F). In addition, the vaccines were attenuated by a deletion within the type I interferon inhibitor Npro protein encoding sequence. The BVDV-2 vaccine candidate is based on the genetic sequence of the glycoproteins E1 and E2 of BVDV-2 strain CS8644 (CS), which were introduced into the backbone of BVDV-1b_synCP7_ΔNpro_Erns Bungo in substitution of the homologous glycoproteins. Vaccine virus recovery resulted in infectious cytopathic virus chimera that grew to titers of up to 106 TCID50/mL. Both synthetic chimera BVDV-1b_synCP7_ΔNpro_Erns Bungo and BVDV-1b_synCP7_ΔNpro_Erns Bungo_E1E2 BVDV-2 CS were avirulent in cattle, provided a high level of protection in immunization and challenge experiments against both BVDV species and allowed differentiation of infected from vaccinated cattle. Our study presents the first report on an efficient BVDV-1 and -2 modified live marker vaccine candidate and the accompanying commercially available serological marker ELISA system.
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Affiliation(s)
- Susanne Koethe
- Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, 17493 Greifswald-Insel Riems, Germany; (S.K.); (P.K.); (K.W.); (F.P.); (I.R.)
| | - Patricia König
- Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, 17493 Greifswald-Insel Riems, Germany; (S.K.); (P.K.); (K.W.); (F.P.); (I.R.)
| | - Kerstin Wernike
- Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, 17493 Greifswald-Insel Riems, Germany; (S.K.); (P.K.); (K.W.); (F.P.); (I.R.)
| | - Florian Pfaff
- Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, 17493 Greifswald-Insel Riems, Germany; (S.K.); (P.K.); (K.W.); (F.P.); (I.R.)
| | - Jana Schulz
- Institute of Epidemiology Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, 17493 Greifswald-Insel Riems, Germany;
| | - Ilona Reimann
- Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, 17493 Greifswald-Insel Riems, Germany; (S.K.); (P.K.); (K.W.); (F.P.); (I.R.)
| | - Birgit Makoschey
- Intervet International B.V., MSD Animal Health, 5831 AN Boxmeer, The Netherlands;
| | - Martin Beer
- Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, 17493 Greifswald-Insel Riems, Germany; (S.K.); (P.K.); (K.W.); (F.P.); (I.R.)
- Correspondence: ; Tel.: +49-38351-71200
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Autonomously Replicating RNAs of Bungowannah Pestivirus: E RNS Is Not Essential for the Generation of Infectious Particles. J Virol 2020; 94:JVI.00436-20. [PMID: 32404522 DOI: 10.1128/jvi.00436-20] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2020] [Accepted: 05/04/2020] [Indexed: 12/31/2022] Open
Abstract
Autonomously replicating subgenomic Bungowannah virus (BuPV) RNAs (BuPV replicons) with deletions of the genome regions encoding the structural proteins C, ERNS, E1, and E2 were constructed on the basis of an infectious cDNA clone of BuPV. Nanoluciferase (Nluc) insertion was used to compare the replication efficiencies of all constructs after electroporation of in vitro-transcribed RNA from the different clones. Deletion of C, E1, E2, or the complete structural protein genome region (C-ERNS-E1-E2) prevented the production of infectious progeny virus, whereas deletion of ERNS still allowed the generation of infectious particles. However, those ΔERNS viral particles were defective in virus assembly and/or egress and could not be further propagated for more than three additional passages in porcine SK-6 cells. These "defective-in-third-cycle" BuPV ΔERNS mutants were subsequently used to express the classical swine fever virus envelope protein E2, the N-terminal domain of the Schmallenberg virus Gc protein, and the receptor binding domain of the Middle East respiratory syndrome coronavirus spike protein. The constructs could be efficiently complemented and further passaged in SK-6 cells constitutively expressing the BuPV ERNS protein. Importantly, BuPVs are able to infect a wide variety of target cell lines, allowing expression in a very wide host spectrum. Therefore, we suggest that packaged BuPV ΔERNS replicon particles have potential as broad-spectrum viral vectors.IMPORTANCE The proteins NPRO and ERNS are unique for the genus Pestivirus, but only NPRO has been demonstrated to be nonessential for in vitro growth. While this was also speculated for ERNS, it has always been previously shown that pestivirus replicons with deletions of the structural proteins ERNS, E1, or E2 did not produce any infectious progeny virus in susceptible host cells. Here, we demonstrated for the first time that BuPV ERNS is dispensable for the generation of infectious virus particles but still important for efficient passaging. The ERNS-defective BuPV particles showed clearly limited growth in cell culture but were capable of several rounds of infection, expression of foreign genes, and highly efficient trans-complementation to rescue virus replicon particles (VRPs). The noncytopathic characteristics and the absence of preexisting immunity to BuPV in human populations and livestock also provide a significant benefit for a possible use, e.g., as a vector vaccine platform.
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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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Rajkhowa TK, Hauhnar L, Lalrohlua I, Mohanarao G J. Emergence of 2.1. subgenotype of classical swine fever virus in pig population of India in 2011. Vet Q 2014; 34:224-8. [PMID: 25365116 DOI: 10.1080/01652176.2014.973122] [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] [Indexed: 10/24/2022] Open
Abstract
BACKGROUND Limited studies are available on molecular epidemiology of classical swine fever virus (CSFV) in India and are restricted to domestic pigs. These studies show the presence of 1.1. genotype. HYPOTHESIS/OBJECTIVES The aim of the present study was to subgenotype four CSFV isolates, two each from the outbreaks of CSF in wild (Sus scrofa) and domestic pigs of Mizoram state, India, in 2011. ANIMALS AND METHODS CSFV isolates were subjected to nucleotide sequencing in E2 and NS5B genomic regions. Phylogenetic analysis of the isolates in both genomic regions was carried out with 39 Indian isolates (4 isolates from the present study of Mizoram state and 35 isolates from the other states of India) and 57 reference sequences retrieved from the GenBank database. Two of the 39 isolates from India were collected from wild boar and were subgenotyped as 2.1. Out of 37 isolates from domestic pigs, only two were subgenotyped as 2.1. RESULTS The analysis revealed the emergence of 2.1. subgenotype of CSFV in both wild and domestic pigs in India. CONCLUSIONS AND CLINICAL IMPORTANCE The isolates from domestic pigs of Mizoram state (CSF/MZ/KOL/73 and CSF/MZ/AIZ/115) were grouped in genotype 1 and subgenotype 1.1., thus confirming that the source of CSF outbreaks in domesticated pigs in Mizoram was not from wild pigs. The current study forms an essential step for better understanding of the epidemiology of 2.1 subgroup as well as the movement and spread of the disease in India.
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Affiliation(s)
- T K Rajkhowa
- a Department of Veterinary Pathology , College of Veterinary Sciences & Animal Husbandry, Central Agricultural University , Selesih , Aizawl , Mizoram , India
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Richter M, Reimann I, Wegelt A, Kirkland PD, Beer M. Complementation studies with the novel "Bungowannah" virus provide new insights in the compatibility of pestivirus proteins. Virology 2011; 418:113-22. [PMID: 21849202 DOI: 10.1016/j.virol.2011.07.014] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2011] [Revised: 07/15/2011] [Accepted: 07/22/2011] [Indexed: 10/17/2022]
Abstract
In recent years several atypical pestiviruses have been described. Bungowannah virus is the most divergent virus in this group. Therefore, heterologous complementation was used to clarify the phylogenetic relationship and to analyze the exchangeability of genome regions encoding structural proteins. Using a BVDV type 1 backbone, chimeric constructs with substituted envelope proteins E(rns), E1 and E2, were investigated. While all constructs replicated autonomously, infectious high titer chimeric virus could only be observed after exchanging the complete E1-E2 encoding region. The complementation of E1 and E2 alone resulted only in replicons. Complementation of BVDV-E(rns) was only efficient if Bungowannah virus-E(rns) was expressed from a bicistronic construct. Our data provide new insights in the compatibility of pestivirus proteins and demonstrate that heterologous complementation could be useful to characterize new pestiviruses.
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Affiliation(s)
- Maria Richter
- Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Suedufer 10, D-17493 Greifswald-Insel Riems, Germany
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Characterization and purification of recombinant bovine viral diarrhea virus particles with epitope-tagged envelope proteins. J Gen Virol 2011; 92:1352-1357. [DOI: 10.1099/vir.0.029330-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Bovine viral diarrhea virus (BVDV) belongs to the genus Pestivirus within the family Flaviviridae. The lipid membrane of the virions is supposed to contain the three glycosylated envelope proteins Erns, E1 and E2, but detailed studies of virus assembly are complicated because no efficient purification method for pestiviruses has been described so far. In this study, we generated infectious BVDV with N-terminally FLAG-tagged Erns or E2 proteins, respectively. The expression of the epitope-tagged Erns and E2 proteins could be shown by immunofluorescence and Western blot experiments. Furthermore, an affinity tag purification protocol for the isolation and concentration of infectious BVDV was established. In the preparation with a titre of 108.75 TCID50 ml−1, spherical particles with a diameter of 43–58 nm (mean diameter: 48 nm) could be detected by negative staining electron microscopy, and immunogold labelling located both Erns and E2 proteins at the virus membrane.
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Leifer I, Hoffmann B, Höper D, Bruun Rasmussen T, Blome S, Strebelow G, Höreth-Böntgen D, Staubach C, Beer M. Molecular epidemiology of current classical swine fever virus isolates of wild boar in Germany. J Gen Virol 2010; 91:2687-97. [PMID: 20660149 DOI: 10.1099/vir.0.023200-0] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Classical swine fever (CSF) has caused significant economic losses in industrialized pig production, and is still present in some European countries. Recent CSF outbreaks in Europe were mainly associated with strains of genogroup 2 (subgroup 2.3). Although there are extensive datasets regarding 2.3 strains, there is very little information available on longer fragments or whole classical swine fever virus (CSFV) genomes. Furthermore, there are no detailed analyses of the molecular epidemiology of CSFV wild boar isolates available. Nevertheless, complete genome sequences are supportive in phylogenetic analyses, especially in affected wild boar populations. Here, German CSFV strains of subgroup 2.3 were fully sequenced using two different approaches: (i) a universal panel of CSFV primers that were developed to amplify the complete genome in overlapping fragments for chain-terminator sequencing; and (ii) generation of a single full-length amplicon of the CSFV genome obtained by long-range RT-PCR for deep sequencing with next-generation sequencing technology. In total, five different strains of CSFV subgroup 2.3 were completely sequenced using these newly developed protocols. The approach was used to study virus spread and evolutionary history in German wild boar. For the first time, the results of our study clearly argue for the possibility of a long-term persistence of genotype 2.3 CSFV strains in affected regions at an almost undetectable level, even after long-term oral vaccination campaigns with intensive monitoring. Hence, regional persistence in wild boar populations has to be taken into account as an important factor in the continual outbreaks in affected areas.
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Affiliation(s)
- Immanuel Leifer
- Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Südufer 10, D-17493 Greifswald-Insel Riems, Germany
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Bintintan I, Meyers G. A new type of signal peptidase cleavage site identified in an RNA virus polyprotein. J Biol Chem 2010; 285:8572-84. [PMID: 20093364 DOI: 10.1074/jbc.m109.083394] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Pestiviruses, a group of enveloped positive strand RNA viruses belonging to the family Flaviviridae, express their genes via a polyprotein that is subsequently processed by proteases. The structural protein region contains typical signal peptidase cleavage sites. Only the site at the C terminus of the glycoprotein E(rns) is different because it does not contain a hydrophobic transmembrane region but an amphipathic helix functioning as the E(rns) membrane anchor. Despite the absence of a hydrophobic region, the site between the C terminus of E(rns) and E1, the protein located downstream in the polyprotein, is cleaved by signal peptidase, as demonstrated by mutagenesis and inhibitor studies. Thus, E(rns)E1 is processed at a novel type of signal peptidase cleavage site showing a different membrane topology. Prevention of glycosylation or introduction of mutations into the C-terminal region of E(rns) severely impairs processing, presumably by preventing proper membrane interaction or disturbing a conformation critical for the protein to be accepted as a substrate by signal peptidase.
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Affiliation(s)
- Ioana Bintintan
- Institut für Immunologie, Friedrich-Loeffler-Institut, Paul-Ehrlich-Strasse 28, D-72001 Tübingen, Germany
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