A single-amino acid substitution in West Nile virus 2K peptide between NS4A and NS4B confers resistance to lycorine, a flavivirus inhibitor.
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ABSTRACT:
SUBMITTER: Zou G
PROVIDER: S-EPMC5388927 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:A common feature associated with the replication of most RNA viruses is the formation of a unique membrane environment encapsulating the viral replication complex. For their part, flaviviruses are no exception, whereupon infection causes a dramatic rearrangement and induction of unique membrane structures within the cytoplasm of infected cells. These virus-induced membranes, termed paracrystalline arrays, convoluted membranes, and vesicle packets, all appear to have specific functions during replication and are derived from different organelles within the host cell. The aim of this study was to identify which protein(s) specified by the Australian strain of West Nile virus, Kunjin virus (KUNV), are responsible for the dramatic membrane alterations observed during infection. Thus, we have shown using immunolabeling of ultrathin cryosections of transfected cells that expression of the KUNV polyprotein intermediates NS4A-4B and NS2B-3-4A, as well as that of individual NS4A proteins with and without the C-terminal transmembrane domain 2K, resulted in different degrees of rearrangement of cytoplasmic membranes. The formation of the membrane structures characteristic for virus infection required coexpression of an NS4A-NS4B cassette with the viral protease NS2B-3pro which was shown to be essential for the release of the individual NS4A and NS4B proteins. Individual expression of NS4A protein retaining the C-terminal transmembrane domain 2K resulted in the induction of membrane rearrangements most resembling virus-induced structures, while removal of the 2K domain led to a less profound membrane rearrangement but resulted in the redistribution of the NS4A protein to the Golgi apparatus. The results show that cleavage of the KUNV polyprotein NS4A-4B by the viral protease is the key initiation event in the induction of membrane rearrangement and that the NS4A protein intermediate containing the uncleaved C-terminal transmembrane domain plays an essential role in these membrane rearrangements.
| S-EPMC1472005 | biostudies-literature
Project description:The nonstructural (NS) proteins of West Nile virus (WNV) have been associated with participation in evasion of host innate immune defenses. In the present study, we characterized immune response to an attenuated WNV strain, which has a P38G substitution in the NS4B protein. The WNV NS4B-P38G mutant induced a lower level of viremia and no lethality in C57BL/6 (B6) mice following a systemic infection. Interestingly, there were higher type 1 IFNs and IL-1? responses compared to mice infected by wild-type WNV. NS4B-P38G mutant-infected mice also showed stronger effector and memory T cell responses. WNV specific antibody responses were not different between mice infected with these two viruses. As a consequence, all mice were protected from a secondary infection with a lethal dose of wild-type WNV following a primary infection with NS4B-P38G mutant. Moreover, NS4B-P38G mutant infection in cultured bone-marrow derived dendritic cells (DCs) were shown to have a reduced replication rate, but a higher level of innate cytokine production than wild-type WNV, some of which were dependent on Myd88 signaling. In conclusion, the NS4B-P38G mutant strain induces higher protective innate and adaptive immune response in mice, which results in a lower viremia and no lethality in either primary or secondary infection, suggesting a high potential as an attenuating mutation in a vaccine candidate.
| S-EPMC3114109 | biostudies-literature
Project description:An adaptive mutation (E249G) within West Nile virus (WNV) NS4B gene was consistently recovered from replicon RNAs in C3H/He mouse cells. The E249G is located at the C-terminal tail of NS4B predicted to be on the cytoplasmic side of the endoplasmic reticulum membrane. The E249G substitution reduced replicon RNA synthesis. Compared with the wild-type NS4B, the E249G mutant protein exhibited a similar efficiency in evasion of interferon-beta response. Recombinant E249G virus exhibited smaller plaques, slower growth kinetics, and lower RNA synthesis than the wild-type virus in a host-dependent manner, with the greatest difference in rodent cells (C3H/He and BHK-21) and the least difference in mosquito cells (C3/36). Selection of revertants of E249G virus identified a second site mutation at residue 246, which could compensate for the low replication phenotype in cell culture. These results demonstrate that distinct residues within the C-terminal tail of flavivirus NS4B are critical for viral replication.
| S-EPMC1952232 | biostudies-literature
Project description:Positive-sense RNA virus intracellular replication is intimately associated with membrane platforms that are derived from host organelles and comprised of distinct lipid composition. For flaviviruses, such as West Nile virus strain Kunjin virus (WNVKUN) we have observed that these membrane platforms are derived from the endoplasmic reticulum and are rich in (at least) cholesterol. To extend these studies and identify the cellular lipids critical for WNVKUN replication we utilized a whole cell lipidomics approach and revealed an elevation in phospholipase A2 (PLA2) activity to produce lyso-phosphatidylcholine (lyso-PChol). We observed that the PLA2 enzyme family is activated in WNVKUN-infected cells and the generated lyso-PChol lipid moieties are sequestered to the subcellular sites of viral replication. The requirement for lyso-PChol was confirmed using chemical inhibition of PLA2, where WNVKUN replication and production of infectious virus was duly affected in the presence of the inhibitors. Importantly, we could rescue chemical-induced inhibition with the exogenous addition of lyso-PChol species. Additionally, electron microscopy results indicate that lyso-PChol appears to contribute to the formation of the WNVKUN membranous replication complex (RC); particularly affecting the morphology and membrane curvature of vesicles comprising the RC. These results extend our current understanding of how flaviviruses manipulate lipid homeostasis to favour their own intracellular replication.
| S-EPMC5945048 | biostudies-other
Project description:Flavivirus replication is mediated by a complex machinery that consists of viral enzymes, nonenzymatic viral proteins, and host factors. Many of the nonenzymatic viral proteins, such as NS4B, are associated with the endoplasmic reticulum membrane. How these membrane proteins function in viral replication is poorly understood. Here we report a robust method to express and purify dengue virus (DENV) and West Nile virus NS4B proteins. The NS4B proteins were expressed in Escherichia coli, reconstituted in dodecyl maltoside (DDM) detergent micelles, and purified to >95% homogeneity. The recombinant NS4B proteins dimerized in vitro, as evidenced by gel filtration, chemical cross-linking, and multiangle light scattering experiments. The dimeric form of NS4B was also detected when the protein was expressed alone in cells as well as in cells infected with DENV type 2 (DENV-2). Mutagenesis analysis showed that the cytosolic loop (amino acids 129 to 165) and the C-terminal region (amino acids 166 to 248) are responsible for NS4B dimerization. trans-Complementation experiments showed that (i) two genome-length RNAs containing distinct NS4B lethal mutations could not trans-complement each other, (ii) the replication defect of NS4B mutant RNA could be restored in cells containing DENV-2 replicons, and (iii) expression of wild-type NS4B protein alone was not sufficient to restore the replication of the NS4B mutant RNA. Collectively, the results indicate that trans-complementation of a lethal NS4B mutant RNA requires wild-type NS4B presented from a replication complex.The reported expression and purification system has made it possible to study the biochemistry and structure of flavivirus NS4B proteins. The finding of flavivirus NS4B dimerization and the mapping of regions important for NS4B dimerization provide the possibility to inhibit viral replication through blocking NS4B dimerization. The requirement of NS4B in the context of the replication complex for successful trans-complementation enhances our understanding of NS4B in flavivirus replication.
| S-EPMC3957939 | biostudies-literature
Project description:A flavivirus (strain 97-103) was isolated from Culex pipens mosquitoes in 1997 following floods in South Moravia, Czech Republic. The strain exhibited close antigenic relationship to West Nile virus (WNV) prototype strain Eg-101 in a cross-neutralization test. In this study, mouse pathogenicity characteristics and the complete nucleotide and putative amino acid sequences of isolate 97-103, named Rabensburg virus (RabV) after a nearby Austrian city, were determined. RabV shares only 75%-77% nucleotide identity and 89%-90% amino acid identity with representative strains of WNV lineages 1 and 2. Another RabV strain (99-222) was isolated in the same location 2 years later; it showed >99% nucleotide identity to strain 97-103. Phylogenetic analyses of RabV, WNV strains, and other members of the Japanese encephalitis virus (JEV) complex clearly demonstrated that RabV is either a new (third) lineage of WNV or a novel flavivirus of the JEV group.
| S-EPMC3320449 | biostudies-literature
Project description:UnlabelledFlavivirus replication is mediated by a membrane-associated replication complex where viral membrane proteins NS2A, NS2B, NS4A, and NS4B serve as the scaffold for the replication complex formation. Here, we used dengue virus serotype 2 (DENV-2) as a model to characterize viral NS4A-NS4B interaction. NS4A interacts with NS4B in virus-infected cells and in cells transiently expressing NS4A and NS4B in the absence of other viral proteins. Recombinant NS4A and NS4B proteins directly bind to each other with an estimated Kd (dissociation constant) of 50 nM. Amino acids 40 to 76 (spanning the first transmembrane domain, consisting of amino acids 50 to 73) of NS4A and amino acids 84 to 146 (also spanning the first transmembrane domain, consisting of amino acids 101 to 129) of NS4B are the determinants for NS4A-NS4B interaction. Nuclear magnetic resonance (NMR) analysis suggests that NS4A residues 17 to 80 form two amphipathic helices (helix α1, comprised of residues 17 to 32, and helix α2, comprised of residues 40 to 47) that associate with the cytosolic side of endoplasmic reticulum (ER) membrane and helix α3 (residues 52 to 75) that transverses the ER membrane. In addition, NMR analysis identified NS4A residues that may participate in the NS4A-NS4B interaction. Amino acid substitution of these NS4A residues exhibited distinct effects on viral replication. Three of the four NS4A mutations (L48A, T54A, and L60A) that affected the NS4A-NS4B interaction abolished or severely reduced viral replication; in contrast, two NS4A mutations (F71A and G75A) that did not affect NS4A-NS4B interaction had marginal effects on viral replication, demonstrating the biological relevance of the NS4A-NS4B interaction to DENV-2 replication. Taken together, the study has provided experimental evidence to argue that blocking the NS4A-NS4B interaction could be a potential antiviral approach.ImportanceFlavivirus NS4A and NS4B proteins are essential components of the ER membrane-associated replication complex. The current study systematically characterizes the interaction between flavivirus NS4A and NS4B. Using DENV-2 as a model, we show that NS4A interacts with NS4B in virus-infected cells, in cells transiently expressing NS4A and NS4B proteins, or in vitro with recombinant NS4A and NS4B proteins. We mapped the minimal regions required for the NS4A-NS4B interaction to be amino acids 40 to 76 of NS4A and amino acids 84 to 146 of NS4B. NMR analysis revealed the secondary structure of amino acids 17 to 80 of NS4A and the NS4A amino acids that may participate in the NS4A-NS4B interaction. Functional analysis showed a correlation between viral replication and NS4A-NS4B interaction, demonstrating the biological importance of the NS4A-NS4B interaction. The study has advanced our knowledge of the molecular function of flavivirus NS4A and NS4B proteins. The results also suggest that inhibitors of the NS4A-NS4B interaction could be pursued for flavivirus antiviral development.
| S-EPMC4403404 | biostudies-literature
Project description:West Nile virus (WNV) is a worldwide distributed mosquito-borne flavivirus that naturally cycles between birds and mosquitoes, although it can infect multiple vertebrate hosts including horses and humans. This virus is responsible for recurrent epidemics of febrile illness and encephalitis, and has recently become a global concern. WNV requires to transit through intracellular acidic compartments at two different steps to complete its infectious cycle. These include fusion between the viral envelope and the membrane of endosomes during viral entry, and virus maturation in the trans-Golgi network. In this study, we followed a genetic approach to study the connections between viral components and acidic pH. A WNV mutant with increased resistance to the acidotropic compound NH4Cl, which blocks organelle acidification and inhibits WNV infection, was selected. Nucleotide sequencing revealed that this mutant displayed a single amino acid substitution (Lys 3 to Glu) on the highly basic internal capsid or core (C) protein. The functional role of this replacement was confirmed by its introduction into a WNV infectious clone. This single amino acid substitution also increased resistance to other acidification inhibitor (concanamycin A) and induced a reduction of the neurovirulence in mice. Interestingly, a naturally occurring accompanying mutation found on prM protein abolished the resistant phenotype, supporting the idea of a genetic crosstalk between the internal C protein and the external glycoproteins of the virion. The findings here reported unveil a non-previously assessed connection between the C viral protein and the acidic pH necessary for entry and proper exit of flaviviruses.
| S-EPMC3715472 | biostudies-literature
Project description:Using constructs that encode the individual West Nile virus (WNV) NS3helicase (NS3hel) and NS3hel linked to the hydrophilic, N-terminal 1-50 sequence of NS4A, we demonstrated that the presence of NS4A allows NS3hel to conserve energy in the course of oligonucleotide substrate unwinding. Using NS4A mutants, we also determined that the C-terminal acidic EELPD/E motif of NS4A, which appears to be functionally similar to the acidic EFDEMEE motif of hepatitis C virus (HCV) NS4A, is essential for regulating the ATPase activity of NS3hel. We concluded that, similar to HCV NS4A, NS4A of WNV acts as a cofactor for NS3hel and allows helicase to sustain the unwinding rate of the viral RNA under conditions of ATP deficiency.
| S-EPMC2887571 | biostudies-literature
Project description:BackgroundWest Nile Virus (WNV) is a flavivirus that requires an efficient humoral and cellular host response for the control of neuroinvasive infection. We previously reported the existence of six alternative open reading frame proteins in WNV genome, one of which entitled WARF4 is exclusively restricted to the lineage I of the virus. WARF4 is able to elicit antibodies in WNV infected horses; however, there was no direct experimental proof of the existence of this novel protein. The purpose of this study was to demonstrate the in vitro production of WARF4 protein following WNV infection of cultured VERO cells and its immunity in WNV infected individuals.ResultsWe produced a monoclonal antibody against WARF4 protein (MAb 3A12) which detected the novel protein in WNV lineage I-infected, cultured VERO cells while it did not react with WNV lineage II infected cells. MAb 3A12 specificity to WARF4 protein was confirmed by its reactivity to only one peptide among four analyzed that cover the full WARF4 amino acids sequence. In addition, WARF4 protein was expressed in the late phase of WNV lineage I infection. Western blotting and bioinformatics analyses strongly suggest that the protein could be translated by programmed -1 ribosomal frameshifting process. Since WARF4 is embedded in the NS4B gene, we rename this novel protein N-NS4B/WARF4. Furthermore, serological analysis shows that N-NS4B/WARF4 is able to elicit antibodies in WNV infected individuals.ConclusionsN-NS4B/WARF4 is the second Alternative Reading Frame (ARF) protein that has been demonstrated to be produced following WNV infection and might represent a novel tool for a better characterization of immune response in WNV infected individuals. Further serological as well as functional studies are required to characterize the function of the N-NS4B/WARF4 protein. Since the virus might actually make an extensive use of ARFs, it appears important to investigate the novel six ARF putative proteins of WNV.
| S-EPMC3574045 | biostudies-literature