RNA-dependent RNA Polymerase Assay for Hepatitis E Virus.
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ABSTRACT:
SUBMITTER: Nair VP
PROVIDER: S-EPMC8410430 | biostudies-literature |
REPOSITORIES: biostudies-literature
Similar Datasets
Project description:A novel nonnucleoside inhibitor of hepatitis C virus (HCV) RNA-dependent RNA polymerase (RdRp), [(1R)-5-cyano-8-methyl-1-propyl-1,3,4,9-tetrahydropyano[3,4-b]indol-1-yl] acetic acid (HCV-371), was discovered through high-throughput screening followed by chemical optimization. HCV-371 displayed broad inhibitory activities against the NS5B RdRp enzyme, with 50% inhibitory concentrations ranging from 0.3 to 1.8 microM for 90% of the isolates derived from HCV genotypes 1a, 1b, and 3a. HCV-371 showed no inhibitory activity against a panel of human polymerases, including mitochondrial DNA polymerase gamma, and other unrelated viral polymerases, demonstrating its specificity for the HCV polymerase. A single administration of HCV-371 to cells containing the HCV subgenomic replicon for 3 days resulted in a dose-dependent reduction of the steady-state levels of viral RNA and protein. Multiple treatments with HCV-371 for 16 days led to a >3-log10 reduction in the HCV RNA level. In comparison, multiple treatments with a similar inhibitory dose of alpha interferon resulted in a 2-log10 reduction of the viral RNA level. In addition, treatment of cells with a combination of HCV-371 and pegylated alpha interferon resulted in an additive antiviral activity. Within the effective antiviral concentrations of HCV-371, there was no effect on cell viability and metabolism. The intracellular antiviral specificity of HCV-371 was demonstrated by its lack of activity in cells infected with several DNA or RNA viruses. Fluorescence binding studies show that HCV-371 binds the NS5B with an apparent dissociation constant of 150 nM, leading to high selectivity and lack of cytotoxicity in the antiviral assays.
| S-EPMC529219 | biostudies-literature
Project description:We report the crystal structure of the RNA-dependent RNA polymerase of hepatitis C virus, a major human pathogen, to 2.8-A resolution. This enzyme is a key target for developing specific antiviral therapy. The structure of the catalytic domain contains 531 residues folded in the characteristic fingers, palm, and thumb subdomains. The fingers subdomain contains a region, the "fingertips," that shares the same fold with reverse transcriptases. Superposition to the available structures of the latter shows that residues from the palm and fingertips are structurally equivalent. In addition, it shows that the hepatitis C virus polymerase was crystallized in a closed fingers conformation, similar to HIV-1 reverse transcriptase in ternary complex with DNA and dTTP [Huang H., Chopra, R., Verdine, G. L. & Harrison, S. C. (1998) Science 282, 1669-1675]. This superposition reveals the majority of the amino acid residues of the hepatitis C virus enzyme that are likely to be implicated in binding to the replicating RNA molecule and to the incoming NTP. It also suggests a rearrangement of the thumb domain as well as a possible concerted movement of thumb and fingertips during translocation of the RNA template-primer in successive polymerization rounds.
| S-EPMC23895 | biostudies-literature
Project description:The NS5B RNA-dependent RNA polymerase encoded by hepatitis C virus (HCV) plays a key role in viral replication. Reported here is evidence that HCV NS5B polymerase acts as a functional oligomer. Oligomerization of HCV NS5B protein was demonstrated by gel filtration, chemical cross-linking, temperature sensitivity, and yeast cell two-hybrid analysis. Mutagenesis studies showed that the C-terminal hydrophobic region of the protein was not essential for its oligomerization. Importantly, HCV NS5B polymerase exhibited cooperative RNA synthesis activity with a dissociation constant, K(d), of approximately 22 nM, suggesting a role for the polymerase-polymerase interaction in the regulation of HCV replicase activity. Further functional evidence includes the inhibition of the wild-type NS5B polymerase activity by a catalytically inactive form of NS5B. Finally, the X-ray crystal structure of HCV NS5B polymerase was solved at 2.9 A. Two extensive interfaces have been identified from the packing of the NS5B molecules in the crystal lattice, suggesting a higher-order structure that is consistent with the biochemical data.
| S-EPMC136118 | biostudies-literature
Project description:Hepatitis C virus (HCV) triggers massive production of reactive oxygen species (ROS) and affects expression of genes encoding ROS-scavenging enzymes. Multiple lines of evidence show that levels of ROS production contribute to the development of various virus-associated pathologies. However, investigation of HCV redox biology so far remained in the paradigm of oxidative stress, whereas no attention was given to the identification of redox switches among viral proteins. Here, we report that one of such redox switches is the NS5B protein that exhibits RNA-dependent RNA polymerase (RdRp) activity. Treatment of the recombinant protein with reducing agents significantly increases its enzymatic activity. Moreover, we show that the NS5B protein is subjected to S-glutathionylation that affects cysteine residues 89, 140, 170, 223, 274, 521, and either 279 or 295. Substitution of these cysteines except C89 and C223 with serine residues led to the reduction of the RdRp activity of the recombinant protein in a primer-dependent assay. The recombinant protein with a C279S mutation was almost inactive in vitro and could not be activated with reducing agents. In contrast, cysteine substitutions in the NS5B region in the context of a subgenomic replicon displayed opposite effects: most of the mutations enhanced HCV replication. This difference may be explained by the deleterious effect of oxidation of NS5B cysteine residues in liver cells and by the protective role of S-glutathionylation. Based on these data, redox-sensitive posttranslational modifications of HCV NS5B and other proteins merit a more detailed investigation and analysis of their role(s) in the virus life cycle and associated pathogenesis.
| S-EPMC6800943 | biostudies-literature
Project description:Hepatitis C virus (HCV) RNA-dependent RNA polymerase replicates the viral genomic RNA and is a primary drug target for antiviral therapy. Previously, we described the purification of an active and stable polymerase-primer-template elongation complex. Here, we show that, unexpectedly, the polymerase elongation complex can use NTPs to excise the terminal nucleotide in nascent RNA. Mismatched ATP, UTP, or CTP could mediate excision of 3'-terminal CMP to generate the dinucleoside tetraphosphate products Ap(4)C, Up(4)C, and Cp(4)C, respectively. Pre-steady-state kinetic studies showed that the efficiency of NTP-mediated excision was highest with ATP. A chain-terminating inhibitor, 3'deoxy-CMP, could also be excised through this mechanism, suggesting important implications for nucleoside drug potency and resistance. The nucleotide excision reaction catalyzed by recombinant hepatitis C virus polymerase was 100-fold more efficient than the corresponding reaction observed with HIV reverse transcriptase.
| S-EPMC3562815 | biostudies-literature
Project description:The hepatitis C virus (HCV) non-structural protein 5B (NS5B) is an RNA-dependent RNA polymerase that is essentially required for viral replication. Although previous studies revealed important properties of static NS5B-RNA complexes, the nature and relevance of dynamic interactions have yet to be elucidated. Here, we devised a single molecule Förster Resonance Energy Transfer (SM-FRET) assay to monitor temporal changes upon binding of NS5B to surface immobilized RNA templates. The data show enzyme association-dissociation events that occur within the time resolution of our setup as well as FRET-fluctuations in association with stable binary complexes that extend over prolonged periods of time. Fluctuations are shown to be dependent on the length of the RNA substrate, and enzyme concentration. Mutations in close proximity to the template entrance (K98E, K100E), and in the center of the RNA binding channel (R394E), reduce both the population of RNA-bound enzyme and the fluctuations associated to the binary complex. Similar observations are reported with an allosteric nonnucleoside NS5B inhibitor. Our assay enables for the first time the visualization of association-dissociation events of HCV-NS5B with RNA, and also the direct monitoring of the interaction between HCV NS5B, its RNA template, and finger loop inhibitors. We observe both a remarkably low dissociation rate for wild type HCV NS5B, and a highly dynamic enzyme-RNA binary complex. These results provide a plausible mechanism for formation of a productive binary NS5B-RNA complex, here NS5B slides along the RNA template facilitating positioning of its 3' terminus at the enzyme active site.
| S-EPMC4022906 | biostudies-literature
Project description:The RNA-dependent RNA polymerase NS5B is a key enzyme of the replication of hepatitis C virus (HCV) and a major therapeutic target. Applying a novel continuous assay with highly purified protein and a fluorescent RNA-template we provide for the first time a comprehensive mechanistic description of the enzymatic reaction. Using fluorescence spectroscopy, the kinetics of NS5B was confirmed to consist of two half-reactions, namely substrate binding and turnover. Determining the binding constants of the substrates and the rate constants of individual reaction steps, NS5B was shown to bind the template single-stranded RNA with high affinity (nanomolar range) and in a stepwise process that reflects the substrate positioning. As demonstrated by CD, NTP(s) binding caused a tertiary structural change of the enzyme into an active conformation. The second half-reaction was dissected into a sequential polymerization and a subsequent, rate-limiting product release reaction. Taking advantage of these tools, we analyzed the mechanism of action of the NS5B inhibitor HCV-796, which was shown to interfere with the formation of double-stranded RNA by blocking the second half-reaction.
| S-EPMC2859531 | biostudies-literature
Project description:The hepatitis C virus (HCV) RNA-dependent RNA polymerase (RdRp), represented by nonstructural protein 5B (NS5B), belongs to a class of integral membrane proteins termed tail-anchored proteins. Its membrane association is mediated by the C-terminal 21 amino acid residues, which are dispensable for RdRp activity in vitro. For this study, we investigated the role of this domain, termed the insertion sequence, in HCV RNA replication in cells. Based on a structural model and the amino acid conservation among different HCV isolates, we designed a panel of insertion sequence mutants and analyzed their membrane association and RNA replication. Subgenomic replicons with a duplication of an essential cis-acting replication element overlapping the sequence that encodes the C-terminal domain of NS5B were used to unequivocally distinguish RNA versus protein effects of these mutations. Our results demonstrate that the membrane association of the RdRp is essential for HCV RNA replication. Interestingly, certain amino acid substitutions within the insertion sequence abolished RNA replication without affecting membrane association, indicating that the C-terminal domain of NS5B has functions beyond serving as a membrane anchor and that it may be involved in critical intramembrane protein-protein interactions. These results have implications for the functional architecture of the HCV replication complex and provide new insights into the expanding spectrum of tail-anchored proteins.
| S-EPMC524999 | biostudies-literature
Project description:Background and aimsHepatitis E virus (HEV) is one of the most common causes of acute hepatitis worldwide. Its positive-strand RNA genome encodes three open reading frames (ORF). ORF1 is translated into a large protein composed of multiple domains and is known as the viral replicase. The RNA-dependent RNA polymerase (RDRP) domain is responsible for the synthesis of viral RNA.Approach and resultsHere, we identified a highly conserved α-helix located in the RDRP thumb subdomain. Nuclear magnetic resonance demonstrated an amphipathic α-helix extending from amino acids 1628 to 1644 of the ORF1 protein. Functional analyses revealed a dual role of this helix in HEV RNA replication and virus production, including assembly and release. Mutations on the hydrophobic side of the amphipathic α-helix impaired RNA replication and resulted in the selection of a second-site compensatory change in the RDRP palm subdomain. Other mutations enhanced RNA replication but impaired virus assembly and/or release.ConclusionsStructure-function analyses identified a conserved amphipathic α-helix in the thumb subdomain of the HEV RDRP with a dual role in viral RNA replication and infectious particle production. This study provides structural insights into a key segment of the ORF1 protein and describes the successful use of reverse genetics in HEV, revealing functional interactions between the RDRP thumb and palm subdomains. On a broader scale, it demonstrates that the HEV replicase, similar to those of other positive-strand RNA viruses, is also involved in virus production.
| S-EPMC9300124 | biostudies-literature
Project description:RNA-dependent RNA polymerase (RdRp) is a unique and highly conserved enzyme across all members of the RNA virus superfamilies. Besides, humans do not have a homolog of this protein. Therefore, the RdRp is an attractive target for a broadly effective therapeutic agent against RNA viruses. In this study, a formerly generated cell-penetrating human single-chain antibody variable fragment (superantibody) to a conformational epitope of hepatitis C virus (HCV) RdRp, which inhibited the polymerase activity leading to the HCV replication inhibition and the host innate immunity restoration, was tested against emerging/reemerging RNA viruses. The superantibody could inhibit the replication of the other members of the Flaviviridae (DENV serotypes 1-4, ZIKV, and JEV), Picornaviridae (genus Enterovirus: EV71, CVA16), and Coronaviridae (genus Alphacoronavirus: PEDV, and genus Betacoronavirus: SARS-CoV-2 (Wuhan wild-type and the variants of concern), in a dose-dependent manner, as demonstrated by the reduction of intracellular viral RNAs and numbers of the released infectious particles. Computerized simulation indicated that the superantibody formed contact interfaces with many residues at the back of the thumb domain (thumb II site, T2) of DENV, ZIKV, JEV, EV71, and CVA16 and fingers and thumb domains of the HCV and coronaviruses (PEDV and SARS-CoV-2). The superantibody binding may cause allosteric change in the spatial conformation of the enzyme and disrupt the catalytic activity, leading to replication inhibition. Although the speculated molecular mechanism of the superantibody needs experimental support, existing data indicate that the superantibody has high potential as a non-chemical broadly effective anti-positive sense-RNA virus agent.
| S-EPMC9355540 | biostudies-literature