scholarly journals De Novo Initiation of RNA Synthesis by the RNA-Dependent RNA Polymerase (NS5B) of Hepatitis C Virus

2000 ◽  
Vol 74 (2) ◽  
pp. 851-863 ◽  
Author(s):  
Guangxiang Luo ◽  
Robert K. Hamatake ◽  
Danielle M. Mathis ◽  
Jason Racela ◽  
Karen L. Rigat ◽  
...  
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Rna Polymerase ◽  
Rna Synthesis ◽  
De Novo ◽  
Oligonucleotide Primer ◽  
Transferase Activity ◽  
Rdrp Activity ◽  
Rna Dependent Rna Polymerase ◽  
Hcv Ns5b

ABSTRACT Hepatitis C virus (HCV) NS5B protein possesses an RNA-dependent RNA polymerase (RdRp) activity, a major function responsible for replication of the viral RNA genome. To further characterize the RdRp activity, NS5B proteins were expressed from recombinant baculoviruses, purified to near homogeneity, and examined for their ability to synthesize RNA in vitro. As a result, a highly active NS5B RdRp (1b-42), which contains an 18-amino acid C-terminal truncation resulting from a newly created stop codon, was identified among a number of independent isolates. The RdRp activity of the truncated NS5B is comparable to the activity of the full-length protein and is 20 times higher in the presence of Mn2+ than in the presence of Mg2+. When a 384-nucleotide RNA was used as the template, two major RNA products were synthesized by 1b-42. One is a complementary RNA identical in size to the input RNA template (monomer), while the other is a hairpin dimer RNA synthesized by a “copy-back” mechanism. Substantial evidence derived from several experiments demonstrated that the RNA monomer was synthesized through de novo initiation by NS5B rather than by a terminal transferase activity. Synthesis of the RNA monomer requires all four ribonucleotides. The RNA monomer product was verified to be the result of de novo RNA synthesis, as two expected RNA products were generated from monomer RNA by RNase H digestion. In addition, modification of the RNA template by the addition of the chain terminator cordycepin at the 3′ end did not affect synthesis of the RNA monomer but eliminated synthesis of the self-priming hairpin dimer RNA. Moreover, synthesis of RNA on poly(C) and poly(U) homopolymer templates by 1b-42 NS5B did not require the oligonucleotide primer at high concentrations (≥50 μM) of GTP and ATP, further supporting a de novo initiation mechanism. These findings suggest that HCV NS5B is able to initiate RNA synthesis de novo.

scholarly journals Characterization of Soluble Hepatitis C Virus RNA-Dependent RNA Polymerase Expressed in Escherichia coli

1999 ◽  
Vol 73 (2) ◽  
pp. 1649-1654 ◽  
Author(s):  
Eric Ferrari ◽  
Jacquelyn Wright-Minogue ◽  
Jane W. S. Fang ◽  
Bahige M. Baroudy ◽  
Johnson Y. N. Lau ◽  
...  
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Rna Polymerase ◽  
Nonstructural Protein ◽  
Full Length ◽  
Dependent Manner ◽  
Rdrp Activity ◽  
Rna Dependent Rna Polymerase ◽  
Hydrophobic Domain ◽  
Hcv Ns5b

ABSTRACT Production of soluble full-length nonstructural protein 5B (NS5B) of hepatitis C virus (HCV) has been shown to be problematic and requires the addition of salts, glycerol, and detergents. In an effort to improve the solubility of NS5B, the hydrophobic C terminus containing 21 amino acids was removed, yielding a truncated NS5B (NS5BΔCT) which is highly soluble and monodispersed in the absence of detergents. Fine deletional analysis of this region revealed that a four-leucine motif (LLLL) in the hydrophobic domain is responsible for the solubility profile of the full-length NS5B. Enzymatic characterization revealed that the RNA-dependent RNA polymerase (RdRp) activity of this truncated NS5B was comparable to those reported previously by others. For optimal enzyme activity, divalent manganese ions (Mn2+) are preferred rather than magnesium ions (Mg2+), whereas zinc ions (Zn2+) inhibit the RdRp activity. Gliotoxin, a known poliovirus 3D RdRp inhibitor, inhibited HCV NS5B RdRp in a dose-dependent manner. Kinetic analysis revealed that HCV NS5B has a rather low processivity compared to those of other known polymerases.

scholarly journals Identification of a C-Terminal Regulatory Motif in Hepatitis C Virus RNA-Dependent RNA Polymerase: Structural and Biochemical Analysis

2003 ◽  
Vol 77 (16) ◽  
pp. 9020-9028 ◽  
Author(s):  
Vincent J.-P. Lévêque ◽  
Robert B. Johnson ◽  
Stephen Parsons ◽  
Jianxin Ren ◽  
Congping Xie ◽  
...  
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Rna Polymerase ◽  
Rna Synthesis ◽  
Rna Binding ◽  
Dimensional Structure ◽  
Synthesis Rate ◽  
Rna Dependent Rna Polymerase ◽  
Hcv Ns5b ◽  
Ns5b Polymerase

ABSTRACT The NS5B RNA-dependent RNA polymerase encoded by the hepatitis C virus (HCV) is a key component of the viral replicase. Reported here is the three-dimensional structure of HCV NS5B polymerase, with the highlight on its C-terminal folding, determined by X-ray crystallography at 2.1-Å resolution. Structural analysis revealed that a stretch of C-terminal residues of HCV NS5B inserted into the putative RNA binding cleft, where they formed a hydrophobic pocket and interacted with several important structural elements. This region was found to be conserved and unique to the RNA polymerases encoded by HCV and related viruses. Through biochemical analyses, we confirmed that this region interfered with the binding of HCV NS5B to RNA. Deletion of this fragment from HCV NS5B enhanced the RNA synthesis rate up to ∼50-fold. These results provide not only direct experimental insights into the role of the C-terminal tail of HCV NS5B polymerase but also a working model for the RNA synthesis mechanism employed by HCV and related viruses.

scholarly journals Regulation of De Novo-Initiated RNA Synthesis in Hepatitis C Virus RNA-Dependent RNA Polymerase by Intermolecular Interactions

2010 ◽  
Vol 84 (12) ◽  
pp. 5923-5935 ◽  
Author(s):  
S. Chinnaswamy ◽  
A. Murali ◽  
P. Li ◽  
K. Fujisaki ◽  
C. C. Kao
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Rna Polymerase ◽  
Single Molecule ◽  
Rna Synthesis ◽  
De Novo ◽  
Enzyme Concentration ◽  
Hcv Rna ◽  
Rna Dependent Rna Polymerase

ABSTRACT The hepatitis C virus (HCV) RNA-dependent RNA polymerase (RdRp) has been proposed to change conformations in association with RNA synthesis and to interact with cellular proteins. In vitro, the RdRp can initiate de novo from the ends of single-stranded RNA or extend a primed RNA template. The interactions between the Δ1 loop and thumb domain in NS5B are required for de novo initiation, although it is unclear whether these interactions are within an NS5B monomer or are part of a higher-order NS5B oligomeric complex. This work seeks to address how polymerase conformation and/or oligomerization affects de novo initiation. We have shown that an increasing enzyme concentration increases de novo initiation by the genotype 1b and 2a RdRps while primer extension reactions are not affected or inhibited under similar conditions. Initiation-defective mutants of the HCV polymerase can increase de novo initiation by the wild-type (WT) polymerase. GTP was also found to stimulate de novo initiation. Our results support a model in which the de novo initiation-competent conformation of the RdRp is stimulated by oligomeric contacts between individual subunits. Using electron microscopy and single-molecule reconstruction, we attempted to visualize the low-resolution conformations of a dimer of a de novo initiation-competent HCV RdRp.

scholarly journals Selection of 3′-Template Bases and Initiating Nucleotides by Hepatitis C Virus NS5B RNA-Dependent RNA Polymerase

2002 ◽  
Vol 76 (14) ◽  
pp. 7030-7039 ◽  
Author(s):  
Jae Hoon Shim ◽  
Gary Larson ◽  
Jim Zhen Wu ◽  
Zhi Hong
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Rna Polymerase ◽  
Rna Synthesis ◽  
De Novo ◽  
Nonstructural Protein ◽  
Initiation Site ◽  
De Novo Synthesis ◽  
Rna Dependent Rna Polymerase ◽  
Selection Of

ABSTRACT De novo RNA synthesis by hepatitis C virus (HCV) nonstructural protein 5B (NS5B) RNA-dependent RNA polymerase has been investigated using short RNA templates. Various templates including those derived from the HCV genome were evaluated by examining the early steps of de novo RNA synthesis. NS5B was shown to be able to produce an initiation dinucleotide product from templates as short as 4-mer and from the 3′-terminal sequences of both plus and minus strands of the HCV RNA genome. GMP, GDP, and guanosine were able to act as an initiating nucleotide in de novo RNA synthesis, indicating that the triphosphate moiety is not absolutely required by an initiating nucleotide. Significant amounts of the initiation product accumulated in de novo synthesis, and elongation from the dinucleotide was observed when large amounts of dinucleotide were available. This result suggests that NS5B, a template, and incoming nucleotides are able to form an initiation complex that aborts frequently by releasing the dinucleotide product before transition to an elongation complex. The transition is rate limiting. Furthermore, we discovered that the secondary structure of a template was not essential for de novo initiation and that 3′-terminal bases of a template conferred specificity in selection of an initiation site. Initiation can occur at the +1, +2, or +3 position numbered from the 3′ end of a template depending on base composition. Pyrimidine bases at any of the three positions are able to serve as an initiation site, while purine bases at the +2 and +3 positions do not support initiation. This result implies that HCV possesses an intrinsic ability to ensure that de novo synthesis is initiated from the +1 position and to maintain the integrity of the 3′ end of its genome. This assay system should be an important tool for investigating the detailed mechanism of de novo initiation by HCV NS5B as well as other viral RNA polymerases.

scholarly journals Oligomerization and Cooperative RNA Synthesis Activity of Hepatitis C Virus RNA-Dependent RNA Polymerase

2002 ◽  
Vol 76 (8) ◽  
pp. 3865-3872 ◽  
Author(s):  
Q. May Wang ◽  
Michelle A. Hockman ◽  
Kirk Staschke ◽  
Robert B. Johnson ◽  
Katharine A. Case ◽  
...  
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Rna Polymerase ◽  
Rna Synthesis ◽  
Order Structure ◽  
Rna Dependent Rna Polymerase ◽  
Hydrophobic Region ◽  
Synthesis Activity ◽  
Hcv Ns5b ◽  
Ns5b Polymerase

ABSTRACT 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, Kd , of ≈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 Å. 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.

scholarly journals Dinucleotide Analogues as Novel Inhibitors of RNA-Dependent RNA Polymerase of Hepatitis C Virus

2003 ◽  
Vol 47 (8) ◽  
pp. 2674-2681 ◽  
Author(s):  
Weidong Zhong ◽  
Haoyun An ◽  
Dinesh Barawkar ◽  
Zhi Hong
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Rna Polymerase ◽  
Rna Synthesis ◽  
De Novo ◽  
Replication Initiation ◽  
Hcv Rna ◽  
Rna Dependent Rna Polymerase ◽  
Initiation Process

ABSTRACT Replication of hepatitis C virus (HCV) RNA is catalyzed by the virally encoded RNA-dependent RNA polymerase NS5B. It is believed that the viral polymerase utilizes a de novo or primer-independent mechanism for initiation of RNA synthesis. Our previous work has shown that dinucleotides were efficient initiation molecules for NS5B in vitro (W. Zhong, E. Ferrari, C. A. Lesburg, D. Maag, S. K. Ghosh, C. E. Cameron, J. Y. Lau, and Z. Hong, J. Virol. 74:9134-9143, 2000). In this study, we further demonstrated that dinucleotide analogues could serve as inhibitors of de novo initiation of RNA synthesis directed by HCV NS5B. Both mononucleotide- and dinucleotide-initiated RNA syntheses were affected by dinucleotide analogues. The presence of the 5′-phosphate group in the dinucleotide compounds was required for efficient inhibition of de novo initiation. Optimal inhibitory activity also appeared to be dependent on the base-pairing potential between the compounds and the template terminal bases. Because the initiation process is a rate-limiting step in viral RNA replication, inhibitors that interfere with the initiation process will have advantages in suppressing virus replication. The use of dinucleotide analogues as inhibitor molecules to target viral replication initiation represents a novel approach to antiviral interference.

scholarly journals Template Requirements for RNA Synthesis by a Recombinant Hepatitis C Virus RNA-Dependent RNA Polymerase

2000 ◽  
Vol 74 (23) ◽  
pp. 11121-11128 ◽  
Author(s):  
C. Cheng Kao ◽  
Xueyong Yang ◽  
Allen Kline ◽  
Q. May Wang ◽  
Donna Barket ◽  
...  
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Rna Polymerase ◽  
Rna Synthesis ◽  
De Novo ◽  
Nonstructural Protein ◽  
Resonance Spectroscopy ◽  
Rna Dependent Rna Polymerase ◽  
Systematic Analysis ◽  
Stem Loop

ABSTRACT The RNA-dependent RNA polymerase (RdRp) from hepatitis C virus (HCV), nonstructural protein 5B (NS5B), has recently been shown to direct de novo initiation using a number of complex RNA templates. In this study, we analyzed the features in simple RNA templates that are required to direct de novo initiation of RNA synthesis by HCV NS5B. NS5B was found to protect RNA fragments of 8 to 10 nucleotides (nt) from RNase digestion. However, NS5B could not direct RNA synthesis unless the template contained a stable secondary structure and a single-stranded sequence that contained at least one 3′ cytidylate. The structure of a 25-nt template, named SLD3, was determined by nuclear magnetic resonance spectroscopy to contain an 8-bp stem and a 6-nt single-stranded sequence. Systematic analysis of changes in SLD3 revealed which features in the stem, loop, and 3′ single-stranded sequence were required for efficient RNA synthesis. Also, chimeric molecules composed of DNA and RNA demonstrated that a DNA molecule containing a 3′-terminal ribocytidylate was able to direct RNA synthesis as efficiently as a sequence composed entirely of RNA. These results define the template sequence and structure sufficient to direct the de novo initiation of RNA synthesis by HCV RdRp.

scholarly journals Hepatitis C Virus RNA-Dependent RNA Polymerase Is Regulated by Cysteine S-Glutathionylation

2019 ◽  
Vol 2019 ◽  
pp. 1-11
Author(s):  
Marina K. Kukhanova ◽  
Vera L. Tunitskaya ◽  
Olga A. Smirnova ◽  
Olga A. Khomich ◽  
Natalia F. Zakirova ◽  
...  
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Recombinant Protein ◽  
Rna Polymerase ◽  
Reducing Agents ◽  
Cysteine Residues ◽  
Rdrp Activity ◽  
Rna Dependent Rna Polymerase ◽  
Redox Switches ◽  
Ns5b Protein

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.

scholarly journals Initiation of RNA Synthesis by the Hepatitis C Virus RNA-Dependent RNA Polymerase Is Affected by the Structure of the RNA Template

Biochemistry ◽  
2014 ◽  
Vol 53 (44) ◽  
pp. 7002-7012 ◽  
Author(s):  
Stefan Reich ◽  
Michael Kovermann ◽  
Hauke Lilie ◽  
Paul Knick ◽  
René Geissler ◽  
...  
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Rna Polymerase ◽  
Rna Synthesis ◽  
Hepatitis C Virus Rna ◽  
Rna Dependent Rna Polymerase ◽  
Virus Rna

scholarly journals Hydrophobic and Charged Residues in the C-Terminal Arm of Hepatitis C Virus RNA-Dependent RNA Polymerase Regulate Initiation and Elongation

2014 ◽  
Vol 89 (4) ◽  
pp. 2052-2063 ◽  
Author(s):  
Amy L. Cherry ◽  
Caitriona A. Dennis ◽  
Andrew Baron ◽  
Leslie E. Eisele ◽  
Pia A. Thommes ◽  
...  
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Rna Polymerase ◽  
De Novo ◽  
Structural Features ◽  
Primer Extension ◽  
Hcv Rna ◽  
Genome Replication ◽  
Rna Dependent Rna Polymerase ◽  
Subgenomic Replicon

ABSTRACTThe RNA-dependent RNA polymerase (RdRp) of hepatitis C virus (HCV) is essential for viral genome replication. Crystal structures of the HCV RdRp reveal two C-terminal features, a β-loop and a C-terminal arm, suitably located for involvement in positioning components of the initiation complex. Here we show that these two elements intimately regulate template and nucleotide binding, initiation, and elongation. We constructed a series of β-loop and C-terminal arm mutants, which were used forin vitroanalysis of RdRpde novoinitiation and primer extension activities. All mutants showed a substantial decrease in initiation activities but a marked increase in primer extension activities, indicating an ability to form more stable elongation complexes with long primer-template RNAs. Structural studies of the mutants indicated that these enzyme properties might be attributed to an increased flexibility in the C-terminal features resulting in a more open polymerase cleft, which likely favors the elongation process but hampers the initiation steps. A UTP cocrystal structure of one mutant shows, in contrast to the wild-type protein, several alternate conformations of the substrate, confirming that even subtle changes in the C-terminal arm result in a more loosely organized active site and flexible binding modes of the nucleotide. We used a subgenomic replicon system to assess the effects of the same mutations on viral replication in cells. Even the subtlest mutations either severely impaired or completely abolished the ability of the replicon to replicate, further supporting the concept that the correct positioning of both the β-loop and C-terminal arm plays an essential role during initiation and in HCV replication in general.IMPORTANCEHCV RNA polymerase is a key target for the development of directly acting agents to cure HCV infections, which necessitates a thorough understanding of the functional roles of the various structural features of the RdRp. Here we show that even highly conservative changes, e.g., Tyr→Phe or Asp→Glu, in these seemingly peripheral structural features have profound effects on the initiation and elongation properties of the HCV polymerase.

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