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Fine mapping and characterization of the L-polymerase-binding domain of the respiratory syncytial virus phosphoprotein.

ABSTRACT: The minimum requirement for an active RNA-dependent RNA polymerase of respiratory syncytial virus (RSV) is a complex made of two viral proteins, the polymerase large protein (L) and the phosphoprotein (P). Here we have investigated the domain on P that is responsible for this critical P-L interaction. By use of recombinant proteins and serial deletions, an L binding site was mapped in the C-terminal region of P, just upstream of the N-RNA binding site. The role of this molecular recognition element of about 30 amino acid residues in the L-P interaction and RNA polymerase activity was evaluated in cellula using an RSV minigenome system and site-directed mutagenesis. The results highlighted the critical role of hydrophobic residues located in this region.Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract illness in infants. Since no vaccine and no good antivirals against RSV are available, it is essential to better understand how the viral machinery functions in order to develop new antiviral strategies. Like all negative-strand RNA viruses, RSV codes for its own machinery to replicate and transcribe its genome. The core of this machinery is composed of two proteins, the phosphoprotein (P) and the large protein (L). Here, using recombinant proteins, we have mapped and characterized the P domain responsible for this L-P interaction and the formation of an active L-P complex. These findings extend our understanding of the mechanism of action of RSV RNA polymerase and allow us to define a new target for the development of drugs against RSV.

SUBMITTER: Sourimant J

PROVIDER: S-EPMC4442346 | biostudies-literature | 2015 Apr

REPOSITORIES: biostudies-literature

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Fine mapping and characterization of the L-polymerase-binding domain of the respiratory syncytial virus phosphoprotein.

Sourimant Julien J Rameix-Welti Marie-Anne MA Gaillard Anne-Laure AL Chevret Didier D Galloux Marie M Gault Elyanne E Eléouët Jean-François JF

Journal of virology 20150204 8

<h4>Unlabelled</h4>The minimum requirement for an active RNA-dependent RNA polymerase of respiratory syncytial virus (RSV) is a complex made of two viral proteins, the polymerase large protein (L) and the phosphoprotein (P). Here we have investigated the domain on P that is responsible for this critical P-L interaction. By use of recombinant proteins and serial deletions, an L binding site was mapped in the C-terminal region of P, just upstream of the N-RNA binding site. The role of this molecul ...[more]

PMID: 25653447

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Project description:UnlabelledThe RNA genome of respiratory syncytial virus (RSV) is constitutively encapsidated by the viral nucleoprotein N, thus forming a helical nucleocapsid. Polymerization of N along the genomic and antigenomic RNAs is concomitant to replication and requires the preservation of an unassembled monomeric nucleoprotein pool. To this end, and by analogy with Paramyxoviridae and Rhabdoviridae, it is expected that the viral phosphoprotein P acts as a chaperone protein, forming a soluble complex with the RNA-free form of N (N(0)-P complex). Here, we have engineered a mutant form of N that is monomeric, is unable to bind RNA, still interacts with P, and could thus mimic the N(0) monomer. We used this N mutant, designated N(mono), as a substitute for N(0) in order to characterize the P regions involved in the N(0)-P complex formation. Using a series of P fragments, we determined by glutathione S-transferase (GST) pulldown assays that the N and C termini of P are able to interact with N(mono). We analyzed the functional role of amino-terminal residues of P by site-directed mutagenesis, using an RSV polymerase activity assay based on a human RSV minireplicon, and found that several residues were critical for viral RNA synthesis. Using GST pulldown and surface plasmon resonance assays, we showed that these critical residues are involved in the interaction between P[1-40] peptide and N(mono) in vitro. Finally, we showed that overexpression of the peptide P[1-29] can inhibit the polymerase activity in the context of the RSV minireplicon, thus demonstrating that targeting the N(0)-P interaction could constitute a potential antiviral strategy.ImportanceRespiratory syncytial virus (RSV) is the leading cause of lower respiratory tract illness in infants. Since no vaccine or efficient antiviral treatment is available against RSV, it is essential to better understand how the viral machinery functions in order to develop new antiviral strategies. RSV phosphoprotein P, the main RNA polymerase cofactor, is believed to function as a chaperon protein, maintaining N as a nonassembled, RNA-free protein (N(0)) competent for RNA encapsidation. In this paper, we provide the first evidence, to our knowledge, that the N terminus of P contains a domain that binds specifically to this RNA-free form of N. We further show that overexpression of a small peptide spanning this region of P can inhibit viral RNA synthesis. These findings extend our understanding of the function of RSV RNA polymerase and point to a new target for the development of drugs against this virus.

Project description:Respiratory syncytial virus (RSV) is a nonsegmented negative-sense (NNS) RNA virus and shares a similar RNA synthesis strategy with other members of NNS RNA viruses, such as measles, rabies virus, and Ebola virus. RSV RNA synthesis is catalyzed by a multifunctional RNA-dependent RNA polymerase (RdRP), which is composed of a large (L) protein that catalyzes three distinct enzymatic functions and an essential coenzyme phosphoprotein (P). Here, we successfully prepared highly pure, full-length, wild-type and mutant RSV polymerase (L-P) complexes. We demonstrated that the RSV polymerase could carry out both de novo and primer-based RNA synthesis. We defined the minimal length of the RNA template for in vitro de novo RNA synthesis using the purified RSV polymerase as 8 nucleotides (nt), shorter than previously reported. We showed that the RSV polymerase catalyzed primer-dependent RNA elongation with different lengths of primers on both short (10-nt) and long (25-nt) RNA templates. We compared the sequence specificity of different viral promoters and identified positions 3, 5, and 8 of the promoter sequence as essential to the in vitro RSV polymerase activity, consistent with the results previously mapped with the in vivo minigenome assay. Overall, these findings agree well with those of previous biochemical studies and extend our understanding of the promoter sequence and the mechanism of RSV RNA synthesis.IMPORTANCE As a major human pathogen, RSV affects 3.4 million children worldwide annually. However, no effective antivirals or vaccines are available. An in-depth mechanistic understanding of the RSV RNA synthesis machinery remains a high priority among the NNS RNA viruses. There is a strong public health need for research on this virus, due to major fundamental gaps in our understanding of NNS RNA virus replication. As the key enzyme executing transcription and replication of the virus, the RSV RdRP is a logical target for novel antiviral drugs. Therefore, exploring the primer-dependent RNA elongation extends our mechanistic understanding of the RSV RNA synthesis. Further fine mapping of the promoter sequence paves the way to better understand the function and structure of the RSV polymerase.

Project description:BACKGROUND: There are no approved small molecule drug therapies for human respiratory syncytial virus (hRSV), a cause of morbidity and mortality in at-risk newborns, the immunocompromised, and the elderly. We have investigated as a potential novel hRSV drug target the protein-protein interaction between the C-terminus of the viral phosphoprotein (P) and the viral nucleocapsid protein (N), components of the ribonucleoprotein complex that contains, replicates, and transcribes the viral RNA genome. Earlier work by others established that the 9 C-terminal residues of P are necessary and sufficient for binding to N. METHODS: We used a fluorescence anisotropy assay, surface plasmon resonance and 2-D NMR to quantify the affinities of peptides based on the C terminus of P for RNA-free, monomeric N-terminal-truncated N(13-391). We calculated the contributions to the free energies of binding of P to N(13-391) attributable to the C-terminal 11 residues, phosphorylation of the C-terminal 2 serine residues, the C-terminal Asp-Phe, and the phenyl ring of the C-terminal Phe. RESULTS: Binding studies confirmed the crucial role of the phosphorylated C-terminal peptide D(pS)DNDL(pS)LEDF for binding of P to RNA-free, monomeric N(13-391), contributing over 90% of the binding free energy at low ionic strength. The phenyl ring of the C-terminal Phe residue contributed an estimated -2.7 kcal/mole of the free energy of binding, the C-terminal Asp-Phe residues contributed -3.8 kcal/mole, the sequence DSDNDLSLE contributed -3.1 kcal/mole, and phosphorylation of the 2 Ser residues contributed -1.8 kcal/mole. Due to the high negative charge of the C-terminal peptide, the affinity of the P C-terminus for N(13-391) decreased as the ionic strength increased. CONCLUSIONS: The results support the idea that the interaction of the C-terminal residues of P with N constitutes a protein-protein interaction hotspot that may be a suitable target for small-molecule drugs that inhibit viral genome replication and transcription.

Project description:ObjectivesRespiratory Syncytial Virus (RSV) is a leading cause of death and hospitalization among infants and young children. People with an immunocompromised status are also at risk for severe RSV infection. There is no specific treatment for RSV infection available. Ribavirin, an antiviral drug approved for severe lung infection by RSV, has shown limited clinical efficacies with severe side effects. Additionally, given the genetic variability of RSV genomes and seasonal change of different strains, a broad-spectrum antiviral drug is highly desirable. The RNA-dependent RNA polymerase (RdRp) domain is relatively conserved and indispensable for the replication of the virus genome and therefore serves as a potential therapeutic target. Previous attempts to identify an RdRp inhibitor have not been successful due to lack of potency or high enough blood exposure. DZ7487 is a novel orally available small molecule inhibitor specifically designed to target the RSV RdRp. Here we present our data showing that DZ7487 can potently inhibited all clinical viral isolates tested, with large safety margin predicted for human.MethodsHEp-2 cells were infected by RSV A and B. Antiviral activities were assessed by in vitro cytopathic effect assay (CPE) and Reverse transcription-quantitative polymerase chain reaction (RT-qPCR). DZ7487 antiviral effects in lower airway cells were evaluated in A549 and human small airway epithelial cells (SAEC) cells. DZ7487 induced RSV A2 escape mutations were selected through continuous culture with increasing DZ7487 concentrations in the culture medium. Resistant mutations were identified by next generation sequencing and confirmed by recombinant RSV CPE assays. RSV infection models in both BALB/c mice and cotton rats were used to evaluate DZ7487 in vivo antiviral effects.ResultsDZ7487 potently inhibited viral replication of all clinical isolates of both RSVA and B subtypes. In lower airway cells, DZ7487 showed superior efficacy than the nucleoside analog ALS-8112. Acquired resistant mutation was predominantly restricted at the RdRp domain resulting asparagine to threonine mutation (N363T) of the L protein. This finding is consistent with DZ7487's presumed binding mode. DZ7487 was well tolerated in animal models. Unlike fusion inhibitors, which can only prevent viral infection, DZ7487 potently inhibited RSV replication before and after RSV infection in vitro and in vivo.ConclusionsDZ7487 demonstrated potent anti-RSV replication effect both in vitro and in vivo assays. It has the desired drug-like physical properties to be an effective orally available anti-RSV replication drug with broad spectrum.

Dataset Information

Fine mapping and characterization of the L-polymerase-binding domain of the respiratory syncytial virus phosphoprotein.

Publications

Fine mapping and characterization of the L-polymerase-binding domain of the respiratory syncytial virus phosphoprotein.

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