ABSTRACTThe 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 withParamyxoviridaeandRhabdoviridae, it is expected that the viral phosphoprotein P acts as a chaperone protein, forming a soluble complex with the RNA-free form of N (N0-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 N0monomer. We used this N mutant, designated Nmono, as a substitute for N0in order to characterize the P regions involved in the N0-P complex formation. Using a series of P fragments, we determined by glutathioneS-transferase (GST) pulldown assays that the N and C termini of P are able to interact with Nmono. 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 Nmonoin 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 N0-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 (N0) 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.
Mechanism of Action for Respiratory Syncytial Virus Inhibitor RSV604
