Gonnin, L. | bioRxiv Science

bioRxiv2023

Structural landscape of the Respiratory Syncytial Virus nucleocapsids

Human Respiratory Syncytial Virus (RSV) is a prevalent cause of severe respiratory infections in children and the elderly. The viral genome, enwrapped by the nucleoprotein N into a helical nucleocapsid (NC), is a template for the viral RNA synthesis and a scaffold for the virion assembly. Although the structures of NC filaments representative of the other major families of the Mononegavirales order have been solved, a detailed understanding of the RSV NCs is missing. This cryo-electron microscopy (cryo-EM) analysis highlights the polymorphism of the RSV nucleocapsid-like assemblies. We reveal in particular the non-canonical arrangement of the RSV NC helix, composed of 16 N per asymmetric unit, and the resulting systematic variations in the RNA accessibility. We demonstrate that this unique helical symmetry originates from recurring longitudinal interactions by the C-terminal arm of the RSV N, whose truncation abrogates the inter-turn contacts. We report the cryo-EM structures of the full-length helical NC filaments, double-headed NCs, ring-capped NCs and double-decameric N-RNA rings, as well as those of the alternative assemblies formed by a C-terminally truncated N mutant. In addition, we demonstrate the functional importance of the interface involved in the formation of the double-headed and the ring-capped interactions. We put all these findings in the context of the RSV RNA synthesis machinery and delineate the structural basis for its further investigation.

microbiology↗

bioRxiv2021

Depletion of TAX1BP1 amplifies innate immune responses during respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is the main cause of acute respiratory infections in young children, and also has a major impact in the elderly and immunocompromised people. In the absence of vaccine or efficient treatment, a better understanding of RSV interactions with the host antiviral response during infection is needed. Previous studies revealed that cytoplasmic inclusion bodies (IBs) where viral replication and transcription occur could play a major role in the control of innate immunity during infection by recruiting cellular proteins involved in the host antiviral response. We recently showed that the morphogenesis of IBs relies on a liquid-liquid phase separation mechanism depending on the interaction between viral nucleoprotein (N) and phosphoprotein (P). These scaffold proteins are expected to play a central role in the recruitment of cellular proteins to IBs. Here, we performed a yeast two-hybrid screen using RSV N protein as a bait, and identified the cellular protein TAX1BP1 as a potential partner of N. This interaction was validated by pulldown and immunoprecipitation assays. We showed that TAX1BP1 suppression has only a limited impact on RSV infection in cell cultures. On the contrary, in vivo experiments showed that RSV replication is decreased in TAX1BP1KO mice, whereas the production of inflammatory and antiviral cytokines is enhanced. In vitro infection of either wild-type or TAX1BP1KO alveolar macrophages confirmed that the innate immune response to RSV infection is enhanced in the absence of TAX1BP1. Altogether, our results suggest that RSV could hijack TAX1BP1 to restrain the host immune response during infection. ImportanceRespiratory syncytial virus (RSV), which is the leading cause of lower respiratory tract illness in infants, still remains a medical problem in the absence of vaccine or efficient treatment. This virus is also recognized as a main pathogen in the elderly and immunocompromised people, and the occurrence of co-infections (with other respiratory viruses and bacteria) amplifies the risks of developing respiratory distress. In this context, a better understanding of the pathogenesis associated to viral respiratory infections, which depends on both viral replication and the host immune response, is needed. The present study reveals that the cellular protein TAX1BP1, which interacts with the RSV nucleoprotein N, participates in the control of the innate immune response during RSV infection, suggesting that N-TAX1BP1 interaction represents a new target for the development of antivirals.

microbiology↗