A single methylation site regulates HRSV nucleocapsid architecture and replication

Basse, V.; Gonnin, L.; Silva, C. S.; Rodrigues-Machado, C.; Henry, C.; Bacia-Verloop, M.; Desfosses, A.; Sourimant, J.; Eleouet, J.-F.; Leyrat, C.; Gutsche, I.; Galloux, M.

doi:10.64898/2026.01.15.699754

bioRxiv · 10.64898/2026.01.15.699754

A single methylation site regulates HRSV nucleocapsid architecture and replication

Basse, V.·Gonnin, L.·Silva, C. S.·Rodrigues-Machado, C.·Henry, C.·Bacia-Verloop, M.·Desfosses, A.·Sourimant, J.·Eleouet, J.-F.·Leyrat, C.·Gutsche, I.·Galloux, M.

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Abstract

The nucleoprotein N of the human respiratory syncytial virus (HRSV) encases the viral genome, forming a flexible N-RNA nucleocapsid helix that serves as template for the viral polymerase L. Recent structural analysis revealed a non-canonical helical nucleocapsid arrangement that modulates RNA accessibility, yet its impact on polymerase function remains unknown. Here, we identified symmetric dimethylation of residue R27 of N as a critical modulator of nucleocapsid architecture and viral replication. We also showed that the methylase PRMT5 interacts with N and likely catalyses R27 methylation. Molecular dynamics simulations of RNA-free N dimers indicate that R27 methylation enhances opening and closing of the RNA-binding cavity, whereas a methylation-mimicking R27M substitution favours a closed state. Cryo-electron microscopy reveals a canonical, markedly straight R27M helix with increased rise and pitch. These findings demonstrate that post-translational modifications fine-tune interactions between N protomers, shaping nucleocapsid assembly, structure and dynamics, and thereby controlling HRSV replication.

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Basse, V., Gonnin, L., Silva, C. S., Rodrigues-Machado, C., Henry, C., Bacia-Verloop, M., Desfosses, A., Sourimant, J., Eleouet, J.-F., Leyrat, C., Gutsche, I., Galloux, M.. 2026-01-15. A single methylation site regulates HRSV nucleocapsid architecture and replication. https://doi.org/10.64898/2026.01.15.699754

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