Structural Dynamics of the C-terminal X Domain of Nipah and Hendra Viruses Controls the Attachment to the C-terminal Tail of the Nucleocapsid Protein

To understand the dynamic interactions between the phosphoprotein (P) and the nucleoprotein (N) within the transcription/replication complex of the Paramyxoviridae and to decipher their roles in regulating viral multiplication, we characterized the structural properties of the C-terminal X domain (P-XD) of Nipah (NiV) and Hendra virus (HeV) P protein. In crystals, isolated NiV P-XD adopted a two-helix dimeric conformation, which was incompetent for binding its partners, but in complex with the C-terminal intrinsically disordered tail of the N protein (N-TAIL), it folded into a canonical 3H bundle conformation. In solution, SEC-MALLS, SAXS and NMR spectroscopy experiments indicated that both NiV and HeV P-XD were larger in size than expected for compact proteins of the same molecular mass and were in conformational exchange between a compact three-helix (3H) bundle and partially unfolded conformations, where helix alpha(3) is detached from the other two. Some measurements also provided strong evidence for dimerization of NiV P(XD )in solution but not for HeV P-XD. Ensemble modeling of experimental SAXS data and statistical-dynamical modeling reconciled all these data, yielding a model where NiV and HeV P-XD exchanged between different conformations, and where NiV but not HeV P-XD formed dimers. Finally, recombinant NiV comprising a chimeric P carrying HeV P-XD was rescued and compared with parental NiV. Experiments carried out in cellula demonstrated that the replacement of P-XD did not significantly affect the replication dynamics while caused a slight virus attenuation, suggesting a possible role of the dimerization of NiV P(XD )in viral replication. (C) 2022 Elsevier Ltd. All rights reserved.