The Henipavirus genome is encapsidated by the nucleoprotein (N) within a helical nucleocapsid that recruits the polymerase complex via the phosphoprotein (P). In a previous study, we reported that in henipaviruses, the N-terminal domain of the phosphoprotein and the C-terminal domain of the nucleoprotein (N TAIL ) are both intrinsically disordered. Here we show that Henipavirus N TAIL domains are also disordered in the context of full-length nucleoproteins. We also report the cloning, purification, and characterization of the C-terminal X domains (P XD ) of Henipavirus phosphoproteins. Using isothermal titration calorimetry, we show that N TAIL and P XD form a 1:1 stoichiometric complex that is stable under NaCl concentrations as high as 1 M and has a K D in the M range. Using far-UV circular dichroism and nuclear magnetic resonance, we show that P XD triggers an increase in the ␣-helical content of N TAIL . Using fluorescence spectroscopy, we show that P XD has no impact on the chemical environment of a Trp residue introduced at position 527 of the Henipavirus N TAIL domain, thus arguing for the lack of stable contacts between the C termini of N TAIL and P XD . Finally, we present a tentative structural model of the N TAIL -P XD interaction in which a short, order-prone region of N TAIL (␣-MoRE; amino acids 473-493) adopts an ␣-helical conformation and is embedded between helices ␣2 and ␣3 of P XD , leading to a relatively small interface dominated by hydrophobic contacts. The present results provide the first detailed experimental characterization of the N-P interaction in henipaviruses and designate the N TAIL -P XD interaction as a valuable target for rational antiviral approaches.

Henipaviruses are newly emerged viruses within the Paramyxoviridae family. Their negative-strand RNA genome is packaged by the nucleoprotein (N) within α-helical nucleocapsid that recruits the polymerase complex made of the L protein and the phosphoprotein (P). To date structural data on Henipaviruses are scarce, and their N and P proteins have never been characterized so far. Using both computational and experimental approaches we herein show that Henipaviruses N and P proteins possess large intrinsically disordered regions. By combining several disorder prediction methods, we show that the N-terminal domain of P (PNT) and the C-terminal domain of N (NTAIL) are both mostly disordered, although they contain short order-prone segments. We then report the cloning, the bacterial expression, purification and characterization of Henipavirus PNT and NTAIL domains. By combining gel filtration, dynamic light scattering, circular dichroism and nuclear magnetic resonance, we show that both NTAIL and PNT belong to the premolten globule sub-family within the class of intrinsically disordered proteins. This study is the first reported experimental characterization of Henipavirus P and N proteins. The evidence that their respective N-terminal and C-terminal domains are highly disordered under native conditions is expected to be invaluable for future structural studies by helping to delineate N and P protein domains amenable to crystallization. In addition, following previous hints establishing a relationship between structural disorder and protein interactivity, the present results suggest that Henipavirus PNT and NTAIL domains could be involved in manifold protein-protein interactions.