Résumé
The phosphoprotein (P) of vesicular stomatitis virus (VSV) interacts with nascent nucleoprotein (N), forming the N-0-P complex that is indispensable for the correct encapsidation of newly synthesized viral RNA genome. In this complex, the N-terminal region (P-NTR) of P prevents N from binding to cellular RNA and keeps it available for encapsidating viral RNA genomes. Here, using nuclear magnetic resonance (NMR) spectroscopy and small-angle X-ray scattering (SAXS), we show that an isolated peptide corresponding to the 60 first N-terminal residues of VSV P (P-60) and encompassing P-NTR has overall molecular dimensions and a dynamic behavior characteristic of a disordered protein but transiently populates conformers containing alpha-helices. The modeling of P-60 as a conformational ensemble by the ensemble optimization method using SAXS data correctly reproduces the alpha-helical content detected by NMR spectroscopy and suggests the coexistence of subensembles of different compactness. The populations and overall dimensions of these subensembles are affected by the addition of stabilizing (1M trimethylamine-N-oxide) or destabilizing (6M guanidinium chloride) cosolvents. Our results are interpreted in the context of a scenario whereby VSV P-NTR constitutes a molecular recognition element undergoing a disorder-to-order transition upon binding to its partner when forming the N-0-P complex.