A Structural and Dynamic Analysis of the Partially Disordered Polymerase-Binding Domain in RSV Phosphoprotein

The phosphoprotein P of Mononegavirales (MNV) is an essential co-factor of the viral RNA polymerase L. Its prime function is to recruit L to the ribonucleocapsid composed of the viral genome encapsidated by the nucleoprotein N. MNV phosphoproteins often contain a high degree of disorder. In Pneumoviridae phosphoproteins, the only domain with well-defined structure is a small oligomerization domain (P(OD)). We previously characterized the differential disorder in respiratory syncytial virus (RSV) phosphoprotein by NMR. We showed that outside of RSV P(OD), the intrinsically disordered N-and C-terminal regions displayed a structural and dynamic diversity ranging from random coil to high helical propensity. Here we provide additional insight into the dynamic behavior of P(Cα), a domain that is C-terminal to P(OD) and constitutes the RSV L-binding region together with P(OD). By using small phosphoprotein fragments centered on or adjacent to P(OD), we obtained a structural picture of the P(OD)–P(Cα) region in solution, at the single residue level by NMR and at lower resolution by complementary biophysical methods. We probed P(OD)–P(Cα) inter-domain contacts and showed that small molecules were able to modify the dynamics of P(Cα). These structural properties are fundamental to the peculiar binding mode of RSV phosphoprotein to L, where each of the four protomers binds to L in a different way.