Interaction of the C-Terminal Domains of Sendai Virus N and P Proteins: Comparison of Polymerase-Nucleocapsid Interactions within the Paramyxovirus Family

Abstract

ABSTRACT Interaction of the C-terminal domains of Sendai virus (SeV) P and N proteins is crucial for RNA synthesis by correctly positioning the polymerase complex (L+P) onto the nucleocapsid (N/RNA). To better understand this mechanism within the paramyxovirus family, we have studied the complex formed by the SeV C-terminal domains of P (PX) and N (N TAIL ) proteins by solution nuclear magnetic resonance spectroscopy. We have characterized SeV N TAIL , which belongs to the class of intrinsically disordered proteins, and precisely defined the binding regions within this latter domain and within PX. SeV N TAIL binds with residues 472 to 493, which have a helical propensity (residues 477 to 491) to the surface created by helices α2 and α3 of PX with a 1:1 stoichiometry, as was also found for measles virus (MV). The binding interface is dominated by charged residues, and the dissociation constant was determined to be 57 ± 18 μM under conditions of the experiment (i.e., in 0.5 M NaCl). We have also shown that the extreme C terminus of SeV N TAIL does not interact with PX, which is in contrast to MV, where a second binding site was identified. In addition, the interaction surfaces of the MV proteins are hydrophobic and a stronger binding constant was found. This gives a good illustration of how selection pressure allowed the C-terminal domains of N and P proteins to evolve concomitantly within this family of viruses in order to lead to protein complexes having the same three-dimensional fold, and thus the same function, but with completely different binding interfaces.