Anti-Measles virus Nucleoprotein Monoclonal antibody, Clone 4H5

The interaction between NTAIL and XD from the measles virus represents a paradigmatic example of molecular recognition between an intrinsically disordered protein and a folded partner. By binding to XD, a small portion of NTAff, (classically denoted as MoRE) undergoes a disorder-to-order transition, populating an alpha-helical structure, while the reminder of the protein remains disordered. Here, we demonstrate an unexpected crosstalk between such a disordered region and the adjacent molecular recognition element (MoRE). This result was obtained by producing a series of truncation and site-directed variants of NTAIL while measuring the effects on the kinetics of folding and binding. We show that the disordered region of NTAIL exerts its inhibitory role by slowing the folding step of the MoRE, thereby tuning the affinity of the interaction.

The mechanism of interaction of an intrinsically disordered protein (IDP) with its physiological partner is characterized by a disorder-to-order transition in which a recognition and a binding step take place. Even if the mechanism is quite complex, IDPs tend to bind their partner in a cooperative manner such that it is generally possible to detect experimentally only the disordered unbound state and the structured complex. The interaction between the disordered C-terminal domain of the measles virus nucleoprotein (N-TAIL) and the X domain (XD) of the viral phosphoprotein allows us to detect and quantify the two distinct steps of the overall reaction. Here, we analyze the robustness of the folding of N-TAIL upon binding to XD by measuring the effect on both the folding and binding steps of N-TAIL when the structure of XD is modified. Because it has been shown that wild-type XD is structurally heterogeneous, populating an on-pathway intermediate under native conditions, we investigated the binding to 11 different site-directed variants of N-TAIL of one particular variant of XD (I504A XD) that populates only the native state. Data reveal that the recognition and the folding steps are both affected by the structure of XD, indicating a highly malleable pathway. The experimental results are briefly discussed in the light of previous experiments on other IDPs.