Understanding Intramolecular Crosstalk in an Intrinsically Disordered Protein.

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 NTAIL (classically denoted as MoRE) undergoes a disorder-to-order transition, populating an α-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.