Molecular mechanisms of folding of intrinsically disordered proteins

In this thesis, we studied the interaction between the intrinsically disordered domain of the nucleoprotein (N) of Measles virus (MeV), NTAIL, and its partner XD, the X domain of the MeV phosphoprotein (P). It had been previously shown that the α-MoRE (residues 489-506) of NTAIL undergoes an α-helical folding after binding to XD (induced fit mechanism) while regions flanking the α-MoRE remain disordered (fuzzy) in the complex. The fuzzy appendage preceding the α-MoRE was shown to decrease the binding affinities towards XD and the rate of folding of the α-MoRE. In this thesis, by producing NTAIL variants (single-site variants, truncation variants, artificial variants) and performing kinetic experiments of the interaction with XD, we studied the folding after binding mechanism of NTAIL at the single residue level, and investigated the mechanisms through which the fuzzy region hampers the binding affinity and the folding rate of the α-MoRE. We concluded that the central part of the helix is responsible for the initial interactions driving the binding with XD. Moreover, we found that the fuzzy region causes a decrease in the folding rate of the α-MoRE through a combination of entropic and enthalpic effects. We also studied the interaction between NTAIL and a variant of XD, I504A, that populates only the native state. These studies showed that both the binding and the folding steps of the NTAIL-XD interaction are highly dependent on the shape of XD, suggesting that this IDP folds by heterogeneous nucleation via a mechanism induced by the shape of the partner (templated folding).