Dynamics, conformational entropy, and frustration in protein-protein interactions involving an intrinsically disordered protein domain.

Intrinsically disordered proteins (IDPs) are abundant in the eukaryotic proteome. However, little is known about the role of sub-nanosecond dynamics and the conformational entropy that it represents in protein-protein interactions involving IDPs. Using NMR side chain and backbone relaxation, stopped-flow kinetics, ITC, and computational studies, we have here characterized the interaction between the globular TAZ1 domain of CREB binding protein, and the intrinsically disordered transactivation domain of STAT2 (TAD-STAT2). We show that the TAZ1/TAD-STAT2 complex retains considerable sub-nanosecond motions, with TAD-STAT2 undergoing only a partial disorder-to-order transition, We report here the first experimental determination of the conformational entropy change for both binding partners in an IDP binding interaction and find that the total change even exceeds in magnitude to the binding enthalpy and is comparable to the contribution from the hydrophobic effect, demonstrating its importance for the binding energetics. Furthermore, we show that the conformational entropy change for TAZ1 is also instrumental in maintaining a biologically meaningful binding affinity. Strikingly, a spatial clustering of very high amplitude motions and a cluster of more rigid sites in the complex exists, which we through computational studies found to overlap with regions that experience energetic frustration and are less frustrated, respectively. Thus, the residual dynamics in the bound state could be necessary for faster dissociation, which is important for proteins that interact with multiple binding partners.