Backbone Dynamics of the TAZ1 Domain of the Creb-Binding Protein Modulate Competition Between Disordered Ligands

Abstract

Intrinsically disordered proteins (IDPs) play important roles in a multitude of cellular processes; however, the mechanisms by which disordered proteins carry out their diverse roles as modulators of cellular signaling are not yet completely understood. IDPs utilize a wide range of mechanisms to interact with folded proteins within the cell, and in many cases, must compete for binding of protein interaction partners. Yet, little is known about the contributions of the folded proteins to the binding and specificity of interactions with multiple disordered ligands. Are folded protein interaction partners simply scaffolds for IDP binding or do they undergo structural and dynamic changes to accommodate different disordered ligands? Using the folded TAZ1 domain of the transcriptional coactivator CBP and the disordered proteins HIF-1α and CITED2 as an example, we demonstrate that conformational dynamics and structural changes of TAZ1 are critical for binding and exchange of different IDPs. CITED2 competes with HIF-1α for TAZ1 binding through an extremely efficient unidirectional allosteric switch that relies not only on the physicochemical properties of the disordered proteins but also on the structure and dynamics of TAZ1. To gain further mechanistic insight into this process, we used NMR relaxation methods to obtain a detailed description of the backbone dynamics that contribute to TAZ1 binding and competition. We found that TAZ1 displays altered backbone dynamics in its free and bound states, with changes in TAZ1 dynamics observed not only in the HIF-1α and CITED2 binding sites but also in regions that differ in structure when bound to HIF-1α or CITED2. These data suggest that backbone dynamics in TAZ1 play a role in modulating binding of disordered ligands and highlight the importance of characterizing both folded and disordered partners in molecular interactions.