Phosphorylation Regulates the Bound Structure of an Intrinsically Disordered Protein: The p53-TAZ2 Case.

Raúl Esteban Ithuralde,Adrián Gustavo Turjanski,Yaakov Koby Levy

doi:10.1371/journal.pone.0144284

Abstract

Disordered regions and Intrinsically Disordered Proteins (IDPs) are involved in critical cellular processes and may acquire a stable three-dimensional structure only upon binding to their partners. IDPs may follow a folding-after-binding process, known as induced folding, or a folding-before-binding process, known as conformational selection. The transcription factor p53 is involved in the regulation of cellular events that arise upon stress or DNA damage. The p53 domain structure is composed of an N-terminal transactivation domain (p53TAD), a DNA Binding Domain and a tetramerization domain. The activity of TAD is tightly regulated by interactions with cofactors, inhibitors and phosphorylation. To initiate transcription, p53TAD binds to the TAZ2 domain of CBP, a co-transcription factor, and undergoes a folding and binding process, as revealed by the recent NMR structure of the complex. The activity of p53 is regulated by phosphorylation at multiple sites on the TAD domain and recent studies have shown that modifications at three residues affect the binding towards TAZ2. However, we still do not know how these phosphorylations affect the structure of the bound state and, therefore, how they regulate the p53 function. In this work, we have used computational simulations to understand how phosphorylation affects the structure of the p53TAD:TAZ2 complex and regulates the recognition mechanism. Phosphorylation has been proposed to enhance binding by direct interaction with the folded protein or by changing the unbound conformation of IDPs, for example by pre-folding the protein favoring the recognition mechanism. Here, we show an interesting turn in the p53 case: phosphorylation mainly affects the bound structure of p53TAD, highlighting the complexity of IDP protein-protein interactions. Our results are in agreement with previous experimental studies, allowing a clear picture of how p53 is regulated by phosphorylation and giving new insights into how post-translational modifications can regulate the function of IDPs.

Highlights

The classical paradigm states that the structure of a protein is related to its function
Our simulations are in agreement with previous experiments and allow a deeper understanding of how phosphorylation regulates the interaction of TAZ2 with p53TAD
The results presented suggest that a pre-folded structure will not clearly favor the binding process, as the phosphorylated p53TAD peptides bound to TAZ2 show less tendency to form folded helix structures

Summary

Introduction

The classical paradigm states that the structure of a protein is related to its function. Disordered regions and Intrinsically Disordered Proteins (IDPs) are involved in critical cellular processes, such as the cell cycle The deregulation of their function may lead to important health problems, such as Parkinson's disease, Alzheimer’s and cancer [1]. Disordered regions may acquire a stable three-dimensional structure upon binding to their partners, so the transition states of these processes are key to understanding this group of biomolecules [2,3,4,5,6]. In this sense there is great interest in unraveling the function of IDPs in cells. Disordered regions may allow the protein to exhibit a greater capture radius, enhancing protein-protein recognition [1,7,8]

Methods

Results

Conclusion