Mechanistic dissection of phosphorylation-dependent regulation of ETS-1 DNA binding

Intrinsically unstructured protein (IUP) regions and conformational disorder are increasingly recognized for their prevalence in the eukaryotic genome and functional importance in disease-related proteins and biological regulatory processes. The dynamic molecular motions inherent in these regions, as well as those found in structured protein regions, are proving to be important targets of regulation. The autoregulation of DNA binding in the transcription factor Ets-1 provides an example of how a flexible, unstructured region can modulate the activity of a structured, regulatable unit by affecting the dynamic character of the protein. This thesis explores the mechanism of phosphorylation-dependent regulation of Ets-1 DNA binding. The serine-rich region (SRR) of Ets-1 is shown to be predominantly unstructured before and after Ca2+-dependent phosphorylation. Phosphorylation of the SRR is shown to stabilize the regulatable unit, which is composed of domains responsible for DNA binding and autoinhibition, and to reduce the DNA-binding affinity of an Ets-1 fragment that is amenable to spectroscopic analysis. NMR-based experiments further determine that phosphorylation partially dampens the fast timescale mobility of the SRR and enhances its localization to the regulatable unit. Aromatic residues adjacent to the phosphor-acceptor sites are found to be required for the reported 100-fold decrease in binding affinity and inhibitory structural alterations. The juxtaposition of phosphoacceptor site and aromatic residue are shown to form a functional unit within the SRR which can be artificially amplified to further increase aromatic residue-dependent, phosphorylation-induced inhibition of Ets-1. We conclude the discovery of a new mechanism whereby phosphorylation of an IUP region enhances a transient hydrophobic interaction, modulating the activity of a structured unit without adopting a structured conformation.