Exploring ATAD2 bromodomain function in the dynamic epigenetic landscape.

The ATPase family, AAA domain-containing protein 2 (ATAD2) is a nuclear co-regulator protein highly expressed in many unrelated cancers. ATAD2 overexpression is linked to poor outcomes in patients. ATAD2 contains a C-terminal bromodomain that "reads" acetylated lysine post-translational modifications (PTM) that occur on histone proteins present in the nucleosome core particle. The epigenetic landscape is dynamic and combinatorial, containing multiple types and numbers of modifications on the histone proteins at any given time. Yet, it is unknown how the presence of other modifications adjacent to acetylated lysine residues impact bromodomain protein recognition and function. We hypothesized that the presence of nearby post-translational modifications including methylation and phosphorylation would modulate the ability of the ATAD2 bromodomain to recognize its acetylated lysine binding partners. Previously, we systemically screened for multiple PTM combinations recognized by the ATAD2 bromodomain using dCypher technology from EpiCypher. In our current study, we further characterized the interaction with these histone ligands using biophysical techniques including isothermal titration calorimetry (ITC), nuclear magnetic resonance (NMR), and X-ray crystallography. Our results indicate that the histone binding activity of the ATAD2 bromodomain is impacted by the presence of nearby PTMs. Our results provide new insights on how the bromodomain functions to target the ATAD2 protein to chromatin, and how this interaction may be fine-tuned via dynamic changes in the epigenetic landscape.