Structural insights into combinations of histone H4 modifications recognized by the ATAD2B bromodomain

Conference: 2022: 72nd ACA Annual Meeting
Margaret Phillips Poster Author
Univeristy of Vermont
Burlington, VT 
07/31/2022: 5:30 PM - 7:30 PM
Poster Session 
Portland Marriott Downtown Waterfront 
Room: Exhibit Hall 


The ATPase family, AAA domain-containing protein 2 (ATAD2, or ANCCA) is an AAA nuclear co-regulator protein containing two ATPase domains and a bromodomain. It's closely related paralogue, ATAD2B (KIAA1240), also contains two ATPase domains and a bromodomain. The AAA ATPase domains are broadly associated with ATP driven molecular remodeling reactions, while bromodomains are evolutionarily conserved chromatin 'reader' domains, known to regulate gene expression through recognition of histone post-translational modifications (PTMs). Extensive studies on ATAD2 discuss its upregulation and correlation with poor prognosis in various cancers, particularly breast cancer, and have successfully mapped the different histone interactions needed for targeting ATAD2 to the chromatin. Despite sharing high structural and sequence similarity with ATAD2, little is known about the unique role of ATAD2B. ATAD2B is expressed during neuronal differentiation and in tumor progression. However, limited information is available on how ATAD2B is involved, or upregulated in various tumors, especially in breast cancer. Our group has recently published a broad range of histone modifications recognized by the ATAD2B bromodomain. These modifications mostly include acetyllysine moieties on histone H4.
Here, we present the structural and functional insights into the factors driving the recognition of various histone post-translational modifications and how their cross-talk can modulate the chromatin 'reader' activity of the ATAD2B bromodomain. Our ITC data confirms that the ATAD2B bromodomain can interact with multiply modified histone H4 ligands. We observe that some combinations of histone PTMs are permissible, while others diminish the binding activity. We also present novel crystal structures of the ATAD2B bromodomain in complex with two acetylated histone ligands. These high resolution structures highlight the polar contacts and hydrophobic interactions that form the molecular basis for the histone H4 acetyllysine recognition. Furthermore, immunoblot experiments confirm that the ATAD2B bromodomain can bind modified H4 histones extracted from breast cancer model-MCF7 cells.
Taken together, our data provide crucial information on how cross-talk between multiple histone modifications modulate the bromodomain activity of ATAD2B and how the histone code dynamics may alter its role as a regulator of gene expression.

Funding Sources:
NIGMS R01GM129338, NCI P01CA240685