Structural Insights into the Recognition of Mono- and Diacetylated Histones by the ATAD2B Bromodomain.

Bromodomains exhibit preferences for specific patterns of post-translational modifications on core and variant histone proteins. We examined the ligand specificity of the ATAD2B bromodomain and compared it to its closely related paralogue in ATAD2. We show that the ATAD2B bromodomain recognizes mono- and diacetyllysine modifications on histones H4 and H2A. A structure-function approach was used to identify key residues in the acetyllysine-binding pocket that dictate the molecular recognition process, and we examined the binding of an ATAD2 bromodomain inhibitor by ATAD2B. Our analysis demonstrated that critical contacts required for bromodomain inhibitor coordination are conserved between the ATAD2/B bromodomains, with many residues playing a dual role in acetyllysine recognition. We further characterized an alternative splice variant of ATAD2B that results in a loss of function. Our results outline the structural and functional features of the ATAD2B bromodomain and identify a novel mechanism regulating the interaction of the ATAD2B protein with chromatin.

The BRPF1 bromodomain is a molecular reader of di-acetyllysine.

Bromodomain-containing proteins are often part of chromatin-modifying complexes, and their activity can lead to altered expression of genes that drive cancer, inflammation and neurological disorders in humans. Bromodomain-PHD finger protein 1 (BRPF1) is part of the MOZ (monocytic leukemic zinc-finger protein) HAT (histone acetyltransferase) complex, which is associated with chromosomal translocations known to contribute to the development of acute myeloid leukemia (AML). BRPF1 contains a unique combination of chromatin reader domains including two plant homeodomain (PHD) fingers separated by a zinc knuckle (PZP domain), a bromodomain, and a proline-tryptophan-tryptophan-proline (PWWP) domain. BRPF1 is known to recruit the MOZ HAT complex to chromatin by recognizing acetylated lysine residues on the N-terminal histone tail region through its bromodomain. However, histone proteins can contain several acetylation modifications on their N-terminus, and it is unknown how additional marks influence bromodomain recruitment to chromatin. Here, we identify the BRPF1 bromodomain as a selective reader of di-acetyllysine modifications on histone H4. We used ITC assays to characterize the binding of di-acetylated histone ligands to the BRPF1 bromodomain and found that the domain binds preferentially to histone peptides H4K5acK8ac and H4K5acK12ac. Analytical ultracentrifugation (AUC) experiments revealed that the monomeric state of the BRPF1 bromodomain coordinates di-acetylated histone ligands. NMR chemical shift perturbation studies, along with binding and mutational analyses, revealed non-canonical regions of the bromodomain-binding pocket that are important for histone tail recognition. Together, our findings provide critical information on how the combinatorial action of post-translational modifications can modulate BRPF1 bromodomain binding and specificity.

Crystallization and preliminary X-ray diffraction analysis of the BRPF1 bromodomain in complex with its H2AK5ac and H4K12ac histone-peptide ligands.

The bromodomain-PHD finger protein 1 (BRPF1) is an essential subunit of the monocytic leukemia zinc (MOZ) histone acetyltransferase (HAT) complex and is required for complex formation and enzymatic activation. BRPF1 contains a structurally conserved bromodomain, which recognizes specific acetyllysine residues on histone proteins. The MOZ HAT plays a direct role in hematopoiesis, and deregulation of its activity is linked to the development of acute myeloid leukemia. However, the molecular mechanism of histone-ligand recognition by the BRPF1 bromodomain is currently unknown. The 117-amino-acid BRPF1 bromodomain was overexpressed in Escherichia coli and purified to homogeneity. Crystallization experiments of the BRPF1 bromodomain in complex with its H4K12ac and H2AK5ac histone ligands yielded crystals that were suitable for high-resolution X-ray diffraction analysis. The BRPF1 bromodomain-H4K12ac crystals belonged to the tetragonal space group P43212, with unit-cell parameters a = 75.1, b = 75.1, c = 86.3 Å, and diffracted to a resolution of 1.94 Å. The BRPF1 bromodomain-H2AK5ac crystals grew in the monoclinic space group P21, with unit-cell parameters a = 60.9, b = 55.6, c = 82.1 Å, ß = 93.6°, and diffracted to a resolution of 1.80 Å. Complete data sets were collected from both crystal forms using synchrotron radiation on beamline X29 at Brookhaven National Laboratory (BNL).

Structural insights into recognition of acetylated histone ligands by the BRPF1 bromodomain.

Bromodomain-PHD finger protein 1 (BRPF1) is part of the MOZ HAT complex and contains a unique combination of domains typically found in chromatin-associated factors, which include plant homeodomain (PHD) fingers, a bromodomain and a proline-tryptophan-tryptophan-proline (PWWP) domain. Bromodomains are conserved structural motifs generally known to recognize acetylated histones, and the BRPF1 bromodomain preferentially selects for H2AK5ac, H4K12ac and H3K14ac. We solved the X-ray crystal structures of the BRPF1 bromodomain in complex with the H2AK5ac and H4K12ac histone peptides. Site-directed mutagenesis on residues in the BRPF1 bromodomain-binding pocket was carried out to investigate the contribution of specific amino acids on ligand binding. Our results provide critical insights into the molecular mechanism of ligand binding by the BRPF1 bromodomain, and reveal that ordered water molecules are an essential component driving ligand recognition.