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.