BRD4 binds the nucleosome via both histone and DNA interactions

Area of Science:

• Molecular Biology
• Structural Biology
• Epigenetics

Background:

• BRD4 (BET family) regulates key cellular processes including cell cycle, differentiation, and cancer.
• Chromatin recruitment is thought to occur via BRD4's bromodomains binding acetylated histone tails.
• Previous studies focused on individual domains, lacking full-length BRD4-nucleosome interaction data.

Purpose of the Study:

• To elucidate the structural and biochemical mechanisms of full-length BRD4 binding to nucleosomes.
• To investigate the role of histone acetylation in BRD4-nucleosome complex formation.
• To understand how BRD4 interacts with both histone tails and nucleosomal DNA.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to determine the structure of BRD4-S bound to a diacetylated nucleosome.
• Biochemical assays to assess BRD4 binding affinities to nucleosomes under varying acetylation states.

Main Results:

• Cryo-EM revealed BRD4 BD1 engaging both histone H4 tail and nucleosomal DNA.
• Biochemical studies demonstrated strong nucleosome binding by BRD4 independent of histone acetylation, mediated by regions outside bromodomains.
• Histone H4 acetylation was found to modulate the conformation of the BRD4/nucleosome complex.

Conclusions:

• BRD4 utilizes both bromodomain-dependent and independent mechanisms for nucleosome binding.
• Non-bromodomain regions contribute significantly to BRD4's stable chromatin association.
• Histone acetylation fine-tunes BRD4-nucleosome interactions, impacting complex conformation and potentially transcriptional regulation.