A histone-mimicking interdomain linker in a multidomain protein modulates multivalent histone binding

Area of Science:

• Epigenetics and Chromatin Biology
• Protein-DNA Interactions
• Molecular Mechanisms of Gene Regulation

Background:

• Histone tails undergo posttranslational modifications recognized by histone-binding proteins.
• BROMO domain adjacent to zinc finger 2B (BAZ2B) is a multidomain protein with PHD and bromodomain reader modules.
• The precise mechanism of H3 binding by BAZ2B and its regulation remain underexplored.

Purpose of the Study:

• To elucidate the mode of H3 binding by BAZ2B.
• To investigate the regulatory role of the interdomain linker in BAZ2B histone binding.
• To understand how BAZ2B interactions contribute to epigenetic regulation.

Main Methods:

• Isothermal titration calorimetry (ITC) to quantify binding thermodynamics.
• Nuclear Magnetic Resonance (NMR) spectroscopy to study protein-domain interactions.
• Biochemical assays to assess histone-binding specificity and affinity.

Main Results:

• Acidic residues in the BAZ2B PHD domain are crucial for H3 binding.
• BAZ2B PHD-BRD engages in polyvalent interactions with H3K14ac.
• The disordered linker electrostatically modulates PHD domain affinity for histone H3.

Conclusions:

• Interdomain linkers can play a dual role in substrate binding and affinity modulation.
• Intramolecular mimicry by the linker inhibits histone binding, revealing a regulatory mechanism.
• Posttranslational modifications on the linker may transiently tune BAZ2B's histone-binding affinity.