Structural insights into γH2Ax containing nucleosomes

Area of Science:

• Structural Biology
• Molecular Biology
• Epigenetics

Background:

• Histone variant H2AX phosphorylation (γH2AX) is a key signal for DNA double-strand break repair.
• BRCA1 carboxy-terminal (BRCT) domains recognize γH2AX to recruit repair proteins.

Purpose of the Study:

• To elucidate the structural basis of γH2AX nucleosomes and their interactions.
• To investigate how BRCT domain binding affects nucleosome structure and chromatin organization.

Main Methods:

• Cryogenic electron microscopy (cryo-EM) to resolve nucleosome structures.
• Geometric analysis of nucleosome stacking parameters.
• Molecular simulations of BRCT-γH2AX interactions.

Main Results:

• Identified three distinct parallel stacked mononucleosome structures with H4 N-terminal tail, H2B, and DNA mediating interactions.
• Demonstrated that BRCT domain binding to γH2AX nucleosomes disrupts stacking.
• Observed dynamic, not stable, BRCT-nucleosome interactions via cryo-EM and simulations.

Conclusions:

• γH2AX nucleosome stacking is regulated by specific inter-nucleosomal contacts.
• Disruption of stacking by BRCT binding may facilitate chromatin decondensation.
• This decondensation could expose the nucleosomal acidic patch, promoting DNA repair factor recruitment.