Mechanisms of RNF168 nucleosome recognition and ubiquitylation.

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• RNF168 is a key E3 ubiquitin ligase in the DNA damage response (DDR).
• It catalyzes histone H2A ubiquitylation at K13/K15, facilitating BRCA1-BARD1 and 53BP1 foci formation.
• These foci are essential for selecting DNA double-strand break (DSB) repair pathways.

Purpose of the Study:

• To elucidate the molecular mechanism of RNF168 in catalyzing H2A ubiquitylation and recognizing its products.
• To understand how RNF168 achieves site-specific ubiquitin recognition and signal amplification in the DDR.
• To provide a dynamic view of RNF168's reaction cycle on the nucleosome.

Main Methods:

• Cryo-electron microscopy (cryo-EM) for structural determination.
• Nuclear magnetic resonance (NMR) spectroscopy for studying molecular interactions and dynamics.
• Functional assays to assess RNF168 activity and binding.

Main Results:

• A molecular description of the RNF168 reaction cycle and its dynamics was provided.
• An interaction between RNF168's ubiquitin-binding domain, ubiquitin, and the nucleosome surface was demonstrated.
• This interaction clarifies the signal amplification loop in RNF168-mediated ubiquitylation.

Conclusions:

• The study offers mechanistic insights into RNF168's function in the DNA damage response.
• It clarifies how RNF168 achieves site-specific ubiquitylation of chromatin.
• Findings aid in understanding the generation and interpretation of chromatin ubiquitylation in DDR.