Molecular Basis for Phosphorylation-dependent SUMO Recognition by the DNA Repair Protein RAP80

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• Double-stranded DNA breaks (DSB) trigger repair pathways.
• BRCA tumor suppressors are recruited to DSB sites via ubiquitin (Ub) and SUMO binding.
• RAP80, part of the BRCA1 A complex, binds Lys(63)-linked poly-Ub chains through Ub interacting motifs (UIMs) for recruitment.

Purpose of the Study:

• To elucidate the molecular mechanism of RAP80's collective function in recruiting BRCA1 to DSBs.
• To investigate the binding interaction between RAP80's SUMO interacting motif (SIM) and SUMO-2.
• To understand how phosphorylation affects this interaction and SUMO-2 specificity.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy to study protein-protein interactions.
• Structural analysis of the SUMO-2·phospho-RAP80 complex.
• Biochemical assays to assess binding affinity and specificity.

Main Results:

• RAP80's SIM specifically binds SUMO-2.
• Phosphorylation of the CK2 site on RAP80 significantly enhances binding affinity and specificity for SUMO-2.
• Structural data reveals that enhanced electrostatic interactions and SUMO-2 isoform-specific sequences mediate this specificity.

Conclusions:

• The combined action of RAP80's UIMs and SIM is essential for efficient BRCA1 recruitment to DSBs.
• Phosphorylation of RAP80 is a key regulatory mechanism that strengthens its interaction with SUMO-2.
• Understanding these molecular interactions provides insights into DNA repair pathway regulation and potential therapeutic targets.