Profiling BRCA1-BRCT interactions and their functional relevance at amino acid resolution.

Area of Science:

• Genetics
• Molecular Biology
• Cancer Research

Background:

• BRCA1 protein is crucial for DNA repair via homologous recombination (HR).
• Its BRCT domains interact with regulators like ABRAXAS1 and CtIP, influencing HR functions.
• The impact of mutations outside the main binding pocket on these interactions is not well understood.

Purpose of the Study:

• To systematically investigate the functional consequences of mutations across BRCA1's BRCT domains.
• To identify specific residues critical for binding ABRAXAS1 and CtIP.
• To correlate mutation-induced binding defects with pathogenicity for improved clinical interpretation.

Main Methods:

• Generated a site-saturation mutagenesis library of BRCA1 BRCT domains (>4,000 variants).
• Utilized yeast two-hybrid screening to assess binding to ABRAXAS1 and CtIP.
• Validated interactions and functional impacts in mammalian cells.

Main Results:

• Created a comprehensive interaction map of BRCA1 BRCT domain variants.
• Identified novel residues essential for ABRAXAS1 and CtIP binding.
• Demonstrated that disruption of CtIP binding significantly impairs HR.
• Discovered separation-of-function mutations allowing selective interaction analysis.

Conclusions:

• The study provides a detailed map of BRCA1 BRCT domain interactions.
• Loss of protein binding strongly correlates with BRCA1 pathogenicity.
• This interaction map is a valuable tool for clinical variant interpretation in breast cancer genetics.