BRCA1 Interaction with Non-Canonical DNA Structures: Insights into Genome Maintenance and Disease Mechanisms

Breast Cancer Susceptibility Gene 1 ( BRCA1 ) plays a crucial role in the homologous recombination (HR) pathway to repair double-stranded breaks (DSBs) in human cells. Interactions between BRCA1 protein and DNA have been mapped to the central region, which could be further divided as two DNA binding domains (DBDs); however, the relative substrate preferences of the DBDs and their functional role in HR remain poorly understood. We hypothesize that the DBDs have distinct binding preferences for DNA repair intermediates, and we have measured the DNA binding affinities of DBD1 (amino acids (aa) 330-554), DBD2 (aa894-1057), and the BRCA1 C-terminal repeats (BRCT) for single-stranded (ssDNA), double-stranded (dsDNA), and G-quadruplex (G4) DNA using biolayer interferometry. Our results indicate that DBD1 has the highest affinity for dsDNA, while DBD2 and BRCT bound tightest to G4 and ssDNA. Based on these findings, we propose a model in which DBD1 targets BRCA1 to DSBs for the promotion of DNA end resection, whereas DBD2 and BRCT target BRCA1 to telomeres to function in chromatin remodeling and telomere regulation.