Domain-specific DNA binding activities of BRCA1 reveal substrate preferences for homologous recombination and telomere regulation

ABSTRACT BRCA1 is a crucial mediator of homologous recombination (HR), a high-fidelity pathway for repairing double-stranded DNA breaks (DSBs) in human cells. The central region of BRCA1 protein contains two putative DNA binding domains (DBDs), yet their relative substrate specificities and functional contributions to HR remain unclear. Here, we characterized the DNA binding properties of DBD1 (amino acids 330-554), DBD2 (amino acids 894-1057), and the BRCA1 C-terminal (BRCT) repeats using biolayer interferometry. We assessed their affinities for single-stranded DNA (ssDNA), double-stranded DNA (dsDNA), and G-quadruplex (G4) structures. DBD1 exhibited the highest affinity for dsDNA, while DBD2 and BRCT bound preferentially to ssDNA and G4. These findings support a model in which DBD1 directs BRCA1 to DSB sites to facilitate DNA end resection during HR, whereas DBD2 and BRCT contribute to the role of BRCA1 in telomere maintenance and chromatin remodeling through the recognition of non-canonical DNA structures.