Abstract 1077 Investigating the effects of variants of unknown significance on the binding interaction between BRCA1 and PALB2

Proper functioning of BRCA1 and PALB2 is essential in preventing tumor formation. Upon detection of DNA damage, BRCA1 binds to PALB2, facilitating the repair of double-stranded DNA breaks via homologous recombination. Mutations in the genes coding for BRCA1 and PALB2 may disrupt this binding interaction, hindering DNA damage repair and increasing breast cancer susceptibility. Variants of unknown significance (VUSs) found in breast cancer patients are genetic variants whose impact on the health of individuals remain unknown. This study aims to characterize the effects of these VUSs on the binding interaction between BRCA1 and PALB2 proteins. Site-directed mutagenesis was employed to generate twelve different BRCA1 and PALB2 VUSs to date. Isothermal titration calorimetry (ITC) was used to assess the effects of the VUSs on the BRCA1-PALB2 binding. Analysis of the ITC data revealed that several VUSs exhibit disruptions of the BRCA1-PALB2 binding interaction, but to varying degrees. Some of the variants tested that completely disrupted binding have also demonstrated deleterious effects on homologous recombination repair in previous cell-based studies. This suggests that complete disruption of BRCA1-PALB2 binding may be associated with loss of cellular function. Notably, all VUSs with proline mutations we tested to date caused complete abrogation of binding. Our findings highlight the role of specific residues in BRCA1-PALB2 binding and their functional effects on DNA damage repair. We will also present findings from our ongoing work to test the hypothesis that proline variants located anywhere within the coiled-coil domains will disrupt binding. This study contributes to a deeper understanding of genetic variants that may be associated with breast cancer risk and aids in the prediction of their functional implications. Thank you to TCU College of Science and Engineering and NIH for funding (R15GM135900).