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bioRxiv · 10.1101/2022.08.09.503292

Multivalent BARD1-nucleosome interactions facilitate H2A ubiquitylation by BRCA1/BARD1

Witus, S. R.·Tuttle, L. M.·Zelter, A.·Kermoade, K. E.·Wilburn, D. B.·Zhao, W.·Davis, T. N.·Brzovic, P.·Klevit, R. E.
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Abstract

BRCA1/BARD1 is a tumor suppressor E3 ubiquitin (Ub) ligase with roles in DNA damage repair and in transcriptional regulation. BRCA1/BARD1 RING domains interact with nucleosomes to facilitate mono-ubiquitylation of distinct residues on the C-terminal tail of histone H2A. These enzymatic domains constitute a small fraction of the heterodimer, raising the possibility of functional chromatin interactions involving other regions such as the BARD1 C-terminal domains that bind nucleosomes containing the DNA damage signal H2A K15-Ub and H4 K20me0, or portions of the expansive intrinsically disordered regions found in both subunits. Herein, we reveal novel interactions that support robust H2A ubiquitylation activity mediated through a high-affinity, intrinsically disordered DNA-binding region of BARD1. These interactions support BRCA1/BARD1 recruitment to chromatin and sites of DNA damage in cells and contribute to their survival. We also reveal distinct BRCA1/BARD1 complexes that depend on the presence of H2A K15-Ub, including a complex where a single BARD1 subunit spans adjacent nucleosome units. Our findings identify an extensive network of multivalent BARD1- nucleosome interactions that serve as a platform for BRCA1/BARD1-associated functions on chromatin.

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Witus, S. R., Tuttle, L. M., Zelter, A., Kermoade, K. E., Wilburn, D. B., Zhao, W., Davis, T. N., Brzovic, P., Klevit, R. E.. 2022-08-09. Multivalent BARD1-nucleosome interactions facilitate H2A ubiquitylation by BRCA1/BARD1. https://doi.org/10.1101/2022.08.09.503292

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