Mechanisms of BRCA1–BARD1 nucleosome recognition and ubiquitylation

• Published in: Nature (London) Vol. 596; no. 7872; pp. 438 - 443
• Main Authors: Hu, Qi, Botuyan, Maria Victoria, Zhao, Debiao, Cui, Gaofeng, Mer, Elie, Mer, Georges
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 19.08.2021; Nature Publishing Group
• Subjects: 101/28; 101/6; 631/337/100/1701; 631/337/1427/2122; 631/337/458/582; 631/535/1258/1259; 631/535/878/1263; 82; 82/16; 82/6; 82/80; 82/83; Amino acids; Ankyrins; BRCA1 protein; BRCA1 Protein - metabolism; Breast cancer; C-Terminus; Cancer; Chromatin; Crosstalk; Cryoelectron Microscopy; Damage localization; Deoxyribonucleic acid; DNA; DNA biosynthesis; DNA Repair; Domains; Electron microscopy; Enzymes; Flexibility; Genetic aspects; Histone H2A; Histones; Histones - chemistry; Histones - metabolism; Homologous Recombination; Homology; Humanities and Social Sciences; Humans; Microscopy; Models, Molecular; multidisciplinary; Mutation; Neoplasms - genetics; NMR; Nuclear magnetic resonance; Nucleosomes; Nucleosomes - chemistry; Nucleosomes - genetics; Nucleosomes - metabolism; Nucleosomes - ultrastructure; Physiological aspects; Protein Domains; Proteins; Recruitment; Repair; Science; Science (multidisciplinary); Spectrum analysis; Target recognition; Tumor suppressor genes; Tumor Suppressor p53-Binding Protein 1 - antagonists & inhibitors; Tumor Suppressor p53-Binding Protein 1 - metabolism; Tumor Suppressor Proteins - chemistry; Tumor Suppressor Proteins - genetics; Tumor Suppressor Proteins - metabolism; Tumor Suppressor Proteins - ultrastructure; Tumors; Ubiquitin; Ubiquitin - metabolism; Ubiquitin-conjugating enzyme; Ubiquitin-Conjugating Enzymes - chemistry; Ubiquitin-Conjugating Enzymes - metabolism; Ubiquitin-Conjugating Enzymes - ultrastructure; Ubiquitin-protein ligase; Ubiquitin-Protein Ligases - chemistry; Ubiquitin-Protein Ligases - genetics; Ubiquitin-Protein Ligases - metabolism; Ubiquitin-Protein Ligases - ultrastructure; Ubiquitination; United States
• ISSN: 0028-0836; 1476-4687; 1476-4687
• DOI: 10.1038/s41586-021-03716-8

The BRCA1–BARD1 tumour suppressor is an E3 ubiquitin ligase necessary for the repair of DNA double-strand breaks by homologous recombination 1 – 10 . The BRCA1–BARD1 complex localizes to damaged chromatin after DNA replication and catalyses the ubiquitylation of histone H2A and other cellular targets 11 – 14 . The molecular bases for the recruitment to double-strand breaks and target recognition of BRCA1–BARD1 remain unknown. Here we use cryo-electron microscopy to show that the ankyrin repeat and tandem BRCT domains in BARD1 adopt a compact fold and bind to nucleosomal histones, DNA and monoubiquitin attached to H2A amino-terminal K13 or K15, two signals known to be specific for double-strand breaks 15 , 16 . We further show that RING domains 17 in BRCA1–BARD1 orient an E2 ubiquitin-conjugating enzyme atop the nucleosome in a dynamic conformation, primed for ubiquitin transfer to the flexible carboxy-terminal tails of H2A and variant H2AX. Our work reveals a regulatory crosstalk in which recognition of monoubiquitin by BRCA1–BARD1 at the N terminus of H2A blocks the formation of polyubiquitin chains and cooperatively promotes ubiquitylation at the C terminus of H2A. These findings elucidate the mechanisms of BRCA1–BARD1 chromatin recruitment and ubiquitylation specificity, highlight key functions of BARD1 in both processes and explain how BRCA1–BARD1 promotes homologous recombination by opposing the DNA repair protein 53BP1 in post-replicative chromatin 18 – 22 . These data provide a structural framework to evaluate BARD1 variants and help to identify mutations that drive the development of cancer. The authors elucidate the mechanisms for the ubiquitylation specificity and recruitment of the ubiquitin ligase complex BRCA1–BARD1 to damaged DNA within chromatin to facilitate homologous recombination.