Journal: Nucleic Acids Res / Year: 2023 Title: BRCA1-BARD1 combines multiple chromatin recognition modules to bridge nascent nucleosomes. Authors: Hayden Burdett / Martina Foglizzo / Laura J Musgrove / Dhananjay Kumar / Gillian Clifford / Lisa J Campbell / George R Heath / Elton Zeqiraj / Marcus D Wilson / Abstract: Chromatin association of the BRCA1-BARD1 heterodimer is critical to promote homologous recombination repair of DNA double-strand breaks (DSBs) in S/G2. How the BRCA1-BARD1 complex interacts with ...Chromatin association of the BRCA1-BARD1 heterodimer is critical to promote homologous recombination repair of DNA double-strand breaks (DSBs) in S/G2. How the BRCA1-BARD1 complex interacts with chromatin that contains both damage induced histone H2A ubiquitin and inhibitory H4K20 methylation is not fully understood. We characterised BRCA1-BARD1 binding and enzymatic activity to an array of mono- and di-nucleosome substrates using biochemical, structural and single molecule imaging approaches. We found that the BRCA1-BARD1 complex preferentially interacts and modifies di-nucleosomes over mono-nucleosomes, allowing integration of H2A Lys-15 ubiquitylation signals with other chromatin modifications and features. Using high speed- atomic force microscopy (HS-AFM) to monitor how the BRCA1-BARD1 complex recognises chromatin in real time, we saw a highly dynamic complex that bridges two nucleosomes and associates with the DNA linker region. Bridging is aided by multivalent cross-nucleosome interactions that enhance BRCA1-BARD1 E3 ubiquitin ligase catalytic activity. Multivalent interactions across nucleosomes explain how BRCA1-BARD1 can recognise chromatin that retains partial di-methylation at H4 Lys-20 (H4K20me2), a parental histone mark that blocks BRCA1-BARD1 interaction with nucleosomes, to promote its enzymatic and DNA repair activities.
Details: 25 mM HEPES pH 7.5, 300 mM NaCl, 5% (v/v) glycerol and 1 mM TCEP
Grid
Model: UltrAuFoil R1.2/1.3 / Material: GOLD / Mesh: 300 / Support film - Material: GOLD / Support film - topology: HOLEY / Pretreatment - Type: PLASMA CLEANING / Pretreatment - Time: 60 sec. / Pretreatment - Atmosphere: AIR Details: UltrAuFoil R1.2/1.3 300-mesh gold grids (Quantifoil Micro Tools GmbH) were cleaned via indirect plasma using a Tergeo EM plasma cleaner (Pie Scientific) at 15 W for 1 min, and with flow ...Details: UltrAuFoil R1.2/1.3 300-mesh gold grids (Quantifoil Micro Tools GmbH) were cleaned via indirect plasma using a Tergeo EM plasma cleaner (Pie Scientific) at 15 W for 1 min, and with flow rates for nitrogen, oxygen and argon gasses of 20.0, 19.8 and 29.0 sscm respectively
Vitrification
Cryogen name: ETHANE / Chamber humidity: 100 % / Chamber temperature: 277 K / Instrument: FEI VITROBOT MARK IV Details: Vitrification was carried out by using a blot force of 6 N and a blot time of 6 s.
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Electron microscopy
Microscope
FEI TITAN KRIOS
Image recording
Film or detector model: FEI FALCON III (4k x 4k) / Detector mode: INTEGRATING / Number grids imaged: 1 / Number real images: 227 / Average exposure time: 1.7 sec. / Average electron dose: 73.0 e/Å2
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
Number selected: 117630 Details: Initially, 1,368 particles were manually picked and used to train crYOLO v1.6.1. This trained model was used for picking on all 227 movies, resulting in 117,630 particles
Startup model
Type of model: OTHER Details: The startup model was derived from this same data following 2D Classification and Ab Initio Reconstruction in cryoSPARC
Final reconstruction
Number classes used: 1 / Applied symmetry - Point group: C1 (asymmetric) / Resolution.type: BY AUTHOR / Resolution: 18.4 Å / Resolution method: FSC 0.143 CUT-OFF / Software - Name: RELION (ver. 3.1.2) / Number images used: 21879
Initial angle assignment
Type: MAXIMUM LIKELIHOOD / Software - Name: cryoSPARC (ver. 1.6.1)
Final angle assignment
Type: MAXIMUM LIKELIHOOD / Software - Name: cryoSPARC (ver. 1.6.1)
Final 3D classification
Number classes: 4 / Software - Name: cryoSPARC (ver. 1.6.1)
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