PAXX binding to the NHEJ machinery explains functional redundancy with XLF

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Seif-El-Dahan, Murielle | Kefala-Stavridi, Antonia | Frit, Philippe | Hardwick, Steven | Chirgadze, Dima | Maia de Oliviera, Taiana | Andreani, Jessica | Britton, Sébastien | Barboule, Nadia | Bossaert, Madeleine | Pandurangan, Arun Prasad | Meek, Katheryn | Blundell, Tom | Ropars, Virginie | Calsou, Patrick | Charbonnier, Jean-Baptiste | Chaplin, Amanda

Edité par CCSD ; American Association for the Advancement of Science (AAAS) -

International audience. Nonhomologous end joining is a critical mechanism that repairs DNA double-strand breaks in human cells. In this work, we address the structural and functional role of the accessory protein PAXX [paralog of x-ray repair cross-complementing protein 4 (XRCC4) and XRCC4-like factor (XLF)] in this mechanism. Here, we report high-resolution cryo–electron microscopy (cryo-EM) and x-ray crystallography structures of the PAXX C-terminal Ku-binding motif bound to Ku70/80 and cryo-EM structures of PAXX bound to two alternate DNA-dependent protein kinase (DNA-PK) end-bridging dimers, mediated by either Ku80 or XLF. We identify residues critical for the Ku70/PAXX interaction in vitro and in cells. We demonstrate that PAXX and XLF can bind simultaneously to the Ku heterodimer and act as structural bridges in alternate forms of DNA-PK dimers. Last, we show that engagement of both proteins provides a complementary advantage for DNA end synapsis and end joining in cells.

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