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bioRxiv · 10.1101/2025.03.14.643254

Structural basis for DNA double-strand break sensing by human MRE11-RAD50-NBS1 and its TRF2 complex

Fan, Y.·Kuybu, F.·Cui, H.·Lammens, K.·Chen, J.-X.·Kugler, M.·Jung, C.·Hopfner, K.-P.
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Abstract

The MRE11-RAD50-NBS1 (MRN) complex is a central, multifunctional factor in the detection, signaling and nucleolytic processing of DNA double-strand breaks (DSBs). To clarify how human MRN binds generic and telomeric DNA ends and can separate DNA end sensing from nuclease activities, we determined cryo-electron microscopy structures of human MRN bound to DNA and to DNA and the telomere protection factor TRF2. MRN senses DSBs through a tight clamp-like sensing state with closed coiled-coil domains, but auto-inhibited MRE11 nuclease. NBS1 wraps around the MRE11 dimer, with NBS1s ATM recruitment motif sequestered by binding to the regulatory RAD50 S site, necessitating an allosteric switch for ATM activation. At telomeric DNA, TRF2 blocks the second S site via the iDDR motif to prevent nuclease and ATM activation. Our results provide a structural framework for topological DNA sensing and separation of sensing, signaling and processing activities of mammalian MRN. Highlights- Human MRN senses DNA ends with an autoinhibited nuclease - NBS1s C-terminus binds one RAD50 S site in the sensing state - TRF2 binds MRNs second S site at telomeres - RAD50 and ATM compete for the NBS1 C-terminus

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Fan, Y., Kuybu, F., Cui, H., Lammens, K., Chen, J.-X., Kugler, M., Jung, C., Hopfner, K.-P.. 2025-03-16. Structural basis for DNA double-strand break sensing by human MRE11-RAD50-NBS1 and its TRF2 complex. https://doi.org/10.1101/2025.03.14.643254

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