Structural mechanism of ATP-dependent DNA binding and DNA end bridging by eukaryotic Rad50.

The Mre11-Rad50-Nbs1 (MRN) complex is a central factor in the repair of DNA double-strand breaks (DSBs). The ATP-dependent mechanisms of how MRN detects and endonucleolytically processes DNA ends for the repair by microhomology-mediated end-joining or further resection in homologous recombination are still unclear. Here, we report the crystal structures of the ATPγS-bound dimer of the Rad50(NBD)(nucleotide-binding domain) from the thermophilic eukaryote Chaetomium thermophilum(Ct) in complex with either DNA or CtMre11(RBD)(Rad50-binding domain) along with small-angle X-ray scattering and cross-linking studies.

Structure of the catalytic domain of Mre11 from Chaetomium thermophilum.

Together with the Rad50 ATPase, the Mre11 nuclease forms an evolutionarily conserved protein complex that plays a central role in the repair of DNA double-strand breaks (DSBs). Mre11-Rad50 detects and processes DNA ends, and has functions in the tethering as well as the signalling of DSBs. The Mre11 dimer can bind one or two DNA ends or hairpins, and processes DNA endonucleolytically as well as exonucleolytically in the 3'-to-5' direction.

Structural studies of DNA end detection and resection in homologous recombination.

DNA double-strand breaks are repaired by two major pathways, homologous recombination or nonhomologous end joining. The commitment to one or the other pathway proceeds via different steps of resection of the DNA ends, which is controlled and executed by a set of DNA double-strand break sensors, endo- and exonucleases, helicases, and DNA damage response factors. The molecular choreography of the underlying protein machinery is beginning to emerge.