Structural and functional studies of Mre11-Rad50-ATPγS complex

DoctorThe Mre11 and Rad50 are conserved among all species, whereas NBS1 is conserved in eukaryotes. Mre11 and Rad50 build the core of the complex. The Mre11-Rad50 (MR) complex plays an important role in sensing DNA double-strand breaks (DSBs), damage signaling, and repairing them through homologous recombination (HR) and non-homologous end joining (NHEJ) pathways. Communication between Mre11 and Rad50 in the MR complex is critical for the maintenance of genomic stability. Although recent studies made an important progress toward understanding the structural and biochemical properties of the MR complex, we have little knowledge on the interplay between Mre11 and Rad50 because the structural information at atomic level is limited to individual domains of Rad50 and Mre11. It is poorly understood how Mre11 recognizes Rad50, which is critical to understanding the MR function. To understand the basis for inter-regulation between Mre11 and Rad50 in the MR complex, we determined the crystal structure of the Methanococcus janaschii Mre11-Rad50-ATPγS complex and analyzed ATP-dependent nuclease activities. Mre11 brings the two Rad50 molecules in close proximity to form an ATP-dependent dimer via (i) holding the coiled coil arm of Rad50 through its C-terminal Z-shape helical domain, (ii) interlocking the lobe II of Rad50 via its capping domain, and stabilizing the signature motif, and P-loop, and His switch of Rad50, and (iii) forming a dimer through the nuclease domain, and promotes ATPase activity of Rad50. ATP-bound Rad50 negatively regulates the nuclease activity of Mre11 by blocking the active site of Mre11. Hydrolysis of ATP disengages Rad50 molecules, and concomitantly the flexible linker that connects the C-terminal domain and the capping domain of Mre11 undergoes substantial conformational change to relocate Rad50 and unmask the active site of Mre11. Our structural and biochemical evidences support the model described above and provide insights into how the interplay between Mre11 and Rad50 facilitates efficient DNA damage repairs