Cryo-EM structure of human DNA-PK holoenzyme

• 来源期刊: 细胞研究（英文版）
• 年，卷（期）: 2017,（11）
• 页码范围: 1341-1350
• 页数: 10页
• 语种: 英文
• DOI: 10.1038/cr.2017.110

摘要

DNA-dependent protein kinase (DNA-PK) is a serine/threonine protein kinase complex composed of a catalytic subunit (DNA-PKcs) and KU70/80 heterodimer bound to DNA.DNA-PK holoenzyme plays a critical role in non-homologous end joining (NHEJ),the major DNA repair pathway.Here,we determined cryo-electron microscopy structure of human DNA-PK holoenzyme at 6.6(A) resolution.In the complex structure,DNA-PKcs,KU70,KU80 and DNA duplex form a 650-kDa heterotetramer with 1∶1∶1∶1 stoichiometry.The N-terminal a-solenoid (～2 800 residues)of DNA-PKcs adopts a double-ring fold and connects the catalytic core domain of DNA-PKcs and KU70/80-DNA.DNA-PKcs and KU70/80 together form a DNA-binding tunnel,which cradles ～30-bp DNA and prevents sliding inward of DNA-PKcs along with DNA duplex,suggesting a mechanism by which the broken DNA end is protected from unnecessary processing.Structural and biochemical analyses indicate that KU70/80 and DNA coordinately induce conformational changes of DNA-PKcs and allosterically stimulate its kinase activity.We propose a model for activation of DNA-PKcs in which allosteric signals are generated upon DNA-PK holoenzyme formation and transmitted to the kinase domain through N-terminal HEAT repeats and FAT domain of DNA-PKcs.Our studies suggest a mechanism for recognition and protection of broken DNA ends and provide a structural basis for understanding the activation of DNA-PKcs and DNA-PK-mediated NHEJ pathway.