title: Structural insights into NHEJ: building up an integrated picture of the dynamic DSB repair super complex, one component and interaction at a time.
abstract: Non-homologous end joining (NHEJ) is the major pathway for repair of DNA double-strand breaks (DSBs) in human cells. NHEJ is also needed for V(D)J recombination and the development of T and B cells in vertebrate immune systems, and acts in both the generation and prevention of non-homologous chromosomal translocations, a hallmark of genomic instability and many human cancers. X-ray crystal structures, cryo-electron microscopy envelopes, and small angle X-ray scattering (SAXS) solution conformations and assemblies are defining most of the core protein components for NHEJ: Ku70/Ku80 heterodimer; the DNA dependent protein kinase catalytic subunit (DNA-PKcs); the structure-specific endonuclease Artemis along with polynucleotide kinase/phosphatase (PNKP), aprataxin and PNKP related protein (APLF); the scaffolding proteins XRCC4 and XLF (XRCC4-like factor); DNA polymerases, and DNA ligase IV (Lig IV). The dynamic assembly of multi-protein NHEJ complexes at DSBs is regulated in part by protein phosphorylation. The basic steps of NHEJ have been biochemically defined to require: (1) DSB detection by the Ku heterodimer with subsequent DNA-PKcs tethering to form the DNA-PKcs-Ku-DNA complex (termed DNA-PK), (2) lesion processing, and (3) DNA end ligation by Lig IV, which functions in complex with XRCC4 and XLF. The current integration of structures by combined methods is resolving puzzles regarding the mechanisms, coordination and regulation of these three basic steps. Overall, structural results suggest the NHEJ system forms a flexing scaffold with the DNA-PKcs HEAT repeats acting as compressible macromolecular springs suitable to store and release conformational energy to apply forces to regulate NHEJ complexes and the DNA substrate for DNA end protection, processing, and ligation.
authors.affiliation: Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States.
authors.forename: Gareth J
authors.initials: GJ
authors.lastname: Williams
authors.affiliation: Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States.
authors.forename: Michal
authors.initials: M
authors.lastname: Hammel
authors.affiliation: Department of Biochemistry & Molecular Biology, Southern Alberta Cancer Research Institute, University of Calgary, Calgary, Alberta, T2 N 4N1 Canada.
authors.forename: Sarvan Kumar
authors.initials: SK
authors.lastname: Radhakrishnan
authors.affiliation: Lineberger Comprehensive Cancer Center, Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 2759, United States.
authors.forename: Dale
authors.initials: D
authors.lastname: Ramsden
authors.affiliation: Department of Biochemistry & Molecular Biology, Southern Alberta Cancer Research Institute, University of Calgary, Calgary, Alberta, T2 N 4N1 Canada; Department of Oncology, Southern Alberta Cancer Research Institute, University of Calgary, Calgary, Alberta, T2 N 4N1 Canada. Electronic address: leesmill@ucalgary.ca.
authors.forename: Susan P
authors.initials: SP
authors.lastname: Lees-Miller
authors.affiliation: Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States; Department of Molecular Biology, Skaggs Institute of Chemical Biology, The Scripps Research Institute, La Jolla, CA 92037, United States. Electronic address: jat@scripps.edu.
authors.forename: John A
authors.initials: JA
authors.lastname: Tainer
mesh_terms: D004247:DNA / Q000378:metabolism; D053903:DNA Breaks, Double-Stranded; D059766:DNA End-Joining Repair; D045643:DNA Repair Enzymes / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D009097:Multienzyme Complexes / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation
chemical_list: D009097:Multienzyme Complexes; D004247:DNA; D045643:DNA Repair Enzymes
keywords: MRN; NHEJ; SAXS; X-ray crystallography