title: Crystal structure of the Xrcc4 DNA repair protein and implications for end joining.
abstract: XRCC4 is essential for carrying out non-homologous DNA end joining (NHEJ) in all eukaryotes and, in particular, V(D)J recombination in vertebrates. Xrcc4 protein forms a complex with DNA ligase IV that rejoins two DNA ends in the last step of V(D)J recombination and NHEJ to repair double strand breaks. XRCC4-defective cells are extremely sensitive to ionizing radiation, and disruption of the XRCC4 gene results in embryonic lethality in mice. Here we report the crystal structure of a functional fragment of Xrcc4 at 2.7 A resolution. Xrcc4 protein forms a strikingly elongated dumb-bell-like tetramer. Each of the N-terminal globular head domains consists of a beta-sandwich and a potentially DNA-binding helix- turn-helix motif. The C-terminal stalk comprising a single alpha-helix >120 A in length is partly incorporated into a four-helix bundle in the Xrcc4 tetramer and partly involved in interacting with ligase IV. The Xrcc4 structure suggests a possible mode of coupling ligase IV association with DNA binding for effective ligation of DNA ends.
authors.affiliation: Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Junop
authors.forename: M
authors.initials: M
authors.lastname: Modesti
authors.forename: A
authors.initials: A
authors.lastname: Guarné
authors.forename: R
authors.initials: R
authors.lastname: Ghirlando
authors.forename: M
authors.initials: M
authors.lastname: Gellert
authors.forename: W
authors.initials: W
authors.lastname: Yang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry; D001665:Binding Sites; D018797:Cell Cycle Proteins / Q000737:chemistry; D003460:Crystallization; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000737:chemistry / Q000378:metabolism; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D006801:Humans; D046911:Macromolecular Substances; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020836:Protein Structure, Quaternary; D012441:Saccharomyces cerevisiae / Q000235:genetics; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C000607891:DNL4 protein, S cerevisiae; C000607893:LIG4 protein, human; D046911:Macromolecular Substances; C118650:SMC protein, Bacteria; C101467:XRCC4 protein, human; D004247:DNA; D011088:DNA Ligases; D000072481:DNA Ligase ATP