Portal de Periódicos da CAPES

Structural and Functional Interaction between the Human DNA Repair Proteins DNA Ligase IV and XRCC4

2009; Taylor & Francis; Volume: 29; Issue: 11 Linguagem: Inglês

10.1128/mcb.01895-08

1098-5549

Peï-Yu Wu, Philippe Frit, Srilakshmi Meesala, Stéphanie Dauvillier, Mauro Modesti, Sara N. Andres, Ying Huang, JoAnn Sekiguchi, Patrick Calsou, Bernard Salles, M.S. Junop,

Genomics and Chromatin Dynamics

Nonhomologous end-joining represents the major pathway used by human cells to repair DNA double-strand breaks.It relies on the XRCC4/DNA ligase IV complex to reseal DNA strands.Here we report the highresolution crystal structure of human XRCC4 bound to the carboxy-terminal tandem BRCT repeat of DNA ligase IV.The structure differs from the homologous Saccharomyces cerevisiae complex and reveals an extensive DNA ligase IV binding interface formed by a helix-loop-helix structure within the inter-BRCT linker region, as well as significant interactions involving the second BRCT domain, which induces a kink in the tail region of XRCC4.We further demonstrate that interaction with the second BRCT domain of DNA ligase IV is necessary for stable binding to XRCC4 in cells, as well as to achieve efficient dominant-negative effects resulting in radiosensitization after ectopic overexpression of DNA ligase IV fragments in human fibroblasts.Together our findings provide unanticipated insight for understanding the physical and functional architecture of the nonhomologous end-joining ligation complex.DNA double-strand breaks (DSBs) represent the most-toxic form of DNA damage in the genome.If left unrepaired, DSBs can result in large-scale loss of genetic information during cell division and, consequently, cell death.DSBs are formed not only in response to endogenous cellular processes, such as V(D)J recombination and oxidative metabolism, but also to various genotoxic agents, such as ionizing radiation, radiomimetic compounds, and topoisomerase inhibitors (38).To cope with such deleterious DNA lesions, cells have evolved various repair mechanisms, among which nonhomologous end-joining (NHEJ) represents the major pathway in mammals (39).NHEJ is a multistep process initiated by the Ku70/Ku80 heterodimer, which binds DNA ends and recruits the DNAdependent protein kinase catalytic subunit (DNA-PKcs) through a direct interaction (15, 20).The resulting DNA-PK holoenzyme (Ku/DNA-PKcs) has a serine/threonine PK activity that is necessary for efficient repair (27).The pivotal role played by DNA-PK in NHEJ is further emphasized by its DNA end-bridging activity (10); its regulatory function toward pro-