title: Crystal structure of human XLF: a twist in nonhomologous DNA end-joining.
abstract: DNA double-strand breaks represent one of the most severe forms of DNA damage in mammalian cells. One pathway for repairing these breaks occurs via nonhomologous end-joining (NHEJ) and depends on XRCC4, LigaseIV, and Cernunnos, also called XLF. Although XLF stimulates XRCC4/LigaseIV to ligate mismatched and noncohesive DNA ends, the mechanistic basis for this function remains unclear. Here we report the structure of a partially functional 224 residue N-terminal fragment of human XLF. Despite only weak sequence similarity, XLF(1-170) shares structural homology with XRCC4(1-159). However, unlike the highly extended 130 A helical domain observed in XRCC4, XLF adopts a more compact, folded helical C-terminal region involving two turns and a twist, wrapping back to the structurally conserved N terminus. Mutational analysis of XLF and XRCC4 reveals a potential interaction interface, suggesting a mechanism for how XLF stimulates the ligation of mismatched ends.
authors.affiliation: Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON L8N 3Z5, Canada.
authors.forename: Sara N
authors.initials: SN
authors.lastname: Andres
authors.forename: Mauro
authors.initials: M
authors.lastname: Modesti
authors.forename: Chun J
authors.initials: CJ
authors.lastname: Tsai
authors.forename: Gilbert
authors.initials: G
authors.lastname: Chu
authors.forename: Murray S
authors.initials: MS
authors.lastname: Junop
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites / Q000235:genetics; D003460:Crystallization; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000737:chemistry / Q000378:metabolism; D004260:DNA Repair; D045643:DNA Repair Enzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D024202:Electrophoretic Mobility Shift Assay; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid
chemical_list: D004268:DNA-Binding Proteins; C508551:NHEJ1 protein, human; C101467:XRCC4 protein, human; D011088:DNA Ligases; D045643:DNA Repair Enzymes; D000072481:DNA Ligase ATP