Vertebrate DNA crosslink repair excises toxic replication-blocking DNA crosslinks. Numerous factors involved in crosslink repair have been identified, and mutations in their corresponding genes cause Fanconi anemia (FA). A key step in crosslink repair is monoubiquitination of the FANCD2-FANCI heterodimer, which then recruits nucleases to remove the DNA lesion. Here, we use cryo-EM to determine the structures of recombinant chicken FANCD2 and FANCI complexes. FANCD2-FANCI adopts a closed conformation when the FANCD2 subunit is monoubiquitinated, creating a channel that encloses double-stranded DNA (dsDNA). Ubiquitin is positioned at the interface of FANCD2 and FANCI, where it acts as a covalent molecular pin to trap the complex on DNA. In contrast, isolated FANCD2 is a homodimer that is unable to bind DNA, suggestive of an autoinhibitory mechanism that prevents premature activation. Together, our work suggests that FANCD2-FANCI is a clamp that is locked onto DNA by ubiquitin, with distinct interfaces that may recruit other DNA repair factors.
Nat Struct Mol Biol
240 - 248
Animals, Binding Sites, Chickens, Cryoelectron Microscopy, Crystallography, X-Ray, DNA, DNA Damage, DNA Repair, Fanconi Anemia Complementation Group D2 Protein, Fanconi Anemia Complementation Group Proteins, Gene Expression, Models, Molecular, Protein Binding, Protein Conformation, alpha-Helical, Protein Interaction Domains and Motifs, Protein Multimerization, Recombinant Proteins, Sf9 Cells, Spodoptera, Ubiquitin, Ubiquitination