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Cell Rep. 2016 Dec 9. pii: S2211-1247(16)31554-6. doi: 10.1016/j.celrep.2016.11.013. [Epub ahead of print]

The FA Core Complex Contains a Homo-dimeric Catalytic Module for the Symmetric Mono-ubiquitination of FANCI-FANCD2.

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  • 1Macromolecular Machines Laboratory, Clare Hall Laboratory, The Francis Crick Institute, Blanche Lane, South Mimms, EN6 3LD, UK.
  • 2Mass Spectrometry Proteomics and Metabolomics, Clare Hall Laboratory, The Francis Crick Institute, Blanche Lane, South Mimms, EN6 3LD, UK.
  • 3Genome Stability Unit, St. Vincent's Institute of Medical Research, 9 Princes St Fitzroy, Victoria, VIC 3065, Australia.
  • 4Macromolecular Machines Laboratory, Clare Hall Laboratory, The Francis Crick Institute, Blanche Lane, South Mimms, EN6 3LD, UK. Electronic address: alessandro.costa@crick.ac.uk.

Abstract

Activation of the main DNA interstrand crosslink repair pathway in higher eukaryotes requires mono-ubiquitination of FANCI and FANCD2 by FANCL, the E3 ligase subunit of the Fanconi anemia core complex. FANCI and FANCD2 form a stable complex; however, the molecular basis of their ubiquitination is ill defined. FANCD2 mono-ubiquitination by FANCL is stimulated by the presence of the FANCB and FAAP100 core complex components, through an unknown mechanism. How FANCI mono-ubiquitination is achieved remains unclear. Here, we use structural electron microscopy, combined with crosslink-coupled mass spectrometry, to find that FANCB, FANCL, and FAAP100 form a dimer of trimers, containing two FANCL molecules that are ideally poised to target both FANCI and FANCD2 for mono-ubiquitination. The FANCC-FANCE-FANCF subunits bridge between FANCB-FANCL-FAAP100 and the FANCI-FANCD2 substrate. A transient interaction with FANCC-FANCE-FANCF alters the FANCI-FANCD2 configuration, stabilizing the dimerization interface. Our data provide a model to explain how equivalent mono-ubiquitination of FANCI and FANCD2 occurs.

KEYWORDS:

DNA repair; Fanconi anemia; cryo-electron microscopy; interstrand crosslink; mono-ubiquitination; ubiquitin ligase

PMID:
27986592
DOI:
10.1016/j.celrep.2016.11.013
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