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

Publication date: Available online 13 December 2016
Source:Cell Reports
Author(s): Paolo Swuec, Ludovic Renault, Aaron Borg, Fenil Shah, Vincent J. Murphy, Sylvie van Twest, Bram Snijders, Andrew J. Deans, Alessandro Costa
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.

Graphical abstract

Teaser

Mono-ubiquitination of FANCI-FANCD2 by the Fanconi anemia core complex activates a major DNA interstrand-crosslink repair pathway important for genome stability maintenance. Here, Swuec et al. reveal the structural basis of this reaction by showing that the core complex exists as a dimeric catalytic module for the symmetric mono-ubiquitination of FANCI-FANCD2.


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