Ubiquitin recognition by FAAP20 expands the complex interface beyond the canonical UBZ domain

Abstract

FAAP20 is an integral component of the Fanconi anemia core complex that mediates the repair of DNA interstrand crosslinks. The ubiquitin-binding capacity of the FAAP20 UBZ is required for re-cruitment of the Fanconi anemia complex to inter-strand DNA crosslink sites and for interaction with the translesion synthesis machinery. Although the UBZ–ubiquitin interaction is thought to be exclu-sively encapsulated within the module of UBZ, we show that the FAAP20–ubiquitin interaction ex-tends beyond such a canonical zinc-finger motif. In-stead, ubiquitin binding by FAAP20 is accompanied by transforming a disordered tail C-terminal to the UBZ of FAAP20 into a rigid, extended -loop that latches onto the complex interface of the FAAP20 UBZ and ubiquitin, with the invariant C-terminal tryp-tophan emanating toward I44Ub for enhanced binding specificity and affinity. Substitution of the C-terminal tryptophan with alanine in FAAP20 not only abolishes FAAP20–ubiquitin binding in vitro, but also causes profound cellular hypersensitivity to DNA interstrand crosslink lesions in vivo, highlighting the indispens-able role of the C-terminal tail of FAAP20, beyond the compact zinc finger module, toward ubiquitin recog-nition and Fanconi anemia complex-mediated DNA interstrand crosslink repair