Abstract
53BP1 performs essential functions in DNA double-strand break (DSB) repair and it was recently reported that Tudor interacting repair regulator (TIRR) negatively regulates 53BP1 during DSB repair. Here, we present the crystal structure of the 53BP1 tandem Tudor domain (TTD) in complex with TIRR. Our results show that three loops from TIRR interact with 53BP1 TTD and mask the methylated lysine-binding pocket in TTD. Thus, TIRR competes with histone H4K20 methylation for 53BP1 binding. We map key interaction residues in 53BP1 TTD and TIRR, whose mutation abolishes complex formation. Moreover, TIRR suppresses the relocation of 53BP1 to DNA lesions and 53BP1-dependent DNA damage repair. Finally, despite the high-sequence homology between TIRR and NUDT16, NUDT16 does not directly interact with 53BP1 due to the absence of key residues required for binding. Taken together, our study provides insights into the molecular mechanism underlying TIRR-mediated suppression of 53BP1-dependent DNA damage repair.
Highlights
In response to double-strand break (DSB); PI3 like kinases, including ATM, ATR, and DNAPK, phosphorylate H2AX in the vicinity of the double-strand breaks (DSBs) and initiate a signaling cascade, which leads to RNF8 and RNF168mediated ubiquitylation of chromatin[3]
The minimal focus-forming region (FFR) of 53BP1 required for localization of 53BP1 to DSBs consists of an oligomerization domain, a tandem Tudor domain (TTD) and the ubiquitin-dependent recruitment (UDR) motif 4,5
It is necessary to suppress the binding of 53BP1 on the chromatin during normal cellular functions and counter these regulations by unmasking H4K20me[2], thereby enabling 53BP1 binding when DSBs occur. This is accomplished by the binding of tandem Tudor motifs on JMJD2A/B to H4K20me[2], and DNA damage triggers degradation of JMJD2A/B thereby allowing the exposure of methylated H4K20 for the binding of 53BP111
Summary
In response to DSBs; PI3 like kinases, including ATM, ATR, and DNAPK, phosphorylate H2AX in the vicinity of the DSB and initiate a signaling cascade, which leads to RNF8 and RNF168mediated ubiquitylation of chromatin[3]. It has been reported that the DNA damage repair functions of 53BP1 are dependent on its recruitment to DSBs via recognition of H4K20me[2], which is the most abundant histone lysine methyl mark, present in around 85% of all histone H4 molecules[8,10]. It is necessary to suppress the binding of 53BP1 on the chromatin during normal cellular functions and counter these regulations by unmasking H4K20me[2], thereby enabling 53BP1 binding when DSBs occur This is accomplished by the binding of tandem Tudor motifs on JMJD2A/B to H4K20me[2], and DNA damage triggers degradation of JMJD2A/B thereby allowing the exposure of methylated H4K20 for the binding of 53BP111. We present 2.0 Å resolution crystal structure of the human 53BP1 TTD in complex with TIRR, and elucidate the structural basis how TIRR suppresses the interaction between 53BP1 TTD and H4K20me[2]
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