The β-isoform of BCCIP promotes ADP release from the RAD51 presynaptic filament and enhances homologous DNA pairing

Abstract

Homologous recombination (HR) is a template-driven repair pathway that mends DNA double-stranded breaks (DSBs), and thus helps to maintain genome stability. The RAD51 recombinase facilitates DNA joint formation during HR, but to accomplish this task, RAD51 must be loaded onto the single-stranded DNA. DSS1, a candidate gene for split hand/split foot syndrome, provides the ability to recognize RPA-coated ssDNA to the tumor suppressor BRCA2, which is complexed with RAD51. Together BRCA2-DSS1 displace RPA and load RAD51 onto the ssDNA. In addition, the BRCA2 interacting protein BCCIP normally colocalizes with chromatin bound BRCA2, and upon DSB induction, RAD51 colocalizes with BRCA2-BCCIP foci. Down-regulation of BCCIP reduces DSB repair and disrupts BRCA2 and RAD51 foci formation. While BCCIP is known to interact with BRCA2, the relationship between BCCIP and RAD51 is not known. In this study, we investigated the biochemical role of the β-isoform of BCCIP in relation to the RAD51 recombinase. We demonstrate that BCCIPβ binds DNA and physically and functionally interacts with RAD51 to stimulate its homologous DNA pairing activity. Notably, this stimulatory effect is not the result of RAD51 nucleoprotein filament stabilization; rather, we demonstrate that BCCIPβ induces a conformational change within the RAD51 filament that promotes release of ADP to help maintain an active presynaptic filament. Our findings reveal a functional role for BCCIPβ as a RAD51 accessory factor in HR.

Human RAD51 rapidly forms intrinsically dynamic nucleoprotein filaments modulated by nucleotide binding state

“…In addition, we have shown that RAD51 paralogs from C. elegans remodel presynaptic filaments into more ‘open’ flexible and stable conformation ( 3 ) and HOP2-MND1 or the Shu complex could promote active NF assembly at different stages of the multiphasic assembly profile ( 50 , 51 ). Observations that BCCIPβ induces a conformational change within the RAD51 NF that promotes release of ADP to help maintain an active presynaptic filament ( 52 ) support our conclusion.…”

Microcephaly family protein MCPH1 stabilizes RAD51 filaments

“…For example, BRCA2 attenuates RAD51 ATPase activity to promote filament stability ( 46 ). Consistent with that notion, the RAD51-interacting partners SWI5-SFR1 and BCCIPβ have been shown to facilitate filament assembly by releasing ADP, which affects ATP hydrolysis of RAD51 ( 29 , 39 , 47 ). Apart from modulating ATP hydrolysis, HOP2-MND1 regulates the interaction of RAD51 with nucleotide cofactors and its DNA-binding specificity to promote DNA strand exchange ( 48 , 49 ).…”

Homologous recombination defects and how they affect replication fork maintenance

“…Stopped-flow experiments suggests that RAD51 filaments formed in the presence of ATP undergo two consecutive isomerization reactions after the initially binding to ATP, one of these isomerization steps is driven by ATP hydrolysis. The β-isoform of BCCIP (BRCA2 and CDKN1A Interacting Protein) interacts with RAD51 to promote ADP release and stimulate an active presynaptic filament [68]. These results suggest that filament assembly and disassembly can be regulated by nucleotide co-factors, but also indicate possible regulatory points by RAD51 accessory proteins and point to the need for positive and negative regulators.…”