Structural basis of poly(ADP-ribose) recognition by the multi-zinc binding domain of checkpoint with forkhead-associated and RING domains (CHFR)


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Jasmeen Oberoi1, Mark Richards1, Simon Crumpler2, Nathan Brown2, Julian Blagg2, Richard Bayliss1
1Section of Structural Biology, The Institute of Cancer Research, London, United Kingdom,2CR-UK Centre for Cancer Therapeutics, The Institute of Cancer Research, Sutton, United Kingdom

Background

CHFR plays an important role in the antephase checkpoint, decondensing chromomsomes and delaying progression through mitosis after exposure to microtubule disrupting agents. CHFR is down-regulated in many cancers mainly due to hypermethylation of its promoter and CHFR knockout mice are more prone to developing cancer. The C-terminal cysteine rich region of CHFR is required for binding to substrates. This domain also contains a PBZ motif (poly(ADP-ribose)/PAR binding zinc finger) and the interaction of CHFR with PAR has been reported to be important for its checkpoint function. Poly(ADP-ribose) is a post-translational modification associated with the mitotic spindle and DNA repair pathways.

Method

We have determined the X-ray crystal structure of the cysteine rich region of CHFR bound to different ligands that are structurally similar to PAR. We have used site-specific mutagenesis and surface plasmon resonance to investigate the structural basis of the interaction between CHFR and PAR.

Results

The cysteine rich region of CHFR is a multi-zinc binding domain unrelated to previously known structures. The adenine groups of PAR-like ligands bind to two hydrophobic pockets on the surface of the CHFR PBZ, and the PAR phosphate linker interacts with an arginine side chain. Based on these structures, we made a model for the interaction between CHFR and PAR. The CHFR-PAR interaction is high affinity (low nanomolar KD), and mutations within the interface reduce the affinity by at least 10-fold.

Conclusion

We have resolved the molecular recoginition of poly(ADP-ribose) by the PBZ motif of CHFR and propose a model to explain the wide range of affinities determined for PBZ-PAR interactions.