PAR recognition by PARP1 regulates DNA-dependent activities and independently stimulates catalytic activity of PARP1

Poly(ADP-ribosyl)ation is predominantly catalyzed by Poly(ADP-ribose) polymerase 1 (PARP1) in response to DNA damage, mediating the DNA repair process to maintain genomic integrity. Single strand (SSB) and double strand (DSB) DNA breaks are bonafide stimulators of PARP1 activity. However, PAR mediated PARP1 regulation remains unexplored. Here, we report ZnF3, BRCT and WGR, hitherto uncharacterized, as PAR reader domains of PARP1. Surprisingly, these domains recognize PARylated protein with a higher affinity compared to PAR but bind with weak or no affinity to DNA breaks as standalone domains. Conversely, ZnF1 and ZnF2 of PARP1 recognize DNA breaks but weakly to PAR. In addition, PAR reader domains, together, exhibit a synergy to recognize PAR or PARylated protein. Further competition binding studies suggest that PAR binding releases DNA from PARP1, and WGR domain facilitates the DNA release. Unexpectedly, PAR showed catalytic stimulation of PARP1 but hampers the DNA-dependent stimulation. Altogether, our work discovers dedicated high-affinity PAR reader domains of PARP1 and uncovers a novel mechanism of allosteric stimulation, but retardation of DNA-dependent activities of PARP1 by its catalytic product PAR. Therefore, our studies can be used as a model to understand the effect of one or more allosteric activators on the regulation of receptors or modular enzyme activities by another allosteric activator.