HPF1 remodels PARP1 active site for ADP-ribosylation of histones on serine

Abstract Upon binding to DNA breaks, poly(ADP-ribose) polymerase 1 (PARP1) ADP-ribosylates itself and other factors to initiate DNA repair. Serine is the major residue for ADP-ribosylation upon DNA damage, which strictly depends on HPF1. Here we report the crystal structures of human HPF1/PARP1-CAT ΔHD complex at 1.98 Å resolution and mouse and human HPF1 at 1.71 Å and 1.57 Å resolution, respectively. These structures and mutagenesis data confirm that the structural insights obtained in the HPF1/PARP2 study apply to PARP1. Moreover, we quantitatively characterize the key residues for HPF1/PARP1 binding. This information clarifies the confusion regarding HPF1/PARP1 assembly and can direct following functional studies. Our data show that through salt-bridging to Glu284/Asp286, Arg239 positions Glu284 for catalyzing serine ADP-ribosylation, maintains the local conformation of HPF1 to limit PARP1 automodification and facilitates HPF1/PARP1 binding through neutralizing the negative charge of Glu284. These findings and the high-resolution structural data may facilitate drug discovery targeting PARP1.