Crystal structures of the catalytic domain of human PARP15 in complex with small molecule inhibitors.

PARP15, or ARTD7, is an enzyme carrying out mono-ADP-ribosylation and regulating activities of a range of cellular proteins. This enzyme belongs to the family of the poly(ADP-ribose) polymerases (PARPs), which comprises of proteins with various potential disease indications. Due to their involvement in a number of cellular processes and important role in DNA repair and regulation, PARPs have been considered attractive therapeutic targets over the past few years. The pursuit of small molecule PARP inhibitors has resulted in several FDA approved drugs for multiple cancers so far. As the use of PARP inhibitors as drug scaffolds is actively explored recently, there is increasing interest in the design of selective inhibitors based on the structural features of the PARP proteins. Here, we solved high-resolution crystal structures of the human PARP15 catalytic domain in complex with three marketed drugs of PARP inhibitors, which includes compounds 3-AB, iniparib and niraparib. The structures reported here contribute to our understanding of the ligand binding modes and structural features in the PARP15 catalytic domain, which can be employed to guide the rational design of selective inhibitors of PARPs.