Using Clickable NAD⁺ Analogs to Label Substrate Proteins of PARPs

ADP-ribosylation has been well known as an important posttranslational modification, which is catalyzed by a family of enzymes called poly(ADP-ribose) polymerases (PARPs). PARPs transfer of a single or multiple adenine diphosphate ribose (ADP-ribose) units from nicotinamide adenine dinucleotide (NAD⁺) to specific amino acids on substrate proteins. Through mono- or poly-ADP-ribosylation enzymatic activities, PARPs regulate various biological processes, including DNA damage repair, chromatin remodeling, transcriptional regulation, RNA processing and metabolism. Notably, PARP inhibitors are in clinical trials to treat human diseases, in particular cancer. To further investigate the biological function of PARPs, and to achieve better therapeutic effect of PARP inhibitors, it is important to identify the physiological substrates of PARPs. Here we describe a protocol to use clickable analog of nicotinamide adenine dinucleotide (NAD⁺) that can be applied for the detection, affinity purification and identification of substrate proteins of PARPs.