Family-wide analysis of poly(ADP-ribose) polymerase activity

Abstract

The poly(adenosine diphosphate (ADP)-ribose) polymerase (PARP) protein family generates ​ADP-ribose (​ADPr) modifications onto target proteins using ​NAD[superscript +] as substrate. Based on the composition of three ​NAD[superscript +] coordinating amino acids, the H-Y-E motif, each PARP is predicted to generate either poly(ADPr) (PAR) or mono(ADPr) (MAR). However, the reaction product of each PARP has not been clearly defined, and is an important priority since PAR and MAR function via distinct mechanisms. Here we show that the majority of PARPs generate MAR, not PAR, and demonstrate that the H-Y-E motif is not the sole indicator of PARP activity. We identify automodification sites on seven PARPs, and demonstrate that MAR and PAR generating PARPs modify similar amino acids, suggesting that the sequence and structural constraints limiting PARPs to MAR synthesis do not limit their ability to modify canonical amino-acid targets. In addition, we identify ​cysteine as a novel amino-acid target for ADP-ribosylation on PARPs.