Detection of ADP-Ribosylation of the Androgen Receptor Using the Recombinant Macrodomain AF1521 from Archaeoglobus fulgidus.

ADP-ribosylation is a posttranslational modification generated by members of the superfamily of ADP-ribosyltransferases, known as the Parp enzymes. Depending on the superfamily member, Parp enzymes can mono- or poly-ADP-ribosylate a protein substrate. Parp superfamily members confer regulation to a variety of biological processes that include cell signaling, DNA repair, transcription, and stress responses. Here, we describe biochemical methods for detection of ADP-ribose conjugated to the androgen receptor (AR) using the archaeal macrodomain, AF1521, from Archaeoglobus fulgidus. The utility of AF1521 is based on its highly selective recognition of ADP-ribose conjugated to protein. AF1521 immobilized on beads can be used to enrich for ADP-ribosylated proteins, which in our application results in recovery of ADP-ribosylated AR from prostate cancer cell extracts. We engineered tandem AF1521 macrodomains and found this improves the recovery of ADP-ribosylated AR under native conditions, and it enabled development of an assay for detection of ADP-ribosylation on blots. Thus, AF1521 can be used to query ADP-ribosylation of protein under both native and denaturing conditions. Our assays should prove useful for understanding how ADP-ribosylation regulates AR function.

Ubiquitin Modification by the E3 Ligase/ADP-Ribosyltransferase Dtx3L/Parp9.

ADP-ribosylation of proteins is emerging as an important regulatory mechanism. Depending on the family member, ADP-ribosyltransferases either conjugate a single ADP-ribose to a target or generate ADP-ribose chains. Here we characterize Parp9, a mono-ADP-ribosyltransferase reported to be enzymatically inactive. Parp9 undergoes heterodimerization with Dtx3L, a histone E3 ligase involved in DNA damage repair. We show that the Dtx3L/Parp9 heterodimer mediates NAD+-dependent mono-ADP-ribosylation of ubiquitin, exclusively in the context of ubiquitin processing by E1 and E2 enzymes. Dtx3L/Parp9 ADP-ribosylates the carboxyl group of Ub Gly76. Because Gly76 is normally used for Ub conjugation to substrates, ADP-ribosylation of the Ub carboxyl terminus precludes ubiquitylation. Parp9 ADP-ribosylation activity therefore restrains the E3 function of Dtx3L. Mutation of the NAD+ binding site in Parp9 increases the DNA repair activity of the heterodimer. Moreover, poly(ADP-ribose) binding to the Parp9 macrodomains increases E3 activity. Dtx3L heterodimerization with Parp9 enables NAD+ and poly(ADP-ribose) regulation of E3 activity.