| PARG serves as the primary enzyme responsible for degrading poly(ADP-ribose) chains synthesized by PARP family members, maintaining a dynamic equilibrium of this critical post-translational modification across nuclear, cytoplasmic, and mitochondrial compartments. Multiple isoforms arise through alternative splicing, with larger variants shuttling between nucleus and cytoplasm to execute endo- and exoglycosidic hydrolysis that sequentially liberates ADP-ribose monomers and shorter oligomers from protein acceptors like histones and repair factors, while sparing the terminal ester linkage in mono-ADP-ribosylated substrates. Catalytic action relies on a conserved macrodomain-like fold that binds linear and branched PAR chains, coordinating magnesium-dependent nucleophilic attack to cleave α-O-P glycosidic bonds and recycle free ADP-ribose for NAD+ replenishment, thereby terminating PARP signaling and enabling rapid reversal of DNA damage-induced modifications. PARG counteracts PARP1/2 hyperactivation by dismantling PAR scaffolds that recruit repair complexes such as XRCC1 and APLF, facilitating progression through base excision repair and homologous recombination pathways while preventing prolonged replication fork stalling. Isoforms localize dynamically to mitochondria, where smaller variants sustain PARG activity during oxidative stress, preserving bioenergetic flux by clearing PARylated pyruvate dehydrogenase subunits that otherwise inhibit TCA cycle entry. PARG orchestrates transcriptional regulation through PAR turnover on RNA polymerase II and chromatin remodelers, fine-tuning gene expression during differentiation and inflammatory responses in immune cells. Depletion or inhibition elevates PAR levels that trap PARP enzymes at damage sites, amplifying synthetic lethality with DNA crosslinkers like cisplatin in repair-deficient tumors through G2/M arrest and mitotic catastrophe. |
Lane 1: Hela, Lane 2: COS-7
