Poly(ADP-ribose) has a branched structure in vivo.

ADP-Ribosylation, a Multifaceted Posttranslational Modification Involved in the Control of Cell Physiology in Health and Disease

“…Evidence has been reported demonstrating that PARG has both exo- and endoglycosidase activity. ,, The endoglycosidase activity seems particularly efficient on very long PAR chains. , More detailed analysis of this activity indicated that the endoglycosidic cleavage ceased when polymers became less than ∼40 ADPr units long . Moreover, it has been argued that in branched PAR chains synthesized by ARTD1 the glycosidic bond at the branch site (2″ to 1″, Figure ) is only very inefficiently hydrolyzed by PARG. , These findings are of note because long polymers that can be generated both in vitro and in cells are branched with roughly one fork per 30–40 ADPr units. ,,, …”

“…221,223 These findings are of note because long polymers that can be generated both in vitro and in cells are branched with roughly one fork per 30−40 ADPr units. 27,28,224,225 Biologically, the loss of Parg110 results in enhanced sensitivity to DNA damaging agents, similar to the loss of ARTD1. 213 Thus, it appears that both the synthesis and the degradation of PAR chains are critical for efficient DNA repair.…”

“…An important step in the analysis of ADP-ribosylation was the realization that it did not simply involve the formation of ADPr polymers, but that proteins themselves were modified, suggesting it to be a PTM. ,,, The more detailed analysis revealed that the PAR chains synthesized by ARTD1 are branched (Figure ; see also Figure ). − Subsequently the gene encoding ARTD1 was cloned. − An additional key finding was also the description of an activity referred to as poly-ADP-ribose glycohydrolase (PARG) that could hydrolyze the ribose–ribosyl O -glycosidic bonds in ADPr polymers . Further work led to the identification of distinct families of cellular enzymes that can ADP-ribosylate proteins in eukaryotic cells and have distinct structural and enzymatic characteristics and subcellular localization .…”

Prostate cancer and PARP inhibitors: progress and challenges

“…PARP is a family of 17 distinct proteins, in which PARP 1 and 2 are involved in DNA repair [12]. PARP1 binds to damaged DNA gaps and, after conformational change, induces PARylation [13]. PARP1 catalyzes the polymerization of ADP-ribose units from NAD + (nicotinamide adenine dinucleotide) molecules and recruits proteins of the DNA SSB repair system (BER or NER systems) [14,15].…”

Nonenzymic ADP-ribosylation of poly(adenosine diphosphate ribose)

“…It is rapidly degraded in situ, and the newly synthesized material has a complete range of sizes up to at least several hundred residues (Tanaka et al, 1978; Benjamin & Gill, 1980a,b; Ikejima et al, 1983). For the most part, the polymer consists of ADPribose residues joined in series by 1"-*-2' glycosidic bonds between ribose residues, but there are branches involving 1'"-*2" ribose-*-ribose bonds approximately every 50-100 residues (Miwa et al, 1979;Juarez-Salinas et al, 1982;Kanai et al, 1982; . The structure of a branch point is shown in Figure 1 A.…”