title: Endoglycosidic cleavage of branched polymers by poly(ADP-ribose) glycohydrolase.
abstract: Post-translational modification of nuclear proteins with poly(ADP-ribose) modules chromatin structure and may be required for DNA processing events such as replication, repair and transcription. The polymer-catabolizing enzyme, poly(ADP-ribose) glycohydrolase, is crucial for the regulation of polymer metabolism and the reversibility of the protein modification. Previous reports have shown that glycohydrolase digests poly(ADP-ribose) via an exoglycosidic mechanism progressing from the protein-distal end of the polymer. Using two independent approaches, we investigated the possibility that poly(ADP-ribose) glycohydrolase also engages in endoglycosidic cleavage of polymers. First, partial glycohydrolase digestion of protein-bound poly(ADP-ribose) led to the production of protein-free oligomers of ADP-ribose. Second, partial glycohydrolase digestion of a fixed number of protein-free poly(ADP-ribose) polymers resulted in a transient increase in the absolute number of polymers while polymer size continuously decreased. Furthermore, endoglycosidic activity produced linear polymers from branched polymers although branch points themselves were not a preferential target of cleavage. From these data, we propose a mechanism whereby poly(ADP-ribose) glycohydrolase degrades polymers in three distinct phases; (a) endoglycosidic cleavage, (b) endoglycosidic cleavage plus exoglycosidic, processive degradation, (c) exoglycosidic, distributive degradation.
authors.affiliation: Institute of Pharmacology and Toxicology, University of Zürich-Tierspital, Switzerland.
authors.forename: S A
authors.initials: SA
authors.lastname: Braun
authors.forename: P L
authors.initials: PL
authors.lastname: Panzeter
authors.forename: M A
authors.initials: MA
authors.lastname: Collinge
authors.forename: F R
authors.initials: FR
authors.lastname: Althaus
mesh_terms: D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D006026:Glycoside Hydrolases / Q000378:metabolism*; D007700:Kinetics; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000378:metabolism; D011064:Poly Adenosine Diphosphate Ribose / Q000378:metabolism; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D013950:Thymus Gland / Q000201:enzymology
chemical_list: D009687:Nuclear Proteins; D011064:Poly Adenosine Diphosphate Ribose; D011065:Poly(ADP-ribose) Polymerases; D006026:Glycoside Hydrolases; C022407:poly ADP-ribose glycohydrolase