title: Visualization of poly(ADP-ribose) bound to PARG reveals inherent balance between exo- and endo-glycohydrolase activities.
abstract: Poly-ADP-ribosylation is a post-translational modification that regulates processes involved in genome stability. Breakdown of the poly(ADP-ribose) (PAR) polymer is catalysed by poly(ADP-ribose) glycohydrolase (PARG), whose endo-glycohydrolase activity generates PAR fragments. Here we present the crystal structure of PARG incorporating the PAR substrate. The two terminal ADP-ribose units of the polymeric substrate are bound in exo-mode. Biochemical and modelling studies reveal that PARG acts predominantly as an exo-glycohydrolase. This preference is linked to Phe902 (human numbering), which is responsible for low-affinity binding of the substrate in endo-mode. Our data reveal the mechanism of poly-ADP-ribosylation reversal, with ADP-ribose as the dominant product, and suggest that the release of apoptotic PAR fragments occurs at unusual PAR/PARG ratios.
authors.affiliation: Cancer Research UK, Paterson Institute for Cancer Research, University of Manchester, Wilmslow Road, Manchester M20 4BX, UK.
authors.forename: Eva
authors.initials: E
authors.lastname: Barkauskaite
authors.forename: Amy
authors.initials: A
authors.lastname: Brassington
authors.forename: Edwin S
authors.initials: ES
authors.lastname: Tan
authors.forename: Jim
authors.initials: J
authors.lastname: Warwicker
authors.forename: Mark S
authors.initials: MS
authors.lastname: Dunstan
authors.forename: Benito
authors.initials: B
authors.lastname: Banos
authors.forename: Pierre
authors.initials: P
authors.lastname: Lafite
authors.forename: Marijan
authors.initials: M
authors.lastname: Ahel
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Mitchison
authors.forename: Ivan
authors.initials: I
authors.lastname: Ahel
authors.forename: David
authors.initials: D
authors.lastname: Leys
mesh_terms: D055162:Biocatalysis; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D018698:Glutamic Acid / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D016296:Mutagenesis; D011064:Poly Adenosine Diphosphate Ribose / Q000737:chemistry / Q000378:metabolism*; D013379:Substrate Specificity; D016808:Tetrahymena thermophila / Q000201:enzymology*
chemical_list: D011064:Poly Adenosine Diphosphate Ribose; D018698:Glutamic Acid; D006026:Glycoside Hydrolases; C022407:poly ADP-ribose glycohydrolase
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