Visualization of poly(ADP-ribose) bound to PARG reveals inherent balance between exo- and endo-glycohydrolase activities

• DOI: 10.1038/ncomms3164
• Publication Date: 2013-08-06T09:45:29Z
• Authors: Eva Barkauskaite; Amy Brassington; Edwin S. Tan; Jim Warwicker; Mark S. Dunstan; Benito Banos; Pierre Lafite; Marijan Ahel; Timothy J. Mitchison; Ivan Ahel; David Leys
• Keywords: Models, Molecular; 570; Poly Adenosine Diphosphate Ribose; 0303 health sciences; [SDV.BBM.BS]Life Sciences [q-bio]/Biochemistry, Molecular Biology/Structural Biology [q-bio.BM]; Glycoside Hydrolases; [SDV.BBM.BS] Life Sciences [q-bio]/Biochemistry, Molecular Biology/Structural Biology [q-bio.BM]; Hydrolysis; Glutamic Acid; Molecular Dynamics Simulation; 540; Crystallography, X-Ray; Article; Substrate Specificity; Tetrahymena thermophila; 03 medical and health sciences; Mutagenesis; glycosidase; poly(adenosine diphosphate ribose); Biocatalysis; Humans; Biology; Conserved Sequence

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.