title: WRN exonuclease structure and molecular mechanism imply an editing role in DNA end processing.
abstract: WRN is unique among the five human RecQ DNA helicases in having a functional exonuclease domain (WRN-exo) and being defective in the premature aging and cancer-related disorder Werner syndrome. Here, we characterize WRN-exo crystal structures, biochemical activity and participation in DNA end joining. Metal-ion complex structures, active site mutations and activity assays reveal a nuclease mechanism mediated by two metal ions. The DNA end-binding Ku70/80 complex specifically stimulates WRN-exo activity, and structure-based mutational inactivation of WRN-exo alters DNA end joining in human cells. We furthermore establish structural and biochemical similarities of WRN-exo to DnaQ-family replicative proofreading exonucleases, describing WRN-specific adaptations consistent with double-stranded DNA specificity and functionally important conformational changes. These results indicate WRN-exo is a human DnaQ family member and support DnaQ-like proofreading activities stimulated by Ku70/80, with implications for WRN functions in age-related pathologies and maintenance of genomic integrity.
authors.affiliation: Department of Molecular Biology and Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
authors.forename: J Jefferson P
authors.initials: JJ
authors.lastname: Perry
authors.forename: Steven M
authors.initials: SM
authors.lastname: Yannone
authors.forename: Lauren G
authors.initials: LG
authors.lastname: Holden
authors.forename: Chiharu
authors.initials: C
authors.lastname: Hitomi
authors.forename: Aroumougame
authors.initials: A
authors.lastname: Asaithamby
authors.forename: Seungil
authors.initials: S
authors.lastname: Han
authors.forename: Priscilla K
authors.initials: PK
authors.lastname: Cooper
authors.forename: David J
authors.initials: DJ
authors.lastname: Chen
authors.forename: John A
authors.initials: JA
authors.lastname: Tainer
mesh_terms: D000818:Animals; D001665:Binding Sites; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D004247:DNA / Q000235:genetics* / Q000378:metabolism*; D004265:DNA Helicases / Q000737:chemistry* / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D005090:Exodeoxyribonucleases; D006801:Humans; D008670:Metals / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017510:Protein Folding; D053484:RecQ Helicases; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D000071657:Werner Syndrome Helicase
chemical_list: D008670:Metals; D004247:DNA; D005090:Exodeoxyribonucleases; D004265:DNA Helicases; D053484:RecQ Helicases; C098785:WRN protein, human; D000071657:Werner Syndrome Helicase