title: Quantitative analysis of WRN exonuclease activity by isotope dilution mass spectrometry.
abstract: Werner syndrome is a disorder characterized by a premature aging phenotype. The disease is caused by mutations in the WRN gene which encodes a DNA helicase/exonuclease which is involved in multiple aspects of DNA metabolism. Current methods mostly rely on radiometric techniques to assess WRN exonuclease activity. Here we present an alternative, quantitative approach based on non-radioactive isotope dilution mass spectrometry (LC-MS/MS). A oligoduplex substrate mimicking the telomeric sequence was used for method development. Released nucleotides, which correlate with the degree of oligoduplex degradation, were dephosphorylated, purified, and quantified by LC-MS/MS. Heavy-isotope-labeled internal standards were used to account for technical variability. The method was validated in terms of reproducibility, time-course and concentration-dependency of the reaction. As shown in this study, the LC-MS/MS method can assess exonuclease activity of WRN mutants, WRN's substrate and strand specificity, and modulatory effects of WRN interaction partners and posttranslational modifications. Moreover, it can be used to analyze the selectivity and processivity of WRN exonuclease and allows the screening of small molecules for WRN exonuclease inhibitors. Importantly, this approach can easily be adapted to study nucleases other than WRN. This is of general interest, because exonucleases are key players in DNA metabolism and aging mechanisms.
authors: Molecular Toxicology Group, Department of Biology, University of Konstanz, 78457 Konstanz, Germany. aswin.mangerich@uni-konstanz.de
authors: Aswin
authors: A
authors: Mangerich
authors: Sebastian
authors: S
authors: Veith
authors: Oliver
authors: O
authors: Popp
authors: Jörg
authors: J
authors: Fahrer
authors: Rita
authors: R
authors: Martello
authors: Vilhelm A
authors: VA
authors: Bohr
authors: Alexander
authors: A
authors: Bürkle
mesh_terms: D000375:Aging / Q000235:genetics / Q000378:metabolism; D004247:DNA / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D005090:Exodeoxyribonucleases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007553:Isotope Labeling; D013058:Mass Spectrometry; D009154:Mutation; D053484:RecQ Helicases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016615:Telomere / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000071657:Werner Syndrome Helicase
chemical_list: D004247:DNA; D005090:Exodeoxyribonucleases; D053484:RecQ Helicases; C098785:WRN protein, human; D000071657:Werner Syndrome Helicase