title: Impact of age-associated cyclopurine lesions on DNA repair helicases.
abstract: 8,5' cyclopurine deoxynucleosides (cPu) are locally distorting DNA base lesions corrected by nucleotide excision repair (NER) and proposed to play a role in neurodegeneration prevalent in genetically defined Xeroderma pigmentosum (XP) patients. In the current study, purified recombinant helicases from different classifications based on sequence homology were examined for their ability to unwind partial duplex DNA substrates harboring a single site-specific cPu adduct. Superfamily (SF) 2 RecQ helicases (RECQ1, BLM, WRN, RecQ) were inhibited by cPu in the helicase translocating strand, whereas helicases from SF1 (UvrD) and SF4 (DnaB) tolerated cPu in either strand. SF2 Fe-S helicases (FANCJ, DDX11 (ChlR1), DinG, XPD) displayed marked differences in their ability to unwind the cPu DNA substrates. Archaeal Thermoplasma acidophilum XPD (taXPD), homologue to the human XPD helicase involved in NER DNA damage verification, was impeded by cPu in the non-translocating strand, while FANCJ was uniquely inhibited by the cPu in the translocating strand. Sequestration experiments demonstrated that FANCJ became trapped by the translocating strand cPu whereas RECQ1 was not, suggesting the two SF2 helicases interact with the cPu lesion by distinct mechanisms despite strand-specific inhibition for both. Using a protein trap to simulate single-turnover conditions, the rate of FANCJ or RECQ1 helicase activity was reduced 10-fold and 4.5-fold, respectively, by cPu in the translocating strand. In contrast, single-turnover rates of DNA unwinding by DDX11 and UvrD helicases were only modestly affected by the cPu lesion in the translocating strand. The marked difference in effect of the translocating strand cPu on rate of DNA unwinding between DDX11 and FANCJ helicase suggests the two Fe-S cluster helicases unwind damaged DNA by distinct mechanisms. The apparent complexity of helicase encounters with an unusual form of oxidative damage is likely to have important consequences in the cellular response to DNA damage and DNA repair.
authors.affiliation: Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, NIH Biomedical Research Center, Baltimore, Maryland, United States of America.
authors.forename: Irfan
authors.initials: I
authors.lastname: Khan
authors.affiliation: Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, NIH Biomedical Research Center, Baltimore, Maryland, United States of America.
authors.forename: Avvaru N
authors.initials: AN
authors.lastname: Suhasini
authors.affiliation: Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, NIH Biomedical Research Center, Baltimore, Maryland, United States of America.
authors.forename: Taraswi
authors.initials: T
authors.lastname: Banerjee
authors.affiliation: Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, NIH Biomedical Research Center, Baltimore, Maryland, United States of America.
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Sommers
authors.affiliation: Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, Florida, United States of America.
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Kaplan
authors.affiliation: Rudolf Virchow Center for Experimental Biomedicine, Institute for Structural Biology, University of Würzburg, Würzburg, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Kuper
authors.affiliation: Rudolf Virchow Center for Experimental Biomedicine, Institute for Structural Biology, University of Würzburg, Würzburg, Germany.
authors.forename: Caroline
authors.initials: C
authors.lastname: Kisker
authors.affiliation: Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, NIH Biomedical Research Center, Baltimore, Maryland, United States of America.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Brosh
mesh_terms: D001105:Archaea / Q000201:enzymology; D019843:Archaeal Proteins / Q000302:isolation & purification / Q000378:metabolism; D004247:DNA / Q000737:chemistry; D004249:DNA Damage; D004265:DNA Helicases / Q000302:isolation & purification / Q000378:metabolism*; D004260:DNA Repair; D003839:Deoxyadenosines / Q000138:chemical synthesis / Q000494:pharmacology*; D003849:Deoxyguanosine / Q000138:chemical synthesis / Q000494:pharmacology*; D006801:Humans; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D019843:Archaeal Proteins; D003839:Deoxyadenosines; D011994:Recombinant Proteins; D004247:DNA; D004265:DNA Helicases; D003849:Deoxyguanosine