title: Protein-DNA charge transport: redox activation of a DNA repair protein by guanine radical.
abstract: DNA charge transport (CT) chemistry provides a route to carry out oxidative DNA damage from a distance in a reaction that is sensitive to DNA mismatches and lesions. Here, DNA-mediated CT also leads to oxidation of a DNA-bound base excision repair enzyme, MutY. DNA-bound Ru(III), generated through a flash/quench technique, is found to promote oxidation of the [4Fe-4S](2+) cluster of MutY to [4Fe-4S](3+) and its decomposition product [3Fe-4S](1+). Flash/quench experiments monitored by EPR spectroscopy reveal spectra with g = 2.08, 2.06, and 2.02, characteristic of the oxidized clusters. Transient absorption spectra of poly(dGC) and [Ru(phen)(2)dppz](3+) (dppz = dipyridophenazine), generated in situ, show an absorption characteristic of the guanine radical that is depleted in the presence of MutY with formation instead of a long-lived species with an absorption at 405 nm; we attribute this absorption also to formation of the oxidized [4Fe-4S](3+) and [3Fe-4S](1+) clusters. In ruthenium-tethered DNA assemblies, oxidative damage to the 5'-G of a 5'-GG-3' doublet is generated from a distance but this irreversible damage is inhibited by MutY and instead EPR experiments reveal cluster oxidation. With ruthenium-tethered assemblies containing duplex versus single-stranded regions, MutY oxidation is found to be mediated by the DNA duplex, with guanine radical as an intermediate oxidant; guanine radical formation facilitates MutY oxidation. A model is proposed for the redox activation of DNA repair proteins through DNA CT, with guanine radicals, the first product under oxidative stress, in oxidizing the DNA-bound repair proteins, providing the signal to stimulate DNA repair.
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
authors.forename: Eylon
authors.initials: E
authors.lastname: Yavin
authors.forename: Amie K
authors.initials: AK
authors.lastname: Boal
authors.forename: Eric D A
authors.initials: ED
authors.lastname: Stemp
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Boon
authors.forename: Alison L
authors.initials: AL
authors.lastname: Livingston
authors.forename: Valerie L
authors.initials: VL
authors.lastname: O'Shea
authors.forename: Sheila S
authors.initials: SS
authors.lastname: David
authors.forename: Jacqueline K
authors.initials: JK
authors.lastname: Barton
mesh_terms: D004247:DNA / Q000378:metabolism*; D004249:DNA Damage; D045647:DNA Glycosylases / Q000378:metabolism*; D004260:DNA Repair; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D004789:Enzyme Activation; D005609:Free Radicals; D006147:Guanine / Q000378:metabolism*; D010084:Oxidation-Reduction
chemical_list: D005609:Free Radicals; D006147:Guanine; D004247:DNA; D045647:DNA Glycosylases; C061738:mutY adenine glycosylase
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