title: Direct observation of radical intermediates in protein-dependent DNA charge transport.
abstract: Charge migration through the DNA base stack has been probed both spectroscopically, to observe the formation of radical intermediates, and biochemically, to assess irreversible oxidative DNA damage. Charge transport and radical trapping were examined in DNA assemblies in the presence of a site-specifically bound methyltransferase HhaI mutant and an intercalating ruthenium photooxidant using the flash-quench technique. The methyltransferase mutant, which can flip out a base and insert a tryptophan side chain within the DNA cavity, is found to activate long-range hole transfer through the base pair stack. Protein-dependent DNA charge transport is observed over 50 A with guanine radicals formed >10(6) s(-1); hole transport through DNA over this distance is not rate-limiting. Given the time scale and distance regime, such protein-dependent DNA charge transport chemistry requires consideration physiologically.
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: H A
authors.initials: HA
authors.lastname: Wagenknecht
authors.forename: S R
authors.initials: SR
authors.lastname: Rajski
authors.forename: M
authors.initials: M
authors.lastname: Pascaly
authors.forename: E D
authors.initials: ED
authors.lastname: Stemp
authors.forename: J K
authors.initials: JK
authors.lastname: Barton
mesh_terms: D004247:DNA / Q000737:chemistry* / Q000235:genetics; D004249:DNA Damage; D004579:Electron Transport; D004591:Electrophoresis, Polyacrylamide Gel; D005609:Free Radicals / Q000737:chemistry; D007288:Inosine / Q000737:chemistry; D008780:Methyltransferases / Q000737:chemistry / Q000235:genetics; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D010083:Oxidants, Photochemical / Q000737:chemistry; D010084:Oxidation-Reduction; D011506:Proteins / Q000737:chemistry* / Q000235:genetics; D012428:Ruthenium / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D005609:Free Radicals; D010083:Oxidants, Photochemical; D011506:Proteins; D007288:Inosine; D012428:Ruthenium; D004247:DNA; D008780:Methyltransferases