DNA-Bound Peptide Radicals Generated through DNA-Mediated Electron Transport

详细信息    查看全文

• 作者：Hans-Achim Wagenknecht ; Eric D. A. Stemp ; and Jacqueline K. Barton
• 刊名：Biochemistry
• 出版年：2000
• 出版时间：May 9, 2000
• 年：2000
• 卷：39
• 期：18
• 页码：5483 - 5491
• 全文大小：223K
• 年卷期：v.39,no.18(May 9, 2000)
• ISSN：1520-4995

文摘

Flash-quench experiments were carried out to explore peptide/DNA electron-transfer reactions.DNA-bound [Ru(phen)₂(dppz)]³⁺ (phen = 1,10-phenanthroline; dppz = dipyridophenazine) and [Ru(phen)(bpy')(dppz)]³⁺ [bpy' = 4-(4'-methyl-2,2'-bipyridyl)valerate], generated in situ by flash-quenchmethodology, are powerful ground-state oxidants, capable of oxidizing guanine or tyrosine intercalatedin DNA. In flash-quench experiments with mixed-sequence oligonucleotides in the presence of Lys-Tyr-Lys, transient absorption spectroscopy yielded a spectrum with a sharp maximum at 405 nm assigned tothe tyrosine radical. Experiments with poly(dG·dC) suggested the intermediacy of the guanine radical,since the rise of the 405 nm signal occurred with the same kinetics as the disappearance of the guanineradical, as monitored at 510 nm. In oligonucleotide duplexes containing [Ru(phen)(bpy')(dppz)]²⁺ tetheredat one end, damage to distant guanines was observed by gel electrophoresis, consistent with the mobilityof the electron hole through the DNA duplex; the presence of the peptide did not inhibit but insteadaltered the distribution of guanine damage. Covalent adducts of the DNA and Lys-Tyr-Lys were detectedas final irreversible products of this peptide-to-DNA electron-transfer chemistry by mass spectrometricand enzymatic digestive analysis. From these different assays and comparison of reactions of Lys-Trp-Lys and Lys-Tyr-Lys, the reactivity of the DNA-bound tyrosine radical was found to differ considerablyfrom that of the tryptophan radical. These results establish that Lys-Tyr-Lys and Lys-Trp-Lys can participatein long-range electron-transfer reactions through the DNA from a distinct binding site. On that basis,proposals for functional roles for these peptide radicals may be considered.