DNA-Bound peptide radicals generated through DNA-mediated electron transport

Area of Science:

• Biochemistry
• Molecular Biology
• Photochemistry

Background:

• Ruthenium complexes like [Ru(phen)2(dppz)]3+ act as potent oxidants for DNA bases.
• Peptides can intercalate into DNA, potentially mediating electron transfer reactions.

Purpose of the Study:

• To investigate peptide/DNA electron-transfer reactions using flash-quench experiments.
• To explore the role of specific amino acids (tyrosine, tryptophan) in mediating these reactions.
• To characterize the products and mechanisms of peptide-DNA electron transfer.

Main Methods:

• Flash-quench experiments to generate reactive intermediates.
• Transient absorption spectroscopy to detect radical species.
• Gel electrophoresis and mass spectrometry to analyze DNA damage and adduct formation.

Main Results:

• DNA-bound ruthenium complexes oxidized intercalated guanine and tyrosine.
• Tyrosine and guanine radicals were observed, with electron transfer kinetics suggesting guanine radical intermediacy.
• Long-range guanine damage was observed in DNA duplexes, with altered distribution in the presence of peptide.
• Covalent adducts between DNA and Lys-Tyr-Lys were identified.
• Tyrosine radical reactivity differed significantly from tryptophan radical reactivity.

Conclusions:

• Lys-Tyr-Lys and Lys-Trp-Lys can mediate long-range electron transfer through DNA from specific binding sites.
• The observed peptide-DNA electron transfer chemistry has implications for understanding DNA repair and signaling.
• The distinct reactivity of peptide radicals offers insights into their potential functional roles.