Quantitative DNA interstrand cross-link formation by coumarin and thymine: structure determination, sequence effect,...

Area of Science:

• Biochemistry
• Molecular Biology
• Photochemistry

Background:

• Coumarin analogues are versatile compounds used across medicine, biology, and material sciences.
• Understanding coumarin interactions with DNA is crucial for assessing their biochemical properties and potential toxicity.

Purpose of the Study:

• To investigate the reactivity of coumarin analogues with DNA.
• To explore the formation and photoreversibility of DNA cross-links induced by coumarins.
• To develop a fluorescence-based method for monitoring DNA cross-linking.

Main Methods:

• Synthesis and incorporation of coumarin analogues into oligodeoxynucleotides.
• Photoirradiation at 350 nm to induce [2 + 2] cycloaddition with thymidine.
• Spectroscopic analysis to monitor DNA interstrand cross-link (ICL) formation and photoreversibility.

Main Results:

• Photoinduced [2 + 2] cycloaddition forms syn- and anti-cyclobutane adducts, which are photoreversible.
• Coumarins with flexible chains efficiently form DNA interstrand cross-links (ICLs).
• ICL formation is kinetically favored at A:T pairs over G:C pairs and is quenched by photoinduced electron transfer with dG.
• Fluorescence quenching upon ICL formation allows real-time monitoring of cross-linking and photoreversibility.

Conclusions:

• Coumarin-induced DNA cross-linking is a quantitative, photoswitchable reaction.
• The fluorescence-based monitoring system provides a novel tool for studying DNA cross-linking and photoreversibility.
• This methodology can potentially detect transversion mutations and serve as mechanistic probes in bioresearch without altering the biological environment.