Sequence-dependent variations of DNA structure modulate radiation-induced strand breakage

Area of Science:

• Biophysics
• Chemical Biology
• Molecular Biology

Background:

• DNA strand breakage is a critical factor in radiation damage and drug interactions.
• Understanding sequence-dependent DNA vulnerability is essential for predicting biological outcomes.

Purpose of the Study:

• To investigate the sequence-dependence of DNA strand breakage induced by hydroxyl radicals (OH•).
• To correlate breakage probability with DNA structural features like minor groove width and atom accessibility.

Main Methods:

• Experimental measurement of strand breakage probability using sequencing gel electrophoresis.
• Computational modeling and Monte Carlo simulations to calculate OH• accessibility and reaction probabilities.
• Analysis of an 80 base pair DNA fragment.

Main Results:

• Reduced DNA strand breakage observed in sequences with narrow minor grooves.
• Low accessibility of H4' and H5' atoms to OH• attack correlates with decreased breakage.
• Sequence structure, not nucleotide identity (A, T, G, C), primarily determines breakage probability.

Conclusions:

• Local DNA sequence modulates intrinsic structure, influencing OH•-induced strand breakage.
• The C4'-centered radical pathway is three times more efficient in causing strand breaks than the C5' pathway.
• Strand breaks result from both 4'- and 5'-centered radical reaction pathways.