Radiosensitivity of DNA in a specific protein-DNA complex: the lac repressor-lac operator complex

Area of Science:

• Molecular Biology
• Radiation Chemistry
• Biophysics

Background:

• Understanding DNA damage mechanisms is crucial for fields like radiation oncology and astrobiology.
• The Escherichia coli lac repressor-lac operator system serves as a model for studying DNA-protein interactions and their influence on DNA stability.

Purpose of the Study:

• To computationally determine the likelihood of radiation-induced frank strand breakage (FSB) at each nucleotide within the E. coli lac repressor-lac operator complex.
• To compare simulation-derived FSB probabilities with experimental data.
• To evaluate the roles of DNA conformational alterations and protein masking in repressor-mediated DNA protection.

Main Methods:

• Utilized crystallography- and NMR-based structures of the DNA-protein complex from the PDB databank.
• Calculated atomic accessibility and FSB probabilities for DNA in the complex, DNA without protein, and linear DNA.
• Irradiated DNA fragments with and without the repressor, determining relative FSB probabilities via sequencing gel electrophoresis.

Main Results:

• Simulations predicted altered accessibility of key DNA atoms (H4' and H5') and modulated FSB probabilities due to protein-induced conformational changes and steric hindrance.
• Calculations based on the crystallography-derived structure showed the best agreement with experimental FSB data.

Conclusions:

• Computational methods can accurately predict radiation-induced "footprints" on DNA within specific DNA-protein complexes.
• Protein-induced conformational changes in DNA play a substantial role in protecting DNA from radiation damage.