Drug-induced DNA repair: X-ray structure of a DNA-ditercalinium complex

Area of Science:

• Molecular Biology
• Structural Biology
• Drug Discovery

Background:

• Ditercalinium is a synthetic anticancer drug that functions by bis-intercalating into DNA.
• This interaction activates DNA repair mechanisms, which are aberrantly triggered in prokaryotic and eukaryotic cells.
• In prokaryotes, the uvrABC system misidentifies DNA-ditercalinium complexes as covalent lesions, while in eukaryotes, mitochondrial DNA repair is excessively activated, leading to degradation.

Purpose of the Study:

• To elucidate the three-dimensional structure of the ditercalinium-DNA complex at high resolution.
• To understand how ditercalinium binding induces DNA structural changes.
• To correlate these structural changes with the observed misrecognition by DNA repair systems.

Main Methods:

• X-ray crystallography was employed to determine the structure.
• A double-stranded DNA fragment, [d(CGCG)]2, was complexed with ditercalinium.
• High-resolution structural analysis (1.7 Å) was performed on the complex.

Main Results:

• The crystal structure of the ditercalinium-[d(CGCG)]2 complex was determined to 1.7 Å resolution.
• Ditercalinium binding induces significant kinking (15 degrees) and unwinding (36 degrees) of the DNA helix.
• The major and minor grooves of the DNA become exceptionally wide in the complex.

Conclusions:

• The drug-induced distortion of DNA, characterized by kinking and groove widening, is a key feature of ditercalinium binding.
• These structural alterations are likely responsible for the misrecognition of the DNA-ditercalinium complex by the uvrABC repair system in prokaryotes.
• Similarly, these distortions may trigger the futile DNA repair observed in eukaryotic mitochondrial systems, contributing to the drug's anticancer activity.