Structure of a DNA intercalation complex as determined by NMR using a paramagnetic probe

Area of Science:

• Biophysical Chemistry
• Molecular Biology
• Structural Biology

Background:

• Proton relaxation rates are sensitive to molecular interactions.
• Paramagnetic ions like manganese (II) can probe molecular environments.
• Understanding DNA-ligand interactions is crucial for molecular biology.

Purpose of the Study:

• To investigate the structural details of the 3,8-dimethyl-N-methyl-phenanthrolinium (DMP) cation intercalated within DNA.
• To utilize proton relaxation data influenced by manganese (II) to differentiate between proposed DMP-DNA intercalation models.
• To elucidate the orientation of the DMP molecule relative to DNA base pairs.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy to measure longitudinal relaxation rates of DMP protons.
• Utilizing paramagnetic effects of manganese (II) ions to probe the proximity of DMP to DNA.
• Analyzing proton relaxation data to discriminate between different DMP-DNA intercalation models.

Main Results:

• Longitudinal relaxation rates of DMP protons are significantly altered by manganese (II) ions in the presence of DNA.
• The electron-nuclear dipolar interaction in the ternary Mn-DNA-DMP complex provides key information.
• Proton relaxation data unequivocally discriminate between two proposed DMP-DNA intercalation models.

Conclusions:

• The study successfully distinguished between two models of DMP-DNA intercalation.
• The findings indicate that the DMP molecule, when intercalated into DNA, adopts an orientation where its long axis is nearly perpendicular to the DNA base-pair hydrogen bonds.