Hg(II) Binding to Thymine Bases in DNA

Area of Science:

• Environmental chemistry
• Biochemistry
• Toxicology

Background:

• Mercury compounds are highly toxic, impacting biological processes through poorly understood mechanisms.
• Mercury(II) ions (Hg(II)) exhibit a unique ability to directly bind to DNA, forming interstrand cross-links in thymine bases within AT-rich DNA sequences.

Purpose of the Study:

• To investigate the interaction between Hg(II) and thymine, the preferred binding mode, and the structural consequences for DNA.
• To characterize the X-ray spectroscopic signature of Hg(II)-thymine binding using a model compound.

Main Methods:

• Small molecule X-ray diffraction
• X-ray spectroscopies
• Computational chemistry
• 1-methylthymine as a model system

Main Results:

• The energetically preferred binding site for Hg(II) on thymine in DNA is the N3 position.
• Hg(II) binding to adjacent thymine nucleotides causes minor DNA distortions, with a preferred twisted geometry (32-43° torsion angle).
• Bis-thymine coordination of Hg(II) yields a distinct X-ray spectroscopic signature, differentiating it from other known Hg(II) biological binding modes.

Conclusions:

• This research clarifies a significant biological interaction of Hg(II) with DNA, specifically targeting thymine bases.
• The identified X-ray spectroscopic signature provides a tool for detecting Hg(II)-DNA binding in complex biological samples like cells and tissues.
• The findings lay the groundwork for future investigations into the mechanisms underlying mercury toxicity.