Structural forms and transitions for the complex of mercury(II) with poly(dG-dC)

Area of Science:

• Biophysical Chemistry
• Molecular Biology
• Spectroscopy

Background:

• DNA structure is dynamic and can transition between different helical forms like B and Z.
• Metal ions, such as mercury(II), can interact with DNA and alter its structural properties.
• Hydration levels play a crucial role in determining DNA conformation.

Purpose of the Study:

• To investigate the effect of mercury(II) complexation on the structural transitions of hydrated poly(dG-dC) DNA.
• To understand the binding sites of mercury(II) on the DNA and its influence on DNA protonation.
• To examine the combined effects of mercury(II), salt, and hydration on DNA structure.

Main Methods:

• Infrared spectroscopy was employed to analyze the structural changes in poly(dG-dC).
• Varying concentrations of mercury(II) and hydration levels were used to induce and observe structural transitions.
• The influence of NaCl and D2O on mercury(II)-DNA complexes was studied.

Main Results:

• At low mercury(II) concentrations (r=0.1), the B-DNA structure was stabilized, and the B* structure was absent at high hydration.
• At higher mercury(II) concentrations (r=0.2), B and Z DNA structures coexisted, with a broad transition to the Z-form upon reduced hydration.
• Mercury(II) bound to guanine residues (N3 or N7), and cytosine protonation was inhibited. NaCl reduced mercury binding and sharpened the B-Z transition, while D2O stabilized the Z-form.

Conclusions:

• Mercury(II) binding to poly(dG-dC) is sequence-specific and concentration-dependent, influencing B-Z DNA transitions.
• The hydration state and ionic environment significantly modulate the structural response of DNA to mercury(II) binding.
• Infrared spectroscopy is a powerful tool for elucidating metal-ion-induced DNA structural dynamics.