Protonated polynucleotide structures : 15. Metastable protonated polydeoxyribonucleotides.

Area of Science:

• Biophysical Chemistry
• Molecular Biology
• Spectroscopy

Background:

• Polydeoxyribonucleotides are crucial for understanding DNA structure and function.
• pH-induced structural transitions in DNA are important for biological processes.
• Circular Dichroism (CD) spectroscopy is a sensitive tool for studying DNA conformation.

Purpose of the Study:

• To investigate the pH-dependent behavior of three specific polydeoxyribonucleotide complexes.
• To characterize the hysteresis phenomenon in these DNA complexes.
• To understand the stability and reversibility of different conformational states.

Main Methods:

• Circular Dichroism (CD) spectroscopy was employed.
• Studies were conducted as a function of pH at a constant temperature (25°C).
• Titration cycles were performed to assess reversibility and hysteresis.

Main Results:

• Poly(dA-G).poly(dT-C) displayed significant hysteresis, unlike the other two complexes studied.
• The hysteretic form (R) of poly(dA-G).poly(dT-C) is metastable at neutral pH.
• This metastable form irreversibly converts to the neutral form (N) upon heating to ~60°C.
• A full titration cycle to pH 2.5 and back to neutral pH is required to recover the metastable form R.

Conclusions:

• The poly(dA-G).poly(dT-C) complex exhibits unique pH-induced conformational changes with hysteresis.
• This hysteresis is linked to a metastable state that can be accessed and lost under specific conditions.
• The findings contribute to the understanding of DNA structural dynamics and phase transitions.