Unique base-pair breathing dynamics in PNA-DNA hybrids

Area of Science:

• Biochemistry
• Molecular Biology
• Chemical Biology

Background:

• Peptide nucleic acid (PNA)-DNA hybrids are crucial in molecular biology and diagnostics.
• Understanding the dynamics of base-pair opening and closing is key to their function.
• Proton nuclear magnetic resonance (1H-NMR) is a powerful tool for studying molecular dynamics.

Purpose of the Study:

• To investigate the kinetic and thermodynamic parameters of PNA-DNA hybrids.
• To compare the base-pair dynamics of PNA-DNA hybrids with DNA duplexes.
• To elucidate the mechanism of base-pair opening in these hybrid systems.

Main Methods:

• 1H-NMR spectroscopy was used to measure imino proton exchange rates.
• Titration with exchange catalysts (ammonia and trimethylamine) was employed.
• Kinetic and thermodynamic parameters were derived from the experimental data.

Main Results:

• PNA bases in hybrids show opening/closing rates at least two orders of magnitude higher than DNA bases.
• DNA thymine bases in hybrids are destabilized, with dissociation constants increased by two orders of magnitude.
• Ammonia and trimethylamine revealed similar kinetic patterns, but trimethylamine showed longer base-pair lifetimes for certain sites.

Conclusions:

• PNA-DNA hybrids possess significantly faster base-pair dynamics compared to DNA duplexes.
• The observed kinetics suggest a distinct mechanism of base-pair opening in hybrids.
• Catalyst accessibility plays a role in probing base-pair dynamics, with some events being inaccessible to trimethylamine.