Effects of hydration on purine motion in solid DNA

Area of Science:

• Biophysics
• Molecular Biology
• Structural Biology

Background:

• Understanding DNA dynamics is crucial for its biological functions.
• The influence of hydration on DNA's structural and dynamic properties remains an active area of research.
• Previous studies have indicated the importance of collective motion in DNA.

Purpose of the Study:

• To investigate the effect of varying hydration levels on the motion of specific DNA base pairs (A8 and G8).
• To correlate changes in base pair motion with spin-lattice relaxation rates (T1).
• To elucidate the role of collective modes of motion in DNA hydration dynamics.

Main Methods:

• Deuterium quadrupole echo spectroscopy was employed to study DNA.
• Spin-lattice relaxation rates (T1) were measured at different frequencies (76.8 and 38.4 MHz).
• Experiments were conducted on calf thymus DNA deuterated at A8 and G8 positions across a range of relative humidities.

Main Results:

• A slight increase in base pair motion amplitude was observed with hydration up to ~20 mol H2O/nucleotide.
• The onset of base motion correlated with a >100-fold decrease in T1.
• Above ~20 mol H2O/nucleotide, base motion amplitude increased substantially, leading to loss of quadrupole echo.

Conclusions:

• Hydration significantly influences DNA base pair dynamics.
• The observed T1 decrease suggests collective modes of motion are involved in DNA hydration.
• These findings provide insights into the relationship between water content and DNA molecular motion.