Cold denaturation of the hammerhead ribozyme

Area of Science:

• Biochemistry
• Thermodynamics
• Molecular Biology

Background:

• Cold denaturation is a known thermodynamic phenomenon in proteins, attributed to heat capacity differences between folded and unfolded states.
• This phenomenon was presumed absent in nucleic acids due to their negligible folding heat capacity (DeltaCp).

Purpose of the Study:

• To investigate the potential for cold denaturation in nucleic acids.
• To determine the low-temperature structural behavior of the hammerhead ribozyme.

Main Methods:

• Circular dichroism spectroscopy was used to analyze the hammerhead ribozyme's structure under varying temperatures and conditions.
• Data were fitted to a two-state model to calculate thermodynamic parameters.

Main Results:

• Cold unfolding of the hammerhead ribozyme was observed at -20°C, indicating tertiary structure loss.
• Both hot and cold unfolding events occurred under specific conditions, with transition temperatures (Tm) of 53°C and -1°C.
• The calculated DeltaCp was 3.4 kJ mol-1 K-1, aligning with values for DNA duplexes.

Conclusions:

• This study provides the first direct evidence of cold denaturation in a nucleic acid.
• The findings underscore the critical role of DeltaCp in the thermodynamics of nucleic acid folding, challenging previous assumptions.