Solution structure of an RNA internal loop with three consecutive sheared GA pairs

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Internal loops in RNA are crucial for folding and function.
• GA base pairs within these loops often contribute to thermodynamic stability.
• Predicting RNA stability and structure requires understanding sequence-dependent molecular interactions.

Purpose of the Study:

• To determine the NMR structure of an oligonucleotide duplex containing a stable internal loop with consecutive GA pairs.
• To investigate the thermodynamic consequences of nucleotide substitutions within this loop.
• To elucidate the molecular basis for the stability of these GA-rich internal loops.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy to determine the three-dimensional structure of the RNA duplex.
• Thermodynamic analysis to quantify the stability of the internal loop and its variants.
• Analysis of hydrogen bonding and base stacking interactions within the loop.

Main Results:

• The NMR structure of the 5'GGA3'/3'AAG5' internal loop revealed three consecutive sheared GA pairs with distinct G and A stacking.
• Nucleotide substitution of the middle GA with AA resulted in significant destabilization (~2 kcal/mol at 37°C).
• The stability of UG/GA and UG/AA motifs was found to be similar to CG/GA, despite UG/UA pairs typically being less stable.

Conclusions:

• The unusual stability of the 5'GGA3'/3'AAG5' internal loop is attributed to its unique base stacking and hydrogen bonding network.
• Consecutive sheared GA pairs are preorganized for potential tertiary interactions and ligand binding.
• This research provides a foundation for predicting RNA folding stability and structure based on internal loop sequences.