Charged nucleobases and their potential for RNA catalysis.

Area of Science:

• Biochemistry
• Molecular Biology
• Chemical Biology

Background:

• Catalysis in living cells involves both protein enzymes and RNA enzymes (ribozymes).
• While protein enzymes have been studied for centuries, ribozymes were discovered only 30 years ago, offering insights into early life and biological catalysis.
• Ribozymes employ catalytic strategies similar to protein enzymes, utilizing simpler side chains for metal ion, general acid-base, and electrostatic catalysis.

Purpose of the Study:

• To examine the evidence for charged nucleobases participating in RNA catalysis.
• To integrate direct measurements on catalytic RNAs with thermodynamic studies on oligonucleotide model systems.
• To understand the driving forces and mechanisms behind the perturbation of nucleobase pKa values.

Main Methods:

• Integration of direct measurements on catalytic RNAs and thermodynamic studies on oligonucleotide model systems.
• Analysis of Raman crystallography and fluorescence spectroscopy data for pKa measurement.
• Examination of RNA structures in databases to assess the prevalence of charged nucleobases.

Main Results:

• Charged nucleobases have been implicated in RNA catalysis as general acid-bases and oxyanion holes.
• Mechanisms for pKa shifts involve electrostatic stabilization and hydrogen bonding, coupling protonation with RNA folding.
• Raman crystallography and fluorescence spectroscopy reveal pKa values for bases A or C at or above neutrality, mimicking histidine and lysine/arginine behavior.
• Analysis of RNA structures indicates that charged bases are common under cellular conditions.

Conclusions:

• Cationic and anionic charge states of nucleobases occur in RNA enzymes.
• These charged states make significant catalytic contributions to ribozyme activity.
• Further experimental and theoretical approaches are needed to fully elucidate outstanding questions in ribozyme catalysis.