Hysteresis and conformational changes in ribosomal ribonucleic acid

Area of Science:

• Biochemistry
• Molecular Biology
• Physical Chemistry

Background:

• Ribosomal RNA (rRNA) plays a crucial role in protein synthesis.
• Understanding the acid-base properties of rRNA is essential for elucidating its structure and function.

Purpose of the Study:

• To investigate the acid-binding properties of rRNA using titration experiments.
• To characterize the phenomenon of hysteresis in rRNA's interaction with acid and alkali.

Main Methods:

• Titration of rat liver and Escherichia coli rRNA with acid and alkali.
• Conducting titrations at approximately 0°C in 0.1 M sodium chloride over a pH range of 3-7.
• Analyzing the resulting pH-dependent binding curves, including boundary and scanning curves.

Main Results:

• rRNA demonstrated irreversible acid binding and significant hysteresis, with binding dependent on titration direction.
• A lag in proton release of at least 1 pH unit was observed.
• Approximately 9-15% of titratable groups (adenine and cytosine) were involved, with energy dissipation of ~4.2 kJ/mol per nucleotide.
• Scanning curves suggested conformational changes, potentially forming poly(A).poly(AαH+)-like regions.

Conclusions:

• Hysteresis in rRNA titration is a significant characteristic, implying slow proton exchange kinetics.
• The observed hysteresis is likely influenced by both the primary nucleotide sequence and secondary structure of rRNA.
• Conformational flexibility of rRNA is implicated in its acid-binding behavior.