Solvent effects on the stability of A7U7p

Area of Science:

• Biochemistry
• Thermodynamics
• Molecular Biology

Background:

• Oligonucleotide duplex formation is crucial for molecular recognition and biological processes.
• Understanding the thermodynamic driving forces behind duplex stability is essential for predicting molecular interactions.
• Previous studies have explored the thermodynamics of nucleic acid duplexes, but solvent effects require further investigation.

Purpose of the Study:

• To measure the thermodynamics of double-helix formation for A7U7 and A7U7p.
• To investigate the influence of solvent mixtures and salt concentrations on A7U7p duplex stability.
• To compare the thermodynamic properties of A7U7p duplex formation with those of proteins and other nucleic acid systems.

Main Methods:

• Spectrophotometry was used to measure the thermodynamics of A7U7 and A7U7p double-helix formation.
• Calorimetric measurements were compared with spectrophotometric data for A7U7.
• The effect of various solvent mixtures and salt concentrations on A7U7p duplex stability was systematically evaluated.

Main Results:

• Spectrophotometric and calorimetric data suggest intermediate states in A7U7 duplex formation.
• The salt dependence of the melting temperature (Tm) for A7U7p was found to be dTm/d(log [Na+]) = 17.4 °C, comparable to poly-(A).poly(U).
• A7U7p duplex stability is maximal in 100% water at 1 M NaCl, and its stability order in 10% solvent mixtures was determined, with hydrophobic bonding and cavity formation being minor contributors to stability.

Conclusions:

• Double-helix formation for A7U7 involves intermediate states.
• Solvent composition plays a critical role in the stability of A7U7p duplexes, with significant differences observed across various organic solvents.
• The thermodynamic behavior of A7U7p suggests distinct solvent interactions compared to proteins, with hydrophobic effects and cavity formation contributing minimally to duplex stability.