Chitosan polyplexes: Energetics of formation and conformational changes in DNA upon binding and release

Area of Science:

• Biophysical Chemistry
• Polymer Science
• Molecular Biology

Background:

• Chitosan (CS) is a biocompatible polymer with potential applications in gene delivery.
• Understanding the interaction between chitosan and DNA is crucial for optimizing polyplex formation and stability.
• The conformational changes of DNA upon binding to chitosan influence its accessibility and functionality.

Purpose of the Study:

• To investigate the energetics of chitosan-DNA polyplex formation.
• To analyze the conformational stability of DNA bound within chitosan polyplexes.
• To explore the dissociation behavior of chitosan-DNA polyplexes under varying conditions.

Main Methods:

• Isothermal Titration Calorimetry (ITC) to study binding energetics.
• High-Sensitivity Differential Scanning Calorimetry (HS-DSC) to assess DNA conformational stability.
• Varying chitosan/DNA weight ratios (r_w) and ionic strengths (pH 5.0 and 7.4).

Main Results:

• CS-DNA binding follows a cooperative mechanism (McGhee-von Hippel model).
• Two DNA conformational forms (intact and globular) were observed, with globular DNA dominating at higher CS content.
• Polyplexes showed phase separation at pH 7.4, immobilizing DNA in the CS-rich phase, with conformational changes at physiological ionic strength.

Conclusions:

• Chitosan binding induces DNA condensation into stable globular forms.
• Polyplex stability and DNA conformation are tunable via CS/DNA ratio and ionic strength.
• Chitosan polyplexes demonstrate potential for DNA immobilization and controlled release applications.