DNA condensation and interaction with zwitterionic phospholipids mediated by divalent cations

Area of Science:

• Biophysics
• Materials Science
• Gene Therapy

Background:

• Artificial viruses are explored for gene therapy, necessitating safe and efficient lipid-DNA complexes.
• Cationic lipids often exhibit toxicity, while neutral lipids are non-toxic but lack direct DNA interaction.
• Zwitterionic lipids require mediators like divalent cations for DNA interaction.

Purpose of the Study:

• To investigate the interaction between calf thymus DNA and zwitterionic 1,2-dimyristoyl-phosphatidylethanolamine (DMPE) lipid monolayers.
• To explore the role of divalent cations (Ca2+ and Mg2+) in mediating DNA-lipid complex formation.
• To characterize the structural and ordering properties of DNA adsorbed onto lipid monolayers.

Main Methods:

• Utilized Langmuir monolayers as a model system at the air/water interface.
• Employed surface pressure-area isotherms, infrared reflection absorption spectroscopy (IRRAS), X-ray reflectivity (XR), grazing incidence X-ray diffraction (GIXD), and Brewster angle microscopy (BAM).
• Studied the adsorption of DNA onto DMPE monolayers in the presence of Ca2+ or Mg2+.

Main Results:

• DNA adsorption onto DMPE monolayers was observed exclusively in the presence of divalent cations.
• Adsorbed DNA partially penetrated the lipid monolayer at low pressures but was expelled at high pressures.
• The adsorption layer exhibited a thickness of 18-19 Å, and GIXD revealed one-dimensional ordering of DNA strands with cation-dependent spacing.

Conclusions:

• Divalent cations are crucial for mediating the interaction and adsorption of DNA onto zwitterionic DMPE lipid monolayers.
• The structural arrangement and adsorption behavior of DNA are influenced by the type of divalent cation and surface pressure.
• These findings contribute to understanding DNA-lipid complex formation for potential gene therapy applications.