DNA-spermine and DNA-lipid aggregate formation visualized by fluorescence correlation spectroscopy

Area of Science:

• Biophysics
• Materials Science

Background:

• Fluorescence correlation spectroscopy (FCS) is a technique for determining single-molecule diffusion coefficients.
• Diffusion coefficients correlate with molecular size and shape, offering insights into conformational changes in plasmid aggregates.

Purpose of the Study:

• To investigate the use of FCS for characterizing DNA-containing aggregates.
• To determine how condensation agents like spermine and cationic liposomes affect DNA aggregate diffusion.

Main Methods:

• A 10-kbp plasmid was stained with PicoGreen.
• Plasmid condensation was induced using either spermine or liposomes (cationic lipid and egg phosphatidylcholine).
• Diffusion coefficients of the resulting aggregates were measured using FCS.

Main Results:

• Spermine addition increased the DNA diffusion coefficient from 1.0 x 10(-12) m2/s to 3.2 x 10(-12) m2/s.
• Cationic liposomes formed complexes with diffusion coefficients ranging from 1.7 to 1.9 x 10(-12) m2/s.
• FCS successfully measured diffusion coefficients of DNA-containing aggregates.

Conclusions:

• FCS is effective for determining diffusion coefficients of DNA-containing aggregates.
• These diffusion coefficients provide valuable information about the topology and homogeneity of the aggregates.
• The study demonstrates FCS's utility in understanding DNA condensation and aggregate formation.