Mechanism of calcium ion induced multilamellar vesicle-DNA interaction

The effect of Ca2+ on the DNA interaction with anionic and neutral multilamellar vesicles (MLV) has been investigated. DNA from wheat (Triticum aestivum L. Gerek) was introduced to a suspension of MLV, composed of phosphatidylcholine (PC):dicetylphosphate (DCP):cholesterol (CHOL) at different molar ratios, to which Ca2+ (5-75 mM) was subsequently added. Indication of aggregation and/or fusion was obtained via light-scattering examination following the addition of Ca2+ and DNA to the MLV medium. Using a UV spectrophotometric assay, it was observed that although DNA alone has no effect on negatively charged MLV, it enhances liposomal interaction in the presence of calcium ions. The minimal Ca2+ concentration required to promote the interaction was detected to be 10 mM, and the highest level of interaction was observed at 75 mM. The aggregation/fusion of vesicles was detected for uncharged MLV (with no DCP in their structure), as well as for the anionic ones containing c. 10% CHOL, but not for anionic MLV containing 40% CHOL. This is explained in terms of cholesterol decreasing the membrane fluidity (above the Tc of components) as a result of which more rigid vesicles become less prone to aggregation/fusion interactions.