Disintegration of Liposomes by Surfactants: Mechanism of Protein and Cholesterol Effects

Biological membranes are formed from the supramolecular aggregates of lipids, cholesterols, proteins, and other components such as carbohydrates. Harshness of personal cleaning products is related to surfactant interactions with proteins and lipids. Surfactants can damage biomembranes either by solubilizing their components in surfactant micelles or by fluidizing lipid bilayers through surfactant penetration. The interactions of surfactants with simpler biomembranes such as phosphatidic acid and phosphatidyl choline liposomes were first studied (Deo, N.; Somasundaran, P. Colloids Surf., A 2001, 186, 33), and then cholesterol and zein protein were added to make the liposomes more realistic. Sodium dodecyl sulfate (SDS) was used as a model surfactant for this purpose. Results show that while cholesterol makes the liposomes more resistant toward SDS, protein enhances the liposome solubilization processes. The mechanisms of the above process were investigated using a multipronged approach involving UV−visible spectroscopy, viscometry, and analytical ultracentrifugation. From viscometry and analytical ultracentrifuge analysis, it was seen that protein undergoes structural reorientation in the presence of SDS due to its strong affinity toward SDS, which stimulates the zein protein to be extracted away first from the bilayers. The preferential exits of zein protein out of the liposome membrane perturb the stability of the liposomes and enhance the liposome disintegration process.