Protein Binding onto Surfactant-Based Synthetic Vesicles

Abstract

Synthetic vesicles were prepared by mixing anionic and cationic surfactants, aqueous sodium dodecylsulfate with didodecyltrimethylammonium or cetyltrimethylammonium bromide. The overall surfactant content and the (anionic/cationic) mole ratios allow one to obtain negatively charged vesicles. In the phase diagram, the vesicular region is located between a solution phase, a lamellar liquid crystalline dispersion, and a precipitate area. Characterization of the vesicles was performed by electrophoretic mobility, NMR, TEM, and DLS and we determined their uni-lamellar character, size, stability, and charge density. Negatively charged vesicular dispersions, made of sodium dodecylsulfate/didodecyltrimethylammonium bromide or sodium dodecylsulfate/cetyltrimethylammonium bromide, were mixed with lysozyme, to form lipoplexes. Depending on the protein/vesicle charge ratio, binding, surface saturation, and lipoplexes flocculation, or precipitation, occurs. The free protein in excess remains in solution, after binding saturation. The systems were investigated by thermodynamic (surface tension and solution calorimetry), DLS, CD, TEM, 1H NMR, transport properties, electrophoretic mobility, and dielectric relaxation. The latter two methods give information on the vesicle charge neutralization by adsorbed protein. Binding is concomitant to modifications in the double layer thickness of vesicles and in the surface charge density of the resulting lipoplexes. This is also confirmed by developing the electrophoretic mobility results in terms of a Langmuir-like adsorption isotherm. Charges in excess with respect to the amount required to neutralize the vesicle surface promote lipoplexes clustering and/or flocculation. Protein-vesicle interactions were observed by DLS, indicating changes in particle size (and in their distribution functions) upon addition of LYSO. According to CD, the bound protein retains its native conformation, at least in the SDS/CTAB vesicular system. In fact, changes in the alpha-helix and beta-sheet conformations are moderate, if any. Calorimetric methods indicate that the maximum heat effect for LYSO binding occurs at charge neutralization. They also indicate that enthalpic are by far the dominant contributions to the system stability. Accordingly, energy effects associated with charge neutralization and double-layer contributions are much higher than counterion exchange and dehydration terms.

Characterization and stability of catanionic vesicles formed by pseudo-tetraalkyl surfactant mixtures

“…In addition, the electrostatic forces play a key role in the interactions between vesicles and biomacromolecules, such as DNA and proteins. [12][13][14][15] Finally, catanionic mixtures are suitable for drug delivery because of a reduced cytotoxicity. 16 As a rule, the latter is much lower than that pertinent to the single species.…”

Interaction of bovine serum albumin with gemini surfactants

“…A Malvern laser-velocimetry Doppler utility, of the HT ZS Nano series, determined the electrophoretic mobility by taking the average of several individual scans. The solutions were located in Ushaped cuvettes, equipped with gold electrodes [45,46]. The temperature is controlled to 25.00 ± 0.05°C by a Peltier heating facility.…”

Delivery of RNA and Its Intracellular Translation into Protein Mediated by SDS-CTAB Vesicles: Potential Use in Nanobiotechnology

“…Catanionic vesicles are supramolecular aggregates formed by mixing in non-stoichiometric ratios cationic and anionic surfactant species [1]. Surfactants of opposite charge tend to aggregate in polar solvents, such as water.…”