Lysenin is a pore-forming protein extracted from the earthworm Eisenia fetida, which inserts large conductance pores in artificial and natural lipid membranes containing sphingomyelin. Its cytolytic and hemolytic activity is rather indicative of a pore-forming toxin; however, lysenin channels present intricate regulatory features manifested as a reduction in conductance upon exposure to multivalent ions. Lysenin pores also present a large unobstructed channel, which enables the translocation of analytes, such as short DNA and peptide molecules, driven by electrochemical gradients. These important features of lysenin channels provide opportunities for using them as sensors for a large variety of applications. In this respect, this literature review is focused on investigations aimed at the potential use of lysenin channels as analytical tools. The described explorations include interactions with multivalent inorganic and organic cations, analyses on the reversibility of such interactions, insights into the regulation mechanisms of lysenin channels, interactions with purines, stochastic sensing of peptides and DNA molecules, and evidence of molecular translocation. Lysenin channels present themselves as versatile sensing platforms that exploit either intrinsic regulatory features or the changes in ionic currents elicited when molecules thread the conducting pathway, which may be further developed into analytical tools of high specificity and sensitivity or exploited for other scientific biotechnological applications.
Liposomes are spherical-shaped vesicles that enclose an aqueous milieu surrounded by bilayer or multilayer membranes formed by self-assembly of lipid molecules. They are intensively exploited as either model membranes for fundamental studies or as vehicles for delivery of active substances in vivo and in vitro. Irrespective of the method adopted for production of loaded liposomes, obtaining the final purified product is often achieved by employing multiple, time consuming steps. To alleviate this problem, we propose a simplified approach for concomitant production and purification of loaded liposomes by exploiting the Electrodialysis-Driven Depletion of charged molecules from solutions. Our investigations show that electrically-driven migration of charged detergent and dye molecules from solutions that include natural or synthetic lipid mixtures leads to rapid self-assembly of loaded, purified liposomes, as inferred from microscopy and fluorescence spectroscopy assessments. In addition, the same procedure was successfully applied for incorporating PEGylated lipids into the membranes for the purpose of enabling long-circulation times needed for potential in vivo applications. Dynamic Light Scattering analyses and comparison of electrically-formed liposomes with liposomes produced by sonication or extrusion suggest potential use for numerous in vitro and in vivo applications.
We have studied how a surfactant (Aerosol OT or AOT) self-assembles in different polar (Water, Ethylene glycol, Formamide, N, N-Dimethylformamide) and non-polar (Isooctane) solvents. AOT is a widely used surfactant in biological and industrial applications. The lamellar phase of the AOT/water system is often used as a model of lipidic membrane. We investigated two surfactant volume fractions (0.2 and 0.6) with visual inspection, SAXS, rheology and electrical conductivity experiments. The results indicate that AOT selfassembles differently depending on solvent type and concentration. SAXS experiments show that the AOT/water systems display lamellar phases. In the other cases, only formamide displays a lamellar phase for 4 = 0.6. The other solvents (and formamide at 4= 0.2) promote the self-assembly of AOT in other microstructures. In these cases, the SAXS spectra display correlation peaks consistent with a disordered array of cylindrical aggregates. The visual inspection, rheology and electrical conductivity results are consistent with the deduced self-assembled structures. We explain most of our results in terms of surfactant packing models and solvent properties.
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