The role of cholesterol in membrane activity of digitonin: Experimental and theoretical model studies

Molecular insight into the digitonin-sterol interaction is essential for potential membrane-associated digitonin applications, including cancer treatment, membrane lysis and membrane transport. Here, interactions of digitonin with monolayers of cholesterol and diosgenin were investigated with the use of Langmuir monolayer techniques, classical dynamics simulation and quantum chemistry methods. The results obtained show that digitonin penetrates and effectively incorporates into sterol monolayers, changing the fluidity of monolayers and lipid arrangement. Both cholesterol and diosgenin form stable complexes with digitonin molecules. Almost all identified complexes were formed via hydrogen bonds between lipid headgroup oxygen atoms and headgroup hydroxyl groups of digitonin. The calculated stabilization energies were greater for diosgenin/digitonin complexes, which was attributed to electrostatic interactions between polar atoms in the hydrophobic parts of both molecules.