Improvement of lipidic bicontinuous cubic phases by the addition of a zwitterion with strong hydration ability and kosmotropicity

Abstract

Lyotropic bicontinuous cubic (Q_II) phases have attracted increasing attention as nanostructured fluidic matrices for some bio-polymers including enzymes and DNA. Owing to the 3D nature of the Q_II phases, the incorporated polymers show unique molecular behavior in the matrices. In many cases, monoolein (MO) is frequently employed as a lipid molecule because of its advanced ability to form Q_II phases under a wide range of conditions. However, there are still several aspects that require improvements in MO/water-based systems. In the present study, we have focused on the improvement of the temporal stability of MO/water-based Q_II matrices by the addition of a zwitterion. We have found that (I) the addition of 3-(1-methyl-3-imidazolio)propanesulfonate (ImZI) results in a decrease in the water activity of the MO/water-based matrices; (II) ImZI is a kosmotropic salt with structure-stabilizing effects on proteins; (III) a polypeptide, dermaseptin, forms a secondary structure in the MO/water/ImZI systems. These results suggest that the present lyotropic systems have great potential to be an ideal matrix for the lipidic cubic phase method that is known as a method to create single crystals of membrane proteins.