Ion-induced Domain Formation in a Bilayer Membrane of Soybean-derived Lipids

We found a novel ion-induced domain formation phenomenon in a lipid bilayer membrane of asolectin, a crudely extracted phospholipid mixture from soybean. Asolectin is widely used in cell-free synthesis systems and functional analyses of membrane proteins, therefore we aimed to prepare supported lipid bilayers (SLBs) of asolectin with good reproducibility and to verify their structure and properties. A homogeneous asolectin SLB was formed on a mica substrate in a buffer solution containing K+ and lipid domains were generated by substituting K+ in the aqueous phase with Na+. The domains expanded in the presence of Ca2+ and disappeared in the K+-containing buffer in a nearly reversible manner. The lipid domain induced by a monovalent cation is a unique phenomenon. We proposed that the effect of Ca2+ is due to the bridging effect of the divalent cation between negatively charged PI molecules. These results provide new insights into the lateral organization within bilayer membranes of naturally derived lipids.