pH Switching That Crosses over the Isoelectric Point(pI) Can Improve the Entrapment of Proteins within Giant Liposomesby Enhancing Protein–Membrane Interaction.

The ability to encapsulate variousmolecules including proteinswithin giant liposomes is needed for studies on model cell membranesand artificial cells. In this report, we demonstrate how to improvethe efficiency of protein entrapment with the gentle hydration (naturalswelling) method, which is a well-known protocol for the preparationof giant liposomes. We found that when the initial pH of a solutionwas kept below the pI of a target protein during hydration and thenchanged to above the pI, the protein could be entrapped more efficientlycompared to the sample that was kept at above the pI during the hydration.An examination of the ratio of the mass of entrapped protein to themoles of phospholipid in liposomes (dioleoylphosphatidylcholine (DOPC)/dioleoylphosphatidylglycerol(DOPG)) indicated that entrapment of target proteins like bovine serumalbumin, myoglobin, and lysozyme could be improved using this procedure,and this trend was consistent with microscopic observations at thelevel of a single giant liposome. The conditions that resulted ingood efficiencies were affected by the NaCl concentration and thetemperature of the hydration solution, implying that protein entrapmentin giant liposomes may be enhanced by associative interaction betweenlipid lamellar membranes and target proteins. [ABSTRACT FROM AUTHOR]