Fusion behaviour of aquaporin Z incorporated proteoliposomes investigated by quartz crystal microbalance with dissipation (QCM-D)

Aquaporin-based biomimetic membranes have potential as promising membranes for water purification and desalination due to the exceptionally high water permeability and selectivity of aquaporins. However, the design and preparation of such membranes for practical applications are very challenging as the relevant fundamental research is rather limited to provide guidance. Here we investigated the basic characteristics and fusion behaviour of proteoliposomes incorporated with aquaporin Z (AqpZ) on to solid surfaces. This study is expected to offer a better understanding of the properties of proteoliposomes and the potential of the vesicle fusion technique. Our results show that after incorporation of AqpZ, the size and surface charge density of the proteoliposomes change significantly compared with those of liposomes. Although the liposome could easily form a supported lipid bilayer on silica via vesicle rupture, it is much more difficult for proteoliposomes to fuse completely into a bilayer on the same substrate. In addition, the fusion of proteoliposomes is further hindered as the density of incorporated AqpZ is increased, suggesting that proteoliposome with more proteins become more robust. However, both the liposome and proteoliposome have difficulty forming supported lipid bilayers on the surface of a polyelectrolyte layer even though it carries an opposite charge, indicating that the polymer may play an important role in stabilising vesicles. It was also observed that a high concentration of AqpZ could be incorporated into the 1,2-diphytanoyl-. sn-glycero-3-phosphocholine (DPhPC) liposome even though its permeability decreased. These findings may provide some useful guidance for preparing such biomimetic membranes.