Display of Recombinant Membrane Receptors on Giant Liposomes: Attempt to Construct a Cell Model with Integrated Membrane Protein Systems

Giant unilamellar vesicles (GUVs), or giant liposomes (GLs), are biochemical compartments enclosed with phospholipid bilayers. The size of GUVs is comparable to that of real cells (~10-100 mum). Thus, GUVs are employed to construct artificial cell models, which are reconstituted from biochemical materials to mimic real cellular functions in a simpler manner for investigation of fundamental mechanisms of living systems. However, transmembrane proteins are difficult to reconstitute on GUV bilayers. In order to obtain GUVs containing transmembrane proteins, giant proteoliposomes, here, we introduce the novel method using membrane fusion between GUVs and recombinant baculovirus (Autographa californica nucleopolyhedrovirus (AcNPV)). It is known that the AcNPV budded virus (BV) displays recombinant membrane proteins on their own envelopes. BVs have fusogenic envelope glycoproteins (gp64) sensitive to acidic pH. Combination of these two features may produce giant proteoliposomes. The fusion properties were observed using fluorescence microscopy to comprehend conditions suitable for reconstitution of proteoliposomes. The display of a 7-fold transmembrane receptor protein (G protein-coupled receptor) on GUVs was also demonstrated using fluoroimmuno microscopic observation.