Reconstitution and Microscopic Observation of G Protein Subunits on Giant Liposomes: Attempt to Construct a Cell Model with Functional Membrane Protein Components

Giant liposomes are cell-size artificial vesicles with phospholipid bilayers. Here, in order to obtain giant liposomes containing membrane proteins (giant proteoliposomes), we have introduced a novel procedure using membrane fusion phenomena between liposomes and recombinant baculovirus. We tried to thereby reconstitute heterotrimeric guanine nucleotide-binding protein (G protein) that is a peripheral membrane protein, i.e., Gs protein consisting of alpha_s, szlig and gamma, in giant proteoliposomes. Western blot analysis showed that expression of these proteins on both recombinant baculovirus budded virus envelopes and liposomes fused with the recombinant virus. Moreover, by using laser-scanning fluorescence microscopy, we observed that GTP analogues specifically bound to Gs alpha subunits on giant liposomes. These results indicate that using the present procedure giant proteoliposomes are prepared with successfully reconstituted G proteins.