A non-ionic vesicle lipid enhances mastoparan-stimulated GTPase activity of heterotrimeric G-proteins.

Isolated heterotrimeric G-proteins exhibit full biological activity when reconstituted into liposomes. Here, we investigated the non-ionic surfactant macrogol-260-cetylstearylether (TA 6) as an efficient vehicle for the reconstitution of G-proteins. Reconstitution efficiency of G-proteins was recorded by GTP gamma S-binding. Their biological potency was measured as basal and mastoparan-stimulated GTPase-activity. G-proteins were fully active when associated with liposomes. On the other hand, G-proteins solubilized by TA 6 micelles or reconstituted into pure TA 6 vesicles exhibited impaired biological activity. However, vesicles containing different ratios of azolectin and non-ionic TA 6 showed about 50% higher reconstitution efficiency as compared to pure liposomes. In addition, basal and mastoparan-stimulated GTPase-activity in vesicles containing an axolectin/TA 6 ratio of 3:1 were 2.7 and 9.1 fold higher than in pure liposomes, respectively. These data emphasize that the composition of the lipid membranous environment significantly influences G-protein activity.