Receptor-independent modulation of reconstituted Galphai protein mediated by liposomes

A cationic amphiphile, BC5 (N-pentadecylpiperidin-4-amine), was recently designed and tested for its ability to directly stimulate the activity of recombinant Galpha inhibitory subunits. However, amphiphilic drugs can self-associate and bind to plasma membranes, causing undesired side effects. In this contribution, we report on the incorporation of BC5 in 1,2-dipalmytoyl-sn-glycerophosphocoline (DPPC) liposomes and on the characterization of the mixed DPPC/BC5 systems at various lipid/drug mole ratios by means of dynamic light scattering, differential scanning calorimetry and fluorescence spectroscopy. The myristoylated Galphai subunit (Galpha-mir) was reconstituted in 1,2-dimiristoyl-sn-glycerophosphocoline (DMPC) bilayers, as a mimic of the drug target. We compare several reconstitution procedures in liposomes and present for the first time a complete characterization of a Galpha subunit reconstitution in model membranes in terms of protein activity as a function of the reconstitution protocol. The incorporation of the drug in DPPC bilayers resulted in enhanced Gi-modulating efficiency (evaluated in terms of binding to GTPgammaS (guanosine-5'-(gamma-thio)-triphosphate)). A correlation of the physico-chemical features and binding activity of protein-containing membrane model is proposed.