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Interaction of the C-Terminal Region of the G Protein with Model Membranes

Francisca Barceló ^*, Jesús Prades ^*, José Antonio Encinar , Sérgio S. Funari , Oliver Vögler ^*, José Manuel González-Ros  and Pablo V. Escribá ^*

^* Laboratory of Molecular and Cellular Biomedicine, Associate Unit of the Instituto de la Grasa (Consejo Superior de Investigaciones Científicas), University of the Balearic Islands, E-07122 Palma de Mallorca, Spain; Instituto de Biología Molecular y Celular, Universidad Miguel Hernández, E-03206 Elche, Spain; and Hamburger Synchrotronstrahlungslabor, D-22603 Hamburg, Germany

Correspondence: Address reprint requests to Francisca Barceló, Depto. de Biología Fundamental, University of the Balearic Islands, E-07122 Palma de Mallorca, Spain. Tel.: 349-7117-3149; Fax: 439-7117-3184; E-mail: francisca.barcelo{at}uib.es.

Heterotrimeric G-proteins interact with membranes. They accumulate around membrane receptors and propagate messages to effectors localized in different cellular compartments. G-protein-lipid interactions regulate G-protein cellular localization and activity. Although we recently found that the Gß dimer drives the interaction of G-proteins with nonlamellar-prone membranes, little is known about the molecular basis of this interaction. Here, we investigated the interaction of the C-terminus of the G₂ protein (P-FN) with model membranes and those of its peptide (P) and farnesyl (FN) moieties alone. X-ray diffraction and differential scanning calorimetry demonstrated that P-FN, segregated into P-FN-poor and -rich domains in phosphatidylethanolamine (PE) and phosphatidylserine (PS) membranes. In PE membranes, FN increased the nonlamellar phase propensity. Fourier transform infrared spectroscopy experiments showed that P and P-FN interact with the polar and interfacial regions of PE and PS bilayers. The binding of P-FN to model membranes is due to the FN group and positively charged amino acids near this lipid. On the other hand, membrane lipids partially altered P-FN structure, in turn increasing the fluidity of PS membranes. These data highlight the relevance of the interaction of the C-terminal region of the G protein with the cell membrane and its effect on membrane structure.