ysics of

S26 Abstracts / Chemistry and Ph

the membrane lipid composition, it must be connectedto the remainder of the protein via a flexible molec-ular hinge that allows transmembrane domain VII toreside in the membrane in the normal mode and exitto the periplasmic side of the membrane in the invertedmode. Therefore, the net charge of the cytoplasmicextra-membrane surface and the charge character of themembrane lipid headgroups determine topology. Finaltopology is established after the N-terminal bundle exitsthe translocon and is therefore primarily determined byprotein–lipid interactions. Although near normal topol-ogy is necessary for uphill transport activity, the effectsof lipids on topology and function are not coupled. Whileproper topology requires balancing of anionic lipids bylipids with net zero charge, only non-bilayer-forminglipids, regardless of their different chemical character,support uphill transport activity.

Acknowledgement: Supported by NIH grantGM20478.

doi:10.1016/j.chemphyslip.2007.06.054

PO 7Effect of G protein lipid modifications on Gprotein membrane interactions

Pablo V. Escriba, Jesus Casas, Rafael Alvarez, VictoriaLlado, Silvia Teres

Molecular CellBiomedicine/Biology-IUNICS/University of theBalearic Islands, Spain

G proteins are in molar excess over G protein-coupledreceptors (GPCR) to enable signal amplification uponagonist binding. Each G protein heterotrimer can bearup to three simultaneous lipid modifications (myristate,palmitate and isoprenyl residues), which contribute toG protein–membrane interactions. In GPCR clusters,the number of G protein lipids inserted in the plasmamembrane could be very high. Because these lipids canregulate the physical properties of membranes, whichin turn regulate the interaction and activity of G pro-teins, we have studied the effect of these lipids on Gprotein–membrane interactions. Thus, we have quan-tified the binding of G proteins to membranes withlamellar and nonlamellar propensity in the presence orabsence of myristate, palmitate or isoprenyl moieties.For this purpose, we used purified G protein monomers(G�), dimers (G��) and trimers (G���) and model

membranes (liposomes) formed with PC and variousconcentrations of PE in the absence or presence ofthe above lipids. G protein binding was determinedby centrifugation analysis, followed by quantitative

Lipids 149S (2007) S23–S49

immunoblotting. We have observed that these lipidsinduced relevant changes in the structural properties ofmembranes and in the interaction of G proteins to mem-branes. The main effects were induced by isoprenylmoieties (geranyl-geraniol), present in the G� protein,which increased nonlamellar (HII) phase propensity(reduction in 12 ◦C in the L-to-HII transition tempera-ture of PE), concomitant with increases in the bindingof G�� and G��� to nonlamellar-prone membranes(increases of about 60 and 120% in the binding of dim-mers and trimers to PC:PE 6:4, mol:mol, membranes,respectively). These results suggest that myristic andpalmitic acid are not as relevant as isoprenyl moieties ofG� subunits in the regulation of the membrane structureand G protein interaction with membranes.

doi:10.1016/j.chemphyslip.2007.06.055

PO 8Changes in structural state of the lipid phaseand cytoskeletal proteins of cellularmembranes under the action of hybridantioxidants

Liudmila Fatkullina 1, Olga Vekshina 1, AlexanderGoloshchapov 1, Elena Burlakova 1, Yuri Kim 2

1 Emanuel Institute of Biochemical Physics, RussianAcademy of Sciences, Russia; 2 Institute of Biophysicsof Cell, Russian Academy of Sciences, Russia

Many membrane pathologies are characterized by oxida-tive stress and significant changes in structural state,lipid composition and functioning of membranes. Theantioxidant (AO) phenozan [�-4-oxy(3,5-ditertbutyl-4-oxyphenyl)potassium propionate] was used at IBCPas the basic compound in the synthesis of hybridAOs—ichfans by addition of choline residue and sat-urated fatty acid “tail” to enhance the anticholinesteraseactivity and to increase the rigidity of membranes respec-tively. Our main aim was to study the effect of AO ina wide range of concentrations on certain structural andfunctional parameters of membranes of erythrocytes andEhrlich ascitic carcinoma cells in vitro. The ionic flowswere measured potentiometrically with recording ofright-angle light scattering; the viscosity of membranes,by EPR-spectroscopy using paramagnetic spin probes.The thermograms of erythrocyte shades were analyzedby differential adiabatic scanning microcalorimetry. Wefound out that the changes in the system of lipid peroxi-

dation homeostasis in membranes result in changes of thestructural state of lipids (microviscosity) and cytoskele-tal proteins, followed by functional shifts of Ca2+–K+

channels and changes of cell reactions. These results