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2 Abstracts / Chemistry and Ph

f biological functions and technical applications. They are mostlyreated on a rather empirical basis because unlike simpler, binary

ixtures, their detailed quantitative treatment with physico-hemical models remains a serious challenge. I will present twoxamples where a quantitative treatment has provided importantnsight. The first example shows how the phenomena of detergent-esistant membranes and detergent-induced domain formationan be understood by modelling interactions in systems comprisingsurfactant and multiple lipids. The second example addresses the

ungicidal, membrane-permeabilizing properties of Bacillus sub-ilis QST713 lipopeptides, a synergistic multi-component mixturef surfactin-, iturin-, and fengycin-type peptides.

oi:10.1016/j.chemphyslip.2010.05.006

L4

on-bilayer intermediates and pathways of membrane remod-ling

adim A. Frolov 1,2,3

Unidad de Biofisica (Centro Mixto CSIC-UPV/EHU), Leioa 48940, SpainDepartamento de Biochimica y Biología Molecular, Universidad delais Vasco, Leioa 48940, SpainIKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain

ellular membrane systems are extremely dynamic forma-ions constantly changing their topology, so specialized protein

achineries have been evolved to conduct membrane fusion andssion. The deep involvement of highly curved membrane inter-ediates in these processes is now well established, yet theechanistic pathways of their creation remain illusive. We demon-

trate that sophisticated cooperation between proteins and lipidss required to compromise, albeit locally, the integrity of the lipidilayer, thus triggering formation of non-bilayer intermediates. Therotein complexes, such as those formed by influenza hemagglu-inin or dynamin, enforce high curvature of the fusion/fission sites.he curvature stresses in closely apposed membrane monolayersramatically alter the lipid packing leading to localized membraneerger. Lipid composition and geometrical arrangement of the

usion or fission sites, defined by the corresponding protein com-lexes, determine the energy barrier for the repacking of lipids

nto a non-bilayer structure. We reveal the critical role of theoordinated hydrophobic insertion, generally featured by theserotein complexes, in minimizing the energy barrier and ensuringhe leak-less membrane remodeling. We finally analyze how thepatio-temporal organization of the dynamin machinery is opti-ized for the task of membrane fission.

oi:10.1016/j.chemphyslip.2010.05.007

L5

afts and ceramides: biophysical perspective of biologically rel-vant membrane domains

runo Castro 1, Sandra Pinto 1, Liana Silva 2, Manuel Prieto 1,∗

CQFM – Centro de Química-Física Molecular and IN – Institute ofanoscience and Nanotechnology, IST, 1049-001 Lisboa, PortugaliMed.UL – Research Institute for Medicines and Pharmaceutical Sci-nces, FFUL, Av. Prof. Gama Pinto, 1649-003 Lisboa, Portugal

ipid rafts are membrane domains involved in several biological

unctions. Ceramide (Cer), a minor lipid of the plasma membrane,s generated (response to a stress signal) by hydrolysis of sphin-omyelin (SM) in the rafts, and induces strong alterations in theroperties of the membranes leading to the activation of signal-

f Lipids 163S (2010) S1–S18

ing cascades. To fully disclose Cer effects on raft membranes astepwise fluorescence methodology was developed. In this way,it was necessary to first identify the effects of different acyl chainCer in single component fluid membranes before evaluating com-plex mixtures resembling the plasma membrane. Our methodologyallowed identifying the formation of Cer-rigid gel domains in binarylipidic systems, and their characteristics are dependent on the spe-cific Cer structure. The additional presence of SM in these mixturespromotes the formation of another type of gel phase, Cer/SM-enriched, that is abolished when Cholesterol (Chol) is present athigh amounts. Chol plays a further role in this process by modulat-ing Cer biophysical outcome: it increases the miscibility of Cer inthe fluid phase, and Cer-enriched domains are only formed whenChol levels are low. Additionally, the Chol in the lipid rafts is a keyfactor for the regulation of sphingomyelinase activity and thus, onthe amount of Cer that is generated by the hydrolysis of SM. Alto-gether, it can be concluded that membrane lipid composition andproperties determines sphingomyelinase activity and Cer-inducedalterations of membrane biophysical properties.

Acknowledgements

FCT (Portugal) is acknowledged for project funding(POCTI/QUI/68151/2006) and research grants BD/46296/2008(SP), BD/36635/2007 (BC).

doi:10.1016/j.chemphyslip.2010.05.008

SO1

The effect of ceramide N-acyl chain methyl-branching onsphingomyelin-enriched domains—thermal stability and steroldisplacement

Terhi Maula 1,∗, Bakarne Urzelai 2, J. Peter Slotte 1

1 Biochemistry, Department of Biosciences, Åbo Akademi University,Turku, Finland2 Department of Biochemistry and Molecular Biology, Faculty of Sci-ences and Technology, the University of the Basque Country, Bilbao,Bizkaia, the Basque Country, Spain

Long-chain, saturated ceramides are known to thermally stabi-lize sphingomyelin-enriched domains in bilayers. Ceramides alsodisplace cholesterol from such SM-domains. Modification of theceramide long-chain base at the head group region does not appearto alter the ability of ceramides to stabilize bilayers and displacesterol (Megha et al., 2007). However, altering the length of theN-linked acyl chain influences the ability of ceramides to affectthe thermal stability of SM-domains (Nybond et al., 2005). Inthis work, we have studied the effect of N-acyl chain methyl-branching on the ability of ceramide to stabilize SM-domains andto displace sterol from such domains. Thermal stabilization wasdetermined from the quenching susceptibility of trans-parinaricacid, which prefers ordered and gel-phase domains, whereas steroldisplacement was determined from the quenching of cholesta-trienol in SM-sterol domains. When the effects of the ceramideanalogs on SM-enriched domains were studied, it was found thatthose analogs which stabilized SM-domains also were able to dis-place sterol from the domains. Ceramides with methyl-branchingat position C15 or C16 stabilized SM-rich domains, although not asefficiently as palmitoyl-ceramide. These ceramides also displaced

sterol from the SM-domains. A ceramide with methyl-branchingat C10, and phytanoyl-ceramide (with methyl-branches at C3, C7,C11 and C15), both failed to stabilize SM-domains and to displacesterol from them. We conclude that the positions of the methyl-branching, and therefore the lateral packing of ceramide, markedly