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Influence of domain size and temperature on structure and elastic fluctuations in complex lipid mixtures by global SAXS data analysis

Nov 27, 2015 | 01:00 PM

Dr. Peter Heftberger, University of Graz, Institute of Molecular Biosciences, Graz, Austria

The spatial organization of lipids in biological membranes plays an important role in diverse cellular processes. Of particular interest are membrane rafts which are considered to enable cellular signal-ing and transport. Such membrane rafts are currently mimicked by liquid ordered (Lo) domains, observed in several lipid-only mixtures. The physical properties of such Lo domains and the coex-isting liquid disordered (Ld) phase are presently not well known. We developed a global small-angle x ray scattering data analysis for multilamellar vesicles that allows to determine membrane structural parameters and bending fluctuations of coexisting lipid domains [1,2]. Different scattering length density profiles were used for modeling the lipid bilayers with increasing details and com-plexity. The technique was applied to different ternary and quarternary phospholipid mixtures of DOPC/DPPC/Chol, DOPC/DSPC/Chol and DOPC/DSPC/POPC/Chol. Of particular interest are four component lipid mixtures entailing the variation of lipid domain size from micron regime down to a few nanometers [3]. We have studied changes of membrane thickness, lateral lipid packing and bending fluctuations for coexisting Lo/Ld phases in the four component lipid mixtures along this domain-size trajectory, including the melting of Lo domains as a function of temperature. Bending fluctuations for coexisting Lo domains were found to be significantly lower than for single Lo phas-es at the boundary of the Lo+Ld regime. In turn, little variation was observed when domains ex-ceeded sizes of 160 nm. Further, we found that the melting of Lo domains as a function of tem-perature is controlled by thickness differences between Lo and Ld and the associated domain line tension. 

[1] P. Heftberger et al., J. Appl. Crystallogr. 47: 173-180 (2013) 

[2] P. Heftberger et al., Biophys. J. 108: 854-862 (2015) 

[3] F.A. Heberle et al., J. Am. Chem. Soc. 135 (18), 6853-6859 (2013)

Time & Location

Nov 27, 2015 | 01:00 PM

Seminar Room T2 (1.4.03)