Biophysical Society Thematic Meeting| Padova 2019

Quantitative Aspects of Membrane Fusion and Fission

Poster Abstracts

44-POS Board 44 INTRINSIC CURVATURE DIFFERENCE DRIVEN DEMIXING OF MEMBRANE LIPID COMPONENTS Radha Ranganathan 1 ; Miroslav Peric 1 ; 1 California State University Northridge, Physics, Northridge, California, USA Stress due to intrinsic curvature difference between lipids in binary lipid membranes is a possible mechanism for membrane fission. With this as a founding hypothesis, we examine the effect of incorporating the inverse-cone shaped oxidized phospholipid, 1-palmitoyl-2-glutaryl- sn -glycero- 3-phosphocholine (PGPC) in each of DPPC, POPC, and DOPC bilayers. The intrinsic curvatures of these bilayer lipids differ from each other due to their state of saturation. Laurdan fluorescence spectra were evaluated by a relatively new approach of fitting the spectra to lognormal functions. In the pure PC bilayers, Laurdan emits from the unrelaxed state at 432 nm and from the charge transfer state at 445nm in the DPPC gel phase and also in DOPC and POPC at T < 20°C. At higher temperatures in the liquid phase the emissions are at 490 and 445 nm at about equal levels. More significantly PGPC causes the 432 nm peak to reappear in the liquid phase. The areas of the emission peaks were evaluated. The 432 nm peak from the unrelaxed state indicates the presence of tighter packed lower polarity regions that can result from interlipid hydrogen bonding. A possible model is that PGPC and bilayer PC do not mix uniformly because of shape differences. Inter PGPC hydrogen bonding via its polar terminal and ester groups promotes component segregation and stabilizes the unrelaxed state of Laurdan (432 nm emission). With further increase in PGPC concentration, curvature mismatch between domains increases stress and PGPC separates as micelles (confirmed by DLS) and the Laurdan spectrum appears similar to that in the pure bilayer PC, indicative that Laurdan mostly remains in the pure PC bilayer. Differences in the spectral emission characteristics between the mixing behaviors of PGPC with the different bilayer PCs support the model of intrinsic curvature stress driven separation of lipid components.

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