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Biophys J. 2018 Jan 9;114(1):146-157. doi: 10.1016/j.bpj.2017.11.009.

Intrinsic Curvature-Mediated Transbilayer Coupling in Asymmetric Lipid Vesicles.

Author information

1
University of Graz, Institute of Molecular Biosciences, Biophysics Division, NAWI Graz; BioTechMed-Graz, Graz, Austria.
2
Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, Canada.
3
Shull Wollan Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee; The Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville, Tennessee; Biology and Soft Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee.
4
Institute for Electron Microscopy and Nanoanalysis and Center for Electron Microscopy, Graz University of Technology, NAWI Graz.
5
Institute of Molecular Biosciences, University of Graz, Graz, Austria; Omics Center Graz, BioTechMed-Graz, Graz, Austria.
6
Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), Forschungszentrum Jülich GmbH, Garching, Germany; Forschungszentrum Jülich GmbH, Institut für Festkörperforschung, Jülich Center for Neutron Science at FRM II Outstation, Garching, Germany.
7
University of Graz, Institute of Molecular Biosciences, Biophysics Division, NAWI Graz; BioTechMed-Graz, Graz, Austria. Electronic address: georg.pabst@uni-graz.at.

Abstract

We measured the effect of intrinsic lipid curvature, J0, on structural properties of asymmetric vesicles made of palmitoyl-oleoyl-phosphatidylethanolamine (POPE; J0<0) and palmitoyl-oleoyl-phosphatidylcholine (POPC; J0∼0). Electron microscopy and dynamic light scattering were used to determine vesicle size and morphology, and x-ray and neutron scattering, combined with calorimetric experiments and solution NMR, yielded insights into leaflet-specific lipid packing and melting processes. Below the lipid melting temperature we observed strong interleaflet coupling in asymmetric vesicles with POPE inner bilayer leaflets and outer leaflets enriched in POPC. This lipid arrangement manifested itself by lipids melting cooperatively in both leaflets, and a rearrangement of lipid packing in both monolayers. On the other hand, no coupling was observed in vesicles with POPC inner bilayer leaflets and outer leaflets enriched in POPE. In this case, the leaflets melted independently and did not affect each other's acyl chain packing. Furthermore, we found no evidence for transbilayer structural coupling above the melting temperature of either sample preparation. Our results are consistent with the energetically preferred location of POPE residing in the inner leaflet, where it also resides in natural membranes, most likely causing the coupling of both leaflets. The loss of this coupling in the fluid bilayers is most likely the result of entropic contributions.

PMID:
29320681
PMCID:
PMC5773765
[Available on 2019-01-09]
DOI:
10.1016/j.bpj.2017.11.009
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