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Title: Joint small-angle X-ray and neutron scattering data analysis of asymmetric lipid vesicles

Abstract

Low- and high-resolution models describing the internal transbilayer structure of asymmetric lipid vesicles have been developed. These models can be used for the joint analysis of small-angle neutron and X-ray scattering data. The models describe the underlying scattering length density/electron density profiles either in terms of slabs or through the so-called scattering density profile, previously applied to symmetric lipid vesicles. Both models yield structural details of asymmetric membranes, such as the individual area per lipid, and the hydrocarbon thickness of the inner and outer bilayer leaflets. The scattering density profile model, however, comes at a cost of increased computational effort but results in greater structural resolution, showing a slightly lower packing of lipids in the outer bilayer leaflet of ~120 nm diameter palmitoyloleoyl phosphatidylcholine (POPC) vesicles, compared to the inner leaflet. Here, analysis of asymmetric dipalmitoyl phosphatidylcholine/POPC vesicles did not reveal evidence of transbilayer coupling between the inner and outer leaflets at 323 K, i.e.above the melting transition temperature of the two lipids.

Authors:
 [1];  [2];  [1];  [3];  [4]; ORCiD logo [1]
  1. Univ. of Graz (Austria); BioTechMed-Graz, Graz (Austria)
  2. Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Univ. of Graz (Austria); BioTechMed-Graz (Austria)
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1351774
Grant/Contract Number:
AC05-00OR22725
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Applied Crystallography (Online)
Additional Journal Information:
Journal Name: Journal of Applied Crystallography (Online); Journal Volume: 50; Journal Issue: 2; Journal ID: ISSN 1600-5767
Publisher:
International Union of Crystallography
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES

Citation Formats

Eicher, Barbara, Heberle, Frederick A., Marquardt, Drew T., Rechberger, Gerald N., Katsaras, John, and Pabst, Georg. Joint small-angle X-ray and neutron scattering data analysis of asymmetric lipid vesicles. United States: N. p., 2017. Web. doi:10.1107/S1600576717000656.
Eicher, Barbara, Heberle, Frederick A., Marquardt, Drew T., Rechberger, Gerald N., Katsaras, John, & Pabst, Georg. Joint small-angle X-ray and neutron scattering data analysis of asymmetric lipid vesicles. United States. doi:10.1107/S1600576717000656.
Eicher, Barbara, Heberle, Frederick A., Marquardt, Drew T., Rechberger, Gerald N., Katsaras, John, and Pabst, Georg. Tue . "Joint small-angle X-ray and neutron scattering data analysis of asymmetric lipid vesicles". United States. doi:10.1107/S1600576717000656. https://www.osti.gov/servlets/purl/1351774.
@article{osti_1351774,
title = {Joint small-angle X-ray and neutron scattering data analysis of asymmetric lipid vesicles},
author = {Eicher, Barbara and Heberle, Frederick A. and Marquardt, Drew T. and Rechberger, Gerald N. and Katsaras, John and Pabst, Georg},
abstractNote = {Low- and high-resolution models describing the internal transbilayer structure of asymmetric lipid vesicles have been developed. These models can be used for the joint analysis of small-angle neutron and X-ray scattering data. The models describe the underlying scattering length density/electron density profiles either in terms of slabs or through the so-called scattering density profile, previously applied to symmetric lipid vesicles. Both models yield structural details of asymmetric membranes, such as the individual area per lipid, and the hydrocarbon thickness of the inner and outer bilayer leaflets. The scattering density profile model, however, comes at a cost of increased computational effort but results in greater structural resolution, showing a slightly lower packing of lipids in the outer bilayer leaflet of ~120 nm diameter palmitoyloleoyl phosphatidylcholine (POPC) vesicles, compared to the inner leaflet. Here, analysis of asymmetric dipalmitoyl phosphatidylcholine/POPC vesicles did not reveal evidence of transbilayer coupling between the inner and outer leaflets at 323 K,i.e.above the melting transition temperature of the two lipids.},
doi = {10.1107/S1600576717000656},
journal = {Journal of Applied Crystallography (Online)},
number = 2,
volume = 50,
place = {United States},
year = {Tue Feb 28 00:00:00 EST 2017},
month = {Tue Feb 28 00:00:00 EST 2017}
}

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  • Some of our recent work has resulted in the detailed structures of fully hydrated, fluid phase phosphatidylcholine (PC) and phosphatidylglycerol (PG) bilayers. These structures were obtained from the joint refinement of small-angle neutron and X-ray data using the scattering density profile (SDP) models developed by Ku erka et al. (Ku erka et al. 2012; Ku erka et al. 2008). In this review, we first discuss models for the standalone analysis of neutron or X-ray scattering data from bilayers, and assess the strengths and weaknesses inherent in these models. In particular, it is recognized that standalone data do not contain enoughmore » information to fully resolve the structure of inherently disordered fluid bilayers, and therefore may not provide a robust determination of bilayer structural parameters, including the much sought after area per lipid. We then discuss the development of matter density-based models (including the SDP model) that allow for the joint refinement of different contrast neutron and X-ray data sets, as well as the implementation of local volume conservation in the unit cell (i.e., ideal packing). Such models provide natural definitions of bilayer thicknesses (most importantly the hydrophobic and Luzzati thicknesses) in terms of Gibbs dividing surfaces, and thus allow for the robust determination of lipid areas through equivalent slab relationships between bilayer thickness and lipid volume. In the final section of this review, we discuss some of the significant findings/features pertaining to structures of PC and PG bilayers as determined from SDP model analyses.« less
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