Phase separation in a ternary DPPC/DOPC/POPC system with reducing hydration

Christopher J Garvey; Saffron J Bryant; Aaron Elbourne; Taavi Hunt; Ben Kent; Martin Kreuzer; Markus Strobl; Roland Steitz; Gary Bryant

doi:10.1016/j.jcis.2023.01.145

Phase separation in a ternary DPPC/DOPC/POPC system with reducing hydration

J Colloid Interface Sci. 2023 May 15:638:719-732. doi: 10.1016/j.jcis.2023.01.145. Epub 2023 Feb 3.

Authors

Christopher J Garvey¹, Saffron J Bryant², Aaron Elbourne², Taavi Hunt², Ben Kent³, Martin Kreuzer⁴, Markus Strobl⁵, Roland Steitz⁶, Gary Bryant⁷

Affiliations

¹ Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München, Lichtenbergstraße 1, 85748 Garching, Germany. Electronic address: christopher.garvey@tum.de.
² School of Science, RMIT University, Melbourne, Australia.
³ Centre for Advanced Macromolecular Design, School of Chemistry, The University of New South Wales, Sydney 2052, Australia; Institute for Soft Matter and Functional Materials, Helmholtz Zentrum Berlin, Hahn-Meitner-Platz 1, Berlin, Germany.
⁴ Institute for Soft Matter and Functional Materials, Helmholtz Zentrum Berlin, Hahn-Meitner-Platz 1, Berlin, Germany; ALBA Synchrotron, Barcelona, Spain.
⁵ Institute for Soft Matter and Functional Materials, Helmholtz Zentrum Berlin, Hahn-Meitner-Platz 1, Berlin, Germany; Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen, Switzerland.
⁶ Institute for Soft Matter and Functional Materials, Helmholtz Zentrum Berlin, Hahn-Meitner-Platz 1, Berlin, Germany.
⁷ School of Science, RMIT University, Melbourne, Australia. Electronic address: gary.bryant@rmit.edu.au.

PMID: 36774881
DOI: 10.1016/j.jcis.2023.01.145

Abstract

The maintenance of plasma membrane structure is vital for the viability of cells. Disruption of this structure can lead to cell death. One important example is the macroscopic phase separation observed during dehydration associated with desiccation and freezing, often leading to loss of permeability and cell death. It has previously been shown that the hybrid lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) can act as a line-active component in ternary lipid systems, inhibiting macroscopic phase separation and stabilising membrane microdomains in lipid vesicles [1]. The domain size is found to decrease with increasing POPC concentration until complete mixing is observed. However, no such studies have been carried out at reduced hydration. To examine if this phase separation is unique to vesicles in excess water, we have conducted studies on several binary and ternary model membrane systems at both reduced hydration ("powder" type samples and oriented membrane stacks) and in excess water (supported lipid bilayers) at 0.2 mol fraction POPC, in the range where microdomain stabilisation is reported. Differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) are used to map phase transition temperatures, with X-ray and neutron scattering providing details of the changes in lipid packing and phase information within these boundaries. Atomic force microscopy (AFM) is used to image bilayers on a substrate in excess water. In all cases, macroscopic phase separation was observed rather than microdomain formation at this molar ratio. Thus POPC does not stabilise microdomains under these conditions, regardless of the type of model membrane, hydration or temperature. Thus we conclude that the driving force for separation under these conditions overcomes any linactant effects of the hybrid lipid.

Keywords: AFM; Domains; Lineactants; Membranes; Neutron scattering; Phase separation; Phospholipids; X-ray Scattering.

MeSH terms

Lipid Bilayers* / chemistry
Phase Transition
Phosphatidylcholines* / chemistry
Water

Substances

1,2-oleoylphosphatidylcholine
Phosphatidylcholines
Lipid Bilayers
Water