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Gel-gel phase separation within milk sphingomyelin domains revealed at the nanoscale using atomic force microscopy.

Authors
  • Guyomarc'h, Fanny1
  • Chen, Maohui2
  • Et-Thakafy, Oumaima1
  • Zou, Shan2
  • Lopez, Christelle3
  • 1 STLO, UMR1253, INRA, Agrocampus Ouest, 35000 Rennes, France. , (France)
  • 2 Measurement Science and Standards, National Research Council of Canada, Ottawa, ON K1A 0R6, Canada. , (Canada)
  • 3 STLO, UMR1253, INRA, Agrocampus Ouest, 35000 Rennes, France. Electronic address: [email protected] , (France)
Type
Published Article
Journal
Biochimica et Biophysica Acta (BBA) - Biomembranes
Publisher
Elsevier
Publication Date
May 01, 2017
Volume
1859
Issue
5
Pages
949–958
Identifiers
DOI: 10.1016/j.bbamem.2017.02.010
PMID: 28215536
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

The milk sphingomyelin (MSM) is involved in the formation of ordered lipid domains in the biological milk fat globule membrane (MFGM), where it accounts for about 30%wt of the polar lipids. Moreover, MSM exhibits a large variety in saturated acyl chain lengths (from C16:0 to C24:0-SM) compared to other natural sphingomyelins, which may impact the packing of MSM molecular species in the gel phase domains and the topography of the MFGM. To investigate this, supported lipid bilayers of synthetic sphingomyelins or of MSM-containing mixtures, including a MFGM polar lipid extract, were imaged at temperatures below the Tm of MSM (i.e. <34°C for which MSM is in the gel phase) in hydrated conditions using atomic force microscopy. In all compositions containing MSM, the MSM-rich gel phase domains exhibited lower and upper height levels H, interpreted as two distinct gel phases with ∆H~0.5-1.1nm. Two (lower and upper) gel phases were also found for pure C24:0-SM bilayers or for bilayers of a C16:0-SM/C24:0-SM equimolar mixture, while C16:0-SM bilayers were uniformly flat and less thick than C24:0-SM bilayers. The upper gel phase of MSM-containing bilayers was interpreted as mixed interdigitated C24:0-SM molecules, while the lower gel phase was attributed both to fully interdigitated C24:0-SM molecules and non-interdigitated C16:0-SM molecules. These results show that the composition of natural sphingomyelins, inducing a mismatch between the d18:1 sphingosine and the acyl chains, is important in both the internal organization and the topography of biological membranes, especially that of the MFGM. This organization could be involved in specific biological functions, e.g. the insertion of proteins. Copyright © 2017 Elsevier B.V. All rights reserved.

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