Lipid asymmetry in DLPC/DSPC supported lipid bilayers, a combined AFM and fluorescence microscopy study

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A fundamental attribute of cell membranes is transmembrane asymmetry, specifically the formation of ordered phase domains in one leaflet that are compositionally different from the opposing leaflet of the bilayer. Using model membrane systems, many previous studies have demonstrated the formation of ordered phase domains that display complete transmembrane symmetry but there have been few reports on the more biologically relevant asymmetric membrane structures. Here we report on a combined atomic force microscopy (AFM) and fluorescence microscopy study whereby we observe three different states of transmembrane symmetry in phase-separated supported bilayers formed by vesicle fusion. We find that if the ... continued below

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Lin, W; Blanchette, C D; Ratto, T V & Longo, M L June 20, 2005.

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A fundamental attribute of cell membranes is transmembrane asymmetry, specifically the formation of ordered phase domains in one leaflet that are compositionally different from the opposing leaflet of the bilayer. Using model membrane systems, many previous studies have demonstrated the formation of ordered phase domains that display complete transmembrane symmetry but there have been few reports on the more biologically relevant asymmetric membrane structures. Here we report on a combined atomic force microscopy (AFM) and fluorescence microscopy study whereby we observe three different states of transmembrane symmetry in phase-separated supported bilayers formed by vesicle fusion. We find that if the leaflets differ in gel-phase area fraction, then the smaller domains in one leaflet are in registry with the larger domains in the other leaflet and the system is dynamic. In a presumed lipid flip-flop process similar to Ostwald Ripening, the smaller domains in one leaflet erode away while the large domains in the other leaflet grow until complete compositional asymmetry is reached and remains stable. We have quantified this evolution and determined that the lipid flip-flop event happens most frequently at the interface between symmetric and asymmetric DSPC domains. If both leaflets have nearly identical area fraction of gel-phase, gel-phase domains are in registry and are static in comparison to the first state. The stability of these three DSPC domain distributions, the degree of registry observed, and the domain immobility have direct biological significance with regards to maintenance of lipid asymmetry in living cell membranes, communication between inner leaflet and outer leaflet, membrane adhesion, and raft mobility.

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PDF-file: 35 pages; size: 1 Mbytes

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  • Journal Name: Biophysical Journal; Journal Volume: 90; Journal Issue: 1

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  • Report No.: UCRL-JRNL-213252
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 881062
  • Archival Resource Key: ark:/67531/metadc885707

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  • June 20, 2005

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  • Sept. 21, 2016, 2:29 a.m.

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  • Dec. 8, 2016, 8:32 p.m.

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Lin, W; Blanchette, C D; Ratto, T V & Longo, M L. Lipid asymmetry in DLPC/DSPC supported lipid bilayers, a combined AFM and fluorescence microscopy study, article, June 20, 2005; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc885707/: accessed August 17, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.