Lo/Ld phase coexistence modulation induced by GM1.
Lipid rafts are assumed to undergo biologically important size-modulations from nanorafts to microrafts. Due to the complexity of cellular membranes, model systems become important tools, especially for the investigation of the factors affecting "raft-like" Lo domain size and the search for Lo nanodomains as precursors in Lo microdomain formation. Because lipid compositional change is the primary mechanism by which a cell can alter membrane phase behavior, we studied the effect of the ganglioside GM1 concentration on the Lo/Ld lateral phase separation in PC/SM/Chol/GM1 bilayers. GM1 above 1mol % abolishes the formation of the micrometer-scale Lo domains observed in GUVs. However, the apparently homogeneous phase observed in optical microscopy corresponds in fact, within a certain temperature range, to a Lo/Ld lateral phase separation taking place below the optical resolution. This nanoscale phase separation is revealed by fluorescence spectroscopy, including C12NBD-PC self-quenching and Laurdan GP measurements, and is supported by Gaussian spectral decomposition analysis. The temperature of formation of nanoscale Lo phase domains over an Ld phase is determined, and is shifted to higher values when the GM1 content increases. A "morphological" phase diagram could be made, and it displays three regions corresponding respectively to Lo/Ld micrometric phase separation, Lo/Ld nanometric phase separation, and a homogeneous Ld phase. We therefore show that a lipid only-based mechanism is able to control the existence and the sizes of phase-separated membrane domains. GM1 could act on the line tension, "arresting" domain growth and thereby stabilizing Lo nanodomains.
UPMC Univ. Paris 06, UFR 925 Physics Department, Paris, France; Laboratoire Matière et Systèmes Complexes (MSC), UMR 7057 CNRS and Université Paris Diderot-Paris 7, Paris, France. Electronic address: nicolas.puff@univ-paris-diderot.fr.
Nicolas
N
Puff
Laboratoire Matière et Systèmes Complexes (MSC), UMR 7057 CNRS and Université Paris Diderot-Paris 7, Paris, France.
Chiho
C
Watanabe
Laboratoire Matière et Systèmes Complexes (MSC), UMR 7057 CNRS and Université Paris Diderot-Paris 7, Paris, France.
Michel
M
Seigneuret
UPMC Univ. Paris 06, UFR 925 Physics Department, Paris, France; Laboratoire Matière et Systèmes Complexes (MSC), UMR 7057 CNRS and Université Paris Diderot-Paris 7, Paris, France.
Miglena I
MI
Angelova
Institute of Biophysics and Biomedical Engineering, Bulgarian Academy of Sciences, Sofia, Bulgaria.
Galya
G
Staneva
D015081:2-Naphthylamine / Q000031:analogs & derivatives; D002462:Cell Membrane / Q000737:chemistry*; D005456:Fluorescent Dyes; D005677:G(M1) Ganglioside / Q000737:chemistry*; D007848:Laurates; D008051:Lipid Bilayers / Q000737:chemistry*; D021962:Membrane Microdomains / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D053835:Unilamellar Liposomes / Q000737:chemistry*
D005456:Fluorescent Dyes; D007848:Laurates; D008051:Lipid Bilayers; D053835:Unilamellar Liposomes; D005677:G(M1) Ganglioside; D015081:2-Naphthylamine; C065580:laurdan
GM1; GUV; L(o)/L(d) phase coexistence; Laurdan; Microdomain; Nanoscale domain