Structural diversity of sphingomyelin microdomains.
In cells plasma membrane, sphingomyelin (SM) plays a key role in the formation of a category of lipid microdomains enriched in cholesterol (Chl) often referred to as rafts. Atomic force microscopy (AFM) was used to analyze the mesoscopic topography of enriched SM microdomains in supported bilayers made of SM/dioleoylphosphatidylcholine (SM/DOPC) and SM/palmitoyl-oleoyl-phosphatidylcholine (SM/POPC) equimolar mixtures, in buffer, at room temperature. Gel-fluid phase separation occurs in both SM/DOPC and SM/POPC bilayers. The gel phase SM-enriched microdomains adopt a variety of size, shape and mesoscopic structure, from homogeneous flat domains of a few hundreds of nanometer in diameter to domains of several micrometers made of closely packed globular structures. Gel-gel phase separation in SM domains is also observed which gives rise to different structures for the diunsaturated and the mixed-saturated PC species. These differences could also extend to the interactions with Chl. This suggests that studies on rafts formation commonly performed using SM/DOPC mixture as a model should also include the physiologically more relevant POPC species.
Giocondi
Marie-Cécile
MC
Centre de Biochimie Structurale, CNRS UMR 5048-Université Montpellier I, INSERM UMR 554, 29 rue de Navacelles, Montpellier Cedex 34090, France.
Boichot
Sylvie
S
Plénat
Thomas
T
Le Grimellec
C Christian
CC
D008051:Lipid Bilayers / Q000737:chemistry; D018625:Microscopy, Atomic Force; D010713:Phosphatidylcholines / Q000737:chemistry; D013109:Sphingomyelins / Q000737:chemistry*
D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D013109:Sphingomyelins; C028694:1-palmitoyl-2-oleoylphosphatidylcholine