Vectorial Budding of Vesicles by Asymmetrical Enzymatic Formation of Ceramide in Giant Liposomes

Sphingomyelin is an abundant component of eukaryotic membranes. A specific enzyme, sphingomyelinase can convert this lipid to ceramide, a central second messenger in cellular signaling for apoptosis (programmed cell death), differentiation, and senescence. We used microinjection and either Hoffman m...

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Bibliographic Details
Published in:Biophysical journal 2000-02, Vol.78 (2), p.830-838
Main Authors: Holopainen, Juha M., Angelova, Miglena I., Kinnunen, Paavo K.J.
Format: Article
Language:English
Subjects:
Bacillus cereus
Boron Compounds - chemistry
Ceramides - chemistry
Fluorescent Dyes
Kinetics
Liposomes - chemistry
Microinjections
Phosphatidylcholines - chemistry
Sphingomyelin Phosphodiesterase - chemistry
Sphingomyelins - chemistry
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Summary:Sphingomyelin is an abundant component of eukaryotic membranes. A specific enzyme, sphingomyelinase can convert this lipid to ceramide, a central second messenger in cellular signaling for apoptosis (programmed cell death), differentiation, and senescence. We used microinjection and either Hoffman modulation contrast or fluorescence microscopy of giant liposomes composed of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC), N-palmitoyl-sphingomyelin (C16:0-SM), and Bodipy-sphingomyelin as a fluorescent tracer (molar ratio 0.75:0.20:0.05, respectively) to observe changes in lipid lateral distribution and membrane morphology upon formation of ceramide. Notably, in addition to rapid domain formation (capping), vectorial budding of vesicles, i.e., endocytosis and shedding, can be induced by the asymmetrical sphingomyelinase-catalyzed generation of ceramide in either the outer or the inner leaflet, respectively, of giant phosphatidylcholine/sphingomyelin liposomes. These results are readily explained by 1) the lateral phase separation of ceramide enriched domains, 2) the area difference between the adjacent monolayers, 3) the negative spontaneous curvature, and 4) the augmented bending rigidity of the ceramide-containing domains, leading to membrane invagination and vesiculation of the bilayer.
ISSN:0006-3495
1542-0086
DOI:10.1016/S0006-3495(00)76640-9