The Surface of Lipid Droplets Is a Phospholipid Monolayer with a Unique Fatty Acid Composition*

By Kumi Tauchi-Sato, Shintaro Ozeki, Toshiaki Houjou, R. Taguchi, T. Fujimoto. Journal of Biological Chemistry, 2002

704 citations recorded by the source corpus.

We found that caveolin-2 is targeted to the surface of lipid droplets (Fujimoto, T., Kogo, H., Ishiguro, K., Tauchi, K., and Nomura, R. (2001) J. Cell Biol. 152, 1079–1085) and hypothesized that the lipid droplet surface is a kind of membrane. To elucidate the characteristics of the lipid droplet surface, we isolated lipid droplets from HepG2 cells and analyzed them by cryoelectron microscopy and by mass spectrometry. By use of cryoelectron microscopy at the stage temperature of 4.2 K, the lipid droplet surface was observed as a single line without any fixation or staining, indicating the presence of a single layer of phospholipids. This result appeared consistent with the hypothesis that the lipid droplet surface is derived from the cytoplasmic leaflet of the endoplasmic reticulum membrane and may be continuous to it. However, mass spectrometry revealed that the fatty acid composition of phosphatidylcholine and lysophosphatidylcholine in lipid droplets is different from that of the rough endoplasmic reticulum. The ample presence of free cholesterol in lipid droplets also suggests that their surface is differentiated from the bulk endoplasmic reticulum membrane. On the other hand, although caveolin-2β and adipose differentiation-related protein, both localizing in lipid droplets, were enriched in the low density floating fraction, the fatty acid composition of the fraction was distinct from lipid droplets. Collectively, the result indicates that the lipid droplet surface is a hemi-membrane or a phospholipid monolayer containing cholesterol but is compositionally different from the endoplasmic reticulum membrane or the sphingolipid/cholesterol-rich microdomain.

Subfields: Biochemistry, Cell Biology, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/cc8b9fe79c0cd1464e0ba9b8fb8ed27bbe861721

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Citations in the corpus

Lipid Droplet Biogenesis (2014, positive): “These lipids are surrounded by a phospholipid monolayer comprising mostly phosphatidylcholine (PC) and phosphatidylethanolamine (PE) [11].”
Reovirus Outer Capsid Protein μ1 Induces Apoptosis and Associates with Lipid Droplets, Endoplasmic Reticulum, and Mitochondria (2006, background): “They are surrounded by a protein-encrusted monolayer of phospholipid (57), and in most cells the major protein associated with this monolayer is ADRP (38).”
Lipid Droplets And Cellular Lipid Metabolism (2012, background): “No lipid signals are known to target proteins to LDs, but it is possible because the lipid composition of the LD surface differs from that of the ER (19, 69).”
Foamy Macrophages from Tuberculous Patients' Granulomas Constitute a Nutrient-Rich Reservoir for M. tuberculosis Persistence (2008, background): “The foamy aspect of these macrophages is the result of intracellular lipid accumulation within lipid bodies, also called lipid droplets or lipid vacuoles [13,14,15].”
Opinion: Lipid droplets: a unified view of a dynamic organelle (2006, background): “Studies such as these support the hypothesis that LDs form from discrete regions of the endoplasmic reticulum (ER”