The surface of lipid droplets is a phospholipid monolayer with a unique fatty acid composition
The surface of lipid droplets is a phospholipid monolayer with a unique fatty acid composition
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DOI：
10.1074/jbc.m207712200
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发表时间：
2002-11-15
影响因子：
4.8
通讯作者：
Fujimoto, T
中科院分区：
文献类型：
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作者：
Tauchi-Sato, K;Ozeki, S;Fujimoto, T
我们发现小窝蛋白-2靶向于脂滴的表面（Fujimoto，T.，Kogo，H.，Ishiguro，K.，Tauchi，K.，和Nomura，R.（2001）J.CellBiol.152，1079 -1085），并假设脂滴表面是一种膜。为了阐明脂滴表面的特征，我们从HepG 2细胞中分离脂滴，并通过冷冻电子显微镜和质谱法对其进行分析。通过在4.2 K的载物台温度下使用冷冻电子显微镜，观察到脂滴表面为没有任何固定或染色的单线，表明存在单层磷脂。这一结果与脂滴表面来源于内质网膜的胞质小叶并可能与之连续的假设一致，但质谱分析表明脂滴中磷脂酰胆碱和溶血磷脂酰胆碱的脂肪酸组成与粗面内质网不同。脂滴中大量游离胆固醇的存在也表明它们的表面与体内质网不同。膜的另一方面，虽然小窝蛋白-2 β和脂肪分化相关蛋白，都定位在脂滴，富集在低密度漂浮馏分，馏分的脂肪酸组成是不同于脂滴。总的来说，结果表明，脂滴表面是一个半膜或磷脂单层含有胆固醇，但在组成上不同于内质网膜或鞘脂/胆固醇丰富的微域。
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-2beta 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.