Lipid droplet (LD), a multi-functional organelle, is often found to associate with other cellular membranous structures and vary in size in a given cell, which may be related to their functional diversity. Here we established a method to separate LD subpopulations from isolated CHO K2 LDs into three different size categories. The subpopulation with smallest LDs was nearly free of ER and other membranous structures while those with larger LDs contained intact ER. These distinct subpopulations of LDs differed in their protein composition and ability to recruit proteins. This method was also applicable to LDs obtained from other sources, such as Huh7 cells, mouse liver and brown adipose tissue, et al. We developed an in vitro assay requiring only isolated LDs, Coenzyme A, and ATP to drive lipid synthesis. The LD subpopulation nearly depleted of ER was able to incorporate fatty acids into triacylglycerol and phospholipids. Together, our data demonstrate that LDs in a given cell are heterogeneous in size and function, and suggest that LDs are one of cellular lipid synthetic organelles.

中文翻译：

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形态和功能不同的脂质小滴亚群。

脂质小滴（LD）是一种多功能细胞器，通常会与其他细胞膜结构缔合，并且在给定的细胞中大小会发生变化，这可能与其功能多样性有关。在这里，我们建立了一种将LD亚群与孤立的CHO K2 LD分为三个不同大小类别的方法。LD最小的亚群几乎不含ER和其他膜结构，而LD较大的亚群则包含完整的ER。LD的这些不同亚群的蛋白质组成和募集蛋白质的能力不同。该方法也适用于从其他来源获得的LD，例如Huh7细胞，小鼠肝脏和褐色脂肪组织等。我们开发了一种体外测定方法，仅需分离的LD，辅酶A和ATP即可驱动脂质合成。几乎耗尽ER的LD亚群能够将脂肪酸掺入三酰基甘油和磷脂中。在一起，我们的数据表明给定细胞中的LDs在大小和功能上是异质的，并表明LDs是细胞脂质合成细胞器之一。