Abstract：
Seipin, a crucial protein for cellular lipid droplet (LD) assembly, oligomerizes at the interface between the endoplasmic reticulum and LDs to facilitate neutral lipid packaging. Using proximity labeling, we identified four proteins-Ldo45, Ldo16, Tgl4, and Pln1-that are recruited to the vicinity of yeast seipin, the Sei1-Ldb16 complex, exclusively when seipin function is intact, hence termed seipin accessory factors. Localization studies identified Tgl4 at the endoplasmic reticulum-LD contact site, in contrast to Ldo45, Ldo16, and Pln1 at the LD surface. Cells with compromised seipin function resulted in uneven distribution of these proteins with aberrant LDs, supporting a central role of seipin in orchestrating their association with the LD. Overexpression of any seipin accessory factor causes LD aggregation and affects a subset of LD protein distribution, highlighting the importance of their stoichiometry. Although single factor mutations show minor LD morphology changes, the combined mutations have additive effects. Lastly, we present evidence that seipin accessory factors assemble and interact with seipin in the absence of neutral lipids and undergo dynamical rearrangements during LD formation induction, with Ldo45 acting as a central hub recruiting other factors to interact with the seipin complex.
摘要：
Seipin,细胞脂滴（LD）组装的关键蛋白质，在内质网（ER）和LD之间的界面处低聚化，以促进中性脂质包装。使用邻近标签，我们确定了四种蛋白质-Ldo45，Ldo16，Tgl4和Pln1-它们被招募到酵母seipin附近，Sei1-Ldb16复合体，仅当seipin功能完好无损时，因此称为seipin附属因素。本地化研究在ER-LD接触部位识别Tgl4，与LD表面的Ldo45、Ldo16和Pln1相反。具有受损seipin功能的细胞导致这些具有异常LD的蛋白质的不均匀分布，支持seipin在协调他们与LD的联系方面的核心作用。任何seipin辅助因子的过表达都会导致LD聚集并影响LD蛋白分布的一个子集，强调其化学计量的重要性。虽然单因子突变显示微小的LD形态变化，组合突变具有累加效应。最后,我们提供证据表明，在缺乏中性脂质的情况下，seipin辅助因子与seipin组装并相互作用，并在LD形成诱导过程中发生动态重排，Ldo45充当中央枢纽，招募其他因素与seipin复合体相互作用。
