Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, 37673 Pohang, Korea.
Department of Life Sciences, Pohang University of Science and Technology, 37673 Pohang, Korea.
Proc Natl Acad Sci U S A. 2020 Sep 15;117(37):23131-23139. doi: 10.1073/pnas.2005600117. Epub 2020 Aug 31.
Lipid droplets (LDs) are intracellular organelles found in a wide range of organisms and play important roles in stress tolerance. During nitrogen (N) starvation, stores large amounts of triacylglycerols (TAGs) inside LDs. When N is resupplied, the LDs disappear and the TAGs are degraded, presumably providing carbon and energy for regrowth. The mechanism by which cells degrade LDs is poorly understood. Here, we isolated a mutant (, Delayed in TAG Hydrolysis 1) in which TAG degradation during recovery from N starvation was compromised. Consequently, the mutant grew poorly compared to its parental line during N recovery. Two additional independent loss-of-function mutants ( and ) also exhibited delayed TAG remobilization. transcript levels increased sevenfold upon N resupply, and DTH1 protein was localized to LDs. DTH1 contains a putative lipid-binding domain (DTH1) with alpha helices predicted to be structurally similar to those in apolipoproteins E and A-I. Recombinant DTH1 bound specifically to phosphatidylethanolamine (PE), a major phospholipid coating the LD surface. Overexpression of DTH1 in phenocopied the mutant's defective TAG degradation, suggesting that the function of DTH1 depends on its ability to bind PE. Together, our results demonstrate that the lipid-binding DTH1 plays an essential role in LD degradation and provide insight into the molecular mechanism of protein anchorage to LDs at the LD surface in photosynthetic cells.
脂滴（LDs）是广泛存在于各种生物中的细胞内细胞器，在应激耐受中发挥重要作用。在氮（N）饥饿期间，LDs 内部储存大量三酰基甘油（TAGs）。当 N 得到补充时，LDs 消失，TAGs 被降解，可能为细胞再生提供碳和能量。细胞降解 LDs 的机制尚不清楚。在这里，我们分离到一个突变体（，延迟 TAG 水解 1），其在从 N 饥饿恢复期间的 TAG 降解受到损害。因此，与亲本系相比，突变体在 N 恢复期间生长不良。另外两个独立的功能丧失突变体（和）也表现出延迟的 TAG 再动员。DTH1 转录本水平在 N 再供应时增加了七倍，并且 DTH1 蛋白定位于 LDs。DTH1 含有一个假定的脂质结合结构域（DTH1），其α螺旋结构预测与载脂蛋白 E 和 A-I 中的相似。重组 DTH1 特异性结合磷脂酰乙醇胺（PE），PE 是涂覆 LD 表面的主要磷脂。DTH1 在中的过表达模拟了突变体的缺陷性 TAG 降解，表明 DTH1 的功能取决于其与 PE 结合的能力。总之，我们的结果表明，脂质结合蛋白 DTH1 在 LD 降解中发挥着重要作用，并为蛋白质在光合细胞中 LD 表面的 LD 锚定的分子机制提供了新的见解。
