Lipid droplets (LDs) are the main organelles for lipid storage, and their surfaces contain unique proteins with diverse functions, including those that facilitate the deposition and mobilization of LD lipids. Among organelles, LDs have an unusual structure with an organic, hydrophobic oil phase covered by a phospholipid monolayer. The unique properties of LD monolayer surfaces require proteins to localize to LDs by distinct mechanisms. Here we review the two pathways known to mediate direct LD protein localization: the CYTOLD pathway mediates protein targeting from the cytosol to LDs, and the ERTOLD pathway functions in protein targeting from the endoplasmic reticulum to LDs. We describe the emerging principles for each targeting pathway in animal cells and highlight open questions in the field.

脂滴 (LD) 是储存脂质的主要细胞器，其表面含有具有多种功能的独特蛋白质，包括促进 LD 脂质沉积和动员的蛋白质。在细胞器中，LD 具有不寻常的结构，其有机疏水油相被磷脂单层覆盖。LD 单层表面的独特特性要求蛋白质通过不同的机制定位到 LD。在这里，我们回顾了已知介导直接 LD 蛋白定位的两条途径：CYTOLD 途径介导从胞质溶胶到LD的蛋白质靶向， ERTOLD途径在从内质网到LD的蛋白质靶向中起作用 秒。我们描述了动物细胞中每个靶向通路的新兴原理，并强调了该领域的开放性问题。