title: Mature lipid droplets are accessible to ER luminal proteins.
abstract: Lipid droplets are found in most organisms where they serve to store energy in the form of neutral lipids. They are formed at the endoplasmic reticulum (ER) membrane where the neutral-lipid-synthesizing enzymes are located. Recent results indicate that lipid droplets remain functionally connected to the ER membrane in yeast and mammalian cells to allow the exchange of both lipids and integral membrane proteins between the two compartments. The precise nature of the interface between the ER membrane and lipid droplets, however, is still ill-defined. Here, we probe the topology of lipid droplet biogenesis by artificially targeting proteins that have high affinity for lipid droplets to inside the luminal compartment of the ER. Unexpectedly, these proteins still localize to lipid droplets in both yeast and mammalian cells, indicating that lipid droplets are accessible from within the ER lumen. These data are consistent with a model in which lipid droplets form a specialized domain in the ER membrane that is accessible from both the cytosolic and the ER luminal side.
authors: University of Fribourg, Department of Biology, Fribourg 1700, Switzerland.
authors: Shirish
authors: S
authors: Mishra
authors: University of Fribourg, Department of Biology, Fribourg 1700, Switzerland.
authors: Rasha
authors: R
authors: Khaddaj
authors: University of Fribourg, Department of Biology, Fribourg 1700, Switzerland.
authors: Stéphanie
authors: S
authors: Cottier
authors: University of Fribourg, Department of Biology, Fribourg 1700, Switzerland.
authors: Vendula
authors: V
authors: Stradalova
authors: University of Fribourg, Department of Biology, Fribourg 1700, Switzerland.
authors: Claire
authors: C
authors: Jacob
authors: University of Fribourg, Department of Biology, Fribourg 1700, Switzerland roger.schneiter@unifr.ch.
authors: Roger
authors: 0000-0002-9102-8396
authors: R
authors: Schneiter
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D019286:Endopeptidase K / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000648:ultrastructure; D017930:Genes, Reporter; D006031:Glycosylation; D049452:Green Fluorescent Proteins / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism / Q000648:ultrastructure; D066292:Lipid Droplets / Q000378:metabolism* / Q000648:ultrastructure; D008322:Mammals / Q000378:metabolism; D008954:Models, Biological; D000070778:Perilipin-1 / Q000378:metabolism; D021382:Protein Sorting Signals; D011506:Proteins / Q000378:metabolism*; D059748:Proteolysis; D012441:Saccharomyces cerevisiae / Q000378:metabolism
chemical_list: D015415:Biomarkers; D000070778:Perilipin-1; D021382:Protein Sorting Signals; D011506:Proteins; D049452:Green Fluorescent Proteins; D019286:Endopeptidase K
keywords: Endoplasmic reticulum; Lipid storage; Membrane topology; Perilipins; Triacylglycerol