PT  - JOURNAL ARTICLE
AU  - Rasha Khaddaj
AU  - Muriel Mari
AU  - Stéphanie Cottier
AU  - Fulvio Reggiori
AU  - Roger Schneiter
TI  - The surface of lipid droplets constitutes a barrier for endoplasmic reticulum residential integral membrane spanning proteins
AID  - 10.1101/2020.07.28.225391
DP  - 2020 Jan 01
TA  - bioRxiv
PG  - 2020.07.28.225391
4099  - http://biorxiv.org/content/early/2020/10/23/2020.07.28.225391.short
4100  - http://biorxiv.org/content/early/2020/10/23/2020.07.28.225391.full
AB  - Lipid droplets (LDs) are globular subcellular structures that mainly serve to store energy in form of neutral lipids, particularly triacylglycerols and steryl esters. LDs are closely associated with the membrane of the endoplasmic reticulum (ER), and are limited by a monolayer membrane of phospholipids harboring a specific set of proteins. Most of these proteins associate with LDs through either an amphipathic helix or a membrane-embedded hairpin motif. Here we address the question whether integral membrane spanning proteins could localize to the surface of LDs. To test this, we fused perilipin 3 (PLIN3), a mammalian LD-targeted protein, to ER resident proteins, such as Wbp1 (a N-glycosyl transferase complex subunit), Sec61 (a translocon subunit), and Pmt1 (a protein O-mannosyltransferase). The resulting fusion proteins localize to the periphery of LDs in both yeast and mammalian cells. This peripheral LD localization of the fusion proteins, however, is due to redistribution of the ER around LDs, as revealed by bimolecular fluorescence complementation between ER- and LD-localized partners in cells coexpressing the membrane-anchored perilipin. A LD-tethering function of PLIN3-containing membrane proteins was confirmed by fusing PLIN3 to the cytoplasmic domain of OM14, an outer mitochondrial membrane protein. Expression of OM14-PLIN3 resulted in close apposition of mitochondria and LDs. Taken together, these data indicate that the LD surface constitutes a barrier for ER-localized integral membrane spanning proteins.Competing Interest StatementThe authors have declared no competing interest.