Neutral lipids are packed into dedicated intracellular compartments termed lipid droplets (LDs). LDs are spherical structures delineated by an unusual lipid monolayer and they harbor a specific set of proteins, many of which function in lipid synthesis and lipid turnover. In mammals, LDs are covered by abundant scaffolding proteins, the perilipins (PLIN1–5). LDs in yeast are functionally similar to that of mammalian cells, but they lack the perilipins. We have previously shown that perilipins (PLIN1–3) are properly targeted to LDs when expressed in yeast and that they promote LD formation from the ER membrane enriched in neutral lipids. Here we address the question whether PLIN5 (OXPAT) has a similar function. Both human and murine PLIN5 were properly targeted to yeast LDs, but the protein localized to the cytosol and its steady-state level was reduced when expressed in yeast mutants lacking the capacity to synthesize storage lipids. When expressed in cells containing high levels of neutral lipids within the membrane of the endoplasmatic reticulum, PLIN5 promoted the formation of LDs. Interestingly, PLIN5 was properly targeted to LDs, irrespective of whether these LDs were filled with triacylglycerol or steryl esters, indicating that PLIN5 did not exhibit targeting specificity for a particular subtypes of LDs as was reported for mammalian cells.
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