Surface tension-driven sorting of human perilipins on lipid droplets
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Perilipins (PLINs), the most abundant proteins on lipid droplets (LDs), display similar domain organization including amphipathic helices (AH). However, the five human PLINs bind different LDs suggesting different modes of interaction. We established a minimal system whereby artificial LDs covered with defined polar lipids were transiently deformed to promote surface tension. Binding of purified PLIN3 and PLIN4 AH was dependent on tension, even with polar lipids favoring packing defects, and showed an inverse correlation between protein and phospholipid densities on LDs. In contrast, PLIN1 bound readily to LDs fully covered by phospholipids; PLIN2 showed an intermediate behavior. In human adipocytes, PLIN3/4 were found in a soluble pool and relocated to LDs upon stimulation of triglyceride synthesis, whereas PLIN1 and PLIN2 localized to pre-existing LDs, consistent with the huge difference in LD avidity observed in vitro . We conclude that the PLIN repertoire is adapted to handling LDs with different surface properties.
Significance statement
Lipid droplets (LDs) are highly dynamic organelles, whose size and surface properties vary during their life-time and also differ between different tissues. Here, we analyze the mode of binding of human perilipins (PLINs), the most abundant LD proteins, to LDs. We have developed a new reconstitution method, which shows that the purified PLIN family members have very different affinities for LDs, which might explain how they handle LDs of different dynamics in the cell.
