Structural insights into perilipin 3 membrane association in response to diacylglycerol accumulation

Abstract

Lipid droplets (LDs) are dynamic organelles that contain an oil core mainly composed of triglycerides (TAG) that is surrounded by a phospholipid monolayer and LD-associated proteins called perilipins (PLINs). During LD biogenesis, perilipin 3 (PLIN3) is recruited to nascent LDs as they emerge from the endoplasmic reticulum. Here, we analyzed how lipid composition affects PLIN3 recruitment to membrane bilayers and LDs, and the structural changes that occur upon membrane binding. We found the TAG precursors phosphatidic acid and diacylglycerol (DAG) recruit PLIN3 to membrane bilayers and define an expanded PAT domain that preferentially binds DAG enriched membranes. Membrane binding induces a disorder/order transition of alpha helices within the PAT domain and 11-mer repeats, with intramolecular distance measurements consistent with the expanded PAT domain adopting a triangular tertiary structure. In cells, PLIN3 is recruited to DAG enriched ER membranes, and this requires both the PAT domain and 11-mer repeats. This provides molecular details of PLIN3 recruitment to nascent LDs and identifies a function of the PAT domain of PLIN3 in DAG binding.

Surface tension-driven sorting of human perilipins on lipid droplets

“…Finally, we tested the effect of 1,2 dioleoyl-glycerol (DOG) on PLIN3 binding properties. Diacylglycerols are intermediates in LD metabolism and have been shown to promote the binding of PLIN3 to lipid bilayers (15,(37)(38)(39). To quantify the effect of DOG on PLIN3 binding to bilayers, we used the membrane environment-sensitive fluorescent probe NBD (19).…”

“…PLINs contain three main regions: (i) an N-terminal PAT domain, the structure of which is not known but which might contain three helices (15), (ii) a central disordered region, which has been shown to target lipid droplets by providing 3-11 amphipathic helices (AH) that bind to the LD interface (16)(17)(18)(19)(20), and (iii) a C-terminal domain, whose structure has been solved in the case of PLIN3 as forming a 4-helix bundle (21). However, PLINs show variations around this canonical scheme.…”

“…This uneven distribution might result from differences in protein turnover during cell differentiation and/or from intrinsic differences in the physicochemical properties of PLINs. These include the amino-acid composition of their AH regions, the presence of additional hydrophobic regions, or the ability of the PAT region or the 4-helix bundle to undergo conformational changes (14,15,20,27).…”

Perilipin membrane-integration determines lipid droplet heterogeneity in differentiating adipocytes

“…The family defining amphipathic PAT domain and the following 11-mers mediate LD-targeting (Fig. S1A) 32,37,40,41 . The PLINs are all thought to target the LD from the cytoplasm and should therefore mix on the same LD class.…”

“…The family defining N-terminal PAT domain and the following 11mers both contain amphipathic regions, which are critical for LD-targeting (Fig. S1A) 31,36,39,40 . All five perilipin family members are thought to target the LD directly from the cytoplasm and should therefore freely mix on the same LD class.…”