Topography of Lipid Droplet-Associated Proteins: Insights from Freeze-Fracture Replica Immunogold Labeling

Figure 2

Freeze-fracture of lipid droplets. In freeze-fracture, lipid droplets have a unique smooth appearance enabling their unambiguous discrimination from other organelles. Three different types of view of the droplet are seen with this technique. (1) The fracture may travel upwards and over the droplet to give a convex fracture, (2) downwards and under to give a concave fracture, (3) or the droplet may be cross-fractured to give what is essentially a cross-section of the core. In concave fracture, the enveloping outer phospholipid monolayer is seen en face (P face); convex fractures give mirror image (complementary, E face) views. In practice, the three alternative fracture paths often occur in combination; concavely fractured droplets often include a portion of the core from small regions of cross-fracture, and some fractures skip along successive layers of the lipid revealing a multilayered onion-like appearance. Bar: 0.2 μm.