Nanoscale Interactions of Lipids and Proteins in Live Cell Membranes Revealed by STED Nanoscopy

The plasma membrane seems to be dynamically structured in regions of different composition and function. However, the spatial and temporal scale of the respective membrane structure is not directly accessible by the diffraction limited resolution of conventional far-field optical microscopes. We report the detection of the membrane heterogeneities in nanosized areas in the plasma membrane of living cells using the superior spatial resolution of stimulated emission depletion (STED) far-field nanoscopy. By combining a (tunable) resolution of down to 30 nm with tools such as fluorescence correlation spectroscopy (FCS), we obtain new details of molecular membrane dynamics. Sphingolipids are transiently (∼ 10 ms) trapped on the nanoscale in cholesterol-mediated molecular complexes, while glycero-phospho-lipids diffuse freely. The results are compared to STED experiments on model membranes, which highlight that the nanoscale trapping in cells is not correlated with liquid order partitioning in model systems. The novel observations shine new light on the distribution and interaction of lipids and proteins in the plasma membrane with respect to the lipid raft hypothesis.