Quantification of lipid sorting during clathrin-mediated endocytosis
Clathrin-mediated endocytosis is a major transport route for proteins from the plasma membrane to the interior of the cell. While the recruitment of cargo proteins to clathrin-coated pits is well understood, it remains an open question if lipids are also sorted by this process. To address this question, we combined super-resolution STED imaging of bifunctional lipid probes with mathematical modeling. Quantification of 10 different lipid species revealed significant differences in pit partitioning, ranging from slight enrichment to moderate exclusion. We find that the lipid asymmetry in the plasma membrane is sufficient to explain the observed trend. Taken together, our findings imply that clathrin-mediated endocytosis has a minor selectivity for cytoplasmic leaflet lipids, but overall does not significantly contribute to lipid sorting compared to non-vesicular trafficking. More broadly, we believe that lipid super-resolution imaging will be a powerful approach to quantify lipid partitioning into membrane structures in cells.