Mechanisms of Lipid Sorting in the Endosomal Pathway

Abstract Eukaryotic cells maintain a highly organized endosomal system. The intracellular organelles of this pathway show differences in protein and also in lipid composition. It is becoming more and more evident that the cells have to actively sort lipids in the endosomal pathway to maintain the necessary lipid distribution between organelles and thereby cellular lipid homeostasis. Lipid classes and species differ in their biophysical properties and can have pronounced effects on the lipid bilayer they are forming. Lipids can influence the properties of each organelle by changing biophysical membrane parameters such as curvature and fluidity. They can also recruit different protein-binding partners that affect protein and lipid sorting of the organelle. In this chapter we will give an overview of the different trafficking pathways in the endosomal system. For each step, starting from endocytosis at the plasma membrane to the final step in the lysosome, we will highlight how sorting processes affect lipids and how these processes are affected by certain lipids. Finally, we will give an overview of emerging technologies to study lipid distribution in the endosomal pathway and the future challenges in the field.