Ludger Johannes

Institute Curie, France

Lectin-driven and glycosphingolipid-dependent construction of endocytic pits for polarized protein distribution in cells

Several endocytic processes do not require the activity of clathrin, and it has been a major question in membrane biology to know how the plasma membrane is bent and cargo proteins are sorted in these cases. Our previous studies have allowed us to propose the GL-Lect hypothesis: Nanodomain construction by GlycoLipid-binding cellular or pathological Lectins induces membrane curvature changes and drives the formation of tubular endocytic pits from which clathrin-independent carriers are generated for the cellular uptake of glycosylated membrane proteins (CD44, integrins…), pathogens (polyoma viruses, norovirus), or pathogenic factors (Shiga and cholera toxins). We are now analyzing how cortical actin dynamics contributes to the clustering of glycosphingolipid-lectin complexes on active membranes, thereby facilitating the nucleation of endocytic tubules exploiting membrane fluctuation force and asymmetric lipid compaction mechanisms that had not been linked before to endocytosis. Furthermore, we are identifying ways by which the GL-Lect mechanism is acutely controlled by growth factor signaling and conformational changes in cargo proteins. Finally, we study how GL-Lect domain construction at the plasma membrane programs the intracellular distribution of cargo proteins via the retrograde transport route, thereby exploiting the polarized secretion capacity of the Golgi apparatus for the distribution of these cargoes to specialized plasma membrane domains in migrating cells (leading edge), epithelial cells (apico-basal sorting and transcytosis), and lymphocytes (immunological synapse). These studies are performed using a combination of cell biological (lattice light sheet microscopy), biochemical (membrane protein purification and reconstitution), and structural biology (cryo-EM) techniques on model membranes, in cells, and living organisms.

©2020 by Sphingolipid Biology: Sphingolipids in Physiology and Pathology