Résumé
Membranes are crucial to the cell’s life in all eukaryotic organisms. The organization of the plasma membrane is dynamic and can be modified during specific cellular functions such as cell division and endocytosis. Septins and F-BAR domain proteins are two groups of proteins with cellular functions that are linked to their ability to interact with the plasma membrane through phospholipids, in particular PI(4,5)P2, and they can sense and/or affect membrane curvature. However, how these proteins organize and remodel membranes and how this is linked to their cellular functions, is not well-understood. To study the molecular mechanisms involved, I combined in vitro and in cellulo systems coupled to sub-diffraction fluorescence imaging with atomic force microscopy. Firstly, I investigated the molecular mechanisms that regulate septins organization and membrane remodeling during cell division using minimal reconstituted systems based on supported lipid bilayers and recombinant proteins. Moreover, I complemented these observations with in cellulo studies in the budding yeast S. cerevisiae. My results showed that septins assemble into filament-based nano-domains that modulate the lateral lipid reorganization of PI(4,5)P2-containing bilayers. Furthermore, I showed that septin nano-domains promote membrane rigidity on supported lipid bilayers. This effect could be explained by septins promoting the packing and phase separation of lipids. Secondly, I investigated the role of the mammalian F-BAR domain protein FCHo1/2 in the initiation of clathrin-mediated endocytosis. Using the same technical approaches mentioned above, I found that FCHo2 self-assembles into rings and promotes a local accumulation of PI(4,5)P2 at the boundary of clathrin-regulated receptors on cellular membranes. Furthermore, I uncovered a role for PI(4,5)P2 in promoting the partition of FCHo2 at the edge of dome-like structures. Finally, I participated to a study on the role of Syp1, the yeast homolog of the mammalian FCHo1/2, in septin organization during cell division. We found that Syp1 induces septin filament bundling and this property is conserved throughout evolution. This study will help to better understand the dysfunction of septin and FCHo-mediated cellular processes, for instance, in the context of cancer, neurodegenerative and infectious diseases in which these proteins have been involved.