Septin filament assembly assists the lateral organization of membranes

Abstract

Compartmentalized interactions of plasma membrane components are essential to support many cell functions, from signaling to cell division, adhesion, migration, or phagocytosis. Cytoskeletal-membrane interactions play an important role in forming membrane compartments, and this feature has been primarily studied through the actin cytoskeleton. Unlike actin, septins directly interact with membranes, acting as scaffolds to recruit proteins to specific cellular locations and as structural diffusion barriers for membrane components. However, how septins interact with and remodel the local membrane environment is unclear. Here we combined minimal reconstituted systems based on fluorescence microscopy and quantitative atomic force microscopy together with live yeast cell imaging and STED microscopy to study septin-mediated membrane organization. Our results show that septins self-assembly into filament-based sub-micrometric patches and high-order structures prompt their membrane-organizing role in vitro and in yeast cells, respectively. Furthermore, we show that the polybasic domain of Cdc11, in addition to the amphipathic helix of Cdc12, plays an essential role in supporting the membrane remodeling and curvature-sensing properties of yeast septins. Collectively, our work provides a framework for understanding the molecular mechanisms by which septins can support cellular functions intimately linked to membranes.