Septin higher-order structure on yeast membranes in vitro
James A. Goodchild, Brandy N. Curtis, Yangang Pan, Yining Jiang, Fang Jiao, Amy S. Gladfelter, Simon Scheuring
Abstract
Septins are cytoskeletal proteins that form filaments and higher-order structures, and remodel membranes in a variety of processes. Structural and cell biological studies provided atomic- and micro-scale details, but the understanding of septin assembly at the mesoscale is limited. Here, we used high-speed atomic force microscopy (HS-AFM) to analyze yeast septin assembly on yeast supported lipid bilayers (SLBs). We found the coexistence of three lipid phases in yeast membranes, where septin polymerized selectively on the liquid-disordered phase. Septin filaments adhered to membranes with a conserved face; and paired filaments, previously reported in less native environments, were not observed. Additionally, septin filaments exhibited lateral and longitudinal alignment. We used HS-AFM force-sweep experiments to disrupt septin structures and observe organizational recovery through self-templating. Finally, septin filaments stacked, where higher layer filament alignment was templated by the layer below. Thus, septins encode their 3D-structural organization, likely tunable by the membrane and bulk environment. The authors use high-speed AFM to study the interaction of yeast septin filaments with yeast lipid membranes, showing that septin is lipid phase selective and organizes into higher-order structures without the contribution of other cellular components.