Septin-Mediated Uniform Bracing of Phospholipid Membranes

Abstract

Cell shape is determined by the interplay between the lipid bilayer and the underlying network of protein polymers. We explored unknown determinants involved in cell morphogenesis as factors that transform phospholipid-based liposomes (diameter 5-20 microm). Unlabeled giant liposomes, observed through dark-field optics, were metastable in an aqueous suspension. In contrast, liposomes robustly protruded uniform tubules immediately after the addition of a brain extract to the suspension. The tubulation reaction was greatly facilitated when the liposomes contained PIP or PIP2. Biochemical analysis of the brain extract revealed that heteromeric complexes of septins, a family of polymerizing GTP/GDP-binding proteins, are responsible for the membrane transformation. Ultrastructural analysis established that each membrane tubule (diameter 0.43 +/- 0.079 microm) is braced by a circumferential array of septin filaments. Although submembranous septin assemblies are associated with diverse cortical morphogenesis from yeast to mammals, the biophysical basis for the septin-membrane interplay remains largely unknown. Further, there is a biochemical discrepancy between the fast septin remodeling in cells and their slow self-assembly in vitro. This membrane-facilitated fast septin assembly demonstrated for the first time by our unique experimental system should provide important clues to characterize these processes.

Biophysical dissection of schistosome septins: Insights into oligomerization and membrane binding

“…For example, upon binding to GUVs the SmSEPT 5, 7.2 and 10 heterocomplex induces formation of discrete lipo-protein clusters on the vesicles, which however do not elongate into tubules as previously observed by Tanaka-Takiguchi et al [37]. In contrast, individual SmSEPT10 proteins are able to self-assemble into characteristic cage-like structures, covering and deforming the whole vesicle.…”

“…It has been reported that septins bind to phosphoinositide lipids, specifically to PIP2 (phosphatidylinositol-4,5-bisphosphate), therefore the reference composition of the GUV membrane in our experiments was chosen to be 95 mol% DOPC and 5 mol% PIP2 [36,37]. Our results show that individual full length SmSEPT5 and SmSEPT10 proteins are both able to bind the GUV membrane after a few minutes of incubation.…”

Septin 9 negatively regulates ubiquitin-dependent downregulation of epidermal growth factor receptor

“…Septins can associate with membrane surfaces enriched in phosphoinositides (Tanaka-Takiguchi et al, 2009). We therefore performed biochemical fractionation experiments to gain insight into the subcellular distribution of SEPT9 upon stimulation with EGF.…”

“…Septin complexes bind to membrane surfaces enriched in negatively charged phospholipids, such as phosphoinositides (Tanaka-Takiguchi et al, 2009). They thereby form diffusion barriers that support the compartmentalization of membranes during a broad range of cellular processes, including cell division, membrane trafficking and signal transduction (Caudron and Barral, 2009).…”

The role of Pnut and its functional domains in Drosophila spermatogenesis

“…Для большинства септинов было показано взаимо-действие с фосфолипидами мембран (Casamayor, Snyder, 2003). Также было показано, что септиновый комплекс человека SEPT2-SEPT6-SEPT7 способен модифицировать морфологию гигантских липосом, содержащих фосфои-нозитиды (Tanaka-Takiguchi et al, 2009). Предложенную нами гипотезу подтверждает тот факт, что у мутанта по ГТФазному домену Pnut отсутствуют специфические пун-ктирные структуры в кортикальной области.…”