Synergistic role of nucleotides and lipids for the self-assembly of Shs1 septin oligomers

Cyntia Taveneau, Rémi Blanc, Gerard Pehau-Arnaudet, Aurélie Cicco, Aurélie Bertin - Laboratoire Physico Chimie Curie, Institut Curie, PSL Research University, CNRS, Paris, France; Sorbonne Universités, Paris, France; Thermo Fisher Scientific, Bordeaux, France; Ultrastructural BioImaging UTechS UBI, CNRS, Institut Pasteur, Paris, France

Amira capacities for membranes and filaments segmentation in cryo-TEM images are featured on the front cover of Biochemical Journal, July 2020.

Budding yeast septins are essential for cell division and polarity. (…) [The authors] have dissected, here, for the first time, the behavior of the Shs1 protomer bound to membranes at nanometer resolution, in complex with the other septins. Using electron microscopy, [the authors] have shown that on membranes, Shs1 protomers self-assemble into rings, bundles, filaments or two-dimensional gauzes.

Septin proteins display highly dynamic structures since they undergo major remodeling events in situ, for instance throughout cell division. This plasticity is certainly regulated, in vivo, by multiple factors. It is thus necessary to dissect their specific role to understand how septins are regulated. Following this strategy, [the authors] (…) have demonstrated that a combination of factors (nucleotides, lipids, ionic strength) are responsible for the plasticity of those septin protomers.

How Amira-Avizo Software is used

“Tomograms were segmented and analyzed using Amira 6.4 (…). Filaments were extracted using a dedicated template matching algorithm, accounting for the missing wedges effects induced by limited tilt angles, while membranes were segmented thanks to a membrane-enhancing filter. The centerlines of both filaments, and membranes, were extracted to facilitate certain measurements and comparisons. Only filaments clearly interacting with the membranes, but not via their endings, were taken into account for the statistics calculations. Their curved length was computed as the length of their centerline representation, while the chord length corresponds to the length of the line segment joining their end-points. The average thickness of the filaments was measured from their voxel representation.”