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Pré-Publication, Document De Travail Année : 2022

Human septins in cells organize as octamer-based filaments mediating actin-membrane anchoring

Carla Silva Martins
Cyntia Taveneau
Francois Iv
Alex Llewellyn
Mayssa Belhabib
Sophie Brasselet
Felix Rico
Gijsje Koenderink
Jérôme Wenger
Manos Mavrakis

Résumé

Septins are cytoskeletal proteins conserved from algae and protists to mammals. Septin knock-out animals have established that septins are essential for animal physiology, but their molecular function remains elusive. A unique feature of septins is their presence as heteromeric complexes that polymerize into filaments in solution and on lipid membranes. Although animal septins associate extensively with actin-based structures in cells, whether actin-decorating septins organize as filaments and if septin organization impacts septin function is not known. Customizing a tripartite split-GFP complementation assay for probing the presence and composition of septin filaments in situ in cells, we show that all septins decorating actin stress fibers are present as filaments whose integrity depends on octameric septin protomers. Atomic force microscopy nanoindentation measurements on cells confirmed that cell stiffness depends on the presence of octamer-containing septin filaments. Super-resolution structured illumination microscopy revealed septin fibers with widths compatible with their organization as paired septin filaments. Nanometer-resolved distance measurements and single-protein tracking further showed that actin-associated septin filaments are membrane-bound and largely immobilized. Finally, reconstitution assays on supported lipid bilayers showed that septin filaments mediate actin-membrane anchoring. We propose that septin organization as octamer-based filaments is essential for septin function in anchoring and stabilizing actin fibers at the plasma membrane.
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Dates et versions

hal-03588456 , version 1 (22-03-2022)
hal-03588456 , version 2 (03-12-2022)

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Carla Silva Martins, Cyntia Taveneau, Gerard Castro-Linares, Mikhail Baibakov, Nicolas Buzhinsky, et al.. Human septins in cells organize as octamer-based filaments mediating actin-membrane anchoring. 2022. ⟨hal-03588456v1⟩
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