Physics-Biology interface seminar: Stéphanie Mangenot & Aurélie Bertin


11:00 - 12:00

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Membrane reshaping induced by Curvature sensitive Septin filaments: A story of paired filaments told by a pair of Orsay alumni

Stéphanie Mangenot & Aurélie Bertin (Institut Curie, Paris)

Septins are cytoskeletal proteins that assemble into a variety of supramolecular organizations from paired filaments to bundles, ring like structures or gauzes of orthogonal filaments [1‐3]. Septins are bound to the inner plasma membrane through specific interactions with phosphoinositides [1,4]. Septins are essential for cell division, participate in the formation of diffusion barrier and might be involved in membrane deformation and rigidity. Throughout cell division, septins undertake major rearrangements. Septin filaments are first aligned toward the mother‐daughter cell axis and then rotate to be circumferential around the constriction site.

We have shown that septins arrange differently on positive or negative curvatures using Scanning Electron Microscopy on micro‐patterned PDMS periodic undulated substrates. Besides, this curvature preference is closely related to the ability of septins to reshape and deform membranes. Indeed, bound to Giant unilamellar Vesicles (GUVs), septins induce striking deformations with regular spikes and hollow micrometric deformations at the surface of liposomes, as visualized by fluorescence microscopy. Smaller vesicles (LUVs of 100‐300 nm in diameter), highly positively curved, are flattened by Septin filaments into “pancake”like objects as shown in 3D by cryo‐electron tomography. With the resolution of cryo‐EM and sub‐tomogram averaging we visualize both the septin filaments and the deformed vesicles. We propose a simple model where the filamentous properties of septins control their curvature sensitivity and thus impose their orientation in situ [5].

  • [1] A. Bertin, et al. (2010), Phosphatydinositol 4,5 biphosphate promotes budding yeast septin filament assembly and organization, J. Mol. Biol., 404(4), 711‐31.
  • [2] G. Garcia et al. (2011), The regulatory budding yeast septin Shs1 promotes ring and gauze formation in a phosphorylation dependent manner., J. Cell. Biol., 195(6), 993‐1004.
  • [3] A.Bertin, et al. (2008), Saccharomyces Cerevisiae septins: supramolecular organization of heterooligomers and the mechanism of filament assembly, Proc.Natl. Acac. Sci USA, 105, 8274‐8279
  • [4] Beber A et al.,Septin‐based readout of PI(4,5)P2 incorporation into membranes of giant unilamellar vesicles. (2018) Cytoskeleton. doi: 10.1002/cm.21480
  • [5] A. Beber et al. (2019), Membrane reshaping by micrometric curvature sensitive septin filaments, Nat. Commun., 10, 420.
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