Stéphanie Mangenot - Membrane reshaping by curvature sensitive  septin filaments
Channel: Institut des Hautes Études Scientifiques (IHÉS)
Date: 2018-03-26

Septins  are  cytoskeletal  proteins able  to  form  supramolecular  structures  such  as  filaments, networks  and  rings.  They  are 
bound  to  the  inner  plasma  membrane at  specific  location 
including  the  separation  between  the  mother  and  daughter  cell  during  cytokinesis  and  the basis  of  cilial  cells. Septins  are  essential  for  cytokinesis,  participate  in  the  formation  of 
diffusion barrier and might be involved in membrane deformation and rigidity. Using simplified  biomimetic  systems, we asked  if  septins  were  sensible  to  curvature,  given their  preference  to  be  located  at  places  of  high  curvature.
To  mimic  specific  curvatures  and geometries observed  in  vivo,  we  have  used  PDMS  substrates  covered  with  a  supported  lipid bilayer.  “Wavy”  PDMS patterned  substrates  display
both  positive  (“bumps”)  and  negative (“valleys”)  curvatures.  To  our  surprise,  we  have seen,  using  Scanning  electron  Microscopy, that  Septin  filaments  have  a  preference   for negative  micrometric  size  curvatures.  On positively  curved  geometries  (bumps),  septins  spontaneously  align along the  “bumps”  and thus orient towards null curvature.This  curvature  preference  is  closely  related  to  the  ability  of  septins  to reshape  and  deform membranes. When  interacting  with  giant  unilamellar  vesicles,  septins  induce μ m  scale deformations
with the formation of regular rigid spikes at the surface of the liposomes. We propose a theoretical model to take into account these observations and could be relevant to describe the organ
ization of septins during cytokinesis in vivo.