Biophysical Society Thematic Meeting| Padova 2019

Quantitative Aspects of Membrane Fusion and Fission

Wednesday Speaker Abstracts

ESCRT-III FILAMENTS HAVE OPPOSITE CURVATURE-RELATED ORIENTATIONS ON MEMBRANES

Nicola de Franceschi* 1,2 ; Aurélie Bertin* 1 ; Sourav Maity 3 ; Maryam Alqabandi 1 ; Nolwen Miguet 2 ; Wouter Roos 3 ; Winfried Weissenhorn 2 ; Stéphanie Mangenot 1 ; Patricia M. Bassereau 1 ; 1 Institut Curie, PhysicoChimie Curie, Paris, Paris, France 2 University Grenoble Alpes, Institut de Biologie Structurale , Grenoble, Isère, France 3 Rijksuniversiteit Groningen, Moleculaire Biofysica, Groningen, The Netherlands The multi-proteins ESCRT-III complexes are involved in membrane scission in many different cellular processes. In contrast to dynamin polymers that assemble outside budding vesicle/tubule necks, they assemble inside the bud necks where the membrane has a curvature Gaussian negative. The organization of the proteins of this complex and even more the mechanism of membrane scission remain highly debated. By combining membrane nanotube pulling experiments, CryoEM and high speed AFM on a minimal set of human ESCRT proteins, we have obtained very unexpected results. We have shown that the CHMP proteins assemble in filaments with contrasted affinities for curved membranes. a) CHMP4 form spiral filaments that do not tubulate membranes and rather flatten them. b) CHMP2A with CHMP3 have affinity for positively curved membranes since they form helical structures on the external side of tubules only. c) Together CHMP4, CHMP2A and CHMP3 deform liposomes into helical tubes (with a corkscrew shape) when incubated with liposomes with orthogonal orientations of the filaments; moreover they are not recruited inside tubes pulled from giant vesicles, but only inside their neck, as observed in cells. The peculiar shape of the membrane reveals the mechanical stresses imposed by these ESCRT-III assemblies to the membranes and might provide new insight on the mechanism of scission in the presence of the ATPase Vps4.

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